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 [Ph2PSeLi·TMEDA]2, 1; a lithium diselenophosphinate [Ph2PSe2Li·THF·TMEDA], 2;
and a dilithiated triselenophosphonate complex [(c-C6H11)PSe3Li2·2TMEDA], 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 (31P and 77Se) and variable-temperature NMR show the anionic
charge to be predominately localized on the Se in 1, and fully delocalized over the PSe2 and PSe3 moieties
respectively in 2 and 3.