Vanadium Insertion into CO2, CS2 and OCS: A Comparative Theoretical Study

The reactions of the ground-state V(s 2 d 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 4 A‘ ‘ and 4 A‘ 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 the three reactions are related to the molecular properties of CO 2, CS 2, and OCS.