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Conversion of 4-Bound Cyclopentadiene into the Complexed Carbene Cyclopentadienylidene.

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around C 2 . . .C5 away from the metal atom. In an q5,q'
bridge (B), the bonds are expected to be nearly equal in
length and only minor deviations from planarity (for steric
reasons) are expected to be observed. In the binuclear
complexes with q5,qi-C5H4bridges"' that have been studied by X-ray diffraction, the picture is complicated by the
presence of a metal-metal bond. In those cases, the ligand
is bent toward the n-bonded metal atom; C3-C4 is shorter
than the other bonds in the ringi5'
Conversion of q4-Bound Cyclopentadiene into the
Complexed Carhene Cyclopentadienylidene
By Hubert Wadepohl* and Hans Pritzkow
The activated exo C H bond of qs-cyclopentadienyl-q4cyclopentadienecobalt 1 readily undergoes reactions such
as hydride abstraction[" or addition to activated alkynes.'21
We now report a reaction in which both CH bonds of the
methylene group are cleaved and a novel, binuclear carbene complex of cyclopentadienylidene is formed.
Complex 1 reacts at 50°C with the Jonas reagent
[CpCo(C,H4),] 2 (Cp = ~ y c l o p e n t a d i e n y lto
) ~form
~ ~ the turquoise, very air-sensitive binuclear complex 3a, which is
poorly soluble in nonpolar solvents. The ethylene ligand in
3a readily undergoes substitution by C O and PMe3 to give
3b and the extremely air-sensitive 3c, respectively.
Fig. 1. Structure of 3c in the crystal. Important bond lengths [A] and angles
(standard deviation) 0.004-0.006A, 0.3"): CoI-(C2.. .C5) 2.029. - -2.056,
C O I - ( C ~ . . - C I O )2.039...2.097, CO2-PI 2.150, C02-CI 1.581, c02(CI1.. .C15) 2.073.. .2.119, CI-CZ(5) 1.447 (1.441), C2(5)-C3(4) 1.41 I
(1.415), C3-C4 1.406; Co2-CI-CZ 125.2, Co2-CI-C5 133.9, PI-Co2-CI 97.0.
According to X-ray structure analysis,['] 3c adopts the
p-(q4-diolefin, ql-carbene) structure A (Fig. 1). The bridging ligand is coordinated through its diene moiety to a
CpCo group. The CC bond lengths in the planar diene
moiety (C2. . .C5, plane E l ) are equal, and the bonds to
the carbene carbon atom C1 are somewhat longer. C1 is
bonded to the CpCo(PMe3) fragment by a very short bond
and is located 0.12 A off E l on the side opposite to Col. The corresponding bond in the p-(q5,q1-cyclopentadienylidene) complexes is surprisingly long; its
length corresponds to that of metal-alkyl
The dihedral angle E1/E2 (E2: C2,Cl,C5) is 7.7" in 3c. In the
crystal, the plane passing through C02, PI and the center
of the C p ring C11 to C15 is perpendicular to El. However, the conformation is more symmetric on the NMR time
scale in solution (only two I3C-NMR signals for C2-C5).
Considering the isolobal relationshipI8]CH,-CoCp(L)
[ML,, Co', d8], complex 3 is analogous to mononuclear
complexes with pentafulvene as ligand. Typical diene systems are present in the q4-pentafulvene complexes of type
4 with dihedral angles E1/E2 of 22.3" for 4a and 8.0" and
10.4" for 4b (cod = 1,5-~yclooctadiene).[~~
N o bond exists
between the ring carbon atom C1 and the metal atom in
4.1101O n the other hand, the C o l - C l distance in 3c
(2.240 A) still indicates the existence of a bonding interaction. In summary, the structural findings for 3c indicate a
small contribution of the dipolar "ylide" resonance structure B to the actual structure. The situation is similar in
the cationic fulvene complexes 4c (angle E1/E2 4.4") and
4d (angle E1/E2 8.8").""
