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On the Reactivity of N-tert-Butyl-1,2-Diaminoethane: Synthesis of 1-tert-Butyl-2-Imidazoline, Formation of an Intramolecular Carbamate Salt from the Reaction with , and Generation of a Hydroxyalkyl-Substituted Imidazolinium Salt

On the Reactivity of N-tert-Butyl-1,2-Diaminoethane: Synthesis of 1-tert-Butyl-2-Imidazoline,... Hindawi Heteroatom Chemistry Volume 2019, Article ID 1094173, 6 pages https://doi.org/10.1155/2019/1094173 Research Article On the Reactivity of N-tert-Butyl-1,2-Diaminoethane: Synthesis of 1-tert-Butyl-2-Imidazoline, Formation of an Intramolecular Carbamate Salt from the Reaction with CO , and Generation of a Hydroxyalkyl-Substituted Imidazolinium Salt Kieren J. Evans , Ben Potrykus, and Stephen M. Mansell Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK Correspondence should be addressed to Stephen M. Mansell; s.mansell@hw.ac.uk Received 9 October 2018; Accepted 14 January 2019; Published 5 February 2019 Academic Editor: Oscar Navarro Copyright © 2019 Kieren J. Evans et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. N-tert-Butyl-1,2-diaminoethane was shown to react rapidly with atmospheric carbon dioxide to generate the zwitterionic ammonium carbamate salt CO N(H)C H N(H) Bu (1). Reaction of N-tert-butyl-1,2-diaminoethane with triethylorthoformate 2 2 4 2 gave 1-tert-butyl-2-imidazoline (2) in 24% yield aeft r fractional distillation, and the hydroxyalkyl-tethered imidazolinium salt [HOC(Me) CH NC H N(CH) Bu][Cl] (3) was synthesised from the sequential reaction of N-tert-butyl-1,2-diaminoethane with 2 2 2 4 isobutylene epoxide, HCl, and triethylorthoformate. 1. Introduction N-substituted-1,2-diaminoethanes to form u fl orenyl tethered diamines [21], which then acted as useful precursors to a 1,2-Diamines, exemplified by ethylenediamine and its deriva- tethered N-heterocyclic stannylene (NHSn) with a Dipp sub- tives, are produced on a large scale and are used for many stituent [21]. During this research we noted the reactivity of purposes including coordination chemistry [1] and CO 2 N-tert-butyl-1,2-diaminoethane [22] with air, which encour- capture [2–6]. Chiral diamines are also well known and have aged us to explore the reactivity of this diamine further. been utilised in the production of various chiral catalysts In this publication, we characterise the reaction product [7–9]. N-substituted ethylenediamines can also function as of N-tert-butyl-1,2-diaminoethane with carbon dioxide, the precursors to 1-substituted-2-imidazolines (dihydroimida- synthesis of 1-tert-butyl-2-imidazoline, and the formation zoles) [10, 11], with the synthesis of unsymmetrical saturated of a hydroxyalkyl imidazolinium salt with an N-tert-butyl N-heterocyclic carbenes (NHCs) one potential application substituent. for these compounds [12, 13]. Examples of 2-imidazolines that are widely used in the synthesis of unsymmetrical saturated NHCs include those with mesityl (2,4,6-Me C H ) 3 6 2 2. Results and Discussion and 2,6-diisopropylphenyl (Dipp: 2,6- Pr C H ) substituents 2 6 3 [12, 13]. 