水对二氧化碳插入TpRu(PPh3)(CH3CN)H生成甲酸根配合物的影响

分别研究了在干燥THF及H2O/THF条件下CO2与TpRu(PPh3)(CH3CN)H(Tp=Hydrotris(pyrazolyl)borate)的反应, 发现水对CO2插入TpRu(PPh3)(CH3CN)H的反应具有显著促进作用. 原位高压NMR研究显示, 在水存在下, CO2插入Ru-H键形成水合甲酸根配合物TpRu(PPh3)(CH3CN)(η1-OCHO)H2O, 其中甲酸根配体与溶剂中水分子形成分子间氢键. B3LYP水平的理论计算表明, CO2插入TpRu(PPh3)(CH3CN)H 中Ru-H键的能垒由于水的存在而显著降低; 在过渡态, CO2分子中碳原子的亲电性由于其氧原子与水分子形成氢键而得到增强. TpRu(PPh3)(CH3CN)(η1-OCHO)*H2O很快转化为另一甲酸根配合物TpRu(PPh3)(H2O)(η1-OCHO), 并与之达成平衡. 后者由于甲酸根配体与水分子配体间形成分子内氢键而稳定.

Water Effect on CO2 Insertion into Ruthenium Hydride Bond of TpRu(PPh3) (CH3CN)H to Form Formate Complexes

A promoting effect of water on CO2 insertion into TpRu (PPh3)(CH3CN)H (Tp = Hydrotris(pyrazolyl)borate) is observed. In situ high-pressure NMR monitoring shows that CO2 readily inserts into Ru-H to form the hydrated metal formate TpRu(PPh3)(CH3CN)(η1-OCHO) · H2O, in which the formate ligand is intermolecularly H-bonded to a water molecule. Theoretical calculations carried out at the B3LYP level show that reaction barrier of the CO2 insertion is significantly reduced in the presence of water. In the transition state of the process, elec trophilicity of the carbon center of CO2 is enhanced by the formation of H-bonds between its oxygen atoms and H2O. The hydrated formate species TpRu(PPh3)(CH3CN)(η1-OCHO) · H2O comes into equilibrium rapidly with another metal formate species TpRu(PPh3)(H2O)(η1-OCHO), in which the coordinated H2O is intramolecularly H-bonded with the formate ligand.