Oxygen bridged Homobinuclear Mn(II) compounds with Anthranilic acid: Theoretical calculations, oxidation and catalase activity

Abstract

Two new homobinuclear manganese compounds with mixed ligands, [Mn2(μ1,1–2‐NH2C6H4COO)2(phen)4](ClO4)2(CH3OH) (1), and [Mn2(μ1,3–2‐NH2C6H4COO)2(bipy)4](ClO4)2 (2) (NH2C6H4COOH = anthranilic acid, bipy = 2,2′‐bipyridine, phen = 1,10‐ phenanthroline) were synthesized and thoroughly characterized by elemental analysis, IR, UV and single crystal X‐ray crystallography. X‐ray structure analysis shows that in the mono‐ and bidentate carboxylate bridged compounds, Mn–Mn distances of 1 and 2 are 3,461 Å, and 4,639 Å, respectively. The energy of the compounds was determined with a DFT (Density Functional Theory) calculation on B3LYP/6‐31G(d,p) optimized geometry by using the B3LYP/6‐31G(d,p) basis set. These compounds acts as biomimetic catalyst and show catalase‐like activity for the hydrogen peroxide dismutation at room temperature in different solvents with remarkable activity (TOF, Turnover frequency = mol of subst./(mol of cat. × time)) up to 12640 h−1 with 1, and 17910 h−1 with 2 in Tris–HCl buffer). Moreover, the catalytic activity of 1 and 2 has been studied for oxidation of alcohols (cinnamyl alcohol, benzyl alcohol, cyclohexanol, 1‐octanol and 1‐heptanol) and alkenes (cyclohexene, styrene, ethyl benzene, 1‐octene and 1‐hexene) in a homogeneous catalytic system consisting t‐butylhydroperoxide (TBHP) as an oxidant in acetonitrile. Both compounds exhibited very high activity in the oxidation of cyclohexene to cyclohexanone (~80% selectivity, ~99% conversion in 1 h, TOF = 243 h−1 and 226 h−1) and cinnamyl alcohol to cinnamaldehyde (~64% selectivity) as the main product with very high TOF value (9180 h−1 and 13040 h−1 in the first minute of reaction) (~100% conversion in 0.5 h) with TBHP at 70 °C in acetonitrile, for 1 and 2, respectively.

Measuring Relative Energies of Ligand Binding Conformations on Nanocluster Surfaces with Temperature-Dependent FTIR Spectroscopy

“…52,53 Notably, the syn−anti bridging conformation is not significantly different in energy from the monodentate motif, suggesting that the energetic bonus of an additional ligand−metal bond is offset by a confounding factor, such as geometric strain. 64,65 Meanwhile, the dative binding conformation we observe has a higher energy relative to the monodentate. This dative motif is difficult to precisely assign to a geometry; previous singlecrystal studies show a single ligand in an asymmetric chelating geometry with a bridging dative bond, but these studies were done at −173 °C with phenylacetate ligands and it is unknown whether this preferred geometry will change to a monodentate, dative motif at higher temperatures or with a longer alkyl tail.…”

“…While the chelating and syn – syn bridging conformations are lower in energy compared to the monodentate motif, the difference is not as large as might be expected from the formation of an additional ligand–metal bond. The energy difference we observe is on the order of 200–400 cm –1 , or 0.57–1.14 kcal/mol, far lower than the 15–20 kcal/mol predicted by theory. , Notably, the syn – anti bridging conformation is not significantly different in energy from the monodentate motif, suggesting that the energetic bonus of an additional ligand–metal bond is offset by a confounding factor, such as geometric strain. , Meanwhile, the dative binding conformation we observe has a higher energy relative to the monodentate. This dative motif is difficult to precisely assign to a geometry; previous single-crystal studies show a single ligand in an asymmetric chelating geometry with a bridging dative bond, but these studies were done at −173 °C with phenylacetate ligands and it is unknown whether this preferred geometry will change to a monodentate, dative motif at higher temperatures or with a longer alkyl tail .…”