A pincer-ligated iridium complex, (PCP)Ir (PCP = kappa(3)-C6H3-2,6-[CH2P(t-BU)(2)](2)), is found to undergo oxidative addition of C(sp(3))-O bonds of methyl esters (CH3-O2CR'), methyl tosylate (CH3-OTs), and certain electron0poor methyl aryl ethers (CH3-OAr). DFT calculations and mechanistic studies indicate that the reactions proceed via oxidative addition of C-H bonds followed by oxygenate migration, rather than by direct C-O addition. Thus, methyl aryl ethers react via addition of the methoxy C H bond, followed by alpha-arylcodde migration to give cis-(PCP)Ir(H)(CH2)(OAr), followed by iridium-to-methylidene hydride migration to give (PCP)Ir(CH3)(OAr). Methyl acetate undergoes C-H bond addition at the carbomethoxy group to give (PCP)Ir(H)[kappa(2)-CH2OC(O)Me] which then affords (PCPCH2)Ir(H)(kappa(2)-O2CMe) (6-Me) in which the methoxy C-O bond has been cleaved, and the methylene derived from the methoxy group has migrated into the PCP C-ipso-Ir bond. Thermolysis of 6-Me ultimately gives (PCP)Ir(CH3)(kappa(2)-O2CR), the net product of methoxy group C-O oxidative addition. Reaction of (PCP)Ir with species of the type ROAr, RO2CMe or ROTs, where R possesses beta-C-H bonds (e.g., R = ethyl or isopropyl), results in formation of (PCP)Ir(H)(OAr), (PCP)Ir(H)(O2CMe), or (PCP)Ir(H)(OTs), respectively, along with the corresponding olefin or (PCP)Ir(olefin) complex. Like the C-O bond oxidative additions, these reactions also proceed via initial activation of a C H bond; in this case, C H addition at the beta-position is followed by beta-migration of the aryloxide, carboxylate, or tosylate group. Calculations indicate that the beta-migration of the carboxylate group proceeds via an unusual six-membered cyclic transition state in which the alkoxy C-O bond is cleaved with no direct participation by the iridium center.