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

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 EE 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.