Synthesis and characterization of neutral technetium(III) complexes with mixed S,P-bidentate phosphine–thiolate ligands. Crystal structure of [Tc(SCH2CH2PPh2)2(SCH2CH2PPh2O)]

Abstract

Reduction–substitution reactions of [TcO₄]^– with an excess of the mixed bidentate thiol–phosphine ligands HLⁿ[L¹= 2-(diphenylphosphino)ethanethiolate; L²= 2-(diphenylphosphino)propanethiolate and L³= 2-(diphenylphosphino)thiophenolate] gave neutral five-co-ordinate technetium(III) complexes of the type [TcLⁿ₂(OLⁿ)](n= 1 1 or 2 2). However, the aromatic phosphine–thiol ligand (n= 3) gave six-co-ordinated [TcL³₃]3. The five-co-ordinated complexes are diamagnetic and exhibit a trigonal-bipyramidal geometry in which two π-acid phosphorus donors of two chelates are co-ordinated mutually trans in the axial positions, with the corresponding thiolate sulfur atoms on the equatorial plane. A further thiolate group completes the basal-plane co-ordination leaving a pendant phosphorus donor outside the co-ordination sphere. This is oxidized to phosphine oxide, which was revealed by a crystal structure determination of 1: triclinic, space group P, with Z= 2, a= 9.991 (4), b= 12.417(4), c= 18.687(8)Å, α= 73.37(3), β= 76.88(3) and γ= 73.68(3)°; R converged to 0.0703 using 2765 observed reflections. In addition, the compounds were characterized by elemental analysis, IR, ¹H and ³¹P NMR, UV/VIS and FAB spectroscopies and cyclic voltammetric measurements. The occurrence of trigonal-bipyramidal vs. octahedral geometry is discussed in terms of ligand steric requirements and electronic factors governing the metal–donor interactions.