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High Oxidation State Organometallic Chemistry A ChallengeЧthe Example of Rhenium.

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High Oxidation State Organometallic Chemistry,
A Challenge-the Example of Rhenium**
By Wolfgang A. Herrmann*
Dedicated to Professor Hans Bock on the occasion of his 60th birthday
Homogeneous catalysis as the major industrial outlet of organometallic basic research has
been enjoying great benefit from organotransition metal species that promote bond forming
between hydrocarbon fragments. Most of the commercially important processes that serve
to produce large-volume organic feedstock chemicals such as linear a-olefins (Shell Higher
Olefins Process), linear aldehydes (hydroformylation), acetaldehyde (Wacker-Hoechst),
acetic acid (Monsanto), adiponitrile (DuPont hydrocyanation of butadiene) operate at lowvalent metal centers. It is thus hardly surprising that by far the most part of organometallic
research during the past few decades has been directed towards an understanding and the
improvement of these catalytic reactions as well as towards the related stoichiometric chemistry. As a matter of consequence, our present knowledge on high-valent organotransition
metal compound is comparatively shallow, nor d o we know much about the chemical relationship and interconvertability of high and low oxidation states within a given class of
compounds. In this article I want to point out some ostensibly challenging perspectives of
future organometallic research by describing a novel class of high oxidation state organorhenium compounds as well as by speculating on possible generalizations for other transition metals.
1. Introduction
When a present days' chemistry student first encounters
organometallic compounds, he may be amazed about the
overwhelming diversity in composition and structures, in
properties and reactivity.['.21 On the other hand, he will no
longer view them as laboratory curiosities as I did when I
took my first chemistry courses at Munich twenty years
ago. At that very time of excitementi3]the recognition of
metal-metal multiple bonds (Cotton et a1.)14,51and metalcarbon multiple bonds (Fischer et al.)[6.71was brand-new,
the catalytic merit of rhodium complexes had just been uncovered (Alderson et al., Osborn and Wilkinson et al.),[','l
and Wifke et al. were using zerovalent 'naked' nickel to tailor cyclic oligomers from butadiene.'"] Faster and more
precise structure and reactivity studies of existing compounds and catalytic cycles became escorted by novel instrumental techniques. Shortly before, Ziegler and Nattd"]
had received the Nobel Prize that could be considered a
first public award to young organometallic chemistry in
blossom. And backstage, the Wacker process of palladiumcatalyzed, highly selective oxidation of ethylene to acetaldehyde was heading towards large-scale production,['21
again demonstrating the synthetic power of the metal-tocarbon bond. Acetylene which had been pioneered by
Reppe et al. of the Badische Anilin- & Sodafabrik back in
the forties,"31 was no longer the major chemical feedstock.
['I Prof
Dr. W. A. Herrmann
Anorganisch-chemisches lnstitut der Technischen Universitat Miinchen
Lichtenbergstrasse 4, D-8046Garching (FRG)
[**I
Second Essay o n Organometallic Chemistry. First Essay: W. A. Herrmann, Comments Inorg. Chem 7 (1988) 73.
Angew. Chem. I n t . Ed. Engl. 27 (1988) 1297-1313
Many more and not less striking examples could be
brought to memory[I4.' I here to support the statement that
the fate and future of organometallic chemistry in those
days were in the hands of the low oxidation states.['"] Since
organotransition metal compounds were so successful in
the construction of carbon-carbon and carbon-hydrogen
bonds, the field more or less merged with organic synthesis, and metal-mediated shortcuts towards sophisticated
pharmaceuticals, insecticides, and fragrances is certainly
a n attractive research domain that greatly relies on the ex']
pertise of both organic and organometallic
At the same time organometallic basic research moved
towards organic synthesis, with all sorts of metals and rnetal compounds nowadays being used by 'straight' organic
chemist^,"^] the gap between organometallic research and
the chemistry of inorganic compounds including inorganic
solid state chemistry became canyon-like. This is all the
more a pity in that the recent desire for 'novel materials'
(e.g., ceramics, glasses, alloys, refractory materials, 'inorganic' polymers, 'electronic materials' etc.) can only come
to scientific success if we understand the structures, the
bonding, and the behavior of inorganic metal compounds
and combine them with organornetallic~.[''~
In doing so, we
ought to open our eyes for the metals' high oxidation
states and learn how to deal with them. Roald Huffmann
has convincingly emphasized the future impact of solid
state chemistry and physics on the rest of chemistry.['"]
This proposal is nothing that would contradict even the
needs of organic chemists. Who would for instance seriously claim to understand how oxidation reactions of organic compounds really work?'"' More precisely: Which
reagent is best used to oxidize a specific alkyne, olefin, o r
alkane? Under which circumstances is an 0x0 group transferred upon a hydrocarbon compound to be oxidized?
0 VCH Verlagsgesellschaji mbH. 0-6940 Weinheim. 1988
0570-0833/88/1010-1297 $ 02.50/0
1297
How does ‘chromium peroxide’ (Cr05) work in oxidation,
which is the active oxidant, what is the nature of the organometallic intermediates involved, and what does or d o
the mechanism(s) look like?[22-241
What are the pivotal mechanistic steps in the industrially so important SOH10
‘ammonoxidation’ process for converting propylene into
acrylonitrile in the presence of bismuth molybdate catal y s t ~ ?These
[ ~ ~ ~are just two examples calling for a phalanx
of organometallic chemists to tackle dozens of problems
involving nothing less important than oxidation chemistry.
2. Organorhenium Compounds as Examples
Let us come u p with a few details. I shall pick the element rhenium for the simple reason that we have found
some unexpected compounds that promise useful applications in various fields of catalysis, not least in hydrocarbon
oxidation. Moreover, the element rhenium-as a child of
our century discovered as late as in 1925 by Walther and
Ida Noddack in Germany-provides us with eleven different oxidation states, from 7 to - 3. Rhenium may thus
be viewed as an inorganic and organometallic ‘chameleon’,
and Figure 1 amplifies on this picture.L261Oxides and halides are expectedly at the higher range of the scale, while
carbon monoxide extends the series towards the negative
oxidation states, with dirhenium heptoxide/rhenium heptafluoride and tetracarbonylrhenate( - 111) terminating at
opposite ends. While the large body of carbonyl compounds has well been known to us organometallic chemists, we have hardly considered (simple?) oxides, halides,
and oxohalides, nor have we thought of combining them
with organic molecules. Still, even their structures are exciting. In dirhenium heptoxide (Re207), for example, we
encounter both tetrahedral and octahedral coordination of
the metal, with the so-called perrhenic acid merely being a
hydrate of this oxide. Rhenium trioxide (ReO,) forms a perovskite-type structure of hexacoordinate rhenium, with a
counter ion being missing in the cavity of the cube; this d ’
compound shows metallic conductivity (!) resulting from
delocalization of the d electrons. In Section 2.3 it will be
shown how successive replacement of two methyl groups
for each oxygen leads to interesting and useful ‘organic’
derivatives.
In the intermediate oxidation state range, rhenium (like
molybdenum and tungsten) forms a wealth of metal-metal
multiply bonded compounds such as Geilmann’s old ‘rhenium trichloride’ which in truth is a polymer in the solid
state containing Re3C19
On the other hand,
even methyl groups have been attached to hexavalent rhenium; Wilkinson has pioneered this chemistry by synthesizing the green explosion hazard hexamethylrhenium,
Re(C H3)6.[271
+
2.1. Trioxo(~5-pentamethylcyclopentadienyl)rhe~ium(vrr)
Re-H
We had to learn that hydrogen peroxide does not necessarily ‘chew up’ the metal-attached n-aromatic ligands‘*’I
when we treated this reagent (or tert-butyl hydroperoxide)
with the low-valent half-sandwich carbonyl precursor compound 1 in a boiling two-phase water/benzene system. According to Scheme 1, the yellow, thermally stable product
2 containing rhenium in its highest possible oxidation
state 7 is rather formed in at least 70% yield.‘291The compound can be sublimed in a high vacuum at ca. 110°C
without any deterioration, and no decomposition point under normal pressure was observed u p to 250°C, showing
that rhenium(vr1) is perfectly compatible even with otherwise oxidizable n-aromatic hydrocarbon ligands. PE spectroscopic comparison of 1 and 2 clearly revealed this difference in metal oxidation state^.^^^-^'^ Light-induced air
oxidation of 1 also generates the title compound 2 , albeit
less conveniently on a preparative scale and in lower
+
Fig. I . Typical rhenium compounds representing oxidation states - 3 to + 7.
The lighter homologue manganese would show up with a similar picture. A
few important differences remain to be noted, however: 1. The high oxidation-state dimanganese heptoxide, MnzO7, is very unstable. 2. High-valent
organomanganese compounds d o not exist (e-g., [(q5-C5Me5)MnOl] and
Mn(CH& are unknown). 3. Manganese-manganese multiple bonds are rare
(example: W. A. Herrmann, R. Serrano, J. Weichmann, J . Organomet. Chem.
246 (1983) C 57; J. D. Korp, 1. Bernal, W. A. Herrmann, R. Serrano, Chem.
Ber. 117 (1984) 434). 4. The oxidation state + 2 is the most common one in
aqueous manganese chemistry, whereas only few well-defined rhenium(i1)
compounds have been described (e.g., [RezCI,(PR,),]: T. J. Barder, F. A. Cotton, K. R. Dunbar, G. L. Powell, W. Schwotzer, R. A. Walton, Inorg. Chem.
24 (1985) 2550).
1298
yield^.[^'.^ ’I
The organorhenium oxide 2 has a conventional pyramidal structure with an entirely symmetrically bonded Cp*[*] General remarks: All drawings of structures have been performed using
the SCHAKAL program (E. Keller: Ein Progrumm fur die graphische Darstellung uon Molekulmodellen, Kristallographisches Institut der Universitat Freiburg (FRG), 1986).-Color code: Re violet, CI green, S yellow, P
brown, 0 red, C black, H orange.
Angew. Chem. In!. Ed. Engl. 27 (1988) 1297-1313
Scheme I .
ligand (Cp* = qs-CSMe5).[321
A space-filling model (Fig. 2,
left)"] tells us that the metal atom is effectively shielded
from the upper side of the molecule while the three oxygen
atoms take u p most of the space on the opposite side. For
this very reason, chemical reactions generally occur at the
'oxidic' part of the molecule (see Fig. 2b and Refs. 136461). An I70-NMR study comes to the result that the 0x0
ligands of compound 2 are relatively electron-rich
( 6 ( 0 )= 646 ppm) while they are rather electron-deficient
( 6 ( 0 )= 829 ppm, CDCI,) in complex 4 (Section 2.2).
Fig. 2. Computer-generated space-filling models of the complexea [(q'.
CsMeS)Re03]2 (left) and [CH3Re03]4 (right) correspond to an X-ray strucfural analysis of [(qS-C5Me4Et)Re03]using acceptable van der Wnals radii
for rhenium (240 pm), carbon (160 pm), oxygen (140 pm), and hydrogen
atoms (120 pm). For compound 4 a rhenium-methyl single bond distance of
210 pm was taken from structural data obtained for the related dinuclear
derivative [(CH3)4ReZ04]9a [47].-These drawings show that the bulky r[bonded pentamethylcyclopentadienyl ligand shields the metal atom from attacking reagents on the upper side of the molecule (left) while the metal atom
of compound 4 (right) is fairly exposed. It is thus understandable that compound 2 resists attachment of further ligands, whereas compound 4 forms
stable adducts with such compounds (e.g., azabicyclo[2.2.2]octane,ammonia,
aniline, bipyridine; see text).
2.2. Methyltrioxorhenium(vrr)
We d o not yet know why the parent cyclopentadienyl
compound [(qs-CsHs)ReO,] has so far resisted all attempts
at its synthesis. Neither d o the oxidation reactions of
Scheme 1 work in the case of [(q'-C,H,)Re(CO>,], nor did
we succeed in making the compound from the 'right' oxidation state
7 by treating chlororheniumtrioxide
(Re0,CI) with various cyclopentadienyl transfer reagents
such as LiC5Hs, TICsHs, (CsHs)Sn(n-C4H9),, etc.
