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An Entry to Chiral Clusters.

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only for tricobalt compounds, can also be studied with other
metals. Moreover, the incorporation of heterometal atoms
in place of cobalt would appear to be a versatile synthetic
procedure in view of the large number of known cobalt clusters.
Preliminary results[71support these expectations.
Experimental
C H ~ C C O ~ ( C O ) ~ - A S M ~ ~ - M O ( C O )( ~
2 eC) ~ (2.34 g,
3.1mmol) is stirred in cyclohexane (50ml) for 8 d at 40°C.
After filtration and concentration to a volume of 20m1, the
reaction solution is chromatographed on a silica gel column
(d= 3, 1 = 30 cm) with hexane/benzene (4 : 1): a short first fraction of CH3CCo3(C0)9is followed by a green solution of
( 3 e ) which is evaporated to dryness in uacuo. Recrystallization
from hexane (5ml) affords (3 e) (1.24 g, 75 %) as black crystals.
s
AsMe,,
/%
(-co(co)2
/
(CO)&O-
‘co’
M(CO),Cp
-+
-(I)
KO),
Received: July 31, 1978 [Z 84a IE]
German version: Angew. Chem. 90, 915 (1978)
Table 1. Melting points and NMR data of the heteronuclear cobalt clusters
(3).
R
( 3 ~ )
(3b)
(3c)
(3d)
(3e)
(3f)
(39)
(3h)
13i)
(3j)
(3k)
H
H
H
‘H-NMR [b]
M
Cr
Mo
W
Cr
Mo
W
Cr
Mo
CH3
CH3
CH3
C6H.5
C6Hs
w
C6H5
pC6H4CH3 Mo
p-C6H4CH3
w
M.p. [“C]
6(R)
fi(C5H5)
129
143
147
155 [a]
200 [a]
205 [a]
137 [a]
165 [a]
173 .
12.91
11.27
11.79
3.94
3.73
3.84
7.22 (m)
7.21 (m)
7.16 (m)
7.06 (m), 2.36
7.02 (m), 2.39
4.96
5.42
5.46
4.91
5.35
5.41
4.68
5.22
5.34
5.23
5.33
151
169
[a] Decomposition. [b] In CCL, rel. to int. TMS; m=multiplet.
The green complexes (3), which are air-stable as solids,
can be readily identified on the basis of their simple NMR
spectra. The well-populated IR spectra are similar in the CO
region [e. g. (3f ) : 2075 vw, 2066 m, 2035 sh, 2029 vs, 2010 s,
2000vs, 1991m, 1944cm-’m]. Confirmation was sought by
determining the crystal and molecular structure of (3 h)f51
(Fig. 1). The molecular parameters of ( 3 h ) correspond to
those expected from reference
61.
Fig. 1. Molecular structure or the hetero-cluster ( 3 h ) . Principal bond lengths:
Co-C0=248.3(1),
Co-M0=267.7(1),
C O X = 193.3(5), Mo<=
210.4(7)pm; bond angles: CoMoCo =55.28(3), CoCoMo=62.36(2),
COCMO=83.0(2), CoCCo= 79.9(3)”.
Complexes (3) demonstrate that the chemistry of methylidyne-trimetal clusters, although so far examined thoroughly
864
CAS Registry numbers:
( Z a ) , 68212-41-9; (Zb), 68185-29-5; (Zc), 68185-30-8; (Zd), 68212-40-8;
(Ze), 68185-31-9; (Zf), 68185-32-0; (29). 68185-33-1; ( Z k ) , 68185-34-2; (Zi),
68185-35-3; ( 2 j ) , 68185-36-4; ( 2 k ) , 68185-37-5; ( 3 a ) , 68185-38-6; ( 3 b ) ,
68185-39-7; ( 3 c ) , 68185-40-0; ( 3 d ) , 68185-41-1; (3e), 68185-42-2; ( 3 f ) ,
68185-43-3; ( 3 g ) , 68185-44-4; ( 3 h ) . 68185-45-5; (3i), 68185-46-6; ( 3 j ) ,
