Visible Light Promoted Hydroxylation of a Si–C(sp³) Bond Catalyzed by Rhodium Porphyrins in Water

Catalytic activation of an unstrained, unactivated Si–C(sp³) bond in water to form methane and silanol by electrophilic rhodium(III) porphyrin [(por)Rh^III] in acidic aqueous solutions under visible light (λ ≥ 420 nm) has been developed. Activation of the Si–C(sp³) bond occurs through direct Si–C bond cleavage, with methyl group transfer to rhodium to give a porphyrin rhodium methyl complex. Photolysis of (por)Rh-CH₃ in water yields methyl radical and (por)Rh^II. Subsequently, (por)Rh^II reacts with water rapidly to produce (por)Rh-H and (por)Rh-OH. (por)Rh-OH is then protonated to regenerate (por)Rh^III-OH₂, and (por)Rh-H undergoes hydrogen atom abstraction by methyl radical to form the observed methane.