However, the even more interesting methyltrioxorhenium(vir), 4, was achieved by Kuchler of our research
group.[471Knowing that dirhenium heptoxide and tetramethyltin are effective catalyst/cocatalyst components in
+
Angew. Chem. Inr. Ed. Engl. 27(1988) 1297-1313
olefin metathesis, even catalyzing metathesis of industrially important unsaturated carboxylic acids and nitriles
under quite mild conditions,1481he allowed these two
chemicals to react in boiling tetrahydrofuran and obtained
according to Scheme 1 not only colorless, completely air
stable, water-soluble (!) 4 (m.p. 106°C) but also the perrhenyl ester 5 (m.p. 213"C, dec.); the product yields are
essentially q ~ a n t i t a t i v e . ' ~With
~ ] such a simple method at
hand, a whole series of high-valent organometal oxides
may be opened u p now, since tetramethyltin seems to be
an extremely selective, non-reductive methylation reagent.
No secondary reactions occur in the given example, even
in the presence of a large excess of the tin reagent. Kuchler's results were all the more exciting in light of the fact
that compound 4 had been obtained before by Beattie and
in small amounts by air oxidation of tetramethyloxorhenium(vl), [(CH,),ReO], which compound in turn is
difficult to make.[s0a1One limitation of this synthetic strategy may, however, arise from the &hydrogen activity of
compounds [R2CHCH2Re03]which is evident from the
reaction of Re207 with Sn(C2Hs), that leads to reduction
of the metal with concomitant ethylene/ethane elimination.ls'l Tetraphenyllead does not form the (still unknown)
phenyl complex [C6HSReO3]with Re207 but rather the
plumboxy derivative [((C6HS)3PbO)Re03].~50h1
The silyl and stannyl esters [((CH,),SiO)ReO,] and
[{(CH,),SnO) ReO,], respectively, undergo reductive alkylation by aluminum alkyls to form d'-rhenium(v1) compounds of general formulas %Re,04 (e.g., 9a) and
&Re203 (e.g., 9b ; see Section 2.3).LS"h.s11
The latter compounds undergo oxidative cleavage with y-picoline N-oxide to form the mononuclear Re"" derivatives R3Re02
(9C).[50h.
5 11
Replacement of the ten-carbon n-ligand of 2 by one methyl group in complex 4 must of course relieve steric
crowding dramatically. Figure 2 gives a pictorial view of
this
Evidently the metal atom is no longer buried
under the surrounding ligands, so attachment of further
groups at the metal should now be possible. Although investigations into the chemistry of 4 have just started, some
typical reactions can already be given. Amines such as
quinuclidine o r 1,4-diazabicyclo[2.2.2]octane (DABCO)
form stable, crystalline adducts of formulas 6a and 6b, respectively, demonstrating the Lewis acidity of the metal
center in compound 4 (X-ray structural analysis for
6a).[s0b1
These two complexes exhibit trigonal-bipyramidal
geometry. Ammonia and bipyridine, however, form octahedral adducts 6c and 6d, respectively, the 0x0 ligands of
,
[CH, Re03]. C,H N
21CH3ReO31.C6H,,N2
6a
6b
ICH,ReO3]-2 NH3
6c
ICH3Re031.CI~HRN2
6d
which are electron-rich. 4 reacts with sodium hydroxide in
the presence of benzo[l5]crown-5 (Bl5C5) according to
equation (a) yielding the perrhenate 6f, very likely via the
intermediate 6e with clean elimination of methane. 6f has
a n unprecedented double-helix crystal structure.fs0c]
1299
[CH,ReO,]
+ NaOH
[Na(B15C5)][CH,Re(OH)03]
6e
4
A
[Na(B15C5)][Re04]+ CH,
(a)
6f
Treatment of 4 with I70-labeled water should proceed
along the same pathway: the intermediate 6g would explain the observed rapid oxygen-exchange reaction.[50c1
[CH3Re03].xH 2 0
[CH3ReOCl2]
6g ( x = l , 2)
7
Thionyl chloride converts 4 at low temperatures into a
sensitive dark-red compound of the composition 7, whose
structure is still unknown.150b1While a mixture of triphenylphosphane and chlorotrimethylsilane converts sterically
crowded 2 reductively into the organorhenium(v) chloride
12 (see Scheme 4),134b-d1
the methyl compound 4 rather
forms the dinuclear product 8 (Scheme 2) in which each
metal atom has a total of six ligands, with the ReORe
backbone being strictly linear (Fig. 3).[741
4
I
P(C,H,),
Scheme 2
Let us speculate for a moment. Scheme 1 does not comprise any redox chemistry. Hence there is no reason to
assume that analogous reactions should not be feasible
in related high-valent metal oxides such as V205 (possibly yielding dimers o r oligomers of net composition
[CH3V0,]), Cr2O3 (yielding a tetramer of net composition
[(CH3)4Cr404],with a cubane-type structure like the known
[(q5-C,H,)4Cr404]),1s31unless the special structural features
of Re207 dictate its chemistry. With only few except i o n ~ ~ ' ~our
. ~ knowledge
~]
of organometallic oxides mainly
suffers from a lack of synthetic strategies.
2.3. Exchange of One Oxygen for Two Methyl Groups
Dimethylzinc is generally considered by organometallic
chemists to be a mild, non-reductive methylating reagent.
This assessment does not apply, however, to its reaction
with Re20, as shown in Scheme 3 . In this case, the rhenium(vi) compound 9a (Fig. 4, left; yellow, sublimable
3
1
9b
Scheme 3
crystals; m.p. 120°C) is formed via 4, from which it can
also be made. The kinetic product 9a is further methylated
by excess dimethylzinc in a non-reductive way to the thermodynamic product 9b (Fig. 4, right; red, sublimable needles; m.p. 88°C).[471
This last-named compound had previously only been accessible via a more tedious indirect
route.[561Only when dirheniumheptoxide 3 is treated with
stoichiometric amounts of dimethylzinc (molar ratio l/l),
can the mononuclear ReV" complex 4 be isolated, thus
proving its intermediacy for the subsequent complexes 9a
and 9b.['Od1This observation gives support to the expectation that phenyl and longer chain alkyl groups can be
achieved in complexes of simple composition RRe03 (metal-oxide substituted alkanes!) by virtue of the easily accessible organozinc compounds.
Fig. 4.Left: Molecular structure of the dinuclear Re" complex 9a. The compound crystallizes upon vacuum sublimation in the monoclinic space group
ph. The hydrogen atoms have not been localized. Right: Molecular structure
of the Re"' complex 9b. T h e diamagnetism observed for this particular organorhenium(v1) oxide is due to a 'super exchange' phenomenon typical for
linear 0x0 bridges. The center of symmetry is marked with an asterix (*). The
drawing was generated from the X-ray data given by Wilkinson et al. in Ref.
IW.
Fig. 3. Molecular structure of the dinuclear Re" complex 8. The molecule
has a center of symmetry (*) located at the central 0x0 bridge.
1300
If one disregards the metal-metal bond present in 9a
(259.3( < 1) pm)J4?]then a strongly distorted square-pyramidal coordination geometry for rhenium is evident in the
solid-state structure [two square pyramids joining the basal
oxygen groups O(1) and 0(2)]. Figure 5 shows how the individual dinuclear molecules are close-packed in the lattice unit cell.
Angew. Chem. Int. Ed. Engl. 27 (1988) 1297-1313
The four compounds shown in Figure 6 form the first
complete series of isovalent methyl/oxo derivatives of any
transition metal. There is again no reason to assume that
similar analyses will fail for other metals. Tungsten, as rhenium’s uncle in the periodic table should play this game as
well, e.g. W 0 3
[(CH,),WO,] (?) + [(CH,),WO] (?) +
[(cH3),WI.[”’
When dimethylzinc reduces rhenium(vr1) by one step in
the reactions of Scheme 3, methyl groups appear to become oxidized at the same time since zinc is already in its
highest possible oxidation state. Observation of ethane
supports the idealized equation (b).
Fig. 5. Space-filling model of the unit cell of 9a, showing that a close-packed
arrangement of the individual dinuclear molecules is supported by the terminal 0 x 0 groups approaching bridging positions at neighboring molecules.
CN6
lNelson.195L)
Reduction processes also come to the fore when higher
tetraalkyltin reagents Sn& are subjected to high-valent
rhenium compounds such as Re207 3 (see Section 2.5).[58‘‘1
Derivatives of compound 9a undergo symmetric cleavage
when treated with alkaline metals M such as lithium, to
give ionic products of the type
Ma[R2Re02]” 9c
-
195prn
-
N 5 (HerrmannJ9871
in which the d2-ReV anion has a distorted tetrahedral
structure (R = CH,C(CH,),).[S’“l Re”“ alkyl complexes of
formulas [R,ReO,Br(L)] (R = alkyl, L = pyridine) and
[R3Re0,] have been presented in further papers by Hoffman et a1.[5’bl
-
C N5
(Wiikinson.1981)
2.4. Functionalizations at Metal Oxide Fragments
*-Re. O=O.O-CH,
Fig. 6. From rhenium trioxide to hexamethylrhenium. I n n o compound of
this series does the metal atom show a coordination number < 5.
The novel methyl(oxo) compound 9a can quite easily be
put in the row of other, known rhenium(v1) species (Fig.
6). Rhenium trioxide is kind of a reference compound.
Due to the low ligand1metal ratio of 311, it must have a
‘polymeric’ (perovskite-type) structure with several oxygen
atoms joined by two metals in order to achieve an acceptable coordination number for rhenium.lz6] Formal replacement of two methyl groups for one oxygen atom yields a
higher ligand/metal ratio (411) with concomitant breakdown of the highly aggregated ReO, structure. This is the
reason why ‘‘(CH3)2Re02”is just a dimer (and not paramagnetic, because of metal-metal spin pairing). Exchange
of another oxygen by two more methyl groups (on paper)
gives Wilkinson’s tetramethyl(oxo)rhenium(vr), which comsince a
pound can exist as a (paramagnetic)
coordination number of five has already been reached. Finally, hexamethylrhenium(v~)represents the fully methylated terminal of this series;[”] like its formal d’-‘precursor’ [(CH3),ReO], it is paramagnetic since spin pairing is
not possible.
Angew. Chem. Inr. Ed. Engl. 27 (1988) 1297-1313
Reductive processes govern the chemistry of [(q5C5Mes)Re03] 2 no matter whether Lewis bases or Lewis
acids are used as reagents. Typical examples are germanium dichloride (as 1,4-dioxane adduct GeC12.C,H,O,) and
alkylating agents such as AIR3 or ZnRz that effect rather
clean formation of the oxodichloro and oxodialkyl compounds 10 and 11, respectively (Scheme 4a). These ReV
*
11
10
Scheme 4a.
1301
species are once again powerful and useful synthetic intermediates for a range of other half-sandwich complexes.
Thus, treatment of the oxodichloride 10 with the reagents
indicated in Figure 7 yields compounds 15a-g, most of
which have (stable) rhenium-oxygen bonds. The rhena(v)-
*
15a
15b
thesized via a detour (Scheme 4b): first, the chiral l l b ,
which is an ideal precursor for complexes l l c - e that contain different alkyl l i g a n d ~ , is~ ~obtained
~]
quantitatively by
hydrolysis (waterlpyridine; molar ratio 1 :2). The dimethyl
derivative l l a can be converted into 13b by means of the
oxophilic organotitanium(1v) reagent [(r1'-CSHs)TiCl,J.L521
This route is all the more useful in that a selective methylation 13a + 13b does not work. Further stepwise methylation employing stoichiometric amounts of Grignard reagents lead according to Scheme 4b via (now isolable) trimethyl 13c ultimately to the tetramethyl derivative 14.IS2]
15c
Re-0SiMe3
O9 \OSiMeJ
Me3SiOSiMe3
*
15d
13a
158
lib
Ilc-e
15f
IR
deAX2CI
0'
kH2CI
CHZNZ
13b
Ila
13 c
14
,
-=CH,
I
159
Fig. 7. Various organorhenium complexes resulting from chlorine substitution of [(qS-CsMes)ReOCIZ]10 by means of the reagents listed underneath
the respective compounds.
cyclobutane 15a eliminates isobutylene, while the carbonato derivative 15b loses carbon monoxide upon gentle
heating. Sulfur dioxide is (reversibly) lost from 1% at elevated temperature. Ionic compounds of type 15f may
serve as intermediates of chiral derivatives of general
composition [(q'-CsMe,)Re(=O)C1(L)]'. The d o x y compound 15d as well as the stannoxy congener [(q5C,MeS)ReO(OSnMe3)2] are also directly available from 2
and hexamethyldisilane (or the distannane, resp.) in boiling toluene [Eqn. ( c ) ] . ~ ' ~Compound
~]
15e may serve as a
simple model of silica-bound organorhenium catalysts.
