摘要:

Mendeleev Communications Electronic Version, Issue 2, 2001 (pp. 43.84) Novel aromatic oxaborabenzene and 9-oxa-1,8-diboranaphthalene systems: an ab initio study Ruslan M. Minyaev,* Vladimir I. Minkin, Tatyana N. Gribanova and Andrei G. Starikov Institute of Physical and Organic Chemistry, Rostov State University, 344090 Rostov-on-Don, Russian Federation. Fax: +7 8632 28 5667; e-mail: minyaev@ipoc.rsu.ru 10.1070/MC2001v011n02ABEH001442 Ab initio [MP2(fu)/6-31+G**, MP2(fu)/6-311+G**] and DFT [B3LYP/6-31+G**, B3LYP/6-311+G**] calculations predict the aromatic stabilization of planar 1,2-oxaborabenzene and 9-oxa-1,8-diboranaphthalene. Aromaticity is an important theoretical concept of chemistry1,2 designed to predict and explain the stability and chemical properties of various, in particular, heterocyclic, compounds.The simplest way to form a heteroaromatic compound starting from the archetype aromatic system of benzene is to replace CH units or CC bonds in a ring by equal numbers of isoelectronic (e.g., N, O+, BH.) or 2¥�-electronic (NH, O, S) centres, respectively. With the use of a starting heteroaromatic system, a series of new heteroaromatics can be produced, some of which exhibit nonclassical structures that cannot be described in terms of Lewis structural formulae.An important question is whether (4n+2)¥�- electronic species thus formed remain persistent to possible distortions of the initial planar structure and display additional stability due to cyclic ¥�-electron delocalization. To solve this question, we performed ab initio calculations for pyrylium cation 1 and a series of six-membered oxaboraheterocycles 2.4 derived from 1.One of these currently unknown heteroaromatic systems, namely, 3, has a nonclassical structure. In addition, we studied another nonclassical oxadiboraheterocycle 5, which can be considered as the result of insertion of a 3¥�-electron HB.O.BH unit into peri-positions of the naphthalene ring.Here, we report the results of ab initio [MP2(fu)/6-31+G**, MP2(fu)/6-311+G**] and density functional theory [B3LYP/ 6-31+G**, B3LYP/6-311+G**]3,4 calculations for compounds 1.4 and bicyclic oxadiboraheterocycle 5, which is ¥�-isoelectronic to naphthalene. The aromatic character of these compounds was estimated using an approach similar to that used for the calculations of Dewar resonance energies.1 According to the calculations, the molecules of all compounds 1.5 possess planar structures and correspond to minima on the respective potential energy surfaces (PESs).Their geometry and energy characteristics are listed in Tables 1 and 2 and shown in Figures 1 and 2. 1,2-Oxaborabenzene 2 was predicted to be the most stable isomer in the family of oxaborabenzenes 2.4. The lengths of the BC bonds in cyclic systems 2.5 lie in the range 1.500. 1.529 A and are shorter than the standard BC bonds in aromatic compounds (~1.56 A).6 At the same time, these values are close to those for the BC bond lengths [1.514(2) A] found by X-ray diffraction analysis in the lithium salts of boratabenzene7 and boratastilbene.8 The calculated BO bond lenghts (1.393.1.398 A) are longer than the lengths of covalent bonds between tricoordinated boron and dicoordinated oxygen (~1.367 A).6 The CO bond lengths in 2.4 (1.337.1.358 A) are close to those in pyrylium salts (~1.35 A).5 Note that all CC bonds in bicyclic Table 1 Ab initio and DFT data for compounds 2.9.a aEtot (a.u.) is the total energy (1 a.u.= 627.5095 kcal mol.1); ZPE (a.u.) is the harmonic zero-point correction; l = 0, l is the number of imaginary harmonic frequencies; w1 (cm.1) is the smallest or imaginary harmonic vibration frequency.Structure, symmetry Method Etot ZPE w1 2, Cs MP2(fu)/6-31+G** MP2(fu)/6-311+G** B3LYP/6-31+G** B3LYP/6-311+G** .254.793351 .254.977024 .255.555651 .255.608372 0.085455 0.084222 0.084650 0.084318 318.9 310.5 332.4 331.5 3, Cs MP2(fu)/6-31+G** MP2(fu)/6-311+G** B3LYP/6-31+G** B3LYP/6-311+G** .254.724767 .254.909008 .255.485647 .255.538568 0.084965 0.083897 0.083936 0.083656 300.1 294.9 321.0 319.5 4, C2v MP2(fu)/6-31+G** MP2(fu)/6-311+G** B3LYP/6-31+G** B3LYP/6-311+G** .254.745222 .254.929331 .255.509674 .255.562959 0.085037 0.083996 0.084152 0.083847 266.2 263.3 283.3 283.7 5, C2v MP2(fu)/6-31+G** B3LYP/6-31+G** B3LYP/6-311+G** .395.301912 .396.515389 .396.592365 0.138469 0.138170 0.137680 68.0 114.8 115.3 6, Cs MP2(fu)/6-31+G** MP2(fu)/6-311+G** B3LYP/6-31+G** B3LYP/6-311+G** .254.667375 .254.853093 .255.438712 .255.494515 0.079462 0.078284 0.078724 0.078439 91.6 89.0 102.7 100.5 7, Cs MP2(fu)/6-31+G** B3LYP/6-31+G** B3LYP/6-311+G** .395.127733 .396.355221 .396.436157 0.130082 0.129496 0.129024 32.0 42.6 40.9 8, Cs MP2(fu)/6-31+G** MP2(fu)/6-311+G** B3LYP/6-31+G** B3LYP/6-311+G** .255.900031 .256.089025 .256.686618 .256.740321 0.107317 0.106044 0.104885 0.104585 231.6 228.7 231.8 229.4 9, Cs MP2(fu)/6-31+G** MP2(fu)/6-311+G** B3LYP/6-31+G** B3LYP/6-311+G** .255.865396 .256.054313 .256.650205 .256.706534 0.103566 0.102047 0.101263 0.101017 56.3 56.8 53.9 56.7 O BH O BH O B O H O B B H H 1, C2v 2, Cs 3, Cs 4, C2v 5, C2v 1.334 1.327 1.333 1.330 1.34 1.380 1.381 1.377 1.372 1.41 1.397 1.397 1.402 1.398 1.39 1.32 1.40 1.38 MP2(fu)/6-31+G** MP2(fu)/6-311+G** B3LYP/6-31+G** B3LYP/6-311+G** Experiment5 1.398 1.393 1.398 1.397 1.348 1.341 1.343 1.340 1.361 1.362 1.360 1.356 1.428 1.428 1.433 1.431 1.375 1.376 1.373 1.369 1.517 1.517 1.518 1.514 117.3 117.6 117.1 117.1 121.7 121.6 122.2 122.1 1, C2v 2, Cs 5, C2v O+ O B B 131.5 131.3 131.5 119.4 119.1 119.2 116.6 116.9 116.8 123.9 123.9 123.9 1.433 1.440 1.438 117.6 117.8 117.9 1.504 1.505 1.506 1.396 1.397 1.394 125.6 126.0 126.0 1.388 1.393 1.390 121.8 122.0 122.1 1.397 1.397 1.394 1.467 1.468 1.463 1.176 1.180 1.178 Figure 1 Geometry parameters of structures 1, 2 and 5 c alculat ed b y ab initio and DFT methods.The bond lengths and angles are given in angstrom units and degrees, respectively. OMendeleev Communications Electronic Version, Issue 2, 2001 (pp. 43.84) naphthalene-like system 5 are equalised, and they are similar to those in benzene (1.397 A).1 To evaluate the thermodynamic stability of the most stable cyclic (2) and bicyclic (5) systems, polyenes 6 and 7 were calculated.The symmetry of polyene 7 was predicted by MP2 calculations to be Cs with the dihedral angle OCCC about 2¡Æ, whereas DFT gives C2v symmetry. The lengths of double BC bonds in polyenes 6 and 7 (~1.400 A) are equal to the lengths of double BC bonds in organoboron compounds.9,10 To evaluate the stabilization due to cyclic ¥�-electron delocalization in 2 (.Earom), we applied the equation (1), where .E is the difference in the total energies of cyclic isomer 2 and polyene 6, and .EBO is the energy of the BO bond in 2 calculated as the difference between the total energies of ring-closed and open structures, 8 and 9, respectively. As is the case in 2, the BO bond in 8 is a part of the conjugated system, slightly distorted in 8 (dihedral angle between CO and CB bonds is approximately equal to 13¡Æ).However, as distinct from 2, no cyclic ¥�-electron delocalization is inherent to 8. As can be seen in Table 2, the .Earom for 2 are about 50. 56 kcal mol.1 depending on the computational level. These values are in the range (23.75 kcal mol.1) typical of the effect of cyclic ¥�-electron delocalization calculated for benzene using different methods and different reference systems.2 Similarly, the cyclic ¥�-electron delocalization energy for 5 was calculated according to the equation where .E(5 . 7) is the difference between the total energies of 5 and 7, and .EBO is the BO bond energy in 2. The values of .Earom(5) thus obtained lie in the range 55.66 kcal mol.1, and they are even higher than those for monocyclic system 2.In conclusion, the results of the calculations of hypothetical compounds 2 and 5, which are isoelectronic to benzene and naphthalene, respectively, demonstrate that they possess stable aromatic structures. This work was supported by the Russian Foundation for Basic Research (grant nos. 00-15-97320 and 01-03-32546).References 1 V. I. Minkin, M. N. Glukhovtsev and Baticity and Antiaromaticity: Electronic and Structural Aspects, Wiley, New York, 1994. 2 T. M. Krygowski, M. K. Cyranski, Z. Czarnocki, G. Hafelinger and A. R. Katritzky, Tetrahedron, 2000, 56, 1783. 3 M. J. Frish, G. W. Trucks, H. B. Schlegel, P. M.W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T.A. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. AlLaham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head- Gordon, C. Gonzalez and J. A. Pople, Gaussian-94, Revision B.3. Gaussian, Inc., Pittsburgh PA, USA, 1995. 4 M.W. Schmidt, K. K. Baldridge, J. A. Boatz, S. T. Elbert, M. S. Gordon, J. H. Jensen, S. Koseki, N. Matsunaga, K. A. Nguyen, S. J. Su, T. L. Windus, M. Dupuis and J. A. Montgomery, J. Comput. Chem., 1993, 14, 1347. 5 A. T. Balaban, A. Dinculescu, G. N. Dorofeenko, G. W. Fischer, A. V. Koblik and V. V. Mezheritskii, Pyrylium Salts: Syntheses, Reactions, and Physical Properties, Academic Press, New York, 1982. 6 F. H. Allen, O. Kennard, D. G. Watson, L. Brammer, A. G. Orpen and R. Taylor, J. Chem. Soc., Perkin Trans. 2, 1987, S. 1. 7 G. E. Herberich, B. Schmidt, U. Unglert and T.Wagner, Organometallics, 1993, 117, 8480. 8 B. Y. Lee, S. Wang, M. Putzer, G. P. Bartholomew, X. Bu and G. C. Bazan, J. Am. Chem. Soc., 2000, 122, 3969. 9 P. P. Power, Inorg.Chim. Acta, 1992, 198.200, 443. 10 W. J. Grigsby and P. P. Power, Chem. Eur. J., 1997, 3, 368. HB O HB O BH 6, Cs 7, Cs .Earom(2) = .E(2.6) . .EBO (1) B O H H H H 8, C1 HB O H H H H 9, C1 Table 2 Relative energies calculated by ab initio and DFT methods for compounds 2.7.a a.E (kcal mol.1) is the relative energy; .EZPE (kcal mol.1) is the relative energy including harmonic zero-point correction; .H and .G (kcal mol.1) are the relative enthalpy and the relative Gibbs free energy under standard conditions (P = 1 atm and T = 298.1 K).b.Earom. Structure, symmetry Metod .E .EZPE .H .G 2, Cs MP2(fu)/6-31+G** MP2(fu)/6-311+G** B3LYP/6-31+G** B3LYP/6-311+G** 57.3b 56.0b 50.5b 50.2b 0 0 0 3, Cs MP2(fu)/6-31+G** MP2(fu)/6-311+G** B3LYP/6-31+G** B3LYP/6-311+G** 43.0 42.7 43.9 43.8 42.7 42.5 43.5 43.4 42.7 42.5 43.5 43.4 42.7 42.5 43.5 43.4 4, C2v MP2(fu)/6-31+G** MP2(fu)/6-311+G** B3LYP/6-31+G** B3LYP/6-311+G** 30.2 29.9 28.8 28.5 29.9 29.8 28.5 28.2 30.0 29.8 28.6 28.3 29.9 29.7 28.9 28.6 5, C2v MP2(fu)/6-31+G** B3LYP/6-31+G** B3LYP/6-311+G** 65.9b 54.8b 55.6b 0 0 0 6, Cs MP2(fu)/6-31+G** MP2(fu)/6-311+G** B3LYP/6-31+G** B3LYP/6-311+G** 79.0 77.8 73.4 71.4 75.3 74.0 69.7 67.8 76.6 75.3 70.9 69.0 73.7 72.4 68.2 66.3 7, C2v MP2(fu)/6-31+G** B3LYP/6-31+G** B3LYP/6-311+G** 109.3 100.5 98.0 103.9 95.1 92.6 105.0 97.2 94.7 102.2 91.9 89.4 .Earom(5) = .E(5 . 7) . 2.EBO, (2) 3, Cs 4, C2v 6, Cs 7, C2v O B O O B B O B B 1.353 1.347 1.350 1.347 1.337 1.331 1.331 1.328 1.383 1.384 1.380 1.376 1.398 1.398 1.402 1.398 1.507 1.508 1.509 1.504 1.501 1.503 1.498 1.493 122.2 122.0 122.5 122.3 113.0 112.9 112.7 112.7 122.0 122.3 122.1 122.1 1.358 1.351 1.357 1.355 1.360 1.361 1.356 1.351 125.6 125.8 125.3 125.1 123.2 123.4 123.2 123.2 1.523 1.523 1.529 1.525 124.1 124.3 123.9 124.0 120.0 120.0 120.6 120.5 1.233 1.222 1.224 1.216 124.5 124.6 124.8 125.0 1.456 1.461 1.457 1.457 120.4 120.3 121.0 121.0 1.357 1.356 1.358 1.353 125.1 125.1 125.5 125.6 1.445 1.447 1.444 1.442 127.9 128.3 129.7 129.6 1.401 1.400 1.397 1.391 178.0 177.7 177.4 177.5 1.168 1.172 1.172 1.169 178.1 177.5 177.5 127.0 128.8 128.8 124.8 125.3 125.5 121.2 121.5 121.4 1.244 1.239 1.231 115.9 115.9 115.7 1.475 1.478 1.478 1.355 1.355 1.351 1.446 1.446 1.444 1.402 1.398 1.392 1.168 1.172 1.169 Figure 2 Geometry parameters of isomers 3, 4, and 6, 7 calculated by ab initio and DFT methods.The symmetry for 7 is predicted by MP2 and DFT calculations to be Cs and C2v, respectively. The bond lengths and angles are given in angstrom units and degrees, respectively. MP2(fu)/6-31+G** MP2(fu)/6-311+G** B3LYP/6-31+G** B3LYP/6-311+G** Received: 19th February 2001; Com. 01/1768

