Introducing Stereogenic Centers to Group XIV Metallatranes

Article pubs.acs.org/IC

Introducing Stereogenic Centers to Group XIV Metallatranes Britta Glowacki, Michael Lutter, Hazem Alnasr, Rana Seymen, Wolf Hiller, and Klaus Jurkschat* Fakultät für Chemie und Chemische Biologie, Technische Universität Dortmund, 44221 Dortmund, Germany S Supporting Information *

ABSTRACT: The syntheses of the novel amino alcohols NH(CH2CMe2OH)2(CMe2CH2OH) (1) and N(CH2CMe2OH)(CMe2CH2OH)(CH2CH2OH) (2) as well as the stannatranes N(CH 2 CMe 2 O)(CMe 2 CH 2 O)(CH2CH2O)SnX (3, X = Ot-Bu), N(CH2CMe2O)3SnOC(O)C 9 H 13 O 2 , 4, and germatranes N(CH 2 CMe 2 O)(CMe2CH2O)(CH2CH2O)GeX (5, X = OEt; 6, X = Br) are reported. The compounds were characterized by 1H, 13C (1− 6), 119Sn (3, 4), and 15N (2, 3, 5) NMR and IR spectroscopy, electrospray ionization mass spectrometry, and single crystal X-ray diffraction analysis. Graphset analyses were performed for compounds 1 and 2. Detailed NMR spectroscopic studies including variable temperature 1H (3, 5, 6) and 119Sn (3, 4) DOSY experiments reveal the stannatrane 3 being involved in a monomer−dimer equilibrium. Both the stannatranes 3 and 4 as well as the germatranes 5 and 6 show Λ ⇌ Δ isomerization of the atrane cages in solution.

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INTRODUCTION In classical metallatranes,1 the group XIV metal or metalloid atom is usually pentacoordinated involving one nitrogen and three oxygen atoms of an amino alcohol and one additional substituent that might be organic such as alkyl or aryl moiety,2 or inorganic such as halide,3 a transition metal complex4 or alkoxide.3,5,6 Characteristic features of metallatranes are (i) an intramolecular N→M (M = metal, metalloid) coordination and (ii) cage structures showing right- or left-handed (Δ and Λ) propeller-type stereochemistry.3 Metallatranes can be divided in two classes, (i) the organo metallatranes containing carbon− metal bonds2 and (ii) inorganic metallatranes without any carbon−metal bond.3−6 Recently we reported inorganic stannatranes and studied in more detail their structures, reactivity, and partial hydrolysis.3,5a,6 The structures of the stannatranes depend on the steric hindrance of the amino alcohol ligand. The compounds are either monomeric, as for example, N(CH2CMe2O)3SnOt-Bu, N(CH2CMe2O)3SnX (X = halide, carboxylate, alkoxide, thiolate), N(CH2CMe2O)2(CH2CH2O)SnOt-Bu, and N(CH2CMe2O)2(CMe2CH2O)SnOt-Bu,3,5a or dimeric, as for instance, [N(CH2CMe2O)2(CH 2 CH 2 CH 2 O)SnOt-Bu] 2 and [N(CH 2 CMe 2 O) 2 (CH2CH2O)SnO-2,6-Me2C6H3]2.3,5a,6 The amino alcoholate moieties in these compounds have three or at least two identical side chains. In continuation of our systematic studies on inorganic metallatranes lacking any metal−carbon bonds, we herein report the synthesis of a novel amino alcohol containing three different side chains. In combination with the remaining alkoxide substituent at the central tin respectively germanium atom, the latter are coordinated by five different substituents and become stereogenic centers. © 2017 American Chemical Society

EXPERIMENTAL SECTION

General Aspects. All solvents, including deuterated solvents for NMR experiments, were dried and purified by standard procedures. All reactions were carried out under an atmosphere of dry argon using Schlenk techniques. Bruker Avance III HD 400 MHz, Bruker Avance III HD 500 MHz, (with Prodigy-probehead), Bruker Avance III HD 600 MHz, (with Cryo-probehead) and Agilent DD2 500 MHz spectrometers were used to obtain 1H, 13C NMR, and the 119Sn-NMR spectra as well as the two-dimensional (2D) spectra. 1H, 13C, 15N, and 119 Sn-NMR chemical shifts are given in ppm and were referenced to SiMe4 (1H, 13C) and SnMe4 (119Sn). The 1H−15N HMBC NMR measurements were referenced to a NH3 (15N) standard. The spectra recorded in CD2Cl2 were referenced to dichoromethane (Bruker Standard: 1H, 5.246 ppm; 13C, 53.4794 ppm). Melting points are uncorrected and were measured on a Büchi MP560 device. The electrospray ionization mass spectra were recorded on a Thermoquest-Finnigan instrument using MeOH, CH2Cl2, or MeCN as the mobile phase. The samples were introduced as solution via a syringe pump operating at a rate of 0.5 μL/min. The capillary voltage was 4.5 kV, while the cone skimmer voltage varied between 50 and 250 kV. Identification of the expected ions was assisted by comparison of experimental and calculated isotope distribution patterns. The m/z values reported correspond to those of the most intense peak in the corresponding isotope pattern. For the high resolution mass measurement a LTQ Orbitrap (Fourier transformation mass spectrometer) coupled to an Accela HPLC-System (consisting of Accela pump, Accela autosampler and Accela PDA detector) from Thermo Electron was used. The eluents were A (0.1% formic acid)/eluent B (0.1% formic acid in acetonitrile). Isocratic 50% A: 50%B. The samples were dissolved in MeCN and introduced via a syringe pump (injection volume 5 μL). The flow rate Received: December 22, 2016 Published: April 10, 2017 4937

DOI: 10.1021/acs.inorgchem.6b03126 Inorg. Chem. 2017, 56, 4937−4949

Article

Inorganic Chemistry was 250 μL/min, and the scan of wavelength range from 200 to 600 nm. Electrospray ionization was operating with a source voltage of 3.8 kV, a capillary voltage of 41 V, a capillary temperature of 275 °C, and a tube lens voltage of 140 V. The scanned mass range was m/z 150 to m/z 2000, and the resolution was set to resolution set to 60 000. Elemental analyses were performed on a LECO−CHNS-932 analyzer under noninert conditions. The infrared spectra were recorded with a PerkinElmer Two (ATR) spectrometer under noninert conditions. Synthesis of 2-[(2-Hydroxy-2-methylpropyl)amino]-2-methylpropan-1-ol, (HN(CH2CMe2OH)(CMe2CH2OH) (1). A mixture of 2-amino2-methylpropan-1-ol (4.02 g, 45.05 mmol) and isobutylenoxide (19.84 g, 270 mmol, 6 equiv) was stirred in a Teflon-sealed glass vessel and heated at 120 °C for 10 days. The volatiles were removed under reduced pressure, and the residue was distilled in vacuo (10−3 mbar, 120 °C). Compound 1 was obtained as colorless oil (7.06 g, 43.81 mmol, 97%) that crystallized upon standing. Single crystals (mp. 45.5 °C) were obtained from isohexane solution. 1 H NMR (500.13 MHz, CDCl3, 27 °C): δ 3.34 (s, 2H, CH2OH), 2.45 (s, 2H, NHCH2), 1.20 (s, 6H, C(CH3)2)OH), 1.06 (s, 6H, NHC(CH3)2). The NH and OH proton resonances were not identified, very likely because of exchange. 13 C{1H} NMR (125.77 MHz, CDCl3, 27 °C): δ 69.4 (s, C(CH3)2)OH), 68.8 (s, CH2OH) 53.3 (s, NHC(CH3)2), 52.3 (s, NHCH2), 27.5 (s, C(CH3)2)OH), 25.2 (NHC(CH3)2). IR spectroscopy (cm−1): 3340 (νOH), 3094 (νNH). Anal. Calcd for C8H19NO2 (161.24 g/mol) C 59.6, H 11.9, N 8.7. Found: C 59.7, H 11.8, N 8.6. MS (ESI+): m/z = 162.1 [1 + H]+. Synthesis of 2-[(2-Hydroxy-2-methylpropyl)(2-hydroxyethyl)amino]-2-methylpropan-1-ol, (N(CH 2 CMe 2 OH)(CMe 2 CH 2 OH)(CH2CH2OH) (2). To a stirred solution of 1 (5.44 g, 33.70 mmol) in deionized water (100 mL) ethylene oxide (18.2 g, 413.17 mmol, 11 equiv) was passed over 24 h, while the reaction mixture was heated at 70 °C. The volatiles were removed under reduced pressure, and the residue was distilled in vacuo (10−3 mbar, 130−140 °C). Compound 2 (6.63 g, 32.27 mmol, 96%) was obtained as a colorless microcrystalline solid. Single crystals (mp. 85−86 °C) were obtained from a saturated toluene solution. 1 H NMR (500.08 MHz, C6D6, 23 °C): δ 4.02 (s br., 3H, OH), 3.49 (t, 3J(1H−1H) = 5.49 Hz, 2H, CH2CH2OH), 3.20 (s, 2H, CH2OH), 2.62 (t, 3J(1H−1H) = 5.49 Hz, 2H, CH2CH2OH), 2.28 (s, 2H, NHCH2), 1.20 (s, 6H, C(CH3)2)OH), 0.81 (s, 6H, NHC(CH3)2). 13 C{ 1H} NMR (125.77 MHz, C6D6 , 23 °C): δ 78.3 (s, NHC(CH3)2), 70.8 (s, C(CH3)2)OH), 69.8 (s, CH2OH), 63.5 (s, CH2CH2OH), 62.3 (s, NHCH2), 54.5 (s, CH2CH2OH), 29.2 (s, C(CH3)2)OH), 22.05 (s, NHC(CH3)2). 1 H−15N HMBC NMR (600.20, 60.83 MHz, C6D6, 25 °C): δ (15N) 38. IR spectroscopy (cm−1): 3247 (νOH). MS (ESI+): m/z = 206.2 [2 + H]+. HRMS (ESI+): m/z = 206.17507 [2 + H]+, 228.15701 [2 + Na]+, found: 206.17517 [2+ H]+, 228.15712 [2 + Na]+. Synthesis of 1-tert-Butoxido-(2,8,9-trioxa-5-aza-3,3,6,6-tetramethyl-1-stannatricyclo[3.3.3.01,5]undecane) 3. Within 10 min at room temperature, a solution of 2 (2.50 g, 12.18 mmol) in dry toluene (30 mL) was added to a stirred solution of tin(IV)-tert-butoxide (5.02 g, 12.20 mmol) in dry toluene (50 mL). The t-butanol formed in the course of the reaction was removed by azeotropic distillation, and the remaining volatiles were removed under reduced pressure. Compound 3, as its toluene solvate 3·0.5C7H8 (here, 3 is seen as the monomer; 4.05 g, 4.60 mmol, 76%), was obtained as a colorless solid. Single crystals (mp. 82 °C) were obtained from its toluene solution at 4 °C. 1 H NMR (400.25 MHz, CD2Cl2, 25 °C δ 7.18−7.06 (m, 2.5 H, CHarom), 3.87 and 3.77 (m, 2H, NCH2CH2O), 3.52 (AB, 2J(1H−1H) = 12.7 Hz, 2H, CH2O), 3.09 and 3.67 (m, 2H, NCH2CH2O), 2.68 and 2.40 (AX, 2J(1H−1H) = 14.2 Hz, 2H, NCH2), 2.26 (s, 1.5 H, CH3, toluene), 1.22 (s, 9H, OC(CH3)3), 1.22 and 1.18 (s, J(1H-117/119Sn = 7.8 Hz, 3H each, C(CH3)2)O), 1.15 and 1.12 (s, 3H each, NC(CH3)2).