Scheme 4h
An interesting exception is the bis(neopenty1) derivative
l l a ' , which is also isolable: upon chlorination with trichloro(q'-cyclopentadienyl)titanium(Iv) cleavage of neohexane leads to formation of the paramagnetic carbyne
complex 13b' (Scheme 4c). This undergoes a reversible
lla'
13b'
Scheme 4c.
Other Lewis base reactions of the title compound 2 are
described in Section 2.10 (Scheme 14).
2.5. Alkylation or Reduction?
A nice comparison for alkylation versus reduction effected by tetramethyltin and its higher homologues is provided by the Re" complex 12 (Scheme 4a) that now presents another very useful key compound in organorhenium
chemistry.[341Even when treated with a n excess of tetramethylstannane, the monomethylated product 13a forms
quantitatively while reduction of rhenium does not occur
at all (Scheme 4a).lS9]Successive methylation reactions of
13a may be achieved, however, with dimethylzinc (no reduction
The fully methylated derivative 14 is a
very water-, air-, light- and temperature-sensitive compound (stable only well below 0°C).[61,621
The partially alkylated members 13b and 13c of this series are best syn1302
one-electron oxidation (El,2 = 0.79 V) and with silver hexafluoroantimonate yields the cationic, diamagnetic product
[(qs-C5Me5)ReC12(=C-CMe,)]'[SbF6] '.lszl
All compounds of the series [(q5-C5MeS)ReL4]are d2Re" systems (L = alkyl, halogen), display singletltriplet
spin equilibria (magnetic measurements and N M R evidence),152.59-61] and have square pyramidal crystal structures with the n-aromatic ligand always occupying the
apex of the polyhedron (Fig. 8).
Tetraethylstannane reacts with the tetrachloride 12 to
give the dinuclear complex 16. The ethylrhenium(v) intermediate [(qs-CsMe5)ReC13(C2Hs)](Scheme 5) is probably
formed but is further reduced to the stable rhenium(1v)
dirner of net composition [(q'-CSMes)ReC1,] with concomitant formation of ethylene and ethane (no hydrogen).[591In
terms of structure, the dimer 16 is related to a-(ReCI,J in
that it also displays two chloro bridges between rhenium
atoms. Due to the bulky five-membered ring ligand, howAngew. Chem. Int. Ed. Engl. 27(1988/ 1297-1313
double bond (250.6( < 1) pm), the rather low reactivity towards neutral ligands such as alkynes becomes evident.
ti&. x A l l [(q'-C',KI)KeLI] complexes have a square-pyramidal ('pianostool') geometry. The example shown here is the first homoleptic organorhenium(v) compound, tetramethyl(q'-pentamethylcyclopentadienyl)rhenium
14. Due to disorder phenomena, individual structural parameters cannot be
given for this particular compound; average Re-Cl.. .C4 distances 217(3)
pm, average CReC angles 81(1) and 136(1)'.
[pm] and angles
["I:
Re-Re' 250.6( < l), Re-Cl(termina1) 240.6( I), Re-
+Sn(C,H,),
Scheme 5
ever, the polymeric chain structure of rhenium tetrachloride[26b1is cut down to dinuclear ensembles in the 'organic'
derivative 16 owing to its bulky n-aromatic ligand (Fig. 9).
The compound is also available from the ReVprecursor 12
by reduction with electropositive metals, preferably powdered aluminum (Scheme 5).
Fig. 9. Molecular structure of the orgahorhenium(iv) complex 1 6 [(q5C5Me4Et)ReCl3j2.1 6 was synthesized by reduction of [(q'-CsMe,Et)ReCIJ
12' with Sn(C2Hh or AI/HgC12. Shown is a computer-generated space-filling model that underlines the cis geometry of the two five-membered ring
ligands. - Re-Re' 307.4( < 1) pm.
The Re:" dimer 17 obtained by further reduction of 16
(and vice versa) by means of HgC1,-activated aluminum
(Scheme 5 ) is shown in Figure 10 for the sake of comparison. From the close packing of both the bridging and the
terminal chloro groups around the (formal) metal-metal
Angew. Chem. Int. Ed. Engl. 27 (1988) 1297-1313
2.6. Olefin Metathesist6''
Schrock has repeatedly pointed out that higher metal oxidation states (e.g. W'") are essential for olefin metathesis,
a mechanistically interesting and commercially important
process.L661Since Re2O7/Sn(CH3),/A1,O3 represents an effective (heterogeneous) olefin metathesis catalyst system, it
appeared obvious that the methylrhenium oxide 4 would
serve as a key to the understanding of this special catalyst/
cocatalyst system.
As a matter of fact, 4 catalyzes both ring opening polymerization of cyclopentene and metathesis of openchained olefins but requires aluminum trichloride and excess tetramethylstannane in order to d o
The Lewis
acid effect upon olefin metathesis has been emphasized by
Osborn et al.,'671 and we believe that the Lewis acid AIC13,
in Our case,
an Oxygen atom Of CH3Re03
in Order
to introduce one o r two more methyl groups so that the
prerequisites for carbene-ligand generation via
of methane according to the generally assumed reaction
sequence (d) are fulfilled. That this may not be a poor hypothesis is demonstrated by the fact that compound 9b
which has the higher CHJRe ratio of 3/1 does effect olefin metathesis, even in the absence of tetramethylstannane.[47.5 8 4
M(CH3)2
4
M=CHZ
+ CH,
(4
1303
In the light of recent work by Osborn et al., it appears
quite obvious that AICI, first forms an adduct with the organometal oxide with subsequent reduction, which possibility is even more likely in that the related reaction (e) is
-&
o/-y\o
0
2
known.[341We have in fact isolated a red, crystalline compound of composition [(q5-C5Me5)ReO(CH,),I.A1C13 18 at
low temperature which decomposes upon warming to ca.
O"C.158'1By way of analogy, reductive chlorination [Eqn.
(f)] of 4 with subsequent chlorine/methyl exchange by excess tetramethylstannane may not be pure fantasy. This
proposal would involve oxidation state + 5 at rhenium to
promote olefin metathesis processes.
+
+
[CH3Re03] AIC13 ---t [CH3ReO2CI2] (AIOCI)
(f)
In continuation of such considerations we have recently
been able to establish a catalyst system which surpasses all
previously known rhenium-containing catalysts in the
metathesis of functionalized (!) 01efins.[~~"'
2.7. Oxidative Coupling of Alkynes; Model Compounds
and Reality
A group at the Amsterdam Shell laboratories reported
the oxidative coupling of two alkyne molecules to give furan derivatives,[681important compounds in industry. This
rather intriguing coupling reaction, in which one C C and
two OC bonds are formed, also involves participation of
the organorhenium(vI1) oxide 2 (Scheme 6). While triphenylphosphane alone reacts with 2 with clean formation of
the Re" dimer 20 according to equation (g), the novel
rhena(v)-pyrans 19 are formed as isolable compounds in
the presence of alkynes, e.g. 2-butyne. These latter compounds 19 undergo double metal-carbon bond cleavage
upon successive treatment with iodine.[681
A further challenge for organometallic oxide chemistry
is to carry out the oxidative coupling outlined in Scheme 6
as a catalytic reaction. A synthesis of pyrroles via participation of imido groups (NR) attached to rhenium should
also be conceivable. An alkyne/alkyne/sulfur coupling
reaction catalyzed by cyclopentadienylcobalt complexes
has recently been described by B6nnemann.[691
The attractive-looking synthesis of heterocycles mentioned in the preceeding paragraph warrants a better understanding of the largely unexplored interactions between
alkynes and organorhenium fragments of intermediate oxidation states.
1304
I
I
Scheme 6.
Alkynes are rarely found as ligands in organorhenium
complexes, even with rhenium in low oxidation states.
Probably best known are alkyne-to-vinylidene isomerizations at Re' centers.[701Trivalent rhenium forms several
structurally simple oxidic alkyne complexes 21a, b , the
synthesis of which has recently been reported by Mayer et
al. (Scheme 7).[28,7'.721
The assignment of oxidation states is
of course rather formalistic here since the alkynes seemingly act as 4e-ligands. The same problem is encountered
in the case of the unprecedented Re" complexes
[(RC=CR),Re,O,] 21c (characterization by means of Xray diffraction techniques).[731
R=CH3.C2H,
21c
Scheme 7.
Clean reductive substitution (Re7@-Re5@)of alkynes
for 0x0 groups occurs at methyltrioxorheniurn(~~~)
(4) in
the presence of polymer-bound (!) triphenylphosphane as
a selective reductant. A whole range of thermally rather
stable n-alkyne complexes 22 has thus been prepared according to Scheme 8.[741The occurrence of isomers in the
cases of 22c and 22e suggests high rotational barriers between the metal and the alkyne ligands. Even the unsubstituted acetylene ligand of compound 22a does not exhibit
fast rotation on the N M R time scale u p to at least 100°C.
Scheme 8. @ = polymer-bound P(C,H,), [74]
Angew. Chem. Int. Ed. Engl. 27 (1988) 1297-1313
(left).[751It derives from the C,-alkyne by loss of a hydrogen atom, with concomitant metal-to-carbon chlorine
transfer. The structure of 24 is best interpreted as an allylidene complex on geometrical
Finally, a third
product 25 of unknown identity proved very useful for
subsequent reductive carbon-carbon coupling processes.
Thus, excess 2-butyne yields a mixture of two isomeric
Re'"-1,3-diene complexes 26 and 27, respectively (Scheme
9). The diene complex 26 can also be prepared under reductive conditions from 12 and 3,4-dimethyl-2,4-hexadiene.r761
Fig. 1 I . Molecular structure of [CH,Re02(q2-C6H5C-CCaHS)I 22h. The
compound crystallizes from melhylenechloride/n-hexane at -25°C in the
monoclinic space group P2,/c.-Selected bond lengths [pm] and angles ["I:
Re-0 174.0(4) and l71.0(1), Re-CH, 209.2(7), C-C(ethyne) 128.0(9); OReO
I19.5(2) 1741.
An X-ray structure of 22h confirms the suggested structure
(Fig. 11) which is in contrast with theoretical predictions.["' Note that all attempts to synthesize the analogous
compounds with a pentamethylcyclopentadienyl ligand in
place of the methyl group have thus far failed. Thus the
butyne-Re"' complex [(q5-C5Me5)ReO(q2-MeC=CMe)]
(33) does not undergo oxidation to give (the hitherto unknown) ReV derivative [(q5-C5Me5)Re02(q2MeC-CMe)].[64"1 Oxidation of 33 (R = Ph) with ferricinium salts cleanly furnished the dinuclear cation [(I$-
Fig. 12. Left: Molecular structure of the allylidene complex 24. Selected
bond lengths [pm] and angles ["I: C13-C2 178.8(3), Re-CII 239.1(1), Re-C12
241.9(1); CIlReC12 82.27(3).-Right: Structure of the cationic bis(q'-butyne)
complex 29 in the crystal, Br instead of CI (see Scheme lo).-Selected bond
lengths [pm]: C=C 136(2) and 124(2), Re-C 199(1)/201(1) and 198(2)/202(2).
The crystal contains dichloromethane ( I : I).
