Mixed-metal clusters strategy

Anionic clusters are good nucleophiles (see Section III,A) and are often easy to make. On the other hand, the electrophilic nature of most monometallic complexes is obvious from ligand substitutions. The combination of these properties makes a strategy for cluster expansion. This strategy was used for the first time by Hieber (130) in making Fe4(CO)fc from Fe3(CO),7 and Fe(CO)s. It is probably active in many syntheses of large metal carbonyl clusters because the Re, Os, Rh, Ir, Ni, and Pt clusters involved are almost always anionic. However, simple stoichiometries can rarely be written for such reactions (122). This route makes mixed metal clusters accessible, e.g.,... 

This strategy is exploited to synthesize numerous mixed-metal carbide clusters by using one of the techniques mentioned earlier to build up a larger mixed-metal cluster from a smaller one and then oxidatively degrading this product to cause metal exchange ... 

Iron-cobalt bonds have also been studied within Fe-Co heterotrimetallics featuring FejCo " and FeCOj " cores [225]. The mixed-metal clusters were synthesized using a novel strategy of metal atom substitution (Co) into a preexisting Fej " core, [(L )Fe3(p-Cl)]2. The addition of 2 and Sequiv. of... 

For metal carbonyl clusters, methods (b), "-" (c), (d), and (e), - - or variations of them have been successfiilly employed. Thus an effective strategy for mixed-metal cluster synthesis is chloride ion displacement from a coordinated R2PCI ligand by a carbonyl metallate. Several new routes to I1-PR2 clusters have been developed in recent years. Vahrenkamp and Keller have successfully adapted a method first described by Benson et al. involving elimination of propene in reactions of complexes... 

The synthetic strategies for Ru-Os mixed-metal clusters can be broadly classified into two categories ionic coupling and condensation that is assisted by coordinated alkyne ligands. Lewis el al. nicely demonstrated the synthetic value of [RuCp(MeCN)3]+ 22-224 [M(y-C6H6)(MeCN)3]2+ (M = Ru, cations as capping... 

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