title: Photochemical CO2 Reduction Catalyzed by Phenanthroline Extended Tetramesityl Porphyrin Complexes Linked with a Rhenium(I) Tricarbonyl Unit.
abstract: A series of heterodinuclear complexes (M-1-Re) based on a phenanthroline (phen) extended tetramesityl porphyrin ligand (H2-1) has been prepared. The phen moiety of this ligand selectively coordinates a Re(I) tricarbonyl chloride unit, whereas the metal in the porphyrin moiety has been varied: namely, Cu, Pd, Zn, Co, or Fe was used. These dinuclear complexes were fully characterized by standard analytical methods. Additionally, a crystal structure of Cu-1-Re·5.5(C7H8)·0.5(C6H6) could be obtained, and extended time-resolved emission lifetime measurements were conducted. Furthermore, their ability to catalyze the photochemical reduction of CO2 to CO was investigated. Light-driven CO2 reduction experiments were performed in dimethylformamide (DMF) using triethylamine (TEA) as the sacrificial electron donor. The TONs (turnover numbers) of CO were determined and revealed a surprising catalytic activity that is obviously independent from the redox activity of the porphyrin metal. We have recently shown that the parent M-1 compounds are active photocatalysts, but the catalytic activity was dependent on the redox activity of the porphyrin metal. In the case of the new heterodinuclear complexes M-1-Re reported in this study, the catalytic active center seems to be the Re(I) moiety and not the porphyrin. Surprisingly, Zn-1-Re proved to be the most active compound in this series showing a TONCO of 13 after 24 h of illumination using a >375 nm cutoff filter while all other compounds showed minimal activity under this condition.
authors.affiliation: Institute of Chemistry, Humboldt-Universität zu Berlin , Brook-Taylor-Strasse 2, 12489 Berlin, Germany.
authors.forename: Corinna
authors.initials: C
authors.lastname: Matlachowski
authors.affiliation: Institute of Chemistry, Humboldt-Universität zu Berlin , Brook-Taylor-Strasse 2, 12489 Berlin, Germany.
authors.forename: Beatrice
authors.initials: B
authors.lastname: Braun
authors.affiliation: Institute of Physics, University of Rostock , Universitätsplatz 3, 18055 Rostock, Germany.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Tschierlei
authors.affiliation: Institute of Chemistry, Humboldt-Universität zu Berlin , Brook-Taylor-Strasse 2, 12489 Berlin, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Schwalbe