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Heterodimetallic Complexes with an Unbridged Polar MetalЦMetal Bond.

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[l I ] T. J. Searr, T. A. Miller. V. E. Bondybey. J Cheni. P l i m 1981. 74,
.. .
[12] T A . Miller. V E. Bondyhey, Molecrrlar Ions. Specrroscopl, Slrucrure, und
Climi/srrr (Eds.: T. A. Miller. V. E. Bondyhey). North-Holland. Amsterdam,
[I31 K. Raghavachari. R. C Haddon. T. A. Miller. V. E. Bondybey. J Cilenr. /‘/in
1983. 79. 1387.
[14] See for example J. Eiding. R. Schnelder. W Domcke, H . Koppel,
W. von
Niessen. Chem. P/IJ,x.Leir. 1991. 177. 345.
[15] L. Yu, D . W Cullln. J. M. Williamson, T. A. Miller. J. Chem. P h ~ s 1993.
[I61 H. Krause. H. J. Neusser, J Chem. Pl~ys.1992, 97. 5923
[17] L. Zhu. P. Johnson. J, Ch‘,.nf. Pl1~s.s.1991, 94. 5769.
1181 K. Muller-Dethlefs. J. Clicm. Phy.5. 1991, 95, 4821.
Heterodimetallic Complexes with an Unbridged, Polar Metal - Metal Bond
Max Herberhold* and Guo-Xin Jin
Among the numerous complexes with a direct metal -metal
bond“. 21 those that are stable without bridging ligands are especially fascinating. Homodinuclear complexes with an unsupported metal-metal linkage are known in particular for metals
in lower ( - I, 0, I) and intermediate oxidation states (11, 111). The
first group includes dinuclear complexes like 1 and 2 and the
cyclopentadienyl metal complexes 3. 4, and 5.
X = CI. Br
2, E
- Ru(CO),(EMe,)]
SI. Ge, Snl,’
8 , M = Mo, W [2]
X = NMe,, OR, CH,SiMe,
3a, M = Cr Fa]
3b, M = MO Fb]
3c, M = W Fb]
4a, M = Cr [6al
4b, M = MO Pb]
412, M = W
10, R = Me, Et
The second group is dominated by dinuclear complexes with
metal-metal multiple bonds.“. *I Complexes that have been intensively studied owing to their formal quadruple bond^include the homonuclear dirhenate ions [X4Re=ReX4IZ- 6 ,
whose molecular halves are eclipsed, and the alkoxidomolybdenum complexes 7a, b. The d3-d3dimers 8 and 9, which contain
a formal triple bond, also display a rich chemistry.[21A related
compound with a metal-metal single bond is the alkyne complex 10. Homodinuclear complexes with unbridged metals in
higher oxidation states such as Tc”’ and Re”’ in complexes 11
are uncommon.
Homodinuclear complexes are generally symmetrical
”dimers” with a nonpolar metal-metal bond. Polarity can be
introduced to a certain degree, while maintaining the oxidation
state of the metal, by “one-sided” exchange of a ligand in ho[*] Prof. Dr. M. Herberhold. Dr. G X . Jin
Laboratonurn fur Anurganiache Chemie der Universitit
Postfkh 101251. D-95440 Bayreuth (FRG)
Telefax: I n t . code + (921)55?515
9, M = Mo, W lz~’ol
X = NMe,, NEt,
V C H ~ , r l r i ~ s j i r r i ~ l l s i / i mhli
D-69451 Wernherrn 1994
R = iPr,C,H,
moleptic complexes, which results in compounds like 12 and 13.
The metal-metal bond is yet more polar when the same metal
is i n different oxidation states in the two centers, as is found in
the unexpected products 14 and 15 and in the bis(dithio ether)
complexes 16.
[(OC),Re - Re(CO),L]
C(Me)OMe, CNtBu
15, R = p-CH,C,H,
= 2,5-dithiahexane,
0570-0833 94 OYOY-0964 5 10 OOf 2 i 0
Angevi Cheni Ini Ed EnRI 1994, 33. No Y
For a number of years dinuclear complexes with different
metals have been popular subjects of study owing to the reactivity and potential catalytic activity of compounds with nietalmetal bonds. The two metals may be adjacent d-block elements
as in 17 and 18 or may come from opposite ends of the periodic
table as in 19-23.
