Novel redox responsive chiral cyclometalated platinum(II) complexes with pinene functionalized C∧N∧N ligands

By oxidation of a couple of chiral cyclometalated platinum(II) complexes, Pt(L-a)(C C-Ph) (1a) and Pt(L-b)(C C-Ph) (1b) (L-a = (-)-4,5-pinene-6'-phenyl-2,2'-bipyridine and L-b = (+)-4,5-pinene-6'-phenyl-2,2'-bipyridine), a novel pair of platinum(IV) enantiomers, Pt(L-a)(C C-Ph)(3) (2a) and Pt(L-b)(C C-Ph)(3) (2b), were obtained. According to the single crystal X-ray diffraction studies of 2a and 2b, the central platinum atom is wrapped by a (CNN)-N-boolean AND-N-boolean AND ligand and three phenylacetylene groups and exhibits a distorted octahedral geometry. Due to the different coordination configurations and electronic structures, complexes 2a and 2b are distinct from 1a and 1b not only in absorption and emission spectra, but also in their chiroptical properties. The oxidation reaction of 1a and 1b is a kinetically controllable process. Given different oxidants to complete the Pt(II)-to-Pt(IV) process, various oxidation rates were presented. The difference between the ECD spectra of complexes 1a and 2a has been confirmed through TD-DFT calculation and can be useful for designing new redox-responsive materials.