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43. A radical approach for the selective C-H borylation of azines

Author

Kim, Ji Hye, Constantin, Timothée, Simonetti, Marco, Llaveria, Josep, Sheikh, Nadeem S., and Leonori, Daniele

Subjects
Nitrogen compounds -- Chemical properties, Hydrogen -- Chemical properties, Chemical reactions -- Methods, Carbon -- Chemical properties, Boron -- Chemical properties, Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

Boron functional groups are often introduced in place of aromatic carbon-hydrogen bonds to expedite small-molecule diversification through coupling of molecular fragments.sup.1-3. Current approaches based on transition-metal-catalysed activation of carbon-hydrogen bonds are effective for the borylation of many (hetero)aromatic derivatives.sup.4,5 but show narrow applicability to azines (nitrogen-containing aromatic heterocycles), which are key components of many pharmaceutical and agrochemical products.sup.6. Here we report an azine borylation strategy using stable and inexpensive amine-borane.sup.7 reagents. Photocatalysis converts these low-molecular-weight materials into highly reactive boryl radicals.sup.8 that undergo efficient addition to azine building blocks. This reactivity provides a mechanistically alternative tactic for sp.sup.2 carbon-boron bond assembly, where the elementary steps of transition-metal-mediated carbon-hydrogen bond activation and reductive elimination from azine-organometallic intermediates are replaced by a direct, Minisci.sup.9-style, radical addition. The strongly nucleophilic character of the amine-boryl radicals enables predictable and site-selective carbon-boron bond formation by targeting the azine's most activated position, including the challenging sites adjacent to the basic nitrogen atom. This approach enables access to aromatic sites that elude current strategies based on carbon-hydrogen bond activation, and has led to borylated materials that would otherwise be difficult to prepare. We have applied this process to the introduction of amine-borane functionalities to complex and industrially relevant products. The diversification of the borylated azine products by mainstream cross-coupling technologies establishes aromatic amino-boranes as a powerful class of building blocks for chemical synthesis. Selective borylation of azines--nitrogen-containing aromatic heterocycles used in the synthesis of many pharmaceuticals--is made possible by forming a radical from an aminoborane using a photocatalyst., Author(s): Ji Hye Kim [sup.1] , Timothée Constantin [sup.1] , Marco Simonetti [sup.1] , Josep Llaveria [sup.2] , Nadeem S. Sheikh [sup.3] , Daniele Leonori [sup.1] Author Affiliations: (1) Department [...]

Published
2021
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50. Experimental and numerical study on thin silicon wafer CO2 laser cutting and damage investigation.

Author

Moghadasi, Kaveh, Tamrin, Khairul Fikri, Sheikh, Nadeem Ahmed, Kram, Abdul Rahman, Barroy, Pierre, Mahmud, Fahizan, and Khan, Amir Azam

Subjects
LASER machining, LASER measurement, CUTTING machines, OPTICAL measurements, MACHINING, LASER beam cutting
Abstract

This study investigates laser-induced damage in thin silicon (Si) wafer ablation both experimentally and numerically. A 40-W continuous-wave CO2 laser is employed as the volumetric heat source. Experiments are conducted that involve variations in the laser cutting speed from 5 to 20 mm/s and the number of passes from one to three while maintaining a constant laser power of 40 W for investigation. The measured output parameters include surface morphologies, heat-affected zone (HAZ), and kerf width. For the first time, a finite element solution based on the brittle–ductile transition (BDT) phenomenon is introduced to predict temperature-stress gradients in the laser cutting region. Johnson–Cook (J-C) plasticity, along with the introduced damage criteria, are employed to analyse the cutting characteristics. The results show that the lowest CO2 laser speed and minimal number of passes enhance Si wafer quality. Nevertheless, increasing cutting speed and the number of passes significantly intensify material ablation and oxidisation due to elevated laser heat input. Using optimal parameters, numerical analysis shows a high level of agreement with experimental findings. Transverse/longitudinal stresses correlate with temperature, while the longitudinal stress is substantially lower compared to the transverse stresses due to thermal expansion and the direction of heat transfer. Following that, computed assessments of compressive and tensile stresses are used to refine specific laser parameters and locations for experimental setup. [ABSTRACT FROM AUTHOR]

Published
2024
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