Alkyne scission in cobalt–molybdenum clusters: synthesis and structures of hexa- and heptanuclear alkylidyne clusters with unusual architectures

Abstract

Heating [Mo₂(μ-RCCR)(CO)₄Cp₂] (R = CO₂Me; Cp = η-C₅H₅) with an excess of dicobalt octacarbonyl affords, in addition to the expected product [Co₂Mo₂(μ₄-C₂R₂)(μ-CO)₄(CO)₄Cp₂], two clusters in which the alkyne ligand has been cleaved: hexanuclear [Co₄Mo₂(μ₄-CR)₂(μ-CO)₂(CO)₈Cp₂] (2) and heptanuclear [Co₅Mo₂(μ₄-CR)(μ₅-C)(CO)₁₂Cp₂] (3), both of which have been shown by X-ray diffraction to contain unusual edge-sharing bitetrahedral metal frameworks. An analogue of the latter, [Co₅Mo₂(μ₄-CH)(μ₅-C)(CO)₁₂Cp₂] (8), was obtained from a similar reaction with R = H, but no counterpart of 2 could be isolated. Treatment of 3 with CO afforded the trinuclear cluster [Co₂Mo(μ₃-CCH₂CO₂Me)(CO)₈Cp] (11), presumably by carbido-alkylidyne coupling; the crystal structures of this cluster and of the related [Co₂Mo(μ₃-CMe)(CO)₈Cp] are also reported.