C{1H} NMR (100.64 MHz, CD2Cl2, 25 °C): δ 137.9 (s, Ci), 129.0 (s, CH o ), 128.2 (s, CH m ), 125.3 (s, CH p ), 71.8(s, J(13C-117/119Sn) = 38.7 Hz, OC(CH3)3), 69.0 (s, J(13C-117/119Sn) = 17.1 Hz, CH2O), 68.1 (s, J(13C-117/119Sn) = 18.0 Hz, C(CH3)2)O), 62.7 (s, J( 13 C- 117/119 Sn) = 55.0 Hz, NC(CH 3 ) 2 ), 59.4 (s, J(13C-117/119Sn) = 44.2 Hz, NCH2), 58.9(s, J(13C-117/119Sn) = 13.0 Hz, NCH2CH2O), 51.3 (s, J(13C-117/119Sn) = 65.8 Hz, NCH2CH2O), 32.9 (s, J(13C-117/119Sn) = 27.0 Hz, OC(CH3)3), 32.1 and 31.7(s, J(13C-117/119Sn) = 56.5 Hz, C(CH3)2)O), 21.9 and 21.3 (s, NC(CH3)2), 21.2 (s, CH3 toluene). 13 C{1H} NMR (100.64 MHz, CD2Cl2, −80 °C): δ 137.7 (s, Ci), 128.6 (s, CHo), 127.9 (s, CHm), 124.9 (s, CHp), 71.2 (s, J(13C-117/119Sn) = 37.7 Hz, OC(CH3)3), 70.3 (s, J(13C-117/119Sn) = 44.3 Hz, OC(CH3)3), 68.4 (s, CH2O), 67.8 and 67.6 (s, C(CH3)2)O), 63.3 (s, J(13C-117/119Sn) = 40.3 Hz, NC(CH3)2), 60.8 and 60.6 (s, NCH2), 59.0 (s, NCH2CH2O), 49.0 (s, NCH2CH2O), 33.3 (s, OC(CH3)3), 32.5, 32.4, and 32.3 (s, C(CH3)2)O), 31.0, 30.6, and 30.1 (s, NC(CH3)2), 21.1 (s, CH3 toluene). The assignment of the resonances was done analogously to the spectra at ambient temperatures. 1 H−15N HMBC NMR (600.20, 60.83 MHz, C6D6, 25 °C): δ (15N) 35 (referenced to NH3). 119 Sn{1H} NMR (149.26 MHz, CD2Cl2, 25 °C): δ −314 (s, ν1/2 1430 Hz). 119 Sn{1H} NMR (149.26 MHz, CD2Cl2, −80 °C): δ −303 (s), −309 (s), − 511 (s, br.), − 512 (s), − 522 (s, ν1/2 274 Hz). Anal. Calcd for C14H29NO4Sn·0.5C7H8 (3·0.5C7H8, 440.17 g/mol) C 47.8, H 7.6, N 3.18. Found: C 45.8, H 7.5, N 3.1, calculated for 3· 0.5C7H8 + 1H2O (3 is hygroscopic): C 45.9, H 7.7, N 3.1. MS (ESI+) in MeCN: m/z = 206.2 [2 + K]+. MS (ESI+) in DCM: m/z = 978.3 [((μ 3-O)(Ot-Bu){Sn(OCH2CH2) (OCH2CMe2) (OCMe2CH2) N}3] or [(μ3-O)(μ3-OtBu){Sn(OCH2CH2) (OCH2CMe2)(OCMe2CH2)N}3) − Ot-Bu]+ MS (ESI−) in DCM: m/z = 693.1 [dimer of 3 − 2Ot-Bu− + 3OH−]−. Synthesis of 1-(1R)-(+)-Camphanoate-(2,8,9-trioxa-5-aza3,3,7,7,10,10-tetramethyl-1-stannatricyclo[3.3.3.01,5]undecane) 4. 1-tert-Butoxido-(2,8,9-trioxa-5-aza-3,3,7,7,10,10-tetramethyl-1stannatricyclo[3.3.3.01,5] undecane) (1 g, 2.29 mmol) was stirred in dry toluene (15 mL) and (1R)-(+)-camphanic acid ((1R)-3-oxo-4,7,7trimethyl-2-oxabicyclo[2.2.1]heptane-1-carboxylic acid) (0.45 g, 2.29 mmol) was added slowly. The t-butanol formed in the course of the reaction was removed by azeotropic distillation, and the remaining volatiles were removed under reduced pressure. Compound 4, as its stoluene solvate 4·C7H8 (1.03 g, 1.61 mmol, 70%), was obtained as a colorless solid. Single crystals (mp. 211 °C) were obtained from its toluene solution at −20 °C. 1 H NMR (400.25 MHz, CD2Cl2, 25 °C): δ 7.15 and 7.08 (m, 5H, CHarom), 2.88 and 2.87 (s, 6H, NCH2), 2.39 (m, 1H, CH2), 2.27 (s, 3H, CH3 toluene) 1.97 (m, 1H, CH2), 1.87 (m, 1H, CH2), 1.58 (m, 1H, CH2), 1.24 and 1.23 (s, 18H, CCH3), 1.01 (s, 3H, CH3), 1.00 (s, 1H, CH3), 0.90 (s, 1H, CH3). 13 C{1H} NMR (100.64 MHz, CD2Cl2, 25 °C): δ 178.3 (s, Cquarternary), 173.6(s, Cquarternary), 138.0 (s, Ci), 129.0 (s, CHo), 128.2 (s, CHm), 125.3 (s, CHp), 91.7 (s, 2C, CCH3), 70.5 and 70.1 (s, NCH2), 54.7 and 54.3 (s, C(CH3)3), 30.9 and 30.8 (s, J(13C-117/119Sn) = 16.3, 18.5 Hz, C(CH3)3), 29.3 (s, CH3), 21.2 (s, C6H5CH3), 16.6 (s, CH3), 16.5 (s, CH3), 9.6 (s, CH3). Not all resonances of the quaternary carbon atoms were found. 119 Sn{1H} NMR (149.26 MHz, CD2Cl2, 25 °C): δ −357 (s, ν1/2 = 43 Hz). 119 Sn{1H} NMR (149.26 MHz, CD2Cl2, 0 °C): δ −356 (s, ν1/2 = 108 Hz). 119 Sn{1H} NMR (149.26 MHz, CD2Cl2, −20 °C): δ −355 (s, ν1/2 = 507 Hz) 119 Sn{1H} NMR (149.26 MHz, CD2Cl2, −40 °C): δ −351 (s, ν1/2 = 251 Hz). 119 Sn{1H} NMR (149.26 MHz, CD2Cl2, −50 °C): δ −351 (s, ν1/2 = 236 Hz). 13

