Iridium Conducts Selective Hydrogenolysis

Lignin is a bountiful biomass feedstock that could be an economical source of fuels and basic aromatic chemicals. The challenge is developing practical methods to chop up the phenolic biopolymer and then catalytically deoxygenate the resulting aryl alcohols and aryl methyl ethers. A bottleneck has been that the oxygenated aromatic rings are more susceptible to metal-catalyzed hydrogenation than they are to cleavage of the C–O bonds (hydrogenolysis). Shuhei Kusumoto and Kyoko Nozaki of the University of Tokyo may have a solution with a set of iridium hydroxycyclopentadienyl catalysts that conduct selective hydrogenolysis of aryl or methyl C–O bonds without destroying the aromatic rings (Nat. Commun. 2015, DOI: 10.1038/ncomms7296). The researchers used the catalysts (one shown) to deoxygenate substituted phenols and naphthols to benzene and naphthalene derivatives and to demethylate aryl methyl ethers to phenols. They further demonstrated the versatility of the catalysts by converting the lignin model compound vanillylacetone, which has three different C–O functional groups, to butylbenzene.