ISSN:0959-9436     

出版商:RSC    

年代:2001

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 2, 2001 (pp. 43.84) Unsymmetrical porphyrazines with annulated 1,2,5-thia(seleno)diazole and 3,6-diamyloxybenzene rings: synthesis, characterization and X-ray crystal structure of H2{XN2}{3,6-(OAm)2Bz}3Pz (X = S, Se) Evgeny V. Kudrik,a Elvira M. Bauer,b Claudio Ercolani,*b Angiola Chiesi-Villa,b Corrado Rizzoli,*c Anna Gaberkorna and Pavel A.Stuzhin*a a Department of Organic Chemistry, Ivanovo State University of Chemical Technology, 153460 Ivanovo, Russian Federation. Fax: +7 0932 37 7743; e-mail: stuzhin@icti.ivanovo.su b Dipartimento di Chimica, Universita degli Studi di Roma ¡®La Sapienza¡�, 00185 Roma, Italy. E-mail:claudio.ercolani@uniroma1.it c Dipartimento di Chimica Generale, Universita di Parma, 43100 Parma, Italy.E-mail: rizzoli@ipruniv.cce.unipr.it 10.1070/MC2001v011n02ABEH001372 Cyclotetramerization of a mixture of 3,4-dicyano-1,2,5-thiadiazole or 3,4-dicyano-1,2,5-selenodiazole with 3,6-diamyloxyphthalodinitrile gives new unsymmetrical porphyrazines with annulated 1,2,5-thia(seleno)diazole and 3,6-diamyloxybenzene rings; the structures of the 1:3 products H2{XN2}{3,6-(OAm)2Bz}3Pz (X = S, Se) has been elucidated by single-crystal X-ray diffraction.Unsymmetrically substituted porphyrazines combining electrondonor and electron-acceptor moieties capable of inducing strong ¥�-electron intramolecular polarization (¡®push-pull¡� porphyrazines) are of special interest because they might exhibit second-order non-linear optical properties.1 Recently, we have used S- and Se-containing monomeric precursors 1,2,5-thia(seleno)diazole- 3,4-dicarbonitriles 1, for the synthesis of new symmetrical phthalocyanine-like macrocycles having peripherally annulated five-membered electron-deficient heterocycles, i.e., tetrakis(1,2,5- thiadiazole)porphyrazines ({M[(SN2)4Pz]}, M = 2H, Mg, Mn, Co, Fe, Ni, Cu and Zn)2,3 and their Se analogues ({M[(SeN2)4Pz]}, M = 2H, Mg and Cu).4 In an extension of our work, efforts have successfully been directed to the synthesis of a new series of low-symmetry porphyrazines using mixtures of species 1 and 2,3-dicyano-5,7- diphenyl-6H-1,4-diazepine with phthalodinitriles 2.5 We report here on the synthesis and structural and spectroscopic characterization of the novel 1:3 species H2{XN2}{3,6-(OAm)2Bz}3Pz (3 X = S, 4 X = Se) obtained from 3,4-dicyano-1,2,5-thiadiazole 1a or 3,4-dicyano-1,2,5-selenodiazole 1b and 3,6-diamyloxyphthalodinitrile 2b.To our knowledge, these species are the first porphyrazine macrocycles with annulated thia- and selenodiazole rings whose structure has been elucidated by single-crystal X-ray diffraction analysis. The reaction of 1a or 1b with 2b in boiling n-amyl alcohol in the presence of lithium or magnesium amylate gives an olivegreen mixture of Li or Mg complexes of unsymmetrical porphyrazines and octa-substituted phthalocyanine, which were then demetallated with either acetic acid (Li) or trifluoroacetic acid (Mg).Column chromatography was used for the isolation of pure 1:3 compounds 3 and 4.¢Ó Well-shaped black crystals of these species for X-ray analysis were obtained by the slow diffusion of acetone in a CHCl3 solution.Unsymmetrical 2:2 and 3:1 species were also isolated and investigated. Crystal data for two macrocycles 3 and 4 show strong similarities.¢Ô Thus, the top and side views of S-containing species 3 are shown in Figure 1. Bond distances and angles within the macrocycle indicate an extended ¥�-electron delocalization and are consistent with the presence of the internal H atoms directly localized on N(3) and N(7) as shown by a difference Fourier map.The structural data (Table 1) of the annulated heterocycles in 3 and 4 are close to the average values found for other quasiaromatic systems containing 1,2,5-thiadiazole and 1,2,5-seleno- Table 1 Selected bond lengths (A) and bond angles (¡Æ) for compounds 3 and 4. Geometric parameter 3 X = S 4 X = Se X(1).N(9) 1.611(4) 1.774(4) X(1).N(10) 1.656(4) 1.840(4) N(9).C(2) 1.332(6) 1.336(6) N(10).C(3) 1.289(6) 1.273(6) C(1).C(2) 1.432(6) 1.427(6) C(2).C(3) 1.413(7) 1.435(7) C(3).C(4) 1.457(6) 1.462(6) N(1).C(1) 1.388(6) 1.396(6) N(1).C(4) 1.355(5) 1.357(5) N(3).C(5) 1.352(6) 1.345(6) N(3).C(12) 1.390(6) 1.412(6) N(5).C(13) 1.391(6) 1.393(5) N(5).C(20) 1.344(5) 1.344(5) N(7).C(21) 1.354(5) 1.337(6) N(7).C(28) 1.387(6) 1.388(6) N(9).X(1).N(10) 102.0(2) 96.4(2) C(1).N(1).C(4) 109.7(3) 110.1(4) C(5).N(3).C(12) 111.6(4) 111.9(4) C(13).N(5).C(20) 107.4(4) 107.3(4) C(21).N(7).C(28) 111.9(4) 111.9(4) ¢Ó Synthetic procedures.H2{SN2}{3,6-(OAm)2Bz}3Pz 3: the refluxing of 1a (0.9 g, 6.6 mmol) and 2b (1.8 g, 6 mmol) with lithium amylate (40 mmol, from 0.28 g of Li) in n-amyl alcohol (30 ml) leads to an olivegreen mixture, which, after addition of acetic acid (5 ml), was poured into acetone (150 ml) to give a dark green precipitate.It was filtered off, washed with acetone and extracted with benzene in a Soxhlet apparatus. The volume of the benzene extract was reduced, and it was chromatographed on aluminium oxide (Reakhim, chromatographic grade).The octaamyloxy substituted phthalocyanine H2Pc(OAm)8 was eluted with benzene, and 1:3 compound H2{SN2}{3,6-(OAm)2Bz}3Pz 3 with tetrachloroethane, from which it was precipitated with acetone (yield 46 mg, 2.2%). 1H NMR (300 MHz, CDCl3, 293 K) d: 7.66 (s, 2H), 7.65 (s, 2H, arom.) and 7.51 (s, 2H, arom.), 4.82 (t, 4H, ¥á-CH2), 4.78 (t, 4H, ¥á-CH2) and 4.67 (t, 4H, ¥á-CH2), 2.42 (m, 4H, ¥â-CH2) and 2.22 (m, 8H, ¥â-CH2), 1.75.1.40 (m, 24H, ¥ã-CH2, d-CH2), 1.11 (t, 6H, Me), 0.97 (t, 6H, Me) and 0.86 (t, 6H, Me), .0.25 (s, 2H, NH). UV.VIS [CH2Cl2, lmax/nm (log e)]: 329 (4.96), 408 sh, 458 (4.29), 520 sh, 663 sh, 699 sh, 730 (5.02), 766 (5.21).MS (FAB) m/z: 1040 [M + H]+ (100%).Found (%): C, 66.70; H, 7.33; N, 13.47; S, 2.56. Calc. for C58H74N10O6S (%): C, 67.03; H, 7.18; N, 13.48; S, 3.08. H2{SeN2}{3,6-(OAm)2Bz}3Pz 4: the synthetic procedure for 4 is similar to that used for 3 with the use of Mg amylate as a tetramerising agent and CF3COOH for demetallation. 1H NMR (300 MHz, CDCl3, 293 K) d: 7.51 (s, 2H, arom.), 7.50 (s, 2H, arom.) and 7.45 (s, 2H, arom.), 4.81 (m, 8H, ¥á-CH2) and 4.68 (t, 4H, ¥á-CH2), 2.40 (m, 4H, ¥â-CH2) and 2.21 (m, 8H, ¥â-CH2), 1.80.1.40 (m, 24H, ¥ã-CH2, d-CH2), 1.10 (t, 6H, Me), 0.94 (t, 6H, Me) and 0.87 (t, 6H, Me), .0.11 (s, 2H, NH).UV.VIS [CH2Cl2, lmax/nm (log e)]: 334 (5.11), 458 (4.26), 527 sh, 657 (4.52), 709 (4.88), 735 (4.90), 785 (5.19). MS (FAB) m/z: 1086 [M + H]+ (100%). Found (%): C, 63.85; H, 7.06; N, 12.95.Calc. for C58H74N10O6Se (%): C, 64.13; H, 6.87; N, 12.89. N X N NC NC R R' R NC NC 1 2 a X = S b X = Se a R = R' = H b R = OAm, R' = H c R = H, R' = But Scheme 1Mendeleev Communications Electronic Version, Issue 2, 2001 (pp. 43.84) diazole rings.6 As to species 3 (the following observations are also valid for species 4), the internal substantially planar N4 core shows significantly different distances for the opposite N atoms, N(1)¡�¡�¡�N(5) [3.861(4) A] and N(3)¡�¡�¡�N(7) [4.100(5) A].The observed planarity is consistent with the presence of two bifurcated hydrogen bonds involving H(3N) [N(1)¡�¡�¡�H(3N), 2.30 A N(5)¡�¡�¡�H(3N), 2.09 A; N(1)¡�¡�¡�H(3N)¡�¡�¡�N(5), 123¡Æ] and H(7N) atoms [N(1)¡�¡�¡�H(7N), 2.22 A; N(5)¡�¡�¡�H(7N), 2.19 A; N(1)¡�¡�¡�H(7N)¡�¡�¡�N(5), 122¡Æ]. The NC4N2S moiety and three isoindole units, distinguishable as containing N(1) and N(3), N(5) and N(7) atoms, respectively, although singly nearly planar, form, in the order given, dihedral angles with the N4 plane of 10.1(1), 4.7(1), 8.0(1), and 13.5(1)¡Æ.Noticeably, the NC4N2S moiety and the opposite isoindole ring, being nearly coplanar [dihedral angle of 10.6(ca. 0.66 A). The distortion from planarity of the entire macrocycle is its most interesting structural feature. Such a type of distortion is much less evident in the octa-substituted phthalocyanines H2Pc(OAmi)8 (ref. 7) and H2Pc(OAm)8.8 Hence, the observed distortion in the above species cannot be related to the steric interaction between adjacent alkoxy chains; rather, it might be assigned to the strong dipole polarization of the ¥�-electron system of the macrocycle arising from the ¡®push-pull¡� interaction between the electron-deficient thiadiazole ring and the strongly electron-donating alkoxy-substituted benzene rings.The intermolecular dipole.dipole interaction determines the crystal packing ¢Ô Crystal data for 3: C58H74N10O6S, M = 1039.3, monoclinic, space group P21/c, a = 17.314(1) A, b = 19.122(2) A, c = 17.794(1) A, b = = 103.07(1)¡Æ, V = 5738.6(8) A3, Z = 4, dcalc = 1.203 g cm.3, F(000) = = 2224, l(MoK¥á) = 0.71073 A, m(MoK¥á) = 1.08 cm.1.For 5354 unique observed reflections [I > 2s(I)] collected at 295 K on a Bruker AXS Smart 100 CCD (5 < 2q < 58¡Æ), the final R is 0.079 (wR2 = 0.188).Crystal data for 4: C58H74N10O6Se, M = 1086.2, monoclinic, space group P21/c, a = 17.305(2) A, b = 19.084(3) A, c = 17.882(2) A, b = = 102.90(2)¡Æ, V = 5756.5(14) A3, Z = 4, dcalc = 1.253 g cm.3, F(000) = = 2296, l(CuK¥á) = 1.54178 A, m(CuK¥á) = 13.35 cm.1. For 3419 unique observed reflections [I > 2s(I)] collected at 295 K on an Enraf-Nonius CAD-4 diffractometer (5 < 2q < 140¡Æ), the final R is 0.062 (wR2 = 0.170 for 8357 unique reflections having I > 0 used in the refinement).The structures of 3 and 4 were solved by direct methods and anisotropically refined for all non-hydrogen atoms except for the disordered ones. Some carbon atoms of the alkyl chains showed rather high thermal parameters indicating the presence of a disorder.The best fit was obtained by splitting the C(31).C(33), C(37), C(38), C(56).C(58) carbon atoms over two positions (called A and B) isotropically refined with site occupation factors for 3 of 0.5 for C(31).C(33), C(56).C(58); 0.6 and 0.4 for the A and B positions, respectively, of C(37), C(38); and for 4 of 0.5 for C(31). C(33); 0.7 and 0.3 for the A and B positions, respectively, of C(56), C(57); 0.65 and 0.35 for the A and B positions, respectively, of C(56).C(58). The hydrogen atoms associated to the nitrogen atoms and to the isoindole units were located from a difference Fourier map, while those associated to the aliphatic chains were put in geometrically calculated positions. All the H atoms were introduced as fixed contributors at the last stage of refinement (Uiso = 0.12 A2 for 3 and 0.10 A2 for 4).Atomic coordinates, bond lengths, bond angles and thermal parameters for both 3 and 4 have been deposited at the Cambridge Crystallographic Data Centre (CCDC). For details, see ¡®Notice to Authors¡�, Mendeleev Commun., Issue 1, 2001. Any request to the CCDC for data should quote the full literature citation and the reference number 1135/80.C(58A) C(57A) C(56A) C(55) C(54) O(6) C(26) C(27) C(25) C(24) C(23) C(22) O(5) C(49) C(50) C(51) C(52) C(53) N(8) C(28) N(7) H(7N) C(21) N(6) C(20) N(5) C(13) C(14) C(19) C(15) C(16) C(17) C(18) O(4) C(44) C(45) C(46) C(47) C(48) O(3) C(39) C(40) C(41) C(42) C(43) C(1) C(2) C(3) C(4) N(1) N(9) N(10) S(1) N(2) C(5) C(6) C(11) C(12) N(4) N(3) H(3N) C(33A) C(32A) C(31A) C(30) C(29) O(1) C(7) C(8) C(9) C(10) O(2) C(34) C(35) C(36) C(37A) C(38A) Figure 1 Top and side views of compound 3.Disorder associated to some alkyl chains has been omitted for clarity. O(6) O(5) N(8) N(6) N(9) N(10) S(1) N(1) N(2) O(1) N(3) N(7) N(5) N(4) O(2) O(3) O(4) a b c Figure 2 Crystal packing in 3. Alkyl chains are omitted for clarity.Absorption 334 330 733 785 306 329 717 766 a b c d 400 600 800 l/nm Figure 3 UV.VIS spectra of (a) 3 and (b) 4 and their deprotonated species (c and d, respectively) in CH2Cl2 (a, b), in the presence of 1% tbaOH in CH2Cl2 (c, d).Mendeleev Communications Electronic Version, Issue 2, 2001 (pp. 43.84) . the molecules are arranged in centrosymmetric parallel pairs (Figure 2).As a consequence, the thiadiazole ring of one molecule in the pair is located over the centrosymmetric isoindole unit. The sterically less crowded conformation allows the N4 cores of the molecules in a pair to approach at an average interplanar distance of 3.273(15) A [3.265(11) A for the Se analogue]. The UV.VIS spectra of 3 and 4 in CH2Cl2 [Figure 3(a),(b)] are characteristic for highly conjugated porphyrazine chromophores with unsymmetrically attached strongly electron-donating substituents: in addition to the B-band in the UV region (329 nm for 3 and 334 nm for 4), intense split Q-bands are observed in the near IR region (700.800 nm).In the case of 3, the maximum of the long-wave Qx component is found at 766 nm, whereas for 4, owing to the presence of the less electronegative Se atom, the corresponding absorption is shifted bathochromically to 785 nm.Deprotonation of 3 and 4 and formation of the corresponding dianions occurring in the presence of tetrabutylammonium hydroxide, (tbaOH), whilst leaving unchanged the C2v symmetry of the chromophore, results [Figure 3(c),(d)] in a hypsochromic shift of the Qx component (to 717 nm for 3 and 733 nm for 4) and associated decrease of the splitting of the Q-band (especially for 3).In the UV region, along with the B-band (306 nm for 3 and 330 nm for 4), a better resolved less intense band due to the n ¢ç ¥�* transition appears at ca. 405 nm. A progressive increase in the acidity of the medium results, as is illustrated for 3 in Figure 4, in the gradual bathochromic shifts of the Q-band maxima (766 ¢ç 856 ¢ç 897 ¢ç 1008 ¢ç 1117 nm) due to the consequent acid.base interaction with all four meso-nitrogens and appearence of four corresponding acid forms.We are grateful to A. D¡�Arcangelo (¡®Tor Vergata¡�, Rome) for the assistance in measuring the mass spectra. This work was supported by the Ministry of Education of the Russian Federation (grant no.SPb 97-0-9.4-362) and by the Italian grant Murst 9903263473. References 1 G. de la Torre, P. Vazques, F. Agullo-Lopez and T. Torres, J. Mater. Chem., 1998, 8, 1671. 2 P. A. Stuzhin, E. M. Bauer and C. Ercolani, Inorg. Chem., 1998, 37, 1533. 3 E. M. Bauer, D. Cardarilli, C. Ercolani, P. A. Stuzhin and U. Russo, Inorg. Chem., 1999, 38, 6414. 4 E. M. Bauer, C. Ercolani, P. Galli, I. A. Popkova and P. A. Stuzhin, J. Porphyrins Phthalocyanines, 1999, 3, 371. 5 C. Ercolani, E. V. Kudrik, S. Moraschi, I. A. Popkova and P. A. Stuzhin, in 1st International Conference on Porphyrins and Phthalocyanines, ICPP-1, Dijon, 2000, p. 575. 6 A. Gieren, H. Betz, T. Hubner, V. Lamm, R. Neidlein and D. Droste, Z. Naturforsch. B, 1984, 39, 485. 7 M. J. Cook, J. McMurdo and A. K. Powell, J. Chem. Soc., Chem. Commun., 1993, 903. 8 C. Ercolani, E. V. Kudrik, C. Rizzoli and P. A. Stuzhin, unpublished results. Absorption 1 0 500 1000 l/nm 766 856 897 1008 1117 a b c d e Figure 4 UV.VIS spectra of (a) H2{SN2}{3,6-(OAm)2Bz}3Pz (6¡¿10.6 mol dm.3) and (b).(e) protonated species in: (a) CH2Cl2, (b) 5% HCOOH in CH2Cl2, (c) HCOOH, (d) 35% H2SO4 in AcOH, (e) 96% H2SO4. The Q-band maxima are indicated on the graph, the B-band maxima are 329, 317, 312, 293 and 296 nm for spectral curves (a).(e), respectively. Received: 7th September 2000;

