A Luminescent Zirconium(IV) Complex as a Molecular Photosensitizer for Visible Light Photoredox Catalysis

• Published in: Journal of the American Chemical Society Vol. 138; no. 40; pp. 13115 - 13118
• Main Authors: Zhang, Yu, Petersen, Jeffrey L, Milsmann, Carsten
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 12.10.2016
• Subjects: alkenes; catalytic activity; dehalogenation; electron transfer; ligands; photoluminescence; photosensitizing agents; pyridines; reducing agents; titanium; zirconium
• ISSN: 0002-7863; 1520-5126; 1520-5126
• DOI: 10.1021/jacs.6b05934

Titanium and zirconium complexes carrying two 2,6-bis­(pyrrolyl)­pyridine ligands have been synthesized and characterized. The neutral complexes Ti­(MePDP)2 and Zr­(MePDP)2 (MePDP = 2,6-bis­(5-methyl-3-phenyl-1H-pyrrol-2-yl)­pyridine) show intense ligand-to-metal charge-transfer bands in the visible region and undergo multiple reversible redox events under highly reducing conditions. Zr­(MePDP)2 exhibits photoluminescent behavior and its excited state can be quenched by mild reductants to generate a powerful electron transfer reagent with a ground state potential of −2.16 V vs Fc+/0. This reactivity was utilized to facilitate dehalogenation reactions, the reduction of electron-poor olefins, and the reductive coupling of benzyl bromide via photoredox catalysis. In these reactions, the earth-abundant metal complex Zr­(MePDP)2 acts as a substitute for the precious metal photosensitizer [Ru­(bpy)3]2+.