摘要:

Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) Synthesis of racemic germicidin Igor P. Lokot,* Felix S. Pashkovsky and Fedor A. Lakhvich Institute of Bioorganic Chemistry, Academy of Sciences of Belarus, 220141 Minsk, Belarus. Fax: +375 172 637 132; e-mail: prostan@ns.iboch.ac.by, lokot@yahoo.com The seven-step synthesis of racemic germicidin in 40% overall yield has been accomplished for the first time.Alkyl derivatives of 4-hydroxy-2-pyrone attract considerable attention because of a broad spectrum of their chemical and biological properties. In recent years, a great number of 3-, 5- and 6-alkyl derivatives of 4-hydroxy-2-pyrone have been isolated from different fungi, plants and molluscs. In the synthesis of complex natural 2-pyrones such as verrucosidin,1 cytreoviridin,2 asteltoxin,3 cytreomontanin4 etc., a wide variety of chemical methods and biosynthetic approaches to the molecular transformations were used.In this paper, we describe the first total synthesis of racemic germicidin 8 (a 3,6-dialkyl derivative of 4-hydroxy-2-pyrone). Germicidin was isolated from Streptomices viridochromogenes NRRL B-1551, and it exhibited an inhibitory effect on the germination of arthrospores of its own producer (at a concentration of 40 pg ml–1).5 Acylation of Meldrum’s acid by 2-methylbutyric acid chloride6 in the presence of pyridine followed by methanolysis of acyl derivative 2 gave rise to methyl ester 3 in 82% overall yield.Dropwise addition of water to a solution of 3 and sodium methylate (1:1 equiv.) in methanol at 5–10 °C and acidification with 1 M HCl led to 4-methyl-3-oxohexanoic acid 4, which was further used for the acylation of Meldrum’s acid in order to obtain tetracarbonyl compound 5, the key precursor for the synthesis of 6-sec-butyl-4-hydroxy-2-pyrone 6.Due to the instability of 3-oxocarboxylic acid chlorides7 we used a modified procedure which consists in acylation of Meldrum’s acid by acid 4 under the action of N,N'-dicyclohexylcarbodiimide (DCC) and a catalytic amount of 4-N,N-dimethylaminopyridine (DMAP).The ring system of 4-hydroxy-2-pyrone 6 was formed by thermal cyclization of tetracarbonyl compound 5 at reflux with toluene. In this case, the sec-butyl substituent at the 6-position was introduced at the stage of pyrone cycle formation.After chromatographic purification, the target 6-sec-butylpyrone 6† was obtained in 82% overall yield on a basis of starting methyl ester 3. The last step in the synthesis of germicidin includes the introduction of an ethyl substituent at the 3-position in the cycle of compound 6. Methods for a,a'-alkylation of cyclic b-dicarbonyl compounds in general and 4-hydroxy-2-pyrones in particular have been developed insufficiently.Direct alkylation of the 4-hydroxy- 6-methyl-2-pyrone anion by methyl iodide8 resulted in the formation of the target product only in 16% yield. The reduction of readily available 3-acetyl-4-hydroxy-6-methyl-2-pyrone (dehydroacetic acid) with a borane–methyl sulfide complex9 resulted in the formation of the 3-ethyl derivative in low yield (23%).Catalytic hydrogenation of 3-acetylpyrones over palladium is also unusable for our purpose, because in this case the D5-bond is primarily reduced.10 This fact results in the formation of 5,6-dihydro-2-pyrone ring. The introduction of the 3-ethyl substituent into 6-sec-butylpyrone 6 was carried out by the previously suggested procedure. 11,12 The procedure includes the preparation of the corresponding b,b'-tricarbonyl compounds followed by the reduction of the oxo-function of acyl substituents by ionic hydrogenation. 3-Acetylpyrone 7‡ was obtained by one-pot acetylation of pyrone 6 by acetic acid in the presence of DCC. The intermediate enolacylate was isomerised in situ under the action of DMAP, and 3-acetyl-6-(2-butyl)-4-hydroxy-2-pyrone 7 was obtained in 91% yield as an oil.Its reduction by triethylsilane in trifluoroacetic acid in the presence of a catalytic amount of LiClO4 gives rise to racemic germicidin 8 in 84% yield as an oily product, which crystallises on standing. Recrystallisation from diethyl ether–hexane resulted in the crystalline product with mp 95–97 °C. Spectral characteristics of the compound obtained§ † Spectroscopic data for 6: 1H NMR, d: 6.00 (d, 1H, J 2 Hz), 5.60 (d, 1H, J 2 Hz), 2.50 (m, 1H), 1.45–1.80 (m, 2H), 1.20 (d, 3H, J 6.5 Hz), 0.90 (t, 3H, J 7.3 Hz).IR (n/cm–1): 1245, 1445, 1575, 1630, 1670, 1700, 2880, 2940, 2970. ‡ Spectroscopic data for 7: 1H NMR, d: 16.70 (s, 1H, OH), 5.93 (s, 1H), 2.70 (s, 3H), 2.53 (m, 1H), 1.50–1.90 (m, 2H), 1.25 (d, 3H, J 7 Hz), 0.92 (t, 3H, J 7.4 Hz).IR (n/cm–1): 1400, 1455, 1580, 1655, 1765, 2890, 2945, 2980. Cl O O O O O O O O O O i ii O OMe O iii O OH O iv O O O O O O OH O C v 1 2 3 4 5 O OH O O O O O vi vii 6 O OH O 7 viii O O OH O 8 rac-germicidin O 1 2 3 4 5 6 Scheme 1 Reagents and conditions: i, 2 equiv. Py, CHCl3, –20 °C, then 5% HCl; ii, MeOH, reflux; iii, MeONa/MeOH, H2O, 5–10 °C, then 1 M HCl; iv, Meldrum’s acid, DCC, 0.3 equiv.DMAP, Et3N, CH2Cl2, then 5% HCl; v, toluene, 6 h, reflux; vi, AcOH, DCC, Et3N, CH2Cl2; vii, 0.3 equiv. DMAP, Et3N, CH2Cl2, then 10% HCl; vii, 3 equiv. Et3SiH, TFA, cat. amount LiClO4.Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) are in good agreement with the literature data for the natural product.5 References 1 K. Whang, R.J. Cooke, G. Okay and J. K. Cha, J. Am. Chem. Soc., 1990, 112, 8985. 2 (a) H. Suh and C. S. Wilcox, J. Am. Chem. Soc., 1988, 110, 470; (b) D. R. Williams and F. H. White, J. Org. Chem., 1987, 52, 5067. 3 (a) K. Tadano, H. Yamada, Y. Idogaki, S. Ogawa and T. Suami, Tetrahedron, 1990, 46, 2353; (b) S. L. Schreiber and K. Satake, J. Am. Chem. Soc., 1984, 106, 4186. 4 (a) H. Venkataraman and J.K. Cha, Tetrahedron Lett., 1987, 28, 2455; (b) P. Patel and G. Pattenden, J. Chem. Soc., Perkin Trans. 1, 1991, 1941. 5 F. Petersen, H. Zähner, J. W. Metzger, S. Freund and R.-P. Hummel, J. Antibiot., 1993, 46, 1126. 6 M. Sato, K. Takayama and S. Kobayashi, Chem. Pharm. Bull., 1990, 38, 94. 7 H. Brintzinger and H.-W. Ziegler, Ber., 1948, 81, 381. § Spectroscopic data for racemic germicidin 8: 1H NMR, d: 6.22 (s, 1H), 2.48 (s + q, 2H + 1H, J 7.4 Hz), 1.24–1.75 (m, 2H), 1.20 (d, 3H, J 6.7 Hz), 1.11 (t, 3H, J 7.5 Hz), 0.89 (t, 3H, J 7.5 Hz). 13C NMR and DEPT, d: 169.6 (C), 168.8 (C), 168.0 (C), 105.0 (C), 100.9 (CH, J 169 Hz), 39.8 (CH, J 125 Hz), 27.5 (CH2, J 125 Hz), 17.7 (Me, J 125 Hz), 16.4 (CH2, J 125 Hz), 12.4 (Me, J 125 Hz), 11.6 (Me, J 125 Hz).MS, m/z: 196 [M+]. IR (n/cm–1): 1160, 1285, 1430, 1595, 1680, 2885, 2945, 2980. 8 E. Suzuku, B. Katsuragawa and S. Inoue, Synthesis, 1978, 144. 9 T. Shimizu, S. Hiranuma and T. Watanabe, Heterocycles, 1993, 36, 2445. 10 (a) W. A. Ayer and Y. D. Villar, Can. J. Chem., 1985, 63, 1161; (b) J. N. Walker, J. Am. Chem. Soc., 1956, 78, 3201. 11 (a) A. A. Akhrem, F. A. Lakhvich, S. I. Budai, T. S. Khlebnikova and I. I. Petrusevich, Synthesis, 1978, 12, 925; (b) F. A. Lakhvich, T. S. Khlebnikova and A. A. Akhrem, Synthesis, 1985, 8, 784. 12 (a) A. A. Akhrem, F. A. Lakhvich, L. G. Lis, V. A. Khripach, N. A. Fil’chenkov, V. A. Kozinets and F. S. Pashkovsky, Dokl. Akad. Nauk SSSR, 1990, 311, 1381 [Dokl. Chem. (Engl. Transl.), 1990, 311, 79]; (b) F. S. Pashkovsky, I. P. Lokot and F. A. Lakhvich, Vesti ANB, Ser. Khim. Navuk, 1993, 81 (in Russian). Received: Moscow, 22nd June 1998 Cambridge, 23rd July 1998; Com. 8/05512B

