Hexanuclear and pentanuclear benzene carbido clusters: synthesis, characterisation and molecular structures of [Os6C(CO)14(η6-C6H6)], [RuOs5C(CO)14(η6-C6H6)] and [RuOs4C(CO)12(η6-C6H6)]

Abstract

Reaction of the pentaosmium-carbido dianion [Os5C(CO)14]2−,1 with [Os(C6H6)(MeCN)3]2+ gave[Os6C(CO)14(η6-C6H6)]2 in fair yield; while the corresponding reaction with [Ru(C6H6)(MeCN)3]2+ gave[RuOs5C(CO)14(η6-C6H6)]3 in moderate yield. Treatment of3 with carbon monoxide produces an unstable species[RuOs5C(CO)15(η6-C6H6)]4a, which on standing in CH2Cl2 undergoes fragmentation to give the species[RuOs4C(CO)12(η6-C6H6)]4b or decarbonylation to3. Clusters2, 3 and4b have been fully characterised by both spectroscopic and crystallographic methods. The X-ray structure analysis shows that both2 and3 are isomorphous. Both molecules contain an octahedral cavity accomodating an interstitial C(carbide) atom, with theη6-C6H6 coordinated to the Ru or Os atom in an apical position. Cluster4b is an unprecedented pentanuclear osmium-ruthenium mixed-metal carbido cluster containing anη6-coordinated benzene ligand.