Metal Bonds in Bimetallic Complexes

General molecular orbital diagram for the metal-metal bond in bimetallic complexes... 

Metal-Metal Bonds in Bimetallic Complexes.—Cotton and co-workers, continuing their study of multiple metal-metal bonds, have published a series of papers on the alkoxyphenyl derivatives of Cr, Mo, and The... 

It is natural to wonder how many bonds, of what type, can exist between the two metal centres in bimetallic complexes. The characteristics presented above will reappear in the description of metal-metal bonds, but the presence of d-type orbitals introduces a significant new feature. 

A rare redox reaction carried out by ETC catalysis is the disproportionation of bimetallic metal carbonyl complexes such as [MoCp(CO)3]2 containing a metal-metal bond, in the presence of a two-electron donor such as PMc3. In this typical example, the reaction leads to the ion pair [Mo Cp(CO)2(PMe3)2][Mo°Cp(CO)2]. The photolysis of the dimer gives the 17-electron iron radical [Mo Cp(CO)3] re-... 

We have shown that metal activation of o-,77-coordinated ligands in bimetallic complexes may facilitate carbon-carbon bond formation. However, only a few examples of C-C coupling reactions of organic substrates have been recorded (Sections I1,C-E), and this aspect of bimetallic activation has not yet been fully exploited. Furthermore, activation of a bridging ligand in both the cr-frame and 77-frame by different transition... 

Based on these data, the primary oxidation products of M(Por)Fe(CO)4 were postulated to be [M (Por)] and Fe3(CO)i2. These fragments are formed after the global abstraction of two electrons from M(Por)Fe(CO)4 and cleavage of the metal-metal bond in the bimetallic complex. Evidence for the above oxidation products came from coulometric values of n and from identification of [M (Por)] and Fe3(CO)i2 as major products of the oxidation ... 

In bimetallic complexes, the oxidation state is calculated hy supposing that the metal-metal bond(s), if any, is/are broken homoly tic-ally. This procedure is justified by the fact that the electronegativities of the two metal centres are equal if they are identical, or similar in hetero-nuclear complexes (see Table 1.2(a)). The presence of one or more bonds between the metals therefore has no effect on their oxidation state. For example, the complex [Mo(Cl)2(PR3)2]2 can initially be considered to be decomposed into two monometallic neutral fragments [Mo(Cl)2(PR3)2] in which the oxidation state of molybdenum is +2. 

Pizzotti et al. employed [/5zbimetallic complexes 36 in good yields. The heterometallic metal-metal bonds of these complexes were found to be weak, as the W(phen)(CO)3 group was easily... 

Bimetallic biconnective bridging can also be symmetric or can display a variable degree of unsymmetry (Scheme 4). This coordination mode occurs in dinuclear complexes and in supramolecular chain-like arrays. When a metal-metal bond is present five-membered rings are formed. 

Shvo and coworkers prepared a bimetallic complex in which the two metals are joined by a bridging hydride as well as by an O-H-O hydrogen bond joining the two substituted Cp ligands [70]. Shvo used this versatile catalyst precursor for hydrogenation of C=C and C=0 bonds at 145 °C under 34 bar H2 (Eq. (41))... 

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