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 PdIIcomplexes 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 λmaxat 585-602 nm upon an increase in the complex concentration in solutions. These PdIIcomplexes can act as photosensitizers for the light-induced aerobic oxidation of amines. In the presence of 0.1 mol % PdIIcomplex, 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 % PdIIcomplex, the oxidative cyanation of tertiary amines could be performed with product yields up to 91 %. The PdIIcomplexes have also been used to sensitize photochemical hydrogen production with a three-component system that comprises the PdIIcomplex, [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 PdIIcomplexes have been examined. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.