C5Mes)zRez(~-O)z(tolan)2]'.~wa1
CH.
CH,~
'
CH,
C
H
AIIHgCI,.THF, 25'C
24
23
60-65%
,
< 5%
1
26
25
30-40%
I
AI/HgCI,;THF, 25°C
Chlorine/pyridine exchange at the stage of 23 to form
compounds of type 28 is achieved by silver hexafluoroantimonate (Scheme 10). Likewise, a second alkyne may be
introduced if one removes a chloride group from 23 by
means of AgSbF, in the presence of the new alkyne to
enter the molecule. The cationic bis(n-alkyne) complexes
29 (Fig. 12, right) exhibit free metal-to-alkyne rotations
only at higher temperatures. Rotational barriers around 60
kJ mol - have been established by temperature-dependent
NMR s p e c t r o ~ c o p y . [ ~ ~ ~ , ~ ~ ]
A synthetically useful acid catalysis effect is demonstrated by 71-alkyne complexes of type 23 (d4-Re'"); CC
coupling processes that d o not work in the absence of
Br~rnstedacids take place when 23 is treated with traces of
27
Scheme 9.
Further deoxidation of compounds 22 is only possible
with polymer-bound triphenylphosphane under more drastic conditions, e.g., boiling toluene. The expected mononuclear Re"' derivatives [CH3Re0(q2-RC-CR)2], however,
are not formed, but rather the dinuclear RefVspecies of
composition [(p-O)(CH3ReO(q2-RC=CR)]2](X-ray structural analysis for R = CH3).["I
The Re"' complex 23 (with 2-butyne as 4e-ligand) is accessible according to Scheme 9 by reduction of the parent
ReVcompound 12.163.751
In terms of further chemical transformations, chlorine replacement at the stage of compound
23 by alkyl and 0x0 groups is particularly
The byproduct of the Rev-reduction outlined in Scheme
9 is the Rev-vinyVcarbene derivative 24, whose unexpected composition and structure are shown in Figure 12
Angew. Chem.
Int.
E d . Engl. 27(1988) 1297-1313
R
CH3
28
23
CH3
29
31
32
29
Scheme 10.
1305
HBF, in the presence of ethylene or cis-2-butene. The 1,3diene complexes 31 and 32 (Fig. 13, left), respectively, are
thus obtained in yields around 80% (Scheme
Stoichiometric amounts of HBF, suffice to achieve fast chlorine substitution in the presence of acetonitrile to give the
(chiral) ionic compound 30 according to Scheme
Fig. 13. Left: Structure of the 1,3-diene complex 32 in the crystal. Right:
Structure of the alkyne(ox0) complex [(qS-C5MeS)ReO(q2-C6HSC=CCOHS)]
33 in the crystal.-Selected bond lengths [pm] and angles ["I: Re-0 171.0( I),
C - C 130.0(2), Re-C(alkyne) 203.0( I), 203.6( I); C(CaHs)-C-C 142.212) and
145.6(2).
The synthetic potential of Re"' alkyne complexes such
as 23 (also Br and I in place of Cl, and R = alkyl, aryl) is
further demonstrated by their smooth hydrolysis to give
novel oxo(a1kyne) derivatives 33 (33, R = Ph, see Fig. 13,
right), and by their reaction with Grignard compounds to
form 34 and 35.1631
33"
34
35
2.8. The Search for Organorheniurn Oxides
that Oxidize Olefins
osmium work on the cis hydroxylation of olefins to 1,2glycol^.[""^^^] In spite of the fact that the osmium tetroxide
used in these catalytic reactions is extremely toxic (maximum working concentration 0.002 mg .m - 3 ! ) , no better replacement has been found as yet. This is a result of our
rather crude general knowledge of the hydrocarbon chemistry occurring at high-valent transition metals. It may certainly be true that metals other than 0s""' are inferior in
oxidation power, but a 'tune up' towards the right potentials and intermediates seem possible by way of tailored
auxiliary ligands. In this important area of metal-mediated
oxidation chemistry, a similar development as that which
occurred in low-valent coordination compounds for hydroformylation, olefin hydrogenation etc. is conceivable.
Instead of the 'soft' phosphanes useful for these latter
processes, the 'hard' 0x0, alkoxide, and imido ligands
might yield step-by-step improvements at the higher oxidation states of transition metals.
To this end, we have synthesized a number of rhenium(v) glycolates as well as their 0 , N - , 0,s-, and S . S
c o n g e n e r ~ . [ ~ ~Apart
, ' ~ ] from a few exceptions, these compounds are in general thermally quite robust, but heating
above the melting points effects selective oxygen-carbon
bond breaking in the case of the glycolate compounds with
formation of the corresponding olefins. Since H @ / H 2 0 2
treatment, on the other hand, cleanly gives glycols and the
rhenium(vI1) oxide 2 (Scheme 1I), the only missing link in
a catalytic cycle is direct cycloaddition of the olefins to the
oxide 2. Since activated carbon-carbon double bonds like
those in ketenes undergo clean [3 21 and [2 + 21 cycloaddition reactions to produce compounds 37 and 38 according
to Scheme 12 (X-ray c h a r a c t e r i ~ a t i o n ) , [ ~it~appears
. ~ ~ ] just
a matter of enhancing the ReO, core reactivity, e.g. by replacement of the C,Me,-ligands by more electron-withdrawing groups (e.g. CF3), in order to reach the penultimate goal of removing the question mark from Scheme 9.
This has been achieved for several derivatives of methyltrioxorhenium(vr1) 4['Ob1 and, at the same time, replaces
the model compounds by a catalytic cycle.
+
The formation of furans from rhena(v)-pyrans according
to Scheme 6 constitutes an oxidative carbon-carbon coupling process during which the metal stays in oxidation
state + 5 ; in this reaction elemental iodine is the oxidizing
agent.@'] Redox-neutral rhenium-oxygen bond cleavage
occurs when five-membered metallocycles of type 36 are
treated with Brclnsted acids such as HBF, according to
Scheme 1
GeClz
\
N a O u O H
L = q5-C,Me5
Scheme 12.
Organometallic glycolate complexes of other metals of
relevance in oxidation processes have also been synthesized. Thus, the organovanadium(v) species 39[80,"1forms
the dinuclear compound 40 having a V,0,C2 seven-membered ring geometry (Fig. 14).[82,971
Scheme I I
The metallocycles 36 may alternatively be viewed as
0.0-glycolate complexes like those known from Sharpless'
1306
Angew. Chem. Inl. Ed. Engl 27 (1988) 1297-1313
I'Pycr
CI
CI . CI
12
Scheme 13.
Fig. 14. Structure of the dinuclear organovanadium(v) complex 40 in the
crystal.-Selected bond lengths [pm] and angles ["I: V=O 159.8(1), V-O(glycolate) l81.0(1), V-O(bridge) 177.7(1); VOV' 127.0(1).
Apart from their catalytic potential (e.g. for amine oxidation), N.0-metallocycles analogous to 38 provide easily
accessible starting materials for the synthesis of imido
Instead of glycolate ligands other anionic chelates can
be attached to rhenium(v); examples are the carbonatoand sulfato compIexes 15b and 15c, respectively (Fig.
7).IS31 Rhenium-attached oxometalates of transition rnet a l ~ @(e.g.
~ ] [Cr2O7JZS)are presently being investigated for
their potential as organometallic catalysts on oxidic metal
surfaces.
2.9. New Polyhydrides of Rhenium
Despite the uniqueness of our two title compounds [(q5C,Me,)Re03] (2) and [CH3Re03](4), it emerges from what
has been outlined in the previous chapters that rhenium
chemistry resembles that of molybdenum and tungsten
much more than the chemistry of any other element, with
the possible exception of osmium on the right and tantalum on the left.[ss1Only with these three elements, molybdenum, tungsten, and rhenium is it possible to catalyze olefin
metathesis at an industrially acceptable
Beyond
this 'catalysis bracket', there are numerous analogous compounds, and the reader need only be reminded of the metal-metal multiple bonded compounds comprising a major, attractive part of the chemistry of these elements.'5f
Moreover, rhenium, like molybdenum and tungsten, is
compatible with hydrogen and hydrido ligands (H2 and H,
resp.) across the entire range of oxidation states.[861Let it
suffice to mention only the textbook example of nonahydridorhenate(vii), [ReH9]2e.rs7JHydrogen atoms attached
to rhenium can also be found at low oxidation states such
as Re' in the examples [HRe(CO),] or [H3Re3(CO)IZ]and
many other complexes.[701As a matter of fact, the redox
versatility of hydridorhenium species is a great advantage
of &/kin's carbon-hydrogen activation catalysts of type
[L2ReH7](L = PR3)[ss1while there is a demand for further
improvement of catalyst activity and ~electivity.[*~]
The novel neutral rhenium(vi1) hydride 41 - air-stable,
sublimable, thermally robust up to the melting point at
192"C!-can be prepared in 75% yield by treatment of the
Re"-complex 10 with lithium aluminum hydride in diethylether at low temperatures and subsequent reaction of the
The yields of
intermediate with methanol (Scheme 13).L901
Angew. Chem. Int. Ed. Engl. 27 (1988) 1297-1313
J
41
Cp*ReD,
-
2
the mononuclear hexahydride 41 are lower when the tetrachloride 12 is used as a starting compound; in this case
the dinuclear hexahydride 42 is also formed. This syntheI(T~-C~M~~)Z
42R ~ ~ H ~ I
sis is mechanistically not fully understood but it is tempting to assume that the Re" precursor compounds 10/12
are first converted into an intermediate [(qs-C5Mej)ReH4],
which subsequently undergoes formal oxidative addition
of H, (from LiAIH4/CH30H). The compound has a fluctional pentagonal-bipyramidal structure (temperature-dependent NMR experiments). Neohexene is hydrogenated
by 41. When [(q5-CSMe5)ReD6]is used, a mixture of several neohexane isotopomers (Scheme 13, bottom) is observed by GC/MS.L58"1
Both thermal ( > 200°C) and light-induced elimination
of hydrogen ( O O C ) from 41 yield the red-colored, air-stable, dinuclear rhenium(1v) hydride 42. According to a lowtemperature X-ray diffraction study ( - 100°C), two terminal and two bridging hydrogen atoms are present on each
rhenium atom of 42' (C,EtMe, instead of CSMe5) (Fig.
15).I9']
Fig. 15. Structure of the organorhenium(1v) complex bis[(p-hydrido)dihydrid~(~~-ethyltetramethylcyclopentadienyl)rhenium](R~
Re) 42' in the crystal
at - 160°C. - Re-Re distance 245.2(1) pm (triple bond).
Photolysis of 41 in the presence of trimethylphosphane,
however, furnishes the derivative 43, whereas treatment
with hot carbon tetrachloride results in formation of the
chloro complex 44 in a radical-type d a r k - r e a ~ t i o n . ~ ~ ~ ]
1307
2.10. How Useful is the
Pentamethylcyclopentadienyl Ligand Really?
polymerization a t
hydrocarbon
liqand
site o f
The n-bonded pentamethylcyclopentadienyl ligand was
fortunately retained at the metal when Serrano first synthesized the title compound 2 by light-induced oxidation of
the parent carbonyl precursor 1 .I3'] Excellent solubility of
compound 2 and of essentially all derivatives in common
organic solvents enabled us to quickly develop this type of
high oxidation state organorhenium chemistry after we
had found that purification of the compounds could be
achieved by low-temperature column chromatography on
silylated silica gel. The bulky ten-carbon ring ligand prevents more complicated reactions to occur but rather directs them to the R e 0 3 core.
On the other hand, cleavage of the rhenium-carbon
bonds of 2 is occasionally encountered. For example,
deoxygenation effected by (p~lymer-bound~'~])
triphenylphosphane cleanly yields the synthetically useful rhenium(v) compound 20 (see Scheme 14 and Section 2.7),
but only if atmospheric oxygen is strictly excluded.1341
Otherwise, partial loss of the n-aromatic ring comes to the
fore, with the perrhenate groups showing u p in the products. The two structurally characterized compounds 45
and 461931are good examples (Scheme 14).