3a. L=C2H4; 3b. L=CO; 3c. L = P M e 3
According to M O calculations, free cyclopentadien- 1ylidene is expected to be bent (18') and to exhibit alternation of the CC bond lengths (C2(4)-C3(5) short, Cl-C2(5)
medium, C3-C4 long).141Complex 3 can be represented
formally by the resonance structures A and B. Examples
of p-q4,q1coordination of cyclopentadienylidene ( A ) were
previously unknown. In this case, we expect to find a
geometry of the bridging ligand characteristic of q4-cyclodiene complexes: CC bond alternation (C3-C4 short,
C2(4)-C3(5) medium, CI-C2(5) long) and puckering
[*] Dr. H. Wadepohl, Dr. H. Pritzkow
Anorganisch-chernisches Institut der Universitat
Im Neuenheirner Feld 270, D-6900 Heidelberg (FRG)
Anqew Chern Int. Ed Engl 26 (1987) No 2
0 VCH Verlagsgeselisehafi mbH. 0-6940 Wernheim. 1987
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161 Monoclinic, space group P 2 , / a , a = 12.40(1), b=8.105(6), c = 16.81(1)
8=93.61(5)”, p=20.8 c m - ’ , 2 = 4 , STOE-two-circle diffractometer
(MoKn radiation, w-scan), 2583 reflections with l>o(l),all non-hydrogen atoms anisotropic, R=0.051, R,, =0.082,w = I / 0 2 ( F ) . Further
details of the crystal structure investigation may be obtained from the
Fachinformationszentrum Energie, Physik, Mathematik GmbH, D-78 14
Eggenstein-Leopoldshafen2 (FRG), on quoting the depository number
CSD-52 127, the names of the authors, and the journal citation.
171 Crystallographically determined C o = C bond lengths are: 1.913(1 I ) in
[(Ph,Ge)(CO),Co{C(OEt)Et)j: F. Carre, G. Cerveau, E. Colomer, R. 1. P.
Corriu, J . C. Young, L. Ricard, R. Weiss, J. Organomel. Chem. 179
(1979) 215; 1.974(15) in [(PhjP)(C0)(NO)Co((S)-1,3,4-trirnethylimidazolidin-2-ylidene}]:A. W. Coleman, P. B. Hitchcock, M. F. Lappert, R.
K. Maskell, J. H. Miiller, J. Organornet. Chem. 250 (1983) C 9 ;
[ I 81.
1.902(3) A in [Cp(SPh)Co( 1,3-dimethylimidazolidin-2-ylidene)]:
(81 R. Hoffmann, Angew. Chem. 94 (1982) 125; Angew. Chem. l n t . Ed. Engl.
21 (1982) 711.
[9I Calculated from data in [IOI.
[lo] F. Edelmann, B. Lubke, U. Behrens, Chem. Ber. 115 (1982) 1328.
[ I l l Z. Dauter, L. K. Hansen, R. J . Mawby, E. J. Probitts, C. D Reynolds,
Acra Crystallogr. Sect. C41 (1988) 850.
[12] H. Diirr, F. Werndorff, Angew. Chem. 86 (1974) 413; Angew. Chem. lnt.
Ed. Engl. 13 (1974) 483.
[I31 R. Gleiter, R. Hoffmann, J. Am. Chem. SOC.90 (1968) 5487.
(141 Comparable values of G(C0): 1923 c m - ’ in [CpCo(CO)(PMe,)l: A.
Spencer, H. Werner, J. Organomel. Chem. 171 (1979) 219; 1915 c m - ’ in
[(C,Me,)Co(CO)(PMe,)]: H. Werner, B. Heiser, B. Klingert, R. Dolfel,
ibid. 240 (1982) 179; 1915 c m - ’ in [CpCo(C0)(1,3-dimetby11midazolidin-2-ylidene)l: (151.
1181 D. W. Macomber, R. D. Rogers, Organometallics 4 (1985) 1488.
The solution chemistry of cyclopentadienylidene reveals
it to be an electrophilic singIet carbene.‘’’] This behavior is
due to the interaction of the carbene orbitals with the antiaromatic 4n-electron ring ~ y s t e m . [ ~ The
. ’ ~ ] very low frequency of the carbonyl band[’41of 3b (V(C0) = 1903 cm (THF)), on the other hand, indicates that the carbene ligand is an extremely good o-donor. The resulting high
electron density at C02 exerts a destabilizing effect on the
Co-P bond in 312, which reacts smoothly with C O to give
3b. Complex 3 is an example of the reversal of the Lewis
acid-base properties of a carbene upon complexation. This
may be ascribed to the fact that the diene n* orbital involved in the bond to Col is no longer available for an
interaction with the electron pair of the carbene carbon
Experimental Procedure
3a: 2 (1.60 g, 8.88 mmol) in 80 mL of petroleum ether (PE) was added t o 1
(1.57 g, 8.26 mmol) in 50 mL of PE at 50°C. The dark solution was then con-
centrated under vacuum to ca. 70 mL. After standing at room temperature
for 24 h, the solution was decanted from the precipitated crystals, which were
washed with PE and recrystallized from toluene. Green platelets (700 mg 3a,
2.06 mmol, 25% yield). M.p. = 146°C (dec.).-’H-NMR (300 MHz, C6D6):
6=4.75 (s, 5 H ; Cp), 4.44 (m, 2 H ; 2 x C H ) , 4.2 (m. 7 H ; C p + 2 x C H ) , 3.63
(m; 2 H of C2Hd), 2.10 (m: 2 H of C2H4).-”C-NMR (75.5 MHz, CODO):
6=85.0 (d), 81.6 (d), 81.0 (d), 78.7 (d), 35.0 (t); the signal for C I could not be
observed for any of the compounds 3.
