Communications
Isocyanates Hot Paper
ꢀ
The Simplest, Isolable, Alkynyl Isocyanate HC CNCO: Synthesis and
Characterization
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Dedicated to Professor Helge Willner
[
10]
Abstract: Alkynyl isocyanates have been postulated as highly
reactive intermediates in synthetic chemistry. Herein, the parent
molecule HCꢀCNCO is isolated for the first time. In sharp
CH NCO have been the focus of numerous experimental
3
and theoretical studies.
Chemically, covalent isocyanates are reactive owing to
facile hydrolysis, self-addition, and condensation reactions.
This is particularly true for alkynyl isocyanates RCꢀCNCO,
contrast to the previously reported short lifetime (ca. 15 s) at
room temperature, we found that HCꢀCNCO has a lifetime of
5
5 h in the gas phase (2 mbar, 300 K) with a melting point of
since isocyanates can undergo inter- and intramolecular
À79.58C and vaporization enthalpy (DHvap
)
of 23.1-
cycloaddition with alkynes for the construction of diverse
À1
1
[11]
(
1) kJmol . Apart from the IR (gas, solid, and matrix), H
heterocycles.
The earliest report on the intermediacy of
1
3
and C NMR, and UV/Vis spectroscopic characterization, its
RCꢀCNCO dates back to 1926, when Curtius and Kenngott
[12]
photoisomerization with a acylnitrene HCꢀCC(O)N and
studied the decomposition of phenylpropiolyl azide. Later
on, the Curtius rearrangement of this azide was studied in
solutions, the formation of PhCꢀCNCO was confirmed based
cyanoketene NCC(H)CO has been observed.
[
13]
I
socyanates are versatile addition and cycloaddition reagents
on the analysis of the trapping products. Afterwards, the
isolation of the decomposition products in solid Ar matrix at
10 K allowed IR spectroscopic identification of PhCꢀ
[
1]
for the synthesis of biologically active heterocycles, such as
[2]
[3]
[4]
indolizidines, quinolizidines, and pyridines. In industry,
isocyanates are building blocks for the fabrication of polyur-
ethane materials. In atmospheric chemistry, isocyanates
involve in the combustion of polyurethane and the degrada-
[
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CNCO. However, the attempts to isolate alkynyl isocya-
nates with bulky substituents such as hept-1-ynyl isocyanate
and [4-(tert-butyl)phenyl]ethynyl isocyanate failed, and it was
found that “it is impossible to isolate the isocyanate for
[5]
[
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tion of pesticides (for example, aldicarb and carbofuran). In
particular, the prototype molecules such as HNCO and
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purification”.
CH NCO have been shown to be products of various forms
As the parent molecule, HCꢀCNCO has been proposed as
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of combustion such as biomass burning, cooking, and
an interstellar candidate formed from the combination of the
[
7]
[16]
[17]
cigarette smoking, and they are also interstellar species
that have been detected in Sgr B2(N), the hot core of a giant
interstellar species HCC with NCO. Its structure, stabil-
ity, and isomerization reactions have been computationally
[8]
[18]
molecular cloud near the galactic center. Therefore, the
studied. Experimentally, HCꢀCNCO has been generated
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structures and reactivity of isocyanates such as HNCO and
by the pyrolysis of N-propynoyl-N,O-bis(trimethylsilyl)hy-
droxylamine with subsequent detection in the gas phase using
[
19]
microwave spectroscopy (MW). Apart from the determi-
nation of the structural parameters using a semirigid bender
model, a half-life of about 15 s at room temperature was
estimated.
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[
*] Y. Y. Qin, B. Lu, C. Song, X. X. Chu, Prof. Dr. X. Q. Zeng
College of Chemistry, Chemical Engineering and Materials Science,
Soochow University
Suzhou 215123 (China)
E-mail: xqzeng@suda.edu.cn
The instability of HCꢀCNCO seems to resemble the
[
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intensively studied alkynyl azide HCꢀCN , alkynyl cyanide
3
[
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Prof. Dr. G. Rauhut
Institute for Theoretical Chemistry, University of Stuttgart
Pfaffenwaldring 55, Stuttgart 70569 (Germany)
HCꢀCCN, and isocyanide HCꢀCNC.
Gaseous HCꢀCN
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decomposes with a half-life of 20 min at room temperature,
and HCꢀCCN undergoes polymerization in the condensed
phases. However, unlike the facile N elimination in HCꢀCN
Dr. M. Hagedorn, Prof. Dr. K. Banert
Chemnitz University of Technology, Organic Chemistry
Strasse der Nationen 62, Chemnitz 09111 (Germany)
2
3
À1
[20e]
(
E = 21 kcalmol , CCSD(T)/cc-pVTZ),
the calculated
a
formidable activation barriers for the highly endothermic
Dr. L. N. Wang, Prof. Dr. X. Q. Zeng
Department of Chemistry, Fudan University
Shanghai 200433 (China)
À1
CO-elimination (70 kcalmol ) and the rearrangement to
À1 [18d]
other isomers (> 80 kcalmol )
suggest that monomeric
HCꢀCNCO should be thermally persistent. Furthermore, the
E-mail: xqzeng@fudan.edu.cn
À1
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[
moderate barriers for the dimerization (> 30 kcalmol ) of
] These authors contributed equally to this work.
HCꢀCNCO render its isolation possible at low temperatur-
Supporting information and the ORCID identification number(s) for
[
18a]
es.
Herein, we report the synthesis and characterization of
HCꢀCNCO (3, Scheme 1) as a neat substance. Apart from the
Angew. Chem. Int. Ed. 2019, 58, 1 – 6
ꢀ 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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