New isomers of [Os3(CO)10(PMe2Ph)2] and [Os3(CO)9(PMe2Ph)3]

The compounds [Os3(CO)10(η4-s-cis-C4H6)](C4H6- buta-1,3-diene), [Os3(CO)10(µ-s-trans-C4H6)], and [Os3(CO)10(MeCN)2] react with PMe2Ph at room temperature to give [Os3(CO)10(PMe2Ph)2] and [Os3(CO)9(PMe2Ph)3] as mixtures of isomers. The decacarbonyl compound separates on silica into a 1,1- and a 1,2-isomer, which do not interconvert at room temperature, although the 1,2-isomer exists as two rapidly interconverting isomers of Cs and C2v symmetry respectively. Likewise the nonacarbonyl compound separates into non-interconvertible 1,2,3- and 1,1,2-isomers. Carbon-13 and 31P n.m.r. studies have demonstrated specific localised and delocalised CO exchanges and that intramolecular phosphine transfer between metal atoms does not occur. Indeed 1,1-[Os3(CO)10(PMe2Ph)2] gives [Os3H(CO)9(µ-Me2PC6H4-o)(PMe2Ph)] readily in refluxing toluene whereas the 1,2-isomer does not react at this temperature, giving other decarbonylation products above 120 °C.