AB-INITIO MOLECULAR-ORBITAL STUDY OF STRUCTURE AND NMR B-11 CHEMICAL-SHIFTS OF LEWIS BASE ADDUCTS OF CO, NH3, PF3, AND PH3 WITH SMALL NIDO-BORANES, B3H7 AND B4H8

The geometries, formation energies, and NMR B-11 chemical shifts of B3 H7CO, B3H7NH3, B4H8CO, B4H8PH3, and B4H8PF3, Lewis base adducts of the B3H7 and B4H8 nido-boranes have been investigated by the ab initio mo lecular orbital method. MP2/6-31G optimized geometries and calculated NMR chemical shifts are in good agreement with experiment. Lewis base s cause pronounced elongation of BB distances and a strong upfield che mical shift for the attacked boron atoms.