THEORETICAL-STUDIES OF SIMPLE ORGANOBORON COMPOUNDS - STRUCTURES AND STABILITIES OF BC2H4 ISOMERS

An ab initio study of the BC2H4 has been carried out. Several isomers have been studied: boron-ethylene complexes resulting from perpendicul ar and sigma interactions, boron-methylcarbene type structures, open a nd cyclic insertion products with a B-H bond, and isomers with two B-H bonds. Geometries at the second-order Moller-Plesset level have been obtained for ten species, and their characteristics have been tested t hrough computation of vibrational frequencies. Special attention has b een paid to their molecular structure, trying to rationalize the bondi ng in these species, particularly in the case of cyclic isomers. Elect ronic energies have been computed at the fourth-order Moller-Plesset l evel. Our theoretical calculations predict that the global minimum is the H2BCCH2 isomer (B-2(2) electronic state), with the HBH plane perpe ndicular to the CCH2 moiety, and that it lies about 66 kcal mol(-1) (2 76 kJ mol(-1)) below groundstate boron+ethylene. Nevertheless there ar e other isomers which are also quite stable and might be accessible to experimental detection, such as HBCHCH2 and H2BCHCH (both with (2)A' electronic states) which lie 8 (33.5) and 13 kcal mol(-1) (54.4 kJ mol (-1)), respectively, above the global minimum, as well as two cyclic s tructures, the insertion product HBC2H3((2)A '') and the boron-ethylen e pi-complex BC2H4 ((2)A(1)), which are relatively stable since they l ie 12 (50) and 22 kcal mol(-1) (99 kJ mol(-1)), respectively, higher t han H2BCCH2.