Spectroscopic Characterization of 1-Naphthyl Isocyanate Anion Radical and of Tris(1-naphthyl) Isocyanurate Atropisomers

Article abstract of DOI:10.1002/ejoc.201500863

Room-temperature potassium metal reduction of 1-naphthyl isocyanate in THF results in a rapid cyclotrimerization (initiated by the 1-naphthyl isocyanate anion radical) that generates two diastereoisomers (atropisomers) of tris(1-naphthyl) isocyanurate. The formation of the syn and anti diastereoisomers was monitored by ¹H and ¹³C NMR spectroscopy. Upon completion of the cyclotrimerization, the two diastereoisomers were isolated, and their configuration was assigned by NMR spectroscopy. Both compounds crystallize in the monoclinic C2/c space group, and single-crystal X-ray diffraction analyses confirm the structures of both isomeric forms. The results from this study prove that alkali metal reduction of isocyanates is a convenient and rapid method for generating isocyanurate compounds even when a sterically bulky substituent is attached to the NCO moiety.

Full text of DOI:10.1002/ejoc.201500863

FULL PAPER
DOI: 10.1002/ejoc.201500863
Spectroscopic Characterization of 1-Naphthyl Isocyanate Anion Radical and of
Tris(1-naphthyl) Isocyanurate Atropisomers
Steven J. Peters,*[a] Mark E. Kassabaum,[a] Michael K. Nocella,[a] and Robert McDonald[b]
Keywords: Atropisomerism / EPR spectroscopy / NMR spectroscopy / Cyclotrimerization / Isocyanurate
Room-temperature potassium metal reduction of 1-naphthyl
isocyanate in THF results in a rapid cyclotrimerization (initi-
NMR spectroscopy. Both compounds crystallize in the mono-
clinic C2/c space group, and single-crystal X-ray diffraction
ated by the 1-naphthyl isocyanate anion radical) that gener- analyses confirm the structures of both isomeric forms. The
ates two diastereoisomers (atropisomers) of tris(1-naphthyl) results from this study prove that alkali metal reduction of
isocyanurate. The formation of the syn and anti diastereoiso- isocyanates is a convenient and rapid method for generating
mers was monitored by 1H and 13C NMR spectroscopy. Upon
isocyanurate compounds even when a sterically bulky sub-
completion of the cyclotrimerization, the two diastereoiso- stituent is attached to the NCO moiety.
mers were isolated, and their configuration was assigned by
anions.[15] Some cyclotrimerization reactions have also been
Introduction
investigated using Lewis acids as catalysts; these include the
use of organotin compounds,[16] as well as copper(II) and
nickel(II) halides.[17] Many of these catalyzed processes have
negative aspects such as low activity of catalysts, formation
of uretidinediones (isocyanate cyclic dimers) and other by-
products, separation of the cyclotrimer from the catalyst,
long reaction times and the use of toxic solvents. Prior to
our work, there have been few catalysts studied that are
effective at driving the cyclotrimerization of both aryl and
alkyl isocyanates, these are the extremely basic pro-azapho-
sphatrane compounds,[14a] and an isopropyl-substituted N-
heterocyclic carbene.[18] Recently, our group has found that
exposure of both alkyl and aryl isocyanate solutions to an
alkali metal (either potassium or sodium) is an effective and
rapid method for the generation of the respective isocyanur-
ates.[19–21] The cyclotrimerization process is believed to pro-
ceed via the reactive isocyanate anion radical formed from
the one-electron reduction of the isocyanate, which rapidly
attacks two more neutral isocyanates.[19,20] In the case of
aryl isocyanates, this protocol is effective at converting
phenyl isocyanate (PhNCO) and a number of para-substi-
tuted PhNCO compounds to their respective isocyanur-
ates.[20] However, we have yet to determine the efficiency of
converting isocyanates with bulky substituents attached to
their respective cyclotrimers. Herein, we report that the al-
kali metal reduction of 1-naphthyl isocyanate (1) results in
the rapid conversion into tris(1-naphthyl) isocyanurate (2)
in very good yield. Both nuclear magnetic resonance
(NMR) spectroscopy and single-crystal X-ray diffraction
studies reveal that atropisomers (e.g., two diasteroisomers
generated as a result of hindered rotation of the three naph-
thyl rings) of tris(1-naphthyl) isocyanurate are produced. To
the best of our knowledge only one other published study
Isocyanurates (1,3,5-triazine-2,4,6-triones), which are
