ABINITIO CALCULATIONS ON BORYLPHOSPHINES - PREDICTION OF A SYNERGISTIC SUBSTITUENT EFFECT IN DIBORYLPHOSPHINE

The results of ab initio calculations on the borylphosphines, H3-nP(BH2)n, n = 1-3, are reported. The barrier to rotation of one BH2 is found to increase on going from n = 1 to n = 2, so that the two BH2 groups in diborylphosphine appear to act cooperatively, rather than competitively. The origin of the apparent synergistic substituent effect in diborylphosphine is shown to be the ability of one conjugated BH2 group to reduce dramatically the energetic cost of planarizing phosphorus. This permits the formation of stronger P-B π-bonds in HP(BH2)2 than in H2PBH2. © 1990, American Chemical Society. All rights reserved.