Highly Robust Hydrogen Generation by Bioinspired Ir Complexes for Dehydrogenation of Formic Acid in Water: Experimental and Theoretical Mechanistic Investigations at Different pH

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• 作者：Wan-Hui Wang ; Mehmed Z. Ertem ; Shaoan Xu ; Naoya Onishi ; Yuichi Manaka ; Yuki Suna ; Hide Kambayashi ; James T. Muckerman ; Etsuko Fujita ; Yuichiro Himeda
• 刊名：ACS Catalysis
• 出版年：2015
• 出版时间：September 4, 2015
• 年：2015
• 卷：5
• 期：9
• 页码：5496-5504
• 全文大小：424K
• ISSN：2155-5435

文摘

Hydrogen generation from formic acid (FA), one of the most promising hydrogen storage materials, has attracted much attention due to the demand for the development of renewable energy carriers. Catalytic dehydrogenation of FA in an efficient and green manner remains challenging. Here, we report a series of bioinspired Ir complexes for highly robust and selective hydrogen production from FA in aqueous solutions without organic solvents or additives. One of these complexes bearing an imidazoline moiety (complex 6) achieved a turnover frequency (TOF) of 322鈥?00 h^鈥? at 100 掳C, which is higher than ever reported. The novel catalysts are very stable and applicable in highly concentrated FA. For instance, complex 3 (1 渭mol) affords an unprecedented turnover number (TON) of 2鈥?50鈥?00 at 60 掳C. Deuterium kinetic isotope effect experiments and density functional theory (DFT) calculations employing a 鈥渟peciation鈥?approach demonstrated a change in the rate-determining step with increasing solution pH. This study provides not only more insight into the mechanism of dehydrogenation of FA but also offers a new principle for the design of effective homogeneous organometallic catalysts for H₂ generation from FA.