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

doi:10.1039/c8sc05287e

Controlling catalytic activity and selectivity for partial hydrogenation by tuning the environment around active sites in iridium complexes bonded to supports

Chem Sci. 2019 Jan 9;10(9):2623-2632. doi: 10.1039/c8sc05287e. eCollection 2019 Mar 7.

Authors

Melike Babucci^{1

2}, Chia-Yu Fang³, Jorge E Perez-Aguilar⁴, Adam S Hoffman⁵, Alexey Boubnov⁵, Erjia Guan³, Simon R Bare⁵, Bruce C Gates⁴, Alper Uzun^{1

2

6}

Affiliations

¹ Department of Chemical and Biological Engineering , Koç University , Rumelifeneri Yolu , Sariyer 34450, Istanbul , Turkey . Email: [email protected].
² Koç University TÜPRAŞ Energy Center (KUTEM) , Koç University , Rumelifeneri Yolu , Sariyer 34450, Istanbul , Turkey.
³ Department of Materials Science and Engineering , University of California , Davis , California 95616 , USA.
⁴ Department of Chemical Engineering , University of California , Davis , California 95616 , USA . Email: [email protected].
⁵ SSRL , SLAC National Accelerator Laboratory , Menlo Park , CA 94025 , USA.
⁶ Koç University Surface Science and Technology Center (KUYTAM) , Koç University , Rumelifeneri Yolu , Sariyer, 34450 Istanbul , Turkey.

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.