Hexanuclear and pentanuclear benzene carbido clusters: synthesis, characterisation and molecular structures of[ Os6C(CO) 14(η 6-C 6H 6)],[ RuOs5C(CO) 14(η 6-C 6H 6)]and[RuOs 4C(CO) 12(η 6-C 6H 6)

Abstract

Reaction of the pentaosmium-carbido dianion [Os 5C(CO) 14] 2−, 1 with [Os(C 6H 6)(MeCN) 3] 2+ gave[ Os 6C(CO) 14(η 6-C 6H 6)] 2 in fair yield; while the corresponding reaction with [Ru(C 6H 6)(MeCN) 3] 2+ gave[ RuOs 5C(CO) 14(η 6-C 6H 6)] 3 in moderate yield. Treatment of 3 with carbon monoxide produces an unstable species[ RuOs 5C(CO) 15(η 6-C 6H 6)] 4a, which on standing in CH 2Cl 2 undergoes fragmentation to give the species[ RuOs 4C(CO) 12(η 6-C 6H 6)] 4b or decarbonylation to 3. Clusters 2, 3 and 4b have been fully characterised by both spectroscopic and crystallographic methods. The X-ray structure analysis shows that both 2 and 3 are isomorphous. Both molecules contain an octahedral cavity accomodating an interstitial C(carbide) atom, with theη 6-C 6H 6 coordinated to the Ru or Os atom in an apical position. Cluster 4b is an unprecedented pentanuclear osmium-ruthenium mixed-metal carbido cluster containing anη 6-coordinated benzene ligand.