The tripyrrin coordination motif,namely a conjugated tripyrrolic fragment of the porphyrin scaffold,is found in numerous metal complexes of oligopyrrolic macrocycles.Because of their typically limited stability,linear...The tripyrrin coordination motif,namely a conjugated tripyrrolic fragment of the porphyrin scaffold,is found in numerous metal complexes of oligopyrrolic macrocycles.Because of their typically limited stability,linear tripyrrins are underutilized in coordination chemistry;however,hexaalkyl-tripyrrindiones featuring the pyrrolinone termini characteristic of biopyrrin pigments have recently emerged as versatile redoxactive ligands.Herein,we report the synthesis of the first example of meso-di(pentafluorophenyl)tripyrrin-1,14-dione through the demethylation of a stable 1,14-dimethoxytripyrrin precursor.The two tripyrrin ligands coordinate palladium(II)in square planar geometries in completely distinct ways:the dimethoxytripyrrin forms a cyclopalladate following C(sp^(3))–H bond activation at one of the methoxy groups,whereas the tripyrrindione binds as a trianionic ligand engaging an adventitious aqua ligand in hydrogen-bonding interactions.When compared to the hexaalkyl substituents of previous tripyrrindiones,the meso-aryl groups significantly alter the electrochemical profile of the Pd(II)tripyrrindione complex,shifting anodically by∼500 mV the one-electron processes to attain the other redox states of the ligand.The formation of a ligand-based radical on the Pd(II)-bound meso-aryl tripyrrindione is confirmed by spectroelectrochemical and electron paramagnetic resonance(EPR)methods.展开更多
基金National Science Foundation(award CHE-2203361 to E.T.)。
文摘The tripyrrin coordination motif,namely a conjugated tripyrrolic fragment of the porphyrin scaffold,is found in numerous metal complexes of oligopyrrolic macrocycles.Because of their typically limited stability,linear tripyrrins are underutilized in coordination chemistry;however,hexaalkyl-tripyrrindiones featuring the pyrrolinone termini characteristic of biopyrrin pigments have recently emerged as versatile redoxactive ligands.Herein,we report the synthesis of the first example of meso-di(pentafluorophenyl)tripyrrin-1,14-dione through the demethylation of a stable 1,14-dimethoxytripyrrin precursor.The two tripyrrin ligands coordinate palladium(II)in square planar geometries in completely distinct ways:the dimethoxytripyrrin forms a cyclopalladate following C(sp^(3))–H bond activation at one of the methoxy groups,whereas the tripyrrindione binds as a trianionic ligand engaging an adventitious aqua ligand in hydrogen-bonding interactions.When compared to the hexaalkyl substituents of previous tripyrrindiones,the meso-aryl groups significantly alter the electrochemical profile of the Pd(II)tripyrrindione complex,shifting anodically by∼500 mV the one-electron processes to attain the other redox states of the ligand.The formation of a ligand-based radical on the Pd(II)-bound meso-aryl tripyrrindione is confirmed by spectroelectrochemical and electron paramagnetic resonance(EPR)methods.
