Synthesis and properties of the divalent 1,2-bis(dimethylphosphino)ethane (dmpe) complexes MCl2(dmpe)2 and MMe2(dmpe)2(M = Ti, V, Cr, Mn, or Fe). X-Ray crystal structures of MCl2(dmpe)2(M = Ti, V, or Cr), MnBr2(dmpe)2, TiMe1.3Cl0.7(dmpe)2, and CrMe2(dmpe)2

Abstract

The reaction of transition-metal dichlorides with 1,2-bis(dimethylphosphino)ethane (dmpe) leads to the brightly coloured, highly-crystalline octahedral complexes trans-MCl₂(dmpe)₂(M = Ti, V, Cr, or Fe). Although the Mn analogue could not be prepared, both trans-MnBr₂(dmpe)₂ and trans-Mnl₂(dmpe)₂ can be obtained from the respective dihalides. Alkylation of the MX₂(dmpe)₂(X = halide) compounds with either LiMe or MgMe₂ leads to the dimethyl complexes trans-MMe₂(dmpe)₂(M = V, Cr, or Mn); the titanium complex isolated under these conditions is a mixture of trans-TiMeCl(dmpe)₂ and trans-TiMe₂(dmpe)₂, while the iron species obtained is cis-FeMe₂(dmpe)₂. Magnetic susceptibility and e.s.r. measurements indicate a low-spin state for all the complexes except the manganese halide derivatives, and metal–ligand bond lengths observed in those complexes structurally characterised by X-ray crystallographic methods are consistent with the proposed ground-state configurations. There is a similarity between the electronic structures of the MCl₂(dmpe)₂ species and the metallocenes M(η⁵-C₅H₅)₂, while the MMe₂(dmpe)₂ compounds resemble M(η⁵-C₅Me₅)₂. Our studies indicate a progressive change in the nature of the M–Me groups upon lowering the electron count from 18 (Fe) to 14 (Ti). Thus, the titanium complex trans-TiMe_1.3Cl_0.7(dmpe)₂ appears to contain a distorted methyl group involving a Ti ⋯ H–C interaction due to donation of C–H bond electrons into an empty orbital on the metal.