DFT Studies On The Mechanisms Of The Borylation Of α,β-Unsaturated Carbonyl Compounds Catalyzed By Transition Metals

In this thesis, the mechanisms of the borylation of α,β-unsaturated carbonylcompounds catalyzed by transition metals, were studied with density functionaltheory by calculating the relevant intermediates and transition states. The maincontents of this paper are:1. The mechanisms of the diboration of acyclic α,β-unsaturated carbonylcompounds, acrolein, methyl acrylate and dimethyl fumarate (DMFU), catalyzed byPt(0) diimine complexes were investigated. For acrolein and methyl acrylate, theresults show that the catalyzed diboration occurs via oxidative addition of the diboronreagent to the Pt(0) complex having diimine and acrolein (or methyl acrylate) as theligands,1,4-conjugate addition of a Pt-B bond to acrolein/methyl acrylate to give anO-bound boron enolate intermediate containing a Pt-C-C=C-O-B linkage, andsubsequent acrolein/methyl acrylate coordination to the Pt(II) center followed byreductive elimination to obtain the1,4-diboration product of acrolein/methyl acrylate,i.e., the β-boryl-substituted O-bound boron enolate. For acrolein, the1,4-diborationproduct is the final product, whereas for methyl acrylate, the1,4-diboration productthen isomerizes to the experimentally observed and thermodynamically favored3,4-addition product, i.e., the β-boryl-substituted C-bound boron enolate, via a1,3-shift ofthe O-bonded boryl group. Slightly different from what we have seen in the catalyzeddiboration of acrolein/methyl acrylate, the catalyzed diboration of DMFU takes placethrough oxidative addition of the diboron reagent to the Pt(0) complex having DMFUand diimine as the ligands,1,6-conjugate addition of both of the two Pt-B bonds to thecoordinated DMFU ligand to give a1,6-addition intermediate containing BegO-C(OMe)=C-C=C(OMe)-OBeg (eg=ethyleneglycolato=-OCH2CH2O-) as a ligand,and then isomerization via two consecutive1,3-shifts of the two O-bonded borylgroups to produce the experimentally observed3,4-diborated diastereomeric products.2. The mechanisms of the β-borylation of cyclic α,β-unsaturated carbonylcompounds (cyclohexenone), catalyzed by Pt(0) phosphine complexes were examined.The1,2electrophilic addition mechanism involves oxidative addition of the diboronreagent to Pt(PPh3)2to produce a bis(boryl)platinum(II) intermediate, one PPh3dissociation and then one cyclohexenone coordination, insertion of the carbonyl groupin cyclohexenone into the Pt-B bond giving a σ-allyl complex, isomerization from theσ-allyl complex to the π-allyl complex, and subsequent reductive elimination to obtain the1,4-diboration product of cyclohexenone, i.e., the β-boryl-substituted O-boundboron enolate.3. The mechanisms of the asymmetric β-borylation of α,β-unsaturated carbonylcompounds, methyl acrylate and (E)-methyl but-2-enoate, catalyzed by chiral Rhcomplexes were observed. It is a3,4nucleophilic addition reaction. The chiral Rh(III)catalyst is initially converted into the Rh(I) active catalyst in the present of basebefore catalyzing the borylation reaction. Subsequently, with the Rh(I) active catalystas the active species, the borylation mechanism of methyl crylate involves oxidativeaddition of the diboron reagent to the Rh(I) complex, methyl acrylate coordination,methyl acrylate insertion into the Rh-B bond, and then reductive elimination affordingthe3,4-diboration product of methyl acrylate. Finally, we investigated the mechanismof this reaction by taking the full model of the ligand for Rh catalyst and (E)-methylbut-2-enoate. The rate-determining barriers for the formation of products havingconfiguration R and S, respectively, were calculated. We expected that the stericrepulsion between the carbonyl oxygen in (E)-methyl but-2-enoate and the substituteof the tridentate ligand in the Rh(III) complex causes the product having configurationS with high enantioselectivity, experimently.