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

Abstract

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 E[BOND]E 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.