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Inorganic Chemistry Scheme 1. Synthesis of the Amino Alcohols 1 and 2

119 Sn{1H} NMR (149.26 MHz, CD2Cl2, −60 °C): δ −352, −348 (shoulder). 119 Sn{1H} NMR (149.26 MHz, CD2Cl2, −80 °C): δ −346 (ν1/2 = 36 Hz), δ −352 (ν1/2 = 25 Hz). Anal. Calcd for C22H37NO7Sn·C7H8 (4·C7H8, 638.39 g/mol) C 54.6, H 7.1, N 2.2. Found: C 53.6, H 7.2, N 2.1. The compound was dried under reduced pressure, so one-fifth of the toluene molecules seemed to be removed (anal. calcd for 4·4/5C7H8 C 53.5, H 7.1, N 2.3). IR spectroscopy (cm−1): 1783 (νC=O). In CH2Cl2 solution: 1784 (νC=O). Synthesis of 1-Ethoxido-(2,8,9-trioxa-5-aza-3,3,6,6-tetramethyl1-germatricyclo[3.3.3.01,5]undecane) 5. To a stirred solution of 2 (0.50 g, 2.44 mmol) in dry toluene (20 mL) germanium(IV) ethoxide (0.62 g. 2.44 mmol) was added within 5 min at room temperature. The ethanol formed in course of the reaction was removed by azeotropic distillation until the reaction mixture reached one-quarter of its original volume. Cooling to room temperature provided 5, as its toluene solvate 5·0.5C7H8 (0.66 g, 1.80 mmol, 74%), as small colorless blocks (mp. 79. °C). 1 H NMR (400.25 MHz, CD2Cl2, 26 °C): δ 7.17−7.05 (m, 2.5 H, CHarom), 3.74 (m, 2H, NCH2CH2O), 3.68 (q, 3J(1H−1H) = 13.7, 6.85 Hz, 2H, OCH2CH3), 3.45 (AB, 2J(1H−1H) = 11.3 Hz, 2H, CH2O), 3.04 and 2.62 (m, 2H, NCH2CH2O), 2.78 and 2.33 (AX, 2J(1H−1H) = 14.2 Hz, 2H, NCH2), 2.26 (s, 1.5 H, CH3, toluene), 1.21 and 1.18 (s, 3H each, C(CH3)2)O), 1.15 and 1.13 (s, 3H each, NC(CH3)2), 1.04 (t, 3J(1H−1H) = 6.9 Hz, 2H, OCH2CH3). 1 H NMR (400.25 MHz, CD2Cl2, − 80 °C): δ 7.13−6.99 (m, 2.5 H, CHarom), 3.87 (m, 0.5 H, NCH2CH2O), 3.81 (m, 0.5 H, OCH2CH3), 3.53 (m, 1.5 H, NCH2CH2O), 3.51 (m, 1.5 H, OCH2CH3), 3.38 (AB, 2 1 J( H−1H) = 33.9 and 11.1 Hz, 2H, CH2O), 3.18 (m, 0.5 H, NCH2CH2O), 2.95 (AX, 2J(1H−1H) = 14.8 Hz, 0.5 H, NCH2), 2.78 (m, 0.5 H, NCH2CH2O), 2.65 (m, 0.5 H, NCH2CH2O), 2.54 (AX, not resolved, 0.5 H, NCH2), 2.41 (AX, 2J(1H−1H) = 12.8 Hz, 0.5 H, NCH2), 2.18 (s, 1.5 H, CH3, toluene), 2.09 (AX, 2J(1H−1H) = 14.8 Hz, 0.5 H, NCH2), 1.13 and 1.10, 1.00, and 0.98 (s each, 6H C(CH3)2)O) and 6 H, NC(CH3)2), 1.93 (t, 3J(1H−1H) = 6.4 Hz, 2H, OCH2CH3). 13 C{1H} NMR (100.64 MHz, CD2Cl2, 26 °C): δ 137.6(s, Ci), 129.0 (s, CHo), 128.2 (s, CHm), 125.2 (s, CHp), 68.9(s, CH2O), 68.3 (s, C(CH3)2)O), 61.2 (s, NC(CH3)2), 59.4 (s, OCH2CH3), 58.4 (s, NCH2CH2O), 57.7 (s, NCH2), 50.0 (s, NCH2CH3), 31.5 and 30.6 (s, C(CH3)2)O), 22.2 and 21.2 (s, NC(CH3)2), 21.1 (s, CH3, toluene),) 18.8 (s, OCH2CH3). 13 C{1H} NMR (100.64 MHz, CD2Cl2, − 80 °C): δ 137.1 (s, Ci), 128.1 (s, CHo), 1.27.3 (s, CHm), 124.4 (s, CHp), 68.1 and 67.5(s, CH2O), 66.9 and 66.8 (s, C(CH3)2)O), 61.6(s, NC(CH3)2), 59.5 and 59.0 (s, NCH2), 58.2, 58.1, 58.1 (s, NCH2CH2O), 56.5 (OCH2CH3), 52.6 (s, NCH2), 50.2 and 46.8 (s, NCH2CH2O), 32.4, 39.9, 28.8, 28.6 (s, C(CH3)2)O), 24.3, 21.9, 20.5 (s, NC(CH3)2 and toluene), 18.5, 18.0, 17.9, 17.6 (s, OCH2CH3). 1 H−15N HMBC NMR (600.20, 60.83 MHz, 25 °C):δ (15N) 42 (referenced to NH3). Anal. Calcd for C12H25NO5Ge·0.5C7H8 (5·0.5C7H8, 366.02 g/mol) C 50.9, H 8.0, N 3.8. Found: C 47.1, H 7.7, 4.0, calculated for 5·(1/ 6)C7H8: C 45.9, H 7.7, N 3.1. (1/3 toluene molecules were removed by drying the product at 10−3 mbar. MS (ESI+): m/z = 322.1 [5 + H]+. Synthesis of 1-Bromido-(2,8,9-trioxa-5-aza-3,3,6,6-tetramethyl1-germatricyclo[3.3.3.01,5]undecane) 6. To a stirred solution of 5· 0.5C7H8 (0.18 g, 0.5 mmol) in dry toluene (7 mL) trimetylbromosilane (0.08 g, 0.50 mmol) was added dropwise. The reaction mixture

was stirred for 1 h at room temperature. The trimethylethoxysilane formed in course of the reaction was removed by distillation. Single crystals of compound 6 (0.17 g, 0.47 mmol, 93%, mp. 245 °C) were obtained from its concentrated toluene solution. 1 H NMR (400.25 MHz, CD2Cl2, 25 °C): δ 3.90, 3.85 (m, 2H, NCH2CH2O), 3.58 (AB, 2J(1H−1H) = 11.7 Hz, 2H, CH2O), 3.18 and 2.77 (m, 2H, NCH2CH2O), 2.84 and 2.50 (AX, 2J(1H−1H) = 14.2 Hz, 2H, NCH2) 1.31 and 1.25 (s, 3H each, C(CH3)2)O), 1.23 and 1.21 (s, 3H each, NC(CH3)2). 13 C{1H} NMR (100.64 MHz, CD2Cl2, 25 °C): δ 71.2 (s, C(CH3)2)O), 70.1 (s, CH2O), 62.5 (s, NC(CH3)2), 60.3 (s, OCH2CH2), 58.4 (s, NCH2), 49.8 (s, NCH2CH2O), 31.2 and 31.5 (s, C(CH3)2)O), 21.5 (s, NC(CH3)2). Anal. Calcd for C10H20BrNO3Ge (354.81 g/mol) C 33.9, H 5.7, N 4.0. Found: C 34.0, H 5.7, N 3.8. MS (ESI + ): m/z = 276.1 [6 − Br‑]+, 317.1 [6 − Br‑ + MeCN]+, 355.2 [6 + H]+, 378.0[6 + Na]+, 394.1 [6 + K]+, 419.1 [6 + Na + MeCN]+, 567.3 [N(CMe2CH2O) (CH2CMe2O) (CH2CH2O)GeOGe(OCH2CH2) (OCH2CMe2) (OCMe2CH2)N + H]+.

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CRYSTALLOGRAPHY Intensity data for all crystals were collected on an XcaliburS CCD diffractometer (Oxford Diffraction) using Mo−Kα radiation at 173 K. The structures were solved with direct methods using SHELXS-2014/77 or SHELXT,8 and refinements were carried out against F2 by using SHELXL-2014/77 or OLEX2.9 The C− H hydrogen atoms were positioned with idealized geometry and refined using a riding model. All non-hydrogen atoms were refined using anisotropic displacement parameters. In compound 3 the carbon atoms C3, C4, and C5 are affected by disorder and refined by a split model over two positions (occupancy values 55:45) and the severely disordered electron densities of noncoordinating solvent molecules were modeled by the SQUEEZE routine of the program Platon10 to improve the main part of the structure. In compound 4 the reflections from the high angle are weak to be counted. In compound 5 the carbon atoms C52 and C53 are affected by disorder and refined by a split model over two positions (occupancy values 75:25). Compound 6 crystallizes as inversion twin with BASF = 0.265. CCDC-1511722 (1), CCDC-1511723 (2), CCDC-1511724 (3), CCDC-1538973 (4), CCDC-1511725 (5), and CCDC1538974 (6) contain the supplementary crystallographic data for this paper. This data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc. cam.ac.uk/data_request/cif. For decimal rounding of numerical parameters and su values, the rules of IUCr have been employed.11 All figures were generated using ORTEP12 or Diamond13 visualization software.

