Co-catalysis In Combination Of Transition Metal Pd-complex And Lewis Acid: Construction And Applications To Carbonylation Of Alkynes

The carbonylation of alkyne catalyzed by transition metal palladium is one of the effective methodologies to produce the high value-added carbonyl compounds such as carboxylic acids,esters,amides etc.Palladium catalyst modified by phosphine ligand and Br?nsted acid additives play crucial roles in facilitating the generation of[Pd-H]⁺active species.However,the introduction of excessive Br?nsted acid usually leads to the alkylation of phosphine ligands,the quenching of[Pd-H]⁺species and even the corrosion of experimental equipments.In comparison to Br?nsted acid,Lewis acid can promote the formation of metal-hydride species by polarizing the O-H bonds of proton-donor like H₂O or alcohol.Therefore,the combination of Lewis acid and main Pd-catalyst can effectively promote the carbonylation of alkyne.The application of co-catalysis of multiple catalysts has successfully overcome numerous challenging problems,which has attracted widespread attention.To solve the problems caused by the presence of the excessive Br?nsted acid,Lewis acid was used instead to construct“transition metal Pd complex-Lewis acid”co-catalysis system in this thesis work.The two kinds of carbonylation of alkynes including bis-alkoxycarbonylation and hydrocarboxylation were investigated over the developed co-catalytic systems.The main results were achieved from the following two aspects:?1?Bis-alkoxycarbonylation of alkynes over bifunctional catalytic system containing Xantphos-modified Pd-complex and Lewis acidic Al?OTf?3 in the way of synergetic catalysisIn this part,the one-pot tandem bis-alkoxycarbonylation of alkynes was accomplished over the bi-functional catalytic system containing Xantphos-modified Pd complex and Lewis superacid of Al?OTf?₃ via physical mixing.The Xantphos-modified Pd-complex was responsible for the activation of CO and the alkynes through coordination to Pd-center while Al?OTf?₃ was in charge of the activation of the alcohol to facilitate the formation of[Pd-H]⁺active species.The combination of these two catalysts greatly expedited the bis-alkoxycarbonylation in the way of synergetic catalysis.It was found that phenylacetylene could be efficiently converted into the target product of dimethyl 2-phenylsuccinate?86%yield?under optimal conditions?Pd 1 mol%,Xantphos 0.05 mmol,Al?OTf?₃ 4 mol%,CO 1 MPa,120?,20 h?.The low cost and easily available Al?OTf?₃ was an ideal candidate to replace the irritative and corrosive proton acid.Meanwhile,the bidentate phosphine ligand of Xantphos with rigid skeleton and chelating effect also played important role in adjusting the performance of Pd-catalyst.The in situ high-pressure FT-IR spectra analysis and the isotope labeling experiments showed that Al?OTf?₃ with oxophilicity could activate MeOH,via Lewis acid-base interaction,to serve as the hydride-source,which made the generation and stability of[Pd-H]⁺species easier.The ¹H/¹³C NMR characterizations further confirmed Al?OTf?₃ Lewis acid could effectively activate MeOH which guaranteed the intermolecular synergic catalysis.In addition,the developed bifunctional catalytic system displayed a good generality with the wide range of susbtrates from different aromatic alkynes and aliphatic ones.?2?Hydroxycarbonylation of alkynes over bi-functional ligand?L2?based co-catalytic systemIn this part,co-catalysis for hydroxycarbonylation of alkynes was studied over the bifunctional ligand based intramolecular bifunctional catalytic system.Firstly,the amphiphilici bi-functional ligand of L2 containing tertiary phosphino group and Lewis acidic phosphonium[P?V?⁺]site was successfully synthesized by the quaternization of BINAP by 1,3-propanesultone.Then,the intramolecular bifunctional catalytic system was constructed by the in stiu coordination of L2 to Pd?II?.It was indicated that the hydroxycarbonylation of alkynes was efficiently co-catalyzed by L2-based Pd?OAc?₂ bifunctional catalytic system,which was advantageous with mild reaction conditions,low catalyst dosage,no additional additives,short reaction time,high product selectivity and good substrate generality.In the bi-functional ligand of L2,the phosphino-group which coordinated with Pd catalyst could stabilize the Pd-complex intermediate,and the Lewis acidic phosphonium group could activate H₂O via Lewis acid-base interaction to facilitate the formation of[Pd-H]⁺active species without the use of corrosive Br?nsted acids.Since the phosphino-group and the[P?V?]⁺Lewis acid group were incorporated in the same organic molecule,the intramolecular co-catalysis over L2-based Pd?OAc?₂system was embodied which was more efficient than that over the physical mixing bi-functional catalytic system.Moreover,the amphiphilicity of L2 due to the presence of the hydrophilic group of-SO₃^-made the substrates of phenylacetylene and H₂O more accessible to L2-modified Pd-catalyst,further accelerating the reaction rate of the hydroxycarbonylation.