物理化学学报2018，Vol.34Issue(10)：1097-1105,9.DOI:10.3866/PKU.WHXB201712131
简单的配体改变调控钌配合物催化还原CO2的活性:硼基配体的对位效应和Ru—H键的性质
Simple Ligand Modifications to Modulate the Activity of Ruthenium Catalysts for CO2 Hydrogenation: Trans Influence of Boryl Ligands and Nature of Ru—H Bond
摘要
Abstract
The development of efficient catalysts for the hydrogenation of CO2 to formic acid (FA) or formate has attracted significant interest as it can address the increasingly severe energy crisis and environmental problems.One of the most efficient methods to transform CO2 to FA is catalytic homogeneous hydrogenation using noble metal catalysts based on Ir,Ru,and Rh.In our previous work,we demonstrated that the activity of CO2 hydrogenation via direct addition of hydride to CO2 on Ir(Ⅲ) and Ru(Ⅱ) complexes was determined by the nature of the metal-hydride bond.These complexes could react with the highly stable CO2 molecule because they contain the same distinct metal-hydride bond formed from the mixing of the so2 hybrid orbital of metal with the 1s orbital of H,and evidently,this property can be influenced by the trans ligand.Since bowl ligands exhibit a strong trans influence,we proposed that introducing such ligands may enhance the activity of the Ru—H bond by weakening it as a result of the trans infiuence.In this work,we designed two potential catalysts,namely,Ru-PNP-HBcat and Ru-PNP-HBpin,which were based on the Ru(PNP)(CO)H2 (PNP =2,6-bis(dialkylphosphinomethyl)pyridine) complex,and computationally investigated their reactivity toward CO2 hydrogenation.Bcat and Bpin (cat =catecholate,pin =pinacolate) are among the most popular bowl ligands in transition metal bowl complexes and have been widely applied in catalytic reactions.Our optimization results revealed that the complexes modified by bowl ligands possessed a longer Ru—H bond.Similarly,natural bond orbital (NBO) charge analysis indicated that the nucleophilic character of the hydride in Ru-PNP-HBcat and Ru-PNP-HBpin was higher as compared to that in Ru-PNP-H2.NBO analysis of the nature of Ru—H bond indicated that these complexes also followed the law of the bonding of Ru—H bond proved in the previous works (Bull.Chem.Soc.Jpn.2011,84 (10),1039;Bull.Chem.Soc.Jpn.2016,89 (8),905),and the d orbital contribution of the Ru atom in Ru-PNP-HBcat and Ru-PNP-HBpin was smaller than that in Ru-PNP-H2.Consequently,the Ru-PNP-HBcat and Ru-PNP-HBpin complexes were more active than Ru-PNP-H2 for the direct hydride addition to CO2 because of the lower activation energy barrier,i.e.,from 29.3 kJ.mol-1 down to 24.7 and 23.4 kJ.mol-1,respectively.In order to further verify our proposed catalyst-design strategy for CO2 hydrogenation,the free energy barriers of the complete pathway for the hydrogenation of CO2 to formate catalyzed by complexes Ru-PNP-H2,Ru-PNP-HBcat,and Ru-PNP-HBpin were calculated to be 76.2,67.8,and 54.4 kJ.mol-1,respectively,indicating the highest activity of Ru-PNP-HBpin.Thus,the reactivity of Ru catalysts for CO2 hydrogenation could be tailored by the strong trans influence of the bowl ligands and the nature of the Ru—H bond.关键词
CO2还原/钌配合物/硼基配体/对位效应/Ru—H键Key words
CO2 hydrogenation/Ru complex/Bowl ligand/Trans influence/Ru—H bond分类
化学化工引用本文复制引用
刘甜,黎军,刘维佳,朱育丹,陆小华..简单的配体改变调控钌配合物催化还原CO2的活性:硼基配体的对位效应和Ru—H键的性质[J].物理化学学报,2018,34(10):1097-1105,9.基金项目
The project was supported by National Key Basic Research Development Program of China (973) (2013CB733505,2013CB733501),National Natural Science Foundation of China (91334202),Natural Science Foundation of Jiangsu Province (BK2012421),Research Fund for the Doctoral Program of Higher Education of China (20123221120015),Project for Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).国家重点基础研究发展计划(973)(2013CB733505,2013CB733501),国家自然科学基金(91334202),江苏省自然科学基金(BK2012421),国家教育部高等学校博士点基金(20123221120015),江苏省高校优势学科建设工程资助项目 （973）
