Tuning Catalytic Activity in the Hydrogenation of Unactivated Olefins with Transition-Metal Oxos as the Lewis Base Component of Frustrated Lewis Pairs

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• 作者：Nikola S. Lambic ; Roger D. Sommer ; Elon A. Ison
• 刊名：ACS Catalysis
• 出版年：2017
• 出版时间：February 3, 2017
• 年：2017
• 卷：7
• 期：2
• 页码：1170-1180
• 全文大小：707K
• ISSN：2155-5435

文摘

The steric and electronic demands of the catalytic olefin hydrogenation of tert-butylethylene with oxorhenium/Lewis acid FLPs were evaluated. The sterics of the ligand were altered by installing bulkier isopropyl groups in the 2,6-positions of the diamidopyridine (DAP) ligand. Lewis acid/base adducts were not isolated for complexes with this ligand; however, species incorporating isopropyl groups were still active in catalytic hydrogenation. Modifications were also made to the Lewis acid, and catalytic reactions were performed with Piers’ borane, HB(C₆F₅)₂, and the aluminum analogue Al(C₆F₅)₃. The rate of catalytic hydrogenation was shown to strongly correlate with the size of the alkyl, aryl, or hydride ligand. This was confirmed by a linear Taft plot with the steric sensitivity factor δ = −0.57, which suggests that reaction rates are faster with sterically larger X substituents. These data were used to develop a catalyst ((MesDAP)Re(O)(Ph)/HB(C₆F₅)₂) that achieved a TON of 840 for the hydrogenation of tert-butylethylene at mild temperatures (100 °C) and pressures (50 psi of H₂). Tuning of the oxorhenium catalysts also resulted in the hydrogenation of tert-butylethylene at room temperature.