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Density functional theory studies of copper(I) mediated borylation and carboxylation reactions

Authors Dang, Li
Issue Date 2010
Summary Theoretical studies on the reaction mechanisms of copper(I) catalyzed borylation of unsaturated compounds such as olefins, aldehydes and α,β-unsaturated carbonyls with diboron reagents as well as carboxylation of arylboronate esters with CO2 are reported in this thesis. The insertion reactions of alkenes into the Cu-B bond in (NHC)Cu(boryl) complexes (NHC = N-heterocyclic carbene) were studied via DFT calculations. The nature of the insertion reactions and the relevant regiochemistry were examined along with β-hydride eliminations followed by reinsertion of the alkene into the Cu-H bond. The relative reactivity of B2cat2 versus B2pin2 in the diboration reaction of alkenes catalyzed by carbene-ligated copper(I) complexes was studied using DFT calculations. Transmetallation reactions of B2cat2 and B2pin2 with (NHC)Cu-OMe were investigated. The detailed mechanism for the diboration of aldehydes catalyzed by (NHC)Cu(boryl) complexes was studied with the aid of DFT calculations. Aldehyde firstly inserted into Cu-B through a nucleophilic attack to give a Cu-O-C(boryl) species followed by σ-bond metathesis with a diboron reagent. We also studied the catalyzed diboration of 2-pyridinecarboxaldehyde, which gave the unexpected reductive coupling product 1,2-di-2-pyridyl-1,2-bis(pinacolboroxy)ethane. The detailed mechanism of the borylation of acrolein and methylacrylate catalyzed by phosphine copper(I) boryl complexes were theoretically investigated. The results showed that the catalyzed borylation occured through C=C insertion into Cu-B to give a β-borylalkyl C-bound Cu(I) enolate intermediate. In the borylation of acrolein, the C-bound Cu(I) enolate underwent a keto-to-enol isomerization to give an O-bound enolate intermediate followed by a σ-bond metathesis with a diboron reagent. While in the borylation of methylacrylate, a keto-to-enol isomerization did not occur due to the inertness of the ester group, but the addition of methanol enhanced the efficiency of the β-borylation. The insertion reactions of ethene, formaldehyde, acrolein and methylacrylate into a Cu-B bond were compared. In addition, the thermodynamics and kinetics of interconversions between O- and C-bound enolates of Cu, B, and Si were investigated. Carboxylation reactions of arylboronate esters with CO2 catalyzed by (NHC)Cu(OMe) was studied by DFT calculations. Transmetalation proceeded via a B-O-Cu bridged intermediate, which was formed from the KOR adduct of the arylboronic acid, or by CuOR complex, was studied. Insertion of CO2 into the Cu-Ar bond was found to be the rate-determining step, in which nucleophilic attack of the aryl ligand on the electron deficient carbon atom of CO2 led to the formation of a new C-C bond. Alkylboronic esters, but not alkynylboronic esters, were predicted to be suitable substrates for the reaction.
Note Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2010
Language English
Format Thesis
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