2-Quinoxalinol diamine Cu(ii) complex: facilitating catalytic oxidation through dual mechanisms

Abstract

The Cu(II) complex 1, Cu(II)-6-N-3,5-di-tert-butylsalicylidene-6,7-quinoxalinol-diamine, has been developed to address problems with current methods of catalytic oxidation using tert-butyl hydroperoxide (TBHP). Complex 1 demonstrated an increased capability to utilize TBHP while limiting interference from free radical reactions and was demonstrated to be highly effective in the oxidations of a variety of olefins.

Ensemble Effects of Explicit Solvation on Allylic Oxidation

“…The catalyst of interest in this work is Cu(II) 7-amino-6-((2-hydroxybenzylidene)amino)quinoxalin-2-ol, first reported in 2014. 22 This catalyst was developed to limit interference from free radical reactions; at the same time, it was found to demonstrate excellent efficiency in allylic oxidation reactions. However, prior gas-phase density functional theory study of the reaction mechanism resulted in a relatively high estimation of reaction barriers; the rate-determining step of H-atom abstraction was reported to consume 43.7 kcal/mol, while the step to release cyclohexenone required 37.5 kcal/mol.…”

“…2 Computational Details 2.0.0.1 MD Simulation Protocol. The Cu(II) 7-amino-6-((2hydroxybenzylidene)amino)quinoxalin-2-ol complex (1) is a slightly simplified catalyst model with respect to the experimental system, 22 wherein the two t-butyl groups (-C(CH 3 ) 3 ) on the quinoxalin-2-ol and salicylidene residues are replaced by -H because they are far from the reactive site that consists of Cu(II) and the attached methyl peroxide (-OOCH 3 ). The molecular structure of catalyst 1 is shown in Figure 1 along with the subsequent reaction intermediates (vide infra).…”

“…32 Then, the catalyst, reactants, and 60 acetonitrile (357 atoms in total) are initialized by random insertion into a periodic cubic box using the Packmol code. 33 The size of the periodic box with edgelength of 17.52 Å is obtained as a result of system equilibration using the NPT-ensemble with the stochastic velocity rescaling method 34 within DFT-MD for 2 ps at 350 K (the experimental temperature 22 ), in the Quantum Espresso package. 35 The PBE functional [36][37][38] was employed with the DFT-D3, long-range London dispersion interaction classical interaction scheme proposed by Grimme, 39 to provide empirical correction terms to the longrange interactions.…”

“…The slightly low density relative to experimental bulk acetonitrile (density = 0.79 g/cm 3 ) is anticipated based upon the small simulation box size wherein about 20% of the volume is occupied by the solutes. [44][45][46] enhances sampling along a specific reaction channel and employed the NVT ensemble at the experimental temperature of 350 K, 22 using the velocity rescaling thermostat. 47 In each bin, we apply a harmonic-bias potential to put a constraint on the chosen reaction coordinate.…”

Ensemble Effects of Explicit Solvation on Allylic Oxidation

“…21 The catalyst of interest in this work is Cu(II) (E)-6-amino-7-((2-hydroxybenzylidene )amino)quinoxalin-2-ol, and was first reported in 2014. 22 This catalyst was developed to limit interference from free radical reactions, at the same time it was found to demonstrate excellent efficiency in allylic oxidation reactions. However prior gas-phase density functional theory study of the reaction mechanism resulted in a relatively high estimation of reaction barriers for the catalyzed oxidation process.…”