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RESULTS AND DISCUSSION

The amino alcohol 2-((2-hydroxy-2-methylpropyl)amino)-2methylpropan-1-ol, HN(CH2CMe2OH)(CMe2CH2OH) (1), was prepared by the reaction of 2-amino-2-methylpropan-1-ol with an excess of 1,1-dimethyloxirane (Scheme 1). The amino 4939


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Inorganic Chemistry

The amino alcohol 1 crystallizes in the monoclinic space group P21/c with four molecules in the asymmetric unit of the unit cell (Z = 4). Selected interatomic distances and angles involving hydrogen bonds are given in Table 1. Both the 2-hydroxy-2-methyl-propyl chain CH2CMe2OH and the 1-hydroxy-2-methyl-propyl chain CMe2CH2OH are involved in intramolecular hydrogen bonds (d(D···A): O(17)− H(17)···N(14) 2.7903(16) Å and (d(D···A): O(11)−H(11)··· O(17) 2.7856(15) Å. The interatomic ∠(DHA) angles in compound 1 are 166.7(19) and 179(2) deg. The proton H(14) at the nitrogen atom N(14) is not involved in a hydrogen bond. Two types of hydrogen bonds a, b were identified (Table 1) and analyzed by graph set analysis.14 The unitary motif N1 contains one ring (R) for the hydrogen bond type a N1 = R22(10) and one chain (C) for the hydrogen bond type b N1 = C(8) . The second level graph set N2 of compound 1 includes three chains N2(a,b) = C22(7), N2(a,b) = C22(13), N2(a,b) = C44(20), and three rings N2(a,b) = R66(30), N2(a,b) = R66(35), and N2(a,b) = R66(42). The amino alcohol 2 crystallizes in the orthorhombic space group P212121 with four molecules in the asymmetric unit of the unit cell (Z = 4). Selected interatomic distances and angles involving the hydrogen bonds are given in Table 2. To the best of our knowledge, compound 2 is the first amino alcohol containing three different chains. Selected interatomic distances and angles involving the hydrogen bonds are given in Table 2. In 2 one intramolecular hydrogen bond and two intermolecular hydrogen bonds are identified. The intramolecular hydrogen bond involves the CH2CMe2OH and the CH 2 CH 2 OH chain (d(D···A: O(11)−H(11)···O(22) 2.6871(18) Å) and the intermolecular ones CMe2CH2OH and CH2CMe2OH (d(D···A: O(17)−H(17)···O(11) 2.6550(18) Å), and CH2CH2OH and CMe2CH2OH (d(D···A: O(22)− H(22)···O(17) 2.6716(19) Å). The intramolecular ∠(DHA) angle (160.8°) is smaller than the intermolecular ∠(DHA) angles (169.6° and 173.7°). The hydrogen bond network in the molecular structure of 2 was characterized by graph set analysis.14 The first level graph set contains three motif descriptors, two chains (C) for the hydrogen bond types a,b N1 = C(8), and one hydrogen-bonded pattern (S) for the hydrogen bond type c N1 = S(8). The binary graph set can be divided in three chains N2(b,c) = C22(10), N2(b,c) = C22(16), N2(b,c) = C44(26) and three ring motives N2(b,c) = R44(26), N2(b,c) = R66(42), N2(b,c) = R66(42) . The second level graph set results only from intermolecular hydrogen bonds. The reaction of tin-tetra-t-butoxide, Sn(Ot-Bu)4, with the unsymmetrically substituted amino alcohol 2 gave the novel stannatrane 3 (Scheme 2). Compound 3 is a colorless solid which shows good solubility in hot toluene, benzene, and dichloromethane. Time-dependent IR measurements under noninert conditions show that it is sensitive toward moisture (Supporting Information, Figure S5). Single crystals of 3, as its toluene solvate 3·0.5C7H8, were obtained from concentrated toluene solution. The molecular

alcohol 2-((2-hydroxy-2-methylpropyl)(2-hydroxyethyl)amino)-2-methylpropan-1-ol, (N(CH2CMe2OH)(CMe2CH2OH)(CH2CH2OH) (2) was prepared by the reaction of 1 with an excess of ethylene oxide (Scheme 1). Compound 1 is a colorless oil, which crystallized upon standing at room temperature for several hours. It is hygroscopic and shows good solubility in common organic solvents such as diethyl ether, tetrahydrofuran, chloroform, dichloromethane, and hot toluene. The amino alcohol 2 is a crystalline solid. It is soluble in the same organic solvents but is less soluble in hot toluene. Single crystals of 1 and 2 were obtained from isohexane and toluene, respectively. The molecular structures of the compounds 1 and 2, as determined by single crystal X-ray diffraction analysis, are shown in Figures 1 and 2, respectively.

Figure 1. Molecular structure of compound 1 (ORTEP presentation at 30% probability of the depicted atoms and atom numbering scheme).

Figure 2. Molecular structure of compound 2 (ORTEP presentation at 30% probability of the depicted atoms and atom numbering scheme).

Table 1. Selected Interatomic Distances [Å] and Angles [deg] of the Hydrogen Bonds in Compound 1 and Unitary Graph Sets Motifs (on Diagonal) and Basic Binary Graph Set (off Diagonal)a

a

D−H···A

d(D···A)

∠(DHA)

hydrogen bonds

a

b

O(17)−H(17)···N(14)#1 O(11)−H(11)···O(17)#2

2.7903(16) 2.7856(15)

166.7(19) 179(2)

a b

C22(10) C22(7)

C(8)

Symmetry transformations used to generate equivalent atoms: #1: −x + 1, −y, −z + 1, #2: −x + 1, y − 1/2, −z + 3/2. 4940


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Table 2. Selected Interatomic Distances [Å] and Angles [deg] of the Hydrogen Bonds in Compound 2 and Unitary Graph Sets Motifs (on Diagonal) and Basic Binary Graph Set (off Diagonal)a

a

D−H···A

d(D···A)

∠(DHA)

hydrogen bonds

a

b

C

O(11)−H(11)···O(22) O(17)−H(17)···O(11)#1 O(22)−H(22)···O(17)#2

2.6871(18) 2.6550(18) 2.6716(19)

160.8 169.6 173.7

a b c

S(8) b b

C(8) C22(10)

C(8)

Symmetry transformations used to generate equivalent atoms: #1: −x + 1, y + 1/2, −z + 1/2, #2: −x, y − 1/2, −z + 1/2. bNo link to binary level.

Scheme 2. Synthesis of the Stannatrane 3 and of the Germatranes 5 and 6

Figure 3. Molecular structure of compound 3·0.5C7H8 (ORTEP presentation at 30% probability of the depicted atoms and atom numbering scheme). Selected interatomic distances [Å]: Sn(1)−O(1) 1.986(2), Sn(1)−O(11) 1.9925(19), Sn(1)−O(17) 1.9930(19), Sn(1)−O(22) 2.1268(18), Sn(1)−O(42) 2.0937(18), Sn(1)−N(14) 2.302(2), Sn(2)−O(22) 2.0799(18), Sn(2)−O(31) 1.9997(19), Sn(2)−N(34) 2.335(2), Sn(2)−O(37) 2.0021(18), Sn(2)−O(42) 2.1809(18), Sn(2)−O(51) 1.9669(17). Selected interatomic angles [deg]: O(1)−Sn(1)−O(22) 164.86(8), O(11)−Sn(1)−O(17) 156.68(9), O(42)−Sn(1)−N(14) 148.91(8), O(22)−Sn(2)−O(31) 155.85(8), O(37)−Sn(2)−O(42) 147.49(7), O(51)−Sn(2)−N(34) 170.34(8).

structure of 3·0.5C7H8, as determined by single crystal X-ray diffraction analysis, is shown in Figure 3. Selected interatomic distances and angles are given in the figure caption. Compound 3·0.5C7H8 crystallized in the monoclinic space group P21/c. It forms a dimer via intermolecular O→Sn coordination to give an almost planar four-membered Sn2O2

ring with intracyclic Sn−O distances varying between 2.0799(18) (Sn2−O22) and 2.1809(18) Å (Sn2−O42). These μ3-O−Sn distances are comparable with those reported for [N(CH2CMe2O)2(CH2CH2CH2O)SnOt-Bu]2 and [N(CH2CMe2O)2(CH2CH2O)SnO-2,6-Me2C6H3]2 ranging between 2.046(2) and 2.232(2) Å.5a Each of the crystallographic 4941


