Nitrido-technetium and -rhenium Complexes with Chelating Phosphines: Synthesis, Reactivity and Crystal Structures

Nitrido-technetium(V) and -rhenium(V) complexes of general formula [MNCl2L][M = Tc or Re; L = bis(diphenylphosphinoethyl)propylamine (L1), 1,8-bis(diphenylphosphino)-3,6-dioxaoctane (L2) or 1,1,1-tris(diphenylphosphinomethyl)ethane (L3)] have been synthesized and characterized. They were prepared by the reduction of [TcVINCl4]– or by the replacement of the two triphenylphosphines of [MNCl2(PPh3)2](M = Re or Tc) by bidentate or tripodal polyphosphine ligands L. Reaction of these complexes with an excess of potassium O-ethyl dithiocarbonate yields neutral dithiocarbonate compounds [MN(S2CO)L], while cationic and neutral complexes [MN(S2CNEt2)L]+ and [MN(S2CNEt2)2] were obtained upon reaction with K(S2CNEt2). The crystal structures of [TcNCl2L1] and [TcNCl2L2] have been determined by X-ray crystallography; the complex [TcNCl2L1] shows square-pyramidal co-ordination at technetium with the Tc atom displaced from the basal plane towards the N atom by 0.410 Å. An unusual trigonal-bipyramidal geometry is observed for [TcNCl2L2]. The Tc[triple bond, length half m-dash]N bond distances (1.60 Å) in both complexes are indicative of a strong triple bond.