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cis-Bis(dinitrogen)tetrakis(trimethylphosphane)chromium.

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Reaction of carbonylmetal halides ( 5 ) with AgAsFd in
SOz [eq. (c)]. Isolation of the intermediate SOz complexes
is unnecessary in the synthesis of symmetrical cations.
General procedure
Compound (1) or ( 2 a ) $ ( 3 a ) (5mmol) are heated under
reflux for 3 d with an equimolar amount of a dipolarophile
in anhydrous tetrahydrofuran (60ml). After distilling off the
solvent, the crude product is purified by column chromatography with hexane/chloroform (2:1) on silica gel. Further purification of (3 b ) was accomplished by preparative layer chromatography on ready-made plates (silica gel 60 F 2 5 4 , Merck).
Exchange of bridging halogens in ( 4 ) with the aid of silver
salts in SO2 [eq. (d)].
Received: September 13, 1976 [Z 591 b IE]
German version: Angew. Chem. 89.61 (1977)
CAS Registry numbers:
( I ) , 60935-02-6; ( Z a ) , 60935-1 1-7; (26), 60935-12-8; ( 2 r ) , 60935-13-9; ( 3 u ) ,
60935-14-0; ( 3 h ) , 60935-15-1 ; ( 4 u ) , 60935-16-2; methyl propiolate, 922-67-8;
dimethyl acetylenedicarboxylate, 762-42-5
Thedesignation I ~ d i p o l e r e f e rto
s the resonancestructureofacornpound
in which the two charges are separated by the maximum distance, see
1.3 dipoles.
[2] K . Burger, H . Schickuneder, and C . Zetfl, Synthesis 1976, 803.
131 G . Muier. Valenzisomerisierungen. Verlag Chemie, Weinheim 1972, and
references cited therein.
[I]
Preparation of Halogen-Bridged Cationic Dinuclear
Complexes of Manganese and Rhenium[**]
By Riidiger Mews[*]
While halogen-bridged anionic complexes of type (1 )[11
and also neutral representatives of this typeLz1are already
known, the cations (2) isoelectronic with ( I ) have not previously been reported. T o our knowledge a bridging function
of individual halogens in cationic complexes has so far only
been demonstrated for complexes of iron[31.
We have now found that four possible pathways are available for the synthesis of complex cations of type (I):
Reaction of the SO2 complexes (3)14] with carbonylmetal
halides [eq. (a)] or with metal halides [eq. (b)].
Whereas reactions according to eq. (a) are complete within
a few minutes, and those according to (c) and (d) within
a few hours, it is difficult to obtain clean products according
to eq. (b).
The strongly yellow manganese salts and their colorless
rhenium counterparts are readily soluble in SO2, but dissolve
only sparingly with decomposition in organic solvents.
The complexes ( 4 ) are thermally stable up to more than
100°C. They were characterized by elemental analysis and
their IR spectra. Although the spectra are complex in the
CO stretching region, the absence of bands below 1900cm-'
rules out bridging by carbonyl groups. The manganese compounds show a strong band at 700cm-' (v3AsF;). The splitting
of this band observed with the rhenium compounds, and
especially the chlorine derivative (715 m, 699 vs), indicates distortion of the AsF, ion in the solid.
Procedure:
To a precisely stoichiometric mixture of the reactants (2
to 3mmol each) at -196°C is condensed SO2 (ca. IOml),
and the reaction mixture is allowed to warm slowly. Reaction
(a) is complete within a short time of reaching room temperature. A clear solution is obtained from which the pure products
precipitate on evaporation of SO2. In the case of reactions
(b) to (d) the precipitated silver halide or alkali metal hexafluoroarsenate is filtered off before evaporation of the SO2.
