Editing Group 7 element (section)

=== Manganese ===

The rarity of rhenium has shifted research toward the manganese version of these catalysts as a more sustainable alternative.<ref name=":2" /> The first reports of catalytic activity of Mn(R-bpy)(CO)<sub>3</sub>Br towards CO<sub>2</sub> reduction came from Chardon-Noblat and coworkers in 2011.<ref>{{Cite journal|last=Bourrez|first=Marc|date=2011|title=[Mn(bipyridyl)(CO)3Br]: an abundant metal carbonyl complex as efficient electrocatalyst for CO2 reduction|journal=Angewandte Chemie International Edition in English |volume=50|issue=42 |pages=9903–9906|doi=10.1002/anie.201103616 |pmid=21922614 }}</ref> Compared to Re analogs, Mn(R-bpy)(CO)<sub>3</sub>Br shows catalytic activity at lower overpotentials.<ref name=":3" />

The catalytic mechanism for Mn(R-bpy)(CO)<sub>3</sub>X is complex and depends on the steric profile of the bipyridine ligand. When R is not bulky, the catalyst dimerizes to form [Mn(R-bpy)(CO)<sub>3</sub>]<sub>2</sub> before forming the active species. When R is bulky, however, the complex forms the active species without dimerizing, reducing the overpotential of CO<sub>2</sub> reduction by 200-300 mV. Unlike Re(R-bpy)(CO)<sub>3</sub>X, Mn(R-bpy)(CO)<sub>3</sub>X only reduces CO<sub>2</sub> in the presence of an acid.<ref name=":3" />