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metallatrane is given in Scheme 3. The red, blue, and yellow colors and the assigned priorities refer to the amino alcohol 2. In compound 3, the Δ and Λ stereoinformation cannot be defined, as a result of the dimerization and the distorted coordination mode of the two amino alcohol chains. As well, the λ and δ notation cannot be used in this case. One N atom of the dimeric 3 is R and the other is S configured. A 1H NMR spectrum (Figure 5) at ambient temperature of the stannatrane 3·0.5C7H8 shows five singlet resonances for the methyl protons and AX spin systems for the NCH2CH2O (δ 3.87 and 3.77), NCH2CH2O (δ 3.09 and 3.67), and the NCH2 protons (δ 2.68 and 2.40, 2J(1H−1H) = 14.18 Hz). An AB-spin system is observed for the CH2O protons (δ 3.52, 2J(1H−1H) = 12.72 Hz, 2H, CH2O). At −80 °C the resonances become broad and unresolved. The assignment of the resonances was supported by 1H−1H COSY, 1H−13C HMBC, and 1H−13C HSQC NMR experiments (see Supporting Information, Figures S10−S14). A 13C NMR spectrum at ambient temperature (Experimental Section, Figure S8) revealed a total of 12 resonances (plus the signals assigned to the toluene solvate molecule). At −80 °C the resonances become broad, and decoalescence of some resonances is observed (Supporting Information, Figure S17). This was not analyzed in more detail. A 119Sn NMR spectrum of 3·0.5C7H8 at ambient temperature showed broad resonances at δ −343 (in C6D6, ν1/2 1430 Hz) and δ − 314 (in CD2Cl2, ν1/2 274 Hz, Supporting Information, Figure S9), respectively. The former is slightly high field shifted as compared to the signals reported for the monomeric stannatranes N(CH2CMe2O)2(CH2CH2O)SnOt-Bu5a (C6D6, δ − 320) and N(CH2CMe2O)2(CMe2CH2O)SnOt-Bu (C6D6, δ − 317).6 However, the resonances are considerably low field shifted as compared to the dimeric stannatranes5a [N(CH2CMe2O)2(CH2CH2CH2O)SnOR]2 (R = t-Bu, δ −400; R = 2,6-Me2C6H3, δ − 417; in CD2Cl2). At −80 °C a 119Sn NMR spectrum (Figure 6) of a solution of 3·0.5C7H8 in CD2Cl2 showed five resonances at δ −303 (ν1/2 10 Hz, integral 25), −309 (ν1/2 24 Hz, integral 10), −511 (ν1/2 460 Hz, integral ∼22.5), −512 (integral 22.5), −522 (ν1/2 460 Hz, integral 17). In addition, there are two signals of rather low intensity at δ −619 and −674 (total integral 3), which are assigned with caution to tin oxoclusters of unknown structures. The NMR data in general and the 119Sn NMR spectra in particular are interpreted in terms of compound 3 being involved in a monomer−dimer equilibrium (Scheme 4). At room temperature, the monomer dominates as the resonance in CD2Cl2 observed at this temperature is close to the two sharp resonances at δ −303 and −309 observed at −80 °C and which

independent Sn1 and Sn2 atoms are hexa-coordinated by one nitrogen and five oxygen atoms and show distorted octahedral environments. The trans angles vary between 147.49(7) (O37− Sn2−O42) and 170.34(8)° (O51−Sn2−N34). The Sn−O distances involving the nonbridging oxygen atoms vary between 1.9669(17) (Sn2−O51) and 2.0021(18) (Sn2−O37) Å. The Sn(1)−N(14) (2.302(2) Å) and Sn(2)−N(34) (2.335(2) Å) are slightly shorter than those reported for the two compounds mentioned above (2.390(2), 2.401(2) Å).5a The essential difference between the coordination environments about Sn(1) and Sn(2) is that at Sn(1) the N(14) atom is trans to the bridging oxygen atom O(42) while at Sn(2) the N(34) atom is trans to the t-butoxido oxygen atom O(51). As result of this, the structure of 3·0.5C7H8 is different from those reported for [N(CH 2 CMe 2 O) 2 (CH 2 CH 2 CH 2 O)SnOt-Bu] 2 and [N(CH2CMe2O)2(CH2CH2O)SnO-2,6-Me2C6H3]25a in which the nitrogen atoms are always trans to the t-butoxido oxygen atoms (Figure 4). Unit cell determinations of four independent

Figure 4. Simplified molecular structures of dimeric tert-butoxidosubstituted stannatranes. Left hand side: cis−trans configured dimer as found in the solid state for compound 3. Right hand side: a trans dimer.5a The atrane cages are omitted for clarity.

single crystals of 3·0.5C7H8 gave identic results. Consequently, it is rather likely that the bulk crystalline material of 3·0.5C7H8 consists of identical dimers. These dimers consist of two enantiomeric stannatrane moieties. Metallatranes are chiral molecules in terms of Δ and Λ stereochemistry (see Scheme 3).3,15 For metallatranes with three different side chains in the atrane cage the N atom can either be R or S configured. The lone electron pair at the nitrogen atom coordinating the metal atom has the lowest priority. In this type of metallatranes the metal atom is coordinated by five different substituents. Consequently, the metal atom is also a stereogenic center (Scheme 3). Looking from the Z substituent along the Z−M−N axis, we define a λ and δ designation. An example for a λ and δ configured

Scheme 3. Chirality of Monomeric Unsymmetrical Metallatranes in the Case of the Amino Alcohol Containing Three Different Side Chains

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Figure 5. 1H NMR spectra of compound 3·0.5C7H8 in CD2Cl2 solution at 25 °C and −80 °C.

Figure 6. 119Sn{1H} NMR spectrum of 3·0.5C7H8 in CD2Cl2 (149.26 MHz, CD2Cl2, −80 °C), R = t-Bu. The two minor intense signals at δ − 619 and −674 are not shown. The atrane cage for 3a and 3b is drawn schematically, the methyl substituents are omitted for clarity, and the nitrogen atoms are in the plane behind the tin center. The dimers 3c and 3c′ are both trans dimers. The difference between both is that 3c′ consists of two equal monomeric subunits, and 3c consists of two enantiomeric subunits as found for 3d in the solid state. An unambiguous discrimination between 3c and 3c′ was not achieved. The explanation why 3a and 3b are diastereomers is given in Figure 11.

The monomers 3a and 3b are diastereomers which epimerize via Λ ⇌ Δ isomerization of the atrane cages. Such an isomerization was previously suggested for tricarbastannatra-

are assigned to the monomeric species 3a and 3b (Figure 6). At low temperature the equilibrium becomes slow on the 119Sn NMR time scale and the population of the dimers increases. 4943


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Inorganic Chemistry Scheme 4. Monomer Dimer Equilibrium of 3 in Solutiona

varies the gradient strengths such as that the 119Sn signal intensities have to change from about 95% to 3% of their maximum intensity. Therefore, the low field signals will provide very noisy individual DOSY spectra and finally no DOSY plot. Notably, a 1H DOSY NMR experiment at −80 °C (Figure S24) showed cross resonances for several species with diffusion coefficients ranging between 3.33 and 4.17 m2/s. With these data at hand, one cannot distinguish between monomeric or dimeric species. Apparently, the monomer−dimer equilibrium is not sufficiently slow on the 1H NMR time scale at −80 °C. A 1H−15N HMBC NMR spectrum of 3·0.5C7H8 in C6D6 showed one resonance at δ (15N) 35 ppm (Figure S15), which is only slightly high field shifted as compared to the resonance of the amino alcohol 2 (C6D6, δ15N 38 ppm, Figure S3). Apparently, there is no significant influence on the 15N chemical shift as result of the N→Sn coordination in compound 3. An ESI MS spectrum (positive mode) of a solution of 3· 0.5C7H8 in acetonitrile showed a mass cluster centered at m/z = 206.2, which is assigned to the ligand ([2 + K]+). An ESI MS spectrum (positive mode) of a solution of 3·0.5C7H8 in dichloromethane showed a mass cluster centered at m/z = 978.3, which corresponds to the trinuclear tin oxocluster cation [(μ3-O)(μ3-Ot-Bu){Sn(OCH2CH2)(OCH2CMe2)(OCMe2CH2)N}3) − Ot-Bu]+ and resembles the oxocluster cation [(μ3-O)(μ3-Ot-Bu){Sn(OCH2CMe2)(OCMe2CH2)2N}3) − Ot-Bu]+ published previously.6 An ESI MS spectrum (negative mode) of a solution of 3·0.5C7H8 in CH2Cl2 showed a mass cluster centered at m/z = 693.1 which is consistent with [23 − 2Ot-Bu + 3OH]−. In principle, the two sharp resonances at δ −306 and −309 observed in the 119Sn{1H} NMR spectrum of 3·0.5C7H8 at −80 °C (Figure 6) could also be assigned to different rotamers of 3, originating from hindered rotation about the Sn−Ot-Bu bond. In order to exclude this option, the stannatrane N(CH2CMe2O)3SnOC(O)C9H13O2, 4, was synthesized by the reaction of N(CH2CMe2O)SnOt-Bu with (1R)-(+)-cam-

L ′ refers to N(CH2CMe2O)(CMe2CH2O)(CH2CH2O).

a 22 0

nes.15b Most remarkably, one diastereomer dominates. From the experimental data at hand, the origin accounting for this phenomenon is not clear. The signal at δ −512 is assigned to the trans dimer 3c containing two chemically equivalent tin atoms. 3c can be a C2symmetric dimer which consists of two identical monomeric subunits (3c′), or it can be a centrosymmetric dimer which consists of two enantiomeric subunits as also found in the cis dimer. An unambiguous discrimination between 3c and 3c′ was not achieved. The two equally intense broad signals at δ −511 and −522 are assigned to the cis dimer 3d containing two nonequivalent tin atoms. It resembles the structure found in the solid state. The interpretation of the two sharp resonances belonging to 3a and 3b gets further support from a, to the best of our knowledge first, 119Sn DOSY NMR experiment at −80 °C (Figure 7). As result of a convection phenomenon at −80 °C, the measured diffusion coefficient is too big. Consequently, the hydrodynamic radius calculated by the Stokes−Einstein equation is too small. However, the magnitude of the values shows unambiguously that these resonances can be assigned to the monomeric species 3a and 3b, both having the same size. The high field signals at δ −511, −512, and −522 ppm assigned to cis and trans dimers are not detectable in the 119Sn DOSY NMR as result of their low intensities compared to the low field signals. The quality of the DOSY NMR experiment depends strongly on the height of the signals and not of the integral. The signals of the high field area are significantly broader because of their shorter transverse relaxation and therefore do not reach the efficient heights particularly for the higher gradient strengths used in the DOSY sequence. The DOSY experiment

Figure 7.

