The co-ordination chemistry of manganese. Part 14. Synthesis of manganese(II) complexes of tertiary phosphine ligands containing 2-cyanoethyl groups

Abstract

Complexes of manganese(II) salts with tertiary phosphine ligands containing 2-cyanoethyl groups have been prepared and characterised, MnX₂L [X = Cl, Br, I, or NCS; L = P(CH₂CH₂CN)₃, PPh(CH₂CH₂CN)₂, or Ph₂PCH₂CH₂CN]. In the solid state and in dichloromethane solution, when L = P(CH₂CH₂CN)₃ or PPh(CH₂CH₂CN)₂ the complexes have pseudo-octahedral dimeric structures involving bridging and terminal X groups and tridentate PN₂ ligands, and molecular-weight measurements confirm the dimeric nature for two of these complexes in dichloromethane; however, for L = Ph₂PCH₂CH₂CN the complexes are pseudo-tetrahedral and the cyano-group is not co-ordinated. In tetrahydrofuran (thf) all the complexes have been assigned a pseudo-octahedral MnX₂(thf)₃L structure in which the ligands are unidentate phosphine donors only. None of the MnX₂L complexes absorbs dioxygen in thf, in contrast to their tertiary alkylphosphine analogues. This is attributed to the better π-acceptor properties of the 2-cyanoethyl ligands. The complex Mnl₂[P(CH₂CH₂CN)₃] can be formed by substitution of PBuⁿ₃ in Mnl₂(PBuⁿ₃) in thf, but the reverse reaction is not possible.