Molecular Mechanism of the Mononuclear Copper Complex-Catalyzed Water Oxidation from Cluster-Continuum Model Calculations

Cluster-continuum model calculations were conducted to decipher the mechanism of water oxidation catalyzed by a mononuclear copper complex. Among various O-O bond formation mechanisms investigated in this study, the most favorable pathway involved the nucleophilic attack of OH^- onto the ^.+ L-Cu^II -OH^- intermediate. During such process, the initial binding of OH^- to the proximity of ^.+ L-Cu^II -OH^- would result in the spontaneous oxidation of OH^- , leading to OH⋅ radical and Cu^II -OH^- species. The further O-O coupling between OH⋅ radical and Cu^II -OH^- was associated with a barrier of 14.8 kcal mol^-1 , leading to the formation of H₂ O₂ intermediate. Notably, the formation of "Cu^III -O^.- " species, a widely proposed active species for O-O bond formation, was found to be thermodynamically unfavorable and could be bypassed during the catalytic reactions. On the basis the present calculations, a catalytic cycle of the mononuclear copper complex-catalyzed water oxidation was proposed.

Unmasking the Action of Phosphinous Acid Ligands in Nitrile Hydration Reactions Catalyzed by Arene-Ruthenium(II) Complexes

The catalytic hydration of benzonitrile and acetonitrile has been studied by employing different arene-ruthenium(II) complexes with phosphinous (PR2OH) and phosphorous acid (P(OR)2OH) ligands as catalysts. Marked differences in activity were found, depending on the nature of both the P-donor and η(6)-coordinated arene ligand. Faster transformations were always observed with the phosphinous acids. DFT computations unveiled the intriguing mechanism of acetonitrile hydration catalyzed by these arene-ruthenium(II) complexes. The process starts with attack on the nitrile carbon atom of the hydroxyl group of the P-donor ligand instead of on a solvent water molecule, as previously suggested. The experimental results presented herein for acetonitrile and benzonitrile hydration catalyzed by different arene-ruthenium(II) complexes could be rationalized in terms of such a mechanism.

THE MECHANISM OF ACID-CATALYZED DECARBOXYLATION OF PYRROLE-2-CARBOXYLIC ACID: INSIGHTS FROM CLUSTER-CONTINUUM MODEL CALCULATIONS

The decarboxylation of pyrrole-2-carboxylic acid comprises the addition of water to the carboxyl group and the C–C bond cleavage leading to the protonated carbonic acid. Herein possible concerted and stepwise mechanisms for the C-protonated and O-protonated pathways were extensively investigated by using the cluster-continuum model. The calculated results indicate that the initial hydration or the nucleophilic attack of water at the carbonyl group of both C- and O-protonated derivatives is the rate-determining step for the overall reaction, and the O-protonated pathway will dominate the whole reaction. The predicted activation Gibbs energies for the overall reaction initialized by the O-protonated species fall in the range of 83.3 ∼ 123.0 kJ/mol, showing good agreement with experimental values of 91.6 ∼ 101.3 kJ/mol. On the basis of extensive calculations, the remarkable dependence of the predicted mechanisms and thermodynamic values on the number of explicit water molecules in the cluster-continuum model was discussed.

Merging domino and redox chemistry: stereoselective access to di- and trisubstituted β,γ-unsaturated acids and esters

Merging is the game! The coupling of a domino reaction and an internal neutral redox reaction constitutes an excellent manifold for the stereoselective synthesis of di- and trisubstituted olefins featuring a malonate unit, an ester, or a free carboxylic acid as substituents at the allylic position (see scheme; MW=microwave). The reaction utilizes simple starting materials (propargyl vinyl ethers), methanol or water as solvents, and a very simple and bench-friendly protocol.

Acid-catalyzed reactions of twisted amides in water solution: competition between hydration and hydrolysis

The acid-catalyzed reactions of twisted amides in water solution were investigated by using cluster-continuum model calculations. In contrast to the previous widely suggested concerted hydration of the C=O group, our calculations show that the reaction proceeds in a practically stepwise manner, and that the hydration and hydrolysis channels of the C-N bond compete. The Eigen ion (H(3)O(+)) is the key species involved in the reaction, and it modulates the hydration and hydrolysis reaction pathways. The phenyl substitution in the twisted amide not only activates the N-CO bond, but also stabilizes the hydrolysis product through n(N)→π(phenyl) delocalization, leading exclusively to the hydrolysis product of the ring-opened carboxylic acid. Generally, the twisted amides are more active than the planar amides, and such a rate acceleration results mainly from the increase in exothermicity in the first N-protonation step; the second step of the nucleophilic attack is less affected by the twisting of the amide bond. The present results show good agreement with the available experimental observations.