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Metallocene Carbene Complexes and Related Compounds of Titanium Zirconium and Hafnium.

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Volume28 . Number4
April 1989
Pages 397 - 534
International Edition in English
Metallocene Carbene Complexes and Related Compounds
of Titanium, Zirconium, and Hafnium
By Gerhard Erker"
The structure and reactivity spectrum of transition-metal carbene complexes has been widened
significantly by the bent metallocenes of titanium, zirconium, and hafnium. Proceeding from
metal carbonyls and reactive (butadiene)-, (aryne)-, or (olefin) MCp, complexes, many new
Fischer-type metaloxycarbene complexes of Zr, Hf, V, Nb, Cr, Mo, W, Mn, Re, Fe, Ru, Os,
Co, Ni, and Rh have been synthesized. The incorporation of titanocene, zirconocene, or
hafnocene fragments allows new types of carbene complexes to be prepared. For
the (alky1idenamido)metallocene complexes [Cp,M(X)( X-U = CRR)], metallocene ylides
[Cp,M(R)( -CHPPh,)] , and binuclear (p-alkyny1)metallocene compounds, some metalligand x bonding is indicated. Metallocene complexes with metallaoxirane units,
Cp,M -CH, -0, show similar chemical behavior to that of binuclear (p-methy1ene)complexes L,M - CH, - ML,. The methylene groups of zirconaoxirane complexes,
which are derived from carbon monoxide, may be expelled as ethylene by thermally induced
CC coupling. With metal hydrides, CH, transfer with insertion into the metal-hydride bond
occurs. In one case, methylene insertion into a metal-carbon bond can even be observed. These
reactions of Ti-group metallaoxiranes could be models for postulated intermediates in the
Fischer-Tropsch synthesis.
-
1. Introduction
Carbene complexes are among the most important
organometallic compounds. The discovery of heteroatomstabilized carbene complexes [L,M = CR(OR)] by E. 0.
Fischer et al.1'1 and of heteroatom-free metal alkylidene complexes [L,M =CR,] by R.R. Schrock et a1.['] laid the foundation for the recognition of reactive carbene complexes as
decisive intermediates for many metal-catalyzed transforma-
[*] Prof. Dr. G. Erker
Institut fur Organische Chemie der Universitat
Am Hubland. D-8700 Wiirzburg
(FRG)
Angen. Chem. Inl. Ed. Engl. 28 (1989) 397-412
tions of organic substrates.[31Carbene complexes are becoming increasingly important as reagents in organic synthesis.
The nucleophilic Schrock-type carbene complexes, obtained
from the early transition metals, have ylide character and
have proved useful as selective Wittig reagents.14] The
CR(0R) units of Fischer-type carbene complexes are being
employed very successfully as C , synthons in template-controlled CC-coupling sequences.[51The - C( = M)OR unit
can activate a neighboring R group, in a manner similar to
that of ester groups - C( = 0)OR'.161Last but not least, the
carbene complexes are significant as the simplest organometallic complexes with a metalkarbon 71 bond.17]
New developments have broadened considerably the preparative routes to and applications of transition-metal car-
Q VCH L'erlagsgesellschaft mbH. 0-6940 Weinheim, 1989
0570-0833j8910404-0397$ 02.5010
397
bene complexes. The bent metallocenes of group 4 transition
metals[8*91have played an important role in this. The chemistry of titanocene, zirconocene, and hafnocene complexes
has erupted with a range of new kinds of organometallic
compounds that resemble the traditional mono- or multinuclear carbene complexes in their bonding properties and reactions. Consequently, the structure and reactivity spectrum
of this class of compounds has been significantly widened.
Selected examples illustrating these developments will be discussed in this article.
2. Synthesis and Properties of Metaloxycarbene
Complexes
2.1. The Fischer Route
In the two-step conversion of metal carbonyls to metal
carbene complexes developed by E. 0.Fischer et al. [Eq. (a)],
a carbon nucleophile is added to the M - C = O unit of 1 in
the first step to form an acylmetalate complex 2.['.'*]
The product 3 results from further reaction with an electrophile. Organometallic compounds (e.g., from elements of
the Ti group) can also function as the electrophile. As
an example, the complexes [(CO),Cr = C(CH,)OTiCICp,]
and [{(CO),Cr=C(CH,)O},TiCp,] are obtained from
Cp,TiCI, .I' 'I
e.70
0
(CO1,M-C-O
Nu
15 (13 -+ 14 -+ 15).
(ai
lCOInMEe
\Nu
3
2
This route to carbene complexes is quite general. The limits of this method are determined by the balance of reactivity
at the acylmetalate intermediate 2. On the one hand, an adequate stabilization of 2 is required, without which it would
not form at all. On the other hand, the success of the second
part of the reaction path can be adversely affected by overly
strong localization of the negative charge at the (CO),M
group. If the intermediate 2 is too stable, it frequently resists
the 0-alkylation in the following step. Metal alkylation or
reaction at another ligand affords acyl complexes rather
than the desired Fischer-type carbene complex.[' The simplest way to bypass the limitations of the Fischer synthesis
would seem to be to reverse the order of the reaction steps in
Equation (a). Titanium and zirconium compounds having a
Lewis acidic metal center and nucleophilic ligands have
proven themselves very successful as reagents for this procedure. Thus, the reaction of [Ti(NMe,),] 5 with [W(CO),] 4 a
affords the carbene complexes 6. Other metal carbonyls
(M = Mo, Fe, Ni) react similarly. The bis(pentamethy1cyclopentadieny1)zirconium dihydride reagent 7 was used to
convert metal carbonyk (M = Zr, Nb, Cr, Mo, W, Rh) into
zirconiumoxycarbene complexes (e.g., 4 b + 8). In several
cases, the addition of the monomeric 7 is reversible.[I3]
4a
5
6
4b
7
8
398
Heteroatom-stabilized cdrbene complexes can be prepared by routes avoiding nucleophilic addition to metal carbonyls. Examples are the L,M-induced cleavage of electronrich olefins (R2N),C= C(NR2)Z[141and reactions of
metalate complexes. Na,ML,. with Vilsmeier salts.
(RCIC = NR,)@CIe, to give the carbene complexes
[L,M =CR(NR,)],[' 'I both developed by Lappert et al. Metal carbonyls can be converted into carbene complexes by
reaction with very reactive q2-olefin complexes of titanocene, zirconocene, or hafnocene. Although these reactions formally resemble the original reaction sequence of
E. 0. Fischcr, they are probably mechanistically quite different [Eq. (b)] and complement the "classical" reaction in
Equation (a). They are reminiscent of a frequently observed
organometallic reaction, namely, the (presumably) concerted ring-closure of bis(o1efin)metal complexes 9 to give metallacyclopentanes
The oxametallacyclopentanes 12
(L,M = Cp,Ti, Cp,Zr, Cp2Hf) are formed analogously
from (q2-ketonej(q2-o1efin)metalcomplexes 11. If the sideonxoordinated organic carbonyl compound is replaced in
11 by a metal carbonyl complex, an analogous ring-closure
reaction affords the metallacyclic metaloxycarbene complex
,/OEl
ICOinMLC
\Nu
1
2.2. Synthesis of Metaloxycarbene Complexes without
Nucleophilic Addition
9
10
13
12
11
14
15
For this reaction. the few known isolable mono(olefin)metallocene complexes of the Ti group are obvious candidates, e.g., (ethylene)bis(q-pentamethylcyclopentadieny1)titanium or (ethylene)bis(indenyljtitanium."7' We have used
(butadiene)bis(cyclopentadienyl)zirconium and related compounds for carbene complex syntheses by Equation (b).
They are available as easily accessible starting materials on
a large scale.
2.2. I . Carbene Complexes from (q4-Diene)rnetalloeenes
(Butadiene)zirconocene exists at room temperature as two
isolable isomers, (s-trans-q4-butadiene)- and (s-cis-q4-butadiene)zirconocene 16 and 18, respectively.["'
The
equilibration (16:18 z 1 : l at 25°C; AG:,,5
(16- 18)
= 22.7 kcal mol - ') presumably occurs through the coordinatively unsaturated intermediate (q2-butadiene)zirconocene 17. The isomers 16 and 18 have very different reactivities."'.
The (s-cis-q4-diene)metallocene has metal alkyl
character and adds to organic carbonyl compounds. behaving as a typical carbon nucleophile. By comparison, the CCcoupling reactions of the non-nucleophilic, coordinatively
saturated (s-trans-q4-diene)metallocenespecies proceed via
the easily obtainable (q 2-diene)metallocene intermediate 17.
Surprisingly, several ketones have been shown to react faster
via this reaction path (17) than by direct nucleophilic addiA t i g r u . Chen?.I n ! . G I . EnRI. 2K (1989) 397-412
tion: under kinetic control, the only observed reaction of a
16/18 mixture with excess ketones is that of the (s-tra12s-q~butadiene)zirconocene. The heterocycle 21 is thereby formed
via 19 and 20. The (s-cis-q4-diene)ZrCp, isomer does not
react until the temperature is increased sufficiently to allow
the 18 + 16 isomerization to
*l
ck2G!
1
R1
ML,=
1
19
20
Cr(COI,. MolCOl,. WICO1, 123a.b.c).
FelCO),. Fe(COl,PPh, (2La.b).
Rh(C0)Cp. C o K O I C p , Co(CO)f?-C,H,CU
NIKOI, 1261.
ZrlCO)Cp,, HfKOICp, 127a.b).
V(CO),Cp 128)
125a.b.cl.
l7
C p 7 Z r g 18
Hexacarbonylchromium reacts slowly at room temperature (12 h) with the equilibrium mixture of (s-cis-/s~rans-q4-butadiene)zirconocene16/18 to form the (q3-al1yl)zirconiumoxycarbene complex 23a. Reaction of 16/18
with Mo(CO), or W(CO), affords the analogous 23b,c.["]
Between -20 "C and O'C, the isomerization 16 F? 18
is frozen out, and only the (s-trans-q4-butadiene)zirconocene 16 reacts (quickly) with [Fe(CO),]. The metallacyclic (q3-allyl)zirconiumoxycarbene complex 24a is formed
as the sole product, since the expected intermediate with
(o-ally1)metallocene structure rearranges very quickly to
the more stable n-ally1 form 24a. The reaction of
[(CO),Fe(PPh,)] with the 16/18 mixture leads just as easily
to the formation of the phosphane-substituted iron carbene
complex 24b.[231Under the usual conditions of the Fischer
synthesis, the 0-alkylation step gives carbene complexes
with negligible amounts of side products 0nl.v with the use of
nitrosyl ligands or very strong alkylating agents. Carbene
transfer reactions (e.g., from [Cp(CO)(NO)Mo = CRPh] to
photochemically generated [Fe(CO,)]) represent alternative
routes to simple tetracarbonyl(carbene)iron complexes.[241
The synthesis of cobalt and rhodium carbene complexes
by the route in Equation (a) requires the presence of ligands
to stabilize the acylmetalate intermediate.12'*261 Carbene
complexes with the (q-cyclopentadieny1)cobalt or -rhodium
fragments have thus far been prepared by alternative reaction
CpRh(CO), reacts at room temperature
with the 16/18 equilibrium mixture to give the carbene complex 25a. At lower temperatures, only the s-fratis isomer 16
The metallacyclic (q3-al1yl)zirconiumoxycarbene complex
25 b crystallizes on cooling the CpCo(CO),/(butadiene)zirconocene reaction mixture. At room temperature in
solution, a fast equilibrium between the carbene complex
and the starting materials is established. In the reverse reaction with CC bond cleavage, only (s-trans-q4-butadiene)zirconocene 16 is formed together with CpCo(CO), under kinetic control. This complex then isomerizes to the s-cis
isomer 18. The equilibrium position between metaloxycarbene complex and starting complexes is influenced by the
introduction of substituents at the Co-bound Cp ligands.
The zirconiumoxycarbene complex 25 c was obtained from
[(q-C,H,CI)Co(CO),] by reaction with the Zr reagent. The
Anjie%i.Chiw. l n t .