Received: October 29, 1976 [Z 597 IE]
German version: Angew. Chem. 89, 53 (1977)
CAS Registry numbers:
( 3 ) , M = M n , 55853-06-0; ( 3 ) , M = R e , 55853-08-2; ( 4 u ) , 61025-92-1; ( 4 b ) ,
) ~
( 4 d ) . 61025-97-6; ( 4 e ) , 61025-99-8; ( 4 f / ,
61025-93-2; ( 4 ~ 61025-95-4;
61026-01-5: ( 4 y ) , 61026-03-7; ( 4 h ) , 61026-05-9; ( 5 ) , M = M n , 14516-54-2;
( 5 1 , M = Re, 14220-21-4; Mn(CO)5CI, 14100-30-2; Re(COI5CI, 14099-01-5
H . Behrem and D. Herniunri, Z. Naturforsch. 21 h, I234 (1966); E. Linilrier
and H . Behrens, Spectrochim. Acta 2 3 4 , 3025 (1967); 3. K . RUE Inorg.
Chem. 7, 1821 (1968).
[2] H . Behrens and R . Schwuh, Z. Naturforsch. 19b, 768 (1964).
[3] E . 0.Fischer and E. Moser, J. Organomet. Chem. 3, 16 (1965); Z.
Anorg. Allg. Chem. 342, 156 (1966).
141 R. Mews, Angew. Chem. 87, 669 (1975); Angew. Chem. Int. Ed. Engl.
14, 640 (1975).
[l]
cis-Bis(dinitrogen)tetrakis(trimethylphosphane~hromium
id): n1
=
M n , x = I,
i e j : 11= R e ,
x=
I
[*] Dr. R. Mews
Anorganisch-chemisches Institut der Universitat
Tammanstrasse 4, D-3400 Gottingen (Germany)
[**I This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie.
56
By Hans Heinz Karsch["]
Almost all transition metals are known to form complexes
with molecular nitrogen, but in the case of some metals-nota-
[*I
Dr. H. H. Karsch
Anorganisch-chemisches Institut der Technischen Universitat
Arcisstr. 21, D-8000 Miinchen 2 (Germany)
Angew. Chem. I n t . Ed. Engl. 16 (1977) N o . I
bly chromium-the examples are few and far between. The
higher homologs, molybdenum and tungsten, on the other
hand, readily bind nitrogen and can even coordinate two
N2-ligands[" 21.To our knowledge, such complexes with metals
of the first transition series have not as yet been reportedf3].
During investigations on the behavior of trimethylphosphane in the presence of low-valency metals[4] it was found
that the complex c ~ s - [ ( C H ~ ) ~ P ) ] ~ C ~(I)
( N ,can
) ~ be isolated
on reduction of CrC13 with Mg in the presence of P(CH3)3
in tetrahydrofuran under nitrogen. Initially, reaction of CrCI3
with P(CH3)3in THF leads to an adduct ( 2 ) , which is crystallizable from ether as brown-violet needles (m.p. 144--147°C).
L = P(CH3)3
Reduction of (3) with Mg at higher temperatures (above
15"C) leads to a further brown, decomposable paramagnetic
complex, which likewise contains nitrogen ( v N E N 1992 cm-')
but, in addition, also a hydridochromium unit (vCrH: 1850
vs (br) cm-'). The IR spectrum also shows bands for coordinated THF (1030 and 840 cm-') and P(CH3)3. Whether
the CrH- function is formed by C-H cleavage of a P(CH3)3
ligandL41, as in the reduction of FeC12/P(CH3)3with Mg, is
still uncertain.
Received: November 10, 1976 [Z 601 IE]
German version: Angew. Chem. 89.57 (1977)
On reduction of (2) with Mg in the presence of excess
phosphane a deep blue solution is formed, from which crystalline (3)[51(m.p. 51 "C) can be isolated.
( 3 ) readily liberates P(CH3)3 in a vacuum at 25°C and
the crystals become brighter.
In the presence of P(CH& under nitrogen, however, (3)
can be reduced further to a deep brown solution:
After removal of volatile components, dark brown (1) can
be extracted from the residue with ~ e n t a n e / P ( C Hand
~ ) ~then
isolated after removal of solvent at -30°C. Complex (I)
slowly decomposes at room temperature with liberation of
N2 and P(CH3)3. Its cis-octahedral structure is confirmed
by spectroscopic findings.