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Mendeleev Communications Electronic Version, Issue 2, 2001 (pp. 43–84) Simulation of anion associates Vitalii Yu. Kotov Higher Chemical College, Russian Academy of Sciences, 125047 Moscow, Russian Federation. Fax: +7 095 200 4204 10.1070/MC2001v011n02ABEH001422 According to the proposed model of anion associates, two singly charged cations would suffice to retain two multiply charged anions in close contact.The formation of ion pairs cannot be neglected even in dilute electrolyte solutions. Thus, at 298 K, 46% anions in a 4×10–3 M K4[Fe(CN)6] solution are associated.1 In more concentrated solutions, associates that contain two or more potassium ions per hexacyanoferrate ion are formed. In concentrated solutions with salt concentrations higher than 0.3 mol dm–3, anion associates in which two complex anions occur at a contact distance can be formed.2–4 In this work, anion associates were simulated in order to obtain information on a minimum number of cations required for their occurrence and on optimum distances between likely charged ions in such associates.In the absence of cations from an associate, negatively charged ions undergo Coulomb repulsion, and the interaction is unfavourable in terms of energy.In the general case, the addition of a singly charged cation also does not result in a stable system. The presence of the second singly charged cation (this situation corresponds to the interaction between two ion pairs) can stabilise the system as a rhombus. Likely charged ions are arranged at the opposite vertexes of the rhombus (Figure 1).The distances and angles between the centres of charged particles in this associate significantly depend on ionic charges. Let us consider the case when the charges of spherical multiply charged anions are equal (z1 = z2). The resultant of forces acting on each of the negatively charged particles, which is aligned with the centre-line between anions, can be written as the difference where A is a constant for a given solvent, d is the distance between the centres of anions, and a is the angle between the centres of two negatively charged particles and a positively charged particle (anion–anion–cation).The resultant force for either of the positively charged particles is The positive or negative sign of F reflects the fact that ions repel each other or have an attraction for each other, respectively.Both singly charged anions and singly charged cations have an attraction for each other in the angle range from 30 to 60° [Figure 2(a)]. With an increase in the negative charge of the anion, this range is shifted towards small angles, and it is 18–37° for a system containing two four-charged anions [Figure 2(d)].In the latter case, the angle at which the attracting forces of anions and cations are equal (F1 = F2) is 26°. To find an optimum distance between the anions in this system, the distance between oppositely charged ions should be known. According to structure data,5 the shortest distance between the hexacyanoferrate ions and potassium ions in ion pairs is equal to 4.07 Å.Then, the optimum distance between the anions in a four-ion associate is 4.07·2·cos 26° = 7.3 Å. For triply charged ions (F1 = = F2 at a = 31°) at the same distance between oppositely charged ions, the distance between the anions in an associate is 7.0 Å. Thus, two singly charged can retain two multiply charged anions in contact at a distance close to 7 Å by the cooperative interaction of ions.The conclusion drawn for the associate that consists of spherical ions can be extended to real structures. Figure 3 illustrates the results of optimising the geometry of the 2NH4 +, 2[RhCl6]3– system containing two octahedral anions and two tetrahedral cations by the ZINDO/1 method.6 Complex anions in this system are arranged along the twofold axes of symmetry of each other.The N–Rh–Rh angle is 28°, which is close to the values obtained from the equality of F1 and F2. The introduction of additional ammonium cations to the simulated system does not significantly change the arrangement of ions in the 2NH4 +, 2[RhCl6]3– unit. This fact suggests that two cations will suffice for binding two anions. Note that values close to 7.0 Å were obtained previously7 by evaluating the distances between anions in anion associates containing hexacyanometallate ions from the rate constant of electron transfer between anions, the dependence of the rate of electron transfer on the ionic strength of solution and the stability constant of the anion associate. The conclusion that the cooperative interactions of ions in solution results in contact of likely charged ions is supported by the fact that the calculated distances between anions in four-ion associates are close to the shortest distances between anions in crystals, where anions are in contact because of the cooperative interactions of ions.Thus, d = 7.05 Å for K4[Fe(CN)6]·3H2O, and d = 6.98 Å for (NH4)2[IrCl6]. The mutual arrangement of ions in these crystals is similar to that shown in Figure 3.F1 = Az1 2 /d2 – 8Az1 cos3 a/d2, F2 = A cot2 a/d2 – 8Az1 cos a2 sin a/d2. Figure 1 Ion associate model. + n– + n– 8 6 4 2 0 –2 –4 –6 10 20 30 40 50 60 70 80 90 Fd2/A a 8 6 4 2 0 –2 –4 –6 10 20 30 40 50 60 70 80 90 Fd2/A a (a) (b) Figure 2 Relative resultant force acting on each of the likely charged particles in a system of four ions (squares and circles indicate multiply charged anions and singly charged cations, respectively) as a function of the angle between the centres of two negatively charged particles and a positively charged particle: (a) z = –1, (b) z = –2, (c) z = –3, and (d) z = –4. 5 0 –5 –10 –15 10 20 30 40 50 60 70 80 90 Fd2/A a (c) 5 0 –5 –10 –15 10 20 30 40 50 60 70 80 90 Fd2/A a (d) Figure 3 Result of optimising the geometry of the 2NH4 +, 2[RhCl6]3– system by the ZINDO/1 method.Mendeleev Communications Electronic Version, Issue 2, 2001 (pp. 43–84) References 1 W. A. Eaton, P. Geor ge and G. I. H. Hanania, J. Phys. Chem., 1967, 71, 2016. 2 R. Billing and D. E. Khostariya, Inorg. Chem., 1994, 33, 4038. 3 D. E. Khostariya, A. M. Kjaer, T. A. Marsagishvili and J. Ulstrup, J. Phys. Chem., 1991, 95, 8797. 4 D. E. Khostariya, R. Meusinger and R. Billing, J. Phys. Chem., 1995, 99, 3592. 5 S. A. Kostina, A. B. Ilyukhin, B. V. Lokshin and V. Yu. Kotov, Mendeleev Commun., 2001, 12. 6 M. C. Zer ner, Rev. Comput. Chem., 1991, 2, 313. 7 V. Yu. Kotov and G. A. Tsirlina, Mendeleev Commun., 1999, 181. Received: 15th January 2001; Com. 01/1748

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Mendeleev Communications Electronic Version, Issue 2, 2001 (pp. 43.84) X-ray diffraction study of DL-1,4-dimethyl-2,5-dioxabicyclo[2.2.1]heptane-3,6-dione: the sense of twist and folding Igor V. Vystorop,a Konstantin A. Lyssenkob and Remir G. Kostyanovsky*c a Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russian Federation. Fax: +7 096 515 3588; e-mail: vystorop@icp.ac.ru b A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 117813 Moscow, Russian Federation. Fax: +7 095 135 5085; e-mail: kostya@xray.ineos.ac.ru c N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow, Russian Federation. Fax: +7 095 938 2156; e-mail: kost@center.chph.ras.ru 10.1070/MC2001v011n02ABEH001421 The title dilactone exists in a crystalline state (110 K) as enantiomeric synchro-(+,+)-(R,R)- and synchro-(.,.)-(S,S)-twist forms (t0 = |1.8¡Æ|) with the retention of C2 symmetry, linked by infinite zig-zag heterochiral chains (space group C2/c) by mutual H-bonds of the CH2.H¡�¡�¡�O=C type.Zelinsky¡�s dilactone 1 has a long history of interest in the synthesis,1.5 optical resolution,6 spectroscopy (CD, VCD)6,7 and theoretical (MP2/6-31G*)6 studies.However, its structure was not determined by X-ray diffraction (XRD), MW or GED in contrast to its bridged homologue 3 (XRD).8 At the same time, the geometry of norbornane 5 and norborna-2,5-diene 6, possessing the parent bicyclo[2.2.1]frame rigid system, was investigated thoroughly by the XRD analysis of their plastic crystals.9,10 Dilactone 1 also tends to form plastic crystals owing to its globular shape.11 However, the polarity of 1 and intermolecular H-bonds prevent such a formation.Nevertheless, in an effort to increase the crystal structure ordering, the XRD analysis of 1¢Ó was performed at a low temperature. The aim of this study was to compare the structural characteristics of 1 with available XRD and theoretical data for bicycles 3,8,12 610 and ¥ã-lactones.13,14 [XRD data for the structure of 2 are unknown (see refs. 5, 7) and those for 5 are unaccurate9].The main characteristic feature of the molecular structure of dilactone 1 with C2 symmetry in a crystal¢Ó is the sense of its skeleton twist as synchro-(+,+) (t0 = 1.8¡Æ) and synchro-(.,.) (t0 = .1.8¡Æ) for (R,R)- (Figure 1) and (S,S)-enantiomeric forms, respectively, which is in accordance with the ab initio model (MP2/6-31G*, t0 = 0.9¡Æ)6 of enantiomer (R,R)-1.The analogous twist character for a bicyclo[2.2.2]skeleton was observed for dilactone (¡¾)-3 in a crystal without the retention of C2 symmetry (t0 = |4.4| and |4.6|¡Æ)8 and confirmed by DFT (B3LYP/6-31G*) models of homochiral dilactones (R,R)-3 and (R,R)-4 [a single synchro-(+,+,+)-twist form, t0 = 2.9¡Æ (3), 3.1¡Æ (4)].12 As expected, the planarity of the lactone group [C.C(O).O.C, t0] and the folding of the dilactone ring [the fold angle between mean planes of lactone groups is f = 109.0¡Æ (XRD),¢Ó 110.2¡Æ (MP2)6] in 1 increased as compared with 3 [f = 124.9¡Æ (XRD)8].Considering the framework of dilactones 1, 2 as a fusion of two ¥ã-lactone rings in the envelope form, it is of interest to compare the sense of their lactone groups twist with that in ¥ã-lactones, which mainly exist in the envelope conformation (XRD).14 However, neither statistical XRD data14 of ¥ã-lactones nor an experimental study of ¥ã-butyrolactone 7 by MW spectroscopy15 cannot evaluate the character of twist related to the enantiomeric conformation16 of the ¥ã-lactone ring.For this reason, we performed DFT calculations¢Ô of 1, 2 and 7, according to which the lactone group of the enantiomeric envelope conformation of a molecule of 7 is reversely twisted (t0 = .2.1¡Æ) as compared with that of the ¥ã-lactone envelope conformation in (R,R)-1 (t0 = 1.2¡Æ), 2 (t0 = 1.4¡Æ) of the same enantiomeric form. This interesting effect is displayed in chiroptical properties, namely in the opposite sign of the n.¥�* Cotton effect (CE) of (R,R)-16 and ¥ã-lactones17 with the same enantiomeric conformation ring (see 7).Previous correlations17,18 between the sign of the n.¥�* CE and the ¥ã-lactone ring enantiomeric conformation did not take into account the sense of twisting of the lactone group. On the other hand, a correlation between the twist sign of the C.NH.CO.C system in lactams and the sign of the n.¥�* CE was a subject of special interest,18 and had an opposite relationship [(+)-t0, (+)-CE (n.¥�*) and vice versa]18 as compared with that for lactones.As can be seen in Figure 1, a strong compression of endocyclic bond angles at bridgehead C(1)/C(4) [¥Òwendo = 303.5¡Æ (XRD), 305.3¡Æ (MP2)6 and 304.7¡Æ (DFT)¢Ô] and carbonyl C(3)/ ¢Ó Crystallographic data for 1: at 1 10(2) K c ry stals of C 7H8O4 1 are monoclinic, space group C2/c, a = 10.379(16) A, b = 8.943(15) A, c = 8.477(13) A, b = 114.22(6)¡Æ, V = 717.6(19) A3, Z = 4, M = 156.13, dcalc = = 1.445 g cm.3, m(MoK¥á) = 1.20 cm.1, F(000) = 328.Intensities of 1236 reflections were measured on a Smart 1000 CCD diffractometer at 110 K [l(MoK¥á) = 0.71072 A, w-scans with a 0.3¡Æ step in w and 10 s per frame exposure, 2q < 55¡Æ], and 618 independent reflections (Rint = 0.0157) were used in the further refinement. The structure was solved by a direct method and refined by the full-matrix least-squares technique against F2 in the anisotropic.isotropic approximation.Hydrogen atoms were located from the Fourier synthesis and refined in the isotropic approximation. The refinement converged to wR2 = 0.1302 and GOF = 1.091 for all independent reflections [R1 = 0.0447 was calculated against F for 546 observed reflections with I > 2s(I)]. The number of the refined parameters was 67 (the ratio of the refined parameters for observed reflections was more than 7).All calculations were performed using SHELXTL PLUS 5.0 on IBM PC AT. Atomic coordinates, bond lengths, bond angles and thermal parameters have been deposited at the Cambridge Crystallographic Data Centre (CCDC). For details, see ¡®Notice to Authors¡�, Mendeleev Commun., Issue 1, 2001. Any request to the CCDC for data should quote the full literature citation and the reference number 1135/81.O O R R O O 1 2 3 4 5 6 7 8 O O R R O O t0 t0 O O 1 1 2 2 3 4 t0 1 R = Me 2 R = H 3 R = Me 4 R = H 5 7 6 9 ¢Ô The geometries of dilactones (R,R)-1, 2, bicycle 6 and ¥ã-butyrolactone 7 were completely optimised at the density functional theoretical level (DFT) with the conventional 6-31G* basis set using procedures implemented in the Gaussian 94 program system.21 For the DFT calculations, a hybrid approach based on Becke¡�s three parameter functional22 was employed (Becke3LYP). Convergence criteria for the density matrix were set to 1¡¿10.8.All calculations were performed on an SGI Power Challenge computer. The calculated energies (in hartrees) and dipole moments (in debyes) are .572.46501 and 4.78 (1), .493.81629 and 4.63 (2), .271.47728 (6), .306.49261 and 4.48 (7), respectively.Mendeleev Communications Electronic Version, Issue 2, 2001 (pp. 43.84) C(6) carbon atoms [105.5¡Æ (MP2)6 and 105.6¡Æ (DFT)¢Ô] beyond their normal values (109.5¡Æ and 120¡Æ) leads to an increase in the p- and s-character of these carbon hybrid orbitals in ¡®internal¡� and ¡®external¡� bonds and hence to lengthening and shortening of these bonds, respectively.A comparison of the crystal structure of 1 with statistical XRD data for ¥ã-lactones [C(1).O(1) 1.350(9) A, C(1)=O(2).515(7) A, C(4). O(1) 1.462(8) A; see numbering for 7]14 and bonds of the types (C)3.C.Me (1.534 A) and (C)3.C.CH2.C (1.538 A)13 confirms this tendency, except for shortened C(7).C(1)/C(4) bridged bonds of 1 (Figure 1), whose length corresponds to the average XRD value for C sp3.C sp3 type bonds (1.530 A).13 The shortening of C(7).C(1)/C(4) bridged bonds (C sp3.C sp3 type) as compared with C(1).C(6)/C(4).C(3) bonds (C sp3.C sp2 type) of the dilactone ring of 1 in a crystal, is in agreement with the MP2 (1.527 A and 1.531 A)6 and DFT models (1.537 A and 1.543 A).¢Ô Interestingly, for norbornadiene 6, the sequence of bond lengths of the C sp3.C sp3 [bridged C(7).C(1)/C(4) bonds: 1.555(1) (XRD),10 1.552 (MP2)10 and 1.560 A (DFT)¢Ô] and C sp3.C sp2 types [C(1).C(2)/C(6) bonds: 1.536(1) (XRD),10 1.533 (MP2)10 and 1.545 A (DFT)¢Ô] is reverse, as compared with dilactone 1.On the other hand, an increase in the folding of the dilactone ring boat of 1 {decreased C(1)¡�¡�¡�C(4) distance [2.216 (XRD), 2.220 (MP2)6 and 2.213 A (DFT)¢Ô] and the angle of folding [f = 110.7¡Æ (DFT)¢Ô]} and almost equal characterictic top angles C(1).C(7).C(4) [92.8(2)¡Æ (XRD), 92.2¡Æ (MP2)6 and 92.1¡Æ (DFT)¢Ô] are observed, as compared with the boat of a sixmembered ring [C(1)¡�¡�¡�C(4) 2.247 A, f = 115.1¡Æ (DFT)¢Ô] and the bridged angle value in norbornadiene 6 [C(1).C(7).C(4) 92.5(1)¡Æ (XRD), 92.4¡Æ (MP2)10 and 92.0¡Æ (DFT)¢Ô], respectively.An increased folding of the boat ring in 1 should also result in an increased strain in the skeleton of 1, as compared to 6. However, the strained folded frame structure of dilactone 1 is probably stabilised by the dominated through-bond intramolecular interaction of ester groups,19 in spite of preferred throughspace intramolecular interactions between two ethylenic moieties10,20 in 6.Thus, the experimental sense of twist of dimethyl-dilactones (1¢Ó, 38) in crystals is confirmed by ab initio models for 1.4 in a free state. In addition to data on the torsional energy surface of (R,R)-216 and (R,R)-412 obtained by the MM2(91) method, these results show that the above twist sense for lactone groups in bridged dilactones 1.4 is a common tendency to form a groundstate conformation. The preference of the found enantiomeric forms over the possible diastereomeric synchro-(+,+)-(R,R)- and synchro-(.,.)-(S,S)-twist forms can be explained by more favourable intramolecular dipole.dipole interaction of C=O groups.12,16 This work was supported by the Russian Foundation for Basic Research (grant nos. 00-03-32738 and 00-03-81187BEL) and INTAS (grant no. 99-0157). References 1 N. D. Zelinsky , Ber. Dtsch. Chem. Ges., 1891, 24, 4006. 2 K. Auwers and H. Kauffmann, Ber. Dtsch. Chem. Ges., 1892, 25, 3221. 3 R. Fittig, Liebigs Ann. Chem., 1907, 353, 3221. 4 A. R. Mattoks, J. Chem. Soc., 1964, 4845. 5 R. G. Kostyanovsky, V.P. Leshchinskaya, Yu. I. El¡�natanov, A. E. Aliev and I. I. Chervin, Izv. Akad. Nauk SSSR, Ser. Khim., 1989, 408 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1989, 38, 355). 6 I. V. Vystorop, A. N. Utienyshev, V.M. Anisimov and R. G. Kostyanovsky, Mendeleev Commun., 1999, 229. 7 A. Rauk, J. L. McCann, H. Wieser, P. Bour, I. V. Vy storop, Yu. I. El¡�natanov and R. G.Kostyanovsky, Can. J. Chem., 1998, 76, 717 (correction: Can. J. Chem., 1998, 76, 1931). 8 A. B. Zolotoi, S. V. Konovalikhin, L. O. Atovmyan, I. V. Vystorop, Yu. I. El¡�natanov and R. G. Kostyanovsky, Izv. Akad. Nauk, Ser. Khim., 1994, 1965 (Russ. Chem. Bull., 1994, 43, 1854). 9 A. N. Fitch and H. Jobic, J. Chem. Soc., Chem. Commun., 1993, 1516. 10 J. Benet-Buchholz, T. Haumann and R.Boese, Chem. Commun., 1998, 2003. 11 J. Timmermans, J. Phys. Chem. Solids, 1961, 18, 1. 12 A. Rauk, C. Jaime, I. V. Vystorop, V.M. Anisimov and R. G. Kostyanovsky, J. Mol. Struct. (Theochem.), 1995, 342, 93. 13 (a) F. H. Allen, O. Kennard, D. G. Watson, L. Brammer, A. G. Orpen and R. Taylor, J. Chem. Soc., Perkin Trans. 2, 1987, 12, S.1; (b) International Tables for Crystallography, ed.A. J. C. Wilson, Kluwer Academic Publishers, Dordrecht, 1992, vol. C, pp. 685.706. 14 W. Scheizer and J. Dunitz, Helv. Chim. Acta, 1982, 65, 1547. 15 J. C. Lopez, J. L. Alonso, R. Cervellati, A. D. Esposti, D. G. Lister and P. Palmieri, J. Chem. Soc., Faraday Trans., 1990, 86, 453. 16 I. V. Vystorop, A. Rauk, C. Jaime, I. Dinares and R. G. Kostyanovsky, Khim. Geterotsikl.Soedin., 1995, 1479 [Chem. Heterocycl. Compd. (Engl. Transl.), 1995, 31, 1280]. 17 A. F. Beecham, Tetrahedron Lett., 1968, 3591. 18 D. N. Kirk, Tetrahedron, 1986, 42, 777. 19 D. C. Frost, N. P. C. Westwood and N. H. Werstiuk, Can. J. Chem., 1980, 58, 1659. 20 R. Gleiter and W. Schafer, Acc. Chem. Res., 1992, 23, 369. 21 M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B.G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, J. Cioslowski, B. B. Stefanov, A. Manayakkara, M. Challacombe, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J.P. Stewart, M. Head-Gordon, C. Gonzalez and J. A. Pople, Gaussian 94, Revision D.1, Gaussian, Inc., Pittsburgh PA, 1995. 22 (a) A. D. Becke, J. Chem. Phys., 1993, 98, 5648; (b) A. D. Becke, Phys. Rev. A, 1988, 38, 3098. H(7B) C(7) H(7A) H(11A) C(11) H(11B) H(11C) C(4) C(3) O(8) O(2) O(5) C(6) O(9) C(1) H(10C) C(10) H(10A) H(10B) Figure 1 Molecular structure of dilactone 1. Atoms C(4), O(5), C(6), O(9), and C(11) are symmetrically equivalent to atoms C(1), O(2), C(3), O(8), and C(10), respectively. Selected bond lengths (A): C(1).O(2) 1.491(3), C(1).C(6) 1.536(3), C(1).C(7) 1.530(3), C(1).C(10) 1.490(3), O(2).C(3) 1.366(3), C(3).O(8) 1.193(2); selected bond and dihedral angles (¡Æ): C(1).O(2).C(3) 106.3(1), C(1).C(6).O(5) 106.3(2), C(1). C(7).C(4) 92.8(2), O(2).C(1).C(6) 102.6(2), O(2).C(1).C(7) 101.7(2), O(2).C(1).C(10) 110.0(2), C(6).C(1).C(7) 99.3(2), C(6).C(1).C(10) 117.5(2), C(7).C(1).C(10) 123.0(2), O(2).C(3).O(8) 123.2(2), C(4). C(3).O(8) 130.4(2), C(1).O(2).C(3).C(4) (t0) 1.8, C(1).O(2).C(3).O(8) .179.8. O(8) C(10) Figure 2 Hydrogen-bonded heterochiral chain in the crystal structure of 1. Geometry parameters of short C(10).H(10B)¡�¡�¡�O(8) contacts: H¡�¡�¡�O 2.40 A, C¡�¡�¡�O 3.393(3) A, C.H¡�¡�¡�O 155¡Æ, H¡�¡�¡�O=C 122.7¡&A

