Controlling Catalytic Activity and Selectivity for Partial Hydrogenation by Tuning the Environment Around Active Sites in Iridium Complexes Bonded to Supports

Melike Babucci, Chia-Yu Fang, Jorge E Perez-Aguilar, Adam S Hoffman, Alexey Boubnov, Erjia Guan, Simon R Bare, Bruce C Gates, Alper Uzun

Chem Sci. 2019 Jan 9;10(9):2623-2632.

PMID: 30996978

Abstract:

Single-site Ir(CO)2 complexes bonded to high-surface-area metal oxide supports, SiO2, TiO2, Fe2O3, CeO2, MgO, and La2O3, were synthesized by chemisorption of Ir(CO)2(acac) (acac = acetylacetonate) followed by coating with each of the following ionic liquids (ILs): 1-n-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF4], 1-n-butyl-3-methylimidazolium acetate, [BMIM][Ac], and 1-(3-cyanopropyl)-3-methylimidazolium dicyanamide, [CPMIM][DCA]. Extended X-ray absorption fine structure spectroscopy showed that site-isolated iridium was bonded to oxygen atoms of the support. Electron densities on the iridium enveloped by each IL sheath/support combination were characterized by carbonyl infrared spectroscopy of the iridium gem-dicarbonyls and by X-ray absorption near-edge structure data. The electron-donor/acceptor tendencies of both the support and IL determine the activity and selectivity of the catalysts for the hydrogenation of 1,3-butadiene, with electron-rich iridium being selective for partial hydrogenation. The results resolve the effects of the IL and support as ligands; for example, the effect of the IL becomes dominant when the support has a weak electron-donor character. The combined effects of supports and ILs as ligands offer broad opportunities for tuning catalytic properties of supported metal catalysts.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP879866747	1-(3-Cyanopropyl)-3-methylimidazolium dicyanamide		879866-74-7	Price