commonly generated by the cyclotrimerization of isocyan-
ates, have considerable commercial importance for their
ability to enhance the physical properties of polyureth-
anes.[1–3] Incorporation of isocyanurates into polymeric
blends of polyurethanes and other copolymer resins make
these materials more flame-retardant, transparent and
chemical- and impact-resistant.[3,4–6] Periodic mesoporous
organosilicas (PMOs) that contain isocyanurate bridging
groups afford materials that show very high adsorption ca-
pacity for mercury(II) and other heavy metal ions from
aqueous solutions.[7] Interestingly, low-toxicity isocyanurate
siderophores have also been investigated as candidates for
drug delivery in mammalian systems,[8] while optically
active isocyanurates having peripheral amino acid units ex-
hibit chiral discrimination of racemic mixtures of enantio-
mers.[9] Tris(aryl) isocyanurates are used as activators in the
copolymerization of β-caprolactam in the formation of
nylon-6.[10]
The importance of isocyanurates commercially has re-
sulted in numerous efforts to develop effective methods for
the rapid cyclotrimerization of isocyanates. Many catalysts
have been found that facilitate the cyclotrimerization
process. A few examples of Lewis bases include amines,[11]
cyanate,[12] fluoride,[13] phosphines,[14] and carbamate
[a] Department of Chemistry, Illinois State University
Normal, IL 61790-4160, USA
E-mail: sjpeter@illinoisstate.edu
http://chemistry.illinoisstate.edu
[b] Department of Chemistry, University of Alberta
Edmonton, Alberta T6G-2G2, Canada
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201500863.
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1-Naphthyl Isocyanate Anion Radical and Tris(1-naphthyl) Isocyanurate Atropisomers
of isocyanurate atropisomers has been reported.[22] (These
Steric crowding between the naphthyl rings and the carb-
studies involved the use of ortho-substituted phenyl isocyan- onyl oxygen atoms within 2 will necessarily force the naph-
ate derivatives.[22]) The one-electron initiated formation and thyl rings to adopt a near perpendicular geometry relative
structures of both 1-naphthyl isocyanurate diastereoisomers to the plane of the isocyanurate moiety. Any rotation of the
are reported here for the first time.
naphthyl rings about the N–C bonds will be greatly hin-
dered as a result of this steric crowding. Thus, two dia-
stereoisomers (atropisomers) are expected upon formation
of 2. The symmetric diastereoisomer (syn-2) will adopt a
C3v symmetry where all three naphthyl rings will be directed
Results and Discussion
Exposure of a [D8]THF solution containing 1-naphthyl above the isocyanurate ring. The other diastereoisomer
isocyanate to a deficient amount of potassium metal ([K (anti-2) has a Cs symmetry where one of the naphthyl
metal] ϽϽ [isocyanate]) results in an immediate color groups is pointing in the opposite direction relative to the
change of the solution from colorless to light yellow-green. other two rings. Each of these stereoisomers should exhibit
Examination of the reduced solution by NMR spec- unique spectroscopic signatures. Upon closer inspection of
troscopy, immediately after exposure to the K metal, reveals the NMR spectroscopic data (Figure 2), three distinct 13C
that nearly half of the 1-naphthyl isocyanate (1) has been carbonyl resonances are clearly present at δ ≈ 149 ppm. In
converted into the cyclotrimer (see Figures 1 and 2). The the case of the syn-2 isomer, all three carbonyl groups are
resonances located at δ ≈ 149.5 ppm in the 13C{1H} NMR chemically equivalent, therefore only one resonance is ex-
spectra (Figure 2B and C) are assigned to the carbonyl car- pected and is found at δ = 149.63 ppm. With the anti-2 iso-
bon atoms in the isocyanurate ring and are evidence of its mer the three carbonyl groups are no longer magnetically
formation upon reduction of 1.[23] Interestingly, with no equivalent. In this molecular system, two of the carbon
further exposure to K metal, we find that the conversion of atoms are equivalent while the third carbon atom is mag-
the isocyanate to the isocyanurate continues to occur, and, netically distinct. Therefore, two unique carbonyl reso-
after approximately 4 h, the formation of the cyclotrimer is nances are expected for the anti-2 isomer in the 13C NMR
nearly complete (Figures 1 and 2). The NMR spectroscopic spectrum where their relative intensity is expected to be 2:1.
