Abstract
π-Electron systems of silicon have attracted attention because of their narrow HOMO-LUMO gap and high reactivity, but the structural diversity remains limited. Herein, new dialkylboryl-substituted disilenes were synthesized by the selective desilylation-borylation of the corresponding trimethylsilyl-substituted disilenes. The dialkylboryl-substituted disilenes were fully characterized by a combination of NMR spectroscopy, MS spectrometry, single-crystal X-ray diffraction analysis, and theoretical calculations. The longest-wavelength absorption bands of boryldisilenes were bathochromically shifted compared to the corresponding silyl-substituted disilenes, indicating a substantial conjugation between π(Si=Si) and vacant 2p(B) orbitals. In the presence of 4-(dimethylamino)pyridine (DMAP), the dialkylboryl groups in the boryl-substituted disilenes were easily converted to trimethylsilyl groups, suggesting the dialkylboryl-substituted disilenes in the presence of a base serve as the surrogates of disilenyl anions (disilenides).
Highlights
Monoborylated disilene 3 was obtained by the following desilylation-borylation reaction (Scheme 1)
1,2-diboryldisilene 4 was obtained as purple crystals in 56% yield from 1 by the double desilylation-borylation reactions without the isolation of 3 (Scheme 3)
Borylsilanes are known to react with a base, such as an alkyllithium, N-heterocyclic carbenes, t-BuOK, etc. to provide the corresponding silyl anion and/or silylborate [20,21,22,23,24], while t-BuOK can add across the Si=Si double bond in (Me3 Si)(i-Pr3 Si)Si=Si(SiMe3 )(Sii-Pr3 ) to provide the corresponding disilanyl anion [25]
Summary
Compounds with silicon-silicon double bonds (disilenes) have been extensively studied as π-electron systems of silicon with fascinating structural and electronic features arising from a higher-lying π orbital and a lower-lying π* orbitals compared to those of the corresponding alkenes [1,2,3,4,5,6,7,8,9]. Disilenes inherently undergo auto-oligomerization due to their weaker π(Si=Si) bond energy compared to the corresponding σ(Si–Si) bond energy, the introduction of judiciously designed bulky protecting groups enables us to synthesize a variety of isolable disilenes that contain functional groups. Boryl-substituted disilenes have been less investigated compared with other functionalized disilenes (Figure 1), the boryldisilenes are anticipated to exhibit the structure and reactivity due to the conjugation between the π(Si=Si) and 2p(B) orbitals and the coordination of a base to the boryl group should alter the electronic structure and reactivity
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