Nitrido-technetium and -rhenium complexes with chelating phosphines: synthesis, reactivity and crystal structures

Abstract

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 [Tc^VINCl₄]^– 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 TcN bond distances (1.60 Å) in both complexes are indicative of a strong triple bond.