024%0
2
oxide anchonng
at incrqanic
suppr t 8
Scheme 15
l e g AlZO3 Si0,I
2.11. Sulfur and Selenium Instead of Oxygen?
The higher homologues of oxygen -sulfur and particularly selenium -are of great interest in organic synthesis
or for medical applications.1951The hitherto unknown sulfur and selenium congeners of compounds 2 and 4 are attractive target molecules. That oxygen is in fact prone to
replacement by sulfur and selenium is evident from two
reactions: (i) Treatment of [(q5-CSMes)ReOCl2]10 with
bis(trimethylsily1) sulfide gives the oxygen-free compound
47 among other organorhenium sulfides from which the
main product has so far resisted
(ii) Four
sulfur atoms are transferred from [(qs-CsH,),TiS5] to the
same organorhenium(v) compound 10 to form the air-stable, mononuclear complex 48 in a surprisingly clean reaction ( 290% yield). The five-membered, non-planar ReS,
ring system thus generated is evident from Figure 16.19']
p
Fig 16 Molecular structure of the ReS4 metallacycle 48 -Selected
distances [pm] R e - 0 171 8(3), Re-S 2264(1) and 2244(2)
Scheme 14. In 45 we have the cornhination ReV/ReV", in 46 Refih6/ReV":
20 is a ReV/Rev complex.
These findings revealed that at some (mechanistically
unknown) stage of the reaction atmospheric oxygen may
split off the hydrocarbon n-ligand, which would therefore
have to be replaced by better ones such as the more tightly
bonded methyl
Now that we have achieved this
goal by preparing methyltrioxorhenium(vr~)(4) from
Re20, and Sn(CH3),, the entire range of compounds merits
a firm place in catalysis research.[471In this context, the alkyl ligand might be exploited for the generation of polymer chains that carry isolated metal oxides MO,. Models
for surface-anchored catalysts may be obtainable via 0,Ochelation (Scheme 15).
1308
bond
Due to the much higher catenation and cyclization tendency of sulfur and selenium over oxygen, this chemistry
appears by far less predictable at present, but nevertheless
presents another exciting challenge for skilled experimentalists.
2.12. Back to Monovalent Rhenium A Play with Oxidation States
We now return to our starting point of monovalent rhenium. Conversely to its mode of formation, the title compound 2 can be reduced by carbon monoxide under pressure or by the oxophilic carbonylation reagent [($
CsHs)2Ti(C0)2]at normal pressure.[361If there is only one
terminal 0x0 group present, reductive carbonylation follows the overall equation (h).
Angew. Chem. I n f . Ed. Enql. 27 (1988) 1297-1313
[L,M"=O]
+ 3 CO +[L,Mx-2(CO)J + C02
(h)
Typically, the ReV chelate complex 38 is reduced to the
Re"' complex 49 (X-ray characterization) with concomitant isomerization of the bidentate 0,C ligand (Scheme
16).L441
38
4. x-Acceptor versus x-Donator Ligands:
Molecular Orbital Reasoning for Stability
Bursten et al. addressed the basic question of d-electron
count vs. stability of high- and low-valent piano-stool comp l e x e ~ . [To
~ ~ this
] end, they subjected the structurally analogous compounds C and D of idealized C, symmetry to
Fenske-Hall molecular orbital calculations, from which the
following message becomes evident (Fig. 18):
49
/-
4a'(
Scheme 16
Clean redox processes also take place when the strongly
reducing zirconium(Ir1) complex 50 reacts with the organorhenium(vI1) oxide 2. The desired rhenium/zirconium
oxide was unfortunately not obtained; instead, the homonuclear redox products 20 (Re") and 51 (Zr'"; X-ray characterization) were isolated (Scheme 17).L461The study of
this type of reversible redox processes has only just begun.
[q
4 a"
6 a'
NO 277
5 a'
4 a'
3 a"
Re
o@ '0 *
50
2
51
20
Scheme 17.
3. Pure Speculation?
Being convinced that 71-aromatic ligands d o in fact survive at even the highest possible oxidation states of transition metals, we may speculate about other congeners still
to be discovered. If the isoelectronic principle is going to
hold promise again, then benzene (or its hexamethyl derivative) should not disguise the WO, fragment to give (stable?) A . On the other hand, one should not be surprised to
see a cyclobutadiene ligand in the osmium compound B
some day (Fig. 17). At least in these two compounds, addi-
Fig. 17. Organometal oxides that are isoelectronic with 2. The tungsten and
osmium compounds are as yet unknown.
tional prerequisites for thermal stability are fulfilled: they
belong to the elements of the third transition metal series
that generally form more stable and less strongly oxidizing
high-valent compounds than their 'lighter brothers'. Secondly, the coordination numbers are high enough to avoid
kinetic lability which, for instance, would result in aggregation to dimers o r oligomers. For this latter reason, the
vanadiumfv) compound '[(C,H,)VO,]' announced by Russian
turned out to be trimeric (X-ray structure
Of [(.ilS-C,Me,),v,06]'98h1).
Angew. Chem. Inl. Ed. Engl. 27 (1988) 1297-1313
C
D
Fig. 18. Simplified molecular orbital diagram of d'-tungsten(i1) and d*-rhenium(v) complexes C and D 1991. The neopentyl derivative [(q'C,H,)W(NO)(CH,C(CH,),],] belonging to type C is a known, stable compound (P. L. Legzdins, S. J. Rettig, L. Sanchez, B. E. Bursten, M. G. Gatter, J.
Am. Chem. SOC. 107 (1985) 1411). The ring-substituted derivative [(q'~
C5MeS)ReO(CH3),]and a series of higher alkyl homologues have been synthesized and structurally characterized [34].
1) In the case of the nitrosyltungsten(i1) complex C two
of the metal-centered 5d orbitals are significantly stabilized as a result of an interaction (4a' and 3a") with the very
strong 71-acceptor ligand nitric oxide. By way of contrast,
the 5a' orbital remains non-bonding because the methyl ligands function only as o-donors in the present case. The
splitting of the metal 't22 orbital set amounts to 2.23 eV
according to these calculations.
2) The opposite picture emerges for the rhenium(v) 0x0
complex D. Since a single 0x0 atom is a n exceedingly
good It-donator ligand (as well as a good o-donor), it interacts with the rhenium-centered 5d orbitals to destabilize
two levels by 2.36 eV (4a" and 6a'); the nonbonding 5a'type orbital becomes the HOMO because of the d 2 configuration of the metal atom.
1309
Bursten et al. came to the conclusion that the stability of
the 16-electron complex C (d4-W") can be attributed to
the nonbonding 5a' orbital generated by the strong n-acceptor ligand NO. On the other hand, the 18-electron rule
must no longer be considered in the case of high-valent
organometallic complexes as in D (d2-Re"), since the dorbital levels are generally destabilized by 71-donors such
as the 0x0 group and thus would rather remain unoccupied anyway. The entire pseudo-t2, set of orbitals is destabilized when the metal atom is surrounded by at least two
0x0 ligands, with the existing compounds of type [L,MO,]
( y 2 2) in fact all exhibiting do configuration. However, the
recently synthesized compounds of type 22 (Section 2.7)
are obvious exceptions to this statement. Molecular orbital
calculations of these and other catalysis-relevant transition
metal oxides have already been carried out by Goddard et
al. and Yamaguchi et al.['ool
5. Just at the Beginning
By no means is it of merit to make an accidental discovery. Much more important is the recognition of possible
consequences that might result from serendipity. Organometallic chemistry has certainly seen many organometal
oxides since E. 0. Fischer and his group first had the cubane-type oxide [ ( ~ l ' - C ~ H ~ ) ~ C in
r ~ 0their
~ 1 hands in
1960.[s3"1Systematic studies have now begun in this field
with the key compounds 2 and 4. We are, as it were, just
starting to learn such apparently simple things as the reaction of dirheniumheptoxide with tetramethyltin. One of the
major short-term goals is to establish the relationship between redox chemistry at the metal and the reactivity of
the ligands surrounding it. Any synthetic enterprise should
be oriented toward new stoichiometric and catalytic hydrocarbon reactions o r towards the improvement of those already known. Rhenium is certainly an ideal case for demonstrating how both low and high oxidation states are
stabilized by good n-acceptor and n-donor ligands, respectively.
Further aims include the correlation of readily obtainable I70-NMR data["'] and electrochemical data with the
redox processes occurring at metals attached to oxygen(s).
Reduction['oz1and oxidation['o31processes of great practical benefit may thus become better understood and optimized. Planned organometallic studies must be carried out
in order to elucidate even simple-looking, useful reactions
occurring at metal oxide structures."o4i The stage is already
set for the anchorage of organometallic oxides to surfaces
in order to gain more insight into the consequences of metal oxide surface effects for catalytic activity.['o51Hardly
anything is known about this important issue to date; and
that what is known can be quite confusing because of a
lack of model substances.'Io6l In addition, the isomerism
between dioxo- and peroxo systems M(O), and M(O,), respectively, is of basic importance."o71
Since this review and previous e ~ i d e n c e [ lo'~. ~Ioyl
. ~ may
~.
convince us that organometallic oxides are compatible
with classical "inorganic" oxides, both these areas of
chemistry should converge in the near future. Suffice it to
say that even bioinorganic problems also fall within the
realms of high-valent organometallic oxides!"'o.'''l
1310
The author is greatly indebted to those co-workers who are
fond of organometallic oxides. Since these scholars only happen to show up in the publications, they at least deserve being
named here in appreciation of their enthusiastic, thoughtful,
and skilled contributions: Dr. Tomas Cuenca, Josef K. Felixberger, Roland A . Fischer, Martina Floel, Dr. Peter Harter,
Karin A. Jung, Dr. Heinz-Josef Kneuper, Josef G. KuchIer,
Dr. Ulrich Kiisthardt, Jiirgen Kulpe, Monika Ladwig, Dieter
Marz, Dr. Babil Menjon, Dr. Jun Okuda, Dr. Rocco Paciello, Dr. Adolf Schayer, Prof: Dr. Ricardo Serrano, Helmut
Theiler, Werner Thiel, Dr. Erdmuthe Voss, Werner Wagner,
and Georg Weichselbaumer. The entire research group particularly acknowledges the outstanding crystallographic performances of Dr. E. Herdtweck assisted by Pavlo Kiprof in
our laboratories. Generous support comes from the Deutsche
Forschungsgemeinschaft, the Fonds der Chemischen Industrie, the German Bundesministerium fur Forschung und
Technologie, Hoechsr Aktiengesellschaft, Degussa A G, Hiils
Aktiengesellschaft, BASF Aktiengesellschaft, Ruhrchemie
AG, Alexander von Humboldt Foundation, Merck'sche Gesellschaft f u r Kunst und Wissenschaft e. V., the Spanish Ministery of Education and the Deutsche Akademische Austauschdienst. We express our gratitude for financial help that
we have been receiving from these companies and institutions. Miss Juliane Geisler is greatfully acknowledged for the
typescript of this article, Erich Krebs for the skilful drawings.
The author had the privilege of being hosted as a 'Professeur
Associk' by his colleagues Didier Astruc (Universitk de Bordeaux I ) and Igor Tkatchenko (C.N.R.S. Toulouse), without
whose generosity this essay may not have materialized. Of
particular benefit were the stimulating discussions with Professor Jean- Marie Basset (C.N. R.S. Lyon- Villeurbanne)
during his visit as an Humboldt Senior Awardee in our department. Freya and our jive children are once again
thanked for their patience.
Received: December 15, 1987 [A 691 IE]
German version: Angew. Chem. 100 (1988) 1269
Publication delayed at author's request
14000 organometallic compounds are listed and referenced in J. Buckingham (Ed.): Dictionary of Organometallic Compounds, Chapman and
Hall, London 1984. -This monumental series of monographs is the
most comprehensive and informative one that has been published up to
the present (nine volumes, 8750 pages): G. Wilkinson, F. G. A. Stone,
E. W. Abel (Eds.): Comprehensiue Organometallic Chemistry. Pergamon
Press, Oxford 1984.
