Research Institute of Energy Frontier, Department of Energy and Environment, National Institute of Advanced Industrial Science and Technology, Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki, 305-8565, Japan.
Chemistry Division, Brookhaven National Laboratory, Upton, NY, 11973-5000, USA.
ChemSusChem. 2017 Nov 23;10(22):4535-4543. doi: 10.1002/cssc.201701676. Epub 2017 Nov 7.
Pentamethylcyclopentadienyl iridium (Cp*Ir) complexes with bidentate ligands consisting of a pyridine ring and an electron-rich diazole ring were prepared. Their catalytic activity toward CO hydrogenation in 2.0 m KHCO aqueous solutions (pH 8.5) at 50 °C, under 1.0 MPa CO /H (1:1) have been reported as an alternative to photo- and electrochemical CO reduction. Bidentate ligands incorporating an electron-rich diazole ring improved the catalytic performance of the Ir complexes compared to the bipyridine ligand. Complexes 2, 4, and 6, possessing both a hydroxy group and an uncoordinated NH group, which are proton-responsive and capable of generating pendent bases in basic media, recorded high initial turnover frequency values of 1300, 1550, and 2000 h , respectively. Spectroscopic and computational investigations revealed that the reversible deprotonation changes the electronic properties of the complexes and causes interactions between pendent base and substrate and/or solvent water molecules, resulting in high catalytic performance in basic media.
五甲基环戊二烯基铱（Cp*Ir）配合物与双齿配体组成，双齿配体由吡啶环和富电子二唑环组成。它们在 50°C、2.0m KHCO3水溶液（pH 8.5）中、1.0 MPa CO/H（1:1）条件下的 CO 加氢反应的催化活性已被报道为光电化学 CO 还原的替代方法。与双吡啶配体相比，含有富电子二唑环的双齿配体提高了 Ir 配合物的催化性能。具有羟基和未配位 NH 基团的配合物 2、4 和 6，是质子响应的，并能在碱性介质中生成悬垂碱，其初始周转率频率分别高达 1300、1550 和 2000 h-1。光谱和计算研究表明，可逆去质子化改变了配合物的电子性质，并导致悬垂碱与底物和/或溶剂水分子之间的相互作用，从而在碱性介质中表现出高催化性能。
