General and Efficient One-Pot Synthesis of Tertiary Phosphane-Borane Complexes Containing Different Alkyl Groups and In Situ Facile Recycling of the Phosphorus Donor Reagent

Tertiary symmetric and asymmetric phosphane-borane complexes containing different alkyl groups, including bulky groups, can be obtained by the addition of different Grignard reagents to benzothiadiphosphole 1 followed by direct complexation with BH3·THF. Treatment of the resulting mixture with PCl3 led to the reformation of the starting reagent 1, which was recovered from the reaction mixture by simple crystallization. The phosphane complexes were purified by chromatography of the mother liquor. This procedure is highly atom-economic and environmentally friendly. All the reaction intermediates were identified