1-Ethyl-2-imidazoline and 1-benzyl-2-imidazoline are N-tert-Butyl-1,2-diaminoethane was synthesised as previ- known compounds [14], but the tert-butyl derivative, to the ously described [21, 22]; however, we noticed that it rapidly best of our knowledge, has not been reported. If the N- reacts with atmospheric CO forming a zwitterionic alky- 3 position is subsequently substituted with a hydrocarbon lammonium carbamate (1, Scheme 1). This was confirmed linker terminating with a donor atom, then these compounds by X-ray crystallographic analysis of a single crystal formed represent useful precursors to tethered saturated NHCs by the reaction of the parent diamine and showed the [15], which have been extensively explored by Arnold and structure to be an intramolecular alkylammonium carbamate coworkers [16–20]. We have recently reported on the use of salt resulting from nucleophilic attack of CO followed by 2 2 Heteroatom Chemistry NH ( . atmospheric #/ HC(OEt) ( . N N HN p-TsOH 2, 26% O neat 60 C, 16 h Cl OH OH Cl H HCl, %N O HC(OEt) HO HN HN N N NH ∘ ∘ .( 0 C to 20 C, toluene 1 hr 3, 12% Scheme 1: Reactions of N- tert-butyl-1,2-diaminoethane. the formal deprotonation of the NH by the N(H) Bu unit a substituted imidazolinium salt was attempted based on (Figure 1). literature precedent (Scheme 1) [16]. In consecutive steps, The solid-state structure of 1 shows dimeric units formed isobutylene epoxide, HCl, and triethylorthoformate were from H-bonding between the two H atoms of the two differ- reacted with N-tert-butyl-1,2-diaminoethane to yield an oil that was puriefi d by crystallisation from acetone in low ent N atoms towards O2 of the carbamate group. An𝑅 (8) yield (12%). Unfortunately, changing the anion to [I] or graph set ring motif is constructed from H-bonding between [BF ] did not aid crystallisation and did not result in an the remaining O atom of the carbamate group and the second improved synthesis. The product was characterised by X-ray H atom on N2. The C-O bond lengths are almost identical crystallography (Figure 2), multinuclear NMR spectroscopy, and C1 has a planar geometry. The molecular structure is and elemental analysis. The molecular structure of 3 similar to that observed for MeN(H) C H N(H)CO ,which 2 2 4 2 showed a 5-membered imidazolinium ring with a tert-butyl was observed to be H-bonding to additional water molecules substituent and a hydroxyalkyl chain. The Cl counter anion [5]. Long and coworkers have structurally characterised is H-bonded to the imidazolinium C-H as well as the O-H, several intramolecular ammonium carbamates based on N- and there are several close contacts to other C-H atoms as substituted ethylene diamines from in situ reactions of CO well. The C-N bond lengths in the ring are similar (C1-N1 with a Mg-based metal-organic framework containing the ˚ ˚ = 1.311(3) A and C1-N2 = 1.323(3) A) and C2-C3 is a single bound diamine [6]. The synthesis of 1- tert-butyl-2-imidazoline (2)was bond (1.530(4) A). H NMR spectroscopic analysis revealed achieved by the acid-catalysed reaction of the diamine the expected signals based on the X-ray structure, with with triethylorthoformate (Scheme 1). Careful fractional the imidazolinium CH as a singlet at 9.54 ppm. The C-2 13 1 distillation yielded the product in low yield (24%). The H resonance was observed at𝛿 158.0 ppm by C{ } NMR atom at the 2-position was observed at𝛿 7.03 ppm by H spectroscopy. NMR spectroscopy as a triplet due to 𝐽 coupling to one H-H of the backbone CH groups via coupling through the C=N 13 1 bond. The C{ H} NMR spectroscopic resonance for C-2 3. Conclusions was also observed at high frequency (154.6 ppm). Accurate mass spectrometry observed the parent molecular ion at N-tert-Butyl-1,2-diaminoethane was found to be a conve- 126.11510 Da. 2 reacts with moisture in the air so should nient starting material for the synthesis of 1-tert-butyl-2- be stored and handled under N . The attempted reaction imidazoline (2) aswell asthe hydroxyalkyl-tethered imi- with isobutylene epoxide (70 C, 5 days) did not yield the dazolinium salt 3.However,N-tert-butyl-1,2-diaminoethane desired hydroalkyl-functionalised carbene (or the related was found to react with atmospheric CO to give the zwitterionic alkoxy-imidazolinium tautomer that was seen alkylammonium carbamate 1,and 1-tert-butyl-2-imidazoline with imidazoles) [23–27], so a different synthetic route to was also found to be unstable in the presence of atmospheric Heteroatom Chemistry 3 H2B O1 O2 C5 H2B N1 C2 C3 C6 N2 C4 H2B O1 N2 O2 H1 H2A N1 H2A H1 H2A O2 O1 H1 C7 H2B C1 O1 N1 H2B O2 O1 O2 Figure 1: Molecular structure of BuN(H) C H N(H)CO (1, left) forming dimeric units and an extended structure through H-bonding 2 2 4 2 (right). eTh rmal ellipsoids set at 50% probability. Hydrogen atoms except for those attached to N atoms are omitted for clarity. Selected bond lengths (A) and angles ( ): O1-C1 1.267(1), O2-C1 1.277(1), N1-C1 1.400(1), N1-C2 1.464(1), O1-C1 O2 123.98(8), C1-N1-C2 120.32(7). H5 O1 H2A H3B C3 C2 H3A C7 H2B C5 C10 C6 N1 N2 C8 C1 C11 C4 H1 C9 Cl1 Figure 2: Molecular structure of 3. erm Th al ellipsoids set at 50% probability. Hydrogen atoms except for those attached to C1 – C3 and O1 are omitted for clarity. Selected bond lengths (A) and angles ( ): C1-N1 1.311(3), N2-C1 1.323(3), C2-C3 1.530(4), N1-C1-N2 114.1(2). moisture, highlighting the greater reactivity of these com- described [21]. NMR spectra were recorded on Bruker AV300 pounds compared to related literature examples with N-aryl or AVIII400 spectrometers at 25 C, and the chemical shifts 𝛿 groups. are noted in parts per million (ppm) calibrated to the residual proton resonances of the deuterated solvent (CDCl 𝛿 =7.27 ppm). X-ray diffraction experiments were performed using a Bruker X8 APEXII diffractometer at 100 K on single crystals 4. Experimental of the samples covered in inert oil and placed under the cold All reactions were performed under an oxygen-free (H O, stream of the diffractometer, with exposures collected using O < 0.5 ppm) nitrogen atmosphere using standard Schlenk Mo K𝛼 radiation (𝜆 = 0.71073 A). Indexing, data collection, line techniques or by using an MBRAUN UNIlab Plus and absorption corrections were performed and structures glovebox unless otherwise stated. Anhydrous toluene was were solved using direct methods (SHELXT) [28] and refined obtained from an MBRAUN SPS-800 and diethyl ether was by full-matrix least-squares (SHELXL) [28] interfaced with distilled from sodium/benzophenone; CDCl was dried over the programme OLEX2 [29] (Table 1). H atoms were placed molecular sieves (4 A). All anhydrous solvents were degassed using a riding model except for those attached to N or O before use and stored over activated molecular sieves. N- atoms, which were located in the electron density map and tert-Butyl-1,2-diaminoethane was synthesised as previously freely refined with a fixed isotropic parameter of 1.2x that of 4 Heteroatom Chemistry Table 1: Crystallographic data for 1 and 3. Empirical formula C H N O C H ClN O 7 16 2 2 11 23 2 Formula weight 160.22 234.76 T/K 100 100 Crystal system monoclinic tetragonal Space group P2 /n I-4 a/A 8.3778(12) 14.6891(14) b/A 9.2202(12) 14.6891(14) c/A 11.8067(18) 13.2031(14) 𝛼 / 90 90 𝛽 / 104.385(8) 90 𝛾 / 90 90 Volume/A 883.4(2) 2848.8(6) Z4 8 𝜌 g/cm 1.205 1.095 calc −1 𝜇 /mm 0.088 0.250 F(000) 352.0 1024.0 Crystal size/mm 0.65× 0.6× 0.15 0.3× 0.2× 0.2 Radiation MoK𝛼 (𝜆 =0.71073) MoK𝛼 (𝜆 =0.71073) 2Θ range for data collection/ 5.386 to 60.266 5.546 to 56.668 Index ranges -11≤ h≤ 11, -13≤ k≤ 12, -16≤ l≤ 16 -16≤ h≤ 19, -19≤ k≤ 19, -17≤ l≤ 16 Reflections collected 18629 8173 Independent reflections 2583 [R =0.0278,R =0.0208]3525[R =0.0337,R =0.0481] int sigma int sigma Data/restraints/parameters 2583/0/112 3525/0/144 Goodness-of-tfi on F 1.049 1.030 Final R indexes [I>=2𝜎 (I)] R =0.0351, wR =0.0891 R =0.0382, wR =0.0840 1 2 1 2 Final R indexes [all data] R =0.0426, wR =0.0935 R = 0.0454, wR = 0.0880 1 2 1 2 −3 Largest diff. peak/hole (e A ) 0.40/-0.20 0.45/-0.21 Flack parameter N/A 0.48(3) the atom they are attached to. CCDC deposition numbers mixture extracted with CHCl (3 x 50 cm ). The organic were 1871407 (1)and 1871406 (3). Elemental analyses were layer was dried over MgSO and CHCl and EtOH were 4 3 conducted using an Exeter CE-440 elemental analyser at removed under reduced pressure. A short path distillation Heriot-Watt University by Dr. Koenraad Collart or by Mr. apparatus was used to fractionally distil the resulting liquid. Stephen Boyer at London Metropolitan University. Electron Triethylorthoformate distilled at 50 C, 20 mbar (diaphragm ionization mass spectrometry (EIMS) was performed using a pump) as the first fraction then 1- tert-butyl-2-imidazoline at ∘ −1 Finnigan (Thermo) LCQ Classic ion trap mass spectrometer 26 – 30 Cat5 x10 mbar (rotary vane pump) as the second at the University of Edinburgh. fraction yielding a moisture sensitive colourless liquid (960 1 ∘ mg, 7.6 mmol, 26%). H NMR (300 MHz, 25 C, CDCl ): 4 3 𝛿 (ppm) 7.00 (t, 𝐽 = 1.8 Hz, 1H, CH), 3.75 (td, 𝐽 4.1. Synthesis of 1. Freshly distilled N-tert-butyl-1,2-diami- H-H H-H 4 3 =9.9 Hz, 𝐽 =1.8 Hz,2H, CH N=CH), 3.23 (t, 𝐽 noethane was exposed to air and a white solid formed rapidly. H-H 2 H-H 𝑡 𝑡 13 1 1 ∘ =9.9 Hz,2H, CH N Bu), 1.23 (s, 9H, Bu). C{ H} NMR H NMR (300 MHz, 25 C, D O):𝛿 (ppm) 3.28 (2H, m, CH ), 2 2 𝑡 13 1 (75.5 MHz, 25 C, CDCl ):𝛿 (ppm) 154.57 (CH), 54.41 (CH ), 3.08 (m, 2H, CH ), 1.31 (s, 9H, Bu). C{ } NMR (75.5 H 3 2 51.91 (CMe ), 44.32 (CH ), 28.47 (CH ). HRMS (EI-MS) m/z: MHz, 25 C, D O):𝛿 (ppm) 164.86 (NCO ), 56.53 (CH ), 43.07 3 2 3 2 2 2 [M] Calcd for C H N 126.11515; Found 126.11510. (CH ), 38.46 (CMe )and 24.83(CH ). 7 14 2 2 3 3 4.2. Synthesis of 1-tert-butyl-2-Imidazoline (2). N-tert-Butyl- 4.3. Synthesis of 3. N-tert-Butyl-1,2-diaminoethane (2.018 g, 1,2-diaminoethane (3.439 g, 29.6 mmol, 1 equiv.) was com- 17.4 mmol, 1 equiv.) was combined with isobutylene oxide (1.252g, 1.54 mL, 17.4 mmol, 1 equiv.) in an ampoule equipped bined with triethylorthoformate (19.7 cm , 118.4 mmol, 4 with a Young’s tap and heated to 60 Cfor 16 h. DryEt O equiv.) and para-toluenesulfonic acid (281 mg, 1.48 mmol, 0.05 equiv.) and then heated under reflux for 16 h. NaOH (30 cm ) was then added to the resultant colourless oil and (10 cm of a 5% solution in H O) was added and the the solution transferred to a Schlenk vessel equipped with 2 Heteroatom Chemistry 5 a large stirrer bar. 1 M HCl in Et O(17.2 cm ,1 equiv.) was [2] C. Gouedard, D. Picq, F. Launay, and P. L. Carrette, “Amine degradation in CO capture. I. A review,” International Journal added at 0 C forming a white solid which was then stirred of Greenhouse Gas Control,vol.10, pp.244–270, 2012. for 16 h at room temperature. The supernatant solution was [3] F. Zheng, D. N. Tran,B.J. Busche etal., “Ethylenediamine- removed by cannula filtration and the white solid dried under 3 3 modified SBA-15 