Alkyl Carbon-Oxygen Bond Cleavage of Aryl Alkyl Ethers by Iridium-Porphyrin and Rhodium-Porphyrin Complexes in Alkaline Media

Alkyl C-O bond cleavage in aryl alkyl ethers was achieved with Rh(ttp)Cl (la; ttp = 5,10,15,20-tetrakis(p-tolyl)porphyrinato dianion) together with competitive alkyl C-H bond activation in alkaline media. In contrast, selective alkyl C-O bond cleavage occurred with the iridium porphyrin Ir(ttp)(CO) Cl (1b)/KOH. Mechanistic investigations indicate the coexistence of M-I(ttp)(-) and M-2(II)(ttp)(2) (M = Rh, Ir) under basic conditions. With a weaker Rh(ttp)-Rh(ttp) bond, Rh-II(ttp). metalroradical exists in an appreciable amount to cleave the alkyl C-H bond, competing with the alkyl C-O bond cleavage via Rh-I(ttp)(-). In contrast, the more nucleophilic Ir-I(ttp)(-) cleaves the alkyl C-O bond exclusively.