Lewis-Acidic Triarylboranes: Optoelectronic Applications and Unusual Reactivities
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A new electron-transport material using a triarylboron-functionalized 2,4,6-triphenyltriazine core has been synthesized. This compound exhibits reversible reduction with low-lying HOMO and LUMO energy levels, as well as a high-energy triplet state. Preliminary experiments incorporating this material into phosphorescent OLEDs as an electron transport layer gave devices with high current and external quantum efficiencies at brightness levels appropriate for applications in the display industry. Furthermore, a nitrogen-containing alkynyltriarylboron compound, 2-(2’-(dimesitylboryl)phenylethynyl)pyridine, has been found to undergo a facile alkyne hydration reaction in the presence of copper(I) iodide and triethylamine. The copper(I)-catalyzed addition of water occurs at room temperature, and produces a brightly luminescent boron-enol compound that is stable under air. Studies of the reaction mechanism were carried out by monitoring product formation under different conditions using 1H NMR. The cooperativity between the Lewis acidic triarylboryl group and Lewis basic pyridyl group is determined to be vital in promoting the hydration process and in stabilizing the enol structure of the product. Finally, we have discovered that diarylplatinum(II) complexes of 2-(2’-(dimesitylboryl)phenylethynyl)pyridine are capable of undergoing an unusual intramolecular double aryl migration/cyclization reaction, resulting in the formation of a unique bicyclic organometallic scaffold. The structures of these remarkable products have been characterized by X-ray crystallography, as well as by 1D and 2D 1H NMR. The reaction mechanism was established by 1H NMR studies and by DFT calculations. The complementary electronic properties of the electron-deficient triarylborane and the electron-rich platinum centers were found to play a key role in this unprecedented transformation.