Aryl ether carbon-​oxygen bond cleavage by group 9 and 10 metals: Studies of selectivity and mechanism

Abstract

The cleavage of aryl ethers is valuable for org. methodol. and biomass conversion. To gain mechanistic insight into aryl-ether bond cleavage in structurally related metal complexes, the reactivity of terphenyl diphosphines bearing aryl, Me or aryl, aryl ether moieties with M(0), M(II) (M = Ni, Pd, Pt) and M(I) (M' = Co, Rh, Ir) centers was investigated. Overall, selective cleavage of the stronger aryl ether C-O was obsd. only with Ni(0) and Rh(I). Pd(0) and Pt(0) can perform aryl ether C-O activation, but if available, they will cleave the weaker O-Me bond. IrI activates both, unselectively. In the presence of H2, the source of reducing equiv. in the C-O to C-H conversion of aryl alkyl ethers was found to be the alkyl group rather than H2, in both stoichiometric and catalytic systems. Changing the electronic character of the aryl ring coordinated to the metal center does not have a large effect on the rates of aryl ether bond activation. The effect of Lewis acidic additives will be discussed.