Pd-Catalyzed Aryl C–H Imidation with Arene as the Limiting Reagent

Abstract

An amine-N-oxide ligated palladium complex, in conjunction with a silver co-catalyst, catalyzes imidation of arenes by the reagent N-fluorobenzenesulfonimide. The reaction enables imidation of a variety of arenes at or below room temperature, requires no coordinating directing group on the substrate, and gives synthetically useful yields with only one equivalent of arene. Mechanistic data implicates an unusual mechanism devoid of commonly invoked organometallic intermediates; oxidation of the palladium catalyst occurs as the turnover-limiting step, while C–H bond functionalization occurs subsequently at a high oxidation state of the catalyst.

Metal-Catalyzed and Metal-Free Intermolecular Amination of Light Alkanes and Benzenes

“…While detailed mechanistic data are not available, the authors propose a turnover-limiting step that involves addition of an electrophilic, metal-bound imidyl radical (Cu–N(SO 2 Ph) 2 ) to the arene. By way of analogy to Ritter’s results, 84 an inverse intermolecular kinetic isotope effect (0.91) has been observed for the imidation of 2-phenylthiophene vs. 2-D-5-phenylthiophene.…”

“…Ritter and co-workers 84 have introduced a bimetallic catalytic system that engages the Pd(II) complex [Pd II ( N -(2-pyridylmethyl)pyrrolidine- N -oxide) 2 ](OTf) 2 (5 mol %) along with [Ag(bipy) 2 ](ClO 4 ) (10 mol%) in MeCN at room temperature (Scheme 32). The latter can be substituted by [Ru(bipy) 3 ](PF 6 ) 2 (2.5 mol%) at 50 °C, suggesting that the Ag(I) or Ru(II) complexes act as electron relays.…”

Palladium catalyzed aryl C–H amination with O2via in situ formation of peroxide-based oxidant(s) from dioxane

“…1 Palladium-catalyzed C–H amination methods typically require strong stoichiometric oxidants, such as diacetoxyiodobenzene, 2 oxone,3 or [F + ] sources. 4,5 A common reaction pathway associated with these reactions involves oxidation of an aryl-Pd II intermediate to a high-valent Pd III or Pd IV species, 6 which then undergoes facile reductive elimination of the C–N bond and circumvents the intermediacy of an unstable Pd 0 species (Scheme 1). 7,8 …”

Direct Aryl C−H Amination with Primary Amines Using Organic Photoredox Catalysis

“…[9–12] Significant challenges exist for C–N couplings using aliphatic amines, since many strategies for functionalization of these substrates involve C–C bond construction adjacent to the nitrogen atom. [13–16] Accordingly, C–H amination of arenes with aliphatic amines has been demonstrated only in select examples (Scheme 1).…”