data clearly shows that the major species in solution is the A closer look at Figure 2C (inset) reveals that two reso-
tris(1-naphthyl) isocyanurate (2) (ca. 90%) and that a small nances are present, found at δ = 149.65 and 149.45 ppm
amount (ca. 10%) of byproduct is also formed in the re- that match the expected 2:1 ratio, respectively, and are
duction process.
therefore assigned to the carbonyl groups in anti-2.
1
Figure 1. (A) 500 MHz H NMR spectrum of a [D8]THF solution containing 1-naphthyl isocyanate at 300 K before exposure to potas-
sium metal. (B) 1H NMR spectrum collected immediately after the same [D8]THF solution had been exposed to a deficient amount of
metal that exhibits almost 50% conversion of isocyanate into isocyanurate. (C) 1H NMR spectrum collected 4 h after the initial exposure
to K metal. The spectrum shows complete conversion to tris(1-naphthyl) isocyanurate.
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FULL PAPER
Figure 2. (A) 125 MHz 13C{1H} NMR spectrum of a [D8]THF solution containing 1-naphthyl isocyanate at 300 K before exposure to
potassium metal. The carbon resonance associated with the NCO moiety (δ = 126.48 ppm) appears as a shoulder on the high-field side
of the strong resonance at δ = 126.52 ppm. (B) 13C NMR spectrum collected immediately after the same [D8]THF solution had been
exposed to a deficient amount of metal that exhibits almost 50% conversion of isocyanate into isocyanurate. (C) 13C NMR spectrum
collected 4 h after the initial exposure to K metal. Spectrum (C) shows complete conversion to tris(1-naphthyl) isocyanurate. The inset is
an expanded region of the isocyanurate carbonyl resonances.
1
Interestingly, nearly all of the H and 13C NMR reso- atoms and the atoms of the naphthyl group attached to it
nances associated with the naphthalene rings also exhibit are disordered about this twofold axis (thus, they were re-
unique chemical shifts for each of the isomers. A complete fined with an occupancy factor of 0.5 with an idealized ge-
chemical shift assignment for all naphthyl ring carbon and ometry for the naphthyl group). As expected, the isocyanur-
hydrogen atoms for each diastereoisomer can be found in ate rings are relatively planar. The C–N bond lengths within
the Supporting Information. Separation of the two dia- the syn-2 and anti-2 isocyanurate rings range from 1.391(3)
stereoisomers by column chromatography made it possible to 1.401(10) Å; these distances are typical for isocyanur-
1
to distinguish between the H NMR resonances associated ates.[24] The C=O bond lengths also compare favorably with
with each stereoisomer (Figure 3). We find that the ratio of previously reported isocyanurates.[24] In addition, it can be
anti-2/syn-2 obtained from the potassium metal reduction seen that all naphthyl groups are planar and are relatively
of 1-naphthyl isocyanate was 70:30.
orthogonal to the isocyanurate ring as predicted by the
Figure 4 shows the density functional theory (DFT) cal- DFT calculations. The average dihedral angle between the
culated structures of both diastereoisomers and their rela- naphthyl and isocyanurate rings in the two isomers is 78.2°;
tive energies. As predicted by the calculation, the orienta- deviation from 90° is likely due to crystal packing. Most
tion of each of the three naphthyl rings is orthogonal to the importantly, the X-ray structural data supports the NMR
isocyanurate ring. The anti-2 isomer, as expected, was found spectroscopic data in confirming the orientation of all three
to be thermodynamically more stable by approximately naphthyl groups in both the syn-2 isomer and in the anti-2
2.3 kJ/mol, which is likely a consequence of the three naph- isomer.
thyl rings in syn-2 exhibiting more steric crowding. These
calculated results would also explain why the sterically less of both alkyl and aryl isocyanate systems, we proposed that
the cyclotrimerization process is initiated by the formation
In our previous studies with the alkali metal reduction
crowded anti-2 is generated in higher yield.
