Density functional theory (DFT) calculations were performed to elucidate the detailed mechanism of catalytic amide hydrogenation mediated by a Ru-PNNH complex bearing a tridentate ligand. Three key reactive sites were identified within the catalyst framework: the methylene group on the phosphine side arm (C1), the methylene group on the amine side arm (C4), and the amino group directly coordinated to the Ru center (N1). The catalytic cycle proceeds through three sequential stages: precatalyst activation, deamination, and aldehyde reduction. The deamination step in stage II, with a free energy barrier of 20.1 kcal/mol, is identified as the rate-determining step (RDS) of the overall catalysis. Among the three reactive sites, C4 shows the highest activity, serving as the key center for both the precatalyst activation and the aldehyde reduction stages. The Ru-coordinated amino group is crucial in the deamination stage, especially for C-N bond cleavage. Notably, a cooperative mechanism emerges during the deamination process, where C4 and N1 act in a complementary and alternating manner to drive the key steps. The synergistic interaction exemplifies metal-ligand cooperative catalysis, demonstrating how site-specific reactivity enhances the overall efficiency and selectivity of the transformation.
A general method for the direct trifluoromethylation and chlorodifluoromethylation of Reformatsky reagents derived from various amides or ketones using YlideFluor or YlideFluor-CF2Cl was described. This reaction proceeds under mild conditions and exhibits a broad functional group tolerance. The utility of this protocol was demonstrated through the synthesis of trifluoromethylated derivatives of two pharmaceutical agents, donepezil and ibudilast.
The use of visible light to catalyze organic reactions has sparked significant interests, particularly in C-H borylation. A notable advancement is the visible-light-induced C-H borylation mediated by Rh complex, i.e., [(NHC)Rh(cod)]. Nevertheless, the fundamental role of light remains poorly understood. To establish the underlying structure-activity relationship, systematic theoretical investigations using multistate complete active space second-order perturbation theory (MS-CASPT2), density functional theory (DFT), and rate constant calculations are performed. For the initial photophysical process, the metal-to-ligand charge transfer (MLCT) state is first reached in the Franck-Condon region, which is followed by a cascade of nonradiative processes that populate the lowest triplet state with a distorted coordination. Two-step isomerization of 1,5-cod ligand affords a Rh complex coordinated with 1,3-cod. Subsequent thermal reactions, instead of photocatalytic reactions as experiments proposed, dominate the C-H borylation, accompanied by a catalytic cycle involving Rh(I) → Rh(III) → Rh(I) redox changes. Moreover, substrate modulation reveals the pivotal role of Rh-N coordination in facilitating the following C-H activation. This work not only elucidates the underlying reaction mechanism but also offers valuable insights for the improvement of current catalytic systems.
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