Synthesis, structure and isomerism of [Mn2(µ-PPhR)2(CO)8](R = H, alkyl, acyl or carboxylate); crystal structures of trans-[Mn2(µ-PPhR)2(CO)8](R = H or COMe)

Abstract

The thermal reaction of [Mn₂(CO)₁₀] with PPhH₂ in undried decalin at 150 °C gives [Mn₂(µ-PPhH)₂(CO)₈] as a cis–trans mixture of isomers. Recrystallisation enables the trans isomer to be separated from this mixture and the structure of this isomer has been determined by X-ray diffraction analysis. The trans isomer is configurationally stable in toluene at room temperature but isomerises in more polar solvents or on heating. Possible mechanisms for this isomerisation are investigated. Deprotonation of [Mn₂(µ-PPhH)₂(CO)₈] followed by treatment with a range of organic halides, RX, gives the complexes [Mn₂(µ-PPhR)₂(CO)₈] which also exhibit cis–trans isomerism in solution. Recrystallisation of one of these complexes, [Mn₂(µ-PPhCOMe)₂(CO)₈], gives the trans isomer, the structure of which has also been determined by X-ray analysis.