as regenerable CO sorbent,” Industrial & vacuum. Toluene (30 cm ) and triethylorthoformate (10 cm ) 2 Engineering Chemistry Research, vol.44,no. 9,pp.3099–3105, were added and the mixture was heated to 90 Cfor 7h.Et O (50cm ) was added which caused a yellow oil to separate and [4] A. Demessence, D. M. DAlessandro, M. L. Foo, and J. R. Long, the supernatant solution was removed by cannula. Acetone 3 ∘ “Strong CO Binding in a Water-Stable, Triazolate-Bridged (ca. 10 cm ) was addedto dissolve the oil, andstorage at -25 C Metal−Organic Framework Functionalized with Ethylenedi- gave colourless crystals of the product (488 mg, 2.08 mmol, amine,” Journal of the American Chemical Society,vol. 131,pp. 12%). 8784–8786, 2009. 1 ∘ H NMR (400 MHz, 25 C, CDCl ): 𝛿 (ppm) 9.54 (s, [5] I. Tiritiris and W. 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On the Reactivity of N-tert-Butyl-1,2-Diaminoethane: Synthesis of 1-tert-Butyl-2-Imidazoline, Formation of an Intramolecular Carbamate Salt from the Reaction with , and Generation of a Hydroxyalkyl-Substituted Imidazolinium Salt

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Hindawi Publishing Corporation
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Copyright © 2019 Kieren J. Evans et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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10.1155/2019/1094173
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Hindawi Heteroatom Chemistry Volume 2019, Article ID 1094173, 6 pages https://doi.org/10.1155/2019/1094173 Research Article On the Reactivity of N-tert-Butyl-1,2-Diaminoethane: Synthesis of 1-tert-Butyl-2-Imidazoline, Formation of an Intramolecular Carbamate Salt from the Reaction with CO , and Generation of a Hydroxyalkyl-Substituted Imidazolinium Salt Kieren J. Evans , Ben Potrykus, and Stephen M. Mansell Institute of Chemical Sciences, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK Correspondence should be addressed to Stephen M. Mansell; s.mansell@hw.ac.uk Received 9 October 2018; Accepted 14 January 2019; Published 5 February 2019 Academic Editor: Oscar Navarro Copyright © 2019 Kieren J. Evans et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. N-tert-Butyl-1,2-diaminoethane was shown to react rapidly with atmospheric carbon dioxide to generate the zwitterionic ammonium carbamate salt CO N(H)C H N(H) Bu (1). Reaction of N-tert-butyl-1,2-diaminoethane with triethylorthoformate 2 2 4 2 gave 1-tert-butyl-2-imidazoline (2) in 24% yield aeft r fractional distillation, and the hydroxyalkyl-tethered imidazolinium salt [HOC(Me) CH NC H N(CH) Bu][Cl] (3) was synthesised from the sequential reaction of N-tert-butyl-1,2-diaminoethane with 2 2 2 4 isobutylene epoxide, HCl, and triethylorthoformate. 1. Introduction N-substituted-1,2-diaminoethanes to form u fl orenyl tethered diamines [21], which then acted as useful precursors to a 1,2-Diamines, exemplified by ethylenediamine and its deriva- tethered N-heterocyclic stannylene (NHSn) with a Dipp sub- tives, are produced on a large scale and are used for many stituent [21]. During this research we noted the reactivity of purposes including coordination chemistry [1] and CO 2 N-tert-butyl-1,2-diaminoethane [22] with air, which encour- capture [2–6]. Chiral diamines are also well known and have aged us to explore the reactivity of this diamine further. been utilised in the production of various chiral catalysts In this publication, we characterise the reaction product [7–9]. N-substituted ethylenediamines