An Iron Complex with a Bent, O‐Coordinated CO2 Ligand Discovered by Femtosecond Mid‐Infrared Spectroscopy

• Published in: Angewandte Chemie International Edition Vol. 57; no. 18; pp. 5000 - 5005
• Main Authors: Straub, Steffen, Brünker, Paul, Lindner, Jörg, Vöhringer, Peter
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 23.04.2018
• Edition: International ed. in English
• Subjects: Activated carbon; Anions; Carbon dioxide; CO2 activation; femtochemistry; Fine chemicals; Greenhouse effect; Greenhouse gases; Heavy metals; Infrared spectroscopy; Iron; Ligands; Metals; Molecular chains; Oxygen atoms; photochemistry; Spectroscopy; Spectrum analysis; time-resolved IR spectroscopy; Transition metals; transition-metal complexes
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201800672

The activation of carbon dioxide by transition metals is widely recognized as a key step for utilizing this greenhouse gas as a renewable feedstock for the sustainable production of fine chemicals. However, the dynamics of CO2 binding and unbinding to and from the ligand sphere of a metal have never been observed in the time domain. The ferrioxalate anion is used in aqueous solution as a unique model system for these dynamics and femtosecond UV‐pump mid‐infrared‐probe spectroscopy is applied to explore its photoinduced primary processes in a time‐resolved fashion. Following optical excitation, a neutral CO2 molecule is expelled from the complex within about 500 fs to generate a highly intriguing pentacoordinate ferrous dioxalate that carries a bent carbon dioxide radical anion ligand, that is, a reductively activated form of CO2, which is end‐on‐coordinated to the metal center by one of its two oxygen atoms. Optical excitation of ferrioxalate leads to an ultrafast cleavage of a neutral carbon dioxide molecule. Thereby, a ferrous dioxalate is generated bearing a bent carbon dioxide ligand in an O‐“end‐on” fashion.