The reactions of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasila-2-yne 1 with an equivalent amount of trans- and cis-3,3',5,5'-tetramethylazobenzenes produced a Si(2)N(2) four-membered ring biradicaloid [RSi(μ-NAr)(2)SiR] 2 (R = Si(i)Pr[CH(SiMe(3))(2)](2), Ar = 3,5-Me(2)C(6)H(3)), which was isolated as air- and moisture-sensitive dark purple crystals. Compound 2 displays no EPR signal, and the molecular structure of 2 was characterized by NMR spectroscopy and X-ray crystallography, revealing that 2 has a planar centrosymmetric Si(2)N(2) four-membered ring. The Si1-Si1' distance is 2.63380(9) Å, and there is no bond interaction between the Si1 and Si1' atoms of 2. The reactions of 2 with methanol and carbon tetrachloride show that 2 has both closed-shell and radical-type reactivity.

Fluorinated [6]- and [9]cycloparaphenylene (CPP) derivatives, 8F-[6]CPP and 12F-[9]CPP, were synthesized based on the previous synthesis of the parent CPPs. While the reductive aromatization conditions used in the final step of the synthesis of the parent CPPs did not work for the fluorinated compounds, the use of PBr and SnCl in acetonitrile successfully accomplished the desired transformation. The structures of F-CPPs were determined by single-crystal X-ray analysis. Photo- and electrochemical analyses and host-guest chemistry revealed the effects of the introduction of fluorine atoms.

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The reaction of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasila-2-yne 1 with diethylamine or diphenylamine produced the corresponding amino-substituted disilenes R(R'(2)N)Si=SiHR 2a, b (R = Si(i)Pr[CH(SiMe(3))(2)](2), R' = Et (2a), Ph (2b)). The reaction of 1 with 9-borabicyclo[3.3.1]nonane afforded the boryl-substituted disilene R(R''(2)B)Si=SiHR 3 (R''(2)B = 9-borabicyclo[3.3.1]nonan-9-yl). Spectroscopic and X-ray crystallographic analyses of 2a, b, and 3 showed that 2a and 3 have a coplanar arrangement of the Si=Si double bond and amino or boryl groups, giving pi-conjugation between the Si=Si double bond and the lone pair on the nitrogen atom or vacant 2p orbital on the boron atom, whereas 2b exhibits no such conjugation.

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The reaction of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasila-2-yne 1 with trimethylsilylcyanide produced the bis-adduct [RSiSiR(CNSiMe(3))(2)] (R = Si(i)Pr[CH(SiMe(3))(2)](2)) 2 and a 1,4-diaza-2,3-disilabenzene analogue 3, which were characterized by spectroscopic data as well as X-ray crystallography (for 2). These two products were produced by different isomers of trimethylsilylcyanide reacting with the disilyne; bis-adduct 2 was formed from the isocyanide form, and compound 3 was produced from the cyanide form followed by cyclization. The bis-adduct 2 is shown on the basis of X-ray crystallography structural data and theoretical studies to exhibit some bis(silaketenimine) character with zwitterionic contributions. The dl-form of dicyano compound 4 was preferentially produced by the reaction of 2 with methanol.

To reduce anthropogenic carbon dioxide (CO2) emissions, it is desirable to develop reactions that can efficiently convert low concentrations of CO2, present in exhaust gases and ambient air, into industrially important chemicals, without involving any expensive separation, concentration, compression, and purification processes. Here, we present an efficient method for synthesizing urea derivatives from alkyl ammonium carbamates. The carbamates can be easily obtained from low concentrations of CO2 as present in ambient air or simulated exhaust gas. Reaction of alkyl ammonium carbamates with 1,3-dimethyl-2-imidazolidinone solvent in the presence of a titanium complex catalyst inside a sealed vessel produces urea derivatives in high yields. This reaction is suitable for synthesizing ethylene urea, an industrially important chemical, as well as various cyclic and acyclic urea derivatives. Using this methodology, we also show the synthesis of urea derivatives directly from low concentration of CO2 sources in a one-pot manner.

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