Ir(III)-PC(sp3)P Bifunctional Catalysts for Production of H2 by Dehydrogenation of Formic Acid: Experimental and Theoretical Study

Reversible storage
of hydrogen in the form of stable and relatively
harmless chemical substances such as formic acid (FA) is one of the
cornerstones of a fossil-fuel-free economy. Recently, Ru­(III)-PC­(sp3)P (where PC­(sp3)P = modular dibenzobarrelene-based
pincer ligand possessing a pendant functional group) complex 1 has been reported as a mild and E-selective
catalyst in semihydrogenation of alkynes with stoichiometric neat
formic acid. Discovery of the additive-free protocol for dehydrogenation
of FA launched further studies aiming at the rational design of highly
efficient catalysts for this reaction operating under neutral conditions.
We now report the results of our investigation on a series of bifunctionl
PC­(sp3)P complexes equipped with different outer-sphere
auxiliaries, that allowed us to identify an amine-functionalized Ir­(III)-PC­(sp3)P complex 3, as a clean and efficient catalyst
for the FA dehydrogenation. The catalyst is suitable for fuel-cell
applications demonstrating a TON up to 5 × 105 and
TOF up to 2 × 104 h–1 (3.8 ×
105 and 1.2 × 104 h–1 with no additives). In addition to the practical value of the catalyst,
experimental and computational mechanistic studies provide rationale
for the design of improved next-generation catalysts.

以稳定且相对无害的化学物质，如蚁酸（FA）的形式可逆存储氢气，是构建无化石燃料经济体系的关键基石之一。近期，一种Ru(III)-PC(sp3)P（其中PC(sp3)P = 拥有旁连功能基团的模块化二苯并环己烯基夹心配体）复合物1被报道为一种温和且E-选择性的催化剂，在以化学计量纯蚁酸进行炔烃半氢化反应中展现出优异性能。发现无添加剂的蚁酸脱氢反应的工艺进一步推动了针对该反应在碱性条件下高效催化剂理性设计的深入研究。本研究团队现报告了对一系列配备不同外层辅助基团的二功能PC(sp3)P复合物的研究成果，该研究使我们成功鉴定出一种氨基功能化的Ir(III)-PC(sp3)P复合物3，作为蚁酸脱氢反应的清洁且高效的催化剂。该催化剂适用于燃料电池应用，表现出高达5 × 10^5的转换数（TON）和2 × 10^4 h^-1的反应速率（在无添加剂条件下为3.8 × 10^5和1.2 × 10^4 h^-1）。除了催化剂的实用性之外，实验和计算机理研究为下一代催化剂的设计提供了理论依据。