Theoretical Study On The Reaction Mechanism Of Hydroformylation And Cycloaddition Reaction Catalyzed By Several Transition Metals

In this dissertation, the reaction mechanisms of hydroformylation and cycloaddition reaction catalyzed by several transition metals have been studied by using density functional theory (DFT). The investigations include five typical systems which were experimentally described recently:(1) Rh(I)-catalyzed intermolecular hydroacylation of vinylsilane with benzaldehyde,(2) Ni(0)-catalyzed intermolecular hydroacylation of alkyne with benzaldehyde,(3) Mo(0)-catalyzed intramolecular Pauson-Khand reaction of3-allyloxy-l-propynylphosphonate,(4) Mo(0)-catalyzed intramolecular [2+2] or [2+2+1] cycloaddition reaction of5-allenyl-1-ynes,(5) Ni(0)/Zn(II)-catalyzed decarbonylative addition reaction of phthalic anhydride to alkyne. We hope to comprehensively understand the reaction mechanism of transition metals-catalyzed reactions, explore the essential of the transition metal catalysis and the effects of ligands, additives, and solvents on total reactions, and reveal the relationship between the reactivity and the structures of the substrates.The reaction mechanisms of Rh(I)-catalyzed intermolecular hydroacylation of vinylsilane with benzaldehyde have been investigated in detail with density functional theory (DFT) at the B3LYP/6-31G(d,p) level (LANL2DZ(f) for Rh). The present study will focus on1) the energitics of the overall catalytic pathways in intermolecular hydroacylation and the rearrangement processes,2) the carbonylation versus decarbonylation reaction,3) the solvation effect of toluene,4) the ligand (Cp=C5H5and Cp'=C5Me4CF3) effect in reaction mechanism. Calculated results indicate that the hydroacylation goes mainly through the oxidative addition reaction of benzaldehyde, a cis-addition to the alkene, the carbonyl elimination reaction, the carbonyl insertion reaction, and the reductive elimination reaction. The formation of the rhodium-ketone complex (i. e. the reductive elimination reaction) is the rate-determining step, the dominant product predicted theoretically is linear ketone. Because of high reaction barriers, the decarbonylation reaction is prohibited, and so an alkane will not be formed. The solvation effect is remarkable, and it deceases greatly free energies of all the species. And it also shows that the formation of the linear ketone is the energetically most favorable pathway. The use of the ligand Cp'(Cp'=C5Me4CF3) decreased generally the free energies of the complexes. And the rate-determining step is also the reductive elimination reaction, which is in good agreement with those discussed using Cp. These results are consistent with Brookhart's experiments.The reaction mechanisms of Ni(0)-catalyzed intermolecular hydroacylation of alkyne with benzaldehyde have been studied at the B3LYP/6-31G(d,p) level. The intermolecular hydroacylation has four possible reaction paths A, B, C, and D. Paht A:the coordination of nickel with alkyne and benzaldehyde, the carbonyl carbon atom of benzaldehyde attacking the alkyne carbon atom, the hydrogen migration reaction. Path B:the complexation reaction of nickel with benzaldehyde, he oxidative addition of benzaldehyde, the coordination of alkyne, the hydrogen migration reaction, the reductive elimination reaction. Path C:the complexation reaction of nickel with benzaldehyde, he oxidative addition of benzaldehyde, the coordination of alkyne, the hydrogen migration reaction, the carbonyl elimination reaction, the carbonyl insertion reaction, the reductive elimination reaction. Path D: the decarbonylation reaction. Calculated results indicate that path B is the most favorable in the overall reaction channels of Ni(0)-catalyzed intermolecular hydroacylation. The oxidative addition of benzaldehyde is the rate-determining step, and the dominant product predicted theoretically is (E)-α,β-enone, which is consistent with the experiments. Therefore, the carbonyl elimination reaction, the carbonyl insertion reaction, the decarbonylation reaction are prohibited. In addition, the oxidative addition of benzaldehyde occurs prior to the coordination of nickel with alkynes.The reaction mechanisms of Mo(0)-catalyzed intramolecular Pauson-Khand reaction of3-allyloxy-l-propynylphosphonate have been investigated in detail with density functional theory (DFT) at the B3LYP/6-31G(d,p) level (LANL2DZ(f) for Mo). The present study focused on the formation of the chiral product, the carbonyl insertion reaction, and the solvation effect (toluene, CH3CN, and THF). The C-C oxidative cyclization reaction is the chirality-determining step. The carbonyl insertion has two reaction modes "a"(the carbonyl insertion reaction into the Mo-C(sp3) bond) and "b"(the carbonyl insertion reaction into the Mo-C=C bond). In the process of forming the product of (S)-chirality P, the reductive elimination reaction is the rate-determining step, and the reaction mode "a" is more favorable (i.e. the carbonyl insertion reaction into the Mo-C(sp3) bond is easier than into the Mo-C=C bond.). And thus in the process of forming the product of (R)-chirality P', the reductive elimination reaction is the rate-determining step for the reaction mode "a", while the carbonyl insertion is the rate-determining step for the reaction mode "b". Evidently, the reaction mode "b" is more favorable, so the carbonyl insertion reaction into the Mo-C=C bond is easier than into the Mo-C(sp3) bond in the process of forming the product of (R)-chirality P'. The dominant product predicted theoretically is of (S)-chirality, which is consistent with the experiments. The reaction is solvent dependent, and toluene is a better solvent than CH3CN and THF. The solvation effect was considerable. It decreased the free energies of all intermediates and transition states.The reaction mechanisms of Mo(0)-catalyzed intramolecular [2+2] or [2+2+1] cycloaddition reaction of5-allenyl-1-ynes have been studied at the B3LYP/6-311++G(d, p) level (LANL2DZ(f) for Mo). Calculated results indicate that Mo(0)-catalyzed intramolecular [2+2] cycloaddition is more favorable than [2+2+1] cycloaddition, which disagrees with the Pauson-Khand reaction. The reactant5-allenyl-1-ynes has characteristic structure:two π bonds which are orthogonal. The complexation reaction of5-allenyl-1-ynes with Mo(CO)6occurred preferentially at the triple bond, and then the complexation with the distal double bond of the allenes. The solvation effect is remarkable, and it decreases the reaction energy barriers and also decreases the free energies of intermediates and transition states.The reaction mechanisms of Ni(0)/Zn(II)-catalyzed decarbonylative addition reaction of phthalic anhydride to alkyne have been investigated in detail with density functional theory (DFT) at the B3LYP/6-31+G(d,p) level. The experiment described the decarbonylative addition with Ni(PMe3)4led to isocoumarin in12%yield. However, on addition of ZnCl2, the reaction proceeded smoothly to furnish isocoumarin in96%isolated yield. To understand the reaction mechanisms and the effect of ZnCl2, we studied theoretically the reaction pathways of the nickel(0)-and nickel(0)/zinc-catalyzed decarbonylative addition of phthalic anhydrides to alkynes, respectively. The alkyne found it is easier to substitute for PMe3than carbonyl in the coordination reaction. The insertion reaction of alkynes into the Ni-C bond occurrs prior to that into the Ni-O bond. And the alkyne insertion reaction was the rate-determining step for this channel. The additive ZnCl2had a significant effect, and it decreased greatly the free energies of all the intermediates and transition states. And it could not change the reaction channel, and it changed greatly the electron and geometry structures of those intermediates and transition states.