Mechanism of Coupling of Alcohols and Amines To Generate Aldimines and H₂ by a Pincer Manganese Catalyst

Abstract

Acceptorless dehydrogenative coupling (ADC) of alcohols and amines using a manganese-based catalyst is able to produce aldimines, which have a wide reactivity, without underestimating the generation of a clean fuel, since as a result of this coupling, molecular hydrogen is also obtained. Therefore, the aldimine synthesis represents an interesting reaction from chemical and clean energy points of view. In this work, the computational study, via density functional theory (DFT) calculations, of a manganese-based catalyst for the acceptorless dehydrogenative coupling of alcohols and amines, together with the elucidation of its catalytic cycle using benzene as a solvent, is carried out. Calculations provided insight not only into the catalytic pathway but also into the noncatalyzed organic transformation to reach the desired aldimine, on the basis of the aldehyde generated in the catalytic cycle. The importance of the alternative isomers of the Mn-pincer complex, previously characterized experimentally, and the assisting role of alcohol or water are also described.

Phenoxylation of Alkynes through Mono‐ and Dual Activation Using Group 11 (Cu, Ag, Au) Catalysts

“…NCI plots computed by the NCIPLOT package, confirmed the significant additional non‐covalent interactions due to the aromatic rings of the IPr* ligand, whereas only the ones between the phenoxide and one of the aryl rings on the diphenylacetylene for the IMe based system (see Figure ). The plot for the IPr ligand is placed in between, and it confirms the effect of the substitution of phenyl by methyl groups, with much less favourable π‐π staking interactions . Thus, NCI plots and EDA analyses here unveil why the sterically more hindered IPr* ligand ends up showing less unfavourable kinetics and thermodynamics than expected for the C–O bond formation.…”

“…The plot for the IPr ligand is placed in between, and it confirms the effect of the substitution of phenyl by methyl groups, with much less favourable π-π staking interactions. [60][61][62][63][64] Thus, NCI plots and EDA analyses here unveil why the sterically more hindered IPr* ligand ends up showing less unfavourable kinetics and thermodynamics than expected for the C-O bond formation.…”

Study of the effect of the ligand structure on the catalytic activity of Pd@ ligand decorated halloysite: Combination of experimental and computational studies

“…Due to the low covalent character presented by the interaction between all the NH groups of the ligands and the oxygen atom of Hal a priori bonded to Pd, together with the H‐bonds, we computed the noncovalent interactions (NCI) plots using the NCIPLOT package, developed by Julia Contreras and co‐workers. Even though the NCI plots allow us to observe and evaluate only qualitatively the strength of the noncovalent interactions, in Figure we represented the results obtained with four different organic chains that stabilize the metal, by two strong bonds, together with two weaker interactions, confirming the MBO analysis undertaken above. In the representations, we plotted the isocontour obtained for a value of 0.5 on the reduced density gradient; whereas for the color scale we used the interval from −0.5 to 0.5 of the second density Hessian eigenvalue, going from red (repulsive) to blue (attractive).…”

Manganese Catalyzed Acceptorless Dehydrogenative Coupling Reactions

“…A lutidine based PNP‐pincer complex Mn‐1 was shown to be a highly efficient catalyst for the ADC of alcohol and amines yielding aldimines (Scheme a) . The catalysis works via metal‐ligand cooperation through the aromatization/dearomatization of the ligand as previously been described by the same group . Contemporarily, Kirchner et al.…”

“…The manganese hydride species thus generated releases a molecule of hydrogen under the reaction condition to generate the active catalyst and to continue the cycle. The produced aldehyde, on the other hand, undergo uncatalyzed reaction with an amine to form an aminal intermediate, which after the loss of a water molecule, gives imines …”