Ed. Enxl. 28 (19891 397-412
equilibrium position for this reaction at room temperature is
such that no starting materials could be detected ('H NMR
spectroscopy).L2'1
The isolation of the nickel carbene complex 26 was complicated by the fast equilibrium with the reactants Ni(CO),
and (s-trans-q4-butadiene)zirconocene16. In solution, 26 is
stabilized by the presence of excess tetracarbonylnickel.[29a.b1 Under the usual conditions, Cp,Zr(CO), and
Cp,Hf(CO), were converted into the metaloxycarbene complexes 27 a and 27 b, respectively.L291
Carbene complexes of vanadium are rare, although it is
possibIe that they play an important role in vanadium-catalyzed reactions.[' 301 Reaction of CpV(CO), with (butadiene)zirconocene affords the vanadium carbene complex 28.
When 28 is dissolved in benzene at room temperature, equilibrium between 28 and the starting materials is established
immediately (28: starting materials ca. I :1 at 25 0C).[311
The
equilibrium position is shifted advantageously by the use of
(butadiene)hafnocene 16'. Reaction of CpV(CO), with
16"".
at room temperature affords the (q3-allyl)metaloxycarbene complex 29. In solution, 29 does not equilibrate with the mononuclear starting materials, but instead
slowly transforms into the isomeric seven-membered ring
(o-ally1)metaloxycarbene complex 30,L3' I eventually establishing an equilibrium (1 :1 at 25 "C). The niobium carbene
complex 31, obtained from 16' and CpNb(CO), behaves
analogo~sly.~~~
Few
" * ~ heteroatom-stabilized
~]
carbene
complexes of niobium have been reported[13b,d, 331 thus far.
30 M:V
32 M:Nb
29 M - V
31 M = N b
The very reactive q4-diene complexes of the actinide element thorium can likewise function as reagents for carbene
syntheses. (q4-Butadiene)ThCpf 34 reacts at 0 "C with
hexacarbonylchromium to afford the thoriumoxycarbene
complex 35. With [Mo(CO),] and [W(CO),], 34 afforded
corresponding products.[341
33
34
35
399
2.2.2. Carbene Complexes from (q2-0lefn)and (q2-Aryne)metallocenes
2.3. Structures of Metallacyclic Zirconiurnoxycarbene
Complexes
Takaya et al. used (q2-ethylene)bis(q-pentamethylcyclopentadieny1)titanium 36 (originally reported by Bercaw et
al.r'7a1)as a reagent for cdrbene complex syntheses. The titaniumoxycarbene complexes 37 a-c were formed by reaction
of 36 with the hexacarbonyl complexes of chromium, molybdenum, and tungsten at - 20 "C. The titdniumoxycarbene
complexes 37 d and 37 e, respectively, are formed analogously by addition of 36 to the carbonyl ligands of Mn,(CO),,
and Re,(CO),,. From the X-ray analysis of the rhenium
carbene complex 37e, it can be seen that the metallacyclic
carbene ligand occupies the trans position at the binuclear
metal carbonyl. Application of the Fischer synthesis [Eq. (a)]
to Mn,(CO),, and Re,(CO),, normally affords cis-configurated monocarbene complexes.[' 1'
There are many X-ray structural analyses of zirconiumoxycarbene complexes.['3, 2 2 , 2 7 , 28, 3 1 , 371 By comparison,
only a few metaloxycarbene complexes of
or
hafniumL3'] have been crystallographically characterized
(see Table 1). These complexes all belong to the same metallacyclic (q3-allyl)metaloxycarbene structural type. This is
true even when the equilibrium position in solution favors
the c3-ally1 isomer. The ZrCr and ZrW complexes 23a and
23 c, respectively, are typical examples.1221
Both compounds
exhibit an unsymmetrical Zr-bound q3-allyl group. The
bonds to the terminal ally1 carbons are short and distances to
C-2 and C-3 of the chain increasingly longer (23a/23c:
Zr-C1 = 2.420(6)/2.421 (14); Zr-C2 = 2.491 (6)/2.497(12);
Zr-C3 = 2.624(7)/2.621 (15) A). The very short carbonoxygen bond in the carbene Iigand is particularly striking. A
comparison of the 0-C carbonyl distances in the metallacyclic zirconiumoxycarbene complexes with those in traditional acyclic Fischer-type carbene complexes demonstrates
this general effect very clearly: d(0-C,,,,,,,,) = 1.254(5) A
for 23a vs. 1.314 (1) A for [H,C,O-C(CH,) = Cr(CO)5].[101
Together with the relatively long M-Ccarbeneand Zr-0
bonds, the short O-Ccarbenebond lengths clearly indicate
acylmetalate character for these zirconiumoxycarbene comp l e ~ e s ' (A
~ ~tf
] B).
36
37a
37b
37C
37d
37e
M,L, = CrlCOIS
M,L,:
MolCOIS
M,L,=WlCOl,
M,L, z trans-Mn21CO1,
M,L, = trans-Re,lC019
(q 2-1,2-Didehydrobenzene)zirconocene and -titanocene
39 (M = Zr, R = H and M = Ti, R = H, respectively) are
easily generated by thermolysis of the diphenylmetallocenes
38. In the absence of other reagents, they react with aromatic
hydrocarbons by C-H activation, in a reversal of the reaction leading to their formation. The (aryne)metallocenes 39
add a broad palette of organic compounds having reactive
7~ systems, with formation of five-membered benzannelated
metallacycles. Thus (C,H,)ZrCp,, thermally generated in
situ at 90 "C from diphenylzirconocene, reacts with the stilbene isomers stereospecifically to give cis- or trans-l ,I -bis(cyclopentadienyl)-2,3-diphenylzirconaindan.~36~
Reaction
between hexacarbonyltungsten and the zirconocene 38
(M = Zr, R = H) at 90 "C affords the five-membered metallacyclic benzannelated zirconiumoxycarbene complex 40. A
labeling experiment showed that this carbene complex is
formed from the (aryne)metallocene intermediate 39. Similarly, bis@-toly1)zirconocene38 (M = Zr, R = CH,) reacts
with W(CO), to afford the zirconiumoxycarbene complexes
40 and 40' in the ratio 60:40. Thermally generated (77'aryne)titanocene also reacts with Mo(CO), or W(CO), immediately to afford analogous compounds.
B
A
All
examples
known
thus
far
of
the
[Cp,M(X)OC{ = M'L, )R] complex type (M = Ti, Zr, Hf)
have significant acyl character. Substitution of the 0-bound
alkyl group in Fischer-type carbene complexes by a very
oxophilic metal complex fragment with strong o-donor
properties leads to a considerable polarization of the
[M -OC(R) = M(CO),] unit (see B).[391
Fischer-type carbene complexes can be described as compounds with weak transition-metal-carbon n bonding. Experimental criteria for such n bonding include a short M = C
bond, a higher activation barrier for rotation about the
M = C bond axis, and a more stable preferred geometry for
the -0-C(R)=ML,
system. The composition of many
Table 1. Selected bond lengths dand 3C NMR chemical shifts 6 of the carbene
carbon for metaloxycarbene complexes [{M'JO- C(R)= MzL,(CO),] [a].
Compound M2L.(CO),
d(0-C) [A]
d(C-M2) [A] 6 [b]
Ref.
23 a
23 c
1.254(5)
2.063 (4)
2.198 (10)
2.250(8) [c]
2.25 (1) [c]
1.829(5)
1.815 (4)
1.925 (3)
2.102 (3)
2.216(6)
363.7
342.2
329.7
[22]
[22. 29c]
[37]
311.9
311.8
300.8
[28b]
[28a]
[27]
[31]
[321
40 a
25 e
25 b
25 a
28
31
Cr(CO),
W(CO),
W(CO),
Co(CpCI)CO
Co(Cp)CO
Rh(Cp)CO
V(CO),Cp
Nb(CO),Cp
1.262(11)
1.21 (2) [c]
1.36(2) [c]
1.286 (6)
1.287(4)
1.278 (4)
1.270 (4)
1.247(7)
--
-
[a] [MI] = Cp,Zr except for 31 (Cp,Hf), R = C,H, (n-ally1 form) except for
40a (R = C,H,). [b] Standard: TMS in C,D,. [c] Crystallographically inde-
pendent units.
400
Angei~.C'hem. Inr. Ed. En,ql. 28 (1989) 397- 412
Fischer-type carbene complexes complicates or hinders the
estimation of the M = C bond strength using such criteria.
Thus. the high local symmetry of the [M(CO),] fragment
generally leads to low M-C rotational barriers in
[R’O - C(R) = M(CO),] carbene complexes.[401Luppert et
al. determined a Rh = C rotational barrier of AG$,*,
z 16 kcal mol- for the heteroatom-stabilizedcarbene complex 41, for which such symmetry-related effects are negligible.[411Similar rhodium carbene complexes have very short
Rh-C,,,,,,,
bond lengths (42a, 1.930 (6) 8,; 42b,
1.930 (1 1) A). The rhodiumxarbon bond in the acyclic
rhodium carbene complex [Cl,(Et,P),Rh = C(H)NMe,] is
considerably longer (1.961 (1 1)
Fig. 2. Molecular structure of 28 1311
R’
N
‘COR‘
42a:X 1O.R’: R2 = P h
42b:X=S.R’:NlC02Et),.R2=OEt
41
Although the carbene carbon in the rhodium carbene
complex 25a has only one heteroatom substituent, the
Rh-C,,,,,,,
bond length determined by X-ray diffraction
(1.925 (3) A) is even shorter than those of 42a, b. The metal
carbene unit in 25a has the geometry expected for a heteroolefin system. The four substituents 0 1 , C12, C16 and D3
( = center of the Cp ring C17-C21; atom numbering
analogous to the cobalt carbene complex 25c, Fig. 1)
are arranged coplanar with the central Rh = C unit (maximum deviation from the best plane: -0.09 A for C12).
Only one geometric isomer was found in the crystal. The
bulky Cp substituent at rhodium has Z geometry with
respect to the OZr group at the carbene carbon
The cobalt carbene complex 25b has an analogous
structure in the crystal. The C o = C bond (1.815(4) A) is
much shorter than those in the open-chain cobalt
carbene complexes [(CO),(GePh,)Co = C(C,H,)OC,H,]
(1.913 (1 1) A),1251
[Cp(PhS)Co=C(C,H,,N,)] (1.902(3) A),
or [(PPh,)(NO)(CO)Co=C(C,H,,N,)]
(1.974(15) A).1431
Complex 25 b also exhibits only one “double-bond isomer”
in the crystal. The CO ligand bound to Co is E-oriented to
the OZr group at the carbene carbon.
Compound 28 is the first vanadium carbene complex for
which an X-ray structural analysis was carried out (Fig. 2).
The bonding in the metallacyclic ring system is typical for
complexes of this type. The q3-alfyI unit is distorted in the
direction of a (0,
z-allyl)ZrCp, structure. The C-0 bond of
the carbene ligand is short [d(Cl-01) = 1.270(4) A]; thus,
28 shows considerable acylmetal complex character. The
vanadium-C,,,,,,,
bond length of 2.102 (3) 8, is clearly
longer than d(V-C,,) ( zI .90 A). For the analogous niobium carbene complex 31, the Nt+C,,,,,,,
distance is
2.21 6 (6) A.
The tungsten carbene complex 40a also has a very short
Ccarbene-Obond length (1.21 (2) A) and hence significant
acylmetal complex character. The peculiarity with 40 a, however, is that in the crystal it exists as an organometallic
oligomer (Fig. 3). The molecular units are joined by the carbony1 group lying trans to the carbene ligand. The carbonyl
oxygen 0 6 functions as a donor ligand in the oligomer, connecting one monomeric unit with the next unit through
CDS
Zr 1
7
CI4
Fig. 1 Molecular structure of 25c [28b].
Angew. Chcm. Inr. Ed. EngI. 28 (1989) 397-412
Fig. 3. Molecular structure of 4 0 a : the asymmetric unit with the two crystallographically independent molecules. Intermolecular interactions between Zr2
and 0 6 as well as Zrl and 0 2 6 are indicated [37].
