Dimerization Processes of Square Planar [PtII(tbpy)(dithiolato•)]+ Radicals

The preparation and structural characterization of the neutral, square planar complexes [PtII(tbpy)(A)] (1), [PtII(tbpy)(B)] (2), and [PtII(PPh3)2(B)] (3) have been accomplished, where (tbpy) = 4,4‘-di-tert-butylpyridine, (A)2- = 3,6-bis(trimethylsilyl)-1,2-benzenedithiolate(2−), and (B)2- = 1,2-bis(4-tert-butylphenyl)ethylene-1,2-dithiolate(2−) and (A•)1- and (B•)1- represent the corresponding monoanionic radicals. Electrochemical and chemical one-electron oxidation of 1 and 2 in CH2Cl2 solution affords the monomeric monocations [PtII(tbpy)(A•)]+ (1a) and [PtII(tbpy)(B•)]+ (2a), both of which possess an S = 1/2 ground state. The corresponding spin doublet monocationic dimers [PtII 2(tbpy)2(A)(A•)]+ (1b) and [PtII 2(tbpy)2(B)(B•)]+ (2b) were electrochemically generated in solution (50% oxidation) and identified by X-band EPR spectroscopy. Complete one-electron oxidation of 1 and 2 yielded the diamagnetic dimers [PtII 2(tbpy)2(A•)2]2+ (1c) and [PtII 2(tbpy)2(B•)2]2+ (2c) which are in equilibrium with the corresponding paramagnetic monomers 1a and 2a in solution. The crystal structure of [PtII 2(tbpy)2(B•)2](PF6)2·3CH2Cl2 (2c) revealed a centrosymmetric, lateral dimer whose bridging part is a PtII 2(μ2-S)2 rhomb; the metal ions possess a square based pyramidal geometry. Solid-state sulfur K-edge X-ray absorption spectra of 1, 2, 2a, 2c, and [PtII(B•)2]0 (4) have been recorded, which clearly show that a sulfur-centered radical (B•)1- is present in 2a, 2c, and 4. The absence of ligand-based radicals in 1 and 2 is also clearly established. One-electron oxidation of [Pt(PPh3)2(B)] (3) afforded only the spin doublet species [PtII(PPh3)2(B•)]+ (3a); no dimer formation was detected. Synthesis and crystal structure of square planar [PtII(B•)2]0·thf are also reported.