Silver(I)-Diene complexes as versatile catalysts for the C -Arylation of N -Tosylaziridines: Mechanistic insight from in situ diagnostics

摘要

(Figure presented) Silver(I) complex [Ag(diene)_2] ~+Y~- (where diene = cyclooctadiene, norbornadiene, and 1,3-cyclohexadiene; Y~- = PF_6~-, BF _4~-) efficiently catalyzes the arylation of N-tosylaziridines with arenes and heteroarenes under ambient condition to provide the corresponding β-aryl amine derivatives with excellent regioselectivity. To understand the nature of substrate activation, and initial bond breaking/making steps, the following studies were conducted with the help of in situ NMR (~1H, ~(31)P, ~(109)Ag) and ESI-MS probe: (I) evaluation of Hammett reaction constant (-); (II) correlation of initial rate (k) versus cone angle (θ) of ligand L for reactions mediated by [Ag(COD)_2]PF_6/L (where L is a phosphine or a phosphite ligand); (III) identification of silver-arene intermediates in solution; and (IV) correlation of initial rate (k) with δ_(HOMO-LUMO) of [Ag(diene)_2]PF_6 obtained from preliminary DFT studies. Study I led to a p-value of -0.586, indicating that the extent of electrophilic perturbation is considerably less than a typical Lewis acid catalyzed process. Study II indicated that initial rate (k) increases with concomitant increase in θ, as well with δ~(31)P_((complex-ligand)), which corroborates to a mechanism involving prior ligand dissociation. Study III showed the plausible formation of [Ag(diene)(arene)]~+ and [Ag(arene)_2]~+ as reactive species in solution. Study IV showed that the dependence of initial rate (k) with diene ligand is in the order COD > NBD > CHD; which corresponds well with the order of hardness of the respective Ag(I) complexes.