can also function as of N-tert-butyl-1,2-diaminoethane with carbon dioxide, the precursors to 1-substituted-2-imidazolines (dihydroimida- synthesis of 1-tert-butyl-2-imidazoline, and the formation zoles) [10, 11], with the synthesis of unsymmetrical saturated of a hydroxyalkyl imidazolinium salt with an N-tert-butyl N-heterocyclic carbenes (NHCs) one potential application substituent. for these compounds [12, 13]. Examples of 2-imidazolines that are widely used in the synthesis of unsymmetrical saturated NHCs include those with mesityl (2,4,6-Me C H ) 3 6 2 2. Results and Discussion and 2,6-diisopropylphenyl (Dipp: 2,6- Pr C H ) substituents 2 6 3 [12, 13]. 1-Ethyl-2-imidazoline and 1-benzyl-2-imidazoline are N-tert-Butyl-1,2-diaminoethane was synthesised as previ- known compounds [14], but the tert-butyl derivative, to the ously described [21, 22]; however, we noticed that it rapidly best of our knowledge, has not been reported. If the N- reacts with atmospheric CO forming a zwitterionic alky- 3 position is subsequently substituted with a hydrocarbon lammonium carbamate (1, Scheme 1). This was confirmed linker terminating with a donor atom, then these compounds by X-ray crystallographic analysis of a single crystal formed represent useful precursors to tethered saturated NHCs by the reaction of the parent diamine and showed the [15], which have been extensively explored by Arnold and structure to be an intramolecular alkylammonium carbamate coworkers [16–20]. We have recently reported on the use of salt resulting from nucleophilic attack of CO followed by 2 2 Heteroatom Chemistry NH ( . atmospheric #/ HC(OEt) ( . N N HN p-TsOH 2, 26% O neat 60 C, 16 h Cl OH OH Cl H HCl, %N O HC(OEt) HO HN HN N N NH ∘ ∘ .( 0 C to 20 C, toluene 1 hr 3, 12% Scheme 1: Reactions of N- tert-butyl-1,2-diaminoethane. the formal deprotonation of the NH by the N(H) Bu unit a substituted imidazolinium salt was attempted based on (Figure 1). literature precedent (Scheme 1) [16]. In consecutive steps, The solid-state structure of 1 shows dimeric units formed isobutylene epoxide, HCl, and triethylorthoformate were from H-bonding between the two H atoms of the two differ- reacted with N-tert-butyl-1,2-diaminoethane to yield an oil that was puriefi d by crystallisation from acetone in low ent N atoms towards O2 of the carbamate group. An𝑅 (8) yield (12%). Unfortunately, changing the anion to [I] or graph set ring motif is constructed from H-bonding between [BF ] did not aid crystallisation and did not result in an the remaining O atom of the carbamate group and the second improved synthesis. The product was characterised by X-ray H atom on N2. The C-O bond lengths are almost identical crystallography (Figure 2), multinuclear NMR spectroscopy, and C1 has a planar geometry. The molecular structure is and elemental analysis. The molecular structure of 3 similar to that observed for MeN(H) C H N(H)CO ,which 2 2 4 2 showed a 5-membered imidazolinium ring with a tert-butyl was observed to be H-bonding to additional water molecules substituent and a hydroxyalkyl chain. The Cl counter anion [5]. Long and coworkers have structurally characterised is H-bonded to the imidazolinium C-H as well as the O-H, several intramolecular ammonium carbamates based on N- and there are several close contacts to other C-H atoms as substituted ethylene diamines from in situ reactions of CO well. The C-N bond lengths in the ring are similar (C1-N1 with a Mg-based metal-organic framework containing the ˚ ˚ = 1.311(3) A