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Mendeleev Communications Electronic Version, Issue 2, 2001 (pp. 43–84) Functionalization of buckminsterfullerene by hypervalent iodine reagents Viktor V. Zhdankin,*a Kari J. Hanson,a Alexey E. Koposov,a Erin Blomquista and Rik R. Tykwinskib a Department of Chemistry, University of Minnesota, Duluth, Minnesota 55812, USA. E-mail: vzhdanki@d.umn.edu b Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2 Canada.E-mail: rik.tykwinski@ualberta.ca 10.1070/MC2001v011n02ABEH001413 Fullerene C60 reacts with hypervalent iodine reagents (azido-, acetoxy-, sulfonyloxy- and chloroiodanes) under mild conditions with the formation of the appropriate functionalized fullerenes. There is currently a significant interest in the chemistry of fullerenes and their derivatives.1 The common procedures for fullerene functionalization are based on the ability of fullerenes to accept extra electrons in reactions with reducing reagents (such as alkali metals) or nucleophiles (for example, the Bingel reaction). Functionalization of fullerenes with electrophilic reagents has also been reported.2 Bromine reacts with C60 to afford the adducts C60Br6, C60Br8 and C60Br24, depending on the reaction conditions.2(a),(b) Fullerenes can be chlorinated,2(c)–(e) fluorinated, 2( f ),(g) nitrated2(h) and cyclosulfated2(i) by reactions with the appropriate electrophilic reagents.Preliminary results on the functionalization of C60 by hypervalent iodine reagents will be discussed here. In the last few years, organic derivatives of hypervalent iodine have found broad synthetic applications as mild oxidising and electrophilic agents for functionalization of various organic substrates.3 We have investigated the reaction of C60 with hypervalent iodine azide PhI(N3)2 1, which was generated in situ from iodosobenzene and azidotrimethylsilane.The PhIO/2TMSN3 combination was shown to be a premier reagent for azidation of various organic substrates.4 The reaction of C60 with 6.1 equivalents of PhI(N3)2 was carried out under typical azidation conditions4 in a solution of o-dichlorobenzene (Scheme 1).† After stirring for about 2 h at –20 °C, the reaction mixture changed from the original purple solution to a dark brown mixture.The solvent and all volatile products were removed in a high vacuum to afford azide 2 as a black highly explosive powder.The IR spectrum of this powder displayed a very intense absorption peak at 2100 cm–1, typical of organic azides. NMR spectroscopy of this product was difficult to perform due to the very low solubility in all common NMR solvents. The 1H NMR spectrum of the low-concentration sample displayed very weak signals between d 7.6 and 7.2 ppm, which are likely attributed to residual iodobenzene trapped in the solid product.Elemental analysis of product 2 showed a nitrogen content of 21.27–21.34%, which is consistent with the average presence of six azido groups in the molecule of product 2·PhI.‡ Due to the low stability of the product, we failed to obtain meaningful results from mass-spectrometric measurements.Azidation of C60 with one equivalent of PhI(N3)2 under similar conditions resulted in the formation of C60(N3)2 as indicated by elemental analysis of the product. A similar reaction of C60 with hypervalent iodine triflate 3 (Zefirov’s reagent) afforded triflate 5 as the final product resulting from the partial hydrolysis of initial bis-triflate 4 (Scheme 2).§ Product 5 was obtained as a black solid after removal of the solvent and volatile by-products in a high vacuum.The IR spectrum of 5 displayed a very broad absorption band at 3233 cm–1 characteristic of hydroxylated fullerenes.2(i) The characteristic absorptions of covalent triflate were present at 1250, 1179 and 1033 cm–1. A broad signal of the hydroxy group was observed at d 1.58. Elemental analysis of the product showed a sulfur content of 2.8%, which is consistent with the presence of one triflate in the molecule of 5.The reaction of C60 fullerene with (diacetoxy)iodobenzene 6 was carried out in tetrachloroethane at 80 °C (Scheme 3). The reaction was monitored using TLC by detecting the disappearance of the initial C60 in the mixture. After the reaction was complete, the solvent and all volatile products were removed in a high vacuum to afford product 7 as a brown solid.The IR spectrum of 7 displayed the characteristic absorption of the acetoxy group at about 1720 cm–1. The 1H NMR spectrum of the sample showed the expected signal of the acetyl methyl at 2.13 ppm. The laser desorption mass spectrum of 7 displayed the 786 and 788 a.m.u. ion peaks corresponding to C60O2(OH)2 and C60(OH)4, as well as an intense peak of the acetyl cation at m/z 43.C60 smoothly reacts with (dichloro)iodobenzene 8 in tetrachloroethane at –25 to 25 °C with the formation of polychlorinated fullerenes 9 (Scheme 4).¶ IR and 13C NMR spectroscopic data for 9 were virtually identical to the published data2(c) for C60Cln (n = 12–15). Specifically, the IR spectrum of 9 displayed the characteristic C–Cl stretching frequencies between 875 and 840 cm–1.The 13C NMR spectrum of the sample showed a broad featureless peak centered near 148 ppm. MALDI-TOF or laser desorption mass-spectrometric analysis of C60Cln in the † Preparation of 2. A sample of C60 (20 mg, 0.028 mmol) was dissolved in 2–3 ml of freshly distilled o-dichlorobenzene at room temperature. The resulting purple solution was cooled to –20 °C, and iodosobenzene (40 mg, 0.18 mmol) and then azidotrimethylsilane (39 mg, 0.34 mmol) were added under nitrogen.The resulting mixture was stirred at –20 °C for 2 h; then, the solvent and all volatile products were removed in a high vacuum to afford a black, highly explosive powder. 1H NMR (CDCl3) d: 7.6–7.2 (group of multiplets). IR (KBr, n/cm–1): 2100 (very strong).Found (%): C, 63.68; H, 0.74; N, 21.34; I, 8.75. Calc. for C60N18·C6H5I (%): C, 67.35; H, 0.43; N, 21.43; I, 10.78. ‡ Azidofullerene 2 and other fullerene products (4, 5, 7) are shown in this paper as single formulas, which are in the closest agreement with the results of elemental analysis. However, all these products most likely represent a distribution of compounds rather than a specific polyadduct. 1 2 (6.1 equiv.) Scheme 1 C60 + PhI(N3)2 C60(N3)6 o-Cl2C6H4 –20 °C to room temperature § Preparation of 5. A sample of C60 (20 mg, 0.028 mmol) was dissolved in 2–3 ml of freshly distilled o-dichlorobenzene at room temperature. The resulting purple solution was cooled to –20 °C, and iodosobenzene (6.2 mg, 0.028 mmol) and then trimethylsilyl triflate (10.5 mg, 0.048 mmol) were added under nitrogen.The resulting mixture was warmed to room temperature and stirred for three days; then, the solvent and all volatile products were removed in a high vacuum to afford a dark brown material. 1H NMR (CDCl3) d: 7.7–7.2 (group of multiplets), 1.58 (br. s, OH). IR (KBr, n/cm–1): 3400–3200 (br., OH), 1250, 1179, 1033 (strong, OTf). F ound ( %): C, 7 0.64; H, 1 .16; S , 2.80; I, 9 .93.C alc . for C60(OH)OSO2CF3·C6H5I (%): C, 73.78; H, 0.55; S, 2.94; I, 11.63. C60 + Ph O I I Ph TfO OTf o-Cl2C6H4 –20 °C to room temperature C60(OTf)2 C60(OH)OTf 3 4 5 H2O Scheme 2 C60 + 2PhI(OAc)2 C60(OAc)4 C2H2Cl4, 80 °C 150 h 6 7 Scheme 3Mendeleev Communications Electronic Version, Issue 2, 2001 (pp. 43–84) positive mode showed only the peak of C60 (M = 720).2(c)–(e) MALDI-TOF analysis for negative ions using a 2,5-dihydroxybenzoic acid matrix, as previously reported,5 was unsuccessful, whereas a dithranol matrix afforded weak signals indicative of C60Cl5, C60Cl7 and C60Cl9. Laser desorption analysis in the negative mode (in the absence of a matrix), however, nicely provided a spectrum consistent with the expected distribution of polychlorinated products,5,†† with C60Cl7 and C60Cl9 as prevalent species.Elemental analysis of product 9, consistent with the molecular composition of C60Cl16, suggests a slightly higher chlorine content than MS analysis. The previously reported preparation of C60Cln involved the chlorination of C60 with chlorine gas at 250 °C or liquid chlorine at –35 °C for one day.2(c)–(e) In conclusion, the first functionalization of fullerene C60 with hypervalent iodine reagents is reported.The treatment of C60 with an excess of azidoiodinane 1 results in addition of up to six azido groups, while a similar reaction with hypervalent iodine triflate 3 affords mono triflate 5 as the main product. (Diacetoxy)iodobenzene reacts with C60 with the formation of tetraacetate 7, which was identified by IR and NMR spectroscopy and mass spectrometry. Chlorination of C60 with (dichloro)- iodobenzene affords polychlorinated fullerene 9, whose IR, 13C NMR and mass spectra are identical with the previously reported data for C60Cln obtained by direct chlorination of C60.This work was supported by the National Science Foundation (grant no.NSF/CHE-9802823), the National Science and Engineering Research Council of Canada, and the University of Alberta. We thank PerSeptive Biosystems for the loan of a Voyager Elite equipped with delayed extraction and Dr. R. Whittal for help with the MS analysis. We are grateful to Professor V. I. Sokolov for thoughtful discussions. References 1 (a) F.Diederich and M. Gomez-Lopez, Chem. Soc. Rev., 1999, 28, 263; (b) A. Hirsch, Top. Curr. Chem., 1999, 199, 1; (c) A. Hirsch, The Chemistry of the Fullerenes, Thieme, Stuttgart, 1994; (d) R. Taylor, The Chemistry of Fullerenes, World Scientific, Singapore, 1995; (e) R. Taylor and D. R. M. Walton, Nature, 1993, 363, 685; (f) A. Hirsch, J. Phys. Chem. Solids, 1997, 58, 1729; (g) C.Bellavia-Lund, J.-C. Hummelen, K. M. Keshavarz, R. Gonzalez and F. Wudl, J. Phys. Chem. Solids, 1997, 58, 1983; (h) V. I. Sokolov, Izv. Akad. Nauk, Ser. Khim., 1999, 1211 (Russ. Chem. Bull., 1999, 48, 1197). 2 (a) P. R. Birkett, P. W. Hitchcock, H. W. Kroto, R. Taylor and D. R. M. Walton, Nature, 1992, 357, 479; (b) F. N. Tebbe, R. L. Harlow, D. B. Chase, D. L. Thorn, G. C.Campbell, J. C. Calabrese, N. Herron, R. J. Young and E. Wasserman, Science, 1992, 256, 822; (c) F. N. Tebbe, J. Y. Becker, D. B. Chase, L. E. Firment, E. R. Holler, B. S. Malone, P. J. Krusic and E. Wasserman, J. Am. Chem. Soc., 1991, 113, 9900; (d) G. A. Olah, I. Bucsi, C. Lambert, R. Aniszfeld, N. J. Trivedi, D. K. Sensharma and G. K. S. Prakash, J. Am. Chem. Soc., 1991, 113, 9385; (e) P.R. Birkett, A. G. Avent, A. D. Darwish, H. W. Kroto, R. Taylor and D. R. M. Walton, J. Chem. Soc., Chem. Commun., 1993, 1230; (f) I. S. Neretin, K. A. Lyssenko, M. Y. Antipin, Y. L. Slovokhotov, O. V. Boltalina, P. A. Troshin, A. Y. Lukonin, L. N. Sidorov and R. Taylor, Angew. Chem., Int. Ed. Engl., 2000, 39, 3273; (g) J. H. Holloway, E. G. Hope, R. Taylor, G. J.Langley, A. G. Avent, T. J. Dennis, J. P. Hare, H. W. Kroto and D. R. M. Walton, J. Chem. Soc. , Chem. Commun., 1991, 966; (h) L. Y. Chiang, R. B. Upasani and J. W. Swirczewski, J. Am. Chem. Soc., 1992, 114, 10154; (i) L. Y. Chiang, L.-W. Wang, J. W. Swirczewski, S. Soled and S. Cameron, J. Org. Chem. , 1994, 59, 3960; (j) V. I. Sokolov, V. V. Bashilov, Q. K. Timerghazin, E. V. Avzyanova, A.F. Khalizov, N. M. Shishlov and V. V. Shereshovets, Mendeleev Commun., 1999, 54. 3 (a) A. Varvoglis, Hypervalent Iodine in Organic Synthesis, Academic Press, London, 1997; (b) P. J. Stang and V. V. Zhdankin, Chem. Rev., 1996, 96, 1123; (c) V. V. Zhdankin, Rev. Heteroatom Chem., 1997, 17, 133; (d) T. Wirth and U. H. Hirt, Synthesis, 1999, 1271. 4 (a) P. Magnus, J. Lacour, P.A. Evans, M. B. Roe and C. Hulme, J. Am. Chem. Soc., 1996, 118, 7716; (b) Y. Kita, M. Egi, T. Takada and H. Tohma, Synthesis, 1999, 885. 5 D. Heymann, F. Cataldo, R. Fokkens, N. M. M. Nibbering and R. D. Vis, Fullerene Sci. Technol., 1999, 7, 159. ¶ Preparation of 9. A sample of C60 (24 mg, 0.033 mmol) was dissolved in 10 ml of 1,1,2,2-tetrachloroethane under nitrogen. The solution was cooled to –25 °C.(Dichloro)iodobenzene (91 mg, 0.33 mmol) was dissolved in 2 ml of dry dichloromethane and added to the cool C60 solution. The mixture was warmed to room temperature and stirred for 120 h. The solvent and all volatile products were removed in a high vacuum. The precipitate was washed with hexane to afford 18 mg of product 9 as an orange-brown solid. 13C NMR, d: 148 (br.). IR (KBr, n/cm–1): 875 to 840 (br.). Found (%): C, 54.8; Cl, 43.6. Calc. for C60Cl16 (%): C 55.96; Cl 44.04. ††Although in some cases low resolution limited matching of the isotopic pattern to the most intense m/z signal for each isomer C60Clx , there is no question that the spectrum confirms polychlorination of C60. C60 + PhICl2 8 (10 equiv.) C60 + Cl2 (liq.) C2H2Cl4, –25 to 25 °C 120 h –35 °C, 24 h ref. 2(c) C60Cln 9 n = 12–16 Scheme 4 30000 20000 10000 0 600 800 1000 1200 1400 1600 m/z Counts 720, C60 897, C60Cl5 967, C60Cl7 1040, C60Cl9 1112, C60Cl11 1182, C60Cl13 Figure 1 Laser desorption mass spectrum of C60Cln showing negative ions. Averaged over 87 scans. Received: 25th December 2000; Com. 00/1739