40 1
Zr. In this way, the zirconium attains an 18-electron configuration. A helical organometallic oligomeric chain is obtained from these “intermolecular” bonds, which are weak
[d(Zr2-06) = 2.49 (2) A; d(Zr1-026) = 2.40 (2) A] compared with the Zr-0 bond in the fivemembered ring
[d(Zrl-01) = 2.16(2)
;02*
2.4. Reactivity of Metaloxycarbene Complexes
The synthesis of metaloxycarbene complexes from metallocenes is a useful extension of the classical synthesis developed by E. 0. Fischer et al. Many reactions undergone by
Fischer-type carbene complexes should also occur with the
metallacyclic metaloxycarbene complexes. However, from
the results thus far, it has become clear that the bonding of
the electropositive early transition metal to the carbene oxygen can lead to a very specific and to some extent unexpected
chemistry (e.g., of the zirconiumoxycarbene complexes).
The solid-state structure of the zirconiumoxycarbene complex 40a, for example, is unexpected. The monomeric carbene complex unit functions as an organometallic Lewis acid
in the crystal.1441Complex 40a even adds suitable donor
ligands (e.g., methylamine) in solution. Dynamic ‘H NMR
spectroscopy shows a fast exchange of the coordinated
amine ligands with the free base in solution.[28a1Organic
carbonyl compounds were added to 40a to form 1:l
adducts: reaction with acetophenone gave complex 43
(IR: ij(C0) = 1647cm-’ vs. 1684cm-‘ for the free keDynamic 13C NMR spectroscopy revealed the
rapid exchange of the organic carbonyl ligand [13Ccarbonyl
resonance of the boundlfree acetophenone (- 80 “C in
CD,Cl,): 6 = 208.4 and 198.2, respectively].
Open-chain multinuclear M - 0 - M-bridged &(carbene) complexes have been obtained from the extremely
moisture-sensitive metallacyclic carbene complexes and H ,O
(e.g., 40b-+44). In the crystaI, complex 44 shows an
unexpected antiperiplanar arrangement of the bulky
0 - C(Ph) = Mo(CO), substituents relative to the linear
central (p-oxo)bis(zirconocene) unit.[461
40 b
44
The tungsten carbene complex 23c reacts with ketones
under mild conditions to give CC coupling at the q3-aIlyl
group. Regioselective addition of the terminal ally1 carbon
was observed with benzophenone, acetone, acetophenone,
and pinacolone. The resulting nine-membered metallacyclic
402
Fig. 4. Molecular structure of the bis(carbene) complex 44 [46]
system 45 has a chiral ring conformation. When these rings
were formed from prochiral ketones, diastereomeric products were observed.[471
The C = M L , group in a Fischer-type carbene complex
is similar to the C = O group in an organic carbonyl
61
Casey et
al. have shown that
conipo~nd.‘~.
[(CO),W = C(Ph)OCH,] reacts with non-stabilized phosphorous ylides in a reaction formally analogous to Wittig
olefination (although probably different mechanistically);
thus, reaction with Ph,P = CH, gave H,C = C(Ph)OCH,
and [(CO),W(PPh,)] .I4’]
The orfho-hydrogen atom very effectively shields the Zr-C
CJ bond in 40a against attack by e l e ~ t r o p h i l e s .Thus
[ ~ ~ ~far,
this bond could only be broken by protic reagents. With
alcohols, one obtains (a1koxy)zirconiumoxycarbene complexes 46. Carbene complexes with chiral auxiliaries at
zirconium can be prepared in this way.
The carbene complex 46 reacts quickly with Ph,P = CH,
at room temperature to form the corresponding zirconium
enolate 47 (R’ = H). Phosphorus ylides with only one alkyl
group at the ylide carbon react in the same way.[381This
reaction can be seen as the synthetic equivalent of a Wittig
olefination of a carboxylate salt-a reaction that cannot be
directly realized because of the reduced carbonyl activity of
carboxylate salts. The zirconium enolates obtained (47) react
readily at room temperature with benzaldehyde in a synselective aldol reaction to give 48.[491
40a
46
47
48
Angen. C k m . In!. Ed. Engl. 28 11989) 397-412
3. Complexes with Metallocene-Ligand IC Bonding
The metallocene units in the carbene complexes described
in the preceding Section performed important roles as auxiliaries. Their presence facilitated (or even made possible) the
synthesis of the carbene complexes and to some extent modified the properties of these carbene complexes compared
with ordinary Fischer-type carbene complexes. On the other
hand, the central metal atom of the bent metallocene unit
can itself be bound to a carbene ligand. The formation of
simple alkylidene units at titanocene Cp,Ti or zirconocene
Cp,Zr can lead to compounds with considerable M = C Rbond character.[’] In principle. complexes with Cp2M= L
n-bond character can also result through combination of the
metallocene unit with organic ligands capable of metal-carbon n conjugation. Thus far, no evidence for a significant
n interaction exists in (o-a1kenyl)- or (o-a1kynyl)metallocene
compounds.[501It is possible that for simple mononuclear
complexes 49, the resulting charge separation is too disadvantageous (resonance structure 50). These unpdvorabk effects can be decreased by the introduction of suitable heteroatoms in the a- or p positions to the metal. In a series of
systems with the general formulas 51 or 53, a considerable
R character of the Cp,M = L bond was demonstrated.
58a
58
59
t
60
62
61
They function as selective Wittig olefination reagents with
organic carbonyl compounds (e.g., 58 a -+ 59).[541On reaction with olefins, 58 a affords metallacyclobutanes, which
can form other (alkylidene)metallocene complexes by a formal 12 + 21 cycIoreversi~n.[~~J
3.2. n Conjugation in Metallocene Complexes
3.2.1. (Alkylidenamido)metallocene Complexes
Alkylidenamido complexes [MI -N = CR, with some
M-N R character have been prepared for a range of transition
The zirconocene complexes 63 are obtained
by hydrozirconation of nit rile^.[^^] Bis(a1kylidenamido)
metallocene complexes 64 are prepared from the reaction
between metallocene dihalides and lithium alkylidena m i d e ~ . [Zirconocene,
~~]
generated in situ, oxidatively adds
benzophenone azine in a reaction involving N-N cleavage.[59]The X-ray structure analysis of 63a shows a nearly
linear Zr-N=CHPh unit (Zr-N-C = 170.5 (5)o).[s7b1This
compound has the shortest reported Zr-N bond thus far
[d(Zr-N) = 2.013 (5) 4. Complex 63a exhibits the stereochemical properties of a heteroallene system.[57b1
3.1. (Alky1idene)metallocene Complexes
The valence orbitals of the bent metallocene that extend
into the “ligand plane” can interact with the sp2 and
p orbitals of alkylidene l i g a n d ~ . Calculations
~~]
performed
on model compounds attribute metallaolefin character to
the X,Ti = CH, group.15‘I The Cp,M = CR, complexes have
a very electrophilic metal center. Stabilization can be
achieved by occupation of the available acceptor orbital at
the metal (e.g., by a phosphane). This hinders the dimerization of the (alky1idene)zirconocene to the stable 1,3-dimetallacyclobutane system. The phosphane-stabilized (carbene)zirconocene complex 57 was obtained from reaction
between bis(cyclopentadienyl)bis(phosphane)zirconium(rI)
55 and an ylide.t521
Cp2Zr (PPh,MeI,
P/PPh2Me -PPh,
-
H2C:PPh31
-PPh,Me
cp2
‘CH2-PPh,
55
56
64a:M=Zr,R=Ph
The bis(a1kylidenamido) complex 64a adopts a similar
structure. The Zr-N distances (Zr-N1 = 2.058 (2) A and
Zr-N2 = 2.063 (2)” A) are only slightly longer than in 63a.
The Zr-N1-C1 angle (173.7(2)”) is somewhat greater than
the Zr-N2-C2 angle (164.1 (2)”) and could point to an easier
rearrangement to a purely o-bound ligand in this compound.
Fast equilibration between the “inward” and “outward” oriented aryl groups at the terminal carbon atoms of the alkylidene moieties in 64a takes place in
/PPh2Me
cp2z\\
CH2
3.2.2. Metallocene YIides
57
Far more significant, though, is the stabilization of the
coordinatively unsaturated Cp,M = CHR unit by 1 :1 complex formation with aluminum halide compounds as in 58
(“Tebbe’s reagent”) or 62.[531
The (alkylidene)metallocene complexes released from
these adducts have a nucleophilic carbene carbon atom.
Angtw. Ckem I n l . Ed. Engl. 28 (i989) 397-412
63a:R=Ph
Metallocene ylides 66-69 are examples of compounds 53
with X = PR, .Iho1 Kaska et al. obtained the zirconocene ylide
66 and its hafnium analogue by reacting metallocene dichlorides with excess methylenetriphenylphosphorane.[6’1 Intramolecular transylidation makes metal-substituted ylides
with at least one alkyl group (usually methyl) at phosphorus
readily
403
analogous reaction of (q2-benzophenone)zirconocene gives
[Cp,Zr(OCHPh,)(CHPPh,)].
From
bis(cyc1opentadienyl)hafnacyclopentane 72, (q2-ethy1ene)hafnocene 7 3 was
generated (reversibly) at 90 "C by liberation of ethylene. Intermediate 7 3 can react with the ylide in two different ways.
Addition and intramolecular hydrogen shift affords
[Cp,Hf(C,H,)(CHPPh,)] 75 (path a). In a competitive reaction, transfer of the whole methylene group from the ylide to
the reactive organometallic intermediate and release of a
molar equivalent of triphenylphosphane gives bis(cyc1opentadieny1)hafnacyclobutane 76 (path b; relative product ratios a: b z 2). At elevated temperature, hafnacyclobutane 76
is stable with respect to cleavage to (methy1ene)hafnocene
and ethylene, in contrast to the titanacyclobutane analogue.
In the presence of benzaldehyde, no Wittig olefination product was observed but rather the formation of the aldehyde
insertion product 77.'641
Fig. 5. Molecular structure of 64a [59]
65
U
CpzLr/CI
'CH=PPh3
+
0
0
CH3PPhgCl
66
CH =PPh3
CH2=CH2
Compounds of the type [Cp,M(R)(CH = PPh,)] (R =
alkyl or aryl) can be obtained from methylenetriphenylphosphorane and (olefin)metallocene complexes in
a reaction involving C-H activation and hydrogen migrat i ~ n . [ ~From
~ J a t :1 mixture of (s-cis-/s-trans-q4-butadiene)hafnocene only the s-trans isomer reacts with the ylide
under kinetic control at 0 "C. Cleavage of a C-H bond at the
ylide carbon and hydrogen migration to the end of the diene
chain takes place. Stereoselective formation of (trans-0-2butenyl)Cp,Hf( - C H = PPh,) was observed. Equilibration
with the cis isomer only occurs above 35 "C. Further stereochemical information is obtained from the reaction of the
(s-cis-/s-trans-q4-butadiene)zirconocene
mixture 16/18 with
CH, = PPh, . The s-cis isomer reacts selectively at - 50 "C to
give the (trans-0-2-butenyl)metalloceneylide trans-71. This
result possibly points to a concerted hydrogen shift in an
organometallic system that occurs analogously to the homo1,5-hydrogen shift in the purely organic methylvinylcyclopropane ---t hexadiene rearrangement. At - 20 "C, trans-71
equilibrates with cis-71.
A mixture of bis(cyclopentadieny1)zirconacyclopentane and CH,=PPh, at room temperature affords
[Cp,Zr(C,H,)(CHPPh,)] after expulsion of ethylene. The
4H3
16
404
trans- 71
05-71
74
75
(q 2-t ,2-Didehydrobenzene)titanocene 79, generated thermally from diphenyltitanocene 78, reacts with methylenetriphenylphosphorane to form the products 80 and 81
competitively (70: 30 at 80 oC).163e7651 In contrast,
(aryne)zirconocene and CH, = PPh, afford only the zirconocene ylide 82.
p
CpzM
'CH
78
=PPh,
79
For these metallocene ylides, a clearly observable increase
in carbene complex character is apparent on going from
hafnium through zirconium to the titanium compound. The
growing 7c character of the M-Cytidebond in the series 75,82,
80 is discernible from the resonances of the C H group moving to increasingly lower field in the N M R spectra ['H/13C:
All
6 = 3.72/91.6 (75); 5.65/106.2 (82); 8.78/165.2
metallocene ylides characterized by X-ray structure analysis
have nearly coplanar arrangements of the four substituents
(two C p hgands, hydrogen, and PPh,) at the central [MICylideunit (see Fig. 6). The dynamic N M R spectra (coalescence of the signals of the diastereotopic C p ligands) showed
that variation of the metal resulted in different AG:t for the
hindered rotation about the M-CHPPh, bond. This rotational barrier increases on going from Hf (75) to Zr (82) and
then Ti (80 (see Table 2). In addition, a clear progressive
A n g e a . Chem. hi.Ed. Engl. 2h' (1989) 397-412
c3
Fig. 6. Molecular structure of the titanocene ylide 80.
