Cluster chemistry tetranuclear complexes

Finally, in analogy with organic chemistry, "polymerization" of metal-metal multiple bonds may lead to clusters as illustrated in eqs. 12 and 13. To date, the only definitely characterized oligomerization reaction of this type has been reported by McCarley et al. (8j(eq. 14), although Chisholm et al. ( ) have observed that Mo2(0Et)6 dimerizes to a tetranuclear complex of unknown structure and that the 0-H bond of isopropanol oxidatively adds to the WeW bond of W2(i-Pr0)6 to give a tetranuclear complex with an "open" as opposed to a closed, or cluster, structure (10). Also, some evidence has been presented that Cp2Mo2(C0)it may form unstable tetrahedrane intermediates (eq. 12) (. 

The best example of chemical activation in cluster chemistry is the use of Me3NO which results in CO replacement under mild conditions (129). In an interesting example taken from alkyne-cluster chemistry, when Me3NO is used dry a monosubstituted cluster derivative is obtained, but with damp Me3NO a tetranuclear vinylidene complex is isolated (130, 131), as illustrated in Eqs. (4) and (5), respectively. 

Polarographic and cycKc voltammetric studies showed the formation of dianions, with one of the dianionic complexes exhibiting further chemical reactivity. Bulk electrolysis and infrared spectroelectro-chemistry were used to confirm the decomposition of the dianionic tetranuclear clusters to stable tricobalt anions. 

The assumption of a sterically enforced cluster formation was corroborated later in silverfi) iodide coordination chemistry ligated by our methylene-bridged NHCP hgands (Scheme 10.12) [48]. Thus, at lower steric bulk, the Af-mesityl ligand Mes-39 in this case still permitted the formation of a dinuclear complex, likely due to the enhanced flexibihty of the system in comparison to the rigid Af-phosphino systems, which allows the N-substituents to twist out of the coordination plane. For greater steric bulk, an N-tert-butyl substitution yielded the tetranuclear iodide cluster 56. 

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