The Role of a Redox‐Active Ligand in Cu(II)‐Nitrenoid Formation and Its Aziridination Reactivity

Abstract

Metal‐nitrenoid species are the key intermediate in nitrene transfer reactions. The bond formation between the open‐shell transition metal and the nitrene species dictates their overall reactivity. Herein, we present an in‐depth electronic structure investigation to uncover how the formation of a Cu(II)‐nitrenoid species is assisted by redox‐active iminosemiquinone (ISQ) ligand in the [CuII(LISQ)2] complex and impact the nitrene‐transfer reactivity. The reaction energetics of the aziridination reaction between N‐tosyliminophenyliodinane and 4‐chlorostyrene is established by DFT calculations, where the formation of the Cu(II)‐nitrenoid intermediate (Int1) is found to be the rate‐determining step. Based on the natural orbital and spin populations obtained from the ab initio multi‐configurational CASSCF(13,13) calculation, the electronic nature of the elusive Cu(II)‐nitrenoid intermediate (Int1) could be formulated as “imidyl” [(LISQ)(LIBQ)CuII─•NTos] (Tos = Tosyl) species. A weak σ interaction between the Cu(II) center and the N‐atom of the nitrene moiety (Cu 20% + N 29%) involving a Cu–N distance of 1.92 Å defines the Cu‐nitrenoid bonding. The interplay between elongated Cu–N bond and high spin population on N‐atom (+0.96) corroborates its high nitrene transfer ability. Furthermore, the intrinsic bond orbital (IBO) analysis unravels a ligand‐to‐substrate electron transfer mechanism that facilitates the formation of the crucial Cu(II)‐nitrenoid species.