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出版商:RSC    

年代:1999

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) Highly diastereoselective one-pot four-component coupling of p-TolSCl, 1-methoxycycloalkene, methyl vinyl ether and a carbon nucleophile leading to the synthesis of polyfunctional compounds Margarita I. Lazareva,a,b Yury K. Kryschenko,a,c Ron Caple,*a Victor G. Young, Jr.d and William A. Smit*b a Chemistry Department, University of Minnesota-Duluth, MN 55812 Duluth, USA.Fax: +218 726 7394 b N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow, Russian Federation. Fax: +7 095 135 5328 c Higher Chemical College, Russian Academy of Sciences, 125819 Moscow, Russian Federation. Fax: +7 095 135 8860 d X-Ray Crystallographic Laboratory, Chemistry Department, University of Minnesota, MN 55455 Minneapolis, USA An one-pot TiCl4 initiated assemblage of polyfunctional compounds via a sequential coupling of p-TolSCl, 1-methoxycycloalkene, methyl vinyl ether and Sn- or Si-capped carbon nucleophile is shown to proceed with high diastereoselectivity at all newly created chiral centres. The sequence of three kinetically independent intermolecular AdE reactions mediated by sulfur-stabilized reagents and intermediates has been recently developed as a versatile method for the one-pot synthesis of polyfunctional compounds from simple precursors in accordance with Scheme 1.1–3 At the first step of this sequence, electrophilic addition of ArSCl to the initial alkyl vinyl ether (VE-I) followed by the treatment of the formed adduct with a Lewis acid produced an episulfonium ion-like intermediate (ESI), which reacted further as an electrophile with another alkyl vinyl ether (VE-II) to give a sulfur-stabilized intermediate of the next generation, namely, the five-membered thiophanium ion (TPI).The third step involved electrophilic addition of the TPI at the double bond of the Alk3Si/Sn-capped p-donors with the concomitant removal of the respective Alk3Si/Sn+ moiety.Various carbon nucleophiles such as allylsilanes and -stannanes, siloxyalkenes and -dienes, cyclic and acyclic silyl ketene acetals were shown to be active as the quenchers at this final step. These data taken together with the previously documented variability of the VE components used for the generation of the TPI-like intermediates well-attested to the generality and preparative promise of the developed procedure. 3 However, it was also found that this coupling, when executed with acyclic vinyl ethers employed as both VE-I and VE-II components, exhibits rather low diastereoselectivity at the newly created 1,3-chiral centres. As a rule, in these cases, nearly 1:1 mixtures of diastereomers are formed, and this ratio was found to be only slightly affected by variations in the reaction parameters (the Lewis acid, the temperature, the solvent and the nature of the ArS substituent).2,3 Here we demonstrate that the utilization of 1-methoxycycloalkenes as VE-I component affects dramatically the stereochemical outcome of the described reaction sequence, and highly stereoselective formation of a single diastereomer can be achieved. 1-Methoxycyclohexene 1, 4-tert-butyl-1-methoxycyclohexene 2 and 1-methoxycyclopentene 3 were used as the starting alkene components.The reaction between equimolar amounts of 1 and p-TolSCl in CH2Cl2 solution proceeded almost instantaneously at –78 °C to give corresponding 1,2-adduct 4 (Scheme 2). No attempts were made to isolate this product, and the latter was immediately treated with 1.2 equiv.of methyl vinyl ether 5 in the presence of 1.2 equiv. of TiCl4. The formation of a cationoid complex, presumably TPI salt 6, was completed within 30 min at –78 °C (TLC monitoring data). After that 2 equiv. of allyltri-n-butyltin 7 was added to the reaction mixture, and it was stirred for 1 h at –78 °C. Subsequent treatment of the resulting solution with an aqueous NaHCO3–diethyl ether mixture followed by the standard work-up and column chromatography furnished Z-1-methoxy-1-(2'-methoxypent-4'-enyl)-2-(p-tolylthio) cyclohexane 8 as a single diastereomer isolated in 73% yield.† The utilization of 1-methoxy-2-methyl-1-trimethylsilylpropene 9 as the quencher for TPI 6 afforded stereochemically pure adduct 10 isolated in 96% yield.Under essentially the same conditions, alkene 2 was converted to adduct 11 isolated as an individual diastereomer (yield 60%) (Scheme 3). The relative structure of adduct 8 was unambiguously established by single-crystal X-ray analysis of the corresponding sulfone 8a (prepared by the oxidation of 8 with OXONE®,4 yield 70%)‡ (Figure 1). It seems reasonable to assume that adducts 8 and 11 belong to the same stereochemical series.R1O VE-I R1O ESI SAr i, ArSCl ii, Lewis acid OR2 VE-II SAr R1O OR2 X MR3 X = O, CH2 M = Si, Sn ArS X OR2 OR1 * * Scheme 1 TPI OMe Cl STol- p MeO p-TolSCl, CH2Cl2, –78 °C TiCl4 OMe STol- p 1 (VE-I) 4 ESI STol- p OMe H OMe 6 (TPI) O STol- p STol- p OMe OMe OMe OMe OMe Me Me (S)* (S)* (R)* OSiMe 3 OMe Me Me SnBu3 OMe 7 5 (VE-II) 9 8 (73%) 10 (96%) Scheme 2Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) A similar reaction sequence was applied to convert vinyl ethers 3 and 5 into the cationoid complex, presumably TPI salt 12. Treatment of this intermediate with pinacolone trimethylsilyl enol ether afforded the expected product also isolated as the only diastereomer (yield 76%), its stereochemistry being tentatively assigned as structure 14 (Scheme 4).It is certainly premature to discuss the steric course of the described reactions in the absence of reliable data on the structure of TPI intermediates 6 and 12. A comparison of the above result on the nearly complete stereoselectivity of the formation of the three stereogenic centres in adducts 8, 10, 11 and 14 with the previously reported non-diastereoselectivity of the similar couplings carried out with acyclic vinyl ethers2,3 enables us to † Consistent analytical and spectral data (1H and 13C NMR, HRMS and/or elemental analysis) were obtained for all new products.Diastereomeric purity was ascertained by the careful analysis of 1H NMR data. For the reactions leading to the formation of adducts 8, 11 and 14, the 1H NMR data of the minor chromatographic fractions revealed the presence of trace amounts of the diastereomeric products (less than 10%), but we were unable to isolate these products from the mixtures containing other impurities. 8: Rf = 0.30 (hexane–EtOAc = 8:1). 1H NMR (CDCl3) d: 1.45–1.55 and 1.69–1.78 (2m, 8H, 4CH2 in ring), 1.80 (dd, 1H, CHA, 1J 2.4 Hz, 2J 15.3 Hz), 2.14 (dd, 1H, CHB, 1J 8.7 Hz, 2J 15.3 Hz), 2.28 (s, 3H, MePh), 2.34 (m, 2H, CH2CH=), 3.20 (s, 3H, MeO), 3.27–3.35 (m, 1H, CHS), 3.29 (s, 3H, MeO), 3.42 (m, 1H, CHOMe), 5.08 (m, 2H, CH2=), 5.81 (ddt, 1H, CH=, 1J 7.2 Hz, 2J 10.1 Hz, 3J 17.2 Hz), 7.06 and 7.31 (2d, 4Harom, J 8.2 Hz). 13C NMR (CDCl3) d: 20.86 (MePh), 21.58, 24.13, 29.36 and 31.47 (4CH2 in ring), 37.55 and 38.19 (2CH2 in chain), 48.43 (CHS), 55.65 and 56.16 (2MeO), 77.02 and 77.27 (CHOMe, COMe), 117.25 (CH2=), 129.30 (2CHarom), 132.03 (2CHarom), 132.86 and 136.08 (2Carom), 134.39 (CH=).MS, m/z: 334 [M+]. Found (%): C, 71.90; H, 9.09; S, 10.01. Calc. for C20H30O2S (%): C, 71.81; H, 9.04; S, 9.59. ‡ 8a: mp 85–87 °C (hexane–diethyl ether). 1H NMR (CDCl3) d: 1.10– 2.04 (4m, 10H, 4CH2 in ring, CH2 in chain), 2.37 (m, 2H, CH2CH=), 2.42 (s, 3H, MePh), 2.83 (dd, 1H, CHSO2, 1J 10.0 Hz, 2J 14.4 Hz), 3.11 (s, 3H, MeO), 3.31 (s, 3H, MeO), 3.59 (dd, 1H, CHOMe, 1J 5.1 Hz, 2J 11.2 Hz), 5.16 (m, 2H, CH2=), 5.86 (m, 1H, CH=), 7.30 and 7.80 (2d, 4Harom, J 8.0 Hz). 13C NMR (CDCl3) d: 21.69 (MePh), 20.99, 24.58, 24.64 and 31.59 (4CH2 in ring), 37.50 and 38.20 (2CH2 in chain), 48.30 (CHSO2), 56.10 and 69.31 (2MeO), 77.82 (CHOMe, COMe), 117.63 (CH2=), 128.85 (2CHarom), 129.15 (2CHarom), 134.42 (CH=), 138.80 and 143.20 (2Carom).X-Ray crystallographic data for sulfone 8a. C20H30O4S, M = 366.50, monoclinic, space group P21, a = 7.9421(5) Å, b = 14.6954(9) Å, c = = 8.5892(5) Å, a = 90°, b = 107.985(1)°, g = 90°, V = 953.48(10) Å3, Z = 2, Dc = 1.277 g cm–3, m = 0.191mm–1, F(000) = 396, 2qmax < 50°.Unit cell parameters and intensities of 2895 (Rint = 0.0286) independent reflections were measured with a Siemens SMART Platform CCD diffractometer, monochromated MoKa (l = 0.71073 Å) radiation at 173(2) K, crystal size 0.22×0.22×0.08 mm. The structure was solved by the direct methods and refined by the full-matrix least-squares procedure on F2 in the anisotropic approximation for non-hydrogen atoms.Refinement converged to R1 = 0.0480 for 2491 reflections with I > 2s(I) based on F; and wR2 = = 0.1083, GOF = 1.061 for all independent reflections. All calculations were carried out using the system SHELXTL-V5.2. Atomic coordinates, thermal parameters, bond lengths and bond angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC).For details, see Mendeleev Commun., Issue 1, 1999. Any request to the CCDC for data should quote the full literature citation and the reference number 1135/38. suggest that the conformational rigidity of the bicyclic TPI-like intermediate derived from methoxycycloalkenes is the main factor that controls the steric outcome of the entire coupling.The observed high diastereoselectivity of the multicomponent coupling greatly enhances the potential of the suggested procedure based on the controlled sequence of AdE reactions as a novel approach to the convergent synthesis of polyfunctional compounds. This work was supported by the National Science Foundation (grant no. 8921358), the U.S. Civilian Research and Development Foundation (award no.RC2-141) and the Russian Foundation for Basic Research (grant no. 98-03-32970a). References 1 A. Hayford, M. Lovdahl, M. I. Lazareva, Yu. K. Kryschenko, T. Johnson, A. D. Dilman, I. P. Smoliakova, R. Caple and W. A. Smit, Mendeleev Commun., 1997, 48. 2 M. I. Lazareva, Yu. K. Kryschenko, A. Hayford, M. Lovdahl, R. Caple and W. A. Smit, Tetrahedron Lett., 1998, 39, 1083. 3 M. I. Lazareva, Yu. K. Kryschenko, A. D. Dilman, A. Hayford, R. Caple and W. A. Smit, Izv. Akad. Nauk, Ser. Khim., 1998, 924 (Russ. Chem. Bull., 1998, 47, 895). 4 B. M. Trost and D. P. Curran, Tetrahedron Lett., 1981, 22, 1287. OMe But 2 (VE-I) i, p-TolSCl ii, TiCl4 iii, OMe TPI SnBu3 7 But STol-p OMe OMe 5 (VE-II) 11 (60%) Scheme 3 OMe STol-p OMe H OMe i, p-TolSCl ii, TiCl4 iii, OMe 5 (VE-II) But OSiMe3 13 3 (VE-I) 12 O OMe But STol-p OMe 14 (76%) Scheme 4 C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(11) C(12) C(13) C(14) C(15) C(16) C(17) C(18) C(19) C(20) O(1) O(2) O(3) S(1) O(4) Figure 1 Molecular structure of sulfone 8a. Received: Moscow, 11th September 1998 Cambridge, 17th November 1998; Com. 8/07975K

