Luminescent Palladium(II) Complexes with π-Extended Cyclometalated [RC^N^NR′] and Pentafluorophenylacetylide Ligands: Spectroscopic, Photophysical, and Photochemical Properties

• Published in: Chemistry, an Asian journal an Asian journal, 2014-02, Vol.9 (2), p.534-545
• Main Authors: Chow, Pui-Keong, To, Wai-Pong, Low, Kam-Hung, Che, Chi-Ming
• Format: Article
• Language: English
• Subjects: Acetylene - analogs & derivatives; Acetylene - chemistry; Amines - chemistry; Carbon - chemistry; Coordination Complexes - chemistry; Crystallography, X-Ray; Electrochemical Techniques; Hydrogen - chemistry; Ligands; luminescence; Molecular Conformation; Nitrogen - chemistry; Oxidation-Reduction; palladium; Palladium - chemistry; photochemistry; photophysics; sensitizers; Spectroscopy, Fourier Transform Infrared; Temperature
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.201301059

A series of cyclometalated PdII complexes that contain π‐extended RC^N^NR′ (RC^N^NR′=3‐(6′‐aryl‐2′‐pyridinyl)isoquinoline) and chloride/pentafluorophenylacetylide ligands have been synthesized and their photophysical and photochemical properties examined. The complexes with the chloride ligand are emissive only in the solid state and in glassy solutions at 77 K, whereas the ones with the pentafluorophenylacetylide ligand show phosphorescence in the solid state (λmax=584–632 nm) and in solution (λmax=533–602 nm) at room temperature. Some of the complexes with the pentafluorophenylacetylide ligand show emission with λmax at 585–602 nm upon an increase in the complex concentration in solutions. These PdII complexes can act as photosensitizers for the light‐induced aerobic oxidation of amines. In the presence of 0.1 mol % PdII complex, secondary amines can be oxidized to the corresponding imines with substrate conversions and product yields up to 100 and 99 %, respectively. In the presence of 0.15 mol % PdII complex, the oxidative cyanation of tertiary amines could be performed with product yields up to 91 %. The PdII complexes have also been used to sensitize photochemical hydrogen production with a three‐component system that comprises the PdII complex, [Co(dmgH)2(py)Cl] (dmgH=dimethylglyoxime; py=pyridine), and triethanolamine, and a maximum turnover of hydrogen production of 175 in 4 h was achieved. The excited‐state electron‐transfer properties of the PdII complexes have been examined. Taking things lightly: Cyclometalated PdII complexes that contain extended π‐conjugated 3‐(6′‐aryl‐2′‐pyridinyl)isoquinoline (RC N NR′) and pentafluorophenylacetylide ligands are emissive, show aggregation‐induced emission in solution at room temperature, and can function as photosensitizers for light‐induced aerobic oxidation of amines and photochemical hydrogen production (see figure).