A Theoretical Study On The Mechanism Of C-H Functionalization Catalyzed With Rhodium(?,?) In Carbonyl-Containing Complex And Nickel-Catalyzed Coupling

The field of organometallic catalysis has attracted considerable interest from both academia and industry due to its broad applications in synthetic transformations. Rh, Ni, and Pd catalysts are critical for many of these transformations, often giving rise to remarkable reactivities that were unthinkable in the past. The efficient and selective activation of C-H bonds catalyzed by transition metal, the elementary building block of hydrocarbons, constitutes an interesting alternative with potentially a huge economic impact. Owing to the tremendous advances in computational methodology, computing power and software, computational tools are increasingly employed to study, rationalize, and predict organometallic reactivities. Computational chemistry has in particular become a powerful tool to gain insights into the mechanisms of catalytic organometallics processes where the active catalytic species or intermediates have been challenging or impractical to study via experimental approaches. Therefore, in present thesis,DFT calculations were carried out to study the mechanisms of three important organometallic reactions initiated by C-H bond activation, elucidate the reactivities, selectivies and direct the design of reaction.What's more, the mechanism of Ni(0) catalyzed intermolecular alkyne-aldehyde reductive coupling reaction and the origin of regioselectivity consistute the final part.In the third section, the newly reported density functional theory(DFT) method, M11-L, has been used to clarify the mechanism of the rhodium-catalyzed transfer hydroformylation triggered by C-H bond activation. DFT calculations depict a deformylation and formylation reaction pathway. The deformylation step involves an oxidative addition to the formyl C-H bond, deprotonation with a counterion, decarbonylation, and ?-hydride elimination. After olefin exchange, the formylation step takes place via olefin insertion into the Rh-H bond, carbonyl insertion, and a final protonation with the conjugate acid of the counterion.Theoretical calculations indicate that the alkalinity of the counterion is important for this reaction because both deprotonation and protonation occur during the catalytic cycle. A theoretical study into the formyl acceptor shows that the driving force of the reaction is correlated with the stability of the unsaturated bond in the acceptor. The computational results suggest that alkynes or ring-strained olefins could be used as formyl acceptors in this reaction.Desymmetrization has emerged as a way to access chiral quaternary-carbon motifs, which are among the most challenging stereocenters to generate with enantiocontrol. Strategies involving C-H bond activation are especially novel. In the fourth section of this thesis, DFT calculations were carried out to study the mechanism, chemo- and enantioselectivity of Rh(I) catalyzed desymmetrization of ?-quaternary centers. Calculated results reveal a cascade process featuring an enantioselective olefinisomerization followed by olefin-hydroacylation, in which involves a C-H bond activation, then one allyl insertion into Rh-H bond followed by ?-hydride elimination, and the other allyl coordination and insertion into Rh-H bond followed by reductive elimination steps. The side reaction of Rh(I) catalyzed desymmetrization is carboacylation resulted in bicycle [2, 2,1] heptanone that proceeds with C-H bond activation, one allyl insertion into Rh-H bond, then the other allyl coordination and insertion into Rh-C bond followed by reductive elimination steps. Obviously, the chemoselectivity is controlled by ?-hydride elimination and allyl insertion into Rh-C bond, and phosphine ligand with high steric hindrance is favored by ?-hydride elimination giving rise to cyclopentanone. Due to the five-membered cycle transition states and intermediate, enantioselectivity emerges in the first allyl insertion into Rh-H bond step, but determined by the reductive elimination step. Moreover, C-H bond activation is calculated to be the rate-limit for the whole catalytic cycle.Catalytic asymmetric dearomatization(CADC) reactions of readily available planar aromatic compounds have attracted considerable attention and emerged as novel enabling methods for rapid construction of highly functionalized three-dimensional structures. Comprehensive DFT calculations have been performed to understand the mechanism of Rh-catalyzed asymmetric dearmatization of naphthols in fifth section of this thesis. The refined mechanism involves deprotonation of naphthols, C-H bond activation, and then alkyne migratory insertion followed by reductive elimination and final catalyst regeneration steps. Different from above two reactions, C-H bond is activated by ?-bond metathesis. Although the C-H activation was suggested to be involved in the turnoverlimiting step, the enantioselectivity of the reaction is found to be determined during the migratory insertion of the alkyne. Different from the originally proposed mechanism, the final dearomatized product is afforded via reductive elimination directly from the eightmembered rhodacyclic intermediate generated from the migratory insertion step. In addition, the critical effect of ligand on the enantioselectivity in this CADC reaction is also considered and the theoretical results indicate the special structure and steric hindrance could be responsible for the required enantioselectivity. These reults would prompt the design of newly chiral Cpx ligand and application to more Rh-catalyzed asymmetric reactions.In the sixth section, DFT calculations are employed to clarify the proposed mechanisms of nickel-catalyzed reductive coupling of alkyne and aldehyde and the prevailing one is confirmed to proceed with oxidative cyclization, transmetallation and reductive elimination. Theoretical calculations indicate that the reactivity, regioselectivity and main product changed with the ligand. Reversal of regioselectivity can be achieved by varying the steric bulkiness of the ligand. The rate-limit is calculated to be transmetallation and the regioslectivity is determined by oxidative cyclization. Moreover, 2D contour maps analysis of ligands and distortion–interaction energy analysis along the whole reaction pathways have provided comprehension of the regioselectivity that is controlled by distortion with IMes as ligand and is determined by the shape and bulkiness of ligand with SIPr as ligand.With comprehensive DFT calculations on above four transition metal catalyzed organic reactions, one can gain insights into the mechanisms of catalytic species or intermediates have been challenging or impractical to study via experimental approaches. The reactivity, regio-, chemo-, and stereoselectivities were elucidated by computational studies. What's more, further understanding of C-H bond activation catalyzed by transition metal is obtained by these DFT studies.