The coordination chemistry of tripodal phosphine chalcogenide ligands with platinum group metals




Wang, Sherrie Fang

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This work set out to develop synthetic routes to transition metal complexes containing the ligands of general type [PPh₂(X)][PPh₂(Y)][PPh₂(Z)]CH and [PPh₂(X)][PPh₂(Y)][PPh₂(Z)]C⁻, where X, Y, Z = various combinations of O, S, Se and electron pairs. The aim would then be to fully characterise the complexes by various spectroscopic methods to determine the modes of coordination of the ligands and rationalise any dynamic processes which may be occurring in solution. Finally the complexes would be investigated in terms of chemical reactivity, especially with regards to potential catalytic activity. The synthesis and characterisation of a series of rhodium, iridium, platinum, and palladium complexes containing the phosphine chalcogenide ligands, [CH(P(S)Ph₂)₃]/[C(P(S)Ph₂)₃]⁻ and [CH (PPh₂)(P(S)Ph₂)₂]/[C(PPh₂)(P(S)Ph₂)₂]⁻, are described.The crystal structures of seven of these complexes plus that of the ligand, [CH(PPh₂)(P(S)Ph₂)₂], have been determined. These structures include [Pd(n³-C₄H₇){CH(PPh₂)(P(S)Ph₂)₂-P,S}]BF₄ 2H₂O, [Pd(n³-QH₇){CH(P(S)Ph₂)₃-S,S,S]BF4, [Rh(cod){C(P(S)Ph₂)₃-S,S}], [Ir(CO)3 {C(P(S)Ph₂)3 -S,S}], [Rh(cod){C(PPh₂(P(S)Ph₂)₂-P,S}] CH₂Cl₂. [Rhl₂CBuNC)₂ {C(PPh₂)(P(S)Ph₂)₂-P,S}], and [Ir(cod){CH(PPh₂)(P(S)Ph₂)₂-P,S}]BF₄ CH₂Cl₂, which are all discussed in detail. The [CH(P(S)Ph₂)₃] ligand coordinates in an n³ mode to metal centres. The anionic ligand [C(P(S)Ph₂)₃]⁻ coordinates to metals in an n² mode using two of its sulphur atoms, leaving a -P(S)Ph₂ group dangling. The ligand, [CH(PPh₂)(P(S)Ph₂)₂], can either coordinate in an n² P,S mode, using a phosphorus and a sulphur atom, or in an n³ P.S.S mode using a phosphorus and two sulphur atoms. The anionic ligand, [C(PPh₂)(P(S)Ph₂)₂], acts as a four electron donor, using one phosphorus and one sulphur atom, to metal centres. The reaction of [Ir(cod){C(P(S)Ph₂)₃-S,S}] with CO to give [Ir(CO)₂{C(P(S)Ph₂)₃-S,S}] is described. The reaction of [Rh(cod){C(PPh₂)(P(S)Ph₂)₂-P,S}] with tBuNC to give [Rh(tBuNC)₂{C(PPh₂)(P(S)Ph₂)₂-P,S}] is discussed. The subsequent oxidative additions of I₂ and benzyl bromide, to give isomeric mixtures of [RhI₂(tBuNC)₂{C(PPh₂)(P(S)Ph₂-P,S}] and [RhBr)(Bz)(tBuNC)₂ {C(PPh₂)(P(S)Ph₂)₂-P,S}] respectively, are also presented. The fluxional behaviours of [Pd(n³-C₄H₇){CH(PPh₂(P(S)Ph₂)₂-P,S}]BF₄, [Pd(n³-₄H₇){C(P(S)Ph₂)3-S,S}, [Pt(MeOcod){C(P(S)Ph₂)₃-S,S}], and [Rh(cod){C(P(S)Ph₂)₃}] are discussed in detail.The two -Ph₂P=S groups in the above complexes undergo a rapid intramolecular site exchange at ambient temperature in solution. Line shape analysis of variable temperature ³¹P{¹H} NMR data gives the following ΔG° for this dynamic exchange of coordinated and noncoordinated sulphur at 298 K. [Pd(n³-C₄H₇){CH(PPh₂)(P(S)Ph₂)₂-P,S)}]BF₄ 48 kJ/mol [Pd(n³-C₄H₇ ){C(P(S)Ph₂)₃-S,S}] 38 kJ/mol [Pt(MeOcod){C(P(S)Ph₂)₃-S,S}] 48 kJ/mol [Rh(cod){C(P(S)Ph₂)₃-S,S}] 46 kJ/mol



Chemical reactions, Complex compounds, Ligands