Dinuclear metal compounds

Most of the compounds with metal-metal double bonding do not arise directly from the analogue of higher bond order discussed above. Thus for instance in the chemistry of rhenium compounds the best known and also most interesting species are the Re (III) trinuclear clusters that will be discussed in the next chapter. In this sense the chemistry of compounds with metal-metal double bonds appears as a transition from the chemistry of dinuclear metal compounds to that of higher metal aggregates. 

Polynuclear Carbonyls. Several stmctures consist of dinuclear metal carbonyls as shown in stmctures (4)—(6). The metal atoms in Mn2(CO) Q, as also for technetium and rhenium, are held together by a metal—metal bond and the compound contains 10 terminal CO ligands, five coordinated to each atom. The CO ligands of Mn2(00) 0 adopt a staggered configuration as illustrated in stmcture... 

In this case, the best results were obtained by precipitating the dinuclear metal complexes as the PF6 salts. Elemental analysis suggests, as already indicated above, that the products are isolated as sodium salts such as Na3[Ru(dcb)2(bpt)]-3H20 for the mononuclear precursor and Na3[Ru(dcb)2(bpt)0s(bpy)2](PF6)2-3H20 for the Ru-Os dyad. The number of sodium atoms incorporated is, however, not always the same but appears to depend on the manner in which the materials are precipitated. Nevertheless, the uncertainty in the composition of the compounds in the solid state does not affect the measurements, since in all cases the protonation state of the compounds in solution is controlled by the pH of the solutions. 

Studies on dinuclear transition-metal compounds containing metal-metal bonds have deeply enriched our understanding of chemical bonding. The nature and... 

Apart from the dinuclear metal complexes 17-19 there are also some mononuclear metal compounds for which the occurrence of M—H—Si three-center bonds appears possible, judging from currently available data. The first complex in this category, 20, was obtained by Jetz and Graham among other products by reaction of trichlorosilane with Cp2(OC)4Fe2 (65). 

All of the compounds discussed to this point in this chapter are accommodated by this assumption that the three filled t2g orbitals do not constitute part of the frontier-orbital set. However, there are well-known organometallic examples where these metal d functions do participate in bonding. Hoffmann labels this behavior into the t2g set. Let s take a look at some dinuclear metal complexes that provide geometric evidence of the partial utilization of the t2g set in bonding. 

Consider the two WRu compounds at the top of Figure 4.19 as dinuclear metal complexes and show that they are electronically saturated 34-cve complexes. Now count the electrons at each metal center. Does this justify Stone s representation of the bonding in the WRuC three-membered ring ... 

Stone considers the compound shown below to be an electronically unsaturated 32-electron dinuclear metal complex. Justify this conclusion. The compound adds PMe3 to yield the product shown. Is it now saturated ... 

The time is ripe for truly exciting developments in the reactivity of dinuclear transition metal compounds. The potential for cyclic sequences of reactions, as is required for catalytic reactions, has already been realized. (1) It has been shown, by Muetterties, et al. (53), that alkynes can be selectively hydrogenated to alkenes (cU 2H-addition) by Cp2Mo2(C0) the rate determining step involves CO dissociation from the acetylene adducts Cp2MO2(C0) (R2C2). (2) We have found that... 

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