Chiroptical Response Control of Planar and Axially Chiral Polymethylene-Vaulted Platinum(II) Complexes Bearing 1,1′-Binaphthyl Frameworks
Masahiro Ikeshita, Nobuyuki Hara, Yoshitane Imai, Takeshi Naota
Abstract
In this study, the synthesis, structure, and chiroptical response control of planar chiral polymethylene-vaulted trans -bis[(β-iminomethyl)aryloxy]platinum(II) complexes bearing axially chiral 1,1′-binaphthyl ligands are described. A series of enantiopure polymethylene ( n = 4–10)-vaulted complexes were prepared in 6 steps using commercially available ( R )- or ( S )-BINOL as the starting material without an optical resolution process. The trans -coordination and three-dimensional vaulted structures of the platinum complexes were elucidated from X-ray diffraction (XRD) studies. The complexes were found to show structural dependence of chiroptical responses in the dilute solution state such that the absolute values of [α] D, dissymmetry factors g abs in circular dichroism (CD), and g lum in circularly polarized luminescence (CPL) increased upon shortening the length of the polymethylene bridges. The enhanced chiroptical responses were theoretically investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations, and the results are discussed in terms of the molecular structures and transition dipole moments of the ground states. The structural dependence of the chiroptical responses was ascribed to the distortion of the coordination platforms caused by restriction of the vaulting methylene linkers.