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Pyridyl-Directed C–H and C–Br Bond Activations Promoted by Dimer Iridium-Olefin Complexes

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journal contribution
posted on 10.10.2018, 17:24 by Pierre-Luc T. Boudreault, Miguel A. Esteruelas, Erik Mora, Enrique Oñate, Jui-Yi Tsai
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.