Table 2. Characteristic data for the M-C(y1ide) bonds in metallocene ylides 75,
82. and 80 [63]
~
dM-C(ylide) [A]
Ad [A1 La1
AG:, ( T ) [kcal mol-
‘1
Zr)
75 (M = Hf)
82 (M
2.149(6)
0.10
< 8 ( < - 100 “C)
2.157(4)
0.1x
8.4 ( - 102 ”C)
=
80 (M =Ti)
n systems of the o-bound ligands and the available acceptor
orbital at zirconium. The geometry of 85a is that of a “normal” pseudo-tetrahedrally coordinated zirconium (IV) compound with a Cp-Zr-Cp angle of 132”. The linear o-propynyl ligands subtend an angle at Zr of 103.6(1)”. The CC
triple bond length is normal (1.206 (4) A). The Zr-C o bonds
to the alkynyl ligands are not shortened (2.249 (3) A).[’’,
The formally d’-configurated [CpzM-C =CR] complexes are different. The reaction between (Cp,TiCI), and
NaC = CPh affords the binuclear diamagnetic titanium compound 87 by CC coupling of the a-alkynyl groups to give a
bridging substituted b~tadiene.[~’]Replacement of the
titanocene group by zirconocene or hafnocene gives a completely different binuclear structural type (without CC coupling) of general formula [Cp,M(CCR)], . Thus, compound
88 was obtained by reaction of the mononuclear
bis(alkyny1)metallocene complexes 85 with a zirconocene
source, either [Cp,Zr(butadiene)J or [Cp,Zr(CO),] . Addition to give 86 is followed by rearrangement involving oalkynyl ligand migration to afford 88. Hafnium analogues of
88 may be synthesized similarly.
r
2.033 (6)
0.22
12.0 ( - 34 “ C )
[a] Shortening of the M-C(ylide) bond owing to IT interaction given relative to
an adjacent M-C 0 bond used as an internal standard.
L
85
85a: R=CH3
shortening of the M-Cylidebond length (referred to a suitable
intramolecular standard) can be seen from the X-ray structure analyses of these compounds.
These data imply that the hafnium compound 75 has a
comparatively small n component of the M-C,,,, bond; in
the zirconium ylide 82 this K component is significantly
greater. The titanium ylides have pronounced carbene complex character. A description of their bonding must therefore
involve resonance form 54 (M = TiPh; Y = PPh,).
This gradually changing carbene complex character is reflected in the reactivity of the metallocene ylides. Under standard conditions, the “carbene complex” 80 does not convert
acetophenone, for example, into the enolate form nor reacts
with carbon monoxide or benzyl isocyanide. It behaves as a
coordinatively saturated compound. By contrast, the
Ph,PCH ligands of the zirconocene and, particularly, the
hafnocene ylides function as carbon bases. With CO or
PhCH,NC, both 82 and the more reactive 75 undergo insertion exclusively into the formally stronger M-CHPPh,
bond,[hl.h3gI
e c
H’
Ph3P’
H/c\?Phl
83
75
R
1
_I
!
86
A
R
88
88a: R.Ph
87
In contrast to the mononuclear bis(alkyny1)zirconocene
85, complex 88 a clearly shows lengthening of the C = C bond
of the alkynyl ligand (d(CI-C2) = 1.261 (2) A). The Zr-C
bond is very short (2.1 88 (2) A) and the bond distances ZrC1* and Zr-C2 * are 2.407 (2) and 2.431 (2) A, respectively.
The large Zr . . . Zr separation (3.506 (1) A) excludes a direct
metal-metal interaction.1681These data justify a description
of these diamagnetic complexes by equivalent resonance
forms involving partial carbene character of the alkynyl ligands.
‘H
84
3.2.3. n Conjugation at Binucleav (AIkynyI)metallocene
Complexes
The X-ray structure analysis of the bis(propyny1)zirconocene 85 a reveals no conjugative interaction between the
Angru.. C‘hem. I n t . Ed. Engi. 28 (1989) 397-412
c4
Fig. 7. Molecular structure of 88a [68]
405
It seems, then, that metalkarbon TI conjugation is significant in (alkynyl)metallocene compounds if the resulting
unfavorable charge distribution can be compensated for. In
the binuclear bis(a1kynylmetallocene) complexes 88 this
occurred by head-to-tail coupling of two identical mononuclear metallocene complex
The X-ray structure analysis of [Cp,Zr(p-CH = CHPh)(pCI)ZrCp,] also reveals a very short Zr-C distance
(2.194 (7) A). A participation of the resonance form with
metal carbene complex character should probably be used
here to describe the structural properties of the binuclear
(alkenyl)metallocene compound.i70]
Metallaoxiranes can be constructed stepwise by the use of
hydrogen and carbon monoxide. Metallocene dihydrides can
be obtained from Cp2M precursors and H2.i761
The reaction
of (Cp,ZrH,), 91 with C O affords trimeric (q2-formaldehyde)zirconocene 92, a compound with a metallaoxirane
structure. Thermolysis of this complex leads to the expulsion
of all three methylene groups and the formation of the “metal oxide” fragment (Cp,ZrO), 93. This example shows that
there are aspects in the chemical behavior of zirconocenederived metallaoxiranes that are related to Fischer-Tropsch
type cherni~try.~~’]
4. Metallocene Compounds with a Metallaoxirane
Structure
In the Fischer-Tropsch synthesis of hydrocarbons from
C O and H,, methylene groups on the surface of the active
catalyst seem to play an important role. In particular, a series
of simple experiments by R. Pettit et al. appears to confirm
the original mechanistic proposal,17 despite many other
formulations of the reaction pathway.1721These results
demonstrate that, under various conditions, diazomethane
can influence an active Fischer-Tropsch catalyst. Expulsion
o f N , possibly leads to the formation of a methylene complex
at the catalyst surface. In the absence of hydrogen, the fast
formation of ethylene as the sole product was observed. On
addition of molecular hydrogen, the dimerization of methylene does not occur. Instead, CH, inserts into the M-H
bonds formed on the surface. The growth of the alkyl chains
occurs on the resulting surface-bound methyl groups. After
removal of the catalyst, the product mixture of hydrocarbons was found to be very similar to that obtained from the
Fischer-Tropsch synthesis. A detailed product analysis has
shown that surface-bound methylene groups participate in
this process both at the initiation and at the chain-growth
steps. A schematic depiction is shown in Section 4.4.i731
Models for this chemistry on a molecular basis have been
developed. In many cases, multinuclear metal complexes
with direct metal-metal bonds bridged by methylene ligands
have been investigated as analogues of parts of a metal surface. Bi- and multinuclear p-methylene complexes, “dimetallacyclopropanes”, have been prepared in large numbers. A
number of the reactions of these complexes show similarities
to proposed steps of the Fischer-Tropsch synthesis.*74’7 5 1
Critically, though, it has not been unambiguously established that Pettit’s experiments investigating parts of the
Fischer-Tropsch synthesis really model the chemistry of the
methylenes at the metal surface. The additional presence of
a not easiIy reducible metal oxide (thorium oxide, zirconium
oxide, titanium oxide) together with the reductive components (usually iron or cobalt) is essential for Fischer-Tropsch
catalysts.r72b1Therefore, the CH,-transforming steps might
well take place at a metal oxide surface. Molecular models
for this exhibit the metallaoxirane group 90 rather than the
dimetallacyclopropane unit 89.
/cc2
-M-089
406
90
91
92
93
4.1. Formation of Metallaoxiranes
4.1. I . (q2-Ketone)- and ($-A Idehyde)metallocene
Compiexes
Many metals from the right-hand side of the periodic table
form complexes containing side-on-bonded ketone or aldehyde ligands; these complexes are obtained by reaction of a
coordinatively unsaturated metal complex fragment with the
organic carbonyl compounds. This method cannot usually
be used for the synthesis of (q2-ketone)- o r (q2-aldehyde)complexes (metallaoxiranes) of titanocene, zirconocene, or
hafnocene, since the resulting metallacyclic three-membered
ring compounds are too reactive. They often add a further
R L R Z C = Omolecule very readily, followed by ring expansion via C C coupling.
Metallaoxiranes of zirconocene can be prepared from (qzacy1)zirconocene complexes 94. The three-membered ring
structure is formed easily by this route. Proceeding from
(77’-acety1)zirconocene chloride, the ketene complex
[Cp,Zr(q2-0 = C = CH,)] (isolated as a dimer) was obtained
after a - d e p r o t o n a t i ~ n . I ~ ~(q’-Ketone)metallocene
I
complexes are frequently obtained by addition of a carbon nucleophile at the carbonyl group of an (11’-acy1)metallocene.
An existing a-bonded alkyl or aryl group in a metal complex
can be used in this way, via an intramolecular nucleophilic
addition. The formation of (11’-benzophenone)zirconocene
95a (isolated at room temperature as the dimer 96a) is a
typical example (Scheme l).f63f.I‘’
Metallaoxiranes containing the bis(cyclopentadieny1)zirconocene fragment are characterized by oligomer formation, which occurs by coupling of the three-membered rings
by bridge formation between the metallaoxirane oxygen
(donor) and the metal (acceptor) in the ring plane.r801
Through this coupling, dimers or trimers with planar
(M - 0 -C)” frameworks were obtained. The bonding between the monomeric units can be very different in strength.
In the cyclodimeric (q2-dipheny1ketene)zirconocene96 b, for
example, there is a central Zr,O, four-membered ring with
four equally short metal-oxygen
whereas in
the cyclotrimeric (q’-forma1dehyde)zirconocene 92 the
bonds between the monomers are significantly l ~ n g e r . ~ ” ]
-
Angew. Chetn. I n r . Ed. Engl. 28 (1989) 397-412
R
94
94-96a:R:Ph
96
95
96b
92
96a
Scheme 1. Formation and structural properties of (q*-ketone)- and (q2-aldehyde)zirconocene complexes (bond lengths in A).
hyde)zirconocene complex 97a (X = CI, R = H), containing
a metallaoxirane structural unit. The carbonylation of
oligomeric 91 affords in a similar manner the cyclotrimeric
92 described above.[771
An (q2-benzaldehyde)Cp,Zr/(q2-formaldehyde)Cp2Zr
1 :1 adduct is obtained from (q2-benzoy1)zirconocene chloride 94 in a reaction sequence involving hydrozirconation,
Cl/H ligand exchange, and carbonylation. The binuclear intermediate,
(q2-benza1dehyde)zirconocenejdihydridozirconocene 98, was
In some cases, the methylene-bridged Zr-0 unit appears
to show a carbonylation chemistry similar to that of several
binuclear p-methylene complexes. Thus, 99 reacts at high
temperature with CO at elevated pressure to give the insertion product 100. Thermolysis of 100 affords the binuclear
enediolate complex 101. Starting from 98, two molecules of
carbon monoxide have thus been reductively coupled via a
metallaoxirane intermediate.[81b1
H
Cyclodimeric (q2-benzophenone)zirconocene 96a is an even
more loosely bound adduct. At high temperatures a considerable amount of the monomeric metallaoxirane 95a is
present in eq~ilibrium.‘~~‘.
791
Similarly. metallaoxiranes are obtained from intermolecular addition of nucleophiles to an (q 2-acyl)metallocene. (Hydrido)metallocenes have proven particularly suitable as
reagents in the formation of (q2-RCHO)MCp, complexes.
In general, they directly afford multinuclear metallocenes
with bridging Cp,M-0-CHR units. Typical examples are
the reactions of (q2-acyl)alkyl- or (q2-acy1)halozirconocene
complexes 94 (X = alkyl or Cl) with the hydrozirconation
reagent 60, which leads to aldehyde-bridged binuclear metallaoxiranes 97. Analogous products were isolated in most
cases from further reaction, arising from 97 by rearrangement (e.g., intramolecular alkylidene shift, see Section 4.2)
and/or halide/hydride ligand exchange with 60.[811
-
co
99 ___
H\ /Ph
/c\
b
CP 2z<-’0,
Ph
C‘’
/ \
Cp,Zi--’O
\
\
n.
