Institute for Inorganic Chemistry, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
Institute for Sustainable Chemistry & Catalysis with Boron, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
Angew Chem Int Ed Engl. 2017 Jun 26;56(27):8009-8013. doi: 10.1002/anie.201704063. Epub 2017 Jun 5.
The diborene 1 was synthesized by reduction of a mixture of 1,2-di-9-anthryl-1,2-dibromodiborane(4) (6) and trimethylphosphine with potassium graphite. The X-ray structure of 1 shows the two anthryl rings to be parallel and their π(C ) systems perpendicular to the diborene π(B=B) system. This twisted conformation allows for intercalation of the relatively high-lying π(B=B) orbital and the low-lying π* orbital of the anthryl moiety with no significant conjugation, resulting in a small HOMO-LUMO gap (HLG) and ultimately a C-H borylation of the anthryl unit. The HLG of 1 was estimated to be 1.57 eV from the onset of the long wavelength band in its UV/Vis absorption spectrum (THF, λ =788 nm). The oxidation of 1 with elemental selenium afforded diboraselenirane 8 in quantitative yield. By oxidative abstraction of one phosphine ligand by another equivalent of elemental selenium, the B-B and C -H bonds of 8 were cleaved to give the cyclic 1,9-diborylanthracene 9.
二硼烯 1 是通过还原 1,2-二-9-蒽基-1,2-二溴二硼(4)(6)和三甲基膦与石墨钾的混合物合成的。1 的 X 射线结构表明，两个蒽环彼此平行，其π(C)系统垂直于二硼烯π(B=B)系统。这种扭曲的构象允许相对高能的π(B=B)轨道和蒽部分的低能π*轨道插入，没有明显的共轭，导致 HOMO-LUMO 间隙(HLG)较小，最终导致蒽单元的 C-H 硼化。1 的 HLG 是通过其紫外/可见吸收光谱(THF，λ=788nm)中长波长带的起始处估计为 1.57eV。1 与元素硒的氧化以定量产率得到二硼硒啉 8。通过另一个当量的元素硒对一个膦配体的氧化消除，8 的 B-B 和 C-H 键被切断，得到环状 1,9-二硼蒽 9。