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出版商:RSC    

年代:1999

数据来源: RSC

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Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) Optically active 2,2-dimethyl-1,3,4-triazabicyclo[4.1.0]heptan-5-one: synthesis, spontaneous resolution and absolute configuration Remir G. Kostyanovsky,*a Pavel E. Dormov,a Peteris Trapencieris,b Boriss Strumfs,b Gulnara K. Kadorkina,a Ivan I. Chervina and Ivars Ya. Kalvin’sb a 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 b Latvian Institute of Organic Synthesis, LV-1006 Riga, Latvia. E-mail: peteris@osi.lanet.lv Bicycle (±)-1 crystallises as a conglomerate (space group P21) and undergoes spontaneous resolution on crystallisation from chloroform or acetone (16–44% ee). The absolute configuration (S)-(–)-1 was determined by synthesis from (S)-Ser-OMe; mutarotation due to the partial conversion of 1 into the corresponding isopropylidene 4 was observed in MeOH solution.Derivatives of aziridine-2-carboxylic acid (Azy)1–4 have been studied intensively.5–7 Some of them (azimexon and leakadine) show high biological activity.8–10 The asymmetric synthesis of Azy derivatives was reported3,4,11 and a higher activity of the L-leakadine (amide of aziridine-2-carboxylic acid, Azy-NH2) with respect to the racemate was observed.10 The synthesis of these compounds in enantiopure form is of interest from the point of contemporary interest for chiral drugs.12 The simplest method for obtaining enantiopure materials is their spontaneous resolution by crystallisation, which may occur when the racemate is a conglomerate.13,14 For the strained aziridine-2-carboxylic acid derivative 2,2-dimethyl-1,3,4-triazabicyclo[ 4.1.0]heptan-5-one 15 the non-centrosymmetric space group P21 was determined by X-ray structural analysis.6 This means that compound 1 forms a conglomerate.Indeed, on crystallisation (from CHCl3 or acetone) of (±)-1 prepared by a known procedure,5 crystalline samples showing (+) or (–) rotation were obtained.† In order to determine its absolute configuration compound 1 was synthesised from commercial (S)-Ser-OMe hydrochloride {[a]D 23 = 3.5° (c 5.0 MeOH)} (Scheme 1), eventually giving (S)-(–)-1.Azy-OMe (S)-(–)-2 was prepared under Mitsunobu conditions15 and was converted into (S)-(–)-1 by a known procedure,5 the mp of (–)-2 is higher than that of its racemate: 135–136 °C and 126–127 °C, respectively. The rotation of (S)-(–)-1 in MeOH was found to decrease gradually from –87° to –68.1° (after 1.6 h), –65.7° (after 2.3 h), reaching a constant value of –59.8° after 24 h.According to 1H NMR, the isomerisation of (S)-(–)-1 into isopropylidenehydrazide (S)-(–)-4 to reach equilibrium 1:4 ª 2 (Scheme 2) is responsible for the observed mutarotation.All compounds were characterised by spectroscopic data (Figure 1). The 1H NMR spectra of aziridines (S)-(–)-2–4 were in line with those obtained from earlier detailed investigations of Azy and their 15N analogues.16 The 1H NMR signals of 1 (Figure 1) were assigned by selective heteronuclear double resonance.Thus, under the conditions {He, d 3.94 ppm}, the 13C NMR signal for carbon MeA (qqd, d 24.14 ppm) transforms † Characteristics and spectroscopic data. NMR spectra were recorded on a Bruker WM-400 spectrometer (with TMS as an internal standard) at 400.13 MHz (1H) and 100.62 MHz (13C). Optical rotation was measured on ‘Perkin Elmer-141’ and ‘Polamat A’ polarimeters. The CD spectra were taken on a JASCO-J-500A instrument with a DP-500N data processor.(±)-1: obtained by method described in ref. 5, mp 126–127 °C (acetone). 1H NMR (CDCl3) d: 1.29 (s, 3H, MeA), 1.40 (s, 3H, MeB), 2.13 (dd, 1H, Hb, 3Jab 5.9 Hz, 2Jbc 1.0 Hz), 2.25 (dd, 1H, Hc, 3Jac 3.0 Hz, 2Jbc 1.0 Hz), 2.65 (ddd, 1H, Ha, 3Jab 5.9 Hz, 3Jac 3.0 Hz, 4Jad 2.7 Hz), 3.94 (s, 1H, He), 6.82 (s, 1H, Hd). 13C NMR (CDCl3) d: 24.14 (qqd, MeA, 1J 127.9 Hz, 3JCH 4.4 Hz, 3JCHe 5.0 Hz), 24.98 (qq, MeB, 1J 127.9 Hz, 3JCHc 4.4 Hz), 25.08 (ddd, 7-C, 1JCHb 181.7 Hz, 1JCHc 162.8 Hz, 2JCHa 2.2 Hz), 32.73 (d, 6-C, 1J 183.8 Hz), 67.80 (s, 2-C), 169.48 (s, 5-C). Spontaneous resolution of (±)-1: by crystallisation of (±)-1 (68 mg) from CHCl3 at slow evaporation at 20 °C samples (+)-1 {2.0 mg, druse, [a]D 20 = 14.2° (c 0.2, MeOH), ee 16.3%} or (–)-1 {4.6 mg, small crystals, [a]D 20 = –14.8° (c 0.5, MeOH), ee 17.0%} were obtained.The crystallisation of (±)-1 (34 mg) from acetone at 4–6 °C gave one crystal (+)-1 {1 mg, [a]D 20 = 40.9° (c 0.1, EtOH), ee 44.3%}. (S)-(–)-1: yield 86%, mp 135–136 °C (acetone), [a]D 20 = –87° (c 2.1, MeOH), [a]D 20 = –92.2° (c 1.2, EtOH), [a]D 20 = –40.8° (c 0.9, CHCl3), De = –3.5 (237.5 nm), De = 0 (223 nm), De = +7.7 (212.5 nm) (c 0.13 mol l–1, MeOH).(S)-(–)-2: yield 36%, bp 72 °C (40 torr), [a]D 20 = –23.1° (c 1.0, MeOH) (cf. ref. 19). (S)-(–)-3: yield 50%, oil, [a]D 20 = –27.8° (c 1.0, MeOH). (S)-(–)-4: mp 117–118 °C (C6H6) (cf. ref. 5); [a]D 20 = –6.7° (c 0.2, MeOH), calculated from [a]D 20 for pure (S)-(–)-1 and [a]D 20 = –34.3° (c 0.2, MeOH) for mixture 4:1 = 2. 1H NMR (CDCl3) d: 1.68 (br. s, 1H, He), 1.87 (s, 3H, MeA), 1.90 (br. m, 1H, Hb), 2.06 (s, 3H, MeB), 2.09 (br. m, 1H, Hc), 2.83 (br. m, 1H, Ha), 8.51 (br. s, 1H, Hd). Ha N Hc Hb O N N Hd He MeA MeB (±)-1 6.82 3.94 2.65 2.25 2.13 1.40 1.29 3JHaHb 3JHaHc MeA MeB Ha Hb Hc Hd He Ha {Hd} Figure 1 1H NMR spectrum of (±)-1 in CDCl3. d/ppm NH (S)-(–)-2 HO CO2Me H3N H Cl CO2Me (S)-(+) i NH (S)-(–)-3 CONHNH2 ii iii (S)-(–)-1 Scheme 1 Reagents and conditions: i, NH3, CH2Cl2, then Ph3P–DIAD, CH2Cl2, 1 h, 3–5 °C and 12 h, 20 °C; ii, dry H2NNH2, 1.5 h, –10 °C, then 5 h, 20 °C; iii, Me2CO, 20 h, 55 °C.Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) into qq, and its coupling constant 3JMeA–He 5.0 Hz. At the same time under the conditions {MeB, d 1.40 ppm}, the spectrum for carbon MeB (qq, d 24.98 ppm) transforms into a pure q.This is in agreement with the molecular structure of 1:6 dihedral angles MeA–C–N–He ª 0°, MeB–C–N–He ª 90°. In addition, we observed two features in the 1H NMR spectrum of 1: large coupling constant 4JHaCNHd 2.7 Hz and a strikingly high difference in the coupling constants D1JCH = 18.9 Hz between protons Hb and Hc (usually for aziridine5 this difference does not exceed 11.6 Hz).17,18 This work was supported by the Russian Foundation for Basic Research (grant no. 97-03-33021) and the Latvian Scientific Council (grant no. 722). References 1 K. Okawa and K. Nakajima, Biopolymers, 1981, 20, 1811. 2 K. Okawa, K. Nakajima and T. Tanaka, J. Synth. Org. Chem. Jpn., 1984, 42, 390. 3 D. Tanner, Angew. Chem., Int. Ed. Engl., 1994, 33, 599. 4 W. H. Pearson, B. W. Lian and S. C. Bergmeier, Aziridines and Azirines: Monocyclic, in Comprehensive Heterocyclic Chemistry II, ed. A. Padwa, Pergamon, New York, 1996, vol. 1A, p. 1. 5 P. T. Trapentsier, I. Ya. Kalvin’sh, E. E. Liepin’sh, E. Ya. Lukevits, G. A. Bremanis and A. V. Eremeev, Khim. Geterotsikl. Soedin., 1985, 774 [Chem.Heterocycl. Compd. (Engl. Transl.), 1985, 21, 646]. 6 A. F. Mishniev, M. F. Bundule, Ya. Ya. Bleidelis, P. T. Trapentsier, I. Ya. Kalvin’sh and E. Ya. Lukevits, Khim. Geterotsikl. Soedin., 1986, 477 [Chem. Heterocycl. Compd. (Engl. Transl.), 1986, 22, 390]. 7 K. F. Koehler, H. Zaddach, G. K. Kadorkina, I. I. Chervin and R. G. Kostyanovsky, Izv. Akad.Nauk, Ser. Khim., 1993, 2136 (Russ. Chem. Bull., 1993, 42, 2049). 8 U. Bicker, Fortsch. Med., 1978, 96, 661. 9 I. Ya. Kalvin’sh and E. B. Astapenok, Belg. Patent, 860239, 1978 (Chem. Abstr., 1979, 90, 34103j). 10 I. Ya. Kalvin’s, N. M. Gipsh, A. G. Merson, E. B. Astapenok and P. T. Trapentsier, USSR Inventor’s Certificate no. 787994, (Byull. Izobret., 1980, no. 46, 214). 11 K. Jahnisch, F.Grundemann and A. Kunath, XIII International Symposium: Synthesis in Organic Chemistry, Oxford, 1993. 12 S. T. Stinson, Chem. Eng. News, 1997, 75 (42), 38. 13 J. Jacques, A. Collet and S. H. Wilen, Enantiomers, Racemates, and Resolutions, Krieger Publ. Comp., Malabar, Florida, 1994. 14 G. A. Potter, C. Garcia, R. McCague, B. Adger and A. Collet, Angew. Chem., Int. Ed. Engl., 1996, 35, 1666. 15 O. Mitsunobu, Synthesis, 1981, 1. 16 I. I. Chervin, A. A. Fomichov, A. S. Moskalenko, N. L. Zaichenko, A. E. Aliev, A. V. Prosyanik, V. N. Voznesenskii and R. G. Kostyanovsky, Izv. Akad. Nauk SSSR, Ser. Khim., 1988, 1110 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1988, 37, 972). 17 I. I. Chervin, A. E. Aliev, V. N. Voznesenskii, S. V. Varlamov and R. G. Kostyanovsky, Izv. Akad. Nauk SSSR, Ser. Khim., 1987, 1917 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1988, 36, 1781). 18 I. I. Chervin, A. E. Aliev, V. N. Voznesenskii and R. G. Kostyanovsky, Izv. Akad. Nauk SSSR, Ser. Khim., 1992, 1688 (Bull. Russ. Acad. Sci., Div. Chem. Sci., 1992, 41, 1312). 19 G. V. Schustov, S. N. Denisenko, I. I. Chervin and R. G. Kostyanovsky, Izv. Akad. Nauk SSSR, Ser. Khim., 1988, 1606 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1988, 37, 1422). Ha N Hc Hb O N N Hd MeB MeA (S)-(–)-4 He (S)-(–)-1 MeOH Scheme 2 Received: Moscow, 17th September 1998 Cambridge, 5th November 1998; Com. 8/07878E