68185-47-7; (3 k ) , 681 85-48-8
[l] Cf. a) H . Vahrenkamp, Struct. Bonding (Berlin) 32, 1 (1977); b) G . Sckmid,
Angew. Chem. 90, 417 (1978); Angew. Chem. Int. Ed. Engl. 17, 392
(1978); c) for very recent examples, see M . R. Churchill, F. 3. Hollander,
3. R. Skapley, D. S. Foose, J. Chem. SOC.Chem. Commun. 1978, 534;
L. J . Farrugia, 3. A . K . Howard, P. Mitrprachachon, 3. L. Spencer,
F. G. A . Stone, P . Woodward, ibid. 1978, 260.
[2] Cf. M . H. Chisholm, M . W Extine, R . L. Kelly, W C . Mills, C . A.
Muriilo, L. A . Rankrl, W W Reickert, lnorg. Chem. 17, 1673 (1978).
[3] Y. L. Baay, A . G . MacDiarmid, lnorg. Chem. 8, 986 (1969).
[4] a) W Ehrl, H . Vahrenkamp, Chem. Ber. 106, 2550 (1973); b) H. 3. Lungenbuck, H . Vahrenkamp, unpublished; c) R. Miifler, H . Vakrenkamp, Chem.
Ber. 110, 3910 (1977).
[5] Orthorhombic, Pnma, 2 = 4 ; a = 1888.0(5),b=1246.2(4), c=905.6(2)pm;
1703 reflections, R =0.036.
[6] R . 3. Deffaca,B . R. Penfold, Inorg. Chem. 1 1 , 1855 (1972); P. W Sutton,
L. F. Dnhl, J. Am. Chem. SOC.89, 261 (1967).
[7] F. Richter, H . Vuhrmkump, Angew. Chem. 90,916 (1978); Angew. Chem.
Int. Ed. Engl. 17, 864 (1978).
An Entry to Chiral
Clusters[**]
By Felix Richter and Heinrich Vahrenkamp[*]
No optically active metal complex‘’] is known whose
chirality arises from differences between the metal atoms.
On the basis of an analogy proposed between clusters and
metal surfaces[’], such a polynuclear complex could serve
as a model compound for asymmetric catalysis. We now report
the first p3-bridged trinuclear complexes whose tetrahedral
skeleton is made up of four different entities and should therefore impart chirality to the molecule.
FeCo2 cluster ( 1 ) and its convenThe readily
tionally preparedC4’substitution products (2) are transformed
into the new clusters (3) containing three different metal
atoms by our newly
method of eliminating
[(C0)3Co-AsMe2],. The complexes (3) are dark red to
black in the solid state and red in solution, and exhibit a
large number of absorption bands in the CO region of their
[*] Prof. Dr. H. Vahrenkamp, Dipl.-Chem. F. Richter
Chemisches Lahoratorium der Universitat
Alhertstrasse 21, D-7800 Freihurg (Germany)
[**I This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie. We are grateful to Dr. P . Merbach,
Universitat Erlangen-Niirnberg. for the mass spectrum.
Angew. Chem. Int. Ed. Engl. I7 (1978) Nu. I 1
IR spectra [e. g. ( 3 b ) ; 2080 s, 2038 vs, 2035 sh, 2020 s, 1998s,
1985m, 1895cm- vw]. Their compositions were confirmed
by the EI mass spectrum of ( 3 a ) . They differ from the sole
known clusters with three different metal atomsr6] in their
facile synthesis and the absence of any symmetry element
in the molecule.
identical centers of asymmetry are seen for ( 4 b ) , and two
different ones for ( 5 b).
Table 1. ’H-NMR data for the P-methyl groups of the clusters ( 4 ) and
( 5 ) (in benzene, rel. to int. TMS).
___
-
______
A(PCH3)
’JPH
[Hzl
1.10, 1.17
1.25, 1.28
1.35, 1.37
1.44, 1.46, 1.48, 1.53
10.0, 10.0
8.8, 8.8
9.0, 9.2
9.0, 9.1, 8.5, 8.8
-
(4a)
(46)
(5a)
(5 b)
(2), M
=
C r , Mo, W
(3)
Fig. 1 . ‘H-NMR spectra of the complexes ( 4 ) and (5) in the P-methyl
region at 60 MHz.
