Pyridyl-directed C-H and C-Br bond activations promoted by dimer iridium-olefin complexes

Complexes [Ir(μ-Cl)(η2-C8H14)2]2 (1) and [Ir(μ-Cl)(η4-C8H12)]2 (2) promote the pyridyl-directed ortho-CH and ortho-CBr activations of the phenyl substituent of 2-(2-bromophenyl)pyridine. The formed products depend upon the olefin of the dimer, which governs the kinetic preference of the activation. The cyclooctene complex 1 reacts with the substituted heterocycle to give (η2-C8H14)2Ir(μ-Cl)2Ir{κ2-C,N-[C6BrH3-py]}2 (3), in acetone, at room temperature. Treatment of 3 with K(acac) affords Ir(acac)(η2-C8H14)2 (4) and Ir(acac){κ2-C,N-[C6BrH3-py]}2 (5; acac = acetylacetone). Under more severe conditions, 2-ethoxyethanol under reflux, the reaction of 1 with the heterocycle gives a yellow solid, which yields a 5:82:7 mixture of 5, Ir(acac){κ2-C,N-[C6BrH3-py]}{κ2-C,N-[C6H4-py]} (6), and Ir(acac){κ2-C,N-[C6H4-py]}2 (7) by reaction with K(acac). In acetone or toluene, at room temperature, 2-(2-bromophenyl)pyridine breaks the chloride bridges of dimer 2 to form IrCl(η4-C8H12){κ1-N-[py-C6BrH4]} (8), which evolves into IrClBr{κ2-C,N-[C6H4-py]}(η4-C8H12) (9) as a result of the oxidative addition of the ortho-CBr of the phenyl substituent to the metal center. Treatment of 9 with Ag2O in acetylacetone leads to Ir(acac){κ2-C,N-[C6H4-py]}{κ1-C, η2-[C8H12-(C3-acac)]} (10), as a consequence of the replacement of the halides by an O,O-chelate acac ligand and the outside to metal nucleophilic attack of a second acac group to the diene C–C double bond disposed trans to bromide.Financial support from the MINECO of Spain (Projects CTQ2017-82935-P and Red de Excelencia Consolider CTQ2016-81797-REDC), the Diputación General de Aragón (E06_17R), FEDER, and the European Social Fund is acknowledged.Peer reviewe