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Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) Effect of copper cations on the formation of radicals in the adsorption of olefins and benzene on Cu/ZSM-5 zeolite Alexander N. Il’ichev,* Valery A. Matyshak and Vladimir N. Korchak N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow, Russian Federation. Fax: +7 095 938 2156 Isolated Cu2+ cations in ZSM-5 zeolite produced oligomeric radicals from propylene and did not result in the formation of radicals in the adsorption of ethylene and benzene.Nitroxyl organic compounds were asserted1 to play an important role in the selective catalytic reduction of NOx by hydrocarbons in an excess of oxygen. Oligomeric radicals can participate in the formation of nitroxyl compounds. Oligomeric radicals were observed on H-ZSM-52 and Cu/ZSM-53 zeolites.However, the role of copper cations in the formation of oligomeric radicals in the adsorption of olefins was not studied. This work is devoted to this problem. The preparation of zeolites and the EPR procedure are described in detail elsewhere.4 EPR measurements were carried out in vacuo (P = 10–4 Pa) at room temperature in H-ZSM-5 (SiO2/Al2O3 = 40) and 0.15–2.86% Cu/ZSM-5 zeolites after the treatment with oxygen at 970 K and P = 200–500 Pa for 1 h.The concentrations of adsorbed molecules were determined by hydrocarbon desorption upon heating of the samples to 800 K. The EPR spectra of oligomeric R· and benzene (C6H6)· radicals (Figure 1, curves 1 and 2) were observed during adsorption of olefins (C2H4 or C3H6) and benzene at room temperature and P = 200 Pa on the H-ZSM-5 sample.The concentration of radicals in the sample was determined by double integration of the EPR spectrum followed by the comparison with the data obtained using CuSO4·5H2O and Mn2+–MgO reference samples. The A value [hyperfine coupling constant (HFC)] was calculated from the ratio A = (Hn – H1)/(n – 1), where H1 and Hn are the field strengths for the first (1) and last (n) lines of the HFC spectrum.The radical concentrations and g and A values are presented in Table 1. Similar spectra and parameters have been obtained previously.2,5,6 The oligomeric radical is stable, because its spectrum (Figure 1) remained unchanged after evacuation of the olefin. The intensity of the spectrum of the benzene radical decreased by a factor of 10 when C6H6 was evacuated for 10 min. The spectra of oligomeric radicals can be observed within the temperature range 300–450 K.Curve 1 in Figure 2 presents the intensities of the spectrum of the radical (J/Jmax) observed after heating of the sample in vacuo for 10 min. The repeated adsorption of the olefin on the sample heated at temperatures higher than 450 K does not result in the formation of radicals.The introduction of copper into H-ZSM-5 zeolite by ion exchange produces isolated Cu2+ cations, which are localized near lattice Al3+ cations.7 The spectrum for the 1.3% Cu/ZSM-5 sample is presented in Figure 3 (curve 1). An analysis of the spectrum shows that copper cations in zeolite occur in both square pyramid [g|| (1) = 2.33, A|| = 170 G] and square planar [g|| (2) = = 2.29, A|| = 180 G] coordination. The admission of propylene at T = 293 K decreased the intensity of the signal from copper cations (Figure 3, curve 2), and the spectrum of the oligomeric R· radical appeared.The spectra of the R· radicals on H-ZSM-5 and 1.3% Cu/ZSM-5 coincide. In addition, the intensity of the signal of the R· radicals decreased as the sample was heated in vacuo.These data are similar to those for H-ZSM-5 (Figure 2, curve 2). These data indicate that the oligomeric radicals are localized at analogous sites in zeolite channels. The dependences of the concentrations of the radicals on the copper content in the sample in the adsorption of propylene and benzene are presented in Figure 4.It can be seen that the presence of copper in zeolite exerts different effects on the formation of R· and (C6H6)· radicals. For example, the concentration of R· radicals increased by an order of magnitude as the copper content in the sample increased from 0.15% to 1.3%. A further increase in the copper content in the sample resulted in a decrease in the EPR signal from the R· radicals and in changes in their spectra, which are manifested as the disappearance of HFC lines.Table 1 Concentrations of adsorbed molecules and radicals on H-ZSM-5 zeolite. Molecule Nad/10–20 g–1 Radicals Ns/10–15 g–1 g A/G C2H4 0.5 R 7.0 2.004 8.0 C3H6 6.0 R 8.7 2.004 8.0 C6H6 4.0 (C6H6) 7.4 2.004 4.5 40 G DPPH 1 2 3 J DPPH 40 G Figure 1 EPR spectra of (1) the oligomeric radical after propylene adsorption and the (C6H6)· radical (2) in a benzene atmosphere and (3) after evacuation of benzene at 293 K.Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) In the case of benzene, an increase in the copper content in zeolite resulted in a decrease in the concentration of benzene radicals.Seven HFC lines were observed only in the spectra of the radical on 0.15–0.25% Cu/ZSM-5 samples, whereas they were not observed in the samples with the copper content of 1.3–2.86%.In the ethylene adsorption, the concentration of the oligomeric radicals decreased, as in the case of benzene radicals, with increasing copper content in the samples. Note that oligomeric radicals are formed in the adsorption of propylene on reduced Cu/ZSM-5 samples, whereas no radicals were observed in the adsorption of the hydrocarbons on H-ZSM-5 zeolite heated in H2 (970 K, P = 200 Pa, 1 h).Olefinic and benzene radicals are formed at the sites created upon heating of H-ZSM-5 zeolite in oxygen at T > 600 K (oxidative centres), and they are deactivated by hydrogen under these conditions.The nature and properties of these oxidative centres were considered in refs. 8 and 9. We believe that these centres are formed due to the cleavage of stressed Si–O–Al bonds. The concentration of these centres in H-ZSM-5 zeolite (SiO2/Al2O3 = 40) can be estimated from the concentration of the radicals observed. It does not exceed 1016 g–1 (Table 1). This value is 0.02% of the concentration of Al3+ cations in the zeolite, which is consistent with the concentration of oxidative centres in H-ZSM-5 estimated in ref. 9. When copper ions are introduced into H-ZSM-5, some of them interact with the oxidative centres to change the capability of generating radicals. The newly formed surface centres lose the ability to generate radicals upon interaction with benzene and ethylene.The study of the copper state in oxidized 0.15–2.86% Cu/ ZSM-5 zeolites shows4 that the concentration of isolated copper cations linearly increased with the copper content of the zeolite. The concentration of oligomeric radicals also increased (Figure 4). A decrease in the concentration of isolated Cu2+ cations in the 1.3% Cu/ZSM-5 sample during its thermal treatment with hydrogen also results in a decrease in the concentration of radicals (Figure 4, curves 1 and 3).This fact suggests that oligomeric radicals are formed at isolated Cu2+ cations during propylene adsorption. The fact that isolated copper ions did not produce radicals during the interaction with benzene and ethylene and did form them during the interaction with propylene can be explained by the difference in the ionization potentials of the molecules,2 which is higher for benzene and ethylene than for propylene.We have found previously4 that isolated Cu2+ cations are the active centres for NO reduction on copper-containing zeolites. The measurements in 1.3% Cu/ZSM-5 zeolite showed that the ratio between the numbers of oligomeric R· radicals and isolated Cu2+ cations does not exceed 2×10–3.In addition, the ratio between the numbers of radicals and adsorbed propylene molecules (Table 1) is 10–4. The data obtained show that the temperature region of the existence of radicals (300–450 K) (Figure 2) is lower than that of the occurrence of the reaction (450–750 K).4,10 These data do not allow us to consider the oligomeric radicals as intermediates in the selective reduction of NOx by hydrocarbons in an excess of oxygen on Cu/ZSM-5.It is noteworthy that the conclusion was drawn without taking into account possible contributions from radical ion reactions. This work was financially supported by the Russian Foundation for Basic Research (grant no. 97-03-32012a). References 1 M. Shelef, Chem. Rev., 1995, 95, 65. 2 A. A. Slinkin, A. V. Kucherov, D. A. Kondrat’ev, T. N. Bondarenko, A. M. Rubinstein and Kh. M. Minachev, Kinet. Katal., 1986, 27, 156 [Kinet. Catal. (Engl. Transl.), 1986, 27, 141]. 1.0 0.8 0.6 0.4 0.2 0.0 250 300 350 400 450 T/K Intensity (J/Jmax) 1 2 Figure 2 Relative intensities of the spectrum of R· radicals on (1) H-ZSM-5 and (2) 1.3% Cu/ZSM-5 after heating of the samples at different temperatures in vacuo for 10 min.DPPH 1 2 ×1 ×10 g|| (1) g|| (2) 200 G g|| (1) DPPH ×1 Figure 3 EPR spectra of (1) pre-oxidized 1.3% Cu/ZSM-5 zeolite and (2) the sample after adsorption of propylene at 293 K and P = 200 Pa. 8 6 4 2 0 1 2 3 10 8 6 4 2 1 2 3 Cu (%) Ns/10–15 g–1 Ns/10–16 g–1 Figure 4 Dependences of the concentrations of (1) oligomeric radicals and (2) (C6H6)· radicals for oxidized samples and of (3) oligomeric radicals for reduced samples on the copper concentration.Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) 3 A. V. Kucherov, J. L. Gerloch, H.-W. Jen and M. Shelef, J. Catal., 1995, 152, 63. 4 V. A. Matyshak, A. N. Il’ichev, A. A. Ukharsky and V. N. Korchak, J. Catal., 1997, 171, 254. 5 A. A. Slinkin, A. V. Kucherov, D. A. Kondrat’ev, T. N. Bondarenko, A. M. Rubinstein and Kh. M. Minachev, Kinet. Katal., 1986, 27, 364 [Kinet. Catal. (Engl. Transl.), 1986, 27, 312]. 6 J. M. Lunsford, Adv. Catal., 1972, 22, 265. 7 A. V. Kucherov and A. A. Slinkin, Usp. Khim., 1992, 1687 (Russ. Chem. Rev., 1992, 61, 925). 8 A. V. Kucherov and A. A. Slinkin, Kinet. Katal., 1983, 24, 947 [Kinet. Catal. (Engl. Transl.), 1983, 24, 804]. 9 A. V. Kucherov and A. A. Slinkin, Kinet. Katal., 1997, 38, 768 [Kinet. Catal. (Engl. Transl.), 1997, 38, 703]. 10 M. Ivamoto, N. Mizuno and H. Yahiro, Proceedings of the 10th International Congress on Catalysis, Budapest, 1992, p. 1285. Received: Moscow, 30th July 1998 Cambridge, 10th November 1998; Com. 8/06227G

