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N-Heterocycles
Published in Navjeet Kaur, Metals and Non-Metals, 2020
Murakami et al. [272–273] synthesized α-isocyano-δ-ketoesters in high yields by Michael reaction of α,β-unsaturated carbonyl compounds and α-isocyanoesters in tetrabutylammonium fluoride. Another Michael reaction using the same reactants, accelerated by N,O-bis(trimethylsilyl)acetamide (BSA), produces silyl enolates under mild conditions. The isocyanide group is activated through coordination by a Lewis acid which promotes different types of nucleophilic cyclizations, following which silylated Michael adducts are cyclized using Zn(OAc)2 to form pyrroline-2-carboxylic acids. This reaction occurs through the cyclization of the complex after coordination of zinc(II) with the isocyano functionality (Scheme 104) [174].
Star-shaped Pd(II) and Pt(II) complexes containing C3-symmetric conjugated thiophenes: Synthesis, characterization, and chemical reactions with organic unsaturated molecules
Published in Journal of Coordination Chemistry, 2022
Hee Kwon Park, Min Gyu Ham, Yong-Joo Kim, Katsuhiko Takeuchi, Jun-Chul Choi
Insertion of organic unsaturated molecules into transition metal-carbon bonds extend π-conjugation and expand potential electronic functionality of the aromatic moiety. Numerous publications have reported small molecule (isocyanide) insertion into dinuclear late transition complexes [17, 28–30]; however, similar insertions into C3-symmetric trinuclear complexes remain unexplored. Here, isocyanide was inserted into Pd-carbon and Pt-carbon bonds. Insertion of organic isocyanides (CN-R) (3 equiv.) with trinuclear Pd(II) complex, 1, afforded Pd(II) imidoyl (C = N(R)) complexes (11–13) in Scheme 6. Partial insertion of CN-R into the thiophenyl–Pd bond was not observed. Similar reactions of Pt(II) complex, 3, with CN-R (R = 2,6-dimethylphenyl) occurred slowly to first afford white solids. Repeated recrystallization and IR monitoring indicated the formation of an imidoyl Pt(II) complex mixture, composed of 14 (major) and 14•(CN-R) (minor). IR spectral band observed at 2171 cm−1 was attributed to metal-coordinated ν(C≡N) of the CN-R. IR spectra of the trinuclear complexes exhibited ν(C = N) at 1580–1550 cm−1, indicating imidoyl formation by CN-R insertion into thiophenyl-Pd/Pt bonds. The 1H-NMR spectral signals for thiophenyl group and benzene core for 11–14 did not undergo the splitting shown in Chart 2, indicating no influence of imidoyl formation on the C3-symmetric plane.
High levels of isocyanic acid in smoke generated during hot iron cauterization
Published in Archives of Environmental & Occupational Health, 2020
The monoisocyanates isocyanic acid (ICA) and methyl isocyanate (MIC) are highly reactive electrophilic compounds that in the body will cause damage to and dysfunction of proteins.1–3 ICA is a strong organic acid that, together with other pollutants, has been found in fire smoke, diesel emissions and in emissions from heated products that contain urea-formaldehyde resins as binders.4–9 ICA and hydrogen cyanide (HCN) have been shown during high-temperature pyrolysis of biofuels with a nitrogen content that varied between 2.9 and 15.5%. The formation of ICA did then increased proportionally with the nitrogen content of the fuel and no ICA was found from bark with only 0.4% nitrogen.10 The chemistry behind the formation of ICA under these conditions is complex. It is however likely that the heating or combustion of nitrogen-containing products first gives rise to HCN, (together with ammonia or possibly other nitrogen-containing gases) and that this HCN then via the intermediate hydrogen isocyanide, is oxidized to ICA.11–13
The role of hydrogen bonds in the mesomorphic behaviour of supramolecular assemblies organized in dendritic architectures
Published in Liquid Crystals Reviews, 2019
Michael Arkas, I. Kitsou, A. Gkouma, M. Papageorgiou
In an attempt to synthesize dendronized p-conjugated poly(isocyanide)s, Tian and his group [129], observed that their isocyanide dendron monomers (Figure 13) did not exhibit liquid crystalline phases whereas respective hydrated precursors bearing formamido (HCONH-) moieties (Figure 14) formed columnar and cubic phases due to dimerization and polymerization via intermolecular hydrogen bonding as confirmed by IR spectroscopy (Figure 15). This is a rare and exceptionally interesting example of a supramolecular liquid crystalline dendronized polymer formed through hydrogen bonds that owes its mesomorphic properties exclusively to them.