Use of a rhodium catalyst with (R)-(S)-BPPFA ligand allows efficient synthesis of sila [n]helicenes via dehydrogenative silylation of CH bonds. By selecting the proper ligands, the current method provides the ability to prepare unsymmetrical sila [n]helicene derivatives without any oxidants. The resulting sila[6]helicene is a rare example of a five-membered ring-fused [6]helicene, which was isolated as a single pure enantiomer without substituents on the terminal benzene rings.Silicon-containing -conjugated molecules show promise as materials useful in the areas of electro-and photoluminescence. 1 The incorporated silicon atom has a significant impact on the energy levels of the frontier orbital, and that of the LUMO is effectively stabilized by the interaction between the low lying * orbital of two exocyclic -bonds of the silicon atom and the * orbital of the conjugated -system of the backbone. Catalytic dehydrogenative silylation of CH bonds is a straightforward, atom-efficient, and sustainable route toward these silicon-containing -conjugated molecules. 2-5 Since our first report in 2010 on the synthesis of silafluorenes, 3a rhodium-catalyzed dehydrogenative silylation has been developed for the synthesis of various silicon-containing -conjugated molecules, such as silicon-bridged p-terphenyl, 3a spirosilabifluorenes, 3b,3j benzosilolometallocenes, 3e-g dihydrobenzosilole, 3i and phenazasilines 3d (Figure 1). To further demonstrate the utility of this silylative cyclization, development of a robust catalyst system with improved reaction efficiency is highly desirable for the synthesis of more challenging siliconcontaining -systems. The present paper describes the synthesis of sila[n]helicenes (n = 4, 5 and 6) with uniquely merged -conjugated systems of helicene and silole. This study also demonstrates that the amino group-substituted (R)-(S)-BPPFA ((R)-N,N-dimethyl-1-[(S)-1',2-bis(diphenylphosphino)ferrocenyl]ethylamine) ligand is highly effective for the rhodiumcatalyzed dehydrogenative silylation of CH bonds.Helicene possesses a unique screw-shaped -system consisting of all ortho-annelated aromatic rings. 6 In addition to a unique function as an optoelectronic material, these compounds can be utilized as ligands and organocatalysts. 6c Despite their promising potential for functional materials, few [n]helicenes could allow customization of their properties, and dehydrogenative silylation with the activation of ubiquitous CH bonds is thought to allow a more straightforward approach. We previously reported that Wilkinson's catalyst, RhCl(PPh 3 ) 3 , is effective for the silylative cyclization of 2-(2-
The stringent regulations that were placed on gasoline vehicles demand significant improvement of the powertrain unit, not only to become cleaner but also more efficient. Therefore, there is a strong need to understand the complex in-cylinder processes that will have a direct effect on the combustion quality. This study applied multiple high-speed optical imaging to investigate the interaction between the in-cylinder flow, the spark, the flame, and combustion performance. These individual elements have been studied closely in the literature but the combined effect is not well understood. Simultaneous imaging of in-cylinder flow and flame tomography using high-speed Particle Image Velocimetry (PIV), as well as simultaneous high-speed spark imaging, were applied to port-injected optical gasoline imaging. The captured images were processed using in-house MATLAB algorithms and the deduced data shows a trend that higher in-cylinder flow velocity near the spark will increase the stretch distance of the spark and decrease the ignition delay. However, these do not have much effect on the combustion duration, and it is the flow-field in the entire area surrounding the flame development that will influence how fast the combustion and flame growth will occur.
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