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Mechanistic aspects of a series of thermal reactions that start from acylpolysilane are discussed from B3LYP density functional theory calculations. The chemistry includes the 1,3-silyl migration on acylpolysilane that leads to the formation of silene and the [2 + 2] cycloaddition between silene and acetylene that gives rise to silacyclobutene, an organosilicon four-membered ring compound. Calculated energies for these reactions are reasonable as chemical processes that proceed under thermolysis conditions. There are two kinds of reaction pathways in the 1,3-silyl migration on acylpolysilane with respect to the stereochemistry of the migrating silyl group; one is a retention pathway and the other is an inversion pathway. The retention pathway is energetically preferred to the inversion pathway, being fully consistent with previous results about similar reactions. Silene thus formed undergoes [2 + 2] cycloaddition with acetylene in a two-step manner, resulting in the formation of silacyclobutene. The reason that this "symmetry-forbidden" reaction occurs under thermolysis conditions is considered from intrinsic reaction coordinate calculations as well as orbital interaction analyses. Because the orbital amplitude is significant on the Si atom of silene, the interaction in the region between the silene Si atom and the diagonal acetylene C atom is dominant in the initial stages of the ring-closure process. Consequently, the formation of the diagonal Si-C bond has a preference over that of the proper Si-C bond finally formed in the four-membered ring. This initial process is important in the avoidance of the symmetry restriction arising from the unfavorable HOMO-LUMO overlap in the [2 + 2] cycloaddition.

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The deposition of diamond-like carbon (DLC) films at atmospheric pressure is a promising technique of achieving in-process coatings regardless of work size. In this study, we aimed at the synthesis of DLC films at atmospheric pressure by nanopulse chemical vapor deposition (CVD) using a unique power source system consisting of a static induction (SI) thyristor and an inductive energy strage (IES). Then, we realized the synthesis of DLC films in open air (101 kPa). The deposition rate was as high as 0.4 µm/min, and the hardness of the film was 20.6 GPa. From Raman spectroscopic analysis results, the quality of films was found to significantly depend on input voltage and deposition time.

Heating silacyclobut-3-ene 2 at 250 °C afforded the trans-silacyclobut-3-ene 4, via the silylsubstituted cycloprop-2-ene 3. The photolysis of 4 gave a 1:1 mixture of 4 and the cis isomer 6, which was transformed into 4 at 250 °C, quantitatively. Preliminary results of the theoretical treatment for the isomerization of 2′ to 3′ are described.