The concept of “early-late” heterodimetallic compounds,
which are formed by combination of a delectron-poor and a
d electron-rich transition metal complex fragment, has proved
to be especially worthwhile;1261
however, products in which the
metal-metal bond is further stabilized by bridging ligands are
usually obtained.
Trinuclear heterodimetallic complexes like 24-26 have also
been prepared and structurally characterized.
Zr(Cp), - Ru(CO),Cp]
- Fe(CO),-
[(ArN),Re - Hg - Re(NAr),]
26. Ar = ~ , ~ - I P ~ , C , H , [ ~ ~ ~
The synthetic approach of combining a hard “metal acid”
([Re(NtBu),]+, [CpM(NtBu),]+ (M = Mo, W), [Cp,Nb(NtBu)]+, [M(NtBu)*]’+ (M = Mo, W), [CpM(NIBu)J’+
(M = Nb, Ta)) with a soft “metal base” ([Mn(CO),]-, [Co(CO)J, [M(CO),Cp]- (M = Mo, w), [Fe(CO),CpJ-) can certainly be expanded, since plenty of precursors are available for
both the high- and the low-valent components.[301In comparison to the analogous oxometal complexes, imido metal compounds have the advantage that the steric demands of the imido
ligand RN can be varied by the choice of the appropriate R
group. It remains to be seen whether the subsequent hydrolysis
of the metal -imido bonds gives oxometal complexes without
affecting the unsupported, polar metal -metal bond.
The significance of steric shielding is also evident in the heterodimetallic complexes synthesized by L. H. Gade et al. starting from the amido-substituted titanium(1v) monobromides
29a, b (To1 = C6H4CH3).f31-321
The tripodal protecting ligand
(L3) stabilizes the titanium(1v) component [ (L,)TiBr] so well,
that its reaction with the carbonyl metalates Na[Co(CO),(PPh,)] and K[M(CO),Cp] (M = Fe, Ru) leads to stable
heterodimetallic complexes with a polar, unsupported metal metal bond. The Ti-Fe complex of type 30 is much more robust
than the related complex 23.
[(L,)Ti - M(CO),Cp]
Strongly polar metal-metal bonds can apparently be expected for heterodimetallic complexes in which the metal centers are
present in significantly different oxidation states. The importance of the difference in oxidation state for the preparation of
unsupported di- and trinuclear complexes with polar metalmetal bonds seems to have been underestimated so far. However. several recent papers129- 3 2 1 have focused on the deliberate
construction of complexes with polar bonds by the combination
of complex fragments with metals in higher and lower oxidation
states. Thus the research group of J. S~ndermeyer[~’]
has treated
imidometal compounds such as [Re(NtBu),Cl] and [Mo(NtBu),CI2] with carbonyl metalate salts like K[Mn(CO),] and
K[M(CO),Cp] (M = Mo, W) to obtain di- and trinuclear complexes of type 27 and 28, respectively.
30, M
These new complexes allow the systematic investigation of the
chemical reactivity of compounds with a strongly polar, unsupported metal-metal bond. Hitherto there have been few studies
on the reactivity of heterodimetallic complexes without bridging
ligands, for example the trinuclear compound [Cp,Zr{Ru(CO),Cp},J analogous to 21.[22b1
A more recent example is
the observed insertion of CO,, but not CS,, under mild conditions into the metal-metal bond of 31, which results in the
carboxylato complexes 32.[331The shielding cyclopentadienyl
ligands are apparently important in protecting the metal -metal
bond in 31. In complexes like 27, 28, and 30 the bulky ligands
M = Fe, Ru
C h o i i . /ti/
Ed. E t g l . 1994. 33, No.9
:(; V C H Verlugsgesells~liufrmbH,049451 Wemheim,1994
X 10.00f ,2510
guarantee the kinetic stabilitv of the comwunds and atmarentlv
prevent the direct
transfer from the low- to the high-valent component. but they also block access to the metal-metal
German version: A n , V n , C'hiw?. 1994. 106. 1016
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21 -23.
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