I
100
H
101
The formation of enediolate complexes from metal alkyls
also occurs via intermediates with metallaoxirane character (i.e., (q2-ketone)metallocenes). Thus, exactly 1.5 molar
equivalents of CO are taken up by the very reactive alkylmetallocene 1,l -bis(cyclopentadienyI)hafnacyclobutane 76
under ambient conditions. This affords compound 102
(Fig. 8), a 1 :1 adduct of mono- and biscarbonylation products; in this case, the proposed intermediate, an (q2-ketone)hafnocene, forms a complex with the enediolate before
further reaction with carbon monoxide 0ccurs.I~~1
4.1.2. a-Metalated Ethers with Metallaoxirane Structures
R
I
Cp2Zr,-
‘,.’
R
/L+o
[Cp2ZrlHlCI],
X
60
Cp2Zr
-O--ZrCpZ
tl
‘x
97
97a:R=H
Ph
H
\ /
I
CI
~
4
r 91 ~c
-[CplZr(H\CIIx 60
Ph
p 1, , ~~ ~ o
H
‘
\
-ZrCp2
H
94
(a-Metalloceny1)-substituted ethers exhibit three local
minima on the (Cp,MX)-CH,OCH, hypersurface. similar
to (q2-acy1)metallocene complexes[841[orientation of the
CH,0CH2 ligands: q l - 0 outside (103), q 2 - 0 outside
(104a), and q2-0 inside (104b)l.
/L\
94
Cp,Zr,-O
H
/
98
H\ /Ph
cc
C p 2 Z/c\
r -o
\
‘0 -zrCp2
\ /
CH2
99
The synthesis of compounds with the Cp,I‘&O-CH,
unit
is a special case. They cannot be made using mononuclear
formyl complexes of the Ti group as starting materials. (q2HCHO)MCp, complexes can, however, be obtained by direct carbonylation of several (hydrido)metallocenes. Floriani
et al. showed in 1978 that the carbonylation of the
oligomeric 60 leads to the binuclear (p-q’ :q2-formaldeA n p n . C‘hi,m. Int. Ed. Engl. 28 (19x9) 397-412
cpzo
CPIO
Fig. 8. Molecular structure of the (q’-ketone)hafnocene/(enedioIato)MCp,
1: 1 adduct 102.
407
Fig. 9. Molecular structure of 106.
The reaction
of
titanocene
dichloride
with
CIMgCH,OCH, affords the q' complex 105, having the q l 0-outside structure. In contrast to this, the reaction of
zirconocene dichloride with the same Grignard reagent
gives the q2-complex 106 with qz-0-inside orientation
[d(Zr-Cl) = 2.271 ( 5 ) A;d(Zr-0) = 2.204 ( 3 ) d(C1-0) =
1.414(6) A](Fig. 9).rs51
A;
trix at which such a migratory reaction can still occur is the
M-0-M unit. (p-q ' :q z - 0= CRRZ)Metallocenes (e.g., 95,
97, and 98; cf. Section 4.1.1) result from saturating this unit
with ligands and bridging an M-0 bond with an alkylidene
moiety.
Fast, thermally induced intramolecular alkylidene shifts
along the M-0-M framework are the rule with complexes
containing the Zr-CR1R2-O-Zrgroup. For example, the reaction of the dimeric (q2-benzophenone)zirconocene 96
(R = Ph) with (Cp,HfH,), at room temperature affords the
binuclear (p-q' :q z - 0= CPh,) hydride-bridged Zr/Hf compound 109. At 60 "C this complex is in equilibrium with its
isomer 112, in which the metal atoms have formally exchanged positions. Above 80 'C, subsequent statistical distribution (108, 109, 111, 112) of metal centers is observed. The
rearrangement 1 0 9 s 112 requires initial opening of the hydride bridge (formation of 110). Fast migration of the
diphenylcarbene group along the Zr-0-Zr framework can
then take place. Closure of the hydride bridge in the rearranged product 113 affords the isomer l12.[63'1
C Ph,
ChZr-
0
\
H-
\
Z r Cp,
/\
CkZr-0
\
\
i
__ Cp2Zr-O-HfCq
__ \H
1
H
108
'CH,
CH3
103
105:X = CI,M = Ti
104a
104b
106:X = Ci. M = Zr
Cp2Hf-H
!
H
111
An analogous complex, 107, is obtained by reacting
Cp,ZrCI, with lithiated benzhydryl methyl ether. In this
case, the Zr-C bond in the three-membered ring (2.395 (6) A)
is considerably longer than the Zr-0 bond (2.215 (4) A).
This can be described in terms of a contribution by the oxonium ylide resonance structure. Compounds of the type
[Cp,Zr(X)CR,OR) can be understood as oxonium ylides internally stabilized by metallaoxirane formation.[861The
binuclear (p-q ' :qZ-forma1dehyde)zirconocenecomplex 97 a
is a further example of this type of compound.
LiCPh,OCH,
C@ZrC12
/C\Ph2
Cp2Zr-O-CY
\
CI
Cp2Zr-H
H
112
113
This alkylidene migratory rearrangement occurs much
faster if there is no hydride bridge at the participating metal
centers that needs to be broken in the rate-determining step.
This is shown by the dynamic NMR spectra of the openchain (p-q ' :q2-forma1dehyde)zirconocene complex 97a.
From the coalescence of the 'HNMR cyclopentadienyl
resonances at - 140"C, an activation barrier of AG?i40,c z
7 kcal mol-' was estimated for the migration of the CH,
group along the Zr-0-Zr moiety.
eCPh,
1
-Cp2Zr-O-CH,
I *
CI
107
97a
4.2. Dynamic Behavior of the MetallaoxiranesIntramolecular Akylidene Migration
A necessary requirement for CC coupling reactions of
methylene units at the heterogeneous Fischer-Tropsch catalyst is the mobility of these groups on the surface. It is difficult to model this important dynamic property with simple
molecular compounds. A larger molecular framework is required. The smallest possible segment of a metal oxide ma408
R=CI
97a
This fast automerization reaction appears to be quite
general for p-q1 : q2-aldehyde complexes of this particular structural type (e.g., [Cp,ZrPh(CH, - O)ZrPhCp,],
sz 1 0 k c a l m o l ~ ' ; [Cp,ZrCI(CHMe-O)ZrClCp,],
sz 13 kcal mol-'). Experimental studies aimed at
explaining the reaction mechanism of the alkylidene migration at these binuclear metallocene complexes[". "I suggest
a concerted "dyotropic" rearrangement.r881Fast dyotropic
Angew. Chem. l n l . Ed. Engl. 2X 11989) 397-412
rearrangements in molecular compounds may possibly serve
as models for migratory reactions on surfaces.
4.3. Alkylidene Transfer Reactions
Several metallocene complexes with metallaoxirane structural units undergo thermally induced alkylidene-coupling
reactions. Thus, the compound 107 decomposes at 40 "C
with formal cleavage of the diphenylcarbene moiety to give
[Cp,Zr(CI)OCH,] and tetraphenylethylene. The methylenebridged complex 106 is thermally more stable. It requires
a temperature of ca. 200°C to decompose to give
[Cp,Zr(CI)OCH,] and CH, =CH, .[851
Alkylidene moieties of metallaoxiranes can be transferred
to hydrido complexes and insert into the M-H bond. Thus,
107 reacts with 60 at 40 "C, transferring the CPh, unit to give
the insertion product benzhydrylzirconocene chloride 118
and 117 [path (a)]. The nucleophilicity of the alkylidene carbon in 107 (the oxonium ylide character of this compound
was confirmed by X-ray structure analysis; see Section 4.1.2)
assists the formation of the intermediate 114, which can then
undergo hydride migration. The side products of this reaction, 119 and 120, can be rationalized as resulting from intramolecular variants of this alkylidene insertion reaction
occurring after Cl/H ligand exchange [path (b)].
CI
97a
I
J
I
L'
60
hydrogenation of carbide intermediate^.^"^] The characteristic series of reactions of the surface methylenes in FischerTropsch catalysis, generally accepted after the experiments
of Pettit et al.,[731are reflected to some extent in the chemistry of molecular metallaoxiranes. The dimerization to give
olefins and the alkylidene insertion into metal-hydride
bonds are particularly noteworthy. These reactions correspond, at least formally, to two important reaction steps of
methylene at the catalyst (Scheme 2).
1
L
j
M-H
L
Scheme 2. A comparison between metallaoxirane reactions (left) and proposed
steps in methylene chemistry at a catalyst surface (right).
Methylene transfer from the metallaoxirane 106 to
(Cp,Zr(H)CI), 60 to give methylzirconocene chloride 123 is
equally facile. The binuclear complex 97a, in which the Zr-0
unit is bridged by a CH, group stemming from CO and H,,
also reacts in this way. At 40 "C in a slow reaction, 123 and
the "metal oxide" 122 are formed very cleanly.[86a'
The chemistry of metallaoxiranes thus Fdr offers no simple
molecular examples modeling the C-C bond-forming steps
of methylene inserting into metalkarbon bonds at the catalyst. Possibly, such a reaction step takes place during the
thermally induced intramolecular formation of ethylene
from 124. Further growth of alkane chains by intermolecular
CH, insertion in this case is prohibited by fast j3-OCH, elimination, with release of ethylene.
r
4.4. Do Aspects of the Chemistry of Zirconocene
Metallaoxiranes Have Relevance to Fischer-Tropsch
Chemistry?
CH3
As far as the formation of methylene groups from CO and
H, at an active heterogeneous Fischer-Tropsch catalyst is
concerned, the question should be answered in the negative.
The surface-bound CH, moieties there presumably result
from carbon monoxide, after dissociative adsorption and
Angcw. Clrcm. In1 Ed. Engt. 28 (1989) 397-412
124
1
L
125
126
The thermal decomposition of metalated thioether complexes iCp,Zr(CR,SCR),] to give ICp,Zr(SR'),] and
R,C = CR, may also possibly occur by this pathway.f901
409
5. Outlook
Very few areas of research have so consistently produced
such new and interesting results over the years as the chemistry of carbene complexes. As many examples in this article
show, structural features first found with “classical” Fischertype carbene complexes are increasingly being found for other types of organometallic compounds as well. It is expected
that typical carbene complex reactions will be found for related compounds with some degree of carbene complex character. Transition-metal carbene complexes are firmly estdblished in organic synthesis with many applications. They are
now helping to make accessible experimental studies at the
borderline between homogeneous and heterogeneous catalysis. Mechanistically oriented studies on the chemistry of
metallaoxirane compounds as described above represent one
of many possible starting points.
The work described here was carried out by a group of
talented co-workers whose names appear in the list of rejerences. To them go m y particular thanks,f;?ra stimulating time
working together that has given me much pleasure. Part of
these results were obtained during time spent at the MaxPlanck-institut fur Kohlenforschung in Miilheim a. d. Ruhr. I
wish to thank Professor Dr. G. Wilke for his very generous
support. I am grateful to the leaders and co-workers of many
groups of the Institute for help and muny stimulating discussions. Financial support from the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie, the Minister fur
Wissenschaft und Forschung des Landes Nordrhein- Westfalen, the Fritz- Thyssen-Stifiung, the St ftung Volkswagenwerk, and the Alfied Krupp von Bohlen und Halbach-Stifiung
is gratefully acknowledged.
Received: February 16, 1988;
revised: June 22, 1988 [A 712 IE]
German version: Angew. Chem. I 0 1 (1989) 411
Translated by Dr. Murk G . Humphrey
[l] E. 0. Fischer, A. Maasbol, Angeir.. Chem. 76 (1964) 645; Angew. Chem.
lnr. Ed. Engl. 3 (1964) 580; Chem. Ber. 100 (1967) 2445; Adv. Urgunomet.
Chem. 14 (1976) 1.
121 R. R. Schrock, J. Am. Chem. So(. 96 (1974) 6796: R. R. Schrock, J. D .
Fellmann, ibid. 100 (1978) 3359.