and C1-N2 = 1.323(3) A) and C2-C3 is a single bound diamine [6]. The synthesis of 1- tert-butyl-2-imidazoline (2)was bond (1.530(4) A). H NMR spectroscopic analysis revealed achieved by the acid-catalysed reaction of the diamine the expected signals based on the X-ray structure, with with triethylorthoformate (Scheme 1). Careful fractional the imidazolinium CH as a singlet at 9.54 ppm. The C-2 13 1 distillation yielded the product in low yield (24%). The H resonance was observed at𝛿 158.0 ppm by C{ } NMR atom at the 2-position was observed at𝛿 7.03 ppm by H spectroscopy. NMR spectroscopy as a triplet due to 𝐽 coupling to one H-H of the backbone CH groups via coupling through the C=N 13 1 bond. The C{ H} NMR spectroscopic resonance for C-2 3. Conclusions was also observed at high frequency (154.6 ppm). Accurate mass spectrometry observed the parent molecular ion at N-tert-Butyl-1,2-diaminoethane was found to be a conve- 126.11510 Da. 2 reacts with moisture in the air so should nient starting material for the synthesis of 1-tert-butyl-2- be stored and handled under N . The attempted reaction imidazoline (2) aswell asthe hydroxyalkyl-tethered imi- with isobutylene epoxide (70 C, 5 days) did not yield the dazolinium salt 3.However,N-tert-butyl-1,2-diaminoethane desired hydroalkyl-functionalised carbene (or the related was found to react with atmospheric CO to give the zwitterionic alkoxy-imidazolinium tautomer that was seen alkylammonium carbamate 1,and 1-tert-butyl-2-imidazoline with imidazoles) [23–27], so a different synthetic route to was also found to be unstable in the presence of atmospheric Heteroatom Chemistry 3 H2B O1 O2 C5 H2B N1 C2 C3 C6 N2 C4 H2B O1 N2 O2 H1 H2A N1 H2A H1 H2A O2 O1 H1 C7 H2B C1 O1 N1 H2B O2 O1 O2 Figure 1: Molecular structure of BuN(H) C H N(H)CO (1, left) forming dimeric units and an extended structure through H-bonding 2 2 4 2 (right). eTh rmal ellipsoids set at 50% probability. Hydrogen atoms except for those attached to N atoms are omitted for clarity. Selected bond lengths (A) and angles ( ): O1-C1 1.267(1), O2-C1 1.277(1), N1-C1 1.400(1), N1-C2 1.464(1), O1-C1 O2 123.98(8), C1-N1-C2 120.32(7). H5 O1 H2A H3B C3 C2 H3A C7 H2B C5 C10 C6 N1 N2 C8 C1 C11 C4 H1 C9 Cl1 Figure 2: Molecular structure of 3. erm Th al ellipsoids set at 50% probability. Hydrogen atoms except for those attached to C1 – C3 and O1 are omitted for clarity. Selected bond lengths (A) and angles ( ): C1-N1 1.311(3), N2-C1 1.323(3), C2-C3 1.530(4), N1-C1-N2 114.1(2). moisture, highlighting the greater reactivity of these com- described [21]. NMR spectra were recorded on Bruker AV300 pounds compared to related literature examples with N-aryl or AVIII400 spectrometers at 25 C, and the chemical shifts 𝛿 groups. are noted in parts per million (ppm) calibrated to the residual proton resonances of the deuterated solvent (CDCl 𝛿 =7.27 ppm). X-ray diffraction experiments were performed using a Bruker X8 APEXII diffractometer at 100 K on single crystals 4. Experimental of the samples covered in inert oil and placed under the cold All reactions were performed under an oxygen-free (H O, stream of the diffractometer, with exposures collected using O < 0.5 ppm) nitrogen atmosphere using standard Schlenk Mo K𝛼 radiation (𝜆 = 0.71073 A). Indexing, data collection, line techniques or by using an MBRAUN UNIlab Plus and absorption corrections were performed and structures glovebox unless otherwise stated. Anhydrous toluene was were solved using direct methods (SHELXT) [28] and refined