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

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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.

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