131 T. J. Katz, Adv. Urganomel. Chem. 16 (1977) 283; N. Calderon. J. P. Ldwrence, E. A. Ofstead, ibid. 17 (1979) 449: H. W. Turner, R. R. Schrock.
J. D. Feldmann, S. J. Holmes, J . A m . Chem. Soc. 105 (1983) 4942: K. J.
Ivin: Ulefin-Merathesis, Academic Press. London 1983; R. H. Grubbs in
G. Wilkinson. F. G. A. Stone, E. W. Abel (Eds.): ComprehensiveUrgunome/allir Chemistry, VOI. 8, Pergamon Press, Oxford 1982, p. 499.
[4] R. R. Schrock, Acr. Chem. Res. 12 (1979) 98; T. Kauffmann, R. Abeln, S.
Welke, D. Wingbermiihle, Angew. Chem. 9811986) 927; Angew. Chem. Inr.
Ed. Engl. 25 (1986) 909.
[5] C. P. Casey in H. Alper (Ed.): Transiriun Metal Orgunomrtulks in Organic SynthesSD. Vol. I , Academic Press. New York 1976. 190: F . J. Brown,
Prog. fnorg. Chem. 27(1980) 1; K. H . Dotz, Angew. Chem. 96 (1984) 573;
Angew. Chem. 1111.Ed. Engl. 23 (1984) 587: W. D. Wulff, P:C. Tang, J.
Am. Chem. Soc. I06 (1984) 434. 1132; C. P. Casey, N. L. Hornung, W. P.
Kosar, ibid. 109 (1987) 4908: M . Brookhart. W. B. Studabaker. Chem.
Rev. 87 (1987) 411; R. Aumann, H . Heinen. C. Kriiger. Chem. Ber. I20
(1987) 1287; A. Parher, H. Rudler, N. Platzer, M. Fontanille, A. Soum, J.
Chem. Sor. Dalron Trans. 1987, 1041.
[6] K. S. Chan. W . D. Wulff, J . Am. Chem. Soc. 108 (1986) 5229; Y.-C. Xu,
W. D. Wulff, J . Urg. Chem. 52 (1987) 3263.
[7] C. N. Wilker. R. Hoffmann, 0. Eisenstein, Nous. J . Chim. 7(1983) 535; J.
Am. Chem. Soc. 104 (1982) 632; J. Ushio, H. Nakatsuji. T . Yonezawa, h i d .
106 (1984) 5892; E. A. Carter, W. A. Goddard 111, ibid. 108 (1986) 4746.
[8] J. W. Lauher, R. Hoffmann, J . Am. Chem. Sor. 98 (1976) 1729.
[Y] J. L. Petersen. L. F. Dahl, J . Am. Chem. Sor. 96 (1974) 2248; ibid. 97
(1975) 6416.6422; J. L. Petersen, D . L. Lichtenberger, R. F. Fenske, L. F.
Ddhl, ihid. 97 (1975) 6433: H. H . Brintzinger. L. S. Bartell, ibid. 92 (1970)
410
1105; H. H. Brintzinger, L. L. Lohr. Jr., K. L. Tang Wong, hid. 97 (1975)
5146; J. H. Osborne, A. L. Rheingold, W. C. Trogler, i h d . 107 (1985)
7945: L. Zhu, N. M. Kostif. J . Organornet. Chem. 335 (1987) 395.
I101 Review: U. Schubert. H. Fischer, P. Hofmann, K. Weiss, K. H. Dotz,
F. R. Kreissl: Trunsitiun Metal Curhene Comp/r.\-r.s.Verlag Chemie. Weinhelm 1983.
1111 E.O. Fischer, S. Fontdna, J . Orgunomer. Chem. 40 (1972) 159: H. G.
Raubenheimer. E. 0. Fischer. ibid. 91 (1975) C23; see also C. P. Casey.
R. E. Palermo, A. L. Rheingold. J . Am. Chem. Soc. 108 (1986) 549.
I121 C. M. Jensen. C. 8. Knobler, H. D. Kaesz. J . Am. Chrm. Sot. 106 (1984)
5926; E. 0. Fischer. V. Kiener, D. S. P. Bunbury, E. Frank. P. F. Lindley.
0. S. Mills. Chrm. Commun. 1968. 1378; W. Wong, K. W. Chlu. G. Wilkinson. A. M. R. Galas, M. Thornton-Pett, M. B. Hursthouse, J. Chrm.
Soc. 1983, 1557; A. W. Parkins, E. 0. Fischer, G. Huttner, D . Regler,
Angel?. Chem. HZ (1970) 635; Anxeu.. Chem. I n ! . Ed. En$. 9 (1970) 633.
1131 a) W. Petz. J . Urganomet. Chem. 72 (1974) 369: J. Pebler. W. Petz. Z.
NururJirsch. B29(1974) 658; b) R. S. Threlkel. J. E. Bercaw. J. Am. Chem.
Sac. 103 (1981) 2650; c) P. T. Barger. J. E. Bercaw. Orgunometullics 3
(1984) 278: J . Organornet. Chem. 201 (1980) C39: G. S. Ferguson, P. T.
Wolczanski, J . Am. Chem. Soc. 108(1986) 8293; d) P. T. Wolczanski. R. S.
Threlkel, J. E. Bercaw, ihid. 101 (1979) 218; e) P. T. Barger. B. D. Santarsiero. J. Armantrout, J. E. Bercaw. ibid. 106 (1984) 5178.
1141 M. F . Lappert. A. J. Oliver, J . Chem. Soc. Dalton Truns. 1974. 65; M . F .
Lappert, P. L. Pyl. ibid. 1977, 2172.
[15] a) A. J. Hartshorn, M. F. Lappert, K. Turner, J . Chrm. Soc. Da/tun Trans.
1978, 348; M. J. Doyle. M . F. Lappert, P. L. Pyl, P. Terreros. ibid. 1984,
2355, and referencescited therein; b) M. F. Lappert. A. J . Oliver, J . Chem.
Suc. Chem. Commun. 1972, 274: c ) J . Chem. Sor. Dalrori 7iun.i. 1974, 65;
d) P. B. Hitchcock, M. F. Lappert, G. M. McLaughlin, A. J. Oliver, ihid.
1974, 68.
[I61 A. Stockis. R. Hoffmdnn, J . Am. Chem. Soc. I02 (1980) 2952; Recent
articles: E. Negishi, S. J . Holmes, J. M. Tour, J. A. Miller, rbid. 107 (1985)
2568; G. Erker. U. Dorf, A. L. Rheingold, 0rgunometallic.s 7 (1988) 138:
S. L. Buchwald, B. T . Watson, J. C. Huffman. J . Am. Chem. Sot.. 109
(1987) 2544; W. A. Nugent, D . L. Thorn, R. L. Harlow. ihtd. 109 (1987)
2788. and references cited therein.
[17] a)S. A. Cohen. P. R. Auburn, J. E.Bercaw. J . Am. Chem. Soc. /05(1983)
1136: b) H. Lehmkuhl, R. Schwickardi, J . Organornet. Chem. 303 (1986)
c43.
[IS] G. Erker. J. Wicher, K . Engel, F’. Rosenfeldt. W. Dietrich, C. Kriiger, J .
Am. Chem. Suc. 102 (1980) 6344.
1191 a) G. Erker. J. Wicher. K. Engel. C. Kriiger. Chem. Ber. 115 (1982) 3300;
G. Erker, K. Engel. C. Kriiger, A.-P. Chiang, ibid. 115 (1982) 3311; U.
Dorf. K. Engel, G. Erker, Orgunometullics 2 (1983) 462; G . Erker. K.
Engel, C. Kriiger, G. Miiller, ibid. 3 (1984) 128; C. Kriiger. G. Miiller. G.
Erker, U. Dorf. K. Engel. ihid. 4 (1985) 215; G. Erker. K. Engel, U. Korek,
P. Czisch, H. Berke, P. Caubere. P. Vanderesse, ihid. 4 (1985) 1531: G.
Erker. T. Miihlenbernd, R. Benn, A. Rufinska, Y.-H. Tsay, C. Kriiger.
Angew. Chem. 97(1985) 336; Angrw. Chem. I n / . Ed. Engl. 24(1985) 321; G .
Erker, T. Miihlenbernd, A. Rufinska, R. Benn, Chem. Ber. 120(1987) 507;
b) H . Yasuda, Y. Kajihara, K. Mashima, K. Nagasuna, K. Lee. A. Nakamura. UrganometullicsIf1982) 388; Y. Kai, N. Kanehisha, K. Miki, N.
KaSdi, K. Mashima, K . Nagasuna. H . Yasuda, A. Nakamura, J . Chem.
Sac. Chem. Comm. 1982. 191: c) R. Bechthaus, K.-H. Thiele, J . Urgnnomet. Chem. 268 (1987) C7: d) R. Benn, G. Schroth. hid. 228 (1982) 71.
I201 Reviews: a) G. Erker, C. Kriiger. G. Miiller. Ady. Organomer. Chem. 24
(1985) 1 ; b) H. Yasuda. K. Tatsumi, A. Nakamura. Acc. Chem. Res. 18
(1985) 120; H . Yasuda. A. Nakamura, Angew. Chem. 99 (1987) 745; Angew. Chem. I n / . Ed. EngI. 26 (1987) 723.
[21] a) G. Erker, K. Engel, J. L. Atwood. W. E. Hunter, Angeiv. Chem. 95
(1983) 506: Angew. Chem. Int. Ed. Engl. 22 (1983) 494,675; G. Erker, U.
Dorf, Angew. Chem. 95 (1983) 800; Angeir.. Chem. I n t . Ed. EngL 22 (1983)
777, 1066; b) H. ydsuda, Y. Kajihara, K. Mashima, K. Nagasuna, A.
Nakamura, Chem. Lerr. 1981, 671; M. Akitd, H. Yasuda. A. Nakamura.
ibtd. 1983, 217.
[22] G . Erker. U. Dorf, R. Benn, R.-D. Reinhardt. J. L. Petersen. J . Am. Chem.
Soc. 106 (1984) 7649.
[23] G . Erker, R. Lecht, J . Orgunornet. Chem. 311 (1986) 45.
[24] a) E. 0. Fischer, F . R. KreiBI, E. Winkler, C . G. Kreiter, Chem. Err. 105
(1972) 588; b) M. F. Semmelhack, R. Fdmura. J . Am. Chem. Soc. f05
(1983) 4099. and references cited therein; E.0. Fischer, H . J. Beck, C. G.
Kreiter. J. Lynch, J. Miiller, E. Winkler, Chrm. Ber. 105 (1972) 162.
[25] Cf. [24a]; D. J. Ddrensbourg, M. Y. Darenshourg. h o g . Chrm. 9 (1970)
1691; F. Carre, G . Cerveau, E. Colomer, R. J. P. Corriu, J. C. Young, J .
Urganomet. Chem. 179 (1979) 215: ibid. 205 (1981) 31; Y. Yamdmoto, H.
Yamazdki. Bill. Chem. Soc. Jpn. 48 (1975) 3691.
W. Paul, R. Feser, R. Zolk. P. Thometzek, Chem. Ber. I l X
D. B. Jacobson, B. S. Freistr, J. Am. Chem. Sor. 107 (1985)
5870; H. C. Clark, K. J. Reimer, fnorg. Chem. 14 (1975) 2133: P. J. Frdser.
W . R. Roper, F . G. A. Stone. J . Chem. Soc. Dalton Trans. 1974,760; P. R.
Branson. R. A. Cable. M. Green, M. K. Lloyd, J . Chem. SOC.Chrm. Cornmun. 1974, 364; P. Hong, N. Nishii, K. Sonogashira. N. Hagihara, ihid.
1972, 993.
[27] G. Erker. R. Lecht. Y.-H. Tsay. C. Kriiger, Chem. Ber. 120 (1987) 1763.
Angew. Chem. Inr. Ed. Engl. 28 (1989) 397-412
[28] a ) C;. Erker, R. Lecht. J. L. Petersen, H. Bonnemann. OrgunomeruNics 6
(1987) 1962; b) G. Erker, R. Lecht, C . Kriiger, Y.-H. Tsdy. H . Bonnemann. J . Orgunomet. Chem. 326 (1987) C75.
