Synthesis and Redox Behaviour of the Chalcogenocarbonyl Dianions [(E)C(PPh₂S)₂]2−: Formation and Structures of Chalcogen–Chalcogen Bonded Dimers and a Novel Selone†

摘要

The lithium salts of the chalcogenocarbonyl dianions [(E)C(PPh₂S)₂]2− (E=S (4 b), Se (4 c)) were produced through the reactions between Li₂[C(PPh₂S)₂] and elemental chalcogens in the presence of tetramethylethylenediamine (TMEDA). The solid-state structure of {[Li(TMEDA)]₂[(Se)C(PPh₂S)₂]}—[{Li(TMEDA)}₂4 c]—was shown to be bicyclic with the Li+ cations bis-S,Se-chelated by the dianionic ligand. One-electron oxidation of the dianions 4 b and 4 c with iodine afforded the diamagnetic complexes {[Li(TMEDA)]₂[(SPh₂P)₂CEEC(PPh₂S)₂]} ([Li(TMEDA)]₂7 b (E=S), [Li(TMEDA)]₂7 c (E=Se)), which are formally dimers of the radical anions [(E)C(PPh₂S)₂]−. (E=S (5 b), Se (5 c)) with elongated central EE bonds. Two-electron oxidation of the selenium-containing dianion 4 c with I₂ yielded the LiI adduct of a neutral selone {[Li(TMEDA)][I(Se)C(PPh₂S)₂]}—[{LiI(TMEDA)}6 c]—whereas the analogous reaction with 4 b resulted in the formation of 7 b followed by protonation to give {[Li(TMEDA)][(SPh₂P)₂CSS(H)C(PPh₂S)₂]}—[Li(TMEDA)]8 b. Attempts to identify the transient radicals 5 b and 5 c by EPR spectroscopy in conjunction with DFT calculations of the electronic structures of these paramagnetic species and their dimers are also described. The crystal structures of [{Li(TMEDA)}₂4 c], [{LiI(TMEDA)}6 c]C₇H₈, [Li(TMEDA)]₂7 b(CH₂Cl₂)_0.33, [Li(THF)₂]₂7 b, [Li(TMEDA)]₂7 c, [Li(TMEDA)]8 b(CH₂Cl₂)₂ and [Li([12]crown-4)₂]8 b were determined and salient structural features are discussed.