Vanadium Insertion into CO_2, CS_2 and OCS: A Comparative Theoretical Study

摘要

The reactions of the ground-state V(s~2d~3) atom with CO_2, CS_2, and OCS molecules have been studied at the B3LYP level of density functional theory in order to compare the insertion process for these three isovalent molecules. The relative stabilities of the adduct and insertion forms are calculated. The reaction barrier between these two forms are estimated for each system from the ~4A" and ~4A' potential energy curves defined in terms of the C-X (X=O,S) intrinsic reaction coordinate. The barrier to metal insertion from the side-on structure is rather low (ca 4 kcal/mol) for CO_2 and CS_2, however, whereas V(CO_2) is well above the OVCO insertion product, the V(CS_2) complex is only 4.2 less stable than SVCS. Consequently, coordination of CS_2 to metal centers is stronger than that of CO_2. Our calculations indicate no energy barrier for the insertion of V in the CS bond of OCS, whereas the insertion in the CO bond is less favored than in CO_2. We show that each insertion reaction proceeds on a single potential energy surface. Differences in the energetics of three reactions are related to the molecular properties of CO_2, CS_2, and OCS.