Synthetic and structural studies of lithium complexes of selenophosphorus ligands

The synthesis and characterization of three lithium complexes of selenophosphorus anions are presented: namely, a lithium selenophosphinite [Ph(2)PSeLi.TMEDA](2), 1; a lithium diselenophosphinate [Ph(2)PSe(2)Li.THF.TMEDA], 2; and a dilithiated triselenophosphonate complex [(c-C(6)H(11))PSe(3)Li(2).2TMEDA], 3. The selenophosphinite 1 was prepared using the insertion reaction of elemental Se into the P-Li bond of lithiated diphenylphosphine, and this was then oxidized by additional Se to give 2. Dilithiation of a primary phosphine followed by reaction with 3 equiv of elemental Se gave the triselenophosphonate 3. X-ray crystallography reveals 1 to be a dimer in the solid state with two different bridging coordination modes exhibited by the selenophosphinite ligands, and 2 and 3 to both be monomeric. In addition, solution studies using multinuclear ((31)P and (77)Se) and variable-temperature NMR show the anionic charge to be predominantly localized on the Se in 1, and fully delocalized over the PSe(2) and PSe(3) moieties respectively in 2 and 3.