CH bond activation in aromatic ketones mediated by iridium-tris(pyrazolyl)borate complexes

Reaction of complex [TpMe2Ir(eta 4-CH200000000000000000000000000000000111111110000000011111111000000000000000000000000C(Me)C(Me)C2)] (1) with a series of aromatic ketones at 130 degrees C renders, by means of a selective ortho-CH activation, Ir(iii)-metallacycles 2-5, which display an Ir-H bond. When [TpMe2Ir(C6H5)2N2] (6) is treated with 2-(trifluoromethyl)acetophenone and 2-fluoroacetophenone at 80 degrees C, the formation of dimeric (7) and trimeric architectures (8) is achieved through the meta- and para-CH activation of the aromatic ketone, respectively. The generation of complexes 2-5 is proposed to occur by the initial formation of Ir(iii) eta 1-ketone adducts as key intermediates, followed by aromatic CH activations and the release of a butadiene ligand. The formation of complexes 7 and 8 involves an assisted process in which a metal center activation of the less sterically hindered C-H bond of the aromatic ketone takes place (releasing a benzene molecule), followed by the coordination of the carbonyl group, which generates the respective dimeric and trimeric structures. Complexes 7 and 8 are efficient catalysts for the transfer hydrogenation of ketones and aldehydes using isopropanol as the hydrogen source. All complexes have been fully characterized by NMR spectroscopy, FT-IR, elemental analysis and, in the cases of 7 and 8, X-ray crystallography. Details of the reaction conditions, isolation of the products, and proposals for the pathways of formation of complexes 2-5 and 7-8 are discussed. Reaction of complex [TpMe2Ir(eta 4-CH2C(Me)C(Me)C2)] (1) with a series of aromatic ketones at 130 degrees C renders, by means of a selective ortho-CH activation, Ir(iii)-metallacycles 2-5, which display an Ir-H bond.

Automated summary

This article investigates the reaction between the complex and aromatic ketones, and finds that Ir(iii)-metallacycles can be obtained through CH activation, which highlights the significance of the Ir-H bond.