Cyclooctadiene iridium complexes [Cp*Ir(COD)X]+ ( X = Cl, Br, I): Synthesis and application for oxidative coupling of benzoic acid with alkynes

The cyclooctadiene iridium complexes [Cp* Ir(COD) X] PF6 ([1a-c] PF6; X = Cl, Br, I) were synthesized by reactions of Cp* Ir(COD) with halogens followed by a counterion exchange. The cyclooctadiene in these complexes is a thermally labile ligand. Complex [1b] PF6 reacts with trimethylphosphite to give [Cp* Ir {P(OMe)(3)}(2)Br]PF6([2]PF6) as a result of the cyclooctadiene replacement. The refluxing of [1b] PF6 in 1,2-dichloroethane affords the dimeric iodide [Cp*IrI2](2). The structures of [1b] PF6, [2] PF6 and [Cp* IrI2](2) were determined by X-ray diffraction. The IreCOD bonding in [1a-c] thorn and the related non-methylated complexes was analyzed by energy decomposition analysis. In the presence of silver salts, complexes [1a-c] PF6 (at 2.0 mol % loading) catalyze the oxidative coupling of benzoic acid with 1-phenyl-1-propyne in methanol at 60 degrees C to selectively give 4-methyl-3-phenylisocoumarin (3) or with diphenylacetylene in o-xylene at 160 degrees C to afford 1,2,3,4-tetraphenylnaphthalene (4). (c) 2018 Elsevier B.V. All rights reserved.