Silver(I)-Diene Complexes as Versatile Catalysts for the C-Arylation of N-Tosylaziridines: Mechanistic Insight from In Situ Diagnostics

Silver(I) complex [Au(diene)(2)](+) Y- (where diene - cyclooctadiene, norbornadiene, and 1,3-cyclohexadiene; Y- = PF6-, BF4-) efficiently catalyzes the arylation of N-tosylaziridines with arenes and heteroarenes under ambient condition to provide the corresponding beta-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 (H-1, P-31, Ag-109) and ESI-MS probe: (I) evaluation of Hammett reaction constant (rho); (II) correlation of initial rate (k) versus cone angle (theta) of ligand L for reactions mediated by [Ag(COD)(2)]PF6/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 Delta(HOMO-LUMO) of [Ag(diene)(2)]PF6 obtained from preliminary DFT studies. Study I led to a rho-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 theta, as well with Delta P-31((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 > CH D; which corresponds well with the order of hardness of the respective Ag(I) complexes.