The IR spectrum (Nujol) shows, in addition to the typical
bands for coordinated P(CH3)3, two very strong bands of
equal intensity at 1990 and 1918 cm-' along with two weaker
bands, also of equal intensity, at 562 and 513 cm-'. The
percentage decrease in frequency (P= 16.2) of VN-N through
fixation of the N2 is twice as large as that in the known
simple N2-complexes of chromium, and thus about equally
as large as in cis-L4M(N2)2 with M=Mo['] or W[']. Since
the isoelectronic carbonyl complexes C~S-L,M(CO)~
(M = Cr,Mo,W)[61prove to have corresponding P-values of
the same order of magnitude, it is clear that there is an
extensive analogy in the bonding of these complexes.
The cis array derived from the IR spectrum leaves the
remaining positions of an octahedral configuration to the four
phosphane ligands which is recognized in the {'H}-31P-NMR
spectrum of ( I ) (24 MHz, toluene, -2O"C, H3P04 ext.) as
an A2Bz pattern (2J(AB)/(vA-~Vg)=0.15,similarly as, e . g . in
C ~ ~ - [ ( C H ~ ) ~ P ] ~ F ~ with
( C H ~6PA
) ~=[ ~ ]13.8,
)
FPB= + 9.4
ppm; 'JPAPB= 16 Hz. For [(CH3)3]4Cr(CO)Ztwo "signals"
(1 : 1) were found at + 16.5 and +5.4 ppm[6J.
The bis(dinitrogen) complex ( 1 ) reacts with carbon monox( 4 ) and [(CH3)3P]3Cr(C0)3i61
ide to give [(CH3)3P]4(C0)2r61
+
(5).
Angew. Chrm. lm. Ed. Engl. 16 ( 1 9 7 7 ) N o . 1
CAS Registry numbers:
( I ), 61202-60-6; ( 2 ) , 61202-61-7; (31, 61202-62-8; 3 ' P , 7723-14-0
[ l ] B. B e / / , J. Chart, and G . J. Leigh, Chem. Commun. I970, 842.
[2] J. Cliott and A. G. Wedd, J. Organomet. Chem. 27, C 1 5 (1971): T
A . George and C . D. Siebokl, ibid. 30, C 13 (1971).
[3] The complexes determined spectroscopically only in a matrix at lower
temperature are not included here.
[4] H . H . Karsch, H . - F . Kleiti, and H . Schmidbaur. Chem. Ber., in press.
[ S ] D. A . Berman. Diss. Abstr. 18. 1240 (1958).
161 R . Muthiru, M . Lenzi, and R. Poilblatic. Inorg. Chem. Y, 2030 (1970).
[7] H . H . Karscli, Chem. Ber., in press.
Electrochemical Reduction of
2,2,2-Trichloroethanols[**l
By Andreas Merz"]
The reductive dehalogenation of vicinal dihalides has been
studied very thoroughly[']. In contrast, little is known about
the concomitant reductive elimination of a halogen and an
adjacent substituent bonded via an oxygen atomc2].
We have found that 2,2,2-trichloroethanols ( I 1, readily
accessible for example by O H - phase-transfer catalyzed addition of chloroform to aldehydes and ketonesc3],can be reduced
at a mercury cathode at - 1.3 to - 1.5 V in acidic electrolytes
to give 1,l-dichloroolefins ( 2 ) ; in some cases good yields are
obtained (Table 1).2,2-Dichloroethanols (3) arise as by-products. Suitable electrolytes are aqueous-organic solvent mixtures containing a mineral acid and an acidic supporting electrolyte, e.g.triethylammonium chloride. The low current yields
due to competing evolution of hydrogen can be improved
by admixture of tetraethylammonium p-toluenesulfonate.
The reaction also commands mechanistic interest on
account of its analogy to the electrochemical dehalogenation
of vicinal dihalides, which is regarded as a synchronous reaction because of its pronounced stereoselectivity"b. 'I.
Since a C-0 single bond is not attacked electrochemically
at the working potentials employed[51,electron transfer must
occur at the trichloromethyl group; in this case a dichloro-
["I
[**I
Dr. A. Merz
lnstitut fur Chemie im Fachbereich Chemie und Pharmazie
der Universitlt
Universitatsstrasse 3 I, D-8400 Regensburg (Germany)
This work was supported by the Deutsche Forschungsgemeinschaft.
57
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