Several readable textbooks on organometallic chemistry have recently
appeared: a) A. Yamamoto: Organotransition Metal Chemistry - Fundamental Concepts and Applications. Wiley, New York 1986; b) C. Elschenbroich, A. Salzer: Organometallchemie. 2nd Edit., Teubner-Verlag, Stuttgart 1988; c) J. P. Collman, L. S. Hegedus, J. R. Norton, R. G.
Finke: Principles and Applications of Organotransition Metal Cbemistrv.
2nd Edit., University Science Books, Mill Valley, CA, USA 1987; d) J.
S. Thayer: Organometallrc Chemistry. VCH Publishers, New York
1988; e) R. H. Crabtree: The Organometallic Chemistry of the Transition
Metals. Wiley, Chichester, England 1988.
Critical assessment of the present state and of the perspectives of organometallic chemistry: a) G. W. Parshall, Organometalhcs 6 (1987) 687;
b) W. A. Herrmann, Kontakte (Darmstadtj 1988. No. 1, p. 3.
a) F. A. Cotton, N. F. Curtis, C. B. Harris, B. F. G. Johnson, S. J. Lippard, J. T. Mague, W. R. Robinson, J. s. Wood, Science 145 (1964)
1305;b) F. A. Cotton, J . Chem. Educ. 60 (1983) 713.
Monographs and reviews on metal-metal bonds: a) F. A. Cotton, R. A.
Walton: Multiple Bonds between Metal Atoms. Wiley, New York 1982:
b) M. H. Chisholm (Ed.): Reactivity ofMeta1-Metal Bonds (ACS Symp.
Ser. Val. 155). American Chemical Society, Washington D.C., USA
1981; c) M. H. Chisholm, I. P. Rothwell, h o g . Inorg. Chem. 29 (1982)
I ; d) M. H. Chisholm, Angew. Chem. 98 (1986) 21; Angew Chem. Int.
Ed. Engl. 25 (1986) 21; e) Bare (unsubstituted) main group element
atoms as multipiy bonded ligands in organotransitionmetal chemistry:
W. A. Herrmann, ibid. 98 (1986) 57 and 25 (1986) 56.
Angew. Chem. Int. Ed. Engl. 27 (1988) 1297-1313
COSir cf. Pure Appl. Chem. 55 (1983) No. I I ; ibid. 5 7 (1985) No. 12;
ibid 59 (1987) No. 1 I .
1181 Recent review articles: K. H. Dotz, Angew. Chem 96 (1984) 573; Angew Chem. Int. E d . Eng/ 23 (1984) 587; B. M. Trost, ibid. 98 (1986) 1
and 25 (1986) I ; J. K. Stille, ibid. 98 (1986) 504 bzw. 25 (1986) 508; H.
Kasuda, A. Nakamura, ibid. 99 (1987) 745 and 26 (1987) 723; L. S. Hegedus, ibid. 100 (1988) 1147 and 27 (1988) l l 13.
1191 Metal-metal multipe bonding is featured by quite a number of simple
(1986) 3139; c) Nouu. J . Chim. 8 (1984) 271; d ) S. Kanemoto, K. Oshima, S Matsubara, K. Takai, H. Nozaki, Tetrahedron Lett. 24 (1983)
2185; e) J. Muzart, ibid 28 (1987) 2131, 2133.
[24] Largely unknown is also the nature of active oxidants in systems such
as Mo(CO),/tBuOOH and MoOJHMPT nor have the issues of solvent effects been resolved as yet, cf. H. Mimoun, 1. S. d e Roch, L. Sajus, Tetrahedron 26 (1970) 37.
1251 R. K. Grasselli, J. D. Burrington, J. F. Brazdil, Faraday Di.scuss. Chem.
Soc. 72 (1982) 203. - The ,activation’ (functionalization) of natural gas
also occurs on oxidic sites, cf. H. Mimoun, New J . Chem. I 1 (1987)
513.
[26] For the chemistry and structures of inorganic rhenium compounds,
see: a) N. N. Greenwood, A. Earnshaw: Chemistry oJthe Elements. Pergamon Press, Oxford 1984, p. 1211ff; b) A. F. Wells: Structural Inorganic Chemistry. 5th Ed.. Clarendon Press, Oxford 1985, p. 424.
[27] a) K. Mertis, D. H. Williamson, G. Wilkinson, J. Chem. Soc. Dalton
Trans. 1975. 607; b) K. Mertis, L. Galyer, G. Wilkinson, J. Organomet.
Chem. 97(1975) C65; c) P. G. Edwards, G. Wilkinson, K. M. A. Malik,
M. B. Hursthouse, J . Chem. Soc Dalton Trans. 1980. 2467; d ) PE spectroscopy: J. C . Green, D. R. Lloyd, L. Galyer, K. Mertis, G. Wilkinson,
ibid. 1978, 1403.
[28] R. Dagani, Chem. Eng. News 62 (1984) No. 30, p. 28.
I291 W. A. Herrmann, E. Voss, M. Floel, J. Organomet. Chem. 297 (1985)
CS; see also: Ref. [34b] for the synthesis procedure.
I301 Original communication: W. A. Herrmann, R. Serrano, H. Bock, Angew. Chem 96 (1984) 364; Angew. Chem. f n t E d . Engl. 23 (1984) 383;
see also: Nachr. Chem. Tech. Lab. 32 (1984) 202.
[31] W. A. Herrmann, R. Serrano, A. Schafer, M. L. Ziegler. E. Guggolz, J .
Organornet. Chem. 272 (1984) 55.
[32] Structure: E. Herdtweck, J. Okuda, W. A. Herrmann, Inorg. Chem. 27
(1988) 1254; see also [34b, c].
[33] This compound was independently prepared by another research
group: A. H. Klahn-Oliva, D. Sutton, Organometallicc 3 (1984) 1313.
[34] Previous reviews on the chemistry of trioxo(q5-pentamethylcyclopentadienyl)rhenium(vil): a) W. A. Herrmann, J . Organomer. Chem. 3(JO
(1986) 1 1 I ; b) W. A. Herrmann, J. Okuda, J . Mol. C a r d 41 (1987) 109;
c) W. A. Herrmann, E. Herdtweck, M. Floel, J. Kulpe, U Kusthardt, J.
Okuda, Polyhedron 6 (1987) 1165: d) W. A. Herrmann in A. d e Meijere,
H. tom Dieck (Eds.): Organic Synthesb with Organometallic Compounds, Springer, Berlin 1987.
[35] Other high-valent organometallic oxides are listed in Ref. [34c].
More recent examples: a) I. Feinstein-Jaffe, D. Gibson, S. J. Lippard.
R. R. Schrock. A. Spool, J . Am. Chem. SOC.106 (1984) 6305 (&,W,O,:
R = neopentyl; linear W 2 0 i core structure); b) A. D. Horton, R. R.
Schrock, J. H. Freudenberger, Organometallics 6 (1987) 893 (reactions
of [Me3SiORe03]);cf. D. S. Edwards, L. V. Biondi, J. W. Ziller, M. R.
Churchill, R. R. Schrock, ibid. 2 (1983) 1505: c) S. G. Blanco, M. P.
Gomez-Sal, S. Martinez-Carreras, M. Mena, P. Royo, R. Serrano, J .
Chem. SOC.Chem. Commun. 1986. 1572 ([(qS-C,Me,)Ti(CH,)OIi): d) B.
Heyn, R. Hoffmann, Z. Chem. 16 (1976) 195, 407 ([mes2MoO2],
mes = mesityl); e) P. Stavropoulos, P. G. Edwards, T. Behling, G. Wilkinson, M. Motevalli, M. B. Hursthouse, J. Chem. SOC. D d t o n Trans.
1987, 169 ([mes2Re02]): 9 H. Arzoumanian, A. Baldy, R. L a . J. Metzger, M -L. Nkeng Peh, M. Pierrot, J . Chem. SOC.Chem. Commun. 1985.
1 151 ; g) R. Lai, S. LeBot, A. Baldy, M Pierrot, H. Arzournanian, ihid
1986. 1208; h) R. R. Schrock, 1. A. Weinstock, A. D. Horton, A. H. Liu,
M. H. Schofield, J . Am. Chem. SOC. 110 (1988) 2686; i) F. M. Su, <‘.
Cooper, S. T. Geib, A. L. Rheingold, J. M. Mayer, rbid. 108 (1986)
3545.
1361 W. A. Herrmann, R. Serrano, U. Kusthardt, M. L. Ziegler, E. Guggolz,
T. Zahn, Angew. Chem. 96 (1984) 498; Angew. Chem. Int. E d Engt 23
(1984) 515.
[37] W. A. Herrmann, R. Serrano, M. L. Ziegler, H. Pfisterer, B. Nuber.
Angew. Chem. 97 (1985) 50; Angew. Chem. lnt. Ed. Engl. 24 (1985)
looking inorganic compounds. For example, La2ReOSand NaNb,05F
contain multiply bonded M2L8 units completely analogous with
[Re2C1,]20: a) K. Waltersson, Acta Crystallogr. Sect. 8 3 2 (1976) 1485;
b) J. Kohler, A. Simon, Angew. Chem. 98 (1986) 1011 ; Angew. Chem.
Int. Ed. Engl. 25 (1986) 996 and references cited therein.
120) R. Hoffmann, Angew. Chem. 99 (1987) 871; Angew. Chem. lnt. E d .
Engl. 26 (1987) 846.
[2 I ] Monographs and reviews on metal-mediated oxidation processes: a) R.
A. Sheldon, J. K. Kochi 1 Metal-Catalyzed Oxidations of Organic Compounds. Academic Press, New York 1981; b) B. Meunier, Bull. SOC.
Chrm. Fr. 59 (1987) 759; c) H. Mimoun in G. Wilkinson, R. D. Gillard,
J . A. McCleverty (Eds.): Comprehensive Coordination Chemistry, Pergamon Press, Oxford 1987, p. 317ff.
[22] a ) G. Cainelli, G. Cardillo: Chromium Oxidations in Organic Chemistry.
Springer, Berlin 1984; b) W. J. Mijs, R. H. d e Jonge (Hrsg.): Organic
Syntheses by Oxidation with Metal Compounds, Plenum Press, New
York 1986: c) R. H. Holm, Chem. Rev. 8 7 (1987) 1401.
[231 Recent examples: a) E. J. Corey, E.-P. Barrette, P. A. Magriotis, Tetrahe&-fin Lett. 26 (1985) 5855; b) J. Muzart, rbid. 24 (1983) 2185; ibid. 27
[38] W. A. Herrmann, R. Serrano, U. Kiisthardt, E. Guggolz, B. Nuber. M.
L. Ziegler, J . Organomet. Chem. 287 (1985) 329.
[39] W. A. Herrmann, U. Kusthardt, M. L. Ziegler, T. Zahn, Angew. Chem.
97 (1985) 857; Angew. Chem. Int. Ed. Engl. 24 (1985) 860.
I401 W. A. Herrmann, U. Kiisthardt, E. Herdtweck, J . Organomet Chem.
294 (1985) C33.
[411 W. A. Herrmann, E. Voss, U. Kiisthardt, E. Herdtweck. J . Organornet.
Chem. 294 (1985) C37.
1421 U. Kiisthardt, W. A. Herrrnann, M. L. Ziegler, T. Zahn, B. Nuber, J .
Organornet. Chem. 311 (1986) 163.
1431 W. A. Herrmann, M. FIoeI, J. Kulpe, J. K. Felixberger, E. Herdtweck,
J . Organomet. Chem.. in press.
[44] W. A. Herrmann, U. Kiisthardt, A. Schafer, E. Herdtweck, Angew
Chem. 98 (1986) 818; Angew. Chem. Int. Ed. Engl. 25 (1986) 817.
[45] W. A. Herrmann, U. Kiisthardt, M. Floel, J. Kulpe, E. Herdtweck, E.
Voss, J . Organomet. Chem. 314 (1986) 151
1461 W. A. Herrmann, T. Cuenca, U. Kiisthardt, J. Organomet. Chem. 309
(1986) CIS.
