Reactions of bis(phosphido)-bridged dimanganese complexes with alkynes and allene

Abstract

The photolytic reactions of [Mn₂(µ-PPh₂)(µ-PPhR)(CO)₈](R = Ph 1a or Me 1b) with acetylene and of 1a with allene have been studied. Although they are highly non-specific, a number of products have been isolated and characterised which contain new ligands derived from the combination of one of the bridging phosphido groups with acetylene or with allene. The reactions can involve the breaking of one or both of the bonds between the metal atoms and the bridging group. Thus the complexes [Mn₂(η⁴-C₄H₄PPhR)-(µ-PPhR′)(CO)₆](R = R′= Ph 2a; R = Ph, R′= Me 2b; R = Me, R′= Ph 2c), containing quaternised phosphole ligands, and [Mn₂(µ-σ:η⁴-C₄H₄PPh₂)(µ-PPh₂)(CO)₅]3 are obtained in the reaction of 1a and 1b with acetylene. The complexes [Mn₂(µ-η³-C₃H₄PPh₂)(µ-PPh₂)(CO)₇]4 and [Mn₂(µ-η³- C₆H₈PPh₂)(µ-PPh₂)(CO)₆]5, containing ligands derived respectively from the combination of one and two allene molecules with a phosphido group, are obtained in the reaction of 1a with allene. Single-crystal X-ray analyses of the molecular structures of 2c, 4 and 5 have been performed, and some reaction pathways are proposed and discussed.