Nuclear magnetic resonance investigation of diastereoisomerism in the unsymmetrical tetra-alkyldiphosphanes R1R2PPMeEt(R1R2= ButPri, ButEt, ButMe, PriEt, and Pri2)

Abstract

Three new unsymmetrical diphosphanes of type R¹R²PPMeEt (R¹R²= Bu^tPrⁱ, Bu^tEt, Bu^tMe, and PrⁱEt) and one of type R₂PPMeEt (R = Prⁱ) have been prepared by the scrambling reaction between symmetrical diphosphanes in CH₂Cl₂, and characterised in situ by ³¹P n.m.r. spectroscopy. The chemical shifts and J(PP) coupling constants are reported and discussed. The compounds R¹R²PPMeEt exist in diastereomeric forms, slightly differing in population under the equilibrium conditions employed. They provide clear examples of the variation of n.m.r. parameters with chirality: the more stable form has the lower ³¹P chemical shift, σ(P), and the larger |¹J(PP)| in each case.