Structural and Spectroscopic Studies of the PCP-Bridged Heavy Chalcogen-Centered Monoanions [HC(PPh2E)(PPh2)]− (E = Se, Te) and [HC(PR2E)2]− (E = Se, Te, R = Ph; E = Se, R = iPr): Homoleptic Group 12 Complexes and One-Electron Oxidation of [HC(PR2Se)2]−

Abstract

Selenium- and tellurium-containing bis(diphenylphosphinoyl)methane monoanions were prepared by oxidation of the anion [HC(PPh2)2]− with elemental chalcogens. The selenium-containing isopropyl derivative was synthesized by generating [H2C(PiPr2)2] via a reaction between [H2C(PCl2)2] and 4 equiv of iPrMgCl prior to insitu oxidation with selenium followed by deprotonation with LiNiPr2. The solid-state structures of the lithium salts of the monochalcogeno anions TMEDA·Li[HC(PPh2E)(PPh2)] (E = Se (Li7a), E = Te (Li7b)) and the dichalcogeno anions TMEDA·Li[HC(PR2Se)2] (R = Ph (Li8a), iPr (Li8c)) revealed five- and six-membered LiEPCP and LiSePCPSe rings, respectively. The homoleptic group 12 complexes {M[HC(PPh2Se)2]2} (M = Zn (9a), Hg (9b)) were prepared from Li8a and MCl2 and shown to have distorted-tetrahedral structures; the nonplanarity of the carbon center in the PC(H)P unit of the Zn complex 9a is attributed to crystal-packing effects. The complexes Li7a, Li7b, Li8a, TMEDA·Li[HC(PPh2Te)2] (Li8b), Li8c, 9a, and 9b were characterized in solution by multinuclear (1H, 7Li, 13C, 31P, 77Se, 125Te, and 199Hg) NMR spectroscopy. One-electron oxidation of Li8a and Li8c with iodine in a variety of organic solvents produced [H2C(PR2Se)2] (R = iPr, Ph) as the final product, presumably owing to hydrogen abstraction from the solvent. DFT calculations revealed a significant contribution from the p orbital on carbon to the SOMO of the radicals [HC(PR2Se)2]• (R = iPr, Ph).