Substituent effects on the kinetics of bifunctional styrene SAM formation on H-terminated Si

Reaction of Dichlorophenylborane with H-Si(100)

Traditional approaches to achieving dopant functionalized Si involve grafting the dopant to the Si substrates through O-Si or C-Si bonds, resulting in indirect attachment of the dopant to the Si. Recently, ultrahigh vacuum work has demonstrated that high densities of direct B-Si bonds enable unprecedented electronic behaviors in Si that make it possible for Si to be used as a next-generation electronic material. As solvothermal approaches are inherently amenable to scale-up, there is currently a push to develop solvothermal approaches for the formation of direct dopant-Si bonds. Thus far, B-Si chemistries for next-generation electronic materials have been demonstrated with boron trichloride and bis(pinacolatodiboron). In this work, we use a combination of experimental work and computational studies to examine the reactivity of a phenyl derivatized boron trichloride, namely dichlorophenylborane, with H-Si(100). We determine that despite the stability and ease for the formation of C-Si bonds, the organic component, the phenyl group remains attached to the B and does not yield competitive formation of products via a Si-C bond. This reaction proved a new solvothermal method for the formation of direct B-Si bonds that, with further work, can be leveraged in developing next-generation electronic materials.

Sonochemical Reaction of Bifunctional Molecules on Silicon (111) Hydride Surface

While the sonochemical grafting of molecules on silicon hydride surface to form stable Si-C bond via hydrosilylation has been previously described, the susceptibility towards nucleophilic functional groups during the sonochemical reaction process remains unclear. In this work, a competitive study between a well-established thermal reaction and sonochemical reaction of nucleophilic molecules (cyclopropylamine and 3-Butyn-1-ol) was performed on p-type silicon hydride (111) surfaces. The nature of surface grafting from these reactions was examined through contact angle measurements, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Cyclopropylamine, being a sensitive radical clock, did not experience any ring-opening events. This suggested that either the Si-H may not have undergone homolysis as reported previously under sonochemical reaction or that the interaction to the surface hydride via a lone-pair electron coordination bond was reversible during the process. On the other hand, silicon back-bond breakage and subsequent surface roughening were observed for 3-Butyn-1-ol at high-temperature grafting (≈150 °C). Interestingly, the sonochemical reaction did not produce appreciable topographical changes to surfaces at the nano scale and the further XPS analysis may suggest Si-C formation. This indicated that while a sonochemical reaction may be indifferent towards nucleophilic groups, the surface was more reactive towards unsaturated carbons. To the best of the author's knowledge, this is the first attempt at elucidating the underlying reactivity mechanisms of nucleophilic groups and unsaturated carbon bonds during sonochemical reaction of silicon hydride surfaces.

Fifty Years of Hydrosilylation in Polymer Science: A Review of Current Trends of Low-Cost Transition-Metal and Metal-Free Catalysts, Non-Thermally Triggered Hydrosilylation Reactions, and Industrial Applications

Hydrosilylation reactions, the (commonly) anti-Markovnikov additions of silanes to unsaturated bonds present in compounds such as alkenes and alkynes, offer numerous unique and advantageous properties for the preparation of polymeric materials, such as high yields and stereoselectivity. These reactions require to be catalyzed, for which platinum compounds were used in the initial stages. Celebrating the 50th anniversary of hydrosilylations in polymer science and, concomitantly, five decades of continuously growing research, hydrosilylation reactions have advanced to a level that renders them predestined for transfer into commercial products on the large scale. Facing this potential transfer, this review addresses and discusses selected current trends of the scientific research in the area, namely low-cost transition metal catalysts (focusing on iron, cobalt, and nickel complexes), metal-free catalysts, non-thermally triggered hydrosilylation reactions (highlighting stimuli such as (UV-)light), and (potential) industrial applications (highlighting the catalysts used and products manufactured). This review focuses on the hydrosilylation reactions involving alkene reactants.