Ditertiary alkylphosphine derivatives of the Group VI metal carbonyls and their oxidation with iodine

Abstract

The preparation and characterisation of the complexes fac,fac-[M₂(CO)₆(dmpe)₃](M = Cr, Mo, W; dmpe is Me₂PCH₂CH₂PMe₂) and cis-[M (CO)₂(dmpe)₂] is reported. The oxidation of cis-[M(CO)₄(dmpe)] with iodine gives [M(CO)₄(dmpe)I]I which can be converted into [M(CO)₃(dmpe)I₂](M = Mo, W). Iodine oxidation of fac,fac-[M₂(CO)₆(dmpe)₃] gives [M₂(CO)₄(dmpe)₃I₄](M = MO, W), which are also obtained from the reaction of [M (CO)₃(dmpe)I₂] with dmpe. Oxidation of cis-[M(CO)₂(dmpe)₂] gives [M(CO)₂(dmpe)₂I]I (M = Mo, W) which are also obtained in the reaction of [M₂(CO)₄(dmpe)₃I₄] with dmpe. The products of these oxidation reactions have been characterised by i.r. and n.m.r. (¹H and ³¹P) spectroscopy. The cations [M(CO)₂(dmpe)₂I]⁺ are shown to be fluxional in the temperature range 220–320 K and a monocapped trigonal prismatic structure is indicated for the low-temperature form. Comparisons are made with analogous complexes containing Ph₂PCH₂CH₂PPh₂(dpe) and differences in their behaviour on oxidation are explained in terms of the steric effect of the substituents (methyl, phenyl) at phosphorus.