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年代:1999

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Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) Detection of EPR spectra in S = 2 states of MnIII(salen) complexes Konstantin P. Bryliakov,a Dmitrii E. Babushkinb and Evgenii P. Talsi*b a Department of Natural Sciences, Novosibirsk State University, 630090 Novosibirsk, Russian Federation. Fax: +7 3832 35 5756 b G. K. Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russian Federation.Fax: +7 3832 34 3766; e-mail: talsi@catalysis.nsk.su The EPR signals of MnIII(salen) complexes (R,R)-(–)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminomanganese(III) chloride 1 and N,N'-bis(salicylidene)ethylenediaminomanganese(III) chloride 2 were detected and used for the characterisation of intermediates in catalytic epoxidation.A recent major achievement in catalytic enantioselective oxidation is the epoxidation of prochiral unfunctionalised olefins catalysed by Mn(salen) complexes.1–4 Two practicable catalytic systems for the enantioselective epoxidation of unfunctionalised olefins were developed. One of them involves a two-phase system with commercial aqueous buffered bleach phase and an organic phase that is a solution of a substrate and a catalyst in a suitable solvent.1 The other system is a solution of m-chloroperbenzoic acid (m-CPBA), N-methylmorpholine N-oxide (NMO) and a catalyst in dichloromethane at a low temperature (–78 °C).5,6 The latter system is effective in the enantioselective epoxidation of styrene.5 To elucidate the mechanism of MnIII(salen)-catalysed oxidation, it is important to monitor transformations of the catalyst in the course of the catalytic reaction.In this work, we report the first EPR data on MnIII(salen) complexes (R,R)-(–)-N,N'-bis(3,5-ditert- butylsalicylidene)-1,2-cyclohexanediaminomanganese(III) chloride 1 and N,N'-bis(salicylidene)ethylenediaminomanganese(III) chloride 2 in various solvent systems.The preliminary data on the interaction of complex 1 with iodosylbenzene (PhIO) and m-CPBA are also presented. EPR spectroscopy has rarely been applied to study the electronic structure of trivalent manganese complexes with an even number of unpaired electrons. This is a result of large zero-field splittings or fast spin relaxation processes. Although a few of EPR studies of trivalent manganese impurity ions and complexes have been reported, these have relied largely on indirect detection methods or very high observation frequencies.7–10 There is the only report where weak EPR transition at g ª 8 was observed for manganese(III) acetylacetonate at 12 K by conventional X-band EPR spectroscopy.11 Dexheimer et al.interpreted the Mn3+ spectrum using the following spin Hamiltonian: The zero-field interaction splits the levels of an S = 2 spin system into two doublets, one of them is a linear combination of the ms = ô±2ñ states, and the other, of the ms = ô±1ñ states, and a singlet corresponding to the ms = ô0ñ state.The forbidden EPR transitions may be observed between the levels of the ô±2ñ non-Kramers doublet.The X-band EPR spectrum of a frozen 0.1 M solution of complex 1 in CH2Cl2 at 77 K is shown in Figure 1(a).† The field position and shape of the observed weak signal at g = 8.0 ± 0.3 are close to those for the signal observed for manganese(III) acetylacetonate and attributed to forbidden transitions within ô±2ñ non-Kramers doublet.11 The relatively sharp resonance at g = 4.3 is characteristic of rhombic FeIII complexes and belongs to very small impurities (less than 1 mol%) of FeIII species in complex 1.The addition of FeCl3·6H2O to a solution of complex 1 gives rise to a sharp increase in the signal at g = 4.3. The FeIII impurities were detected not only in our particular sample. The EPR spectrum of the optical isomer of † General experimental details.Complex 1 [(R,R)-(–)-N,N'-bis(3,5-ditert- butylsalicylidene)-1,2-cyclohexanediaminomanganese(III) chloride] and N-methylmorpholine N-oxide from Aldrich were used as received. Iodosylbenzene was prepared by hydrolysis of the corresponding diacetate (Aldrich) with aqueous sodium hydroxide and stored at 253 K. Complex 2 [N,N'-bis(salicylidene)ethylenediaminomanganese(III) chloride] and its MnII precursor were prepared as described in ref. 12. All other chemicals and solvents were of reagent grade, and they were used without further purification. EPR spectra were recorded in quartz tubes (d = 5 mm) at 77 K using a Bruker ER-200D X-band spectrometer. O H N Mn O H N H H Cl O H N Mn O H N Cl 1 2 H=b(gz Hz Sz +gy HySy+gzHzSz) + D(Sz 2 – 2) + E(Sz 2 – Sy 2) (1) (a) (b) (c) (d) (e) * 0.03 0.13 0.23 0.33 H(T) 0.067 0.093 g = 8.0 g = 4.3 g = 2.0 Mn A = 43 G H(T) Figure 1 X-band EPR spectra (77 K) of 0.05 M solutions of complex 1 (a) in CH2Cl2 and (b)–(c) in CH2Cl2 containing N-methylmorpholine N-oxide ([NMO] = 1 M); (d) EPR spectrum (77 K) of 0.05 M solution of a MnII(salen) precursor of complex 2 in DMSO; (e) EPR spectrum (77 K) of MnIV(salen) complex recorded 1 min after the onset of reaction of complex 1 ([1] = 0.05 M) with one equivalent of m-chloroperbenzoic acid at 273 K [spectrometer frequency, 9.3 GHz; microwave power, 40 mW; modulation frequency, 100 kHz; modulation amplitude, 20 G; gain, 2.5×105 (a)–(c), 2.5×103 (d), 2.5×104 (e)].Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) complex 1 (S,S)-(+)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2- cyclohexanediaminomanganese(III) chloride 1' (Aldrich) also exhibited a resonance signal at g = 4.3 but its intensity was lower than that in complex 1 by a factor of two.The signals at g = 8.0 for complexes 1 and 1' coincided. The nature of the additional low-field line marked in Figure 1(a) with an asterisk is still unclear. Coordination of N-methylmorpholine N-oxide to complex 1 changes the shape of the EPR signal, and the six-line hyperfine structure from one manganese ion (I = 5/2) can be clearly seen [Figures 1(b)–(c)].The hyperfine splitting (44±3 G) that appears at the g = 8 signal is rather close to that determined for MnIII impurity ions in TiO2 (Az = 53 G)10 and for manganese(III) acetylacetonate (Az = 55 G).11 We have compared the EPR signals of 0.1 M solutions of complexes 1 and 2 in dimethylsulfoxide (DMSO) at 77 K.DMSO was used as a solvent owing to proper solubility of both complexes. The positions, shapes and intensities of the signals observed at g = 8.0 for complexes 1 and 2 coincided. This result supports the assignment of a resonance at g = 8.0 to complex 1 rather than to any manganese impurities.It is improbable that the concentrations of such impurities were equal in complexes 1 and 2. Low-symmetry S = 5/2 MnII species, which may be present as impurities in MnIII compounds, can also give rise to downfield EPR signals. The two species can be clearly distinguished, however, because the S = 5/2 MnII(salen) system produces very intense resonance at g = 2.0 in addition to any other downfield signals.Figure 1(d) shows the EPR spectrum of a MnII(salen) precursor of complex 2 in DMSO, which was prepared according to the procedure described in ref. 12. This spectrum was recorded at an amplification lower than that in Figure 1(a) by two orders of magnitude. It is seen that MnII(salen) exhibits an intense signal at g = 2.0 with the partially resolved hyperfine splitting (87 G) from the manganese nucleus.The MnIV(salen) complex obtained via a reaction of complex 1 with one equivalent of m-CPBA in CH2Cl2 at 273 K exhibits a resonance at g = 5.7±0.3, with the hfs splitting (73 G) from manganese nucleus typical of MnIV species with D > hn13–16 [Figure 1(e)]. The amplification in Figure 1(e) is lower than that in Figure 1(a) by one order of magnitude, while concentrations of MnIII and MnIV species are equal.Thus, the signal of MnIII(salen) is much weaker than that of MnIV(salen) at equal manganese concentrations. This result agrees with the literature data. It was found for manganese impurity ions in TiO2 that the resonances of MnIII are about an order of magnitude weaker than those of the same quantity of corresponding MnIV species.10 Based on the aforesaid, we can conclude that it is mononuclear MnIII(salen) complex 1 that exhibits the EPR signal at g = 8.0±0.3.Dimers or higher aggregates of 1 can be ruled out. Based on the data for MnIII/MnIV and MnII/MnIII mixed-valence binuclear complexes, more than six line hyperfine splitting is expected for dimeric or oligonuclear species.17,18 The EPR signal of complex 1 was found to be very sensitive to the nature of axial ligands [compare Figures 1(a) and 1(b)].Another illustration of this fact is presented in Figure 2. It can be seen, that the intensity and shape of the resonance at g = 8.0 dramatically changed with an increase in the concentration of (a) (b) (c) (d) (e) (f) 0.0 0.08 0.16 H(T) g = 8.0 g = 4.3 Figure 2 X-band EPR spectra (77 K) of 0.05 M solutions of complex 1 (a) in CH2Cl2 and (b)–(f) in CH2Cl2 containing various amounts of pyridine: (b) [Py] = 0.0125 M, (c) 0.025 M, (d) 0.0375 M, (e) 0.05 M, (f) 0.1 M.The spectrometer settings are given in Figure 1. (a) (b) g = 8.0 g = 4.3 0.03 0.13 H(T) Figure 3 (a) X-band EPR spectrum (77 K) of a 0.05 M solution of complex 1 in CH2Cl2; (b) EPR spectrum of sample (a) 3 min after stirring with one equivalent of PhIO at 273 K.Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) pyridine in the solution of complex 1. This change was stopped when the [Py]/[1] ratio reaches unity, in agreement with the coordination of one pyridine molecule per molecule of complex 1. The reason for the decrease of the EPR signal of complex 1 via pyridine coordination is still unclear.It is known that axial ligands dramatically affect the D value in MnIII porfirazine complexes.11 Unfortunately, we have not found the relations between the D value and the probability of the ô–2ñ ® ô+2ñ transition in the literature. The interaction of complex 1 with one equivalent of m-CPBA at 183 K in CH2Cl2 gives rise to an immediate five-fold decrease in the intensity of the resonance at g = 8.0 similarly to that observed in Figure 2 via pyridine coordination.The valent state of manganese remains unchanged during this reaction, because a very weak signal of MnIV can be detected. Thus, the observed drop of the intensity of the EPR signal at g = 8.0 is caused by the conversion of complex 1 into another MnIII complex, which is characterised by a lower intensity of the MnIII resonance.This complex will be referred to as complex 3. Complex 3 is extremely unstable. It exists only at 183–213 K and rapidly and quantitatively decomposes at higher temperatures to form metastable MnIV species, which were detected by EPR. By analogy with the well-known formation of acylperoxo complexes via the interaction of MnIII porphyrins with m-CPBA at low temperatures,19 it is reasonable to suggest that complex 3 is the acylperoxo complex MnIII(salen)(OOCOAr).The reactivity of this complex toward alkenes will be further investigated. An interesting behaviour was observed in the interaction of complex 1 with PhIO. Immediately after 3 min stirring of a 0.05 M solution of complex 1 with a suspension of PhIO in CH2Cl2 at 273 K, the EPR signal of complex 1 was transformed into another signal of MnIII.The field position, shape and intensity of this signal markedly differ from those of 1 [compare Figures 3(a) and 3(b)]. Thus, a new complex of MnIII, which is further denoted as complex 4, is formed. Probably, complex 4 is the adduct MnIII(salen)(OIPh).Recently, this adduct was detected by electrospray tandem mass spectrometry in the catalytic system 1 + PhIO in CH2Cl2.20 Further studies are needed to support our assumption. In conclusion, we have observed for the first time X-band EPR spectra of MnIII(salen) complexes and demonstrated the applicability of EPR to studies of these practically important systems. 1H NMR and EPR spectroscopic studies of the transformations of the MnIII(salen) catalyst in the course of enantioselective epoxidation are in progress.This work was supported by the Russian Foundation for Basic Research (grant no. 97-03-32495a). References 1 E. N. Jacobsen, W. Zhang, A. R. Muci, J. R. Ecker and L. Deng, J. Am. Chem. Soc., 1991, 113, 7063. 2 T.Katsuki, Coord. Chem. Rev., 1995, 140, 189. 3 M. Palucki, N. S. Finney, P. J. Pospisil, M. L. Guler, T. Ishida and E. N. Jacobsen, J. Am. Chem. Soc., 1998, 120, 948. 4 W. Adam, R. T. Fell, V. R. Stegmann and Ch. R. Saha-Moller, J. Am. Chem. Soc., 1998, 120, 708. 5 M. Palucki, P. J. Pospisil, W. Zhang and E. N. Jacobsen, J. Am. Chem. Soc., 1994, 116, 9333. 6 M. Palucki, G. J. McCormick and E.N. Jacobsen, Tetrahedron Lett., 1995, 36, 5457. 7 D. P. Goldberg, J. Telser, J. Krzystek, A. Garrido Montalban, L. S. Brunel, A. G. M. Barrett and B. M. Hoffman, J. Am. Chem. Soc., 1997, 119, 8722. 8 A.-L. Barra, D. Catteschi, R. Sessoli, G. L. Abbati, A. Cornia, A. C. Fabretti and M. G. Uytterhoeven, Angew. Chem., Int. Ed. Engl., 1997, 36, 2329. 9 R. L. Aurbach and P. L.Richards, Phys. Rev. B., 1975, 12, 2588. 10 H. J. Gerritsen and E. S. Sabisky, Phys. Rev., 1963, 132, 1507. 11 S. L. Dexheimer, J. W. Gohdes, M. K. Chan, K. S. Hagen, W. H. Armstrong and M. P. Klein, J. Am. Chem. Soc., 1989, 111, 8923. 12 K. Srinivasan, P. Michaud and J. K. Kochi, J. Am. Chem. Soc., 1986, 108, 2309. 13 S. Pal, Ph. Ghosh and A. Chakravorty, Inorg. Chem., 1985, 24, 3704. 14 D. P. Kessissglou, W. M. Butler and V. L. Pecoraro, J. Chem. Soc., Chem. Commun., 1986, 1253. 15 A. Smegal and C. L. Hill, J. Am. Chem. Soc., 1983, 105, 3515. 16 J. T. Groves and M. K. Stern, J. Am. Chem. Soc., 1988, 110, 8628. 17 G. C. Dismukes, J. E. Sheats and J. A. Smegal, J. Am. Chem. Soc., 1987, 109, 7202. 18 B. Mabad, J.-P. Tuchagues, Y. T. Hwang and D. N. Hendrickson, J. Am. Chem. Soc., 1985, 107, 2801. 19 J. T. Groves and Y. Watanabe, Inorg. Chem., 1986, 25, 4808. 20 D. Feichtinger and D. A. Plattner, Angew. Chem., Int. Ed. Engl., 1997, 36, 1718. Received: Moscow, 31th July 1998 Cambridge, 23rd October 1998; Com. 8/06228E

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年代:1999

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Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) Evaluation of the hydrophobicity of polyurethane foams Stanislava G. Dmitrienko* and Elena Ya. Gurariy Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation. Fax: +7 095 939 4675; e-mail: dmitrienko@analyt.chem.msu.ru A method for estimating the hydrophobicity of polyurethane foams in comparison with other sorbents is proposed using the distribution coefficient of pyrene between the sorbent and aqueous, acetonitrile–water and ethanol–water solutions as a measure of hydrophobicity.The application of polyurethane foams (PUFs) for concentrating inorganic and organic compounds is relatively recent. Great achievements in this area are presented in a monograph1 and reviews.2–4 To describe the sorption of metal acidocomplexes, some mechanisms (a cation-chelated mechanism, ligand connection or exchange and extraction1,5) are proposed.Our previous studies5–11 allowed us to conclude that the mechanism of extraction by PUFs depends on both the nature of the sorbed compound (this is rather obvious) and the chemical structure of the monomer unit of the polymers: based on ethers (R1–NH–CO–O–[R2–O]n–), esters (R1–NH–CO–O–[CO–R2–O]n–) and their copolymers (R1–NH–CO–O–[R2O–CO–R3–CO]n–).To evaluate the PUF hydrophobicity (and virtually the contribution of the extraction mechanism to sorption processes), we used pyrene as a model nonpolar compound. Previously, pyrene was used for determining the hydrophobicity of the internal region of n-b-octylglucoside micelles.12 The distribution coefficients (D) of pyrene between the micelles and aqueous solutions in comparison with the D values for aqueous–organic systems served as a measure of hydrophobicity.This seems to be reasonable because the distribution coefficient is directly related to the free energy for the transfer of pyrene molecules between the phases.Pyrene was adopted for solving the problem because, as we found previously, its distribution coefficient is independent of the aqueous phase acidity within the range from pH 14 to 6 M HCl and of the concentration of alkali metal cations regardless of the chemical nature of PUFs. Moreover, pyrene solutions exhibit intense luminescence. This fact can be used for determining the high distribution coefficients of pyrene because the limit of detection is rather low (1×10–4 mg ml–1 in aqueous solution).There are several ways for estimating the hydrophobicity of substances, i.e. a versatile hydrophobicity scale is absent. A generally accepted way is to use the Hansh parameter, which is the logarithm of the distribution constants of substances in aqueous–organic systems.13 n-Octanol is the most frequently used organic phase.The aim of this work is to compare the hydrophobicity of polyurethane foams with that of other sorbents, which are applied for concentrating polycyclic aromatic hydrocarbons (silica modified with alkyl groups and active carbons) using the distribution coefficient of pyrene between the sorbent and aqueous, acetonitrile–water and ethanol–water solutions as a measure of hydrophobicity.The following sorbents were used (the trade names are given in parentheses): polyurethane foams based on ethers (M-40, 5-30, 140), esters (2200, 35-08) and their copolymers (VP). The foams were obtained from NPO Polimersintez (Vladimir, Russia) and GPO Radical (Kiev, Ukraine). Diasorbs C4, C8, C16, phenyl and carboxyl (particle sizes of 6, 10, 10, 10 and 6 mm, respectively, the amount of carbon at the surface was 6.0, 10.2, 14.6, 10 and 0.5%, respectively) from BioKhimMak (Russia), Amberlite XAD-8 from Serva (USA), microcrystalline cellulose for column chromatography from Reanal (Hungary), cellulose triacetate synthesised at the Department of Analytical Chemistry, M.V. Lomonosov Moscow State University and AX-21 active carbon were also used.The polyurethane foams were used as tablets (10 mm in height and 16 mm in diameter; the sample weight varied from 0.04 to 0.09 g depending on the PUF type) cut from commercial polymer sheets. The sorption was carried out in the batch mode. A tablet was immersed in the test solution and pressed out with a glass stick to remove air bubbles.In other cases, a sorbent sample (~0.06 g) was placed in a vessel with the test solution. The vessels were shaken using a shaker until the sorption equilibrium was attained (no longer than for 60 min for all of the sorbents). The equilibrium concentrations of pyrene were determined on a MPF-2A Hitachi spectrofluorimeter. The distribution coefficients were calculated from the following equation: where R is the degree of pyrene extraction (%), V is the volume of the pyrene solution (ml) and m is the weight of the sorbent (g).The starting pyrene concentration (1×10–7 M) lies in the linear portion of the sorption isotherm. Table 1 shows that the distribution coefficients of pyrene for its sorption from aqueous solutions by different polyurethane foams; Diasorbs C4, C8 and C16; Amberlite XAD-8 and AX-21 active carbon are rather high (lg D ª 5) and do not differ significantly from each other. However, the D values are much greater than the distribution coefficients for less hydrophobic sorbents.To find the differences between the distribution coefficients of pyrene for the most hydrophobic sorbents, we examined the sorption from acetonitrile–water (30:70 v/v) and ethanol–water (20:80 v/v) solutions, in which the solubility of pyrene is higher than in water.Changes in the hydrophobicity series of sorbents (Table 1) for pyrene sorption from aqueous and aqueous–organic solutions are probably connected with the competition between the solvent and pyrene for the potential sorption centres at the surface.Table 1 Distribution coefficients of pyrene (Pyr) on its sorption from aqueous, acetonitrile–water and ethanol–water solutions; CPyr = 1×10–7 M, msorbent ª 0.06 g, V = 25ml. Sorbent Solvent H2O MeCN–H2O (30:70) EtOH–H2O (20:80) Diasorb carboxyl 2.6±0.1 — — Cellulose 2.6±0.1 — — Cellulose triacetate 2.9±0.1 — — Amberlite XAD-8 4.5±0.2 4.6±0.2 3.1±0.1 Diasorb C4 4.6±0.2 2.2±0.1 2.8±0.1 Diasorb C8 4.6±0.2 2.6±0.1 3.0±0.1 PUF M-40 4.6±0.3 5.3±0.2 4.9±0.2 PUF 2200 4.6±0.2 5.2±0.2 4.5±0.2 Diasorb C16 4.8±0.2 4.7±0.2 3.6±0.2 Diasorb phenyl 4.8±0.2 2.5±0.1 3.5±0.1 PUF 5-30 4.8±0.1 5.0±0.2 4.5±0.2 PUF 35-08 4.9±0.2 5.0±0.2 4.6±0.2 Active carbon AX-21 5.0±0.2 5.5±0.2 5.3±0.2 PUF 140 5.2±0.2 — — PUF VP 5.2±0.2 5.1±0.2 4.7±0.2 lg D± (n= 5, P = 0.95) tpS n1/2 RV (100 – R)m D= ,Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) Table 1 shows that all the polyurethane foams are characterised by approximately the same hydrophobicity and lie between Diasorb C16 and AX-21 active carbon. The results obtained allow us to draw two interesting conclusions on the sorption of nonpolar compounds by polyurethane foams. First, PUFs, regardless of the chemical structure of their monomer units, extract pyrene from aqueous solutions with virtually equal high efficiency (lg D ª 5; see Table 1).On the contrary, the sorption of polar compounds depends on the structure of monomer units of the polymer. In particular, the extraction of metal acidocomplexes,5 phenols10 and naphthols11 with the use of PUFs based on ethers is more effective than that with PUFs based on esters.Copolymers of ethers and esters occupy an intermediate position. Second, the distribution coefficients of two other less hydrophobic (in comparison with pyrene) polycyclic aromatic hydrocarbons, naphthalene and phenanthrene, in the sorption by polyurethane foams are virtually equal (the logarithms of their distribution coefficients are equal to 4.7 and 4.9, respectively).Thus, we can assume that the efficiency of the extraction of hydrophobic compounds (at least the polycyclic aromatic hydrocarbons examined) by polyurethane foams is determined by the hydrophobicity of the polymer rather than by their own hydrophobicity. Thus, the hydrophobicity of PUFs is reasonable and insignificantly depends on the chemical structure.We are grateful to Professor V. K. Runov for his participation in the discussions. This work was supported by the Russian Foundation for Basic Research (grant no. 96-03-33578a). References 1 T. Braun, J. D. Navratil and A. B. Farag, Polyurethane Foam Sorbents in Separation Science, CRC Press, Boca Raton, 1985, p. 220. 2 T.Braun, Fresenius’ Z. Anal. Chem., 1983, 314, 652. 3 T. Braun and A. B. Farag, Anal. Chim. Acta, 1978, 99, 1. 4 T.Braun, Fresenius’ Z. Anal. Chem., 1989, 333, 785. 5 S. G. Dmitrienko, O. A. Kosyreva, V. K. Runov and Yu. A. Zolotov, Mendeleev Commun., 1991, 75. 6 S. G. Dmitrienko, E. V. Loginova, E. N. Myshak and V. K. Runov, Zh. Fiz. Khim., 1994, 68, 1295 (Russ. J. Phys. Chem., 1994, 68, 1172). 7 S. G. Dmitrienko, L. N.Pyatkova, L. P. Bakhaeva, V. K. Runov and Yu. A. Zolotov, Z h. Anal. Khim., 1996, 51, 493 (J. Anal. Chem., 1996, 51, 453). 8 S. G. Dmitrienko, L. N. Pyatkova and V. K. Runov, Zh. Anal. Khim., 1996, 51, 600 (J. Anal. Chem., 1996, 51, 549). 9 S. G. Dmitrienko, L. N. Pyatkova, N. V. Malinovskaya and V. K. Runov, Zh. Fiz. Khim., 1997, 71, 709 (Russ. J. Phys. Chem., 1997, 71, 623). 10 S. G. Dmitrienko, E. N. Myshak, V. K. Runov and Yu. A. Zolotov, Chem. Anal. (Warsaw), 1995, 40, 291. 11 S. G. Dmitrienko, E. N. Myshak, A. V. Zhigulyev, V. K. Runov and Yu. A. Zolotov, Anal. Lett., 1997, 30, 2527. 12 H. Itoh, S. Ishido, M. Nomura, T. Hayakawa and S. Mitaku, J. Phys. Chem., 1996, 100, 9047. 13 C. Hansch and A. Leo, Substituent Constants for Correlation Analysis in Chemistry and Biology, Wiley, New York, 1979, p. 399. Received: Moscow, 11th August 1998 Cambridge, 11th September 1998; Com. 8/06558F

