Smolentsev Grigory, Soldatov Mikhail A, Probst Benjamin, Bachmann Cyril, Azzaroli Nicolo, Alberto Roger, Nachtegaal Maarten, van Bokhoven Jeroen A
Paul Scherrer Institute, Villigen, 5232, Switzerland.
Smart Materials International Research Center, Southern Federal University of Russia, Rostov-on-Don, 344090, Russian Federation.
ChemSusChem. 2018 Sep 21;11(18):3087-3091. doi: 10.1002/cssc.201801140. Epub 2018 Aug 22.
Cobalt polypyridyls are highly efficient water-stable molecular catalysts for hydrogen evolution. The catalytic mechanism explaining their activity is under debate and the main question is the nature of the involvement of pyridyls in the proton transfer: the pentapyridyl ligand, acting as a pentadentate ligand, can provide stability to the catalyst or one of the pyridines can be involved in the proton transfer. Time-resolved Co K-edge X-ray absorption spectroscopy in the microsecond time range indicates that, for the [Co (aPPy)] catalyst (aPPy=di([2,2'-bipyridin]-6-yl)(pyridin-2-yl)methanol), the pendant pyridine dissociates from the cobalt in the intermediate Co state. This opens the possibility for pyridinium to act as an intramolecular proton donor. In the resting state, the catalyst returns to the original six-coordinate high-spin Co state with a pentapyridyl and one water molecule coordinating to the metal center. Such a bifunctional role of the polypyridyl ligands can be exploited during further optimization of the catalyst.
钴多吡啶配合物是高效的析氢水稳定分子催化剂。解释其活性的催化机制仍存在争议，主要问题是吡啶基在质子转移中的参与性质：五吡啶基配体作为五齿配体，可以为催化剂提供稳定性，或者其中一个吡啶可以参与质子转移。微秒时间范围内的时间分辨钴K边X射线吸收光谱表明，对于[Co (aPPy)]催化剂（aPPy = 二([2,2'-联吡啶]-6-基)(吡啶-2-基)甲醇），在中间Co状态下，侧链吡啶从钴上解离。这使得吡啶鎓有可能作为分子内质子供体。在静止状态下，催化剂恢复到原始的六配位高自旋Co状态，一个五吡啶基和一个水分子与金属中心配位。在催化剂的进一步优化过程中，可以利用多吡啶基配体的这种双功能作用。
