title: Luminescent palladium(II) complexes with π-extended cyclometalated [R-C^N^N-R'] and pentafluorophenylacetylide ligands: spectroscopic, photophysical, and photochemical properties.
abstract: A series of cyclometalated Pd(II) 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 Pd(II) complexes can act as photosensitizers for the light-induced aerobic oxidation of amines. In the presence of 0.1 mol% Pd(II) 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% Pd(II) complex, the oxidative cyanation of tertiary amines could be performed with product yields up to 91%. The Pd(II) complexes have also been used to sensitize photochemical hydrogen production with a three-component system that comprises the Pd(II) 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 Pd(II) complexes have been examined.
authors.affiliation: State Key Laboratory of Synthetic Chemistry, Institute of Molecular Functional Materials, HKU-CAS Joint Laboratory on New Materials, Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong (P.R. China), Fax: (+852) 2915-5176.
authors.forename: Pui-Keong
authors.initials: PK
authors.lastname: Chow
authors.forename: Wai-Pong
authors.initials: WP
authors.lastname: To
authors.forename: Kam-Hung
authors.initials: KH
authors.lastname: Low
authors.forename: Chi-Ming
authors.initials: CM
authors.lastname: Che
mesh_terms: D000114:Acetylene / Q000031:analogs & derivatives* / Q000737:chemistry; D000588:Amines / Q000737:chemistry; D002244:Carbon / Q000737:chemistry; D056831:Coordination Complexes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D055664:Electrochemical Techniques; D006859:Hydrogen / Q000737:chemistry; D008024:Ligands; D008968:Molecular Conformation; D009584:Nitrogen / Q000737:chemistry; D010084:Oxidation-Reduction; D010165:Palladium / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature
chemical_list: D000588:Amines; D056831:Coordination Complexes; D008024:Ligands; C044736:phenylacetylene; D010165:Palladium; D002244:Carbon; D006859:Hydrogen; D009584:Nitrogen; D000114:Acetylene
keywords: luminescence; palladium; photochemistry; photophysics; sensitizers