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

Abstract

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 C_s and C_2v 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.