Depolymerization of wood lignin to isolated products using main group and organometallic catalysts
Résumé
Lignin represents the most abundant source of renewable aromatics. Yet, although the paper industry alone produces about 1.1 million tons of lignin each year, only <3 % integrate a value chain after transformation.[1]
Lignin indeed features a complex and heterogeneous structure, which varies with the wood species and relies on inert C–C and ether C–O bonds. Depolymerization methods applied so far in lignin conversion suffer from harsh reaction conditions and yield complex mixtures of products, from which isolation of pure products is an issue.[2] To circumvent this limitation, we have developed a novel strategy based on the reductive depolymerization of lignin with main group and metal catalysts, using hydrosilanes reductants.[3]
Boron and iridium organometallic complexes are active catalysts in the hydrosilylation of lignin and their reaction chemistry with lignin models provides an efficient entry to C-O bond cleavage in β-O-4 and α-O-4 linkages.[4] They have been successfully applied for the depolymerization of 15 different wood species.[3] This methodology enables the isolation of four different aromatic products, for the first time. Combining the selection of the plant species with the lignin extraction method and the depolymerization method was shown control the nature, the purity and the yield of the final product