Sn{1H} DOSY NMR experiment of 3·0.5C7H8 in CD2Cl2 solution at −80 °C.

119

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Å. Caused by the anisobidentate coordination of the axial substituent, the Oatrane−Sn−N angles are (O(11)−Sn(1)−(1) 80.9(3)°, O(21)−Sn(1)−N(1) 82.1(2)°, and O(31)−Sn(1)− N(1) 80.2(2)°). A 1H NMR spectrum (CD2Cl2) of the stannatrane 4·C7H8 at ambient temperature (Supporting Information, Figure S26) shows a split multiplett at δ 2.88 and 2.87 which is assigned to the NCH2 protons of the atrane cage and two overlapped single resonances (δ 1.24 and 1.23) for the OCCH3 protons. For the diastereotopic CH2 protons of the chiral substituent multiplett resonances were found at δ 2.39, 2.34, 2.04, and 1.93. The signals at δ 1.08, 1.07, and 0.95 were assigned to the CH3 protons of the chiral substituent. The integration of the 1H NMR spectrum shows the 1:1 ratio of stannatrane 4 and solvate toluene. The assignment of the resonances was supported by 1 H−1H COSY, 1H−13C HMBC, and 1H−13C HSQC NMR experiments. A 13C NMR spectrum (CD2Cl2) at room temperature (Experimental Section, Supporting Information, Figure S27) revealed a total of 12 resonances (plus the signals assigned to the toluene solvate molecule; not all signals of the quaternary carbon atoms were found). Two single resonances were observed for the NCH2 (δ 70.5 and 70.1) and CCH3 (δ 30.9 and 30.8) carbon atoms of the atrane cage, respectively. 117/119 Sn satellites of 16.3 and 18.5 Hz were observed for the CCH3 resonance with coupling constants. At−80 °C the CCH3 resonance becomes broad, and decoalescence of some resonances is observed. This was not analyzed in more detail. Figure 9 shows 119Sn NMR spectra of 4·C7H8 (CD2Cl2) at variable temperatures. At ambient temperature a sharp resonance is observed at δ − 357 (ν1/2 = 43 Hz) that becomes broad at −20 °C (ν1/2 = 507 Hz). At −40 °C it becomes sharp again (ν1/2 = 251 Hz) before at −60 °C the onset of decoalescence is observed. Finally, at −80 °C, two sharp resonances at δ − 346 (ν1/2 = 36 Hz) and δ − 352 (ν1/2 = 25 Hz) with an integral ratio of 2:3 are observed. The two signals at −80 °C are assigned to the two diastereomers Λ-4 and Δ-4 (without knowing which resonance belongs to which diastereomer) the interconversion between both by Λ ⇌ Δ isomerization of the atrane cage is slow on the 119Sn NMR time scale at this temperature. The origin for the broadening of the signal at −20 °C is not clear yet. It was not investigated in more detail. A change of the coordination mode of the carboxylate substituent between mono- and unisobidentate can be ruled out as the IR spectra in the solid state (νCO = 1783 cm−1) and in CH2Cl2 solution (νCO = 1784 cm−1) are almost identic. The reaction of germanium tetraethoxide, Ge(OEt)4, with the amino alcohol 2 gave the germatrane 5 as a colorless crystalline material (Scheme 2). Its solubility in organic solvents is comparable to that of the stannatrane 3. But in contrast to the latter, it is stable against hydrolysis by atmospheric moisture for at least 1 day (Supporting Information, Figure S6). Single crystals of 5, as its toluene solvate 5·0.5C7H8, were obtained from its toluene solution. The molecular structure of 5·0.5C7H8 as determined by single crystal X-ray diffraction analysis is shown in Figure 10. Selected interatomic distances and angles are given in the figure caption. The compound crystallized in the monoclinic space group P21/n with two pairs of crystallographic independent molecules A and B in the unit cell. The interatomic distances and angles in A and B differ only slightly. Consequently, only those of molecule A are discussed (Figure 10). A figure showing B is given in the Supporting Information (Figure S4).

phanic acid (Scheme 5). In compound 4 the nitrogen atom is not a stereogenic center, but there is a stereoinformation in the axial substituent. Scheme 5. Synthesis of the Stannatrane 4

Single crystals of 4, as its toluene solvate 4·C7H8, were obtained from concentrated toluene solution. The molecular structure of 4·C7H8, as determined by single crystal X-ray diffraction analysis, is shown in Figure 8. Selected interatomic distances and angles are given in the figure caption.

Figure 8. Molecular structure of compound 4·C7H8 (ORTEP presentation at 30% probability of the depicted atoms and atom numbering scheme). The toluene solvate molecule is removed for clarity. Selected interatomic distances [Å]: Sn(1)−N(1) 2.295(7), Sn(1)−O(11) 1.983(6), Sn(1)−O(21) 1.973(5), Sn(1)−O(31) 1.984(5), Sn(1)−O(41) 2.172(6), Sn(1)−O(43) 2.309(5), N(1)− Sn(1)−C(42) 163.0(3), N(1)−Sn(1)−O(43) 140.4(3), O(11)− Sn(1)−N(1) 80.9(3), O(11)−Sn(1)−O(31) 117.6(2), O(11)− Sn(1)−O(41) 85.1(2), O(11)−Sn(1)−O(43) 137.8(2), O(21)− Sn(1)−N(1) 82.1(2), O(21)−Sn(1)−O(11) 107.3(2), O(21)− Sn(1)−O(31) 127.7(3), O(21)−Sn(1)−O(41) 119.2(2), O(21)− Sn(1)−O(43) 78.3(2), O(31)−Sn(1)−N(1) 80.2(2), O(31)−Sn(1)− O(41) 90.9(2), O(31)−Sn(1)−O(43) 85.2(2), O(41)−Sn(1)−N(1) 157.4(2), O(41)−Sn(1)−O(43) 58.0(2).

Compound 4·C7H8, in the crystal actually measured, crystallizes in the orthorhombic space group P212121, and all atrane cages are Δ configured. The tin atom in 4·C7H8 is hexacoordinated. The deprotonated camphanic acid coordinates the tin atom in an anisobidentate manner (Sn(1)−O(41) 2.172(6) Å, Sn(1)−O(43) 2.309(5) Å). Compound 4 is comparable to the benzoate-substituted stannatrane N(CH2CMe2O)3SnOC(O)C6H53 where a longer intramolecular O→Sn coordination (2.473(3) Å and 2.574 (3) Å) of the benzoate is observed. The Sn−Oatrane distances are between 1.973(5) and 1.984(5) Å, and the N → Sn distance is 2.295(7) 4945


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Figure 9.

119

Sn{1H} NMR spectra of compound 4·C7H8 in CD2Cl2 solution at different temperatures.

a result of three nonequal ligand arms the nitrogen atom is a stereogenic center. The germanium center is coordinated by five different substituents, making it a stereogenic center as well. Looking from the Ge atom or N atom along the N→Ge axis the different priority of amino alcohol arms makes both stereogenic centers dependent on each other. In the Δ enantiomer the Ge atom is δ configured (see Scheme 3) and the N atom S configured, and correspondingly in the Λ enantiomer the Ge atom has a λ and the N atom an R configuration. Including the R and S and Λ and Δ a total of four isomers are possible (Figure 11). In 5·0.5C7H8 the Ge(1) (A) and Ge(2) (B) atoms are pentacoordinated and show distorted trigonal bipyramidal environments (Δ∑(ϑ)16 = 71° (A), 70° (B)) with O(1) and N(14) occupying the axial (for molecule B: O(51) and N(64))

Figure 10. Molecular structure of compound 5·0.5C7H8 (molecule A, ORTEP presentation at 30% probability of the depicted atoms and atom numbering scheme). Selected interatomic distances [Å] and angles [deg]: Ge(1)−O(1) 1.791(5), Ge(1)−O(11) 1.779(5), Ge(1)−O(17) 1.794(5), Ge(1)−O(22) 1.789(5), Ge(1)−N(14) 2.138(6), O(1)−Ge(1)−O(11) 97.6(2), O(1)−Ge(1)−O(17) 91.2(3), O(1)−Ge(1)−O(22) 97.5(2), O(1)−Ge(1)−N(14) 176.0(2), O(11)−Ge(1)−O(17) 120.9(2), O(11)−Ge(1)−O(22) 116.7(2), O(17)−Ge(1)−O(22) 119.8(2), O(11)−Ge(1)−N(14) 84.0(2), O(17)−Ge(1)−N(14) 84.9(2), O(22)−Ge(1)−N(14) 85.0(2), and C(2)−O(1)−Ge(1) 121.2(5). The data for the enantiomer molecule B are rather similar and are given in the Supporting Information (Figure S4).

