STRUCTURAL AND NUCLEAR-MAGNETIC-RESONANCE STUDIES OF TRIOSMIUM AND TRIRUTHENIUM CARBONYL CLUSTER DERIVATIVES CONTAINING PENTAPHENYLCYCLOPENTAPHOSPHANE

The reaction of pentaphenylcyclopentaphosphane (PPh)(5) with [Os-3(CO) (10)(NCMe)(2) in 1:1 molar ratio afforded a pair of inversion isomers, 1 and 2, with the molecular formula [Os-3(CO)(10){(PPH)(5)}]. A Simil ar reaction in 3:1 molar ratio gave a different cluster [Os-3(CO)(10){ (PPh)(5)}(2)]3. The clusters [Os-3(CO)(11){(PPh)(5)}]4 and [{Os-3(CO)( 11)}(2){(PPh)(5)}]5 were obtained from reaction of (PPh)(5) with [Os-3 (CO)(11)(NCMe)]. Compound 4 reacted with [Ru-3(CO)(11)(NCMe)] to gener ate the cluster [(OC)(11)Os-3{(PPh)(5)}Ru-3(CO)(11)]6. Compounds 4 and 5 were converted into 1 and 2 when heated in sealed tubes at 80 degre es C. In clusters 1 and 2 the triosmium unit is chelated by the cyclop hosphane ligand through the 1,3-phosphorus atoms of the ring, and thei r main difference lies in the orientations adopted by the aromatic rin gs attached to the unco-ordinated phosphorus. Variable temperature NMR studies showed that the two inversion isomers can undergo interconver sion. In 4 one osmium atom of the triosmium unit is co-ordinated to on e phosphorus atom of the cyclophosphorus ligand, while in 5 the two tr iosmium units are each linked via co-ordination of one Os atom to a ph osphorus atom of the cyclophosphane ring. With the help of two-dimensi onal P-31 NMR spectroscopy, the correlations between phosphorus atoms for clusters 1, 2, 4 and 5 were established.