Department of Chemistry, Biochemistry and Pharmaceutical Sciences, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland.
Inorg Chem. 2023 Feb 13;62(6):2905-2912. doi: 10.1021/acs.inorgchem.2c04363. Epub 2023 Jan 31.
Donor-flexible ligands are an emerging class of noninnocent ligands. Their ability to adapt their donating strength toward a metal center has had numerous catalytic advantages yet has never been utilized to stabilize and isolate intermediate complexes within these processes. We demonstrate through the use of a pincer ligand containing two donor-flexible pyridylidene amide (PYA) arms in coordination with platinum(II) that this ligand adaptability revealed remarkably stable hydride and formate complexes. These are typically fleeting catalytic intermediates within formic acid dehydrogenation and CO hydrogenation catalytic cycles. The PYA platinum hydride complexes are indefinitely stable in air, while formate complexes show no sign of β-hydrogen elimination. This robustness allowed us to investigate hydride protonation as a seemingly simple reaction, though in-depth kinetic analysis reveals a pre-equilibrium step prior to platinum hydride protonation. This initial step has been attributed to adduct formation and is slower than the protonation, and therefore a relevant aspect when designing catalytic cycles for hydrogen release and its microscopic reverse, , hydrogen uptake.
供体柔性配体是一类新兴的非配位配体。它们能够调节对金属中心的供电子能力，在催化方面具有诸多优势，但从未被用于稳定和分离这些过程中的中间配合物。我们通过使用含两个供体柔性吡啶甲酰胺（PYA）臂的夹持配体与铂（II）配位证明了这种配体的适应性可以揭示出非常稳定的氢化物和甲酸盐配合物。这些配合物通常是甲酸脱氢和 CO 加氢催化循环中的短暂催化中间体。PYA 铂氢化物配合物在空气中稳定存在，而甲酸盐配合物没有β-氢消除的迹象。这种坚固性使我们能够研究氢化物质子化这一看似简单的反应，但深入的动力学分析揭示了铂氢化物质子化之前存在预平衡步骤。这个初始步骤归因于加合物的形成，并且比质子化慢，因此在设计用于氢气释放及其微观逆反应（即氢气吸收）的催化循环时，这是一个相关的方面。