Single crystals of syn-2 and anti-2 were isolated and char- of the respective anion radical.[19,20] The strongly nucleo-
acterized by X-ray crystallography, and the structures of philic anion radical is expected to attack the carbon atom
these diasteroisomers can be seen in Figure 5. Notably, the within the NCO moiety of a neutral species (a strong elec-
anti isomer has a crystallographic twofold axis of symmetry trophile) to initiate the cyclotrimerization process. Attack
upon which the O1 and C1 atoms are located. The N2 of a third neutral isocyanate will complete the cyclo-
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1-Naphthyl Isocyanate Anion Radical and Tris(1-naphthyl) Isocyanurate Atropisomers
1
Figure 3. (A) 500 MHz H NMR spectrum collected 4 h after the initial exposure to K metal (same as Figure 1C). Spectrum (A) shows
resonances from both diastereoisomers of 2 in a ratio of 70:30 (anti-2/syn-2). (B) and (C) 1H NMR spectra associated with the anti-2 and
syn-2 isomers, respectively, once isolated.
trimerization process. We envision that the formation of the
tris(1-naphthyl) isocyanurate is also driven by the small
amount of 1-naphthyl isocyanate anion radical (1·–) gener-
ated by the potassium metal reduction of the neutral species
(Scheme 1). The anion radical will then attack two ad-
ditional neutral isocyanates resulting in the formation of
the isocyanurate anion radical. Equilibrium electron trans-
fer processes will regenerate 1·–, which will further propa-
gate the cyclotrimerization (Scheme 1, bottom). Detection
of 1·– spectroscopically would provide strong evidence for
this proposed mechanism, therefore the [D8]THF solution
was also interrogated by using EPR techniques immediately
after exposure to the potassium metal.
Figure 4. DFT B3LYP/6-31G* predicted geometries for the dia-
stereoisomers of tris(1-naphthyl) isocyanurate (syn-2 and anti-2)
with their relative energies (E).
Figure 6 shows the EPR spectrum obtained from the
same solution used to monitor the conversion of 1 to 2 by
NMR spectroscopy. A nearly perfect computer simulation
reveals that the odd electron is coupled to seven protons
and one nitrogen atom, which strongly suggests that the
EPR signal comes from the anion radical of 1. This result is
significant, because 1·– is only the second isocyanate anion
radical system to be observed spectroscopically while in
solution and under ambient temperature conditions.[25] The
EPR coupling constants for all protons and the one nitro-
gen atom found for 1·– are similar in magnitude to those
coupling constants measured for the phenyl isocyanate
anion radical, obtained under similar conditions, that were
previously reported by us.[20] To help assign the coupling
Figure 5. ORTEP diagrams of syn-2 and anti-2. Hydrogen atoms
omitted for clarity, and ellipsoids are at 30% probability.
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S. J. Peters, M. E. Kassabaum, M. K. Nocella, R. McDonald
FULL PAPER
Scheme 1. Potassium metal reduction of 1-naphthyl isocyanate resulting in a rapid cyclotrimerization and the formation of tris(1-naphthyl)
isocyanurate. The bottom reaction describes the equilibrium electron transfer process to propagate the synthesis of isocyanurate.
