Transition metal mediated carbon-​oxygen bond activation of aryl ethers bearing pendant phosphines

Abstract

Cleavage of aryl C-O bonds of lignin affords phenols and aroms. that might serve as useful precursors in chem. synthesis. C-O bond activation of aryl ethers allows for their use as cross coupling partners and removable protecting groups. An aryl Me ether bearing pendant phosphines was synthesized to investigate ether bond cleavage mediated by different transition metals. Three modes of bond activation were obsd. at group 9 and 10 transition metals: oxidative addn. across the aryl C-O bond, oxidative addn. across the alkyl C-O bond, and Lewis-acid mediated alkyl halide elimination. Metal oxidn. state as well as π-backbonding interactions between the central arene and the metal center were correlated to which mode(s) of C-O bond activation were obsd. These results and implications for the design of intermol. aryl C-O bond cleavage systems will be presented.