Triarylboron Functionalized Isomerizable Dinuclear Pt(?) Complex And Four-coordinate Boron Compounds Study

Taking into account the excellent optoelectronic properties of triarylboron compounds,a series of triarylboron functionalized N ^ C chelate Pt(?)dinuclear metal complexes linked via a photoactive bis(4-pyridyl)ethylene(bpe)bridging unit were prepared.Due to the enlarged conjugated system,the energy gap between HOMO and LUMO orbitals was decreased.In order to excite the photoactive state and overcome the barrier of trans-cis-olefin isomerization,high energy irradiation(? < 300 nm)is usually required which greatly limits their real applications.As a result,low energy irradiation such as visible light is more desirable for triggering such transformations.In this work,the prepared Pt(?)complexes display visible light induced olefin isomerization.In this work,a series of boron containing indole based N ^ C chelate ligands as well as the corresponding mono-and dinuclear Pt(?)complexes were successfully synthesized and fully characterized.All the metal complexes are emissive in solution at both room temperature and in frozen states.In solution,the trans-isomers exist as the major component.Upon UV irradiation,only about 5-10% of cis-isomers were detected.When the solvent was slowly evaporated under ambient light,the cis-geometry crystals were isolated as the main product,which may be attributed to the different solubility of the transand cis-isomers that continuously removes the cis-geometry products out of the solution through crystallization,thereby helping to accumulate the higher energy product.The crystal structure of cis-isomer is similar to that of a bowl.We previously reported that N ^ C chelate four-coordinated boron compounds have photochromic property and the structure of the chelate backbone has a great influence on the photoisomerizaiton efficiency of the compound.In this work,naphthalene moiety was used as the chelate backbone to construct a novel four-coordinate boron compound.Upon365 nm irradiation,the photochemical reaction was completed quickly.Unlike previous reported analogoues which undergo thermally reversible photochromic reactions,this compound did not fully convert to single isomer.After TLC purification,the separated major product was obtained.Its structure was confirmed by 2D NMR and X-ray diffraction analysis,which confirm the carbon-carbon bond of the naphthalene ring opening and the migration of the mesityl group on the boron atom during the phtochemical process.In summary,a new type of photoreactivity of organoboron compounds that leads to unprecedented C-C bond breaking in naphthalene and derivatives have been established.This work provides a new and simple approach in rupturing arene C-C bonds and a new synthetic method for constructing new borepin systems that have potential applications in organic materials.