obtained from an MBRAUN SPS-800 and diethyl ether was by full-matrix least-squares (SHELXL) [28] interfaced with distilled from sodium/benzophenone; CDCl was dried over the programme OLEX2 [29] (Table 1). H atoms were placed molecular sieves (4 A). All anhydrous solvents were degassed using a riding model except for those attached to N or O before use and stored over activated molecular sieves. N- atoms, which were located in the electron density map and tert-Butyl-1,2-diaminoethane was synthesised as previously freely refined with a fixed isotropic parameter of 1.2x that of 4 Heteroatom Chemistry Table 1: Crystallographic data for 1 and 3. Empirical formula C H N O C H ClN O 7 16 2 2 11 23 2 Formula weight 160.22 234.76 T/K 100 100 Crystal system monoclinic tetragonal Space group P2 /n I-4 a/A 8.3778(12) 14.6891(14) b/A 9.2202(12) 14.6891(14) c/A 11.8067(18) 13.2031(14) 𝛼 / 90 90 𝛽 / 104.385(8) 90 𝛾 / 90 90 Volume/A 883.4(2) 2848.8(6) Z4 8 𝜌 g/cm 1.205 1.095 calc −1 𝜇 /mm 0.088 0.250 F(000) 352.0 1024.0 Crystal size/mm 0.65× 0.6× 0.15 0.3× 0.2× 0.2 Radiation MoK𝛼 (𝜆 =0.71073) MoK𝛼 (𝜆 =0.71073) 2Θ range for data collection/ 5.386 to 60.266 5.546 to 56.668 Index ranges -11≤ h≤ 11, -13≤ k≤ 12, -16≤ l≤ 16 -16≤ h≤ 19, -19≤ k≤ 19, -17≤ l≤ 16 Reflections collected 18629 8173 Independent reflections 2583 [R =0.0278,R =0.0208]3525[R =0.0337,R =0.0481] int sigma int sigma Data/restraints/parameters 2583/0/112 3525/0/144 Goodness-of-tfi on F 1.049 1.030 Final R indexes [I>=2𝜎 (I)] R =0.0351, wR =0.0891 R =0.0382, wR =0.0840 1 2 1 2 Final R indexes [all data] R =0.0426, wR =0.0935 R = 0.0454, wR = 0.0880 1 2 1 2 −3 Largest diff. peak/hole (e A ) 0.40/-0.20 0.45/-0.21 Flack parameter N/A 0.48(3) the atom they are attached to. CCDC deposition numbers mixture extracted with CHCl (3 x 50 cm ). The organic were 1871407 (1)and 1871406 (3). Elemental analyses were layer was dried over MgSO and CHCl and EtOH were 4 3 conducted using an Exeter CE-440 elemental analyser at removed under reduced pressure. A short path distillation Heriot-Watt University by Dr. Koenraad Collart or by Mr. apparatus was used to fractionally distil the resulting liquid. Stephen Boyer at London Metropolitan University. Electron Triethylorthoformate distilled at 50 C, 20 mbar (diaphragm ionization mass spectrometry (EIMS) was performed using a pump) as the first fraction then 1- tert-butyl-2-imidazoline at ∘ −1 Finnigan (Thermo) LCQ Classic ion trap mass spectrometer 26 – 30 Cat5 x10 mbar (rotary vane pump) as the second at the University of Edinburgh. fraction yielding a moisture sensitive colourless liquid (960 1 ∘ mg, 7.6 mmol, 26%). H NMR (300 MHz, 25 C, CDCl ): 4 3 𝛿 (ppm) 7.00 (t, 𝐽 = 1.8 Hz, 1H, CH), 3.75 (td, 𝐽 4.1. Synthesis of 1. Freshly distilled N-tert-butyl-1,2-diami- H-H H-H 4 3 =9.9 Hz, 𝐽 =1.8 Hz,2H, CH N=CH), 3.23 (t, 𝐽 noethane was exposed to air and a white solid formed rapidly. H-H 2 H-H 𝑡 𝑡 13 1 1 ∘ =9.9 Hz,2H, CH N Bu), 1.23 (s, 9H, Bu). C{ H} NMR H NMR (300 MHz, 25 C, D O):𝛿 (ppm) 3.28 (2H, m, CH ), 2 2 𝑡 13 1 (75.5 MHz, 25 C, CDCl ):𝛿 (ppm) 154.57 (CH), 54.41 (CH ), 3.08 (m, 2H, CH ), 1.31 (s, 9H, Bu). C{ } NMR (75.5 H 3 2 51.91 (CMe ), 44.32 (CH ), 28.47 (CH ). HRMS (EI-MS) m/z: MHz, 25 C, D O):𝛿 (ppm) 164.86 (NCO ), 56.53 (CH ), 43.07 3 2 3 2 2 2 [M] Calcd for C H N 126.11515; Found 126.11510. (CH ), 38.46 (CMe )and 24.83(CH ). 7 14 2 2 3 3 4.2. Synthesis of 1-tert-butyl-2-Imidazoline (2). N-tert-Butyl- 4.3. Synthesis of 3. 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