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

Abstract The cyclooctadiene iridium complexes [Cp*Ir(COD)X]PF 6 ([ 1a−c ]PF 6 ; 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 ]PF 6 reacts with trimethylphosphite to give [Cp*Ir{P(OMe) 3 } 2 Br]PF 6 ([ 2 ]PF 6) as a result of the cyclooctadiene replacement. The refluxing of [ 1b ]PF 6 in 1,2-dichloroethane affords the dimeric iodide [Cp*IrI 2 ] 2. The structures of [ 1b ]PF 6 , [ 2 ]PF 6 and [Cp*IrI 2 ] 2 were determined by X-ray diffraction. The Ir–COD bonding in [ 1a−c ]+ and the related non-methylated complexes was analyzed by energy decomposition analysis. In the presence of silver salts, complexes [ 1a−c ]PF 6 (at 2.0 mol % loading) catalyze the oxidative coupling of benzoic acid with 1-phenyl-1-propyne in methanol at 60 °C to selectively give 4-methyl-3-phenylisocoumarin (3) or with diphenylacetylene in o -xylene at 160 °C to afford 1,2,3,4-tetraphenylnaphthalene (4). Graphical abstract Image 1 Highlights • A general approach to new family of cyclooctadiene iridium complexes was developed. • The complexes prepared were used as catalysts for the formation of isocoumarin or naphthalene moieties. • The selectivity of catalytic reactions strongly depends on the reaction temperature. [ABSTRACT FROM AUTHOR]