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年代:1999

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Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) Electronic structure and hybridization effects in hypothetical orthorhombic carbon oxynitride Alexander L. Ivanovskii,* Nadezhda I. Medvedeva and Gennady P. Shveikin Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, 620219 Ekaterinburg, Russian Federation. Fax: +7 3432 74 4495; e-mail: ivanovskii@ihim.uran.ru The quantum-chemical examination of the electronic structure and hybridization of the valence states in the orthorhombic Si2N2O and hypothetical C2N2O compounds suggests that the cohesive properties can be improved by the substitution of carbon for silicon in a silicon oxynitride crystal. Sialons (SiAlONs) are solid solutions with the general formula Si6 – xAlxOxN8 – x.1,2 A large class of sialon ceramic materials, which are of crucial technological and commercial importance, is presently known.3–5 Intensive studies are carried out in the field of modification of unique properties of sialon materials combining hardness, high abrasive ability, wear resistance, thermal stability, chemical inertness, etc.1–5 A serious effort was made to search for optimum composition and microstructure of ceramics whose functional properties depend on the grain characteristics (SiAlONs) and are controlled by the morphology, structure and chemical composition of the grainboundary phase.3–5 As a preliminary, it is reasonable to consider the microscopic properties of simple compounds of this system such as AlN, b-Si3N4, Si2N2O.One of the possible ways to optimise the cohesive properties of the Si2N2O phase can be isovalent substitution of carbon atoms for silicon in its lattice.Recent theoretical results predicting extreme thermomechanical properties of the crystalline carbon nitride C3N4 with the basic structure b-Si3N4 allow this supposition (see ref. 6 for a review). In this work, we report on a quantum-chemical study of the electronic structure, chemical bonding and cohesive energy of the orthorhombic Si2N2O and the hypothetical isostructural phase C2N2O.The calculations were carried out by the self-consistent ab initio full-potential linear muffin-tin orbital method (FLMTO).7 The lattice parameters of Si2N2O corresponded to those given in ref. 8. The unit cell included four formula units.The FLMTO calculations were performed in a scalar relativistic version; Si 3s, 3p, 3d and (C,N,O) 2s, 2p orbitals were inserted into the basis as valent states. To take into account the lattice relaxation effect in C2N2O, which is associated with differences in the atomic radii of Si and C, the total energy (Etot) of the crystal was calculated as a function of the unit cell volume (V).The miminum Etot was obtained at V/V0 = 0.80 (V0 is the volume of a Si2N2O cell), which corresponds to the mean decrease in interatomic distances in the hypothetical compound C2N2O by ~7%. Total and local densities of states for Si2N2O and C2N2O are given in Figures 1 and 2. The energy spectrum of Si2N2O (Figure 1) contains three valence bands. The lower energy band is composed predominantly of O 2s states with an admixture of Si 3s states, and the next band includes the contributions of N 2s and Si 3s,3p states.The upper valence band exhibits a mixed character and contains hybridized p states of Si, N and O. The conduction band is made up of antibonding N 2p, O 2p and Si 3p,3d states. The three valence bands are separated by the forbidden gaps DEv, DE'v and DEg (between the valence band and the conduction band) (Table 1).The results of our FLMTO computations are in good agreement with the recent calculations of Si2N2O performed by the OLCAO method.9 The main differences in the electronic spectrum of C2N2O are attributed to a noticeable widening of the basic valence bands of this hypothetical compound, which reflects an increase in the degree of hybridization of p states of the constituting atoms (Figure 2).For the equilibrium volume V/V0 = 0.80, the forbidden gaps DEv and DE'v disappear; the DEg value decreases by ~37% (Table 1). Table 1 presents the cohesive energies (Ecoh) of silicon and carbon oxynitrides. The cohesive energy is calculated as Ecoh = = Etot – SEat, where Etot is the total energy of the crystal and Eat is the energy of free atoms constituting its sublattices.7 The maximum Ecoh value corresponds to Si2N2O.When lattice ‘compression’ occurs, Ecoh of C2N2O dramatically increases approaching the cohesive energy of silicon oxynitride at V/V0 = = 0.80 (Table 1). The Ecoh value is an integrated characteristic of the chemical bonding energy and describes the total effect of interatomic interactions.According to our computations, the chemical bonding in silicon and carbon oxynitrides is of a combined covalent-ionic aV is the cell volume of the calculated oxynitrides; V0 is the cell volume of the real Si2N2O phase.8 Table 1 Charges in the muffin-tin spheres (q, e), cohesion energies Ecoh (eV atom–1) and forbidden band gaps (eV) for Si2N2O and C2N2O.Si2N2O C2N2O C2N2 O V/V0 a 1.00 1.00 0.80 Si, C qs 0.62 1.19 1.02 qp 0.87 1.87 1.92 qd 0.34 — — N qs 0.85 0.88 0.68 qp 1.89 1.59 1.49 O qd 0.99 1.05 0.85 qp 2.39 2.18 1.98 –Ecoh 7.08 5.99 6.89 DEv 0.95 — — DE'v 2.83 0.64 — DEg 3.24 1.14 2.04 Total Si N O 100 0 10 0 20 0 20 0 –2 –1 0 1 E/Ry DOS/Ry–1 Figure 1 Total and local densities of states of the orthorhombic Si2N2O.Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) type. When substituting C for Si, the charges in the muffin-tin spheres of N and O decreased and those in the muffin-tin spheres of carbon increased as compared to silicon. The above effect of p–p hybridization strengthening (covalent bonding) for C2N2O is readily illustrated by the maps of valence charge densities (Figure 3).It can be seen that the degree of hybridization of C–N bond states increases in comparison with Si–N. It also follows from Figure 3 that the charge density distribution (CDD) is essentially non-spherical with different degrees of CDD delocalization along the directions of particular interatomic bonds (Si–N, Si–O, C–N, etc.). The channels (along the c axis) with low CDD are responsible for anisotropic properties of oxynitrides.In our calculations, the lattice relaxation for C2N2O was simulated by uniform compression of a cell of the initial Si2N2O crystal, i.e., all interatomic distances decreased simultaneously. However, in real situations, we usually have low concentrations of an impurity, which results in local distortions around the dopant atoms preserving the crystal structure as a whole.Such local displacements (relaxation) of the nearest atoms around the impurity will lower the total energy and, therefore, increase the absolute value of the cohesive energy. Based on the performed analysis of hybridization effects, we can anticipate that the cohesive energy of Si2N2O with a C dopant will increase owing to stronger hybridization of covalent C–N and C–O bond states.These tentative results of the quantum-chemical simulation of the hypothetical carbon oxynitride allow us to suppose that the doping of the orthorhombic Si2N2O structure will improve the cohesive properties of Si2 – xCxN2O as compared with the isoelectronic Si2N2O. We also suggest that partial or complete isovalent substitution of C for Si in the lattice of sialons can be an efficient way of modifying the functional properties of SiAlON-based ceramic materials, and theoretical and experimental studies in this field can be of great practical importance for the development of a new class of non-metallic ceramic materials based on the C–Al–O–N system.This work was supported by the Russian Foundation for Basic Research (grant no. 98-03-32512). References 1 T. Ekstroem and M. Nygren, J. Am. Ceram. Soc., 1992, 75, 259. 2 R. Metselaar, J. Eur. Ceram. Soc., 1998, 18, 183. 3 Y.-B. Cheng and J. Drennan, J. Am. Ceram. Soc., 1996, 79, 1314. 4 J. E. Gilbert and A. Mosset, Mater. Res. Bull., 1997, 32, 1441. 5 R. N. Katz, Industrial Ceram., 1997, 17, 3. 6 (a) D. M. Teter, MRS Bull., 1998, 1, 22; (b) B.I. Korsounskii and V. I. Pepekin, Usp. Khim., 1997, 66, 901 (Russ. Chem. Rev., 1997, 66, 1003). 7 M. Methfessel and M. Scheffler, Physica, 1991, B172, 175. 8 S. R. Srinivasa, L. Curtz, J. Jorgensen, T. G. Worlton, R. Beyerlein and M. Billy, J. Appl. Crystallogr., 1977, 10, 146. 9 Y.-N. Xu and W. Y. Ching, Phys. Rev., 1995, B51, 17379. Total C N O 100 0 10 0 20 0 20 0 –2 –1 0 1 E/Ry DOS/Ry–1 Figure 2 Total and local densities of states of the hypothetical orthorhombic carbon oxynitride C2N2O (for the ‘equilibrium’ cell volume V/V0 = = 0.80, see the text). 0.5 0.4 0.3 0.2 0.1 0.0 –0.1 –0.2 –0.3 –0.4 –0.5 –0.5 –0.4 –0.3 –0.2 –0.1 0.0 0.1 0.2 0.3 0.4 0.5 Si N N C 0.5 0.4 0.3 0.2 0.1 0.0 –0.1 –0.2 –0.3 –0.4 –0.5 –0.5 –0.4 –0.3 –0.2 –0.1 0.0 0.1 0.2 0.3 0.4 0.5 (b) (a) Figure 3 Maps of the valence charge density distribution in the plane (yz) of (a) Si2N2O and (b) C2N2O cells. FLMTO calculations. Received: Moscow, 3rd August 1998 Cambridge, 1st October 1998; Com. 8/06229C

