Transfer hydrogenation is a useful method to reduce unsaturated bonds without the need for hydrogen gas. The mechanism of hydrogen transfer commonly occurs via metal-ligand cooperativity between a basic moiety on the ligand and the metal center. Although examples of iridium complexes containing diamine ligands that catalyze transfer hydrogenation are known, no examples exist of iridium complexes that contain pyridinesulfonamide ligands, and the catalytic activity of such complexes is not previously reported. The O’Connor group is interested in exploring new catalysts for transfer hydrogenation catalysis using air and moisture tolerant iridium complexes containing pyridinesulfonamide ligand scaffolds. Here we report the synthesis, characterization, and catalysis of new Cp*Ir(III)Cl (Cp* = pentamethylcyclopentadienyl) complexes containing various pyridinesulfonamide ligands. These complexes are active in hydrogen transfer catalysis, as aryl-alkyl ketones with electron withdrawing and electron donating substituents are effectively reduced to an alcohol at 90<sup>o</sup>C (80-90% conversion) with 1 mol% of the iridium precatalyst. The reaction time varies between 6 to 12 hours depending on the substrate; aryl-alkyl ketones that possess electron rich substituents are reduced more slowly. Variation of the electronic parameters on the catalyst was also explored and it was found that the addition of electron withdrawing groups slightly reduced catalytic activity. Preliminary results describing mechanistic studies are also included in this presentation.

Catalytic transfer hydrogenation of aryl-alkyl ketones using Cp*Ir(III)Cl pyridinesulfonamide complexes

249th National Meeting (2015)

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