An official website of the United States government
The catalytic effects of iridium pincer complexes for the hydrogenation of carbon dioxide were investigated with the Unified Reaction Valley Approach (URVA), exploring the reaction mechanism along the reaction path traced out by the reacting species on the potential energy surface. Further details were obtained with the Local Mode Analysis performed at all stationary points, complemented by the Natural Bond Orbital and Bader’s Quantum Atoms in Molecules analyses. Each of the five reaction paths forming the catalytic cycle were calculated at the DFT level complemented with DLPNO-CCSD(T) single point calculations at the stationary points. For comparison, the non-catalytic reaction was also investigated. URVA curvature profiles identified all important chemical events taking place in the non-catalyzed reaction and in the five reactions forming the catalytic cycle, and their contribution to the activation energy was disclosed. The non-catalytic reaction has a large unfavorable activation energy of 76.3 kcal/mol, predominately caused by HH bond cleave in the H2 reactant. As shown by our study, the main function of the iridium pincer catalyst is to split up the one–step non-catalytic reaction into an energy efficient multistep cycle, where HH bond cleavage is replaced by the cleavage of a weaker IrH bond with a small contribution to the activation energy. The dissociation of the final product from the catalyst requires the cleavage of an IrO bond, which is also weak, and contributes only to a minor extent to the activation energy. This, in summary, leads to the substantial lowering of the overall activation barrier by about 50 kcal/mol for the catalyzed reaction. We hope that this study inspires the community to add URVA to their repertoire for the investigation of catalysis reactions.
more »
« less
Unexpected C–O Bond Cleavage by a Copper–Phosphido Compound
Copper methoxide compound IPrCuOMe was unexpectedly formed in a reaction of IPrCuPPh2 with methyl acrylate. The alkoxide product was identified from the reaction mixture spectroscopically and structurally characterized. This C–O bond cleavage reaction likely depends on nucleophilicity of the Cu–P bond of IPrCuPPh2.
more »
« less
- Award ID(s):
- 2101766
- PAR ID:
- 10428233
- Date Published:
- Journal Name:
- Molbank
- Volume:
- 2023
- Issue:
- 2
- ISSN:
- 1422-8599
- Page Range / eLocation ID:
- M1659
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Transition metal‐catalyzed C−H bond oxidation of free carboxylic acid stands as an economic, selective, and efficient strategy to generate lactones, hydroxylated products, and acetoxylated products and attracts much of the chemists’ attention. Herein, we performed a density functional theory study on the mechanism and selectivity in Pd‐catalyzed and MPAA ligand‐enabled C−H bond acetoxylation reaction. It was found that the ligand, base, and substrate are important in determining the reaction mechanism and the selectivity. The acetic anhydride additive is critical in leading the reaction to be acetoxylation, instead of the lactonization, through a facile σ‐bond metathesis mechanism that leads to the Pd‐OAc in‐termediate. Our study sheds light on the further development of transition metal‐catalyzed C−H bond oxidation reactions.more » « less
-
Enzymatic carbon‒carbon (C–C) bond formation reactions have become an effective and invaluable tool for designing new biological and medicinal molecules, often with asymmetric features. This review provides a systematic overview of key C–C bond formation reactions and enzymes, with the focus of reaction mechanisms and recent advances. These reactions include aldol reaction, Henry reaction, Knoevenagel condensation, Michael addition, Friedel-Crafts alkylation and acylation, Mannich reaction, Morita–Baylis–Hillman (MBH) reaction, Diels-Alder reaction, acyloin condensations via Thiamine Diphosphate (ThDP)-dependent enzymes, oxidative and reductive C–C bond formation, C–C bond formation through C1 resource utilization, radical enzymes for C–C bond formation, and other C–C bond formation reactions.more » « less
-
High-valent nitridorhenium( v ) complexes containing PNP ligands: implications of ligand flexibilityThe synthesis of (PNP)Re(N)X (PNP = [2-P(CHMe 2 ) 2 -4-MeC 6 H 3 ] 2 N, X = Cl and Me) complexes is described. The methylnitridorhenium complex 3 was found to react differently with CO and isocyanides, leading to the isolation of a Re( v ) acyl complex 4 and an isocyanide adduct 6 . Two parallel pathways were observed for the reaction of 3 with CO: (1) CO inserts into the Re–Me bond to afford 4 , and (2) 3 isomerizes by distortion of the aryl backbone of the PNP ligand to afford the isomer 3′ . This is followed by the reaction of 3′ with CO to afford the tricarbonyl complex 5 , which was fully characterized. The contrasting reaction of 3 with 2,6-dimethylphenyl isocyanide lends further support for the proposed isomerization pathway. DFT (M06) calculations suggest that insertion of CNR into the Re–Me bond (27.2 kcal mol −1 ) is inaccessible at room temperature. Instead the substrate adds to the metal center via the most accessible face i.e. syn to the rhenium–nitrido bond, to afford 6 . The addition of CO to isomer 3′ is proposed to proceed with a similar mechanism to 2,6-dimethylphenyl isocyanide.more » « less
-
A systematic investigation into the effects of acids and hydrogen bond acceptors on the reaction rates and equilibria of enamine formation is reported. Acids can accelerate the reaction but do not change the reaction equilibria. In comparison, hydrogen bond acceptors facilitate the enamine formation via their strong hydrogen bonding interaction with the water generated in the reaction.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/M1659
