title: Substituent Directed Phototransformations of BN-Heterocycles: Elimination vs Isomerization via Selective B-C Bond Cleavage.
abstract: Electron-rich and -poor BN-heterocycles with benzyl-pyridyl backbones and two bulky aryls on the boron (Ar = tipp, BN-1, Ar = MesF, BN-2) have been found to display distinct molecular transformations upon irradiation by UV light. BN-1 undergoes an efficient photoelimination reaction forming a BN-phenanthrene with ΦPE = 0.25, whereas BN-2 undergoes a thermally reversible, stereoselective, and quantitative isomerization to a dark colored BN-1,3,5-cyclooctatriene (BN-1,3,5-COT, BN-2a). This unusual photoisomerization persists for other BN-heterocycles with electron-deficient aryls such as BN-3 with a benzyl-benzothiazolyl backbone and Mes(F) substituents or BN-4 with a benzyl-pyridyl backbone and two C6F5 groups on the boron. The photoisomerization of BN-4 goes beyond BN-1,3,5-COT (BN-4a), forming a new species (BN-1,3,6-COT, BN-4b) via C-F bond cleavage and [1,3]-F atom sigmatropic migration. Computational studies support that BN-4a is an intermediate in the formation of BN-4b. This work establishes that steric and electronic factors can effectively control the transformations of BN-heterocycles, allowing access to important and previously unknown BN-embedded species.
authors: Department of Chemistry, Queen's University , Kingston, Ontario K7L 3N6, Canada.
authors: Deng-Tao
authors: DT
authors: Yang
authors: Department of Chemistry, Queen's University , Kingston, Ontario K7L 3N6, Canada.
authors: Soren K
authors: SK
authors: Mellerup
authors: Department of Chemistry, Queen's University , Kingston, Ontario K7L 3N6, Canada.
authors: Jin-Bao
authors: JB
authors: Peng
authors: Department of Chemistry, Queen's University , Kingston, Ontario K7L 3N6, Canada.
authors: Xiang
authors: X
authors: Wang
authors: Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, School of Chemistry, Beijing Institute of Technology , Beijing 100081, P. R. China.
authors: Quan-Song
authors: QS
authors: Li
authors: Department of Chemistry, Queen's University , Kingston, Ontario K7L 3N6, Canada.|Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, School of Chemistry, Beijing Institute of Technology , Beijing 100081, P. R. China.
authors: Suning
authors: S
authors: Wang