[6] E. 0. Fischer, A. Maasbol, Angew. Chem. 76 (1964) 645; Angew. Chem.
In!. Ed Engl. 3 (1964) 580; Chem. Ber. I00 (1967) 2445.
171 Rekiews and monographs o n metal-carbon multiple bonds: a) E. 0.
Fischer, Angew Chem. 86 (1974) 651 (Nobel Lecture); Adu. Organornet.
Chem. 14 (1976) I ; b) J. E. Hahn. Prog. Inorg. Chem. 31 (1984) 205; C)
L Schubert, H. Fischer, P. Hofmann, K. Weiss, K. H. Dotz, F. R.
Kreissl: Transition Metal Carbene Complexes. Verlag Chemie, Weinheim 1983.
[S] a ) The classical paper demonstrating the advantages of rhodium and its
complexes in catalytic processes of olefins should be consulted: J. A.
Osborn, F. H. Jardine, J. F. Young, G. Wilkinson, J . Chem. SOC.A 1966.
171 I ; b) Review: B. R. James, Adv. Organornet. Chem. 17(1979) 319; c)
Asymmetric hydrogenation: J. Halpern, Pure Appl. Chem. 55 (1983) 99;
d ) Mechanistic Aspects: J. Halpern, Inorg. Chim. Acta 50 (1981) 11.
[9] The DuPont butadiene/ethylene coupling process had landmarked the
catalytic power of rhodium in industrial catalysis several years before:
a ) T. Alderson, US-Pat. 3013066 (1961); Chem. Abstr. 57 (1962)
I I016h; cf: T. Alderson, R. V. Lindsey, jr., J. Am. Chem. Soc. 87(1965)
5638: b) Review: A. C. L. Su, Adu. Organomet. Chem. 17(1979) 269.
[LO] a ) G. Wilke, J . Organornet. Chem. 200 (1980) 349; b) P. W. Jolly, G .
Wilke: 7he Organic Chemistry of Nickel, Vol. I and 2, Academic Press,
New York 1975; c) G. Wilke, Angew. Chem. 100 (1988) 189; Angew.
Chem I n t . Ed Engl. 27(1988) 185.
[ I I ] a ) “Metallorganische Mischkatalysatoren”: K. Ziegler, E. Holzkamp,
H Breil, H. Martin, Angew. Chem. 67 (1955) 541 ; b) K. Ziegler, ibid. 76
(1964) 545 (Nobel Lecture); Adu. Organomet. Chem. 6 (1968) I ; c) G.
Natta, Angew. Chem. 68 (1956) 393; d) G. Natta, ibid. 76 (1964) 553
(Nobel Lecture); e) A. Clark, Coral. Reu. 3 (1969) 145 (Phillips Catalysts); 9 H. Sinn, W. Kaminsky, Adt;. Organomet. Chem. 18 (1980) 99.
[I21 a) J. Smidt, W. Hafner, J. Sedlmeier, R. Jira, R. Riittinger, DBP
I049845 (August 6, 1959); b) W. Hafner, R. Jira, J. Sedlmeier, R. Sieber. R. Riittinger, H. Kojer, Angew. Chem. 71 (1959) 176: J. Smidt, R.
Jira, W. Blau, D. Grimm, Hydrocarbon Process. (1976) No. 3, p. 97; c)
Review: A. Aguilo, Adu. Organomet. Chem. 5 (1967) 321; d) R. Jira, R.
J. Laib, H. M. Bolt in: Ullmann‘s Encyclopedia of Industrial Chemistry, Vol. A I . VCH Verlagsgesellschaft, Weinheim 1985, p. 31 ff.
[I31 a) W. Reppe: Neuere Entwicklungen auJdem Gebiete der Chemie des
Acet.vtens und Kohlenoxids, Springer, Berlin 1949; b) Recent applications and developments: K. P. C. Vollhardt, Pure Appl. Chem. 57 (1985)
1819; Angew. Chem. 96 (1984) 525; Angew. Chem. Int. Ed. Engl. 23
(1984) 539.
[I41 Industrial impact of transition metal homogeneous catalysis: a) G W.
Parshall, R. E. Putscher, J. Chem. Educ. 63 (1986) 189; b) G. W. Parshall: Homogeneous Catalysis. Wiley, New York 1980.
[IS] For further examples cf. W. A. Herrmann, Comments Inorg. Chem. 7
(1988) 73; Chem. Unserer Zeit 22 (1988) 113.
[I61 Leading references to the historical development of Organometallic
Chemistry: a) J. S. Thayer, Adu. Organomet. Chem. 13 (1975) 1; b) W.
A. Herrmann, J . Organornet. Chem. 250 (1983) 319.
1171 Monographs: a) E.-I. Negishi: Organometallics in Organic Synthesis,
Wiley, New York 1980; b) S. G. Davies: Organofransition Metal Chemittr?: Applications to Organic Synthesis. Pergamon Press, Oxford 1982;
c) F. R. Hartley, S. Patai: The Chemistry of the Metal-Carbon Bond. Vol.
1-4. Wiley, New York 1981-1986. - For more recent individual work,
the reader is referred to the proceedings of the InternationalSymposium
on Organometallic Chemistry Directed Towards Organic Synthesis ( O M -
Angew (%em. Int. Ed. Engl. 27 11988) 1297-1313
50.
131 1
[471 W. A. Herrmann, J. G. Kuchler, W. Wagner, J. K. Felixberger, E.
Herdtweck, Angew. Chem. I00 (1988) 420; Angew. Chem. Int. Ed: Engl.
27 (1988) 394.
I481 a) R. H. A. Bosma, G. C. N. van den Aardweg, J. C. Mol, J. Organomet.
Chem. 255 (1983) 159; b) X. Xiaoding, J. C. Mol, J. Chem. Sac. Chem.
Commun. 1985, 631 (metathesis of unsaturated carboxylic acids); c) G.
C. N. van den Aardweg, R. H. A. Bosma, J. C. Mol, ibid. 1983. 262
(metathesis of unsaturated C, nitriles with n > 5); d ) No sufficiently
characterized organometallic compound has hitherto been obtained
from catalytically active WCI,/SnR, and RezO,/SnR,/Al20, systems;
see for instance: VIth Int. Symp. Olefin Metathesis, Hamburg, 26.-30.
August 1985; cf. J. Mol. Catal. 36 (1986). - A compound of composition [CISWCH3] has reportedly been obtained from WClh and
Sn(CH&. but was not conclusively characterized: W. Grahlert, K. Milkowski, U.Langbein, 2. Chem. 14 (1974) 287; K. H. Thiele, W. Grahlert, rbid. 9 (1969) 310; Z . Anorg. Allg. Chem. 383 (1971) 144.
[491 I. R. Beattie, P. J . Jones, Inorg. Chem. 18 (1979) 2318.
[SO] a) J. G. Kuchler, Diplomarbeit. Technische Universitat Miinchen 1987;
b) W. A. Herrmann, J. G. Kuchler, E. Herdtweck, unpublished results
C) W. A. Herrmann, G . Weichselbaumer, unpublished results
d ) W. A. Herrmann, M. Ladwig, unpublished results 1988.
[511 a) S. Cai, D. M. Hoffman, J. C. Huffman, D. A. Wierda, H.-G. Woo,
Inorg. Chem. 26 (1987) 3693; Synthesis of [ReO(PMe,)(CH,SiMe,),]: S.
Cai, D. M. Hoffman, D. Lappas, H . 3 . Woo, Organometaiiics 6 (1987)
2273; b) S. Cai, D. M. Hoffman, D. A. Wierda, J. Chem. Soc. Chem.
Commun. 1988. 313.
I521 J. K. Felixberger, E. Herdtweck, W. A. Herrmann, unpublished results
1987/88.
I531 [(qS-CsHS)dCr404]:a) Synthesis: E. 0. Fischer, K. Ulm, H. P. Fritz,
Chem. Ber. 93 (1960) 2167; b) Improved synthesis and structure: F.
Bottomley, D. E. Paez, P. S. White, J. Am. Chem. SOC.103 (1981) 5581;
ibid. 104 (1982) 5651.
[54] [(qs-C,Hs),V,O,]: a) F. Bottomley, P. S. White, J. Chem. SOC.Chem.
Commun. 1981, 28; b) F. Bottomley, D E. Paez, P. S . White, J. Am.
Chem. SOC.107 (1985) 7226; c) F. Bottomley, D. F. Drummond, D. E.
Paez, P. S. White, J. Chem. SOC.Chem. Commun. 1986. 1752; d) F
Bottomley, L. Sutin, ibid. 1987. 11 12; e) Review: F. Bottomley, L. Sutin, Aduan. Organornet. Chem. 28 (1988) 339.
[SS] [(riS-CsHS)nTiaOs-nCl"]"~
(n=4, 2, 0): a) 3. C. Huffman, J. G. Stone,
W. C. Krusell, K. G. Caulton, J. Am. Chem. SOC.99 (1977) 5829; b) A
Roth, C. Floriani, A. Chiesi-Villa, C. Guastini, ibid. 108 (1986) 6823; c)
The recently reported Ti4" compounds of composition I($CsMe,).,Ti,O6] resembles a n adamantane-type structure: L. M. Babcock, V. W. Day, W. G. Klemperer, J. Chem. SOC.Chem. Commun.
1987, 858.
I561 P. Stavropoulos, P. G. Edwards, G. Wilkinson, M. Motevalli, K. M.
Abdul Malik, M. B. Hursthouse, 1. Chem. SOC. Dalton Trans. 1985.
2167.
1571 Only the (explosive) hexamethyltungsten (CH3)6W has been reported:
a) A. J. Shortland, G. Wilkinson, J. Chem. SOC.Dalton Trans. 1973.
872; b) L. Galyer, K. Mertis, G. Wilkinson, J. Organomet. Chem. 85
(1975) C37, C65.
[58] a) W. A. Herrmann, W. Wagner, unpublished results 1987/88; b) W. A.
Herrmann, D. Marz, unpublished results 1987188; c) W. A. Herrmann,
R. A. Paciello, unpublished results 1987/88.
I591 a) W. A. Herrmann, J. K. Felixberger, E. Herdtweck, A. Schafer, J.
Okuda, Angew. Chem. 99 (1987) 466; Angew. Chem. Int. Ed. Engl. 26
(1987) 466; b) J. K. Felixberger, Diplomarbeit. Technische Universitat
Miinchen 1986.
[60] J. Okuda, unpublished results 1986.
[61] M. Floel, E. Herdtweck, W. Wagner, J. Kulpe, P. Harter, W. A. Herrmann, Angew. Chem. 99 (1987) 787; Angew. Chem. Int. Ed. Engl. 26
(1987) 787.
[62] Alkyl(oxo) complexes of the series [(qs-CSMes)Re(=O)R2]including a
rhena(v)cyclobutane are also accessible by means of Grignard reagents: a) H. J. R. deBoer, B. J. J. van d e Heisteeg, M. Floel, W. A.
Herrmann, 0. S. Akkerman, F. Bickelhaupt, Angew. Chem. 99 (1987)
8 8 ; Angew. Chem. Int. Ed. Engl. 26 (1987) 73; b) W. A. Herrmann, M.
Floel, E. Herdtweck, J. Organomet. Chem. (1988), in press.
[63] W. A. Herrmann, R. A. Fischer, E. Herdtweck, J. Organomet. Chem.
329 (1987) C 1.
[64] a) W. A. Herrmann, R. A. Fischer, W. Amslinger, E. Herdtweck, J. Organomet. Chem., in press; b) W. A. Herrmann, R. A. Fischer, J. K.
Felixberger, R. A. Paciello, P. Kiprof, E. Herdtweck, Z . Natur/orsch.
8 4 3 (1988), in press.
[6S] Monographs and reviews on olefin metathesis: a) V. Dragutan, A. T.
