Cleavage of the βO4 linkage of lignin using group 8 pincer complexes: A DFT study

•The lignin βO4 bond cleavage was studied using group 8 pincer complexes.•CO bond activation is controlled by the metal center’s ability to donate electrons.•Ru(II)–PCP complex is the most favorable catalyst for lignin βO4 cleavage.

The catalysis of CO bond activation of the lignin βO4 model compound, 2-phenoloxy-1-phenolethanol, was investigated using group 8 (Fe, Ru and Os) pincer complexes. Reaction mechanisms and thermodynamics for the catalysis were studied using B3LYP/CEP-31G. Solvent effects were considered using a SMD solvation model for 1,4-dioxane. The considered pincer complexes include combinations of the three metals with five different pincer ligands (PNP, NNN, PCP, PCN and NCN). All possible multiplicities and conformations were taken into account. The reaction energetics of all metal-ligand combinations were compared and the thermodynamic nature of transition metal activation of the βO4 bond was discovered. The studies suggest that CO bond activation by transition metal catalysts is essentially controlled by the ability of the metal center to donate electrons to the CO bond; ligands that donate electrons to the metal center tend to facilitate the cleavage of the CO bond.

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