4.20
4.35
4.33
[a] In benzene, re]. to int. TMS.
Experimental
The chirality of the clusters ( 3 ) can be demonstrated by
‘H-NMR spectroscopy of suitable phosphane derivatives with
diastereotopic P-substituents. The same applies to the starting
complex ( 1 ) which likewise becomes chiral on CO/PR2R
exchange. With this purpose in mind, the dimethyl(pheny1)phosphane complexes (4a), (4b), (5a), and ( 5 b ) were prepared and their structures assigned on the basis of the finding
that ligand exchange in ( 1 ) first takes place at the two cobalt
atoms[’] and that the ease of substitution decreases with decreasing number of CO groups attached to a metal atom.
In all four substituted clusters the phosphane ligands are
attached to asymmetric metal atoms; a meso form is present
in the case of ( 4 b)[*l.
PPhMe,
Me,PhP
PPhMe,
(4b)
( 4a)
PPhMe,
Our results show that the synthesis of chiral clusters is
now feasible. Attempts to introduce other metals into ( 1 )
and to resolve the enantiomers of the pure clusters are currently
in progress.
Me,PhP
l5a)
PPhMez
(56)
Table 1 and Figure 1 list the relevant NMR information;
in all four cases the spectra have the expected appearance.
It is informative to compare the disubstituted clusters: two
Angew. Chem. Int. Ed. Engl. 17 (1978) N o . 11
Compound ( 2 b ) (M = Mo) (OSOg, 0.64mmol) is heated
in cyclohexane (50ml) with stirring for 2d at 70°C. The reaction mixture is then chromatographed on a silica gel column
(d=3, L=70cm) with benzene/hexane (1 :2), the second, red,
fraction being collected. After evaporation to dryness, recrystallization from hexane (20ml) affords ( 3 b ) (0.24g, 70 %)
as black-red crystals.
Compounds ( 3 a ) and ( 3 c ) were obtained similarly. The
preparation of the phosphane-substituted clusters was accomplished in a manner resembling known procedures[’’.
Received: July 31, 1978 [Z 84b IE]
German version: Angew. Chem. 90. 916 (1978)
CAS Registry numbers:
( 2 a ) , 68185-53-5; ( 2 b ) , 68185-54-6; (Zc), 68212-39-5; ( 3 a ) , 68212-38-4;
( 3 b ) , 68185-55-7; ( 3 c ) . 68185-56-8; ( 4 a ) , 68185-57-9; ( 4 b ) , 68185-58-0;
( S a ) , 68185-59-1; ( 5 b ) , 68185-60-4
Cf. H. Brunner, Angew. Chem. 83, 274 (1971); Angew. Chem. Int. Ed.
Engl. 10, 249 (1971).
H. Kzhrenkamp, Struct. Bonding (Berlin) 32, 1 (1977); E . L. Muetterties,
Angew. Chem. 90, 577 (1978); Angew. Chem. Int. Ed. Engl. J7, 545
(1978).
L. Markd, personal communication; S . A . Khatcab, L. Markd, G. Bor,
B. Markd, J. Organomet. Chem. I , 373 (1964).
W Ehrl, H. Vahrenkamp, Chem. Ber. 106, 2550 (1973); R. Miiller, H.
Vahrenkamp, ibid. 110, 3910 (1977).
H. Beurich, H. Vahrenkamp, Angew. Chem. 90, 915 (1978); Augew. Chem.
Int. Ed. Engl. 17, 863 (1978).
G. L. Geoffrey, W L. Gladfelter, J. Am. Chem. SOC.99, 7565 (1977).
S. A i m , L. Milone, R . Rosserti, P. L. Stanghellini, Inorg. Chim. Acta
25, 103 (1977).
Complexes ( 4 ) and / 5 j were characterized by elemental analysis and
spectra. The NMR data (Table 1) were determined by measurement at
two different frequencies.
865
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