Computational Studies of the Energetics and Reaction Pathways of Molecular Transformations of Benzoheterocycles on Triosmium Clusters

Density functional theory (DFT) calculations have been performed on the series of complexes Os 3 (CO) 10 - n (μ m -η 2 -(L-H))(μ-H) (L = benzoxazole ( 1 ), benzothiazole ( 2 ), quinoline ( 3 ), indoline ( 4 ), 1,2,3,4-tetrahydroquinoline ( 5 ); for 1 − 5, n = 0; m = 2; for 1 ‘− 3 ‘, n = 1, m = 3) and on the precursors to these complexes, Os 3 (CO) 10 (CH 3 CN) 2 and Os 3 (CO) 12 . The optimized geometry of the coordinately unsaturated 44e system Os 3 (CO) 10 is used as a reference point for evaluating the relative binding energies of the heterocycles and the acetonitrile and carbonyl ligands. A discussion of how the intramolecular trans/cis isomerization of Os 3 (CO) 10 (CH 3 CN) 2 relates to the reactivity of this complex with the heterocyclic ligand is presented. The relative binding energies of the benzoheterocycles provide insight into the relative stability of the intermediates involved in the subsequent formation of the μ 3 -nonacarbonyl derivatives Os 3 (CO) 9 (μ 3 -η 2 -(L-2H))(μ-H) 2 (L = indoline ( 4 ‘), 1,2,3,4-tetrahydroquinoline ( 5 ‘)) from their μ-decacarbonyl precursors ( 4 and 5 ). The transition states for the N−H bond activation/decarbonylation that constitutes the transformation of 4 into 4 ‘ have also been investigated. A discussion of the atomic and ligand group natural charges based on natural population analysis (NPA) calculations is presented as it relates to the donor abilities of the heterocycles and the polarization of the carbonyl ligands for the various structural types.