[29] a ) R. Lecht. Disserfurion, Universitat Wiirzburg 1987: b) J. L. Simunic,
A. R. Pinhas. OrganometuNics 6 (1987) 1358; c) U. Dorf. Disserrution,
Universitit Bochum 1985.
[30] J. Martin, C . Moise, J. Tirouflet, C. R. Seunres Acud. Scr. Ser. 2. 292
(1981) 1143.
[31] G . Erker, R. Lecht, R. Schlund. K. Angermund, C. Kriiger. Angew. Chem.
99 (1987) 708; Anpew. Chem. I n / . Ed. Engl. 26 (1987) 666.
[32] X-ray crystal structure analysis: E. Herdtweck, unpublished.
[33] Cf. M. F, Lappert. C. R. C. Milne. J . Chem. Soc. Chem. Comnrun. 1978,
925.
[34] G. Erker. T. Muhlenbernd. R. Benn. A . Rufinska. Organomefu11ics 5
( 1986) 402.
(351 K . Mashima, K . Jyodoi, A. Ohyoshi. H. Fdkaya, J . Chem. Sue. Chem.
C'ummun. 19x6. 1145; K. Mashima, K. Jyodoi, A. Ohyoshi, H. Fdkaya.
Orgonomr/u//ic~
6 (1987) 885.
[36] a ) K. Kropp, G. Erker, 0rgunomeruNie.r 1 (1982)1246; b) G. Erker, K.
Kropp. J . Am. Chem. Soc. 101 (1979) 3659; J . Orgunomer. Chem. 194
(1980) 45: c) S. L. Buchwald, B. T. Watson. J. C. Huffman. J . iim. Chem.
Sw. / O X (1986) 7411.
[37] G. Erker, U. Dorf, R. Mynott. Y.-H. Tsay, C. Kruger. Angcw. Chem. 97
(1985) 572: Angeir. Chcm. Inr. Ed. En%/. 24 (1985) 584.
[38] G. Erker, in A. de Meijere. H. tom Dieck (Eds.): OrgunomeruNics in
Orgunic .Yynrheris. Springer Verlag, Berlin 1987, p. 143: Pulyhedron 7
(1988) 2451.
[39] P. M. Fritz. M. Steimann, W . Beck, Cltem. Ber. 120 (1987) 253, and
references cited therein.
1401 C. G . Kreiter. V. Formacek, Angew. Chem. 84 (1972) 155: Angew. Chem.
h i . Ed. Engl. I 1 (1972) 141: E. 0. Fischer, H . Hollfelder, P. Friedrich.
F. R. Kreifll. G. Huttner, Chem. Eer. 110 (1977) 3467.
[41] M . J. Doyle, M. F. Lappert, J . Chem. Soc. Chem. Commun. 1974. 679.
[42] M. Cowie. J. A. Ibers. Inorg. Chem. 15 (1976) 552: K. Itoh. I. Matsuda. F.
Ueda.Y. Ishii, J. A. Ibers. J . Am. Chem. Sot. 99(1977)2118: M. J. Doyle,
M F. Lappert, G. M. McLaughlin, J. McMeeking. J . Chem. Sot. Dullon
7i.un.s. 1974, 1494; A. W. Coleman. P. B. Hitchcock, M. F . Lappert, R. K.
Maskell. H . J. Miiller, J . Orgunomet. Chem. 296 (1985) 173; C . Bianchini.
C . Mealli. A. Meli. M. Sabat. J. Silvestre. R. Hoffmann, Orgunomerul1rcs
5 (19x6) 1733: P. B. Hitchcock, M. F. Lappert, G. M. McLaughlin. A. J.
O h e r , J . Chem. Soc. Dalton Trans. 1974.68; B. Cetinkaya, M. F. Lappert,
G. M. McLaughlin, K. Turner, ihid. 1974, 1591.
[43] D. W . Macomber, R. D . Rogers, OrgunomeruNrcs 4 (1985) 1485; A. W.
Coleman. P. B. Hitchcock, M. F. Lappert, R. K. Maskell. H. J. Miiller, J .
Orgunornet. C h m . 250 (1983) C9.
1441 a ) M. Appel. W. Sacher. W. Beck, J . Orgunomer. Chem. 333 (1987) 237;
322 (1987) 351; M. Appel, W. Beck, ihid.319 (1987) C1; b) S. F. Pedersen,
J. C . Dewan, R. R. Eckman. K. B. Sharpless, J. Am. Chem. Soc. 109 (1987)
1279; M. T. Reetz. M. Hullmann, T. Seitz, Angew. Chem. 99 (1987) 478;
Angwi. C h m . inr. Ed. Engl. 26 (1987) 477; H. Hartmdnn, A. F . Abdel
Hady. K. Sartor, J. Weetman. G. Helmchen, ibid. 99 (1987) 1188 and 26
(1987) 1143;T.Poll,J.O. Metter,G.Helmchen,ihid.97(1985)116and24
(1985) 112:c)T. R. Ke1ly.A. Whit1ng.N. S. Chandrakumar, J.Am. Chem.
S U I . / O X (1986) 3510; S. Danishefsky, J. F. Kerwin, Jr., S. Kobaydshi. h i d . 104 (1982) 358.
[45] G. Erker. M. T. Ashby. M. Aulbach, unpublished: cf. B. P. Susz. P.
Chalandon. Helv. Chrm. Acru 41 (1958) 1332.
I461 G. Erker. U. Dorf, C. Kruger, Y.-H. Tsay, OrganometuNic.~6(1987) 680.
[47] G. Erker. F. Sosna, unpublished.
1481 T. J. Burkhardt. C . P. Casey, 3. Am. Chem. S ~ J C
94. (1972) 6543.
[49] G. Erker, P. Czisch, unpublished; cf. Y. Yamamoto. K. MarUyama, Terruhedi-u-ori Lett 21 (1980) 4607: D . A. Evans, L. R. McGee. ihid. 21 (1980)
3975: M . T. Reetz. R. Peter. ihid. 22 (1981) 4691.
(501 D. .I. Cardin, M . F. Lappert. C . L. Raston: C/irmisrrJ uf Orgum-Ztrconrum und -Hu/nrum Compounds. Wiley, New York 1986: P. C. Wailes,
R. S . P. Coutts. H. Weigold: O~gunornetuliieChrmiJrryof Tirumum, Ztrconitrm irnd Hufnnm. Academic Press. New York 1974.
[Sl] R. J. Goddard. R. Hoffmann. E. D. Jemmis, J . Am. Chem. Sue. lfJ2(1980)
7667; A. K . Rappe, W. A. Goddard 111, ihrd. 104 (1982) 297; M. M.
Francl. W. J. Pietro. R. F. Hout. Jr., W. J. Hehre. Orgunomctultics 2
(1983) 281, 815; M. M. Francl, W. J. Hehre, ihrd. 2 (1983) 457; T. E.
Taylor. M. B. Hall, J . Am. Chem. Soc. 106 (1984) 1576; D. S. Marynick.
C. M. Kirkpatrick. ihrd. 107(1985) 1993; A. R. Gregory. E. A. Mintz, ihid.
107 (1985) 2179
I521 J. Schwartz. K. 1. Cell, J. Orgunumer. Chem. 1x4 (1980) C1.
(531 F . N. Tebbe., G . W. Parshall. G. S. Reddy,J. Am. Chcm. Soc. 100 (1978)
361 1: E. V. Anslyn. R. H. Gruhbs, hid. 109 (1987) 4880; S. M. Clift. J.
Schwartz. ihid. 106 (1984) 8300: F. M. Hartner, Jr.. S . M. Clift. J .
Schwartz, T. H. Tulip, Orgunomerul1ic.s 6 (1987) 1346.
[54] K . A. Brown-Wensley. S. L. Buchwald, L. F. Cannizzo, L. E. Clawson, S.
Ho. J. D. Meinhart. J. R. Stille, D. Strauss. R. H. Grubbs, Purr Appl.
Ch~m
55 (1983) 1733; S. H. Pine, R. Zahler, D. A. Evans. R. H. Grubbs,
J . Am. Chem. Sue. 102(1980) 3270; S. H. Pine, R. J. Pettit, G. Geib. S. G.
Angm.. C'hcw?. h i . Ed. Engl. 28 (1989) 397-412
1551
[56]
I571
[SS]
Cruz, C. H. Gallego, T. Tijerina, R. D . Pine. J . Org. Ch~w7.50(1985)1212:
W. A. Kinney. M. J. Coghlan, L. A. Paquette. J . A m . Climi. SIJC.107
(1985) 7352; T. Okazoe, K . Fdkai. K. Oshima. K . Utimoto. J . Org. Chem.
52(1987)4410: see also G. M. Smith. M. Sabat. T. J . Marks. J . Am. Chem.
Soc. I09 (1987) 1854.
F . Bickelhaupt, Angel<.Chem. 99(1987) 1020; Angen. C h ~ mInr.
. E d . En$.
26 ( I 987) 990.
a) M . Kilner, Adv. Organornet.Chem. 10 (1972) 162; b) Selected examples:
R. E. Cramer. K. Panchanatheswaran, J. W. Gilje. J . Am. Chem. Soc. 106
(1984) 1853; M . Green, R. J . Mercer, C. E. Morton, A. G. Orpen, AngPw.
Chem. 97 (1985) 422; Angeu. Chem. Inr. Ed. Eng1. 24 (1985) 422: J. E.
Bercaw, D. L. Davies, P. T. Wokzanski, Organomeru//icsS (1986) 443:
I. A. Latham, G. J. Leigh. G. Huttner, I. Jibril, J . Chem. Sue. Dulron
Truns. 1986. 377; M. Bochmdnn. L. M. Wilson. J . Chem. Soc. C h i m
Commun. 1986, 1610; H. Werner, W. Knaup, M . Dziallas. Angen. Clirm.
99 (1987) 277: Angea.. Chem. Int. Ed. Engl. 26 (1987) 248; R F. Jordan.
C. S. Bajgur. W. E. Dasher. A. L. Rheingold, Orgunornetu11ic.s 6 (1987)
1041; E. J. Roskamp, S. F. Pedersen, J . Am. Chem. Soc. 109 (1987) 3152;
D. S. Richeson, J. F . Mitchell, K. H. Theopold. ihid. 109 (1987) 5868.
a) P. Etievant, G . Tainturier. G . Gautheron. C . R. Seuncrs Acuti. SI I . Scv
C283 (1976) 233: BUN.Soc. Chrm. Fr. 1978. 292; b) G. Erker. W. Friimberg. J. L. Atwood, W. E. Hunter, Angen-. Cheni. 96 (1984) 72; Angcw.
Chem. h t . Ed. Engl. 23 (1984) 68: W. Fromberg, G. Erker, J . Orgunomet.
Chem. 280 (1985)343.
a) K. Farmery, M. Kilner. J . Organomer. Chrm. 16 (1969) P51: H. R.
Keable. M . Kilner, Chem. Commun. 1971, 349, W . Clegg. R. Smith.
H. M. M. Shearer. K . Wade. G. Whitehead, J . Chcjm. Sue. Doiron Trum
1983, 1309; b) M . R. Collier, M . F. Lappert, J. McMeeking, Inurg. Nuci.
Chrm. L m . 7 (1971) 689.
1591 G. Erker, W. Fromberg. C Kruger, E. Raabe, J . Atn. Chrm. Sue. 110
(1988) 2400.
[60] W. C. Kaskd, Coord. Chem. Rev. 48 (1983) 1
[61] J. C . Baldwin, N. L. Keder, C. E. Strouse. W. C. Kaska. Z. Nurur/or.si.h.
835 (1980) 1289.
[62] H. Schmidbaur, W. Scharf, H.-J. Fuller. Z.Nururforsch. 8 3 2 (1977) 858:
W. Scharf, D . Neugebauer,U.Schubert. H. Schmidbaur. Angew. Chem. YO
(1978) 628; Angew. Chem. lnr. Ed. Engl. 17 (1978) 601: K I. Cell. .I.
Schwartz. Inorg. Chem. 19 (1980) 3207; G. W. Rice, G. B. Ansell. M. A.
