Phosphorus-31 and carbon-13 nuclear magnetic resonance studies of unsymmetrical tetra-alkyldiphosphanes R1R2PPMe2 and R1R2PPEt2

Abstract

A series of unsymmetrical tetra-alkyldiphosphanes of general formulae R1R2PPMe2 and R1R2PPEt2(with R1, R2= Me, Et, Pri, But) have been obtained by scrambling reactions between the corresponding symmetrical diphosphanes in CH2Cl2 solution and have been studied by n.m.r. spectroscopy in situ. Values of 31P and 13C chemical shifts, together with (P,P) and (P,C) coupling constants, are reported and discussed in relation to substituent effects and conformation. The parameter 1JPC+2JPC is shown to be a good predictor of the preferred rotamer, and it is concluded that 1JPC and 2JPC must be opposite in sign.