Mechanistic insights into intramolecular ortho-amination/hydroxylation by nonheme Fe-IV=NTs/Fe-IV=O species: the sigma vs. the pi channels

Comparative oxidative abilities of nonheme Fe-IV=NTs and Fe-IV=O species using DFT has been explored. Our calculations reveal that the Fe-IV=NTs is found to be a stronger oxidant in two electron transfer reactions and react exclusively via pi channels while the Fe-IV=O species is found to be a stronger oxidant when the sigma-pathway is activated such as in HAT reactions

Synthesis, structure, redox behavior, catalytic activity and DFT study of a new family of ruthenium(III)1-(arylazo)naphtholate complexes

Treatment of [RuCl2(DMSO)(4)] with 1-(arylazo)naphthol ligands in benzene under reflux afford the air stable new ruthenium(III) complexes with general composition [Ru(L-R)(3)] (L = bidentate O, N donor; R = H, CH3, OCH3, Br, NO2) in good yield. The 1-(arylazo)naphthol ligands behave as tris-bidentate 0, N donors via naphtholic proton and azo nitrogen. The molecular and electronic structure of the complexes have been established by elemental analysis and spectral (FT-IR, UV-vis & EPR) methods. DFT calculations were also carried out on the complexes 1 and 3 along with X-ray crystallized geometry of complex 5. These complexes in dichloromethane solution show intense ligand-to-metal charge transfer (LMCT) transitions in the visible region. The absorption and g-tensor value of these complexes (1, 3 & 5) were also computed and compared along with the available experimental results. The redox behavior of the complexes has been investigated by cyclic voltammetry and the potentials are observed with respect to the electronic nature of substituents (R) in the 1-(arylazo)naphthol ligands. These complexes have shown great promise as catalysts for the conversion of aldehydes to primary amides in good yield. (C) 2016 Elsevier B.V. All rights reserved

Theoretical studies on concerted versus two steps hydrogen atom transfer reaction by non-heme Mn-IV/III=O complexes: how important is the oxo ligand basicity in the C-H activation step?

High-valent metal-oxo complexes have been extensively studied over the years due to their intriguing properties and their abundant catalytic potential. The majority of the catalytic reactions performed by these metal-oxo complexes involves a C-H activation step and extensive efforts over the years have been undertaken to understand the mechanistic aspects of this step. The C-H activation by metal-oxo complexes proceeds via a hydrogen atom transfer reaction and this could happen by multiple pathways, (i) via a proton-transfer followed by an electron transfer (PT-ET), (ii) via an electron-transfer followed by a proton transfer (ET-PT), (iii) via a concerted proton-coupled electron transfer (PCET) mechanism. Identifying the right mechanism is a surging topic in this area and here using [Mn(III)H(3)buea(O)](2-) (1) and [Mn(IV)H(3)buea(O)](-) (2) species (where H(3)buea = tris[(N'-tert-butylureaylato)-N-ethylene]aminato) and its C-H activation reaction with dihydroanthracene (DHA), we have explored the mechanism of hydrogen atom transfer reactions. The experimental kinetic data reported earlier (T. H. Parsell, M.-Y. Yang and A. S. Borovik, J. Am. Chem. Soc., 2009, 131, 2762) suggests that the mechanism between 1 and 2 is drastically different. By computing the transition states, reaction energies and by analyzing the wavefunction of the reactant and transitions states, we authenticate the proposal that the Mn-III=O undergoes a step wise PT-ET mechanism where as the Mn-IV=O species undergo a concerted PCET mechanism. Both the species pass through a [Mn-III-OH] intermediate and the stability of this species hold the key to the difference in the reactivity. The electronic origin for the difference in reactivity is routed back to the strength and basicity of the Mn-oxo bond and the computed results are in excellent agreement with the experimental results

Application of activation hardness in perturbed pericyclic reactions: a case study involving electrocyclic ring opening reactions of heterocyclobutenes

Cyclobutene undergoes electrocyclic ring opening through conrotatory mode to give 1,3-butadiene and similarly its skeletally substituted analogues viz. phosphetene, thietene, oxetene and azetene isomerize to give their respective heterodienes. Quantum mechanical investigations on these perturbed pericyclic isomerizations at B3LYP level with 6-31G(d) and 6-311 + G(d,p) basis sets reveal that hetero - atoms significantly lower the barrier and alter the reaction free energies. Interestingly frontier orbital correlation diagram shows that σ and σ levels are perturbed significantly while π and π* levels undergo little changes during the reaction; the lone pairs on hetero - atoms are slightly stabilized in the TS. This results in s becoming HOMO in the TSs of phosphetene and thietene isomerizations and σ* becoming LUMO in all the cases. This necessitates defining hardness values based on closely interacting frontier orbitals for reactants and TSs and use them to compute activation hardness values to interpret relative reactivity