Synthesis of µ-carbene and µ-carbyne complexes of rhodium and cobalt from substituted diazirines. Crystal structures of [Rh2(η5-C5Me5)2(CO)2{µ-C(C6H4F-4)(OMe)}] and [Rh2(η5-C5Me5)2(µ-CO)(µ-C6H4Me-4)][BPh4]

Abstract

The reaction of aryl(methoxy)diazirines with [M₂(η⁵-C₅Me₅)₂(µ-CO)₂](M = Rh or Co) affords the µ-carbene complexes [M₂(η⁵-C₅Me₅)(CO)₂{µ-CR(OMe)}](R = aryl) in excellent yield. The carbonyl groups are terminal in the rhodium complexes, as demonstrated conclusively in an X-ray diffraction study, but bridging for the cobalt complex. Thermolysis of the rhodium complexes results in loss of CO and the formation of [Rh₂(η⁵-C₅Me₅)₂(µ-CO){µ-CR(OMe)}]. Protonation of either the mono- or di-carbonyl rhodium complex with HBF₄ led to the formation of a stable cationic carbyne complex, [Rh₂(η⁵-C₅Me₅)₂(µ-CO)(µ-CR)][BF₄]; the structure of the related [BPh₄]^– salt was established in a diffraction study. Dynamic processes in the complexes were investigated by variable-temperature NMR spectroscopy.