Reactions of hydridocarbonylmanganese compounds with acetylenes

Abstract

Hydridopentacarbonylmanganese reacts with the acetylenes HC⋮C·CO₂Me, HC⋮C·CHO, or RO₂C⋮C·CO₂R (R = H or Me) to give cis-MeO₂C·CH:CH·Mn(CO)₅, cis-OHC·CH:CH·Mn(CO)₅, and trans-RO₂C·CH:C(CO₂R)·Mn(CO)₅ respectively by a trans-addition of the hydride to the acetylenic bond. When trans-MeO₂C·CH:C(CO₂Me)·Mn(CO)₅ is heated it loses carbon monoxide, by a reversible process, to give trans-MeO₂C·CH:C(CO₂Me)Mn(CO)₄; this is in contrast to cis-MeO₂C·CH:CH·Mn(CO)₅ which undergoes a novel rearrangement when heated to give bis(tricarbonylmanganese)dimethyl cis,cis-muconate, (MeO₂C·CH:CH·CH:CH·CO₂Me)Mn₂(CO)₆. The compound trans-MeO₂C·CH:C(CO₂Me)·Mn(CO)₅ reacts with triphenylphosphine to give trans-MeO₂C·CH:C(CO₂Me)·Mn(CO)₃PPh₃, which has also been obtained in high yield from the reaction of trans-MeO₂C·CH:C(CO₂Me)·Mn(CO)₄ and triphenylphosphine. The reaction of HC⋮C·CO₂Me or MeO₂C·C⋮C·CO₂Me with cis-HMn-(CO)₄PPh₃ gives low yields of trans-MeO₂C·CH:CH·Mn(CO)₄PPh₃ and cis-MeO₂C·CH:C(CO₂Me)Mn(CO)₄PPh₃ respectively by a cis-addition of the hydride to the acetylenic bonds. The i.r. and n.m.r. spectra of the new compounds are discussed.