Study On The Mechanism Of CC/CH Selective Activation Mediated By Transition Metal Cobalt/nickel Complexes

With the development of organic metal catalysis,many researchers have turned their attention away from precious metals such as palladium and rhodium to cheaper metallic iron,cobalt,and nickel.Since transition metals such as iron,cobalt,and nickel are widely available,economically inexpensive,and belong to the fourth cycle,they have similar chemical properties.Scientists have conducted in-depth explorations of these chemical reactions of organic metals with great potential.For example,as reported before 2017,the decarbonylation reaction of most simple unstrained ketones required the addition of a stoichiometric amount of a ruthenium complex.Therefore,with abundant first-row transition metals,there is still broad prospects for improvement for more types of C-C and C-H activation.We first explored the decarbonylation mechanism of Ni?II?-mediated simple unstrained ketones,examined the emerging development potential of NHC ligands in experiments,the chemical selectivity of inert C-C bonds,and explored a design catalyst dosage.The path of the decarbonylation reaction is relatively brief:?1?coordination of the catalyst Ni/NHC with the substrate ketone,?2?oxidation addition of the C-C bond cleavage,?3?migration of the carbonyl group,?4?reduction eliminationtoaffordthebiarylproduct.Thedecarbonylationof4-methyl-4'-trifluoromethyl benzophenone and 3-quinolinyl benzophenone was studied in the system.An equivalent and catalytic amount of Ni?COD?₂/IMes^Me?HCl was used to achieve the decarbonylation reaction of the different ketones.(IMes^Me)Ni mediates the first decarbonylation cycle and generates biaryl product and(IMes^Me)NiCO,which is inactive for the substrate 1.However,when the substrate is3-quinolinyl ketone 2,(IMes^Me)NiCO can mediate the decarbonylation of 2 again and realize the catalytic cycle.Decarbonylation is the rate-determining step controlling whether the transformation can be mediated catalytically.Based on our analysis,while the differences of noncovalent interactions are negligible,the stabilization energy E^?2?of BD_{C?=O?-C?methyl phenyl?}?LV_Ni for the decarbonylation transition state may play a dominant role for the catalytic cycle.Furthermore,when an electron-withdrawing group and an electron-donating group are simultaneously present in the biaryl ketone,an accelerated effect is exerted on the decarbonylation reaction.The Cobalt-catalyzed cyclization of 1,6-enynes with aldehydes developed by Cheng and co-workers provides an efficient strategy to synthesize functionalized pyrrolidines and dihydrofurans with high chemo-and stereoselectivity.Density functional theory calculations?B3LYP?revealed that ligands controlled highly chemo-and stereoselective cobalt-catalyzed hydro-acylation and-arylation reactions.The calculations indicate that the hydroacylation in the presence of dppp ligand is achieved via oxidative cyclization,carbonyl insertion and?-hydride elimination.The favourable path of hydroarylation reaction occurs via oxidative cyclization,followed by C-H cobaltation and reductive elimination,when dppen is used as the ligand.The theoretically observed ligand-controlled selectivity is attributed to a combination of electronic and steric effects in the reactions.Analysis of different ligand steric parameters,ligand steric contour maps,ligand-substrate repulsions and the computed activation barriers revealed the origin of the positive correlation between ligand and reactivity.These systematical studies have not only theoretically explored the activation of the common C-C and C-H bonds,but also discovered many new and worthwhile questions.They all have certain implications for the future related synthesis methods,novel reaction mechanisms,and the exploration of potential catalytic systems.