Effects of Chemically-Modified Polypyridyl Ligands on the Structural and Redox Properties of Tricarbonylmanganese(I) Complexes

Abstract

Carbonyl complexes with manganese(I) as the central metal are very attractive catalysts. The introduction of redox-active ligands, such as quinones and methyl viologen analogs into these catalysts, would be expected to lead to superior catalyst performances, since they can function as excellent electron carriers. In this study, we synthesized four tricarbonylmanganese(I) complexes containing typical bidentate polypyridyl ligands, including 1,10-phenanthroline (phen) and 2,2′-bipyridine (bpy) frameworks bound to redox-active ortho-quinone/catechol or methyl viologen-like units. The molecular structures of the resulting complexes were determined by X-ray crystallography to clarify their steric features. As expected from the infrared (IR) data, three CO ligands for each complex were coordinated in the facial configuration around the central manganese(I) atom. Additionally, the structural parameters were found to differ significantly between the quinone/catechol units. Electrochemical analysis revealed some differences between them and their reference complexes, namely [MnBr(CO)3(phen)] and [MnBr(CO)3(bpy)]. Notably, interconversions induced by two-electron/two-proton transfers between the quinone and catechol units were observed in the phenanthroline-based complexes. This work indicated that the structural and redox properties in tricarbonylmanganese(I) complexes were significantly affected by chemically modified polypyridyl ligands. A better understanding of structures and redox behaviors of the present compounds would facilitate the design of new manganese complexes with enhanced properties.

Thermoluminescent Tb(III) and Dy(III) complexes with redox‐active ligands: experimental and theoretical study

“…It is known that 1,10-phenanthrolines are redox-active ligands and can exist in neutral, anion radical, and dianionic forms. [38][39][40][41] The same results were obtained for the electronic structure of II.…”

“…It is known that 1,10‐phenanthrolines are redox‐active ligands and can exist in neutral, anion radical, and dianionic forms. [ 38–41 ]…”

Manganese(I) Diimine(tricarbonyl) Complexes with a Redox-active Free Catechol Unit: Redox-induced Molecular Conversion of Catechol to Quinone by Electrochemical Redox Reactions on the Complex

“…Microanalysis data were obtained using a Perkin Elmer 2400II series CHN analyzer (Yokohama, Japan). The 1 H and 13 C{ 1 H} NMR spectra were recorded using a JEOL LMN-AL300 spectrometer (Tokyo, Japan) operating at 1 H and 13 C frequencies of 300 and 75.5 MHz, respectively. Both spectra were referenced to external (CH 3 ) 4 Si via the residual protons of the solvent ( 1 H) or the solvent itself ( 13 C).…”

“…12 Previously, we reported the interconversion between quinone and catechol on a complex by various electrochemical experiments on a manganese(I) tricarbonyl complex containing the dpq ligand ([MnBr(CO) 3 (dpq)]). 13 A reductive reaction system can be constructed from the quinone because dpq contains a stable quinone (oxidized) form. However, few studies have examined the oxidation reactions of A-diimine complexes containing a catechol (reduced) form.…”

“…However, few studies have examined the oxidation reactions of A-diimine complexes containing a catechol (reduced) form. 13,14 In this work, we focused on 4-(3,4-benzenediol)-2,2B-bipyridine (bpyCat), in which the stable catechol unit is introduced into the Scheme 1. Reversible 2e ¹ /2H + (PCET) process of catechol.…”