constants to the appropriate hydrogen atoms, we performed spin densities (Figure 7). We find that these predicted spin
a DFT geometry optimization on 1·– at the B3LYP/6- densities (shown in parentheses in Figure 7) are in good
311++G** level of theory along with predicted pz electron agreement with the experimental spin densities (upper num-
bers) that were obtained from the measured coupling con-
stants (Figure 7) and the McConnell relationship.[26] The
discrepancies that are found between some of the experi-
mental and theoretical spin densities (especially with the ni-
trogen spin density) are not surprising since ion association
effects between the NCO moiety within 1·– and the potas-
Figure 6. (Top) X-band EPR spectrum recorded at 295 K after a
[D8]THF solution containing 1-naphthyl isocyanate (1) had been
exposed to a deficient amount of K metal under vacuum. (Bot-
tom) Computer-generated EPR spectrum using aN = 1.03 G (1 N)
Figure 7. B3LYP/6-311++G** predicted geometry for the 1-naph-
and aH = of 1.64 G (1 H), 1.34 G (1 H), 0.76 G (1 H), 0.73 G (1 H), thyl isocyanate anion radical (1·–). The calculated pz spin densities
0.68 G (2 H), 0.080 G (1 H). The peak-to-peak line width (Δwpp) is are given in parentheses, and the empirical spin densities are shown
0.1 G.
above them.
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1-Naphthyl Isocyanate Anion Radical and Tris(1-naphthyl) Isocyanurate Atropisomers
sium cation are expected in THF.[27] The presence of ion
association would likely augment the amount of electron
density residing in the NCO group, which would account
for the larger experimental spin density at the nitrogen atom
than was predicted by these calculations.[28]
either a 400 or a 500 MHz Bruker Avance III spectrometer. EPR
spectra were recorded with a Bruker EMX X-band EPR spectrom-
eter. Once the conversion into isocyanurate was complete, the appa-
ratus and the second NMR tube were opened and the contents
removed. The two diastereoisomers of the tris(1-naphthyl) isocyan-
urate (syn and anti) were separated by silica gel column chromatog-
raphy using a dichloromethane/ethyl acetate (98:2) mixture as the
mobile phase. Upon removal of the mobile phase, a pure, white
crystalline solid was obtained for both isomers. anti-C33H21N3O3
(507.16): calcd. C 78.00, H 4.00, N 8.30; found C 78.67, H 4.16, N
8.29. syn-C33H21N3O3 (507.16): calcd. C 78.00, H 4.00, N 8.30;
found C 73.48, H 4.56, N 7.13.
Conclusions
It has been shown that two atropisomers of tris(1-naphth-
yl) isocyanurate, resulting from the hindered rotation of
the N–naphthyl bonds, have been successfully synthesized
by the alkali metal reduction of 1-naphthyl isocyanate. The
cyclotrimerization is initiated, and propagated, by a small
amount of 1-naphthyl isocyanate anion radical present in
solution. The presence of this species was confirmed by
EPR spectroscopy. The two diastereoisomers of tris(1-
naphthyl) isocyanurate were isolated, and their structure
was confirmed by using 1H and 13C{1H} NMR spec-
troscopy. Single-crystal X-ray analysis also confirmed the
arrangement of the naphthyl rings in the syn and anti iso-
mers. Our results show that the alkali metal reduction of
isocyanates can be a convenient and rapid method for the
production of many interesting substituted isocyanurates,
which may be studied for their unique physical and struc-
tural properties.
Experimental Section
Materials: Perdeuteriated tetrahydrofuran ([D8]THF) was pur-
chased from Cambridge Isotope Inc. and stored under vacuum
over NaK.
Reduction of 1-Naphthyl Isocyanate in [D8]THF for EPR and NMR
Experiments: The 1-naphthyl isocyanate was purified by vacuum
distillation prior to use in all reduction experiments. A sealed glass
tube (with fragile ends) was charged with 30 mg (0.18 mmol) of 1-
naphthyl isocyanate and placed into bulb E of the Pyrex glass appa-
ratus shown in Figure 8. A small amount of potassium metal was
placed into bulb B, which was then sealed at point A, and the entire
apparatus was evacuated. The alkali metal was distilled into bulb
D to form a pristine metal mirror; after this, bulb B was sealed at
point C. Approximately 2.5 mL of THF (dried with NaK) were
distilled from the vacuum system directly into bulb E, and the evac-
uated apparatus was sealed from the vacuum line at point F. The
glass tube containing the isocyanate was broken by shaking and
the solution was well mixed. Prior to beginning the reduction with
Figure 8. Glass apparatus used in the NMR and EPR experiments
for the potassium metal reduction of 1-naphthyl isocyanate in
[D8]THF.