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Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) Electronic structure of hexagonal Ti3AlC2 and Ti3AlN2 Alexander L. Ivanovskii* and Nadezhda I. Medvedeva Institute of Solid State Chemistry, Ural Branch of the Russian Academy of Sciences, 620219 Ekaterinburg, Russian Federation. Fax: +7 3432 74 4495; e-mail: ivanovskii@ihim.uran.ru The self-consistent full-potential LMTO method was used to study the electronic properties of the new hexagonal phases Ti3AlC2 and Ti3AlN2, and their chemical stability was compared with the stability of the isostructural compound Ti3SiC2 on the basis of cohesive energy calculations.Among a large group of ternary carbides and nitrides obtained in the M–X–(C,N) systems, where M is a d metal, and X is a group IIIB or IVB element (see ref. 1), only one phase of the composition Ti3SiC2 was known until recently, which has a hexagonal structure (space group D4 6h, P63/mmc).2–5 Unusual properties of this phase (high melting temperature, chemical inertness and plasticity) made it interesting, in particular, as a candidate material for creating novel construction ceramics.6–11 Nonempirical quantum-chemical calculations of Ti3SiC2 made it possible to investigate in detail the electronic properties and chemical bonding of hexagonal titanium carbosilicide and to predict their variation for a series of hypothetical isostructural phases with different d metals is changed (Zr3SiC2, V2SiC2), when C vacancies appear (nonstoichiometry in the carbon sublattice: Ti3SiC2 – x, V3SiC2 – x) and when Ti3SiC2-based solid solutions are formed (Ti3SiC2 – xNx, Ti3SiC2 – xOx).13,14 Recently, H.D. Lee and W. T. Petuskey15 found the new hexagonal phase Ti3AlN2 in the Ti–Al–N system in a narrow temperature range (~1523–1673 K) and determined its lattice parameters. The existence of the metastable phase Ti3AlC2 16 (Ti2AlC2 – x)17 with a hexagonal Ti3SiC2-like structure was reported.In this work we have performed self-consistent calculations of the electronic structure of the new ternary compounds Ti3AlC2 and Ti3AlN2 with the Ti3SiC2-type structure by the full-potential linear muffin-tin orbitals method (FLMTO).18 The results were compared with analogous computations for isostructural titanium carbosilicide.13–15 A fragment of the crystal structure of hexagonal (D4 6h) Ti3AlC2, Ti3AlN2 is given in Figure 1.The unit cell includes two formula units [6Ti, 2Al and 4(C,N) atoms]. The structure is formed by layers of adjoining octahedra Ti6C (Ti6N) alternating with plane nets of Al atoms. Titanium atoms occupy two structurally nonequivalent sites [Ti(1) and Ti(2)]. Ti(1) atoms constitute the (100) layers neighbouring Al atom nets. Ti(2) atoms are located inside the carbide (nitride) layers and have carbon (nitrogen) atoms in their nearest surroundings. Figure 2 demonstrates total and local densities of states (TDOS, LDOS) of Ti3AlC2 and Ti3AlN2.The valence band of Ti3AlC2 contains two separate energy bands (A and B, Figure 2). The lower band A is composed predominantly of C 2s states and is separated from the upper occupied band (B) by a forbidden gap (DEg).The band B contains mixed contributions from Ti(1,2) 3d, 4s, 4p, C 2p and Al s, p, d states. The Fermi level (EF) is in the local TDOS minimum. The bottom of the conduction band is formed by antibonding Al 3d, 3p, Ti 3d and C 2p states. For Ti3AlN2, the main changes in the TDOS are associated with an essential decrease in the energy of N 2s states, an increase in DEg and occupation of some antibonding (for Ti3AlN2) Ti 3d, Al 3d, N 2p states as a result of an increase in the valence electron concentration (vec) in the cell.The chemical stability of the hexagonal titanium alumocarbide and alumonitride can be compared based on FLMTO calculations of their cohesive energies (Ecoh) determined as Ecoh = = Etot – SEat.Etot is the total energy of crystal, SEat is the sum of energies of isolated atoms constituting the crystal.18 According to the data of Table 1, the cohesive energy of Ti3AlC2 is higher than that of Ti3AlN2. This fact corresponds to lowering Ecoh in the series14 of hexagonal Ti3AlC2 ® ‘Ti3AlN2’ and can be related to weakening the covalent bonds Ti(1,2)–N in comparison with Ti(1,2)–C, as it was found for ‘pure’ binary cubic (B1) TiC and TiN.19 Let us consider the nature of chemical bonding in Ti3AlC2 and Ti3AlN2 in greater detail.As follows from the present calculations, the chemical bonding in these phases is of a complex combined ionic–covalent–metallic type. The ionic component of bonding is determined by the polarization of electronic density, so that additional charges are concentrated in the muffin-tin (MT) spheres of nonmetallic atoms.The effective charges of MT spheres for Ti3AlC2 are: Ti(1), +0.210 e; Ti(2), +0.283 e; Al, –0.219 e and C, –0.256 e. For Ti3AlN2, the charge polarization of Ti(2)–N increases by ~0.33 e. Also noteworthy are the differences in the charge states of structurally nonequivalent titanium atoms [Ti(1) and Ti(2)].The metallic bonding in Ti3AlC2, Ti3AlN2 is due to the collectivisation of delocalized states. It also differs considerably for crystallographically nonequivalent atoms Ti(1) and Ti(2). This can be seen in the distribution profile of near-Fermi LDOS of Ti(1) and Ti(2) (Figure 2), which form metallic Ti–Ti bonds aValence electron concentration (e, in unit cell). Table 1 Cohesive energy (Ecoh/Ry per unit cell) and total density of states at the Fermi level [N(EF)/Ry–1] for hexagonal (D4 6h) Ti3AlC2, Ti3AlN2 as compared with Ti3SiC2.14 FLMTO calculations.Structure –Ecoh N(EF) veca Ti3AlC2 7.223 45.66 46 Ti3AlN2 6.770 122.52 50 Ti3SiC2 7.601 75.68 48 Ti(1) Ti(2) Al C,N Figure 1 Fragment of the crystal structure of hexagonal (D4 6h –P63/mmc) Ti3AlC2, Ti3AlN2.Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) in the crystal. The ratio of LDOS at the Fermi level [N(EF)] for nonequivalent centres [N(EF)Ti(1)/N(EF)Ti(2)], which is 1.91 for Ti3AlC2, can serve as a qualitative characteristic of the degree of anisotropy of metallic bonds. Note that, in spite of the rapid growth of the total N(EF) for Ti3AlN3 (Table 1), i.e.‘metallisation’ of the alumonitride, the ratio [N(EF)Ti(1)/N(EF)Ti(2)] changes rather insignificantly (~1.83). The above anisotropy of separate [Ti(1)–Ti(1) and Ti(2)–Ti(2)] bonds can be clearly seen in Figure 3 where the maps of valence charge densities (CD) in the (100) planes including Ti(1) and Ti(2) atoms are presented. Ti(2) atoms have the maximum number of carbon atoms in their nearest surroundings and form the strongest covalent bonds Ti(2)–C.As a result, Ti(2)–Ti(2) bonds are relatively small, whereas for Ti(1) atoms (at the boundary with plane nets of Al atoms) the CD concentration in the interatomic space [Ti(1)–Ti(1) bond] is much more considerable (Figure 3). Taking into account the layered structure of the hexagonal phases, a formal analogy can be drawn between the evolution of separate types of bonds (covalent and metallic) for nonequivalent titanium atoms, for example, in Ti3AlC2 and in the proximity of the polar (111) face of cubic TiC (see ref. 20). In both cases, the weakening of the covalent bond Ti–C [for Ti(1) atoms of the alumocarbide or Ti atoms of the outer monolayer of the (111) face of TiC] considerably strengthens the metallicity of the bond as a consequence of redistribution of electrons between the subbands of Ti 3d–C 2p (p–d covalent bond) and Ti 3d, 4s (d–d metallic bond) states.The ‘layered’ anisotropy of covalent bonds can be seen in Figure 2. For Ti3AlC2, the LDOS maximum of Ti(2) coincides with LDOS maxima of carbon atoms. This fact is indicative of the formation of local hybrid bonds Ti(2)–C inside the ‘carbide’ layer, as it takes place in binary cubic carbides.19 The LDOS of Ti(1) has a more complicated shape and reflects both the 400 200 0 40 –0.5 0.0 0.5 1.0 EF Total Ti(1) Ti(2) Al E/Ry DOS/Ry–1 N 0 0 0 0 40 20 20 400 200 0 40 –0.5 0.0 0.5 1.0 EF Total Ti(1) Ti(2) Al E/Ry DOS/Ry–1 C 0 0 0 0 40 20 20 Figure 2 Total DOS (top) and local DOS of Ti3AlC2 and Ti3AlN2. 1.0 0.8 0.6 0.4 0.2 0.0 –0.2 –0.4 –0.6 –0.8 –1.0 Ti(1) Ti(2) –1.0 –0.8 –0.6 –0.4 –0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.0 0.8 0.6 0.4 0.2 0.0 –0.2 –0.4 –0.6 –0.8 –1.0 –1.0 –0.8 –0.6 –0.4 –0.2 0.0 0.2 0.4 0.6 0.8 1.0 Ti(1) Ti(2) Figure 3 Charge density distribution in the (100) monolayers composed of Ti(1) and Ti(2) atoms (see Figure 1) for Ti3AlC2 according to FLMTO calculations.Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) formation of the covalent bonds Ti(1)–C inside the octahedra and the ‘interlayer’ interaction Ti(1)–Al. As follows from the analysis performed, the covalent bonds C–Ti(1)–Al (along the c axis, Figure 1) are considerably weaker than the C–Ti(2)–C bonds. Note that, in the organization of Ti–Al and Al–Al hybrid bonds, 3d functions of aluminium, which are vacant in the atomic state, take part.Thus, according to our calculations, the electronic configuration of aluminium in Ti3AlC2 is Al 3s1.203 3p1.703 3d0.313. Until the present time, the physico-chemical properties of Ti3AlC2 and Ti3AlN2 have not been studied. Based on the computations, the following tentative predictions can be made.The properies of the hexagonal alumocarbide determined by the cohesive energy (for example, thermomechanical properties such as hardness, thermal stability, enthalphy of formation, etc.), and the chemical stability will be better than those for the isostructural titanium alumonitride. At the same time, the cohesive properties of these phases will be inferior to those of Ti3SiC2.The metallic properties determined by the concentration of delocalised states will be anisotropic and much higher for Ti3AlN2 than for Ti3AlC2. For Ti3AlC2, EF is in the local TDOS minimum, and EF for Ti3AlN2 is located on a plateau in the vicinity of the local TDOS maximum (Figure 2). Consequently, the change of vec in the Ti3AlN2 cell (for instance, owing to the formation of lattice vacancies or the presence of substitutional impurities) does not lead to abrupt changes in N(EF) and in the total energy of the crystal, as is the case for Ti3AlC2.Hence, based on the known chemical stability–electronic structure relationship,21,22 it should be expected that nonstoichiometric phases like substitutional solid solutions will form more probably on the basis of Ti3AlN2 than on the basis of Ti3AlC2.This work was supported by the Russian Foundation for Basic Research (grant no. 96-03-32037). References 1 A. L. Ivanovskii, A. I. Gusev and G. P. Shveikin, Kvantovaya khimiya v materialovedenii. Troinye karbidy i nitridy perekhodnykh metallov i elementov IIIb, IVb podgrupp (Quantum Chemistry in Materials Science. Ternary Carbides and Nitrides Based on Transition Metals and IIIb, IVb Subgroup Elements), Nauka, Ekaterinburg, 1996 (in Russian). 2 W. Jeitschko and H. Nowotny, Monatsh. Chem., 1967, 98, 329. 3 J. Nickl, K. K. Schweitzler and P. Luxenburg, J. Less-Common Met., 1972, 26, 335. 4 B. Gottselig, E. Gyarmati, A. Naoumidis and H. Nickel, J. Eur. Ceram. Soc., 1990, 6, 153. 5 T. Goto and T. Hirai, Mater. Res. Bull., 1987, 22, 1195. 6 J. Lis, R. Pampuch, J. Piekarczyk and L. Stobierski, Ceram. Ont., 1993, 19, 219. 7 R. Pampuch, J. Lis, J. Piekarczyk and L. Stobierski, J. Mater. Synth. Proc., 1993, 1, 93. 8 C. Recault, F. Langlais and C. Bernard, J. Mater. Sci., 1994, 29, 3941. 9 C. Recault, F. Langlais, R. Naslain and Y. Kihn, J. Mater. Sci., 1994, 29, 5023. 10 P. Komarenko and D. E. Clarc, Ceram. Eng. Sci.Proc., 1994, 15, 1028. 11 B. Goldin, P. V. Istomin and Yu. I. Rjabkov, Neorg. Mater., 1997, 33, 691 [Inorg. Mater. (Engl. Transl.), 1997, 33, 577]. 12 A. L. Ivanovskii, D. L. Novikov and G. P. Shveikin, Mendeleev Commun., 1995, 90. 13 N. I. Medvedeva and A. L. Ivanovskii, Zh. Neorg. Khim., 1998, 43, 336 (Russ. J. Inorg. Chem., 1998, 43, 398). 14 N. I. Medvedeva, A. L. Ivanovskii, G. P. Shveikin, D. L. Novikov and D. J. Freeman, Phys. Rev. B, 1998, 54, 16042. 15 H. D. Lee and W. T. Petuskey, J. Am. Ceram. Soc., 1997, 80, 604. 16 M. A. Pietzka and J. C. Schuster, J. Phase Equilib., 1994, 15, 392. 17 M. A. Pietzka and J. C. Schuster, J. Am. Ceram. Soc., 1996, 79, 2321. 18 M. Methfessel and H. Scheffer, Physica, 1991, B172, 175. 19 A. L. Ivanovskii and G. P. Shveikin, Phys. Status Solidi B, 1994, 181, 251. 20 A. L. Ivanovskii and V. A. Zhilyaev, Phys. Status Solidi B, 1991, 168, 9. 21 J. Xu and A. J. Freeman, Phys. Rev. B, 1989, 40, 11927. 22 X. Wang, D.-C. Tian and L. Wang, J. Phys.: Condens. Matter, 1994, 6, 10185. Received: Moscow, 17th August 1998 Cambridge, 17th November 1998; Com. 8/06561F

