Synthesis Of N-heterocyclic Carbene Palladium Complexes And The Study On Their Catalyzing Suzuki And Buchwald-Hartwig Reactions

Bulky hindered?hetero?aromatic rings—?hetero?aromatic rings,and heterocyclic-?hetero?aromatic amine structures,which are widely used in medicine,pesticides,photoelectric materials,and natural products.However,these structures can be efficiently constructed by Suzuki reaction and Buchwald-Hartwig reaction.The N-heterocyclic carbene palladium complexes have advantages of low toxicity,high catalytic activity and high stability relative to the phosphine ligands,and can efficiently catalyze the Suzuki reaction and the Buchwald-Hartwig reaction,and have now become a hot spot in the field of organic catalysis.However,the synthesis of ortho-tetrasubstituted biaryl compounds and aromatic?hetero?-cyclic aromatic amines by these two coupling reactions has the disadvantages of poor catalytic activity,harsh reaction conditions,and low product yield.This paper attempts to design and synthesize a novel class of N-heterocyclic carbene palladium complexes that can overcome the above drawbacks and apply them to the above two types of reactions.1.A novel N-heterocyclic carbene palladium complex?C1 and C3?were designed and synthesized.Their structures were characterized by ¹H NMR and ¹³C NMR.The single crystal structure was subjected to X-ray single crystal diffraction to obtain single crystal data.The FT-IR spectra of the N-heterocyclic carbene iridium complex were determined,and the TEP value was calculated theoretically,which indicated that C1 showed enhanced electron donor property compared to other classical Pd-NHCs.Remarkably,C1 showed electron ability similar with that of the CAAC?Cyclic alkyl amino carbene?,which could be attributed to the introduction of both acenaphthyl-backbone and isopentyl groups.Therefore,the electron-rich Pd-PEPPSI complex would exhibit profound effect on the Pd-catalyzed cross-coupling reactions.At the same time,its bulky-yet-flexible chain can protect the catalytic active center from being trapped by oxygen molecules,which greatly increases its stability in air.2.BulkyhinderedSuzukireactionsandheterocyclic Buchwald-Hartwig reactions was catalyzed by the two N-heterocyclic carbene palladium complexes,respectively.The best solvent and base were screened.Under the optimized reaction conditions,the steric hindrance problem in the substrate and the compatibility of functional group on the two types of reactions were investigated.80 tetra-substituted biaryl structures and 43 aromatic ring-aryl amine structural products were obtained.3.The results show that:?1?The bulky steric hindrance can effectively protect the active center.?2?Isoamyl groups have the flexibility to oscillate.When catalyzing large hindered substrates,they can contribute to the oxidative addition and subsequent transfer of Suzuki reaction.?3?The introduction of bis?imino?acenaphthene?BIAN?and isoamyl groups in the structure greatly increases the electron donating ability and thus accelerates the rate of oxidation addition,the rate-determining step.?4?Two excellent catalytic reaction systems were found,whichcanefficientlycatalyzethesynthesisof ortho-tetrasubstituted biaryl compounds and aromatic ring-aryl amine products under air conditions with lower catalyst loading.