X-ray Crystallography: Single crystals of syn-2·2CH2Cl2 and anti-
2·2CH2Cl2 were grown from CH2Cl2/Et2O by the vapor diffusion
potassium metal, a sample of the [D8]THF solution was collected
1
in one of the NMR tubes so that H and 13C{1H} NMR spectra technique. The crystals selected for diffraction experiments were
of the isocyanate could be obtained. Exposure of the [D8]THF
solution to a deficient amount of potassium was done by simply
pouring a portion of the solution onto the K metal. Once the solu-
tion turned to a greenish yellow solution, a second NMR sample
was collected and periodically monitored by NMR spectroscopy
to observe the cyclotrimerization of 1-naphthyl isocyanate to form
tris(1-naphthyl) isocyanurate. The remaining solution in the appa-
ratus was not exposed further to potassium metal once the second
NMR sample had been harvested. This remaining solution was im-
mediately analyzed, after the second NMR sample was collected,
by X-band EPR spectroscopy for the presence of any anion radicals
formed in the reduction. All NMR spectra were recorded with
coated with Paratone-N oil and then placed under a cold N2 gas
stream of a Bruker D8 diffractometer equipped with an APEX II
CCD detector. Diffraction measurements were obtained by using
graphite-monochromated Mo-Kα (λ = 0.71073 Å) radiation with
the crystal cooled to –100 °C. Data were corrected for absorption
by Gaussian integration from the indexed and measured crystal
faces (SADABS).[29] SHELXD was used to solve the structure, and
the data were refined by full-matrix least squares on F2 using
SHELXL-2014.[30,31] Hydrogen atoms were included as riding
atoms and were placed in geometrically idealized positions with
isotropic displacement parameters 120% of those of the Ueq values
for their parent atoms. In solving the structure of anti-2·2CH2Cl2
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[10] a) Z. Bukac, J. Sebenda, Chem. Prum. 1985, 35, 361–363; b) J.
Horsky, U. Kubanek, J. Marick, J. Kralicek, Chem. Prum.
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[11] a) I. Kogon, J. Am. Chem. Soc. 1956, 78, 4911–4914; b) R.
Richter, H. Ulrich, Synthesis 1975, 7, 463–464; c) A. Giuglio-
Tonolo, C. Spitz, T. Terme, P. Vanelle, Tetrahedron Lett. 2014,
55, 2700–2702.
[12] F. Tanimoto, T. Tanka, H. Kitano, K. Fukui, Bull. Chem. Soc.
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[13] Y. Nambu, T. Endo, J. Org. Chem. 1993, 58, 1932–1934.
[14] a) J. Tang, T. Mohan, J. Verkade, J. Org. Chem. 1994, 59, 4931–
4938; b) S. Raders, J. Verkade, J. Org. Chem. 2010, 75, 5308–
5311.
the following pairs of distances were constrained to be equal
(within 0.03 Å) during the refinement: d(N1–C1) = d(N1–C2),
d(N2–C2) = d(N2–C3). The naphthyl group containing carbon
atoms C20 through C29 was refined with an idealized geometry,
with all C–C bond lengths fixed at 1.390 Å and all bond angles
within this group fixed at 120.0°. See Table 1 for a summary of
crystallographic data. CCDC-1408225 (for syn-2·2CH2Cl2) and
-1408226 (for anti-2·2CH2Cl2) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
[15] M. Khajavi, M. Dakamin, H. Hazarkhani, J. Chem. Res. 2000,
145–147.
Table 1. Summary of crystallographic data.
[16] S. Foley, G. Yap, D. Richeson, Organometallics 1999, 18, 4700–
4705.
syn-2·2CH2Cl2
anti-2·2CH2Cl2
[17] J. Villa, H. Powell, Synth. React. Inorg. Met.-Org. Chem. 1976,
Empirical formula C33H21N3O3·2CH2Cl2 C33H21N3O3·2CH2Cl2
6, 59–63.
