Structural Characterization of the Solvate Complexes of the Lithium Salts of Diorganophosphides and Phosphinideneborates; A Pathway to Phosphorus-Boron Double Bonds

Abstract
The structures of several solvated lithium diorganophosphides are described. These may take a variety of structures including chain-like polymers with alternating Li+ and PR2 groups, dimeric species with PR2 groups bridging two Li+ ions or mononuclear species having terminal PR2 groups which have pyramidal geometries at phosphorus. The Li+ ions in all structures are solvated by either THF or Et2O bases. Separation of the Li+ can be effected using 12-crown-4 to coordinate Li+ as [Li(12-crown-4)2]+ affording free [PR2] counterions. An extension of these techniques has led to the synthesis of the first compounds which have B-P double bonds. These are the compounds [Li(Et2O)2PRBMes2] and [Li(12-crown-4)2][PRBMes2](R=Ph, C6H11,Mes) which have B-P bond lengths of 1.82 – 1.83Å.