Unsaturated iridium(III) complexes supported by a quinolato-carboxylato ONO pincer-type ligand: Synthesis, reactivity, and catalytic C-H functionalization

Abstract

The unsaturated σ,π-cyclooctenyl iridium(III) pincer compound [Ir(κ3-hqca)(1-κ-4,5-η-C8H13)] (1) has been prepared by the reaction of [Ir(cod)(CH3CN) 2]BF4 with lithium 8-oxidoquinoline-2-carboxylate (Li 2hqca) and obtained as two isomers derived from the relative disposition of the pincer and the σ,π-cyclooctenyl ligands. Compound 1 can be prepared as a single isomer by reaction of 8-hydroxyquinoline-2- carboxylic acid (H2hqca) with [Ir(μ-OMe)(cod)]2. Reaction of [Ir(μ-OH)(coe)2]2 with H2hqca gave the square-pyramidal iridum(III) complex [IrH(κ3-hqca) (coe)] (3). This compound exists as dinuclear assemblies [IrH(κ 3-hqca)(coe)]2 in noncoordinating solvents and as the corresponding labile mononuclear solvates in more polar solvent solutions. The dimerization of 3 was established by 1H-DOSY NMR spectroscopy and an ESI+ mass spectrum and supported by DFT calculations. Reaction of 3 with pyridine gave the adduct [IrH(κ3-hqca)(coe)(py)] (4) and the bis-pyridine complexes [IrH(κ3-hqca)(R-py)2] (R = H (6), 2-Me (7)) by replacement of the coe ligand. Compound 4 was transformed into the bromo derivative [IrBr(κ3-hqca)(coe)(py)] (5) by reaction with N-bromosuccinimide. Carbonylation of 4 gave the cyclooctenyl complex [Ir(κ3-hqca)(1-κ-C8H 15)(CO)(py)] (8), which is stable only under a carbon monoxide atmosphere. The pincer complexes were active in the catalytic borylation of arenes under thermal conditions. © 2013 American Chemical Society.