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Mendeleev Communications Electronic Version, Issue 2, 2001 (pp. 43–84) New approach to [a]-fused fluoroquinolones: the synthesis of 5-oxo-1,2,3,3a,4,5-hexahydropyrrolo[1,2-a]quinolines Elizaveta Tsoi,a Valerii N. Charushin,*a Emiliya V. Nosova,a Galina N. Lipunovaa and Alexey V. Tkachevb a Department of Organic Chemistry, Urals State Technical University, 620002 Ekaterinburg, Russian Federation. Fax: + 7 3432 74 0458; e-mail: charushin@prm.uran.ru b N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russian Federation. Fax: +7 3832 34 4752; e-mail: atkachev@nioch.nsc.ru 10.1070/MC2001v011n02ABEH001323 The reaction of N-(ethoxycarbonyl)methyl substituted ethyl 6,7-difluoro-, 6,7,8-trifluoro- and 5,6,7,8-tetrafluoro-4-oxo-1,4-dihydroquinoline- 3-carboxylates with methyl methacrylate results in the [3 + 2] adducts, hexahydropyrrolo[1,2-a]quinolones, which can be precursors of [a]-fused fluoroquinolones.Among the tricyclic N1–C2 fused fluoroquinolones, compounds with excellent antimicrobial and other kinds of biological activity have been found.1–3 A common strategy for the synthesis of this type of fused fluoroquinolones is based on condensation reactions of appropriately substituted heterocyclic synthons A–C (Scheme 1).In particular, pyrrolo[1,2-a]quinolones were obtained by the intramolecular condensation of cyclic derivatives of ethyl 3-amino-2-benzoyl acrylates A.2 The second approach is based on the ring closure reactions of appropriate C2-substituted quinolones B.4 The first successful example of using the nucleophilic substitution of hydrogen at C2 in fluoroquinolones C for the construction of [a]-fused tricyclic systems was performed through intramolecular addition of the Grignard reagent followed by oxidation of the intermediate ó-adduct.5 Later we reported a new approach towards pyrazolo[1,5-a]quinolones via the [3 + 2] annelation resulting from the reaction of 1-amino- 6-fluoro-4-quinolones with â-diketones.6 A similar synthetic route to the same heterocyclic system of pyrazoloquinolones was developed by D.Barrett and co-workers via the tandem addition reaction of N-aminoquinolones with alkyl acrylates and other activated alkenes under basic condition.7,8 We report here the extension of this [3 + 2] annelation methodology based on tandem addition reactions.However, instead of the =N–NHR moiety, we used the CH-active N-(ethoxycarbonyl) methyl fragment in fluoroquinolones 1a–c to generate nucleophilic species. We found that the reaction of ethyl 6,7-difluoro-, 6,7,8- trifluoro- and 5,6,7,8-tetrafluoro-4-oxo-1,4-dihydroquinoline-3- carboxylates 1a–c with methyl methacrylate proceeds smoothly in an anhydrous DMF solution in the presence of sodium hydride and affords 5-oxo-1,2,3,3a,4,5-hexahydropyrrolo[1,2-a]quinolines 2a–c in 50–61% yields (Scheme 2).The 1H NMR spectroscopy of reaction products 2a–c† revealed that the mixtures of three stereomers were obtained in all cases in a ratio of approximately 2.5:1:trace. The major isomers were separated by silica gel column chromatography followed by crystallisation from hexane.The relative configuration of substituents in major diastereomers 2a and 2b was determined by NMR spectroscopy. The proton–proton coupling 3JH-4,H-3a » 14 Hz for both compounds demonstrates the anti-periplanar (trans-) position of H-4 and H-3a, whereas the cis-arrangement of the pairs C-10 and H-3a, H-1 and H-2â is evident from the nuclear Overhauser effects (NOE, Scheme 3).Although the NOE for 2c have not been measured, it is clear that the stereostructure of 2c is just the same due to similarities of its spectral NMR characteristics to those of 2a,b. In conclusion, note that the reaction discovered provides an alternative route to fused pyrrolo[a]quinoline derivatives, the key intermediates for potential fluoroquinolone antibacterials.Moreover, compounds 2a–c are of interest as novel representatives of the tricyclic fluoroquinolone system bearing the bridge-headed nitrogen atom and having structural similarities to natural alkaloids. X NH O O OEt F F N O OEt O H Z YH F N O OEt O C A B C Scheme 1 † The 1H and 19F NMR spectra were recorded in CDCl3 solutions on Bruker WP-250 and Bruker WP-80-SY instruments (250 MHz for 1H and 75 MHz for 19F).Homonuclear 1H–1H Overhauser effects for compounds 2a,b and the 13C NMR spectrum of 2a in CDCl3 were obtained on a Bruker DRX-500 spectrometer (500 MHz for 1H and 125 MHz for 13C). Mass spectra were recorded using a Varian MAT 311A spectrometer. 1,4-Di(ethoxycarbonyl)-3-methoxycarbonyl-3-methyl-7,8-difluoro-5-oxo- 1,2,3,3a,4,5-hexahydropyrrolo[1,2-a]quinoline 2a.A solution of ethyl N-(ethoxycarbonyl)methyl-6,7-difluoro-1,4-dihydro-4-oxoquinoline-3-carboxylate 1a (0.35 g, 1mmol) in dry DMF (5ml) was treated with sodium hydride (60% dispersion in oil) (50 mg, 1.2 mmol) and stirred for 15 min. Methyl methacrylate (0.33 ml, 3 mmol) was added to the reddish reaction mixture, which was allowed to stand at room temperature for 24 h (until 1a disappeared and the solution became yellowish green).The reaction mixture was diluted with 10 ml of water; the pH of the solution was adjusted to 7.0 with 6% hydrochloric acid; and the contents were extracted with dichloromethane. The organic layers were washed with water, dried (Na2SO4) and evaporated. The oily residue was treated with diethyl ether–hexane to give 2a (0.27 g, 61%) as a yellow powder.Major individual diastereoisomer 2a was isolated as a colourless powder by silica gel column chromatography (eluent: hexane–ethyl acetate, 10:1) followed by crystallisation from hexane to yield 0.13 g (30%), mp 102– 103 °C. 1H NMR, d: 1.21 (t, 3H, Me, 3J 7.2 Hz), 1.33 (t, 3H, Me, 3J 7.2 Hz), 1.35 (s, 3H, Me), 1.85 (dd, 1H, 2-Há, 2J2-Há,2-Hâ 13.4 Hz, 3J2-Há,1-H 6.4 Hz), 3.08 (dd, 1H, 2-Hâ, 2J2-Hâ,2-Há 13.4Hz, 3J2-Hâ,1-H 9.0 Hz), 3.46 (d, 1H, 4-H, 3J4-H,3a-H 14.4 Hz), 3.70 (s, 3H, OMe), 4.19 (q, 2H, OCH2, 3J 7.2 Hz), 4.30 (q, 2H, OCH2, 3J 7.2 Hz), 4.38 (d, 1H, 3a-H, 3J3a-H,4-H 14.4 Hz), 4.48 (dd, 1H, 1-H, 3J1-H,2-Há 6.4 Hz, 3J1-H,2-Hâ 9.0 Hz), 6.17 (dd, 1H, 9-H, 3J9-H,8-F 11.9 Hz, 4J9-H,7-F 6.1 Hz), 7.51 (dd, 1H, 6-H, 3J6-H,7-F 10.2 Hz, 4J6-H,8-F 9.0 Hz). 13C NMR, d: 14.0 (C-18), 14.02 (C-15), 21.94 (C-10), 40.51 (C-2, 1J2-C,2-H 139.0 and 133.6 Hz), 52.19 (C-12), 52.32 (C-3), 55.56 (C-4, 1J4-C,4-H 131.5 Hz), 59.37 (C-1, 1J1-C,1-H 150.7 Hz), 61.39 (C-17), 61.63 (C-14), 67.39 (C-3a, 1JC-3a,3a-H 145.9 Hz), 101.22 (C-9, 1JC-9,9-H 162.7 Hz), 113.12 (C-5a), 116.08 (C-6, 1J6-C,6-H 166.8 Hz), 143.46 (C-7, 1J7-C,7-F 242.2 Hz), 145.32 (C-9a), 157.77 (C-8, 1J8-C,8-F 257.6 Hz), 167.33 (C-16), 172.29 (C-13), 173.46 (C-11), 186.55 (C-5). 19F NMR, d: 125.11 (ddd, 7-F, 3J7-F,8-F 22.0 Hz, 3J7-F,6-H 12.7 Hz, 4J7-F,9-H 9.8 Hz), 151.70 (ddd, 8-F, 3J8-F,7-F 22.0 Hz, 3J8-F,9-H 9.8 Hz, 4J8-F,6-H 5.9 Hz). MS, m/z: 439 (10%, M+), 366 (100), 339 (25), 320 (20), 267 (40).Mendeleev Communications Electronic Version, Issue 2, 2001 (pp. 43–84) This work was supported in part by the US Civilian Research and Development Foundation (award no.REC-005) and the Russian Foundation for Basic Research (grant no. 00-03-32785a). References 1 I. Segawa, M. Kitano, K. Kazuno, M. Tsuda, I. Shirahase, M. Ozaki, M. Matsuda and M. Kise, J.Heterocycl. Chem., 1992, 29, 1117. 2 D. T. W. Chu and A. K. Claiborne, J. Heterocycl. Chem., 1987, 24, 1537. 3 Y. Ito, H. Kato, S. Yasuda, N. Yagi, T. Yoshida and T. Suzuki, Japanese Patent, 117388, C07d, 1992 (Chem. Abstr., 1992, 117, 111597d). 4 G. A. Mokrush ina, E. V. Nosova, G.N. Lipunova and V. N. Ch arushin, Zh. Org. Khim., 1999, 35, 1447 (Russ. J. Org. Chem., 1999, 35, 1413). 5 M. C. Sch roeder and I. S. Kiely, J. Heterocycl. Chem., 1988, 25, 1769. 6 O. N. Chupakhin, Y. A. Azev, S. G. Alekseev, S. V. Shorshnev, E. V. Tsoi and V. N. Charushin, Mendeleev Commun., 1992, 151. 7 D. Barrett, H. Sasaki, T. Kinoshita and K. Sakane, Chem. Commun., 1996, 61. 8 D. Barrett, H. Sasaki, T. Kinoshita, A. Fujikawa and K. Sakane, Tetrahedron, 1996, 52, 8471. Scheme 2 Reagents and conditions: i, DMF, NaH, room temperature, 24 h; ii, H2O, pH 7 (6% HCl).N F F X Y O COOEt COOEt N F F X Y O O O H H Há Hâ H O O Me O O 1 2 3 4 5 6 3a 5a 7 8 9 9a 10 11 12 13 14 15 16 17 18 H2C Me COOMe 1a–c 2a–c a X = Y = H b X = H, Y = F c X = Y = F i, ii Compounds 2b,c were obtained analogously. 2b (major isomer): yield 0.145 g (32%), mp 106–107 °C. 1H NMR, d: 1.23 (t, 3H, Me, 3J 7.1 Hz), 1.32 (t, 3H, Me, 3J 7.1 Hz), 1.32 (s, 3H, Me), 1.80 (dd, 1H, 2-Há, 2J2-Há,2-Hâ 13.4 Hz, 3J2-Há,1-H 6.3 Hz), 3.11 (dd, 1H, 2-Hâ, 2J2-Hâ,2-Há 13.4 Hz, 3J2-Hâ,1-H 9.5 Hz), 3.55 (d, 1H, 4-H, 3J4-H,3a-H 14.5 Hz), 3.71 (s, 3H, COOMe), 4.18 (q, 2H, OCH2, 3J 7.1 Hz), 4.25 (d, 1H, 3a-H, 3J3a-H,4-H 14.5 Hz), 4.29 (q, 2H, OCH2, 3J 7.1 Hz), 4.95 (dd, 1H, 1-H, 3J1-H,2-Há 6.3 Hz, 3J1-H,2-Hâ 9.5 Hz), 7.46 (ddd, 1H, 6-H, 3J6-H, 7-F 9.9 Hz, 4J6-H,8-F 8.1 Hz, 5J6-H,9-F 2.1 Hz). 19F NMR, d: 148.33 (dd, 7-F, 3J7-F,8-F 22.0 Hz, 3J7-F,6-H 9.8 Hz), 149.35 (ddd, 8-F, 3J8-F,7-F 22.0 Hz, 3J8-F,9-F 17.1 Hz, 4J8-F,6-H 8.3 Hz), 151.60 (ddd, 9-F, 3J9-F,8-F 17.1 Hz, 4J9-F,7-F 6.8 Hz, 5J9-F,6-H 2.4 Hz). MS, m/z: 457 (M+, 10%), 384 (100), 338 (15), 306 (20), 285 (25), 252 (25), 238 (30).For 2c (major isomer): yield 0.155 g (33%), mp 104–105 °C. 1H NMR, d: 1.27 (t, 3H, Me, 3J 7.1 Hz), 1.35 (t, 3H, Me, 3J 7.1 Hz), 1.35 (s, 3H, Me), 1.81 (dd, 1H, 2-Há, 2J2-Há,2-Hâ 13.4 Hz, 3J2-Há,1-H 6.7 Hz), 3.11 (dd, 1H, 2-Hâ, 2J2-Hâ,2-Há 13.4 Hz, 3J2-Hâ,1-H 9.2 Hz), 3.61 (d, 1H, 4-H, 3J4-H, 3a-H 14.0 Hz), 3.74 (s, 3H, OMe), 4.26 (q, 2H, OCH2, 3J 7.1 Hz), 4.28 (q, 1H, 3a-H, 3J3a-H,4-H 13.7 Hz), 4.38 (q, 2H, OCH2, 3J 7.1 Hz), 5.01 (dd, 1H, 1-H, 3J1-H,2-Há 6.7 Hz, 3J1-H,2-Hâ 9.5 Hz). 19F NMR, d: 141.86 (m, 1F), 147.26 (m, 1F), 158.56 (m, 1F), 172.59 (m, 1F). MS, m/z: 475 (M+, 10%), 402 (100), 388 (18), 374 (15), 296 (15), 270 (18), 256 (28). Scheme 3 Homonuclear 1H–1H Overhauser effects for compounds 2a and 2b. EtOOC N F F H O COOEt H H Há Hâ H COOMe CH3 1 2 3 4 3a 2a 1% 4% 4% 6% EtOOC N F F F O COOEt H H Há Hâ H COOMe CH3 1 2 3 4 3a 2b 1% 4% 5% 5% 2% 6% Received: 18th May 2000; Com. 00/1649