M [gmol–1]
Space group
a [Å]
b [Å]
c [Å]
677.38
677.38
[18] H. Duong, M. Cross, J. Louie, Org. Lett. 2004, 6, 4679–4681.
[19] S. Peters, J. Klen, N. Smart, Org. Lett. 2008, 10, 4521–4524.
[20] M. Servos, N. Smart, M. Kassabaum, C. Scholtens, S. Peters,
J. Org. Chem. 2013, 78, 3908–3917.
[21] S. Peters, J. Klen, J. Org. Chem. 2015, 80, 5851–5858.
[22] L. Lunazzi, M. Mancinelli, A. Mazzanti, J. Org. Chem. 2012,
77, 3373–3380.
C2/c (no. 15)
20.8470(9)
14.1127(6)
21.6173(10)
102.9425(5)
6198.4(5)
8
C2/c (no. 15)
22.5158(19)
16.9754(15)
8.6721(7)
106.6746(10)
3175.2
4
–100
Mo-Kα (0.71073)
1.417
0.414
β [°]
V [Å3]
[23] The 13C NMR chemical shift at δ ≈ 149 ppm for the carbonyl
groups is typical for all substituted isocyanurates: a) D. Duff,
G. Maciel, Macromolecules 1990, 23, 3069–3079; b) ref.[22]
[24] a) V. Thalladi, K. Panneerselvam, C. Carrell, H. Carrell, G.
Desiraju, J. Chem. Soc., Chem. Commun. 1995, 341–342; b) S.
Chong, C. Seaton, B. Kariuki, M. Tremayne, Acta Crystallogr.,
Sect. B 2006, 62, 864–874; c) X. Zhou, L. Zhang, M. Zhu,
R. Cai, L. Weng, Organometallics 2001, 20, 5700–5706; d) V.
Thalladi, A. Katz, H. Carrell, A. Nangia, G. Desiraju, Acta
Crystallogr., Sect. C 1998, 54, 86–89; e) P. Tallapally, G. Desi-
raju, Acta Crystallogr., Sect. C 2000, 56, 572–573.
[25] The only other example of detecting isocyanate anion radicals
spectroscopically under room-temperature conditions was our
work with phenyl isocyanate systems, see ref.[20]
[26] J. E. Wertz, J. R. Bolton in Electron Spin Resonance – Elemen-
tary Theory and Practical Applications, Chapman and Hall,
London, 1986, pp. 97–98.
[27] For examples of ion association effects with anion radicals in
THF, see: a) P. Ayscough, R. Wilson, Proc. Chem. Soc. 1962,
229–230; b) G. Canters, E. De Boer, Mol. Phys. 1973, 26, 1185–
1198; c) S. Peters, M. Turk, M. Kiesewetter, R. Reiter, C. Ste-
venson, J. Am. Chem. Soc. 2003, 125, 11212–11213.
[28] The fact that well-resolved NMR spectroscopic data (e.g., line-
widths) could be collected with paramagnetic 1·– in solution
must indicate that the concentration of 1·– is small relative to
that of 1 and 2. For a discussion of how paramagnetic species
influence NMR relaxation effects and linewidths, see: J. San-
ders, B. Hunter in Modern NMR Spectroscopy, A Guide for
Chemists, 2nd ed., Oxford University Press, Oxford, 1993, pp.
163–164.
Z
T [°C]
–100
Mo-Kα (0.71073)
1.452
0.424
0.0583
Radiation (λ [Å])
ρcalcd. [gcm–3]
μ [mm–1]
R1 [I Ն 2σ(I)][a]
wR2 (all data)[a]
0.0684
0.2078
0.1872
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|; wR2 = {Σ[w(Fo – Fc ) ]/Σ[w(Fo4)]}1/2
.
2
2 2
Acknowledgments
Acknowledgment is made to the donors of the American Chemical
Society Petroleum Research Fund for support of this research
(ACS-PRF 51677-UR4). We also wish to thank Professor Lisa F.
Szczepura from the Illinois State University for her assistance with
analyzing the X-ray crystallographic results.
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Received: June 30, 2015
Published Online: August 11, 2015
6046
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