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.