Bis(μ-oxo) Dicopper(III) Species of the Simplest Peralkylated Diamine: Enhanced Reactivity toward Exogenous Substrates

Abstract

N,N,N′,N′-tetramethylethylenediamine (TMED), the simplest and most extensively used peralkylated diamine ligand, is conspicuously absent from those known to form a bis(μ–oxo)dicopper(III) (O) species, [(TMED)2Cu(III)2O2]2+, upon oxygenation of its Cu(I) complex. Presented here is the characterization of this O species and its reactivity towards exogenous substrates. Its formation is complicated both by the instability of the [(TMED)Cu(I)]1+ precursor and by competitive formation of a presumed mixed-valent trinuclear [(TMED)3Cu3(μ3-O)2]3+ (T) species. Under most reaction conditions, the T species dominates, yet, the O species can be formed preferentially (> 80%) upon oxygenation of acetone solutions, if the copper concentration is low (< 2 mM) and [(TMED)Cu(I)]1+ is prepared immediately before use. The experimental data of this simplest O species provides a benchmark by which to evaluate DFT computational methods for geometry optimization and spectroscopic predictions. The enhanced thermal stability of [(TMED)2Cu(III)2O2]2+ and its limited steric demands compared to other O species allows more efficient oxidation of exogenous substrates, including benzyl alcohol to benzaldehyde (80% yield), highlighting the importance of ligand structure to not only enhance the oxidant stability but also maintain accessibility to the nascent metal/O2 oxidant.

Toward a mechanistic understanding of oxidative homocoupling: the Glaser–Hay reaction

“…Although O 2 and some Cu/O 2 species are recognized as good outer sphere oxidants it should be expected that this kind of systems react following an inner sphere pathway; 27,28 in fact, the studied Cu(I)/TMEDA/O 2 system is reported to act as such in C-H activation processes. 47 The explicit use of dioxygen introduces a lot of additional steps in the catalytic cycle, and because of this we start by presenting a simplified picture of the overall mechanism in Scheme 5, where only the most significant species are shown. The three main steps described above (Scheme 3) for the reaction with the external oxidant are conserved: (i) alkyne deprotonation (from G1 to G3), (ii) copper oxidation (from G3 to G5), and (iii) reductive elimination (from G5 to G1).…”

Self-assembly of the oxy-tyrosinase core and the fundamental components of phenolic hydroxylation

“…The formation of synthetic Cu-O 2 species is often highly sensitive to the conditions of oxygenation 33,34 ; if conditions allow significant accumulation of reactive intermediates, the yields of the desired oxygenated species can be attenuated. Typically, the injection of a preformed ligand-Cu I complex into a saturated O 2 solution (Fig.…”

Copper(II) Catalysis of Water Oxidation

“…Rapid progress has recently been made based with single site polypyridyl Ru [1][2][3][4] and Ir [5][6][7] complexes, pre-prepared Mn oxide clusters, [8] Co and Ni clusters that spontaneously form in solution, [9,10] Co 3 O 4 (spinel) particles, [11] cobalt-based polyoxometallates, [12,13] colloidal IrO 2 ·n H 2 O, [14] amorphous iridium oxide deposited from organometallic precursors, [15] and, most recently, copper-bipyridine complexes. [17][18][19][20][21][22][23][24] With a propensity for square-planar coordination, d 8 Cu III is found as an intermediate in reactions of organocopper compounds and [**] [17][18][19][20][21][22][23][24] With a propensity for square-planar coordination, d 8 Cu III is found as an intermediate in reactions of organocopper compounds and [**]…”

“…[17][18][19][22][23][24] Cu IV complexes stabilized either by fluoride ligands or as linear O = Cu = O are also known. [17][18][19][22][23][24] Cu IV complexes stabilized either by fluoride ligands or as linear O = Cu = O are also known.…”

“…[17][18][19][22][23][24] Cu IV complexes stabilized either by fluoride ligands or as linear O = Cu = O are also known. [22][23][24] We report here that, under appropriate conditions, simple Cu II salts at a variety of electrodes are highly active in electrocatalytic water oxidation. [22][23][24] We report here that, under appropriate conditions, simple Cu II salts at a variety of electrodes are highly active in electrocatalytic water oxidation.…”