154: H. Schmidbaur. R. Pichl,
Modrick, S. Zentz. Or~unomeruNie.~2(1983)
Z . Nafurj'orsch. 840 (1985) 352: H. Schmidbaur. R. Pichl. G. Miiller. hid.
8 4 1 (1986) 395; Angen. Chen?.9X (1986) 572: Angew. Chem. l n t . Ed. Engl.
25 (1986) 574: Chem. Ber. 120 (1987) 39.
[63] a) G. Erker. P. Czisch, R. Mynott, Z. Nuturjorsch. 840 (1985) 1177; h) G.
Erker, P. Czisch. C . Kriiger. J . M. Wallis, 0rgunometulitc.s4 (1985) 2059;
c ) G . Erker, P. Czisch, R. Mynott, Y.-H. Tsay, C. Kriiger. ihkl. 4 (1985)
1310; d)G. Erker, P. Czisch. R. Mynott. J . Orgunomer. Chc>m.334 (1987)
9 1 , d) H. J. R. de Boer, 0. S. Akkerman, F. Bickelhaupt, G. Erker. P.
Czisch, R. Mynott. J. M. Wallis. C. Kriiger. Angeii.. Chem. 98 (1986) 641 :
Angen. Cbem. I n t . Ed. Engl. 25 (1986) 639: f ) G. Erker, U. Dorf. P. Czisch,
J. L. Petersen, Orgunomrialtics 5 (1986) 668: g) G. Erker. U. Korek. J. L.
Petersen. J . Orgonome!. Chem. 355 (1988) 121.
[64] Cf. W. R. Tikkanen, J. L. Petersen, Organomeru//ics3 (1984) 1651.
[65] Cf. R. Neidlein. A. Rufinska, H . Schwager. G. Wilke, Angeir.. Chrm. 98
(1986) 643: Angeiv. Chem. I n ! . Ed. Engi. 25 (1986) 640; C. Kriiger, K.
Laakmann, G. Schroth. H. Schwdger, G.Wilke, Chem. Ber. 120 (1987)
471: A. R. Bulls. W . P. Schaefer. M. Serfas, J . E. Bercaw. OrguiiomeruNics
6 (1987) 1219.
[66] W. Fromberg, Drsserruiion, Universitdt Bochum 1986; X-ray crystal structure analysis: C. Kruger, E. Raabe. W. Fromberg, unpublished.
[67] J. H. Teuben. H J . de Liefde Meijer, J . Orgunomrr. Chem. 17 (1969) 87;
D . G. Sekutowski, G. D. Stucky. J . Am. Chem. Soc. 98 (1976) 1376.
[68] G. Erker. W. Fromberg, R. Mynott, B. Gabor, C. Kruger. Angtw. Cbiwr.
9X (1986) 456; Angen. Chcm. In/. Ed. Eii'yl. ZS (1986) 463: G. Erker. Juhrh.
Akud. Wiss. Gorringen 1985, 19.
[69] J. L. Atwood. W. E. Hunter, A. L. Wyada, W. J. Evans. Inorg. Chizm. 21)
(1981)4115;W. J. Evans, I. Bloom, W. E. Hunter, J. L.Atwood. Orgunornerul/ics2(1983) 709; B. Schubert. E. Weiss. Chivn. Ber. 116 (1983) 3212:
N . A. Bell, I.W. Nowell. G . E. Codtes, H. M. M. Shearer. J . Orgunonrri.
Chem. 273 (1984) 179: P. N. V. P. Kumar, E. D. Jemmis, J . Am. Chrm.
Soc. I10 (1988) 125.
[70] G. Erker, K. Kropp. J. L. Atwood, W. E. Hunter. Orgunon~erul/ic.\2
(1983) 1555.
[71] F. Fischer, H . Tropsch. Brennsl. Chem. 7 (1926) 97: C/wm. Ber. 59 (1926)
830.
[72] a) J. Kummer, P. H. Emmett. J . Am. Cliem. Sue. 75 (1953) 5177; H.
Pichler, H . Schultz, Chem. Ing. Pch. 42 (1970) 1160; b) H. H. Storch. N.
Goulombic, R. B. Anderson; The Fischrr- Tropsch arid Relured Synrh
Wiley. New York 1951 ; R. Eisenberg. D . E. Hendriksen. Adv. C'urul.
2x11979) 79; E. L. Mutterties. J. Stein, Chem. Re),.79 (1979) 479: W. A.
Herrmann. Angrw. Chem. 94 (1982) 118; Angew. Chem. i n / . Ed. Engl. I1
(1982) 117: C . K . Rofer-DePoorter. Ch<,m.Rev. 81 (1981) 447; C. Masters.
Ad,. Orgunomer. Chem. 17 (1979) 61; G . Henrici-Olivk. S . Olive. Angew.
Chrm. 88 (1976) 144: Angeu. Chem. Inr. Ed. Eng1. 15 (1976) 136: J. Falbe
41 1
(Ed.): Nen Syntheses Kith Carbon Munoside, Springer Verlag. Berlin 1980;
E. L. Kugler, F. W. Steffgen (Eds.): Hydrocarbon Synrhesis,from Carbon
Monoxide and Hydrogen. Adv. Chem. Ser. 178 (1979).
[73] R. C. Brady 111, R. Pettit, J . Am. Chem. Sue. 102 (1980) 6181; ibrd. 103
(1981) 1287.
[74] C. E. Sumner. Jr., P. E. Riley. R. E. Davis, R. Pettit. J . Am. Chem. Soc.
tW(1980) 1754; W. A. Herrmann. Adv. Organumel. Chem. 20(1982) 159:
J . Organumel. Chem. 250 (1983) 319; K. H. Theopold, R. G. Bergman, J .
Am. Chem. Six. 105 (1983) 464; M. Cooke, N. J. Forrow, S. A. R. Knox,
J . Chem. Soc. Dalton Trans. 1583, 2435; J. Holton, M. F . Lappert, R .
Pearce. P. 1. W. Yarrow, Chem. Rev. 83 (1983) 135: P. M. George, N. R.
Avery, W. H . Weinberg, F. N. Tehbe, J. Am. Chem, Sue. 105(1983) 1393;
J. E. Hahn, Prug. Inurg. Chem. 31 (1984) 205; H. Fischer, S. Zeuner, K.
Ackermann. J. Schmid, Chem. Ber. 1 / 9 (1986) 1546; I. M. Saez. N. J.
Meanwell, A. Nutton, K . Isobe, A. Vazquez de Miguel, D. W. Bruce, S.
Okeya, D. G. Andrews, P. R. Ashton, I. R. Johnstone, P. M. Maitlis, J.
Chem. Soc. Dalton Trans. /986. 1565.
[75] G:W. Wang, H. Hattori, H. Itoh, K. Tanabe, J . Chem. Sue. Chem. Cummun. 1982, 1256; D. R. Fahey, J . Am. Chem. Sur. / 0 3 (1981) 136; S . 4 .
Sung, R. Hoffmann, ibid. 107 (1985) 578; K. Maruya, A. Inaha, T. Maehashi. K. Domen. T. Onishi, J . Chem. Suc. Chem. Cummun. 1985, 487;
M. H. Chisholm. J . Organomet. Chem. 334 (1987) 77: I. M. Saez, P. M.
Maitlis, ibid. 234 (1987) C14; cf. J. C. Hayes, G . D. N. Pearson, N. J.
Cooper, J . Am. Chem. Sue. 103 (1981) 4648; R. Koster, M. Yalpani, Angen. Chem. 57 (1985) 600; Angen. Chem. Int. Ed. Engl. 24 (1985) 572; H.
Werner, H. Kletzin. A. Hohn. W . Paul, W. Knaup, M. L. Ziegler, 0.
Serhadli, J . Organumer. Chern. 306 (1986) 227, R. McCrindle, G. J. Arsenault, R. Farwaha, M. J. Hampden-Smith, A. J . McAlees, J . Chem. Suc.
Chem. Commun. 1986. 943; P. M. Loggenberg, L. Carlton. R. G. Copperthwaite, G . J. Hutchings, ibid. 1587, 541.
[76] S . Couturier, B. Gautheron, J . Organumer. Chem. 157 (1978) C61; J. M.
Manriquez, D. R. McAhster, R. D. Sanner, J. E. Bercaw, J. Am. Chem.
Sue. 98 (1976) 6733.
[77] K. Kropp, V. Skibbe, G. Erker, C. Kruger. J . Am. Chem. Suc. 105 (1983)
3353.
[78] a) R. M. Waymouth, B. D. Santarsiero, R. J. Coots, M. J. Bronikowski.
R. H . Grubbs, J . Am. Chem. Suc. 108 (1986) 1427: b) G. S. Bristow, P. B.
Hitchcook. M. F . Lappert, J . Chem. SOC. Chem. Cumm. 1582, 162.
41 2
1791 F. Rosenfeldt. G. Erker, Teirahedron Letr. 21 (1980) 1637: G. Erker, F.
Rosenfeldt. J. Organumer. Chem. 224 (1982) 29: Tetrahedron 38 (1982)
1285.
[80] H. Takayd, M. Yamakdwa. K. Mashima, J . Chem. Soc. Chem. Cummun.
1583, 1283; S . Stella, C. Floriani, ibid. 1586, 1053; B. M. Martin, S. A.
Matchett, J. R. Norton, 0. P. Anderson, J . Am. Chem. Sue. 107 (1985)
7952..
[81] a) G. Erker, K. Kropp, C. Kruger, A,-P. Chiang, Chem. Ber. 115 (1982)
2447: h) G. Erker, Acc. Chem. Res. 17(1984) 103; P. T. Wolczanski, J. E.
Bercaw, hid. / 3 (1980) 121.
[82] G . Fachinetti. C. Floriani. A. Roselli, S. Pucci, J . Chem. SUC.Chem. Cummun. 1578, 269; X-ray crystal structure analysis: S. Gamharotta. C .
Floriani, A. Chiesi-Villa, C . Guastini, J . Am. Chem. SOC.105 (1983) 1690.
1831 a) J. M. Manriquez. D. R. McAlister. R. D. Sanner. J. E. Bercaw, J . Am.
Chem. Sue. 100 (1978) 2716; F. Rosenfeldt, Dissertution, Universitzt Bochum 1981; P. Hofmann, M. Frede, P. Stduffert, w . L a s e r , U. Thewalt,
Angen. Chem. 97 (1985) 693; Angew. Chem. Inr. Ed. Engl. 24 (1985) 712;
see also C. D. Wood, R. R. Schrock. J . Am. Chem. SUC.101 (1979) 5422;
b) G. Erker. P. Czisch, R. Schlund. K. Angermund, C. Kruger, Angen..
Chem. 98 (1986) 356; Angen. Chem. Int. Ed. Engl. 25 (1986) 364; c) J. D .
Meinhart, B. D. Santarsiero, R. H . Grubbs, J . Am. Chem. Soc. /OX (1986)
3318.
[84] P. Hofmann, P. Stauffert, K. Tatsumi, A. Nakamurd, R. Hoffmann, Orgunometullics 4 (1985) 404; J . Am. Chem. Sur. 107 (1985) 4440.
[85] a) G. Erker, C. Kruger, R. Schlund, 2. Narurfursch. 5 4 2 (1987) 1009; G.
Erker, R. Schlund, C . Kruger. J . Organomet. Chem. 338 (1988) C4: b) J .
Chem. Sue. Chem. Cumnrun. 1986, 1403.
[86] a) G. Erker, U. Dorf. J. L. Atwood, W. E. Hunter, J . Am. Chem. Soc. 108
(1986) 2251: b) G. Erker. F. Rosenfeldt, Evrahedi-on Lett 22 (1981) 1379.
[87] a) G . Erker, K. Kropp, Chem. Ber. 115 (1982) 2437: h) K. 1. Cell, G. M.
Williams. J. Schwdrtz, J . Chem. Soc. Chem. Commun. 1580, 550.
[88] Review: M. T. Reetz. Ads. Organumef.Chem. 16 (1977) 33.
[89] G. Erker. R. Schlund, unpublished.
[YO] A. S. Ward, E. A. Mintz, M. R. Ayers, Organometallics 5 (1986) 1585;
A. S. Ward, E. A. Mintz, M. P. Kramer. ibid. 7 (1988) 8.
Angen. Chem. Inr. Ed Engl. 28 (1985) 397-412
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