DFT Studies On The Mechanisms Of The Ni-catalyzed Borylation Of Unsaturated Compounds

To unravel the mechanisms for Ni-catalyzed borylation of unsaturatedcompounds, in this thesis, we investigated the corresponding reactions with the aid ofdensity functional (DFT) calculations. All of the transition states and intermediateswere performed with the B3LYP method. We divide this paper into two parts:1. The mechanisms of the diboration of conjugated alkenes, catalyzed by Ni(0)complexes were investigated. The results show that the reaction is a1,4-diborationprocess instead of1,2-diboration one. It proceeds through a mechanism involvingfour steps: coordination, oxidative boron migration, reductive elimination and ligandexchange. The rate-determining step is oxidative boron migration. This mechanism isdifferent from the commonly accepted mechanism for diboration of unsaturatedcompounds with group10metals, which involves oxidative addition and reductiveelimination. Furthermore, we have utilized natural bond orbital (NBO) analysis andBader’s atoms in molecules (AIM) analysis to analyze the intermediates andtransition states corresponding to the oxidative boron migration step. The NBO andAIM analysis also suggests the interaction between B-B bond of B2eg2and the Nicenter should be coordination instead of oxidative addition, which is in goodagreement with the results that the nickel diboryl complex cannot be observedthrough oxidative addition in the experiments till now.2. In comparison，the mechanisms of the borylation of simple alkenes，catalyzedby Ni(0) complexes were investigated. For styrene, the computational results showthat Ni(0) complexes aren’t able to catalyze the diboration reaction of simple alkenes.Different from what we have seen in the catalyzed diboration of1,3-butadiene, thecatalytic cycle of Ni-catalyzed borylation of styrene tends to generate the β-Helimination product rather than diboration one after the process of oxidative boronmigration and the formation of Ni-H agnostic bond. We aslo investigated themechanism of hydroborylation of styrene, the computational results have shown thatalthough Ni(0) complexes cannot catalyze the diboration of styrene, they cancatalyze the hydroborylation. The hydroborylation of styrene proceeds through amechanism involving three steps: coordination, oxidative hydrogen migration andreductive elimination.