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Mendeleev Communications Electronic Version, Issue 2, 2001 (pp. 43–84) Pyrido[2,3-b]- and pyrimido[4,5-b]quinoxalines: the first fluorine-containing derivatives Valerii N. Charushin,* Svetlana K. Kotovskaya, Natalya M. Perova and Oleg N. Chupakhin Department of Organic Chemistry, Urals State Technical University, 620002 Ekaterinburg, Russian Federation. Fax: +7 3422 74 0458; e-mail: charushin@htf.ustu.ru 10.1070/MC2001v011n02ABEH001333 Fluorinated derivatives of pyrido[2,3-b]- and pyrimido[4,5-b]quinoxalines 5–8 have been prepared through the condensation of 2-amino-3-cyano- and 2-amino-3-aminocarbonyl-substituted 6-fluoro-7-R-quinoxalines 1–4 with dimethyl acetylenedicarboxylate and triethyl orthoformate, respectively.Quinoxaline 1,4-dioxides and their condensed analogues are biologically active compounds.1 In particular, 2,3-di(hydroxymethyl)- and 2,3-di(acetoxymethyl)quinoxaline 1,4-dioxides are effective antibacterials.2 We became interested in fluorinated derivatives of quinoxaline 1,4-dioxides3 because the introduction of a fluorine atom into heterocyclic compounds can dramatically increase their biological potency, as examplified by the development of the family of fluoroquinolones.4 W e ha ve recently described novel derivatives of fluorinated furo[3,4-b]- and pyrrolo[3,4-b]quinoxalines.5,6 Now, we report the first synthesis of fluorinated pyrido[2,3-b]- and pyrimido[4,5-b]quinoxalines. The published data2,7 on the synthesis of pyrido[2,3-b]quinoxaline 5,10-dioxides are limited.Some derivatives of pyrido- [2,3-b]quinoxalines proved to possess antibacterial and anticancer activities.2,8,9 Pyrimido[4,5-b]quinoxaline 5,10-dioxides are also little known, although these compounds proved to be antibacterials,10,11 blood platelet anti-aggregating and antihypertensive agents.12 Aromatic ortho-aminonitriles are starting materials for the construction of fused pyridines through condensation reactions with dimethyl acetylenedicarboxylate (DMAD).13–15 However, the annelation of a pyridine ring to quinoxalines by the condensation of ortho-aminonitriles with DMAD was not described previously.We have tried to apply this methodology to the synthesis of fluorinated pyrido[2,3-b]quinoxaline 5,10-dioxides on the basis of 2-amino-3-cyano-6-fluoro-7-R-substituted quinoxaline 1,4-dioxides 1a,b used as the starting materials.3 The reaction of 1a with DMAD in DMSO or acetonitrile was found to proceed smoothly at room temperature in the presence of potassium carbonate to afford 2,3-bis(methoxycarbonyl)-7,8- difluoro-4-imino-1,4-dihydro-1H-pyrido[2,3-b]quinoxaline 5,10- dioxide 5a in good yield (Scheme 1).The reaction takes only 30 min; prolongation of the reaction time up to 24 h has no effect. The reaction of 1b with DMAD proceeds slower and requires 30 days at room temperature to be finished, however, at 60 °C, it goes much faster and takes 1 h. 2-Amino-3-cyano- 6,7-difluoroquinoxaline 2 obtained from 1a by reduction with sodium dithionite was found to react with DMAD in a similar way affording 2,3-bis(methoxycarbonyl)-7,8-difluoro-4-imino- 1,4-dihydro-1H-pyrido[2,3-b]quinoxaline 6.However, the reaction takes place only on heating in DMSO at 120 °C. The fluorine derivatives of pyrimido[4,5-b]quinoxalines 7 and 8 were prepared in two steps: (i) by conversion of orthoaminonitriles 1a and 2 into corresponding carboxamides 3 and 4 on treatment with concentrated (98%) sulfuric acid (yields 87–92%) (Scheme 1), followed by (ii) cyclisation of orthoaminocarboxamides 3 and 4 with triethyl orthoformate.All compounds gave satisfactory elemental analyses and 1H NMR, mass and IR spectra.† This work was supported by the US Civilian Research and Development Foundation (grant no. REC-005) and the Russian Foundation for Basic Research (grant no. 00-03-32785). References 1 Y. Kurasava, A. Takada and H.S. Kim, J. Heterocycl. Chem., 1995, 32, 1085. 2 G.W. H. Cheesman and R. F. Cookson, in The Chemistry of Heterocyclic Compounds, eds. A. Weisberger and E. C. Taylor, Wiley–Interscience, New York, 1979, vol. 35. 3 S. K. Kotovskaya, V. N. Charushin, O. N. Chupakhin and E. O. Kozhevnikova, Zh. Org. Khim., 1998, 34, 399 (Russ. J. Org. Chem., 1998, 34, 369). 4 D. Bouzard, in Antibiotics and Antiviral Compounds, eds.K. Krohn, H. A. Rirst and H. Maag, VCH, Weinheim, 1993. 5 O. N. Chupakhin, S. K. Kotovskaya, N. M. Perova, Z. M. Baskakova a nd V. N. Cha rushin, Khim. Geterotsikl. Soedin., 1999, 520 [Chem. Heterocycl. Compd. (Engl. Transl.), 1999, 35, 459]. 6 S. K. Kotovskaya, N. M. Perova, V. N. Charushin and O. N. Chupakhin, Mendeleev Commun., 1999, 76. 7 M.J. Abu El-Ha j, B. W. Doming, J. D. Johnston, M. J. Hadda din a nd C. H. Jssidorides, J. Org. Chem., 1972, 37, 589. N N N F R O O NH H CO2Me CO2Me 5a,b N N N F F NH H CO2Me CO2Me 6 N N NH2 CN F R O O 1a,b DMAD/K2CO3 N N NH2 CN F F 2 DMAD/K2CO3 N N NH2 CONH2 F F O O 3 H2SO4 N N NH2 CONH2 F F 4 H2SO4 Na2S2O4 N N F F O O 7 HC(OEt)3 N N F F 8 HC(OEt)3 N NH O N NH O a R = F b R = pyrrolidinyl-1 Scheme 1 R = F R = FMendeleev Communications Electronic Version, Issue 2, 2001 (pp. 43–84) 8 M. Pesson, P. De Lajudie, M. Antoine, S. Cnabassin and P. Gurard, C. R. Acad. Sci., Ser. C, 1976, 282, 861 (Chem. Abstr., 1976, 85, 63035). 9 W.Pa r ri, Giorn, Ital. Chemioterap., 1956, 3, 588 (Chem. Abstr., 1958, 52, 11289). 10 F. Seng and K. Ley, German Patent 2.034.476, 1971 (Chem. Abstr., 1972, 76, 153787f). 11 F. Seng and K. Ley, German Patent 2.122.571, 1973 (Chem. Abstr., 1973, 78, 43522z). 12 A. Monge, J. A. Palop and I. Urbasos, J. Heterocycl. Chem., 1989, 26, 1623. 13 E. C. Taylor and A. McKillop, in Advances in Organic Chemistry, The Chemistry of Cyclic Enaminonitrile and o-Aminonitrile, ed. E. C. Taylor, Interscience, New York, 1970, vol. 7. 14 J.M. Robinson, L. W. Brent, C. Chau, K. A. Floyd, S. L. Gillham, T. L. McMaham, D. J. Magda, T. J. Motycka, M. J. Pack, F. L. Roberts, L. A. Seally, S. L. Simpson, R. R. Smith a nd K. N. Za iesny, J. Org. Chem., 1992, 57, 7352. 15 Y. Tominaga and N. Yoshioka, Heterocycles, 1996, 42, 53. † 2-Amino-3-cyano-6,7-difluoroquinoxaline 2. A solution of sodium dithionite (1.0 g, 6.0 mmol) in 15 ml of water was added dropwise to a suspension of compound 1a3 (0.48 g, 2.0 mmol) in 40 ml of ethanol.The reaction mixture was kept at 65–70 °C for 1.5 h with stirring and then cooled to 0–5 °C. The addition of cold water (60–70 ml) and stirring for 1 h at 5–10 °C gave a precipitate, which was filtered off and recrystallised from ethanol to give yellow crystals. Yield 0.25 g (61%), mp 201– 202 °C. 1H NMR ([2H6]DMSO) d: 7.39 (br. s, 2H, NH2), 7.47 (dd, 1H, 3JHF 11.5 Hz, 4JHF 8.0 Hz), 7.77 (dd, 1H, 3JHF 10.6 Hz, 4JHF 8.0 Hz) (H-5 and H-8). IR (KBr, n/cm–1): 3440–3240, 3040, 2240. MS, m/z: 206 (M+, 100). 2-Amino-3-aminocarbonyl-6,7-difluoroquinoxaline 1,4-dioxide 3. Compound 1a (0.5 g, 2.1 mmol) was added dropwise with stirring to 1.8 ml of concentrated sulfuric acid (d = 1.83), which was previously heated up to 55 °C.The reaction mixture was kept at 50–55 °C with stirring for 1 h and then at ambient temperature for 1 h, cooled to 0 °C and poured into ice. The reaction mixture was adjusted to pH 9 with aqueous ammonia and allowed to stand for 8–10 h in a refregerator at 0–5 °C. The precipitate formed was filtered off and recrystallised from acetic acid to give orange crystals.Yield 0.47 g (87%), mp 265–266 °C. 1H NMR ([2H6]DMSO) d: 8.26 (br. s, 2H, NH2), 8.25 (dd, 1H, 3JHF 10.6 Hz, 4JHF 7.6 Hz) and 8.42 (dd, 1H, 3JHF 10.6 Hz, 4JHF 7.9 Hz), (H-5 and H-8), 8.56 (br. s, 1H, NH), 9.76 (br. s, 1H, NH). IR (KBr, n/cm–1): 3400–3200, 3100–3000, 1670, 1380, 1340. MS m/z: 256 (M+, 100). Compound 4 was obtained analogously to 3.Yield 92%, mp 270– 271 °C. 1H NMR ([2H6]DMSO) d: 7.54 (dd, 1H, 3JHF 12.1 Hz, 4JHF 8.4 Hz) and 7.79 (dd, 1H, 3JHF 10.8 Hz, 4JHF 8.6 Hz), (H-5 and H-8), 7.94 (br. s, 2H, NH2), 8.34 (br. s, 1H, NH), 9.46 (br. s, 1H, NH). IR (KBr, n/cm–1): 3480–3320, 3320–3200, 1660. MS, m/z: 224 (M+, 100). 2,3-Bis(methoxycarbonyl)-7,8-difluoro-4-imino-1,4-dihydro-1H-pyrido- [2,3-b]quinoxaline 5,10-dioxide 5a.K2CO3 (0.34 g, 2.5 mmol) was added to a solution of 1a (0.24 g, 1.0 mmol) in 10 ml of DMSO or 35 ml of acetonitrile. Dimethyl acetylenedicarboxylate (DMAD) (0.21 g, 1.5 mmol) was added dropwise, and the reaction mixture was kept at ambient temperature for 0.5 h with stirring. The addition of cold water (70 ml) and stirring for 1 h at 5–10 °C gave a precipitate, which was filtered off and recrystallised from water–acetonitrile (1:1) to give red crystals.Yield 0.19 g (50%), mp 280–281 °C. 1H NMR ([2H6]DMSO) d: 3.86 (s, 3H, COOMe), 3.90 (s, 3H, COOMe), 8.54 (dd, 1H, 3JHF 10.2 Hz, 4JHF 8.2 Hz) and 8.59 (dd, 1H, 3JHF 9.9 Hz, 4JHF 8.0 Hz), (H-6 and H-9), 9.16 (br. s, 1H, =NH), 11.51 (br. s, 1H, NH). IR (KBr, n/cm–1): 3370, 3230, 3070, 2950, 1730, 1680, 1340, 1300.MS, m/z: 380 (M+, 74). 2,3-Bis(methoxycarbonyl)-7-fluoro-4-imino-8-(pyrrolidin-1-yl)-1,4-dihydro- 1H-pyrido[2,3-b]quinoxaline 5,10-dioxide 5b. Potassium carbonate (0.18 g, 1.3 mmol) was added to a solution of compound 1b3 (0.15 g, 0.5 mmol) in 10 ml of DMSO. DMAD (0.11 g, 0.75 mmol) was added dropwise, and the reaction mixture was kept at 60 °C for 1 h with stirring and then cooled to 0–5 °C and allowed to stand at this temperature for 1 h.The precipitate was filtered off and recrystallised from ethanol to give dark red crystals. Yield 0.13 g (88%), mp 250–252 °C. 1H NMR ([2H6]DMSO) d: [2.27 (m, 4H), 3.44 (m, 4H), pyrrolidin-1-yl], 3.86 (s, 3H, COOMe), 3.90 (s, 3H, COOMe), 7.23 (d, 1H, H-9, 4JHF 8.9 Hz), 8.12 (d, 1H, H-6, 3JHF 14.4 Hz), 9.16 (br.s, 1H, =NH), 11.51 (br. s, 1H, NH). IR (KBr, n/cm–1): 3330–3300, 2950–2860, 1740, 1700, 1350, 1310. MS, m/z: 431 (M+, 70). 2,3-Bis(methoxycarbonyl)-7,8-difluoro-4-imino-1,4-dihydro-1H-pyrido- [2,3-b]quinoxaline 6. K2CO3 (0.14 g, 1.0 mmol) was added to a solution of compound 2 (0.1 g, 0.4 mmol) in 10 ml of DMSO. DMAD (0.085 g, 0.6 mmol) was added dropwise, and the reaction mixture was kept at 120 °C for 1 h with stirring and then cooled to 0–5 °C.The addition of cold water (50 ml) and stirring for 1 h at 5–10 °C gave a precipitate, which was filtered off and recrystallised from ethanol to give dark red crystals. Yield 0.12 g (71%), mp 239–240 °C. 1H NMR ([2H6]DMSO) d: 3.89 (s, 3H, COOMe), 3.91 (s, 3H, COOMe), 7.95 (dd, 1H, 3JHF 10.7 Hz, 4JHF 8.7 Hz) and 8.25 (dd, 1H, 3JHF 11.2 Hz, 4JHF 8.4 Hz), (H-6 and H-9), 8.60 (br. s, 1H, =NH), 8.82 (br.s, 1H, NH). IR (KBr, n/cm–1): 3430–3240, 3050–2850, 1740, 1700. MS, m/z: 348 (M+, 78). Received: 26th May 2000; Com. 00/1659 7,8-Difluoropyrimido[4,5-b]quinoxaline-4(3H)-one 5,10-dioxide 7. A mixture of compound 3 (0.2 g, 0.8 mmol) and triethyl orthoformate (10 ml) was refluxed for 20 h. The resulting dark orange solution was evaporated to dryness in vacuo.The solid was recrystallised from acetic acid to give yellow crystals. Yield 26%, mp > 300 °C. 1H NMR ([2H6]DMSO) d: 8.25 (dd, 1H, 3JHF 11.3 Hz, 4JHF 8.2 Hz) and 8.40 (dd, 1H, 3JHF 10.7 Hz, 4JHF 8.6 Hz), (H-6 and H-9), 8.43 (s, 1H, H-2), 12.74 (br. s, 1H, NH). IR (KBr, n/cm–1): 3500–3300, 3050, 1700, 1380, 1300. MS, m/z: 266 (M+, 100). 7,8-Difluoropyrimido[4,5-b]quinoxaline-4(3H)-one 8. A mixture of compound 4 (0.1 g, 0.45 mmol) and triethyl orthoformate (5 ml) was refluxed for 1.5 h. The resulting brown solution was cooled; the precipitate formed was filtered off and recrystallised from acetic acid to give yellow crystals. Yield 87%, mp > 300 °C. 1H NMR ([2H6]DMSO) d: 8.22 (dd, 1H, 3JHF 11.3 Hz, 4JHF 8.6 Hz) and 8.38 (dd, 1H, 3JHF 11.0 Hz, 4JHF 8.5 Hz), (H-6 and H-9), 8.43 (s, 1H, H-2), 12.74 (br. s, 1H, NH). IR (KBr, n/cm–1): 3050, 2900–2700, 1700. MS, m/z: 234 (M+, 100).

