Impact of the Electronic Variation at the Ligand Backbone on the Redox Chemistry of Bipyridine‐Mn(CO) ₃ Br Complexes

Herein, we investigate the impact of electronic variation in 4,4′‐position of the bipyridine ligand in [L R Mn(CO) 3 Br], 1 R , on the coupled electrochemical and chemical reactions proceeding initial reduction of 1 R (L R = 4,4′‐R‐2,2′‐bipyridine). We choose −CF 3 , −OMe, and −Ph residues as electron‐withdrawing, ‐donating, and ‐neutral substituents, respectively. Kinetic and thermodynamic analysis reveal that the processes after initial reduction are similar in all complexes and follow the previously reported reaction pathway after initial reduction of 1 H . The redox potentials correlate with the Hammett parameter σ p , that is, 1 CF3 and its follow‐up products require the least negative and 1 OMe the most negative potentials. Initial reduction of 1 R is coupled to bromide loss leading to [L R Mn(CO) 3 ], 2 R , which is always easier to reduce than 1 R . However, the equilibrium constant K 1 for bromide loss after initial reduction of 1 R in [L R Mn(CO) 3 Br] − , 1 R − , largely depends on the electronic variation: It is endergonic in 1 CF3− , which has the electron‐withdrawing substituent –CF 3 , and exergonic for 1 Ph− and 1 OMe− . The free energy difference in K 1 is similar to the free energy difference in the redox potential E 0 1 of the initial reduction of 1 R . The impact of these findings on catalysis involving the two‐electron reduced species 2 R− is discussed.