Tuning the geometry and biomimetic catalytic activity of manganese(III)-tetrabromocatecholate based robust platforms by introducing substitution at pyridine

• Manganese(III) complex with redox-noninnocent tetrabromocatecholate ligand
• Coordination environment of managanese(III) center over the substitution at pyridyl ring
• Influence of pyridyl substitution on the catalytic activity mimicking the function of Catechol oxidase
• Impact of electronic property and structural distortion on catecholase activity

The present report describes synthesis, characterization, crystal structures and catecholase activity of a series of five new manganese(III) complexes (1–5) derived from redox-noninnocent tetrabromocatecholate ligand in combination with different substituted pyridines. X-ray crystallography reveals that the geometry of manganese(III) centers in 1 and 2 is square pyramidal and they are pseudo-dimeric in the solid state resulting from the weak bonding of manganese(III) with a catecholate oxygen atom from the adjacent manganese(III) unit together with other weak interactions like hydrogen bonding and π ⋯ π stacking interactions. On the other hand, complexes 3–5 are discrete octahedral structures. All the complexes exhibit strong catecholase activity and their diverse catalytic activity can nicely be explained by the nature of substitution at pyridine ring — better electron donor inhibits the reduction of the metal center thereby lowering catecholase activity and vice versa (1 and 2 vs. 3–5). Besides the donor property of ancillary ligands, the structural distortion has also significant role in the biomimetic catalytic activity (1 vs. 2).

Five new manganese(III) complexes derived from redox-noninnocent tetrabromocatecholate ligand in combination with different substituted pyridines have been structurally characterized. Influence of the substitution on the coordination environment of the metal center and the biomimetic catalytic activity is critically analyzed.Figure optionsDownload as PowerPoint slide