Cleavage of sp³ C-O bonds via oxidative addition of C-H bonds

(Chemical Equation Presented) (PCP)Ir (PCP = K³-C ₆H₃-2,₆-[CH₂P(t-Bu) ₂]₂) is found to undergo oxidative addition of the methyl-oxygen bond of electron-poor methyl aryl ethers, including methoxy-3,5-bis(trifluoromethyl)benzene and methoxypentafluorobenzene, to give the corresponding aryloxide complexes (PCP)Ir(CH₃)(OAr). Although the net reaction is insertion of the Ir center into the C-O bond, density functional theory (DFT) calculations and a significant kinetic isotope effect [k_CH3OAr/k_CD3OAr = 4.3(3)] strongly argue against a simple insertion mechanism and in favor of a pathway involving C-H addition and ;-migration of the OAr group to give a methylene complex followed by hydride-to-methylene migration to give the observed product. Ethoxy aryl ethers, including ethoxybenzene, also undergo C-O bond cleavage by (PCP)Ir, but the net reaction in this case is 1,2-elimination of ArO-H to give (PCP)Ir(H)(OAr) and ethylene. DFT calculations point to a low-barrier pathway for this reaction that proceeds through C-H addition of the ethoxy methyl group followed by ß-aryl oxide elimination and loss of ethylene. Thus, both of these distinct C-O cleavage reactions proceed via initial addition of a C(sp ³)-H bond, despite the fact that such bonds are typically considered inert and are much stronger than C-O bonds.