Reactions of hydride complexes of ruthenium(II) with alkynes

Abstract

The complex [Ru(CO)₂Cl(H)(PMe₂Ph)₂] reacts with alkynes RCCR′(R = H, R′= Ph or CMe₃; R = R′= CO₂Me) to yield vinyl complexes [Ru(CO)₂(CRCHR′)Cl(PMe₂Ph)₂]. Addition of Ru-H across the alkyne triple bond is cis for HCCPh and HCCMe₃, but may be trans for MeO₂CCCCO₂Me. The dihydride [Ru(CO)₂H₂(PMe₂Ph)₂] hydrogenates alkynes HCCR (R = Ph or CMe₃) to H₂CCHR and PhCCPh to cis- PhCHCHPh, with the accompanying formation of alkynyl complexes [Ru(CO)₂(CCR)H(PMe₂Ph)₂] and the alkyne complex [Ru(CO)₂(PhCCPh)(PMe₂Ph)₂] respectively. The reaction sequence is believed to involve rate-determining formation of vinyl hydride complexes by cis addition of Ru-H to the alkyne, followed by rapid alkene elimination and reaction of [Ru(CO)₂(PMe₂Ph)₂] with a second molecule of alkyne. With MeO₂CCCCO₂Me, the complexes [Ru(CO)₂H₂L₂](L = PMe₂Ph or AsMe₂Ph) form long-lived vinyl hydride complexes [Ru(CO)₂{C(CO₂Me)CH(CO₂Me)}HL₂] which exist in solution as mixtures of conformers.