High Atom-Economical One-Pot Synthesis of Secondary Phosphines and Their Borane Complexes Using Recycling Phosphorus Donor Reagent

A general new method for the one-pot preparation of secondary phosphines 11 and in situ generation of their borane complexes 12 is described. This method consists of the sequential addition, at room temperature, of equivalent amounts of R1MgBr and R2MgBr to 1 equiv of the phosphorus atom donor reagent 1. Final treatment with water gives secondary phosphines R1R2PH (or the corresponding phosphine−borane complexes if treated with BH3·THF) and the end product 6, which can be recycled.