侧臂含膦茂配体铑配合物[Rh(Ph_(2)PC_(6)H_(4)C_(5)R_(4))(biph)]的合成与结构表征

Synthesis and structural characterization of[RhPh_(2)PC_(6)H_(4)C_(5)R_(4)(biph)]complexes containing phosphocyanine ligands on side arms

半夹心茂铑配合物常用来催化各类C—H键官能团化反应,目前常提出以下两种铑催化循环过程:1)Rh(Ⅰ)/Rh(Ⅲ);2)Rh(Ⅲ)/Rh(Ⅳ)或Rh(Ⅲ)/Rh(Ⅴ).前者已经通过大量Rh(Ⅲ)中间体证实,而后者中的Rh(Ⅳ)或Rh(Ⅴ)中间体(氧化中间体或高价铑物种)则尚未有事实性证据支持.本研究利用苯基作为桥连基团合成环戊二烯基膦配体(Cp^(4R)-P=Ph_(2)PC_(6)H_(4)C_(5)R_(4);R=H,Me,Et),再分别引入2,2'-联苯双阴离子(biph)和2-苯基吡啶单阴离子(2-phpy)配体构建两类电性不同的有机金属铑(Ⅲ)配合物.通过核磁共振、质谱、X射线单晶衍射手段对合成的配合物进行表征,并通过循环伏安实验研究其相应的电化学性质,确认铑(Ⅲ)联苯配合物在测试条件下具有稳定的氧化还原行为,因此有望捕获、分离相关氧化中间体,为上述铑催化循环过程提供事实性证据.

Half-sandwich cyclopentadienyl rhodium complexes are often used to catalyze various C—H bonds functionalization.The following two rhodium-catalyzed cycle processes have been proposed:1)Rh(Ⅰ)/Rh(Ⅲ);2)Rh(Ⅲ)/Rh(Ⅳ)or Rh(Ⅲ)/Rh(Ⅴ).At present,the former has been confirmed by a large number of Rh(Ⅲ)intermediates,while the Rh(Ⅳ)or Rh(Ⅴ)intermediates(oxidative intermediates or high-valent rhodium species)in the latter process have not yet been supported by factual evidence.In this study,cyclopentadienylphosphine ligands(Cp^(4R)-P=Ph_(2)PC_(6)H_(4)C_(5)R_(4);R=H,Me,Et)were synthesized using phenyl as a bridging group,and 2,2'-biphenyl dianion(biph)and 2-phenylpyridine monoanion(2-phpy)ligands were respectively introduced to construct two types of organometallic rhodium(Ⅲ)complexes with significantly different electrical properties.The above complexes were characterized by nuclear magnetic resonance,mass spectrometry and X-ray single crystal diffraction.The corresponding electrochemical properties were examined by cyclic voltammetry experiments.Results of this study confirmed that electroneutral rhodium(Ⅲ)biphenyl complexes have stable redox behavior under the test conditions.Therefore,it is achievable to capture and separate related oxidation intermediates to provide factual evidence for the above rhodium-catalyzed cycle process.