Preparation And Application Of NHC-Pd And Graphene-supported Diimine Palladium Catalyst

Diarylketones,amides,and biaryl compounds are widely used and difficult to synthesize.The homogeneous catalyst NHC-Pd catalyzes aryl esters with low-toxic and inexpensive instead of the traditional expensive and toxic electrophiles and amines to construct amide compounds to meet the requirements of green chemistry in this paper.Similarly,aryl ester is used as an electrophile and aryl boronic acid was catalyzed by homogeneous catalyst NHC-Pd to synthesize diaryl ketones,which is low in cost and high in yield,it meets the concept of atom economy.In addition,with the increasing maturity of C-C bond construction research,it has become a common method to synthesize various biaryl compounds.However,the loss of precious metal as a catalyst in the reaction is terrible,and it pollutes the product,which severely limits its large-scale application.Therefore,designing a suitable heterogeneous catalyst has become one of the hot spots in the field of organic catalysis.In this paper,two homogeneous catalyst which were NHC-Pd were synthesized to catalyze the cleavage of C-O bond to build C-C and C-N bonds;one heterogeneous catalyst which was graphene-supported diimine palladium was used to catalyze the construction of C-C bond.By screening the reaction conditions of different palladium complexes,131diaryl ketones,amides,biaryl compounds were obtained.The detail is shown as follows:1.The benzoquinone was used as the skeleton to build NHC-Pd with a rigid and highly sterically hindered diphenylmethyl group at the meta-position of nitrogen aryl group,and 3-chloropyridine was used as the auxiliary ligand.Obtained precatalyst?K1?was used to catalyze the reaction of phenyl benzoate and aromatic boric acid to construct diaryl ketone.The reaction conditions were optimized as follows:base:K₃PO₄?2.0 equiv.?,palladium content:0.2-0.6 mol%,solvent:THF:H₂O=1:3?4.0 mL?.The reaction was carried out at 100°C for 10 h,and 26 diaryl ketones were obtained in a yield of 62-99%.2.NHC-Pd C1 was synthesized and used as a precatalyst to catalyze the amide reaction with phenyl benzoate and amine,reaction conditions were optimized as follows:base:K₃PO₄?2.0 equiv.?,palladium content:0.3 mol%,H₂O?0.2 mL?,solvent:1,4-dioxane?4.0 mL?,26 amide compounds were synthesized after reacting at 110°C for 10 h in the yield of 69-99%.3.A diimine-Pd complex with both suitable steric hindrance of isopropyl groups and electron supply provides excellent protection for palladium active centers was synthesized and anchored on graphene oxide?GO?to get a reusable heterogeneous catalyst?Pd-DI@GO?in this paper.The structure of diimine was determined by ¹H NMR,¹³C NMR and ESI-MS.Pd-DI@GO was characterized and determined by FT-IR,SEM,XRD,ICP-AES and XPS.Pd-DI@GO was used as a heterogeneous catalyst in the Suzuki reaction,the optimal reaction condition was as follows:base:K₂CO₃?2.0equiv.?,palladium content:0.047 mol%,solvent:EtOH?4.0 mL?.The reaction was performed at 65°C for 2 h under the optimal reaction system.A series of brominated aromatic and arboric acid containing various functional groups were reacted,such as benzene,naphthalene,phenanthrene,pyridine,melidine,quinoline,etc.64 products were constructed with the yield between 44-99%.Notably,Pd-DI@GO can be recycled after Suzuki reaction via filtering or centrifuging easily,presenting a yield above 90%for the 4th run.C-H direct arylation can also be catalyzed by Pd-DI@GO.15 biaryl compounds containing aromatic rings,pyridine rings,thiazole rings,etc.were synthesized with a yield of 20-99%.6 new compounds were successfully constructed.