Addition of diphenylphosphine to molybdenum alkynyl complexes

The reaction of [CpMo(CO)3(CCR)] (Cp=η-C5H5) with PPh2H in the presence of Me3NO gives the expected substituted complex [CpMo(CO)2(PPh2H)(CCPh)] as the major product when R=Ph. The phosphine ligand in this compound can be subjected to a deprotonation–alkylation sequence to afford [CpMo(CO)2(PPh2Me)(CCPh)]. In contrast, when R=CO2Me, treatment of [CpMo(CO)3(CCR)] with PPh2H and Me3NO leads directly to [CpMo(CO)2(PPh2CCHCO2Me)] by addition of the PH bond across the alkynyl triple bond; this compound has been structurally characterised and contains a three-membered (MoPC) ring with an exocyclic CHCO2Me group.