N- versus P-co-ordination for N–B and P–B bonded BH3 adducts for various phosphinamine ligands – An experimental and computational study

The reaction between phosphinamines [Ph2PNH(CHPh2)] (1), [Ph2PNH(CPh3)] (2) [Ph2PNH(CMe3)] (3), [Ph2PNH(2,6-Me2C6H3)] (4), and [Ph2PNH(2,6-iPr2C6H3)] (5) with BH3.SMe2 yields corresponding adduct [Ph2P(BH3)NH(CHPh2)] (1a), [Ph2P(BH3)NH(CPh3)] (2a), [Ph2P(BH3)NH(CMe3)] (3a), [Ph2P(BH3)NH(2,6-Me2C6H3)] (4a), and [Ph2P(BH3)NH(2,6-iPr2C6H3)] (5a) respectively. The solid state structures of all the compounds were established by single crystal X-ray diffraction analysis and in the solid state, all the compounds reveal that the phosphorus atom is preferably coordinated to the boron atom. Density functional theory (DFT) based electronic structure calculations were carried out taking various model phosphinamines to react with borane to establish the fact that the basicity of nitrogen atom adjacent to phosphorus in phosphinamines is reduced and thereby least preferred for coordination with borane.