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DOI: 10.1055/a-2110-5359
Remote Back Strain: A Strategy for Modulating the Reactivity of Triarylboranes
This project was supported by the Environment Research and Technology Development Fund (JPMEERF20211R01 to Y.H.) of the Environmental Restoration and Conservation Agency of the Ministry of the Environment of Japan, and Grants-in-Aid for Transformative Research Area (A) Digitalization-driven Transformative Organic Synthesis (JSPS KAKENHI Grant 22H05363 to Y.H.). Y.H. acknowledges financial supports from the Yazaki Memorial Foundation for Science and Technology, the Kansai Research Foundation for Technology Promotion, and the Takeharakenzai Alpsclean Co., Ltd. M.S. gratefully acknowledges a JST SPRING grant (JPMJSP2138).
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Abstract
A strategy for modulating the Lewis acidity of triarylboranes is proposed based on the concept of remote back strain. Steric repulsion and noncovalent interactions, both generated between the aryl meta-substituents of triarylboranes, are found to be critical for determining the strength of the remote back strain. Applying this concept, we synthesized B[2,6-F2-3,5-(TMS)2-C6H]3 and the liquid B[2,6-F2-3,5-(allyl)2-C6H]3 and we demonstrated their superior catalytic activity for the hydrogenation of quinoline relative to B(C6F5)3 or B(2,6-F2C6H3)3. Moreover, we established the first example of the catalytic hydrogenation of quinoline by using B[2,6-F2-3,5-(allyl)2-C6H]3 in the presence of a gaseous 1:1:1 molar mixture of H2, CO, and CO2.
Key words
triarylboranes - Lewis acids - frustrated Lewis pairs - hydrogenation - boron catalysis - hydrogen separationSupporting Information
- Supporting information for this article is available online at https://doi.org/10.1055/a-2110-5359.
- Supporting Information
Publication History
Received: 30 May 2023
Accepted after revision: 14 June 2023
Accepted Manuscript online:
14 June 2023
Article published online:
14 September 2023
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- 21 1,2,3,4-Tetrahydroquinoline; Typical Procedure A 30 mL autoclave was charged with Qin (263.2 mg, 2.0 mmol), B2 (59.8 mg, 0.1 mmol; 5 mol%), tetradecane (142.5 mg; internal standard), and toluene (1.3 mL). Once sealed, the autoclave was pressurized with H2, CO, CO2 (20 atm each) and heated 100 °C for 8 h; yield: >99% (GC).
Recently, Greb et al. have proposed that Lewis acidity could be classified as global, effective, or intrinsic. These labels refer to the thermodynamic energy change during adduct formation (∆E/ΔG), the spectroscopic changes observed on the Lewis base (e.g., the Gutmann–Beckett method) upon forming an adduct, and the intrinsic properties of the free boranes (e.g., the energy level of the empty p orbitals and its electron affinity), respectively, for details, see:
For selected examples, see:
For examples that include trialkylsilyl groups, see:
For selected examples, see: