Alkali Metal Phenylphosphandiides, [M2PnPhn] (M = Li, Na)

Abstract

The reaction of phenyldichlorophosphane, PhPCl2, a commercially important precursor for organophosphorus compounds, with lithium and sodium as reducing metals was re-investigated with the aim to well-characterize the resulting oligophosphandiides, [M2(PnPhn)(solv)x] (M = Li, Na). Experimental conditions for the optimal formation of these compounds were found for both series with M = Li and M = Na and several of these were crystallized and characterized by X-ray diffraction studies. As a result, we find that sodium strongly prefers ion triple structures [M2(PnPhn)(solv)x] over solvent-separated ion pairs, [M(solv)m]+[MPnPhn(solv)n]?, which have a higher tendency to form with M = Li. Also, while [Na2(P4Ph4)(solv)x] retains its structure in thf solution, [Li2(P4Ph4)(solv)x] partially dissociates into the radical anion (Ph2P2).? which is detected by EPR spectroscopy. The knowledge about the structures and the behavior of the alkali metal diphosphandiides allows us to propose a reaction mechanism for their formation.