Abstract
Following on from our previous study on the resonance/inductive structures of ethynylaniline, this report examines similar effects arising from resonance structures with aromatic aminothiophenol with dual electron-donating substituents. In brief, 2- and 3-aminothiophenol were thermally grafted on silicon (111) hydride substrate at 130 °C under nonpolar aprotic mesitylene. From the examination of high resolution XPS Si2p, N1s, and S2p spectrum, it was noticed that there was a strong preference of NH2 over SH to form Si–N linkage on the silicon hydride surface for 2-aminothiophenol. However, for 3-aminothiophenol, there was a switch in reactivity of the silicon hydride toward SH group. This was attributed to the antagonistic and cooperative resonance effects for 2- and 3-aminothiophenol, respectively. The data strongly suggested that the net resonance of the benzylic-based compound could have played an important role in the net distribution of negative charge along the benzylic framework and subsequently influenced the outcome of the surface reaction. To the best of the authors’ knowledge, this correlation between dual electron-donating substituents and the outcome of the nucleophilic addition toward silicon hydride surfaces has not been described before in literature.
Highlights
Nucleophilic addition to silicon-hydrogenated surfaces has always been an interesting alternative to classical hydrosilylation surface reaction on silicon-hydrogenated substrates [1,2,3,4]
The addition of the lone pair from NH2 directly onto the silicon hydride surface will typically result in the formation of a stable Si–N type linkage
Under low temperature (130 ◦ C), it was thought that there would be no homolysis of the silicon hydride bond and that the nucleophilic NH2 and SH would react to the surface via direct nucleophilic addition mechanism
Summary
Nucleophilic addition to silicon-hydrogenated surfaces has always been an interesting alternative to classical hydrosilylation surface reaction on silicon-hydrogenated substrates [1,2,3,4]. While the chemistry of hydrosilylation has been heavily investigated over the years, reaching a general consensus amongst researchers with regard to the precise chemical mechanism has been somewhat challenging, especially for different reaction types (thermal, photoionization, or catalyst-driven). Bifunctional compound with both unsaturated carbon (alkene/alkyne) and potential nucleophiles, such as OH and NH2 , are often avoided to minimize the risk of attachment to silicon hydride surfaces via direct nucleophilic addition that can outcompete the more preferred route of reacting through the unsaturated carbon end (alkynes and alkenes) [11] Such reaction interference has been well-recognized in early reports, such as those from Bitzer et al [12] and Rummel et al [13].
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