Reversible Photoswitching of the Coordination Numbers of Silicon in Organosilicon Compounds Bearing a 2-(Phenylazo)phenyl Group

摘要

Several organosilicon compounds bearing a 2-(phenylazo)phenyl group were synthesized from the corresponding chlorosilanes and 2-lithioazobenzene prepared by halogen-lithium transmetalation of 2-iodoazobenzene.Their structures were determined by ~1H,~(13)C,~(19)F,and ~(29)Si NMR spectra,UV-vis spectra,and X-ray crystallographic analyses.In the UV-vis spectra,silyl groups caused red shifts of both the n-pi* and pi-pi* transitions of the azo group compared with the transitions of the unsubstituted azobenzene.The E-isomers of the fluorosilanes showed an intramolecular interaction between a nitrogen atom of the azo group and the silicon atom,leading their intermediate structures between a distorted trigonal bipyramidal structure and a tetrahedral structure around the silicon atoms,which were revealed by the X-ray crystallographic analyses and the NMR spectra.On the other hand,silanes without fluorine atoms showed tetrahedral structures in the absence of such an interaction.The photoirradiation of the E-isomers of the fluorosilanes afforded reversibly the corresponding Z-isomers in good yields.The silicon atoms of the Z-isomers were found to be tetracoordinate in the absence of Si-N interactions by the ~(29)Si NMR spectra.The coordination numbers of the silicon atom of the fluorosilanes were reversibly switched between four and five by photoirradiation.These properties were compared to those of a tetrafluoro[2-(phenylazo)phenyl]-silicate.