The Mechanisms of the Reactions of W and W+ with COx (x = 1, 2): A Computational Study

The mechanisms of the reactions of W and W + with CO x ( x = 1, 2) were studied at the CCSD(T)/[SDD + 6-311G(d)]//B3LYP/[SDD + 6-31G(d)] level of theory. It was shown that the gas-phase reaction of W with CO 2 proceeds with a negligible barrier via an insertion pathway, W( 7 S) + CO 2 ( 1 A 1 ) → W(η 2 -OCO)( 6 A‘) → OW(η 1 -CO)( 1 A) → WO ( 3 Σ + ) + CO( 1 Σ). This oxidation process is calculated to be exothermic by 32.4 kcal/mol. Possible intermediates of this reaction are the W(η 2 -OCO) and OWCO complexes, among which the latter is 37.4 kcal/mol more stable and lies 39.7 and 7.3 kcal/mol lower than the reactants, W( 7 S) + CO 2 ( 1 A 1 ), and the products, WO ( 3 Σ + ) + CO( 1 Σ), respectively. The barrier separating W(η 2 -OCO) from OWCO is 8.0 kcal/mol (relative to the W(η 2 -OCO) complex), which may be characterized as a W +δ −(CO 2 ) -δ charge-transfer complex. Ionization of W does not change the character of the reaction of W with CO 2: the reaction of W + with CO 2, like its neutral analog, proceeds via an insertion pathway and leads to oxidation of the W-center. The overall reaction W + ( 6 D) + CO 2 ( 1 A 1 ) → W(η 1 -OCO) + ( 6 A) → OW(η 1 -CO) + ( 4 A) → WO + ( 4 Σ + ) + CO( 1 Σ) is calculated to be exothermic by 25.4 kcal/mol. The cationic reaction proceeds with a somewhat large (9.9 kcal/mol) barrier and produces two intermediates, W(η 1 -OCO) + ( 6 A) and OW(η 1 -CO) + ( 4 A). Intermediate W(η 1 -OCO) + ( 6 A) is 20.0 kcal/mol less stable than OW(η 1 -CO) + ( 4 A), and separated from the latter by a 35.2 kcal/mol barrier. Complex W(η 1 -OCO) + ( 6 A) is characterized as an ion−molecular complex type of W + -(CO 2 ). Gas-phase reactions of M W/W + with CO lead to the formation of a W−carbonyl complex M(η 1 -CO) for both M W and W + . The C−O insertion product, OMC, lies by 5.2 and 69.3 kcal/mol higher than the corresponding M(η 1 -CO) isomer, for M W and W +, respectively, and is separated from the latter by a large energy barrier.