As a consequence of the lower Lewis acidity of germanium alkoxides as compared to tin alkoxides and in contrast to the stannatrane 3, the germatrane 5·0.5C7H8 crystallized as a monomer in the monoclinic space group P21/n. Both enantiomers of the propeller-type compound are present in the unit cell, one with Λ and the other with Δ conformation. As

Figure 11. Schematic view of the four possible isomers of monomeric metallatranes in which the atrane cage consists of three different side chains, as for instance in compounds 3, 5, and 6. The methyl substituents at the atrane cages, the Ot-Bu (for 3), the OEt (for 5), and the Br (for 6) substituents are omitted for clarity. 4946


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Figure 12. Variable temperature 1H NMR spectra of compound 4·0.5C7H8 in CD2Cl2 solution (the signal at 2.25 ppm is assigned to the CH3 protons of the toluene). The signals b, b′, and e, e′ are not shown here but in Figure S43.

Figure 13. 1H DOSY NMR experiment of 4·0.5C7H8 in CD2Cl2 solution at −80 °C.

2.62). The CH2O protons show an AB-spin system (δ 3.45, 2 1 J( H−1H) = 11.3 Hz). Four equally intense resonances are observed for the cage-bound methyl protons, whereas the methyl protons of the ethoxy substituent appear as triplet resonance. The assignment of the resonances was supported by 1 H−1H COSY, 1H−13C HMBC, and 1H−13C HSQC NMR experiments at ambient temperature as well as at −80 °C (compare Figures S31, S33−S36, and S40, S42−S44). A 1 H−1H TOCSY NMR experiment at −80 °C of 4·0.5C7H8 clearly shows the spin system of the unsubstituted ligand chain CH2CH2O (Supporting Information, Figure S37). 1 H NMR spectra at variable temperature (between −85 and 30 °C) of the germatrane 5·0.5C 7 H 8 were recorded (Supporting Information, Figure S47) and for the sake of

and O(11), O(17), and O(22) occupying the equatorial positions (for molecule B: O(61), O(67), O(72)). The Ge(1)−N(14) distance is 2.138(6) Å (molecule B: Ge(2)− N(64) 2.140(6)). It is comparable to germatrane N(CH2CMe2O)2(CH2CH2O)Ge-i-Pr17 (2.179(5) Å). The Ge− O distances vary between 1.779(5) and 1.794(5) Å, which is similar to the germatrane mentioned before (1.756(5) 1.781(5)).17 An ESI MS spectrum (positive mode) of 5 shows a mass cluster centered at m/z = 322.1, which is assigned to the protonated germatrane [5 + H]+. A 1H NMR spectrum of compound 5·0.5C7H8 in CD2Cl2 (Supporting Information, Figure 29) exhibits resonances assigned to AX-spin systems of the NCH2 (δ 2.78 and 2.33, 2 1 J( H−1H) = 14.2 Hz) and NCH2CH2O protons (δ 3.04 and 4947


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Inorganic Chemistry clarity Figure 12 shows a reduced picture (region between 2−4 ppm). The spectra recorded between 30 °C and −30 °C are very similar. By lowering the temperature the resonances become broad, especially for the CH2 protons, and at about −60 °C a coalescence temperature is reached. Going stepwise to −85 °C about 10 resonances increase and become sharper. The assignment of the resonances at −85 °C was supported by 1 H−1H COSY, 1H−13C HMBC, and 1H−13C HSQC NMR experiments (−80 °C). Focusing at the diastereotopic CH2 protons labeled with c and g (Figure 12) in the spectrum collected at −85 °C four signals were observed, the ratio of which cannot be defined unambiguously. Accordingly, at 30 °C an AB-type resonance was observed for these protons. Decoalescence is also observed for the proton resonances marked with f, h, and i. However, some of these signals are superimposed. The 1H NMR measurements at variable temperatures show the presence of two isomers that interconvert by a Λ ⇌ Δ isomerization. This is fast until −30 °C and slow at about −80 °C on the 1H NMR time scale. This interpretation is confirmed by a 1H DOSY NMR experiment of 5·0.5C7H8 in CD2Cl2 at low temperature (−80 °C) (Figure 13) where two species are identified which are monomeric showing very little difference of their diffusion coefficients. The average calculated hydrodynamic radius is 12 Å. This value is, as expected, slightly bigger than the radius of approximately 9.5 Å taken from the molecular structure as determined by single crystal X-ray diffraction analysis. Compared to the stannatrane 3·0.5C7H8 (δ 15N 35 ppm), a 1 H−15N HMBC NMR spectrum of 5·0.5C7H8 in C6D6 showed a low field-shifted resonance at δ (15N) 42 ppm (Supporting Information, Figures S45 and S46). In order to prove the Λ ⇌ Δ isomerization to be responsible for the decoalescence phenomena at low temperature and not a hindered rotation about the GeOEt bond, a germatrane without a flexible axial substituent was synthesized. The reaction of 5· 0.5C7H8 with trimetylbromidosilane gave the 1-bromido substituted germatrane 6 (Scheme 2). Single crystals suitable for X-ray diffraction analysis were obtained from its concentrated toluene solution. The molecular structure is shown in Figure 14, and selected interatomic distances and angles are given in the figure caption. Compound 6 crystallized in the orthorhombic space group P212121 as an inversion twin. The atrane cages are not clearly Λ or Δconfigured. In 6 the germanium atom is pentacoordinated and shows a distorted trigonal bipyramidal environment (Δ∑(ϑ)16 = 77°), with Br(1) and N(14) occupying the axial and O(11), O(17) and O(31) occupying the equatorial positions. The Ge(1)−N(14) distance of 2.105(7) Å is shorter compared to the 1-eythoxy-germatrane 5 (N→Ge 2.138(6) Å). It induces an elongation of the Ge−Br distance (Ge(1)− Br(1) 2.3741(10) Å). The Ge−O distances vary between 1.769(5) and 1.792(5) Å, which is comparable to 5 (between 1.779(5) and 1.794(5) Å). The N(14)−Ge(1)−Br(1) angle of 179.44(18)° is close to the ideal value of 180°. A 1H NMR spectrum of compound 6·in CD2Cl2 (Supporting Information, Figure S48) exhibits resonances assigned to AXspin systems of the NCH2 (δ 2.92 and 2.57, 2J(1H−1H) = 14.2 Hz) and NCH2CH2O protons (δ 3.26 and 2.84, 2J not resolved). The CH2O protons show an AB spin system (3.65, 2 1 J( H−1H) = 11.7 Hz). Four equally intense resonances are

Figure 14. Molecular structure of compound 6 (ORTEP presentation at 30% probability of the depicted atoms and atom numbering scheme). Selected interatomic distances [Å]: Ge(1)−Br(1) 2.3741(10), Ge(1)−O(11) 1.769(5), Ge(1)−O(17) 1.782(5), Ge(1)−O(31) 1.792(5), Ge(1)−N(14) 2.105(7), O(11)−Ge(1)− O(17) 118.8(3), O(11)−Ge(1)−O(31) 119.5(3), O(17)−Ge(1)− O(31) 120.4(3), O(11)−Ge(1)−N(14) 85.8(2), O(17)−Ge(1)− N(14) 86.3(3), O(31)−Ge(1)−N(14) 86.2(2), O(11)−Ge(1)− Br(1) 94.72(18), O(17)−Ge(1)−Br(1) 93.19(18), O(31)−Ge(1)− Br(1) 93.76(18), N(14)−Ge(1)−Br(1) 179.44(18).

observed for the methyl protons. A 13C NMR spectrum shows a total of nine resonances (see Experimental Section and Supporting Information, Figure S49). To investigate the Λ and Δ isomerization of the atrane cage in compound 6, 1H NMR spectra at variable temperature (between −85 and 30 °C) were recorded (Supporting Information, Figures S50 and S51). The spectra recorded between 30 °C and −20 °C are very similar. Going to lower temperature the resonances become broad, especially for the CH2 protons, and at about −60 °C a coalescence temperature is reached. At −80 °C decoalescence is observed. The 1H NMR spectra at variable temperature of 6 resemble those of 5· 0.5C7H8, proving unambiguously that hindered rotation about the GeOEt bond in the latter compound is not operative.

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CONCLUSION The novel amino alcohols HN(CH2CMe2OH)(CMe2CH2OH) (1) and N(CH2CMe2OH)(CMe2CH2OH)(CH2CH2OH) (2) show different structural patterns of hydrogen bonds in the solid state. The metallatranes N(CH2CMe2O)(CMe2CH2O)(CH2CH2O)MX (3, M = Sn, X = Ot-Bu; 5, M = Ge, X = OEt; 6, M = Ge, X = Br) based on the amino alcohol 2 are the first such compounds in which the nitrogen as well as the tin and germanium atoms are stereogenic centers. The stannatrane 3 is an oxygen-bridged, trans-configured dimer in the solid state. It is the first example for such a dimer reported so far. In solution, it is involved in a monomer−dimer equilibrium that is slow on the 1H and 119Sn NMR time scales at −80 °C. At this temperature, both the cis−trans- and trans-configured dimers are present. The monomer exists as two diastereomers in the ratio of 2.5:1. The stannatrane N(CH2CMe2O)3SnOC(O)C9H13O2 (4) containing a chiral axial substituent is monomeric both in solution and in the solid state. In solution at −80 °C, 4948


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1-(2′-methoxypgenyl)-3,7,10-trimethylstannatrane. J. Struct. Chem. 1994, 35 (5), 750−753. (3) Zö ller, T.; Dietz, C.; Iovkova-Berends, L.; Karsten, O.; Bradtmöller, G.; Wiegand, A.-K.; Wang, Y.; Jouikov, V.; Jurkschat, K. Novel Stannatranes of the Type N(CH2CMe2O3)SnX (X = OR, SR, OC(O)R, SP(S)Ph2, Halogen). Synthesis, Molecular Structures, and Electrochemical Properties. Inorg. Chem. 2012, 51, 1041−1056. (4) Rickard, C. E. F.; Roper, W. R.; Woodman, T. J.; Wright, L. J. Chem. Commun. 1999, 837−838. (5) (a) Zöller, T.; Jurkschat, K. Novel Trialkanolamine Derivatives of Tin of the Type [N(CH2CMe2O)2(CH2)nOSnOR]m (m = 1, 2; n = 2, 3; R = t-Bu, 2,6-Me2C6H3) and Related Tri- and Pentanuclear Tin(IV) Oxoclusters. Syntheses and Molecular Structures. Inorg. Chem. 2013, 52, 1872−1882. (b) Li, J.; Tang, Y.-J.; Liu, H.; Dong, S.-P.; Xie, Q.-L. Synthesis and Characterization of 1-Acyloxy(acylamino)-2,8,9-trioxa-5aza-1-stannatricyclo[3,3,3,01.5] undecanes. Gaodeng Xuexiao Huaxue Xuebao 1998, 19, 1074−1077. (6) Glowacki, B.; Lutter, M.; Schollmeyer, D.; Hiller, W.; Jurkschat, K. Novel Stannatrane N(CH2CMe2O)2(CMe2CH2O)SnO-t-Bu and Related Oligonuclear Tin(IV) Oxoclusters. Two Isomers in One Crystal. Inorg. Chem. 2016, 55 (20), 10218−10228. (7) Sheldrick, G. A Short History of SHELX. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64 (1), 112−122. (8) Sheldrick, G. M. Crystal Structure Refinement with SHELXL. Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71 (1), 3−8. (9) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.; Puschmann, H. OLEX2: A complete structure solution, refinement and analysis program. J. Appl. Crystallogr. 2009, 42 (2), 339−341. (10) Spek, A. L. Structure validation in chemical crystallography. Acta Crystallogr., Sect. D: Biol. Crystallogr. 2009, 65 (2), 148−155. (11) Clegg, W. Some guidelines for publishing SHELXL-generated CIF results in Acta Crystallographica. Acta Crystallogr., Sect. E: Struct. Rep. Online 2003, 59 (1), e2−e5. (12) (a) Farrugia, L. J. ORTEP −3 for Windows - a version of ORTEP -III with a Graphical User Interface (GUI). J. Appl. Crystallogr. 1997, 30 (5), 565. (b) Farrugia, L. J. WinGX and ORTEP for Windows: An update. J. Appl. Crystallogr. 2012, 45 (4), 849−854. (13) Brandenburg, K. DIAMOND 3.2k; Crystal Impact GbR: Bonn, Germany, 1999−2014. (14) Bernstein, J.; Davis, R. E.; Shimoni, L.; Chang, N.-L. Patterns in Hydrogen Bonding: Functionality and Graph Set Analysis in Crystals. Angew. Chem., Int. Ed. Engl. 1995, 34, 1555−1573. (15) (a) Mehrotra, R. C.; Gupta, V. D. Ethanolamine Derivatives of Sn(IV). Indian J. Chem. 1967, 5, 643−645. (b) Mügge, C.; Pepermans, H.; Gielen, M.; Willem, R.; Jurkschat, K.; Tzschach, A. NMR Investigations on Stannabicycloundecanes of the Type RSn(CH2CH2CH2)N. Z. Anorg. Allg. Chem. 1988, 567, 122−130. (16) Kolb, U.; Dräger, M.; Dargatz, M.; Jurkschat, K. Unusual Hexacoordination in a Triorganotin Fluoride Supported by Intermolecular Hydrogen Bonds. Crystal and Molecular Structures of 1-Aza-5-stanna-5-halotricyclo[3.3.3.0 1 . 5 ]undecanes N(CH2CH2CH2)3SnF·H2O and N(CH2CH2CH2)3SnX (X = Cl, Br, I). Organometallics 1995, 14, 2827−2834. (17) (a) Moon, J. H.; Kim, S. H.; Lee, K. M.; You, T.-S.; Do, Y.; Kim, Y. Synthesis and X-ray Diffraction Analysis/Crystal Structure of new Germatranes Containing Methyl Substituents in three Five-Membered Chelating Rings. Polyhedron 2011, 30, 2333−2338. (b) Gauchenova, E. V.; Karlov, S. S.; Selina, A. A.; Chernyshova, E. S.; Churakov, A. V.; Howard, J. A.K.; Troitsky, N. A.; Tandura, S. N.; Lorberth, J.; Zaitseva, G. S. Synthesis and characterization of 3- and 4-phenylgermatranes: Xray crystal structures of N(CH2CH2O)2(CH2CHPhO)GeZ (Z = F, OSiMe3, C-CPh) and N(CH2CH2O)2(CHPhCH2O)GeOH. J. Organomet. Chem. 2003, 676, 8−21.

two diastereomers in the ratio of 3:2 are observed. The corresponding germatranes N(CH2CMe2O)(CMe2CH2O)(CH2CH2O)GeX (5, X = OEt; 6, X = Br) are monomeric in the solid state as well. In solution, as shown by 1H NMR spectroscopy at low temperature, each exists as two diastereomers, the ratio of which, with the experimental data at hand, could not be established unambiguously. The epimerization of the stanna- and germatranes mentioned above proceeds via Λ ⇌ Δ isomerization of the corresponding atrane cage. This process, on the 119Sn respectively 1H NMR time scale, is slow at −80 °C but fast at room temperature. Future efforts will be devoted (i) to explore the origin for the diastereomeric excess observed in solution for the stannatranes and (ii) to synthesize metallatranes containing stereogenic centers in the atrane cage.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b03126. NMR spectra; IR spectra (PDF) Crystallographic information files (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Klaus Jurkschat: 0000-0001-9930-858X Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful to TU Dortmund for financial support. We acknowledge Prof. H. Rehage for providing viscosity data of CH2Cl2. We thank an anonymous reviewer for rather valuable hints!

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DEDICATION Dedicated to Professor Dr. Adolf Zschunke on the occasion of his 80th birthday. REFERENCES

(1) (a) Verkade, J. G. Main Group Atranes: Chemical and Structural Features. Coord. Chem. Rev. 1994, 137, 233−295. (b) Puri, J. K.; Singh, R.; Chahal, V. K. Silatranes: a Review on their Synthesis, Structure, Reactivity and Applications. Chem. Soc. Rev. 2011, 40, 1791−1840. (c) Srivastav, N.; Mutneja, R.; Singh, N.; Singh, R.; Kaur, V.; Wagler, J.; Kroke, E. Diverse Molecular Architectures of Si and Sn [4.4.3.01,6 ]Tridecane Cages Derived from a Mannich Base Possessing SemiRigid Unsymmetrical Podands. Eur. J. Inorg. Chem. 2016, 2016, 1730− 1737. (2) (a) Zschunke, A.; Tzschach, A.; Pö nicke, K. 1H-NMR Untersuchung zur Innermolekularen Beweglichkeit in pentakoordinierten Zinnverbindungen. J. Organomet. Chem. 1973, 51, 197−201. (b) Jurkschat, K.; Mügge, C.; Tzschach, A.; Zschunke, A.; Engelhardt, G.; Lippmaa, E.; Mägi, M.; Larin, M. F.; Pestunovich, V. A.; Voronkov, M. G. 1H, 13C, 15N and 119Sn NMR Investigations on Stannatranes. J. Organomet. Chem. 1979, 171, 301−308. (c) Swisher, R. G.; Day, R. O.; Holmes, R. R. The First Crystal Structure of a Stannatrane. Trimeric Methyl(2,2′,2″-nitrilotriethoxy)stannatrane Hexahydrate. Inorg. Chem. 1983, 22, 3692−3695. (d) Ovchinnikov, Y. E.; Struchkov, Y. T.; Baryshok, V. P.; Voronkov, M. G. Crystal and Molecular Structure of 4949


Introducing Stereogenic Centers to Group XIV Metallatranes

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