The effect of axial ligand on the oxidation of syringyl alcohol by Co(salen) adducts

Experimental work on the oxidation of the lignin model, syringyl alcohol, using oxygen and a Co(salen) catalyst has revealed variations in yield with different imidazole-based axial ligands. A reasonable linear relationship was found between product yield and pKa of the axial ligand. The current work, using density functional calculations, examined geometric, electronic, and energetic parameters to determine if additional quantitative relationships can be identified and used in subsequent catalyst design. Good relationships with yield were identified with the geometry of the salen ligand and the charge on the ligand nitrogen coordinated to the cobalt.