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RESEARCH PRODUCT

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

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The lithium salts of the chalcogenocarbonyl dianions [(E)C(PPh(2)S)(2)](2-) (E=S (4 b), Se (4 c)) were produced through the reactions between Li(2)[C(PPh(2)S)(2)] and elemental chalcogens in the presence of tetramethylethylenediamine (TMEDA). The solid-state structure of {[Li(TMEDA)](2)[(Se)C(PPh(2)S)(2)]}-[{Li(TMEDA)}(2)4 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)[(SPh(2)P)(2)CEEC(PPh(2)S)(2)]} ([Li(TMEDA)](2)7 b (E=S), [Li(TMEDA)](2)7 c (E=Se)), which are formally dimers of the radical anions [(E)C(PPh(2)S)(2)](-) (.) (E=S (5 b), Se (5 c)) with elongated central E--E bonds. Two-electron oxidation of the selenium-containing dianion 4 c with I(2) yielded the LiI adduct of a neutral selone {[Li(TMEDA)][I(Se)C(PPh(2)S)(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)][(SPh(2)P)(2)CSS(H)C(PPh(2)S)(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)}(2)4 c], [{LiI(TMEDA)}6 c]⋅C(7)H(8), [Li(TMEDA)](2)7 b⋅(CH(2)Cl(2))(0.33), [Li(THF)(2)](2)7 b, [Li(TMEDA)](2)7 c, [Li(TMEDA)]8 b⋅(CH(2)Cl(2))(2) and [Li([12]crown-4)(2)]8 b were determined and salient structural features are discussed.