Palladium-Catalyzed Cycloarbonylation Ofallylicalcohols: Insights From A DFT Study

Asymmetric cylcocarbonylation of allylic alcohols is very useful inindustries. Although the mechanisms of cylcocarbonylation of allylicalcohol have been proposed in both experimental and theoretical studies,the reasons accounting for the mechanisms of Pd-catalyzedcyclocarbonylation of allylic alcohols are still unknown. In thisdissertation, we not only proposed the whole mechanism of carbonylationof allylic alcohol catalyzed by Pd complex but also explained well whymethanol assistance could effective decrease the energy barrier of therate-determining step. The result is applicable to cyclocarbonylationcatalyzed by Pd complex, and provides insights in illustrating the reactionmechanisms. The main work of this dissertation can be summarized asfollows:(1) The carbonylation mechanisms of allylic alcohol catalyzed byPdHCl[H₂P (CH₂)₂PH₂] and PdH[H₂P (CH₂)₂PH₂] Complexes werestudied using a density function theory (DFT) method. The wholecatalytic cycle consists of alkene insertion, CO insertion and hydrogentransfer and product elimination steps. Each step has been performedusing ten paths denoted by A-Cl, A, B-Cl, B, AClP, AP, A-ClOH, AOH,BOH and B-ClOH. In the alkene insertion step, the paths without Cl (Aand B) are more favorable than those with Cl (A-Cl and B-Cl). In COinsertion step, paths A-Cl and A are more favorable than B-Cl and B. Thehydrogen transfer and product elimination step is the rate-determiningstep of the whole catalytic cycle except Paths AOH, AClP, BOH and B-ClOH. The paths assisted with methanol (A-ClOH, AClP, AP, AOH,BOH and B-ClOH) are more favorable than those without methanol(A-Cl, A, B-Cl and B). And the path AOH is more favorable than PathBOH. It means that the S-conformation product takes the large advantage.After the departure of product, the catalyst would be regenerated andcoordinated with a substrate. These results well agree to the experimentalreports. Our results in this paper indicate that methanol assistance playsan important role in decreasing the barrier of rate-determining step andprovides theoretical support in the investigation of the mechanism of Pdcatalysis.(2) The carbonylation mechanisms of allylic alcohol catalyzed byPdHCl(BPPM) complex were studied using a density function theory(DFT) level. The results show that the catalytic cycle consists of threemain steps: alkene insertion, CO insertion, hydrogen transfer and productelimination. Pathway with a Pd(II) character is more favorable than thatwith Pd(IV) character. Methanol serves as the proton shuttle incarbonylation process and reduces the energy barrier15.4kcal/mol thanthat without methanol assistance.