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数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 2, 2001 (pp. 43–84) Selective reduction of the azido groups of 2,4,6-triazidopyridines Sergei V. Chapyshev*a and Matthew S. Platzb a Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russian Federation. Fax: +7 096 515 3588; e-mail: chap@icp.ac.ru b Department of Chemistry, Ohio State University, Columbus, OH 43210–1173, USA.Fax: +1 614 292 5151; e-mail: platz.1@osu.edu DOI: 10.1070/MC2001v011n02ABEH001412 Upon treatment with SnCl2 in methanol at room temperature, 2,4,6-triazidopyridines undergo selective reduction of the ã-azido groups to give the corresponding 4-amino-2,6-diazidopyridines in high yields. The reduction of azides to amines is an important reaction in organic synthesis.1 In the last decade, much attention was focused on the development of methods allowing the selective and mild reduction of the azido groups in polyfunctional compounds bearing carbon–carbon double bonds, nitro and carbonyl groups and other functionalities.2 However, because of the lack of suitable model compounds, the selective reduction of nonequivalent azido groups in aromatic polyazides was not studied.Recently, we have shown that 2,4,6-triazidopyridines are characterised by the nonequivalent distribution of bonding electron density in the á- and ã-azido groups and, as a result, readily undergo selective derivatization in reactions with electron-rich3 and electron-deficient dipolarophiles,4 nucleophilic addition5 and upon photolysis.6 This work is devoted to the selective reduction of nonequivalent azido groups in 2,4,6-triazidopyridines.1(a),(b) SnCl2 was chosen for study owing to its ability to efficiently reduce various aromatic azides to amines7 under mild conditions. The reactions of 1a,b with an equivalent amount of SnCl2 in methanol at room temperature for 30 min afforded amines 5a,b in high yields.† The structures of 5a,b were supported by elemental analysis and spectroscopic investigations.‡ Thus, for instance, the presence of only three signals at dC 80.4 (C-3, C-5), 160.6 (C-4) and 161.0 ppm (C-2, C-6) for the carbon atoms of the pyridine ring of 5a and at dC 100.0 (C-3, C-5), 147.7 (C-2, C-6) and 150.8 ppm (C-4) for the carbon atoms of the pyridine ring of 5b in the 13C NMR spectra unambiguously demonstrates that the amino groups of these compounds are located at the 4-position of the pyridine ring.Upon treatment with an excess o f SnCl2 in methanol at room temperature, aminodiazide 5a was readily reduced to diaminoazide 6‡ in 87% yield. By contrast, due to weaker electron-withdrawing substituents at the pyridine ring, chlorine-substituted diazide 5b did not react with SnCl2 even after prolonged reflux in methanol.The selective reduction of the ã-azido groups in 1a,b can be rationalised by an analysis of the bonding electron density distribution in these molecules. According to the theory,1 t h e first step of the reaction involves a single electron transfer from reductant to azide. The most prominent feature of the azide radical anions thereby formed is the considerable bending of the azido group (from about 170° in starting azides to about 130° in radical anions) and a dramatic decrease in the activation energy of N–N2 bond dissociation (from 35 to 6 kcal mol–1, respectively).8 As can be seen in Figure 1, the ã-azido groups in 1a,b have the lowest bonding orbital density at the Ná and Nâ atoms, so the structural changes in these groups on the way from 1a,b to 2a,b should6(b) require less energy, making the dissociation of the ã-groups in 2a,b the more facile process.This assumption is supported by PM3 computations§ of 2a † Typical procedure for the synthesis of 4-amino-2,6-diazidopyridines 5a,b. A powder of SnCl2 (1 mmol) was slowly added in small portions to a stirred solution of triazide 1a,b (1 mmol) in 50 ml of methanol at room temperature.The mixture was kept at room temperature for 30 min, and then the solvent was evaporated under reduced pressure. The solid residue was chromatographed on a silica gel column using a mixture of benzene and ethyl acetate (4:1 for 5a, 9:1 for 5b) as an eluent. Yields: 5a, 88%; 5b, 78%. ‡ 5a: mp 155–156 °C (decomp.). 1H NMR ([2H6]acetone) d: 7.24 (br. s, 2H, NH2). 13C NMR ([2H6]acetone) d: 80.4 (C-3, C-5), 113.0 (CN), 160.6 (C-4), 161.0 (C-2, C-6). IR (microcrystalline film, nmax/cm–1): 3352 (s, ías NH), 3232 (s, ís NH), 2234 (s, CN), 2158 and 2143 (s and s, N3), 1683 (s, äs NH), 1588 and 1560 (s and vs, C=N, C=C), 1411 (vs), 1321 (m), 1233 (w), 1199 (w), 767 (m), 665 (w), 592 (m), 544 (w), 515 (w), 492 (w).Found (%): C, 37.31; H, 0.97; N, 61.72. Calc. for C7H2N10 (%): C, 37.19; H, 0.85; N 61.96. 5b: mp 170–171 °C (decomp.). 1H NMR ([2H6]acetone) d: 6.28 (br. s, 2H, NH2). 13C NMR ([2H6]acetone) d: 100.0 (C-3, C-5), 147.7 (C-2, C-6), 150.8 (C-4). IR (microcrystalline film, nmax/cm–1): 3502 (s, ías NH), 3399 (s, ís NH), 2172 and 2143 (s and s, N3), 1629 (s, äs NH), 1576 and 1544 (w and s, C=N, C=C), 1413 (vs), 1390(vs), 1354 (w), 1316 (w), 1230 (s), 1096 (s), 1004 (w), 828 (m), 737 (s), 678 (w), 635 (w), 540 (m).Found (%): C, 24.68; H, 0.93; N, 45.62. Calc. for C5H2Cl2N8 (%): C, 24.51; H, 0.82; N 45.73. 6: mp 177–178 °C (decomp.). 1H NMR ([2H6]acetone) d: 6.77 (br. s, 2H, 4-NH2), 6.60 (br. s, 2H, 2-NH2). 13C NMR ([2H6]acetone) d: 71.9 (C-3), 74.6 (C-5), 114.3 and 115.2 (CN), 160.9 (C-4), 161.4 (C-6), 162.8 (C-2). IR (microcrystalline film, nmax/cm–1): 3378 and 3338 (s and s, ías 2-NH and 4-NH), 3234 and 3225 (s and s, ís 2-NH and 4-NH), 2210 (vs, CN), 2140 (s, N3), 1660 and 1618 (s and vs, äs 2-NH and 4-NH), 1574 and 1553 (vs and vs, C=N, C=C), 1473 (m), 1386 (s), 1332 (m), 772 (w), 669 (w), 497 (w), 477 (w), 438 (m). Found (%): C, 42.16; H, 2.14; N, 55.70.Calc. for C7H4N8 (%): C, 42.01; H, 2.01; N 55.98. N R N3 N3 R N3 N R N3 N3 R N3 e– SnCl2 N R N3 N R N3 – N2 H+ 1a,b 2a,b 3a,b N R N3 NH R N3 4a,b e–, H+ SnCl2 N R N3 NH2 R N3 5a,b SnCl2 N NC N3 NH2 CN NH2 6 a R = CN b R = Cl Figure 1 The orbital density distribution in the HOMO of 1a,b. The lower bonding orbital density at the Ná atom of the ã-azido groups in the HOMO of 1a,b indicates that these groups more easily achieve the geometry of the azide radical anions.HOMO of 1a HOMO of 1bMendeleev Communications Electronic Version, Issue 2, 2001 (pp. 43.84) (S = 1/2, q = .1), which yield the ¥ã-azido group distorted (the N.N.N angle is about 127¡Æ, the N.N2 bond length is about 1.40 A) conformer of 2a by preference.Computations of the ¥á-azido group distorted (the N.N.N angle is about 128¡Æ, the N.N2 bond length is about 1.40 A) conformer of 2a were performed using the computational bending of the ¥á-azido group in 2a to 125¡Æ prior the geometry optimization. As expected, the ¥á-azido group distorted conformers of 2a,b appeared to be 3 and 6 kcal mol.1 higher in energy than the respective ¥ã-azido group distorted conformers of 2a,b.This confirms that generation of low-energy conformers of the ¥ã-azido group of 2a,b from 1a,b is indeed the less energy consuming process and supports the electron density bonding arguments. Selective reduction of nonequivalent azido groups in aromatic polyazides can be a useful method for the preparation of new organic compounds.Obviously, the greater the difference in the HOMO orbital density distribution on the azido groups in polyazides, the higher the selectivity of the reduction. References 1 E. F. V. Scriven and K. Turnbull, Chem. Rev., 1988, 88, 297. 2 (a) H. Firouzabadi, B. Tamami and A. R. Kiasat, Synth. Commun., 2000, 30, 587; (b) M. L. Kantam, N. S. Chowdari, A. Rahman and B. M. Choudary, Synlett., 1999, 1413; (c) A.Kamal and B. S. N. Reddy, Chem. Lett., 1998, 593; (d) H. Firouzabadi, M. Adibi and B. Zeynizadeh, Synth. Commun., 1998, 28, 1257; (e) A. Kamal, N. V. Rao and E. Laxman, Tetrahedron Lett., 1997, 38, 6945; ( f ) Y. Huang, Y. Zhang and Y. Wang, Tetrahedron Lett., 1997, 38, 1065; (g) M. Baruah, A. Boruah, D. Prajapati, J. S. Sandhu and A. C. Ghosh, Tetrahedron Lett., 1996, 37, 4559; (h) C.Goulaouic-Dubois and M. Hesse, Tetrahedron Lett., 1995, 36, 7427; (i) L. Benati, P. C. Montevecchi, D. Nanni, P. Spagnolo and M. Volta, Tetrahedron Lett., 1995, 36, 7313; (j) B. C. Ranu, A. Sarkar and R. Chakraborty, J. Org. Chem., 1994, 59, 4114; (k) H. Rao, P. Surya and P. Siva, Synth. Commun., 1994, 24, 549; (l) A. A. Malik, S. B. Peterson, T.G. Archibald, M. P. Cohen and K. Baum, Synthesis, 1989, 450. 3 (a) S. V. Chapyshev and T. Ibata, Heterocycles, 1993, 36, 2185; (b) S. V. Chapyshev, Khim. Geterotsikl. Soedin., 1993, 1560 [Chem. Heterocycl. Compd. (Engl. Transl.), 1993, 29, 1426]; (c) S. V. Chapyshev, U. Bergstrasser and M. Regitz, Khim. Geterotsikl. Soedin., 1996, 67 [Chem. Heterocycl. Compd. (Engl. Transl.), 1996, 32, 59]; (d) S.V. Chapyshev and V. M. Anisimov, Khim. Geterotsikl. Soedin., 1997, 1521 [Chem. Heterocycl. Compd. (Engl. Transl.), 1997, 33, 1315]; (e) S. V. Chapyshev, Khim. Geterotsikl. Soedin., 2000, 1497 (in Russian). 4 S. V. Ch apysh ev, Mendeleev Commun., 1999, 164. 5 S. V. Ch apysh ev, Mendeleev Commun., 1999, 166. 6 (a) S. V. Chapyshev, R. Walton and P. M. Lahti, Mendeleev Commun., 2000, 187; (b) S. V. Chapyshev, R. Walton, J. A. Sanborn and P. M. Lahti, J. Am. Chem. Soc., 2000, 122, 1580. 7 (a) K. R. Gee and J. F. W. Keana, Synth. Commun., 1993, 23, 357; (b) S. N. Maiti, M. P. Singh and R. G. Micetich, Tetrahedron Lett., 1986, 27, 1423. 8 M. F. Budyka and T. S. Zyubina, Zh. Fiz. Khim., 1998, 72, 1634 (Russ. J. Phys. Chem., 1998, 72, 1475). 9 (a) J. J. P. Stewart, J. Comput. Chem., 1989, 10, 221; (b) Spartan version 4.0, Wavefunction, Inc., USA, 1995. ¡× The structures of the ¥á- and ¥ã-isomers of radical anions 2a,b (S = 1/2, q = .1) were calculated with the full optimization of geometrical parameters using the PM3 method (UHF, SCF level).9 Received: 22nd December 2000; Com. 00/1738

