Platinum(II) Complexes Bearing a Thiolate/Thioether Ligand - Hemilability vs. Dealkylation

Substitution of the chloro ligands of cis-[Pt(PEt3)(2)Cl-2] by 4-methylthio-2-thioxo-1,3-dithiole-5-thiolate (L) leads to the thiolato complexes trans-[Pt(PEt3)(2)ClL] (2) and trans-[Pt(PEt3)(2)L-2] (1), which have been characterised by X-ray crystallography. In the solid state, the square planar arrangement is capped by an endocyclic sulfur atom of L, which gives rise to distorted square-pyramidal and pseudooctahedral geometries for 2 and 1, respectively. Complex 1 coexists in solution with [Pt(PEt3)(eta(1)-L)(eta(2)-L)] (3), which results from the reversible dissociation of one phosphane ligand. The combination of eta(1)-(thiolato) and eta(2)-(thiolato/thioether) L in 3 has been established by variable-temperature H-1 NMR spectroscopy and crystal structure determination. The eta(2)-coordination mode of L is also observed in cis-[Pt(PEt3)(2)L](+) (4), which results from the abstraction of the chloro ligand of 2 by excess TlPF6. An S-demethylation reaction occurs when 1 is heated in acetonitrile to yield the structurally-characterised dithiolene complex [Pt(PEt3)(2)(dmit)] (5) (dmit(2-) = 2-thioxo-1,3-dithiole-4,5-dithiolate) and MeL. Treatment of cis-[Pt(PPh3)(2)Cl-2] with 2 equiv. of L leads to a mixture of [Pt(PPh3)(2)(dmit)] (6) and [Pt(PPh3)(eta(1)-L)(eta(2)-L)] (7). Complex 7 predominates in solution over its parent compound, [Pt(PPh3)(2)L-2]. The identification of CH3Cl by H-1 NMR spectroscopy proves that [Pt(PPh3)(2)ClL] is involved as an intermediate in the demethylation process. The reaction of L with platinum precursors that are blocked in a cis arrangement by chelation of 1,1-bis(diphenylphosphanyl) methane (dppm) and 1,1-bis(diphenylphosphanyl) ethane (dppe) leads to the formation of the thiolato complexes cis-[Pt(eta(2)-dppm)L-2] (8) and cis-[Pt(eta(2)-dppe)L-2] (9). The solid-state structure of 8 reveals the occurrence of an additional weak interaction between a thiomethyl group and the platinum centre (Pt-S 3.073 angstrom).