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 = ^<i>i</i>Pr): 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(PPh(2))(2)](-) with elemental chalcogens. The selenium-containing isopropyl derivative was synthesized by generating [H(2)C(P(i)Pr(2))(2)] via a reaction between [H(2)C(PCl(2))(2)] and 4 equiv of (i)PrMgCl prior to in situ oxidation with selenium followed by deprotonation with LiN(i)Pr(2). The solid-state structures of the lithium salts of the monochalcogeno anions TMEDA.Li[HC(PPh(2)E)(PPh(2))] (E = Se (Li7a), E = Te (Li7b)) and the dichalcogeno anions TMEDA.Li[HC(PR(2)Se)(2)] (R = Ph (Li8a), (i)Pr (Li8c)) revealed five- and six-membered LiEPCP and LiSePCPSe rings, respectively. The homoleptic group 12 complexes {M[HC(PPh(2)Se)(2)](2)} (M = Zn (9a), Hg (9b)) were prepared from Li8a and MCl(2) 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(PPh(2)Te)(2)] (Li8b), Li8c, 9a, and 9b were characterized in solution by multinuclear ((1)H, (7)Li, (13)C, (31)P, (77)Se, (125)Te, and (199)Hg) NMR spectroscopy. One-electron oxidation of Li8a and Li8c with iodine in a variety of organic solvents produced [H(2)C(PR(2)Se)(2)] (R = (i)Pr, 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(PR(2)Se)(2)](*) (R = (i)Pr, Ph).