Promoting effect of alcohol in hydrogenation of CO2 to formic acid catalyzed by ruthenium complex

作者：Yin Chuan Qi^*; Feng Quan Wu; Chen Yao; Bai Zheng Wu; Li Zao Ying

来源：Acta Chimica Sinica, 2007, 65(8): 722-726.

• ruthenium complex
• alcohol effect
• in situ high-pressure NMR
• catalytic mechanism

The promoting effect of alcohols in the catalytic hydrogenation of CO2 to formic acid with the solvento complex [TpRu(PPh3)(2)(H2O)]BF4 [Tp=hydrotris(pyrazolyl) borate] is observed. High-pressure NMR monitoring of the catalytic reactions shows that the observable intermediate is a formate complex TpRu(PPh3)(2)(eta(1)-OCHO)center dot HOCH3, which is formed from CO2 insertion into Ru-H bond of TpRu(PPh3)(2)H and stabilized by hydrogen-bonding interaction between the formato ligand and a methanol molecule. The metal formato species comes into equilibrium with another metal formate TpRu(PPh3)(CH3OH)(eta(1)-OCHO); the second metal formato species contains a coordinated methanol, which is intramolecularly hydrogen-bonded with the formato ligand. In view of the stability of these two formates under catalytic conditions, it is very likely that they are not within the major catalytic cycle of the reaction. The productive catalytic cycle of the reactions conducted in a variety of alcohols is proposed. The key species in the cycle is the transient alcohol hydride intermediate, TpRu(PPh3)(ROH)H. It is proposed that TpRu(PPh3)(ROH)H is able to transfer a hydride and a proton simultaneously to an approaching CO2 molecule to produce formic acid, itself being converted to a transient alkoxo species, which then associates a H-2 molecule to regenerate TpRu(PPh3)(ROH)H via or-metathesis between the alkoxo and eta(1)-H-2 ligands.

• 出版日期2007-4-28
• 单位武汉工程大学; 武汉大学