摘要
The visible-light photoredox catalysis has been subject of extensive experimental studies, however the detailed mechanism is far from being exhausted. Accurate quantum chemical calculations at the CASPT2//CASSCF/PCM level of theory associated with energy-consistent relativistic pseudopotentials provide for the first time an extensive mechanistic understanding in the single-electron-transfer(SET) of photoredox α-vinylation reaction mediated by a tris(2-phenylpyridine)iridium catalyst. The activation of C-H bond is initially triggered by the first step SET originating from the electron promotion of α-amino lone pair to the S orbital of iridium center in the triplet manifold. The followed SET from iridium center to the C-S σ* orbital of vinyl sulfone facilitates the occurrence of intra-molecular proton transfer(ESIPT) from the activated C-H to the O-S of leaving group in the repulsive ~3nσ* state. The protonated leaving group in neutral was formed through the cleavage of C-S bond together with the charge redistribution among different species, producing a diradical intermediate. The final product of allylic amine is eventually generated by the recombination of the diradical in the ground state. These computational insights provide useful benchmarks for understanding the SET mechanism of photoredox catalysis reaction and also facilitate mechanism-based design for enantioselective catalysts.
The visible-light photoredox catalysis has been subject of extensive experimental studies, however the detailed mechanism is far from being exhausted. Accurate quantum chemical calculations at the CASPT2//CASSCF/PCM level of theory associated with energy-consistent relativistic pseudopotentials provide for the first time an extensive mechanistic understanding in the single-electron-transfer(SET) of photoredox α-vinylation reaction mediated by a tris(2-phenylpyridine)iridium catalyst. The activation of C-H bond is initially triggered by the first step SET originating from the electron promotion of α-amino lone pair to the S orbital of iridium center in the triplet manifold. The followed SET from iridium center to the C-S σ* orbital of vinyl sulfone facilitates the occurrence of intra-molecular proton transfer(ESIPT) from the activated C-H to the O-S of leaving group in the repulsive ~3nσ* state. The protonated leaving group in neutral was formed through the cleavage of C-S bond together with the charge redistribution among different species, producing a diradical intermediate. The final product of allylic amine is eventually generated by the recombination of the diradical in the ground state. These computational insights provide useful benchmarks for understanding the SET mechanism of photoredox catalysis reaction and also facilitate mechanism-based design for enantioselective catalysts.
引文
[1]Ciamician,G.Science.1912,36:385.
[2]Nicewicz,D.A.;Mac Millan,D.W.C.Science.2008,322:77.
[3]Yang,W.J.;Chen,X.B.Phys.Chem.Chem.Phys.2014,16:4242.
[4]Yang,W.J.;Chen,X.B.;Su,H.Z.;Fang,W.H.;Zhang,Y.Chem.Commun.2015,51:9616.
