Structural Characterization of the [CuOR]²⁺ Core

Abstract

Formal Cu(III) complexes bearing an oxygen-based auxiliary ligand ([CuOR] 2+ , R = H or CH 2 CF 3 ) were stabilized by modulating the donor character of supporting ligand L Y (L Y = 4-Y, N,N′-bis(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamide, Y = H or OMe) and/or the basicity of the auxiliary ligand, enabling the first characterization of these typically highly reactive cores by NMR spectroscopy and X-ray crystallography. Enhanced lifetimes in solution and slowed rates of PCET with a phenol substrate were observed. NMR spectra corroborate the S = 0 ground states of the complexes, and X-ray structures reveal shortened Cu−ligand bond distances that match well with theory.

Sulfur-Containing Analogues of the Reactive [CuOH]2+ Core

“…Treatment of solutions of [Bu 4 N]­[ 1 ] or [Bu 4 N]­[ 2 ] at −80 °C with ferrocenium tetrakis­(3,5-bis­(trifluoromethyl)­phenyl)­borate (FcBAr F ) led to an immediate color change to deep blue or purple, loss of the EPR signal, and the appearance of an intense UV–vis absorption peak with λ max = 582 nm (ε ≈ 6900 M –1 cm –1 ) or 538 nm (ε ≈ 11 700 M –1 cm –1 ), respectively (Figure ). These features are similar to those observed for LCuOH and LCuZ (Z = OOR, halide, O 2 CR), which were assigned as charge-transfer transitions (see theory results below). Repeated experiments with varying amounts of FcBAr F (0.2–2 equiv) showed the maximum intensity of the product spectral features upon addition of 1 equiv (Figures S3 and S4).…”

“…Among the various copper–oxygen complexes that have been studied, those comprising the formally high-valent [CuOH] 2+ core supported by sterically hindered, dianionic bis­(carboxamido) ligands (Figure ) have been shown to be highly reactive in a proton-coupled electron-transfer (PCET) involving substrate C–H and O–H bonds, processes that are relevant to catalytic oxidations . Comparative studies of analogues with [CuZ] 2+ (Z = OOR′, halides, or carboxylates) units also have been performed, leading to a greater understanding of electronic structural aspects and detailed PCET mechanisms.…”

Synthesis of Sulfilimines Enabled by Copper-Catalyzed S-Arylation of Sulfenamides

“…For these pathways, the possible spin states for the disproportionation intermediates (IV and IX) and reductive elimination transition states (V and X) were explored since Cu(III) can exist as a singlet or triplet. 29,30 The triplet spin state for the nitrogen-bonded compounds IX and X was over 20 kcal/mol higher in energy than the singlet. No triplet reductive elimination transition state for the sulfur pathway would optimize.…”

Oxidative versus basic asynchronous hydrogen atom transfer reactions of Mn(iii)-hydroxo and Mn(iii)-aqua complexes

“…Mechanisms of hydrogen atom transfer (HAT) reactions from organic substrates (SH) to metal-oxygen complexes, such as metal-oxo, metal-hydroxo, [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] metal-(hydro)peroxo [40][41][42][43][44] and metal-superoxo, [45][46][47][48][49][50][51][52][53][54] have been investigated extensively, as summarized in Scheme 1. HAT proceeds via the transfer of both a proton and an electron which can be transferred simul-spectrum of "asynchronicity", in which the transition state for the HAT reaction can contain either more PT or more ET character (Scheme 1).…”

“…Mechanisms of hydrogen atom transfer (HAT) reactions from organic substrates (SH) to metal–oxygen complexes, such as metal-oxo, 1–23 metal-hydroxo, 24–39 metal-(hydro)peroxo 40–44 and metal-superoxo, 45–54 have been investigated extensively, as summarized in Scheme 1. HAT proceeds via the transfer of both a proton and an electron which can be transferred simultaneously in a coupled fashion (concerted proton–electron transfer, CPET) or a stepwise fashion (proton transfer–electron transfer, PT/ET, or electron transfer–proton transfer, ET/PT) (Scheme 1).…”