Designing Iridium Catalysts for Selective C-O Cleavage

Abstract

Catalytic C-O cleavage via ether silylation holds promise for the generation of valueadded, and biologically relevant molecules from renewable biomass-derived feedstocks. Current catalysts for secondary C-O cleavage lack selectivity necessary for applications in the reduction of complex substrates. Using a series of air-stable, cationic iridium bis(phosphine) catalysts has led to the development of a tunable manifold for secondary C-O cleavage on 6-membered carbocycles of varying complexity. We found that axial and equatorial methyl ethers show distinct reactivity profiles. Catalyst-controlled selectivity in C-O reduction was observed. Resting state analysis showed comparable speciation between catalysts with opposite reactivity in the form of (PR3)2IrH4SiEt3, suggesting that selectivity is dictated by the electronic environment of the metal center. Selectivity and mechanism of light-promoted transfer of an iridium hydride in alkyl ether cleavage will also be discussed.