P-chiral phosphinoselenoic chlorides and phosphinochalcogenoselenoic acid esters:: Synthesis, characterization, and conformational studies

P-Chiral alkyl or aryl phenylphosphinoselenoic chlorides were obtained by reacting PhPCl2 with Grignard reagents and elemental selenium. P-Chiral dialkyl chlorides were also obtained by treating PCl3 with two different Grignard reagents and elemental selenium. The structure of the chloride was determined by X-ray molecular structure analysis. P-Chiral phosphinochalcogenoselenoic acid esters bearing a P=Se double bond were synthesized by treating the chlorides with alkali metal alkoxide and chalcogenolates, whereas those bearing a P-Se single bond were obtained by sequential treatment of the chlorides with sodium hydroxide, sulfide or selenide, and alkyl iodides. X-ray molecular structure analyses of esters showed that they adopted gauche conformations. The computational results supported the observed conformational preference. Natural bond orbital analyses of the model compounds showed that two types of nonbonding orbital interactions, n(E') --> sigma*(P=E) and n(E) --> sigma*(P-E'), are important in these compounds. Linear correlations were observed between the experimental Se-77 NMR chemical shifts or the coupling constants of P-Se bonds in the esters and the calculated P-Se bond lengths of the model compounds.