Design,synthesis And Catalytic Applications Of Novel Spirocyclic CCC Pincer NHC–Ir Complexes

The reactivity of organometallic compounds depends on their structures to great extent.Thus,exploration of novel transition metal complexes with unique structures and properties is a continuously attracting hotspot in organometallic chemistry,in which the ligand design plays a critical role in controlling the activity and chemical selectivity of the transition metal-catalyzed homogeneous reactions.Pincer complexes have occupied a key position in this field for many years because of their high stability,versatility and easy modification.Based on our group's long-term research and exploration of spirocyclic skeleton and N-heterocyclic carbene(NHC)ligands/catalysts,this dissertation focuses on the design,synthesis and catalytic reactivity of a series of novel spirocyclic CCC pincer NHC–Ir complexes.The catalytic applications mainly include C–C bond formation and C–H bond functionalization,such as the homo/hetero addition of non-activated olefin and C–H silylation reactions.This dissertation consists of four parts:Chapter 1:Introduction.We reviewed the research progress of a particular category of pincer complexes,and introduced the multianionic pincer complexes which possess di-or tri-M–C covalent bonds.This part is composed according to the type of bonding property of pincer donor atoms and the central metal.Chapter 2:Design and synthesis of novel spirocyclic CCC pincer NHC–Ir complexes.A novel spirocyclic pincer complex SNIr-H was simply and efficiently synthesized under mild conditions.We determined the structure by NMR spectra,HRMS and X-ray diffraction analysis,and found the complex possess a stable Ir–H bond and unique CCC pincer structure(including two M–C covalent bonds and one M?C coordination bond).The experimental and density functional theory(DFT)calculation results suggested that the spirocyclic framework played an important role in the formation and stabilization of this complex.Further investigation found that the complex SNIr-H can be transformed into corresponding chloride SNIr-Cl or trifluoromethyl-sulfonate SNIr-OTf under mild conditions,which can be further converted into other CCC pincer complexes.Chapter 3:Ir-catalyzed homo/hetero addition of non-activated olefins.We examined the catalytic reactivity of the above synthesized Ir-complexes in the homo/hetero addition of non-activated olefins.Catalyst SNIr-Cl showed the highest activity,and a series of head-to-tail addition olefin dimerization products were synthesized with high selectivity,up to 99%conversion rate and 92%yield.In addition,Ir-catalyzed cyano transfer reaction was primarily tested.Chapter 4:Ir-catalyzed C–H silylation.We applied the above synthesized SNIr-Cl to catalyze the C–H silylation of heteroaryl compounds.Multiple types of intermolecular sp~2C–H or sp~3C–H silylation can be achieved at ????? or ? positions of heteroatoms with excellent regioselectivities,generating a variety of heteroarylsilanes.The key experimental intermediates and DFT calculation results suggested that the catalyst could combine with the substrate,forming a highly active“hemi-open”hemiliable structure during the catalytic cycle to adapt to the steric circumstance of different substrates,so as to obtain broader substrate scope.