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年代:1999

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Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) Novel heterocyclizations of N,N'-diarylformamidines: 1,4,2,5-diazadiphosphorinanes Gennady V. Oshovsky,* Alexander M. Pinchuk, Alexander N. Chernega, Igor I. Pervak and Andrey A. Tolmachev Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 253660 Kyiv, Ukraine. Fax: +7 044 543 6843; e-mail: oshovsky@carrier.kiev.ua The heterocyclization of N,N'-diarylformamidines with phosphorus trichloride to form 1,4,2,5-diazadiphosphorinanes was found to proceed via the key stage of aliphatic electrophilic ylide substitution at the formamidine carbon atom.The first examples of aliphatic electrophilic substitution at the formamidine carbon atom in reactions with trivalent phosphorus halides were found recently.1 There is no published data on similar reactions of formamidines with other electrophilic agents.C-Substitution in N,N,N'-trisubstituted formamidines is an extension of well-studied N-phopshorylation of NH-amidines.2 In this work, we report a novel approach to N,N'-diarylformamidines as N,C-bifunctional compounds, in which classical substitution at the nitrogen atom is followed by the formation of a bond with the formamidine carbon atom.This is a new feature of using formamidines in syntheses of heterocyclic compounds. Using a model reaction of the title compounds with phosphorus trichloride, we implemented a new promising synthesis of 1,4,2,5-diazadiphosphorinane3 (Scheme 1). The first step of the reaction leads to N-phosphorylated2 amidines 2.Compounds 2 are transformed into 3 only in a basic medium (a mixture of pyridine and NEt3).† This fact suggests that the transformation occurs via the ylide mechanism4 of electrophilic C-substitution at the HCXY moiety (X, Y = NR, N, S, O) of heterocyclic compounds and is similar to acylation5 and phosphorylation6 of azoles. The transformation of 2 into 3 can be easily monitored by 31P NMR. This process is considerably slower than the formation of 2 from amidine and PCl3.The 31P NMR spectrum of 3 exhibits two signals as a result of two possible isomers of 3. These isomers are interconvertable in solution; it is likely that this conversion is caused by the presence of trace acids.‡ The mixture of isomers 3 reacts smoothly with secondary amines and sulfur leading to a mixture of stable isomers 5.The difference in solubility allows the separation of stable isomers 5a and 5a'. X-ray analysis confirmed the structure of 5a' (Figure 1).§,¶ Compound 5a' corresponds to the cis isomer, and the diazadiphosphorinane ring has a boat conformation in crystals. The second isomer 5a is trans. Both cis and trans isomers are sterically hindered.Judging from very wide signals in the 1H NMR spectra corresponding to Ar bonded to endocyclic nitrogen and amide moieties at phosphorus,†† one can conclude that the energy difference between conformers of each isomer should be insignificant. This is not surprising, because the 1,4,2,5-diazadiphosphorinane ring involves sp2 carbons. Therefore, there is a dynamic equilibrium between the conformers, instead of an excess of one of them, in contrast with less sterically hindered phosphaheteroannelated cyclohexanes.7 † General method for the synthesis of 3, 4a–c, 5a,a': 0.005 mol of an amidine was dissolved in 10 ml of pyridine and 0.0125 mol of NEt3; next 0.005 mol of PCl3 was added to this reaction mixture cooled to –70 °C. The reaction mixture was allowed to stand for 7 h at room temperature.Next, (A) to prepare compounds 3, the reaction mixture was filtered and evaporated to dryness. By-products were extracted with dry acetonitrile (up to 100 ml). (B) To prepare compounds 4a–c, 5a, 0.015 mol of NEt3 was added to the reaction mixture, and, after cooling to –50 °C, 0.006 mol of a secondary amine was added. The reaction mixture was allowed to stand for 1 h, then 0.005 mol of S was added.After standing for 2 h, the precipitate was filtrered off and washed three times with hot benzene; the solvent was evaporated to dryness in a vacuum, and by-products were extracted with acetonitrile (up to 100 ml). The solid residue was recrystallised from toluene (crystallisation from dioxane is also acceptable). To prepare 5a', the acetonitrile extract was evaporated to dryness, and the product was crystallised from octane and ethyl acetate.‡ 2b (R = Me): d31P = 152.3 ppm (Py); 3b d31P = 67.31 (prevailing isomer), d31P = 67.61 (minor isomer), yield of the isomers mixture 42%. The yields of isomers strongly depend on the temperature and the nature of substituents at phosphorus and of aryl substituents at nitrogens.§ To confirm the structure of isomers 4a, 4b and 5a, mass spectroscopy (molecular desorption) was used: 4a, 690±5 (calc. 686.48); 4b, 747±5 (calc. 742.85); 5a, 660±5 (calc. 658.78). Elemental analysis corresponds to the calculated data to within 0.25%. ¶ Crystallographic data for 5a'. A crystal of compound 5a' as a transparent prism (crystal dimensions 0.16×0.34×0.62 mm) was grown from ethyl acetate, C34H40N6P2S2, M = 658.80, monoclinic, a = 8.723(3), b = 38.29(1), c = 10.938(5) Å, b = 109.06(3)°, V = 3453.4 Å3 (by the least-squares refinement of the setting angles for 24 automatically centered reflections), space group P21, Z = 4, Dc = 1.27 g cm–3, m = = 2.70 cm–1.‘Enraf-Nonius CAD4’ diffractometer was used, w/2q scan mode with the w scan width 0.71 + 0.34tg q, w scan speed 1.7–6.7 ° min–1, graphite-monochromated MoKa radiation (l = 0.71069 Å), 6338 reflections were measured (2 < q < 30°), 5473 unique (merging R = 0.017), giving 4044 with I > 3s(I).The structure was solved using direct methods, full-matrix least-squares refinement against F with all non-hydrogen atoms in anisotropic approximation (793 variables, observations/variables = 5.1).All crystallographic calculations were carried out using the CRYSTALS program package. Atomic coordinates, bond lengths, bond angles and thermal parameters have been deposited at the Cambridge Crystallographic Data Centre. For details, see Mendeleev Commun., Issue 1, 1999. Any request to the CCDC for data should quote the full literature citation and the reference number 1135/37.Ar NH CH N Ar + PCl3 Py, NEt3 – NEt3·HCl Ar N CH N Ar PCl2 NEt3 – NEt3·HCl N P N P Cl Ar N Cl Ar N Ar Ar i, R2NH, NEt3 ii, S N P N P Ar N Ar N Ar Ar S NR2 S R2N 1a–c 2 3a–c 4a–c, 5a,a' R' Ar = a R' = H b R' = Me c R' = Br 4 R2N = N O 5 R2N = Et2N Scheme 1Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) †† Spectral data: 3b (prevailing isomer): 1HNMR (C6D6) d: 7.43 (d, 4H, a, Jag 7.2 Hz), 6.76–6.92 (m, 12H, bgd), 1.96 (s, 12H, et, Me). 4a: yield 56%, mp 302–303 °C. 1H NMR (C6D6) d: 7.45 (br. s, 4H, a), 7.015 (d, 4H, b, Jbd 7.5 Hz), 6.90 (t, 4H, d), 6.70 (t, 2H, t, Jtd 7.2 Hz), 6.63 (br. s, 6H, ge), 3.36, 3.08 and 2.72 (br. s, 16H, Y = NR2). 31P NMR (pyridine) d: 67.2. 4b: yield 49%, mp 295–296 °C. 1H NMR (C6D6) d: 7.45 (br. s, 4H, a), 7.06 (d, 4H, b, Jbd 8.1 Hz), 6.77 (d, 4H, d), 6.62 (br. s, 4H, g), 3,40, 3.16 and 2.83 (br. s, 16H, Y = NR2), 2.00 and 1.84 (s, 12H, et). 31P NMR (pyridine) d: 68.4. 4c: yield 37%, mp > 350 °C. 1H NMR (C6D6) d: 7.29 and 7.10 (br. s, 8H, ag), 7.22 and 6.62 (d, 8H, bd, Jbd 7.8 Hz), 3.37, 3.21 and 3.06 (br. s, 16H, Y = NR2). 31P NMR (benzene) d: 57.3. 5a (trans): yield 48%, mp 260–262 °C. 1HNMR (C6D6) d: 7.52 and 7.43 (br. s, 4H, a), 7.07 (d, 4H, b, Jbd 7.2 Hz), 6.91 (t, 4H, d, Jtd 7.2 Hz), 6.8–6.6 (br. s, 8H, get), 3.39 and 3.18 [br. s, 8H, Y = NR2:(CH2)], 0.58 [br. s, 12H, Y = NR2:(Me)]. 31P NMR (C6D6) d: 61.42. 5a' (cis): yield 12%, mp 208–209 °C. 1HNMR (C6D6) d: 7.72 (br. s, 4H, a), 6.9–7.2 (br. s, 6H, ge), 6.99 (t, 4H, d), 6.82 (t, 2H, t, Jtd 7.5 Hz), 6.40 (d, 4H, b, Jbd 6.8 Hz), 3.42 [br.s, 8H, Y = NR2:(CH2)], 1.15 [br. s, 12H, Y = NR2:(Me)]. 31P NMR (MeCN) d: 60.72. G. V. Oshovsky is grateful to the International Science Educational Program (ISEP) of the International Science Foundation and to the International Renaissance Foundation for partial financial support of this work (grant nos.PSU073017 and PSU083047). References 1 (a) A. A. Tolmachev, A. S. Merkulov, G. V. Oshovsky and A. B. Rozhenko, Zh. Obshch. Khim., 1996, 66, 1930 (Russ. J. Gen. Chem., 1996, 66, 1877); (b) A. A. Tolmachev, A. S. Merkulov and G. V. Oshovsky, Khim. Geterotsikl. Soedin., 1997, 1000 [Chem. Heterocycl. Compd. (Engl. Transl.), 1997, 877]. 2 (a) V. I. Shevchenko, A. D. Sinitsa and V. I.Kal’chenko, Zh. Obshch. Khim., 1976, 46, 541 [J. Gen. Chem. USSR (Engl. Transl.), 1976, 46, 535]; (b) V. V. Negrebetskiy, V. I. Kal’chenko and L. I. Atamas’, Zh. Obshch. Khim., 1990, 60, 517 [J. Gen. Chem. USSR (Engl. Transl.), 1990, 60, 450] and references therein; (c) L. N. Markovsky, V. I. Kal’chenko and V. V. Negrebetskiy, New. J. Chem., 1990, 14, 339 and references therein. 3 (a) