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7Clathrochelates
Клатрохелаты
Макрогэтэроцмклы
Communication
Сообщение
http://macroheterocycles.isuct.ru
DOI: 10.6060/mhc141141b
Free-Radical Reaction of Iron(II) Dichloroclathrochelate with 1,3-Dioxolane Radical Derivative: Synthesis and Structure of Macrobicyclic tris-Dioximate Bearing 1,3-Dioxolan-2-yl Ribbed Substituent
Mikhail A. Vershinm,a Alexey B. Burdukov,a@ Natalie V. Pervukhma,a Ilia V. Eltsov,b and Yan Z. Voloshinc
aNikolaev Institute of Inorganic Chemistry SB RAS, 630090 Novosibirsk, Russia bNovosibirsk State University, 630090 Novosibirsk, Russia
cNesmeyanov Institute of Organoelement Compounds RAS, 110991 Moscow, Russia @Corresponding author e-mail: lscc@niic.nsc.ru
Free-radical substitution of chlorine atom of the fluoroboron-capped iron(II) dichloroclathrochelate with 1,3-dioxolan-2-yl radical proceeds with high regioselectivity, predominantly yielding the corresponding monofunctionalized cage complex. Its molecular structure has been determined both in solution and in solid state using multinuclear NMR spectroscopy and a single-crystal X-ray diffraction experiment, respectively.
Keywords: Clathrochelates, iron(II), reactions of coordinated ligands, homolytic reactions.
Свободно-радикальная реакция дихлорзамещенного клатрохелата железа(П) с радикалом 1,3-диоксолана: синтез и структура макробициклического трис-диоксимата с реберным 1,3-диоксолановым заместителем
М. А. Вершинин^ А. Б. Бурдуков,^ Н. В. Первухина^ И. В. Ельцов,ь Я. З. Волошин
аИнститут неорганической химии им. А.В. Николаева СО РАН, 630090 Новосибирск, Россия ьНовосибирский государственный университет, 630090 Новосибирск, Россия Институт элементоорганических соединений им. А.Н. Несмеянова РАН, 110991 Москва, Россия @Е-таИ: lscc@niic.nsc.ru
Свободно-радикальное замещение атома хлора в дихлорзамещенном клатрохелате железа(11), сшитом группой Б^, радикалом 1,3-диоксолан-2-ила проходит c высокой региоселективностью и в основном приводит к продукту монозамещения. Его молекулярная структура была определена в растворе и твердой фазе методом спектроскопии ЯМР на различных ядрах и РСА.
Ключевые слова: Клатрохелаты, железо(П), реакции координированных лигандов, гомолитические реакции.
Recently we have reported[1-4] that the iron(II) dichloroclathrochelate FeBd2(Cl2Gm)(BF)2 (where Bd2-and Cl2Gm2- are a-benzyldioxime and dichloroglyoxime dianions, respectively) smoothly undergoes the free-radical substitution with carbon-centered radical species - the derivatives of cyclohexane, alcohols and cyclic ethers (such as 1,4-dioxane and tetrahydrofuran) (Scheme 1,i). In this paper, we describe synthesis, spectra and X-ray structure of the macrobicyclic complex FeBd2(Cl(Diox)Gm)(BF)2 (where Diox is 1,3-dioxolan-2-yl radicals) with one functionalizing ribbed substituent as a product of the similar substitution reaction with free-radical derivative of 1,3-dioxolane (Scheme 1,ii).[5]
atoms are located in almost one plane (the deviations from their mean plane do not exceed 0.06 A), whereas the bridging carbon atom is deviated from this plane by 0.34 A. It should be noted that, although the lack of chiral centers, the molecule FeBd2(Cl(Diox)Gm)(BF)2, crystallizes in chiral space group P212121 like its chiral macrobicyclic analogs FeBd2(ClGm(THF))(BF)2 and FeBd2(ClGm(Dx)) (BF)2 (where THF and Dx are tetrahydrofuryl and 1,4-dioxanyl substituents, respectively); all these crystals have the similar unit cell dimensions.
The macrobicyclic structure of the complex FeBd2(Cl(Diox)Gm)(BF)2 was also confirmed by solution NMR spectra; assignment of the signals is represented
C>H3VoHH3VoH
^ H3C H
R"
-cr
ferf-BuOOH reflux ^
-cr
FeBd2(CI(R)Gm)(BF)2
FeBd2(CIGm)(BF)2
FeBd2(CI(Diox)Gm)(BF)2
Scheme 1.
The reaction of the dichloroclathrochelate precursor FeBd2(Cl2Gm)(BF)2 with 1,3-dioxolane in boiling benzene in presence of feri-butylhydroperoxide as a radical initiator proceeds smoothly and affords the monofunctionalized macrobicyclic product FeBd2(Cl(Diox)Gm)(BF)2 in a good yield (Scheme 1); such result is also characteristic for other earlier-studied reagents of this type. We also isolated a small amount of the disubstituted clathrochelate product FeBd2((Diox)2Gm)(BF)2 and characterized it by 'H NMR spectroscopy (81H = 6.32 (s, 2H, C2H), 4.17 (m, 8H, CH2), 7.38 (m, 20H, Ph)}; however, we failed to evaluate a reproducible synthetic protocol for the iron(II) cage complex. The molecular structure of this monofunctionalized clathrochelate FeBd2(Cl(Diox)Gm) (BF)2 was confirmed by single-crystal X-ray diffraction study in solid state and by multinuclear NMR experiments in solution.
General view of the molecule FeBd2(Cl(Diox)Gm) (BF)2 is shown in Figure 1 (X-ray diffraction data). Its cage framework possesses a geometry that is intermediate between a trigonal-prism (TP) and trigonal antiprism (TAP) characteristic of the boron-capped tris-dioximate iron(II) clathrochelate:[10] the average distortion angle 9 of the Fe^-coordination polyhedron is equal to 25.8° (9 = 0° for an ideal TP; 9 = 60° for a TAP), and the height h of such TP-TAP polyhedron is approximately 2.31 A; the Fe-N distances fall in the narrow range (1.891(1)-1.919(1) A). The ribbed 1,3-dioxolan-2-yl substituent at this cage framework has an envelope conformation: its four carbon
Figure 1. General view of the clathrochelate FeBd2(Cl(Diox)Gm)(BF)2.
in Scheme 2. The proton spin system of the ribbed 1,3-dioxolanyl substituent at cage framework was additionally analyzed by computer simulation; Scheme 2
A. B. Burdukov et al.
Scheme 2. Attribution of NMR signals for FeBd2(Cl(Diox)GmCl2)(BF)2.
illustrates its experimental 'H NMR spectrum, while the corresponding chemical shifts and the 'H-'H coupling constants are summarized in Table 1.
Table 1. 'H-'H J-coupling constants (Hz) and chemical shifts (ppm) for the !,3-dioxolanyl substituent
J
4.'28
4.328 6.555
HA' HB HB' HC
HA 7.00 -7.4' 6.50 0.22
HA' 5.88 -7.88 -0.39
HB 6.64 0.55
H -0.52
H
Thus, the free-radical substitution of iron(II) dichloro-clathrochelate with carbon-centered dioxanyl radical afforded the monofunctionalized macrobicyclic complex; this substitution occurs via the bridging carbon atom of functionalizing 1,3-dioxanyl substituents. This reaction proceeds with high regioselectivity; no other isomers of such cage complex were detected in the reaction mixture; this result can be explained by the stabilization of 1,3-dioxan-2-yl radical species by two adjacent oxygen atoms.[11]
Acknowledgements. The authors thank Dr. N. Kuratieva (NIIC SB RAS) for collecting the single-crystal X-ray diffraction data.
References and Notes
1. Burdukov A.B., Vershinin M.A., Pervukhina N.V., Kozlova S.G., Eltsov I.V., Voloshin Y.Z. Russ. Chem. Bull. Int. Ed. 2011, 60, 2504-2509.
2. Vershinin M.A., Burdukov A.B., Pervukhina N.V., Eltsov I.V., Voloshin Y.Z. Inorg. Chem. Commun. 2013, 30, 159-162.
3. Vershinin M.A., Burdukov A.B., Eltsov I.V., Reznikov V.A., Boguslavsky E.G., Voloshin Y.Z. Polyhedron 2011, 30, 12331237.
4. Vershinin M.A., Burdukov A.B., Pervukhina N.V., Eltsov I.V., Voloshin Y.Z. Macroheterocycles 2012, 5, 11-16.
The dichloroclathrochelate precursor FeBd2(Cl2Gm)(BF)2 was prepared as described in ref. [6]. Benzene was washed with concentrated sulfuric acid and then distilled. 1,3-dioxolane was dried with KOH and distilled off. The commercially available tert-butylhydroperoxide solution in n-decane (SAF), silica gel 230-400 mesh (Alfa Aesar), other solvents and reagents (SAF) were used without purification. The 1H, 11B, 19F and 13C{1H} NMR spectra of the complex obtained were recorded in CD2Cl2 solution with a Bruker Avance III 500 spectrometer (working frequencies 500.13 (1H), 160.46 (11B), 470.59 (19F), and 125.76 MHz (13C)). The 1H and 13C NMR chemical shifts are given in the 5 scale and referred to residual proton and carbon signals of this solvent (5.34 ppm for CHDCl2, 53.8 ppm for CD2Cl2), the signal assignment in the corresponding spectra and structure determination were carried out on the basis of 2D HMBC NMR spectra. The 11B and 19F NMR chemical shifts are referred to external standarts BF3 • O(C2H5)3 and TFT, respectively. 15N NMR spectrum was obtained as projection of 2D 1H-15N-correlation. The 15N-scale was calibrated with respect to the liquid ammonia (8(15N)=0 ppm). The 1H-1H J-couplings and the positions of signals of 1,3-dioxolane fragment were obtained and refined with spin-system modeling; NAMMRIT algorithm and the method of total-line-shape fitting were used (RMS = 0.0396). All calculations were made using the Bruker Topspin v. 2.1 program package.
FeBd2 (Cl (Diox) Gm)(BF)2:1,8-bis(2-fluorobora)-2,7,9,14,15,20-hexaoxa-3,6,10,13,16,19-hexaaza-4,5,11,12-tetraphenyl-17-chloro-18-(1,3-dioxolan-yl-2)bicyclo[6.6.6]eicosa-3,5,10,12, 16,18-hexaeno(2-) iron (2+). Complex FeBd2(Cl2Gm)(BF)2 (0.11 g, 0.15 mmol) was dissolved in benzene (20 ml) and 1,3-dioxolane (2 ml) and 5.5 M solution of tert-butylhydroperoxide in n-decane (0.81 ml, 4.6 mmol) were added. The reaction mixture was refluxed for 3 h, cooled to r.t. and the additional portion of this radical initiator (0.76 ml, 4.2 mmol) was added. The reaction mixture was refluxed for 5 h, then rotary evaporated to dryness and the oily residue was dried in vacuo. The solid product was extracted with chloroform and the extract was chromatographically separated on silica gel (1x20 cm column, eluent: CHCl3). The first elute, containing mainly the dichloroclathrochelate precursor, was thrown out and the second elute was collected, evaporated to dryness and dried in air. The solid product was recrystallized from dichloromethane:heptane 1:1 mixture and dried in vacuo. Yield: 0.071 g (60 %). Anal. Calc. for C, H .NOClBTTe: C, 50.5; H, 3.6; N, 10.2. Found: C,
33 25 6822 ' j J J J
50.5; H, 3.2; N, 10.7 %. 1H NMR (CD2Cl2): 4.13 (m, 2H, CHA CHA,) and 4.33 (m, 2H, CHB CHB,), 6.56 (s, 1H, CHC), 7.38 (m, 20H, Ph). 13C{1H} NMR (CD2Cl2): 66.85 (s, CH2), 94.58 (s, CH), 128.45, 128.46 (two s, 3-C (Ph)), 129.32, 129.33 (two s, 1-C (Ph)), 130.81 (s, 4-C (Ph)), 130.95 (s, 2-C (Ph)), 131.97 (s, N=CCl), 152.16 (s, N=C-Diox), 157.45, 157.78 (two s, PhC=N). 11B NMR (BF3O(C2H5)2): 3.62 (d, J,,B «F = 17.5 Hz), 3.65 (d, J,,B ,9F = 17 Hz). 19F NMR (PhCF3): -169.29 (m, O3B'F + O3B"F). 15N NMR (NH3(liq)): 319.8 (N=CCl), 321.9 (N=CPh), 339.1 (N=C-Diox).
Single crystals of the complex FeBd2(Cl(Diox)Gm) (BF)2-3 CH2Cl2, suitable for the X-ray diffraction experiment, were grown by slow evaporation of its saturated solution in dichloromethane:heptane 1:2 mixture at room temperature. The crystal system of C36H29B2Cl7F2FeN6O8 (M= 1037.27) is orthorhombic at 240 K: a = 15.557(3), b = 16.757(4), c = 16.879(4) A, V= 4400.0(16) A3, space group P222, Z = 4, dcalc = 1.566 g-cm-3. The intensities of 14603 reflections were measured with a Bruker Nonius X8Apex equipped with a 4K CCD detector using graphite monochromated Mo-Ka radiation (A = 0.71073 A, 28 < 56.56°). 8627 independent reflections (R(int) = 0.0425) were used for the solution and refinement
5
8
of the structure. The semiempirical absorption correction was applied using intensities of equivalent reflections (SADABS). [7] The structure was solved by the direct method[8] and refined by full-matrix least squares against F2. Non-hydrogen atoms were found on difference Fourier maps and refined with anisotropic displacement parameters (except those for one disordered solvate dichloromethane molecule). The positions of hydrogen atoms were calculated and included in the refinement in isotropic approximation by the riding model. C-Cl bond lengths for one of the solvate dichloromethane molecules were restrained during the refinement. The final convergence factors were R1(F) = 0.0756 and wR2 = 0.234 for 4092 reflections with I > 2a(I) and 569 parameters. Goodness-of-fit (F2)=0.973 for all reflections included in the last stage of refinement. All calculations were made using the SHELXTL-97 program package.[9] CCDC reference number is 1036510.
6. Voloshin Y.Z., Zavodnik V.E., Varzatskii O.A., Belsky V.K., Palchik A.V., Strizhakova N.G., Vorontsov I.I., Antipin M.Y. Dalton Trans. 2002, 1193-1202.
7. Bruker AXS Inc., APEX2 (Version 1.08), SAINT (Version 7.03), and SADABS (Version 2.11). Bruker Advanced X-ray Solutions, Madison, Wisconsin, USA, 2004.
8. Burla M.C., Caliandro R., Camalli M., Carrozzini B., Casca-rano G.L., De Caro L., Giacovazzo C., Polidori G., Spagna R. J. Appl. Cryst. 2005, 38, 381-388.
9. Sheldrick G.M. SHELXS97 and SHELX97. Programs for the Refinement of Crystal Structure, Release 97-2, University of Gottingen, Germany, 1998.
10. Voloshin Y.Z., Kostromina N.A., Krämer R. Clathrochelates: Synthesis, Structure and Properties. Amsterdam: Elsevier, 2002. 432 p.
11. Zipse H. Top. Curr. Chem. 2006, 263, 163-189.
Received 27.11.2014 Accepted 10.12.2014
