Cobalt mixed-metal carbonyl clusters

It was thought that the formation of inactive cobalt clusters such as Co4(CO)i2, formed by dimerisation of the remaining cobalt carbonyl species after release of the cyclopentenone product, were responsible for the shutdown of the catalytic cycle when dicobalt octacarbonyl was employed.51 Krafft and co-workers were able to show that Co4(CO)12 can actually be exploited as a catalytic species in the PK reaction and were able to obtain excellent yields if cyclohexylamine was introduced as an additive alongside the metal cluster.57,58 The use of metal clusters as catalysts for the reaction has been extended to involve mixed metal clusters.59... 

Within this context, the present article concentrates on transition metal cluster complexes of cobalt, iron and manganese with mixed chalcogen/carbonyl ligand spheres obtained by reaction of simple binary metal carbonyls with alkali-metal sulfides, alkali-metal thiolates or transition-metal thiolate complexes and their selenium or tellurium counterparts. 

Compared with cluster complexes of lower nuclearities, the number of mixed chalcogen/carbonyl complexes having more than six metal atoms is small. Besides some complexes containing iron and cobalt, no manganese compound within this class of complexes is known. 

Photoreactions can also be used to both synthesize and fragment mixed-metal oligomers and clusters. An example of such a transformation is the photochemical extrusion of mercury from the heterotrimetallic cobalt-mercury cluster complex HgCo2(CO)8. Photolysis into the MMCT transition of HgCo2(CO)g results in the formation of cobalt carbonyl, Co2(CO)g, and elemental mercury ... 

A series of Ru-Co mixed-metal nitride and nitrene carbonyl clusters 230-236 was synthesized from the interactions of [Ru3(/x-H)2(/X3-NOMe)(GO)9] with mononuclear cobalt reagents such as [Gp Go(GO)l2] and [Gp Go(GO)2]. The alkyne derivative [Ru3(/X3-NOMe)(/X3-77 -PhG2Ph)(GO)9] has also been used. It is interesting to observe the formation of 237,... 

A few clusters of interest containing germanium and transition metals have been reported.136-138 Dimethylgermane was found to replace only the bridging carbonyls between cobalt in a mixed germanium/cobalt/iron cluster complex (Equation (107)), and replacement of the carbonyl bridging the iron metal centers was not observed.137 A similar reaction leads to replacement of a bridging carbonyl in a mixed cobalt/silicon cluster (Equation (108)).136... 

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