3b, 3c: 3a was allowed to react with I bar C O (-60°C to room temperature)
or with excess PMe, (room temperature), respectively, in toluene. After removal of the solvent from the filtered, deep green solution, analytically pure
3b ( L = C O , 97%) was obtained; 3c ( L = PMe,) was recrystallized from toluene (68%). 3b: green needles (dec. above 200°C). Correct C,H analyses.‘H-NMR (90 MHz, C6D6): 6=4.88 (“s,” 7 H ; C p + Z x C H ) , 4.8 (m, 2 H ;
2 x C H ) , 4.23 (5, 5 H ; Cp).-”C(’H}-NMR (75.5 MHz, C6D6): 6=87.3, 83.7,
82.2, 79.9. 3c: green platelets (dec. above I7OoC).-’H-NMR (90 MHz,
A Biocatalyst for the Preparation of
(R)- and (S)-2-Hydroxycarboxylic Acids**
By Haike Skopan, Helmut Ciinther, and Helmut Simon*
We have reported several times on the use of Proteus vulgaris in the presence of a catalytic amount of methyl- or
benzylviologen to reduce structurally diverse 2-oxomonoand 2-oxodicarboxylates to (R)-2-hydroxycarboxylates,
such as (R)-1 (R=alkyl, arylalkyl, etc.) of very high enantiomeric purity [reaction (a)]. Possible electron donors include hydrogen, formate, and the cathode of an electrochemical cell (for electron flow and conditions, see ref. [I]).
Productivity numbers are thereby attained that are approximately one to three orders of magnitude larger than those
obtained in, for example, the reduction of carbonyl groups
C6D6):6=5.0(m,2H;2xCH),4.54(s,5H;Cp),4.32(s,8H;Cp),3.87(m,with yeast.[’-31 The reductase catalyzing these reactions
2 H ; 2 x C H ) , 1.40 (3,’’9 H ; PMe,).-”)CI’H}-NMR (78.8 MHz, C6Dh):
does not employ NADH or NADPH;[’] its natural electron
6 = 9 2 (br), 80.1, 78.6, 75.9, 21 (br).
donor is still unknown. We have not been able to effect
reversal of reaction (a) using methyl- (MV2@)or benzylviologen, even when we employed, for example, hexacyanoReceived: September 8, 1986;
revised: October 15, 1986 [Z 1924 IE]
German version: Angew. Chem. 99 (1987) 132
[ I ] E. 0. Fischer, G. E. Herberich, Chem. Ber. 94 (1961) 1517; Reactions of
the endo C H bond of several exo-substituted complexes are known: N.
El Murr, J. Organornet. Chem. 208 (1981) C9, and references cited therein.
[2] G. R. Knox, M. Nutley, P. L. Pauson, S. Toma, W. E. Watts, P. A. Elder,
R. Griffiths, J. Chem. Res. Mrniprinl 1981, 1901.
131 a) K. Jonas, C. Kruger, Angew. Chem. 92 (1980) 513; Angew. Chem. Int.
Ed. Engl. I9 (1980) 820; b) K. Jonas, E. Deffense, D. Habermann, ibid.
95 (1983) 729 and 22 (1983) 716; Angew. Chem. Suppl. 1983, 1005.
[41 M. 2. Kassaee. M. R. Nimlos, K. E. Downie, E. E . Waali, Tetrahedron 4 /
(1985) 1579.
[S] W. A. Herrmann, G. Kriechbaum, C. Bauer, E. Guggolz, M. L. Ziegler,
Angew. Chem. 93 (1981) 838; Angew. Chem. Inr. Ed. Engl. 20(1981) 815,
and references cited therein.
0 VCH Verlagsgesellschaft mbH. 0-6940 Weinheim. 1987
Prof. Dr. H. Simon, DipLChem. H. Skopan, Dr. H. Giinther
Lehrstuhl fur Organische Chemie und Biochemie
der Technischen Universitat Miinchen
Lichtenbergstrasse 4, D-8046 Garching (FRG)
This work was supported by the Deutsche Forschungsgemeinschaft
(Sonderforschungsbereich 148) and the Fonds der Chemischen Industrie. We thank C. Frank and L. Riesinger for dedicated and skilled work.
We thank Dr. P. Rauschenbach and F. Wendling for working out the
conditions of the HPLC analyses.
0570-0833/87/0202-0128 $ 02.50/0
Angew. Chem. 1111. Ed. Engl. 26 (1987) No. 2
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bound, carbene, cyclopentadienylidene, complexes, cyclopentadienyl, conversion
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