Balaban, M. Dimonie: Olefin Metathesis and Ring-Opening Polymerization oJCyclo-Olefins. Wiley, New York 1985; b) K. J . Ivin: Olefin Metathesis, Academic Press, London 1983; c) R. Streck, Chem.-Ztg. 99
(1975) 397 (industrial applications); d) R. H. Grubbs in G. Wilkinson,
F. G. A. Stone, E. W. Abel (Eds.): Comprehensiue Organometallic
Chemistry, Yo/. 8. Pergamon Press, Oxford 1982, p. 499ff; e) R. H.
Grubbs, Prog. Inorg. Chem. 24 (1978) I ; 0 T. J. Katz, Adv. Organomet.
1312
Chem. 16 (1977) 283: g) B. Calderon, J. P. Lawrence, E. A. Ofstead,
ibid. 17 (1979) 449; h) N. Calderon, E. A. Ofstead, W. A. Judy, Angew.
Chem. 88 (1976) 433; Angew. Chem. Int. Ed. Engl. 15 (1976) 401.
[661 a) R. R. Schrock, Arc Chem Res. 12 (1979) 98; b) J. Organomet. Chem.
300 (1986) 249; c) Acc. Chem. Res. 19 (1986) 342.
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I681 E. J. M. deBoer, J. deWith, G. Orpen, J. Am. Chem. Sor. 108 (1986)
827 I .
[691 H. Bonnemann, W. Brijoux, New J. Chem. 11 (1987) 549; see Fig. 27
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I701 N. M. Boag, H. D. Kaesz in G. Wilkinson, F. G. A. Stone, E. W. Abel
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[731 a) E. Valencia, B. D. Santarsiero, S. J. Geib, A. L. Rheingold, J. M.
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J. C. Calabrese, E. Valencia, ibid. 109 (1987) 157.
I741 J. K. Felixberger, J. G. Kuchler, E. Herdtweck, R. A. Paciello, W. A.
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[751 W. A. Herrmann, R. A. Fischer, E. Herdtweck, Angew. Chem. 99 (1987)
1286; Angew. Chem. I n t . Ed. Engl. 26 (1987) 1283.
1761 W. A. Herrmann, R. A. Fischer, E. Herdtweck, Angew. Chem. I00
(1988) No. I I ; Angew. Chem. I n f . Ed. Engl. 27(1988) No. 11.
[77] W. A. Herrmann, D. Marz, E. Herdtweck, A. Schafer, W. Wagner, H.-J.
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(1987) 462.
I781 Review on oxidation reactions of unsaturated hydrocarbons with osmium tetraoxide: M. Schroder, Chem. Reu. 80 (1980) 187.
1791 W. A. Herrmann, D. Marz, unpublished results 1986/87.
[XO] W. A. Herrmann, G Weichselbaumer, H.-J. Kneuper, J. Organornet.
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[Sl] F. Bottomley, J. Darkwa, L. Sutin, P. S. White, Organometallics S (1986)
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[82] W. A. Herrmann, E Herdtweck, G. Weichselbaurner, J. Organomer.
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[83] W. A. Herrmann, K. A. Jung, A. Schafer, H.-J. Kneuper, Angew. Chem.
99 (1987) 464; Angew. Chem. Int. Ed. Engl. 26 (1987) 464.
I841 W. A. Herrmann, K. A. Jung, unpublished results 1987.
[85] Compounds of general formula [(qs-CsRs)M(CH,),] (M = Ta, W, Ir)
are known, too: a) R. C. Murray, L. Blum, A. H. Lin, R. R. Schrock,
Organometallicr 4 (1985) 954; see also: J. M. Mayer, C. J. Curtis, J. E.
Bercaw, J. Am. Chem. Sac. 105 (1983) 2651; 6) S. J. Holmes, R. R.
Schrock, Organometallics 2 (1983) 1463; c) K. Isobe, A. V. d e Miguel,
A. Nutton, P. M. Maitlis, J. Chem. Sac. Dalton Trans. 1984. 929 (first
organoiridium(v) complex); d) K. Isobe, P. M. Bailey, P. M. Maitlis, J.
Chem. SOC. Chem. Commun. 1981. 808; e) S . F. Pedersen, R. R.
Schrock, M. R. Churchill, H. J. Wasserman, J. Am. Chem. Sac. I04
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ibid. 108 (1986) 1681.
(861 a) E. L. Muetterties: Transition Metal Hydrides, Marcel Dekker, New
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[87] S. C. A b r a h a m , A. P. Ginsberg, K. Knox, Inorg. Chem. 3 (1964) 558.
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Soc. Chem. Commun. 1983. 788; b) D. Baudry, M. Ephritikhine, H.
Felkin, J. Zakrzewski, Tefrahedron Lett. 25 (1984) 1283.
[89] Monographs and reviews on carbon-hydrogen activation: a) A. E. Shilov: The Activation of Saturated Hydrocarbons by Transition Metal
Complexes, Reidel, Dordrecht 1984; b) R. Hoffmann, J. Am. Chem.
Soc. 106 (1984) 2006 (theoretical aspects of CH-activation); c) R. H.
Crabtree, Chem. Rev. 85 (1985) 245.
[90] W. A. Herrmann, J. Okuda, Angew. Chem. 98 (1986) 1109; Angew.
Chem. Int. Ed. Engl. 25 (1986) 1092.
19 I ] W. A. Herrmann, E. Herdtweck, unpublished results 1987.
1921 W. A. Herrmann, H. Theiler, W. Wagner, E. Herdtweck, unpublished
results 1987.
a) P. Hofmann, N. Rosch, J.
1931 MO theory of [(qs-C5HS),Re3(p-O)6]2Q:
Chem. Sor. Chem. Commun. 1986. 843; b) P. Hofmann, N. Rosch, H.
R. Schmidt, Inorg. Chem. 25 (1986) 4470.
[94] This compound withstands prolonged heating in a sealed tube at
200°C. Only traces of methane are formed under such conditions
[58a].
[9S] See for example: D. Medina, 5th Int. Symp. Chem. Selenium and Tellurium, Oak Ridge, TN, USA, 24.-28. August 1987.
I961 H. Theiler, Diplomarbeit. Technische Universitat Miinchen 1986.
(971 J. Kulpe, E. Herdtweck, G. Weichselbaumer, W. A. Herrmann, J. Organomet. Chem. 348 (1988) 369.
1981 a) V. N. Latyaeva, V. V. Pereshein, A. N. Lineva, Tr. Khim. Khrm. Tekhno!. 1974, 32 [Chem. Abstr. 83 (1975) 17926121; b) F. Bottomley, L.
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Angew. Chem. Inf. Ed. Engl. 27(1988) 1297-1313
[99] B. E. Bursten, R. H. Cayton, Organometallics 6 (1987) 2004.
1001 a) Bonding theory and reaction of CrO2CI2and CrOC1,: A. Rappe, W.
A. Goddard 111, J . Am. Chem. SOC.102 (1980) 5114; ibid. 104 (1982)
448; b) ab-initio Mo calculations for oxidic coordination compounds:
K. Yamaguchi, Y . Tdkahard, T. Fuenco i n V. H. Smith, jr. (Ed.): Ap-
plied Quantum Chemutry. Reidel, Dordrecht 1986, p. 155 ff.
loll H.-J. Kneuper, P. Hatter, W. A. Herrmann, J . Organomet. Chem. 340
(1988) 353.
[I021 Catalytic photoreduction of C 0 2 to C O by [Re(bpy)(CO)3C1]: a) J. Hawecker, JLM. Lehn, R. Ziessel, J . Chem. SOC.Chem. Commun. 1983,
536; ibid. 1984, 328; b) R. Ziessel in M. Aresta, G. Forti (Eds.): Carbon
Dioxide as a Source of Carbon. NATO AS1 Series. Yo/. 206. Reidel,
Dordrecht 1987, p. 113ff.
[ 1031 Enantioselective oxidations by chiral coordination compounds: a) S.
Yamada, T. Mashiko, S. Terashima, J . Am. Chem SOC.99 (1977) 1988;
b ) R. C. Michaelson, R. E. Palermo, K. B. Sharpless, ibid. 99 (1977)
1990.
[I041 Recent examples: a) T. Kauffmann, R. Abeln, S. Welke, D. Wingbermuhle, Angew. Chem. 98 (1986) 927; Angew. Chem. I n t . Ed. Engl. 25
(1986) 909; b) T. Kauffmann, M. Enk, W. Kaschube, E. Toliopoulos,
D. Wingbermuhle, ibrd. 98 (1986) 928 and 25 (1986) 910.
[I051 a ) F. J. Feher, J . Am. Chem. SOC.108 (1986) 3850; b) W. G. Klernperer,
V. V. Mainz, R.-C. Wang, W. Shum, Inorg. Chem. 24 (1985) 1968.
[I061 J. Schwartz, Acr. Chem. Res. 18 (1985) 302.
[I071 J . W. Faller, Y . Ma, OrganometaNics 7 (1988) 559; see also: P. Legzdius, E. C . Phillips, S. J. Rettig, L. Sanchez, J. Trotter, Y . C. Lee, ibid. 7
(1988) 1877.
[lo81 Organometal/metal oxide combinations of defined structure are quite
new; some highlights: a) C. J. Besecker, W. G. Klemperer, V. W. Day,
Angew. Chem. Int. Ed. Engl. 27 (1988) 1297-1313
J . Am. Chem. SOC.104 (1982) 6158; b) C. J. Besecker, W. G. Klemperer,
ibrd. 102 (1980) 7598; c) V. W. Day, M. F. Frederick, M. R. Thompson,
W. G. Klemperer, R.-S. Liu, W. Shum, ibid. 103 (1981) 3597; d) V. W.
Day, C. W. Earley, W. G. Klemperer, D. J . Maltbie, ibid. 107 (1985)
8261 ; e) C. J. Besecker, V. W. Day, W. G. Klemperer, M. R. Thompson,
ihid. 106 (1984) 4125.
(1091 Since writing this review numerous papers o n organometallic oxides
have appeared, of which the following are cited as examples: a) J. M.
Huggins, D. R. Whitt, L. Lebioda, J . Organomet. Chem. 312 (1986) C
15; b) N . Zhang, P. A. Shapley, Inorg. Chem. 27 (1988) 976; c) J. C.
Bryan, R. E. Stenkamp, T . H. Tulip, J. M. Mayer, ibrd. 26 (1987) 2283;
d) J. C. Bryan, J. M. Mayer, J. Am. Chem. Sac. 109 (1987) 7213; e) E.
N. Jacobsen, M. K. Trost, R. G. Bergman, ibid. 108 (1986) 8092; f) D.
8.Morse, T. B. Rauchfuss, S . R. Wilson, ibid 110 (1988) 2646; g) K. G.
Moloy, Inorg. Chem. 27 (1988) 677; h) G. A. Vaughan, P. B. Rupert, G.
L. Hillhouse, J . Am. Chem. SOC.109 (1987) 5538; i) J. F. Buzinkai, R. R.
Schrock, Organomefallics 6 (1987) 1447; j) P. Jernakoff, C . d e Meric d e
Bellefon, G. L. Geoffroy, A. L. Rheingold, S . J. Geib, ibid. 6 (1987)
1362; k) G. Schoettel, J. Kress, J. Fischer, J. A. Osborn, J. Chem. SOC.
Chem. Commun. 1988. 914; I) L. M. Babcock, V. W. Day, W. G. Klemperer, ibid. 1988, 519; m) A. van Asselt, B. J. Burger, V. C. Gibson, J. E.
Bercaw, J . Am. Chem. SOC.108 (1986) 5347; J. W. Faller, Y . Ma, J .
Organornet. Chern. 340 (1988) 59.
[110] L. Y . Kuo, M. G. Kanatzidis, T. J. Marks, J . Am. Chem. Sor 109 (1987)
7209.
[I I I] Organomolybdate complexes relevant in enzyme chemistry: a) G. N.
Schrauzer, E. L. Moorehead, J. H. Grate, L. Hughes, J . Am. Chem. SOC.
100 (1978) 4760; b) G. N. Schrauzer, L. A. Hughes, N. Strampach, Z .
Naturforsch. 8 3 7 (1982) 380.
1313
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