MOLECULAR-ORBITAL STUDY OF BONDING AND STABILITY ON RH(I)-ALKYNE ISOMERS

Ab initio and extended Huckel calculations were carried out on the iso mers of trans-RhCl(eta(2)-C2H2)(PH3)(2) (1). Due to pi-back donation i n 1 complex, the rotational energy barrier of alkyne ligand is compute d to be in the range of 18.6-25.2 kcal/mol at MP4 levels. The optimize d hydrido-alkynyl complex (2) at ab initio level has the distorted tri gonal bipyramidal structure. Vinylidene complex (3) is computed to be more stable than 1 complex by 17.1 kcal/mol at MP4//MP2 level. The sta bilities of isomers show similar trend at the various level calculatio ns, that is, EHT, MP4//HF, and MP4//MP2 levels. The optimized geometri es at ab initio level are in reasonable agreement with experimental da ta. A detailed account of the bonding in each isomers (1-3) have been carried out in terms of orbital analyses.