Silver(I)-diene complexes as versatile catalysts for the C-arylation of N-tosylaziridines: mechanistic insight from in situ diagnostics.

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 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 ((1)H, (31)P, (109)Ag) 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)]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 Delta(HOMO-LUMO) of [Ag(diene)(2)]PF(6) 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(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.