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Mendeleev Communications Electronic Version, Issue 2, 2001 (pp. 43.84) Structural and spectral investigation of a neptunium(V) complex with 2,2'-bipyridine Grigorii B. Andreev,a Alexander M. Fedosseev,*a Nina A. Budantsevaa and Mikhail Yu. Antipinb a Institute of Physical Chemistry, Russian Academy of Sciences, 117915 Moscow, Russian Federation. Fax: +7 095 335 2005; e-mail: fedosseev@ipc.rssi.ru b A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 117813 Moscow, Russian Federation. Fax: +7 095 135 5085; e-mail: xray@xray.ineos.ac.ru 10.1070/MC2001v011n02ABEH001438 The new neptunium(V) complex [NpO2(bipy)(H2O)3](NO3) was synthesised, and its structure was determined by X-ray diffraction analysis and IR spectroscopy. The coordination of nitrogen atoms to the neptunyl ion NpO2 + is of interest because only two complexes with 2,6-pyridinedicarboxylate anions acting as chelate ligands are known.1 The nitrogen atoms of pyridine and 2,2'-bipyridine easily enter into the coordination sphere of uranyl.2.6 Although the coordination interactions of neptunyl and uranyl are similar, the coordination behaviours of these ions are different, for instance, in the tendency of the neptunyl ion to so-called cation.cation interactions.In this respect, the capability of neptunyl to coordinate nitrogen atoms is not predictable. To clarify this uncertainty, we studied the structure of a neptunyl complex with 2,2'-bipyridine. The blue prismatic crystals for X-ray analysis were chosen from a solid phase obtained by mixing NpO2ClO4¡�nH2O and 2,2'-bipyridinium nitrate solutions in ethanol followed by evaporation to dryness and repeated recrystallisation from ethanol.toluene at ambient temperature. NpO2ClO4¡�nH2O was prepared by the dissolution of neptunyl hydroxide in a stoichiometric amount of an aqueous 0.5 M perchloric acid solution and the evaporation at a temperature lower than 120 ¡ÆC.The crystal structure of 1 consists of [NpO2(bipy)(H2O)3]+ cations (Figure 1) and NO3 . anions.¢Ó The coordination polyhedron of the Np atom is a pentagonal bipyramid which equatorial positions occupied by two nitrogen atoms of a 2,2'-bipyridine molecule acting as a bidentate ligand and three water molecules. The Np.O distances lie in the range 2.45(1).2.49(1) A. The Np.N bonds are significantly longer, and the bond lengths are equal to 2.66(1) and 2.62(1) A.The maximum deviation of atoms from the mean equatorial plane is equal to 0.298 A. The shortest distance between neptunium atoms is 5.560 A. The O.Np.O bond angle in the NpO2 group is close to 180¡Æ, and it is equal to 178.5(4)¡Æ while the Np.O bond lengths differ and are equal to 1.86(1) and 1.77(1) A.The N.C and C.C distances in the 2,2'-bipyridine molecule lie in the range 1.35(2).1.41(2) and 1.31(2).1.41(2) A for rings containing the N(1) and N(2) atoms, respectively. The angle between these rings is equal to 2.9¡Æ. The maximum deviations of atoms from mean planes are 0.038 and 0.022 A. The nitrate group acts as the second sphere anion, which is not typical for neptunium complexes.In addition, there is a short contact [1.72(2) A] between one oxygen atom of the nitrate group and the water molecule entering the first coordination sphere of the neptunyl group. The N.O distances of the NO3 group lie in the range 1.23(2).1.29(2) A. The NIR and IR spectra of [NpO2(bipy)(H2O)3](NO3) were obtained using Shimadzu UV3100 and Specord M80 spectrophotometers, respectively.Samples were prepared by pressing a triturated mixture of the compound with molten NaCl. The IR spectrum contains many overlapped absorption bands. These bands are difficult to assign. For instance, some intense bands in the region 3500.3100 cm.1 are associated with the stretching vibrations ¥í(C.H) and ¥í(O.H); however, not all of these groups take part in the H-bond formation.The vibrations ¥ä(C.N) and ¥í(NO3 .) and the skeleton vibrations of pyridine rings arise in the region 1600.1250 cm.1. The asymmetry of NpO2 + induced by a significant distinction between the interatomic distances Np(1).O(1) and Np(1).O(2) leads to the low frequency shift of ¥ías(NpO2 +) to 762cm.1 (in comparison with ¥ías 824 cm.1 in the IR spectrum of a NpO2ClO4 solution7) and the appearance of the symmetric mode ¥ís(NpO2 +) 740 cm.1.¢Ó All crystallographic data were obtained on a Siemens P3/PC singlecrystal X-ray diffractometer using graphite monochromated MoK¥á radiation. The collection of data was carried out up to 2qmax = 62¡Æ measured for 0 h 30, 0 k 11, 0 l 12 using a q/2q scan technique. The structure was solved by a direct method.All non-hydrogen atoms were refined with anisotropic thermal parameters by a full-matrix least-squares procedure on F2. Hydrogen atoms of the 2,2'-bipyridine molecule were fixed in the ideal positions, while hydrogen atoms of water molecules were not localised. All calculations were performed using the SHELXTL PLUS program package. Crystallographic data for [NpO2(bipy)(H2O)3](NO3): space group Pca21 (no. 29), a = 21.023(6), b = 7.872(2), c = 8.870(3) A, V = 1467.9(7) A3, Z = 4, dcalc = 2.929 g cm.3, R = 0.042, RW = 0.108, Flack parameter 0.06(5). Atomic coordinates, bond lengths, bond angles and thermal parameters have been deposited at the Cambridge Crystallographic Data Centre (CCDC). For details, see ¡®Notice to Authors¡�, Mendeleev Commun., Issue 1, 2001. Any request to the CCDC for data should quote the full literature citation and the reference number 1135/82.< < < < < < C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) N(1) N(2) Np(1) H(1) H(2) H(3) H(4) H(7) H(8) H(9) H(10) O(1) O(2) O(3) O(4) O(5) Figure 1 Structure of the cation [NpO2(bipy)(H2O)3]+. Selected bond lengths (A): Np.N(2) 2.62(1), Np.N(1) 2.66(1), Np.O(2) 1.86(1), Np.O(1) 1.77(1), Np.O(5) 2.46(1), Np.O(3) 2.46(1), Np.O(4) 2.49(1); principal bond angle: O(1).Np.O(2) 178.5(4)¡Æ. Absorption 985 1032 1099 1126 l/nm 1000 1100 1200 Figure 2 NIR spectrum of [NpO2(bipy)(H2O)3](NO3) (6.54 mg in a NaCl matrix).Mendeleev Communications Electronic Version, Issue 2, 2001 (pp. 43–84) In the NIR spectrum of solid [NpO2(bipy)(H2O)3](NO3), a set of bands of various intensities is observed (Figure 2).The most intense narrow band of NpV corresponding to the f–f electron transition has a maximum at 985 nm, which insignificantly differs from the position in the spectrum of a hydrated ion (981 nm).8 This fact is unexpected because it was demonstrated that the increasing of Np–Ooxo distances during O-donor coordination (including cation–cation interactions), as a rule, is accompanied by a considerable low frequency shift of the f–f absorption band.9,10 It may be assumed that the participation of 5f-electrons in the coordination of a bipyridine molecule by NpO2 + is not dominant.Probably, the formation of a coordination bond is due to the 6d-electrons of NpV and the electrons of a ligand.Compound 1 represents the first example of a pentavalent neptunium complex with 2,2'-bipyridine. Only two such compounds of hexavalent neptunium are known at present. These are the complexes NpO2(bipy)(NO3)2 and NpO2(bipy)(OAc)2,2 which are isomorphous and isostructural to UVI analogues. In their structures, the neptunium atom has a hexagonal bipyramidal coordination; the equatorial plane consists of two N atoms of 2,2'-bipyridine with Np–N distances ranging from 2.564 to 2.630 Å and four O atoms of two nitrate or acetate groups, which act as bidentate ligands. This work was supported by the Russian Foundation for Basic Research (grant nos. 00-15-97359 and 99-07-90133).References 1 G. B. Andreev, V. N. Khrustalev, M. Yu. Antipin, A. M. Fedo sseev, N.A. Budantseva, J. C. Krupa and C. Madic, 30iemes Journees des Actinides, Dresden, Germany, 2000, p. 42. 2 N. W. Alco ck, D. J. Flanders and D . Brown, J. Chem. Soc., Dalton Trans., 1985, 1001. 3 S. Degetto, G. Marangoni, G. BombierForsellini, L. Baracco and R. Graziani, J. Chem. Soc., Dalton Trans., 1974, 1933. 4 N. W. Alcock, D. J. Flanders, M. Pennington and D. Brown, Acta Crystallogr., Sect. C, 1987, 43, 1476. 5 G. B. Deacon, P. I. Mackinnon and J. C. Taylor, Polyhedron, 1985, 4, 103. 6 N. W. Alco ck, D. J. Flanders and D . Brown, J. Chem. Soc., Dalton Trans., 1984, 679. 7 L. H. Jones and R. A. Penneman, J. Chem. Phys., 1953, 21, 512. 8 R. Sjoblom and J. C. Hindman, J. Am. Chem. Soc., 1951, 73, 1744. 9 A. M. Fedoseev, N. A. Budantseva and A. A. Bessonov, 24iemes Journees des Actinides, Austria, 1994, p. 67. 10 M. S. Grigoriev, N. A. Budantseva, A. M. Fedoseev and N. A. Baturin, Radiokhimiya, 1993, 35, 29 [Radiochem. (Engl. Transl.), 1993, 35, 151]. Received: 31st January 2001; Com. 01/1764

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Mendeleev Communications Electronic Version, Issue 2, 2001 (pp. 43.84) Quantum-chemical simulation of the interaction between the Ti8C12 metallocarbohedrene and the CHCl3 molecule Alexander L. Ivanovskii,*a Andrei A. Sofronovb and Yuri N. Makurinb a Institute of Solid State Chemistry, Urals Branch of the Russian Academy of Sciences, 620219 Ekaterinburg, Russian Federation. Fax: +7 3432 74 4495; e-mail: ivanovskii@ihim.uran.ru b Department of Physical and Colloid Chemistry, Urals State Technical University, 620002 Ekaterinburg, Russian Federation 10.1070/MC2001v011n02ABEH001340 The interactions of the Ti8C12 metallocarbohedrene with halogen-containing addends are discussed on the basis of ab initio calculations of the Ti8C12(CHCl3) adduct.Pioneering studies of the reactivity of a new class of cage-like molecular nanostructures,4.6 M8C12 metallocarbohedrenes (M = = d-metals), interacting with three types of addends (polar, ¥�-bonding and halogen-containing molecules) were carried out.1.3 We performed a quantum-chemical analysis of the interactions between Ti8C12 and ¥�-bonding molecules of ethylene and considered the formation mechanism of coordination bonding between the addend and the Ti8C12 met-car taking the Ti8C12¡¿ ¡¿(C2H4)4 adduct as an example.7 As is known,8 Ti8C12 has an open electronic shell, which makes it a potentially active reactant in redox reactions.Of particular interest is the interaction of Ti8C12 with halogencontaining addends. In this case, the following processes may take place: the reduction of a halogen (Hal), addend degradation and the formation of the stable adduct Ti8C12.Hal.Using the energies of chemical bonds,9 the probabilities of the transformations Hal.R + Ti8C12 > Ti8C12Hal + R0 can be compared. Below are given some estimates [.E ¡í E(Ti.Hal) . E(Hal.R)] for the reactions It can be seen that the formation of met-car adducts with chlorine-containing reactants is the most probable process.The nature of such transformations can be described by the charge-fluctuation model.10 The gist of the proposed model boils down to the following. Electronic density transfer from one reactant to another leads to a local deformation of the molecule and may bring about its destruction. In terms of the molecular orbital (MO) theory, this means that either antibonding MO become occupied or bonding MO get empty.As a result, the corresponding interatomic bonds weaken, and their fluctuation frequencies decrease to a certain ¡®critical¡� level (w¡Ì kT/ ) and subsequent thermal dissociation. To study the rearrangement of electronic states of the met-car when it interacts with halogen-containing reactants, we carried out ab initio calculations of the electronic energy structure (EES) of the Ti8C12(CHCl3) complex, which is an adduct of Ti8C12 with chloroform (Figure 1).The self-consistent nonempirical discrete variation (DV) method of electronic density functional was used in the computations.11 Its details and the results of DV investigations of Ti8C12 with Th and Td symmetry were published elsewhere.8 The number of integration points was 30000.The Ti8C12(CHCl3) complex possesses no space symmetry. The model densities of states (MDOS) of Ti8C12(CHCl3) and CHCl3 molecules are presented in Figure 2. Effective atomic charges (Qeff) and bond populations (BP) are listed in Table 1. When the adduct is formed, the states of chlorine atom [Cl(1)], through which a chloroform molecule is coordinated, undergo the greatest changes.These changes concern the bonding MO y1 with an energy of ~(.8) eV, which is comprised of C 2p- and Cl 3p-AO, and the corresponding vacant antibonding MO y2 with an energy of ~(+4) eV (Figure 2). It can be seen that the y1 MO has a large bonding energy and is not capable of participating in the stabilization of two-electron interactions with vacant Ti8C12 MO.The four-electron interactions with occupied Ti8C12 MO destabilise the complex (for more information about the effect of interorbital interaction types on the chemical stability of adducts see refs. 7 and 12). On the contrary, the energy of the antibonding y2 MO of the molecule decreases sharply when it interacts with Ti8C12 (Figure 2), and this orbital in the complex becomes partially occupied.Consequently, stabilising interactions here are the so-called zero-electron interactions. The data make it possible to consider the interactions of halogen-containing reactants with met-cars including those in condensed states. In the latter case, assume that the energy spectrum of the ¡®nanocrystalline carbide¡� is characterised by the Fermi energy (EF), and a chloroform molecule interacts with the ¡®active centre¡� of the nanocrystal surface according to Figure 1.When the molecular orbital Y = 2.1/2[y2 + j(Ti)] is formed (Figure 3), this interaction can be described by a linear three-atom fragment .C.Cl(1).Ti. model. It follows from the computations that this MO is bonding relative to [Cl(1).Ti] and antibonding relative to [C.Cl(1)] interactions.Further transformations of the CHCl3 molecule are determined by the relative position of EF of the nanocrystal (HOMO of ¡®isolated¡� met-car) and the energy of the considered MO E(Y). If E(Y) > EF, the [C.Cl(1)] bonding energy experiences no considerable changes, and the stability of CHCl3 is retained. This situation is analogous to the interaction of Ti8C12 with ethylene7 when coordination bonding is formed between the addend and Ti8C12 without dissociation of the former.When EF > E(Y), Y-MO becomes occupied. As a result, the CHCl3 molecule dissociates due to its antibonding character [relative to the C.Cl(1) interaction]: Ti8C12(CHCl3) > Ti8C12Cl + CHCl2. In the case under consideration (for ¡®isolated¡� met-car), we observe a ¡®borderline¡� situation: EF(HOMO) ~ E(Y).Table 1 indicates that the BP [C.Cl(1)] here decreases considerably. The qualitative criterion for dissociation of chemical bonds in the addend (or adsorbate molecule) occurring when the adduct (adsorption complex) is formed can be formulated on the basis of the obtained results in the following way. Dissociation will take place if the antibonding MO responsible for the chemical bonding in question stabilises as a result of interaction with the MO of nanoparticle atom (or energy state of the active centre of (.C.F) + Ti8C12 > Ti8C12F (.C.Cl) + Ti8C12 > Ti8C12Cl (.C.I) + Ti8C12 > Ti8C12I Cl2 + Ti8C12 > Ti8C12Cl .E = 109 kJ mol.1 .E = 201 kJ mol.1 .E = 75 kJmol.1 .E = 251 kJ mol.1 h Figure 1 Coordination of a chloroform molecule to Ti8C12.C H Cl(1) Cl(2) C(1) C(2) TiMendeleev Communications Electronic Version, Issue 2, 2001 (pp. 43.84) nanocrystalline substrate) in such a way that it becomes below the HOMO of the nanoparticle (below the Fermi level of the nanocrystal). Let us consider the conditions when this criterion is met. In the above example, the fulfilment of this criterion is favoured by considerable values of the overlap integrals of Ti(3d,4p)- and Cl(1)(3p)-AO and similar energies of the antibonding orbital y2 of the molecule and vacant MO of Ti8C12.This ensures the stabilization energy .E > [E(y2) . EF]. Therefore, the formation of a stable adduct with addend dissociation depends not only on the total stabilization energy .E, but also on the [E(y2) .EF] value, i.e., the energy interval between the antibonding MO of the addend and the HOMO of a nanoparticle (the Fermi level of a nanocrystal). For halogen-containing addends, this condition is fulfilled fairly well. References 1 K. P. Kerns, B. C. Guo, Y. T. Deng and A. W. Castleman, J. Am. Chem. Soc., 1995, 117, 4026. 2 H. T. Deng , K. P. Kerns and A.W.Castleman, J. Am. Chem. Soc., 1996, 118, 446. 3 J. V. Poblet, C. Bo, M. M. Rohmer and M. A. Benard, Chem. Phys. Lett., 1996, 260, 577. 4 B. C. Guo, K. P. Kerns and A. W. Castelman, Science, 1992, 255, 1411. 5 T. Pradeep and P. T. Manoharan, Curr. Sci., 1995, 68, 1017. 6 R. Selvan and T. Pradeep, Curr. Sci., 1998, 74, 666. 7 Yu. N. Makurin, A. A. Sofronov and A. L.l.Ross. Akad. Nauk, 2000, 372, 340 [Dokl. Chem. (Engl. Transl.), 2000, 90]. 8 A. A. Sofronov, Yu. N. Makurin and A. L. Ivanovskii, Koord. Khim., 1999, 25, 597 (Russ. J. Coord. Chem., 1999, 25, 556). 9 Energii razryva khimicheskikh svyazei. Ionizatsionnye potentsialy i srodstvo k elektronu (Energies of Chemical Bond Rupture. Ionization Potentials and Electron Affinity), ed.V. N. Kondratiev, Nauka, Moscow, 1974 (in Russian). 10 Yu. N. Makurin and R. N. Pletnev, Dokl. Ross. Akad. Nauk, 1999, 364, 495 [Dokl. Phys. Chem. (Engl. Transl.), 1999, 28]. 11 M. R. Press and D. E. Ellis, Phys. Rev. B, 1987, 35, 443. 12 A. A. Sofronov, PhD Thesis, Institute of Solid State Chemistry, Ekaterinburg, 2000. 100 50 0 10 0 20 10 0 10 0 20 10 0 80 40 0 40 0 .15 .10 .5 0 5 E/eV MDOS (arbitrary units) (a) (b) Ti 3d,4s,4p Cl(1) 3s,3p C 2s,2p Cl(2) 3s,3p Cl 3s,3p C 2s,2p Figure 2 Model densities of states (MDOS) of (a) the Ti8Cl12(CHCl3) adduct and (b) the free molecule CHCl3.Self-consistent DV calculations. Table 1 Calculation results of Ti8C12Cl and Ti8C12Cl2 complexes. Mulliken charges on atoms and FB of AO of chlorine atom in Cl2 molecule are given. Q(Ti) Q[C(1)]a aC(1) and C(2) are nonequivalent C atoms in the Th Ti8C12 structure.7 Q[C(2)] Q[Cl(1)] Q[Cl(2)] Q(C) Q(H) BP(Cl.C)/10.4 e 3p.2s 3p.2p 3s.2s CHCl3 . . . .0.02 .0.02 .0.19 0.24 1491 2923 611 Ti8C12(CHCl3) 1.02 .0.70 .0.72 0.04 .0.01 .0.18 0.00 815 1733 410 Figure 3 Orbital interactions in the reaction of a halogen-containing addend with a titanium atom of Ti8C12. The formation of the antibonding MO Y and its location relative to the HOMO of the met-car (EF of nanocrystalline ¡®titanium carbide¡�) and the antibonding orbital y2 of the addend (chloroform molecule) are shown for the three-atom fragment .C.Cl(1).Ti.. y2 .E Ti 3d EF Y Received: 15th June 2000; Com. 00/16

ISSN:0959-9436     

出版商:RSC    

年代:2001

数据来源: RSC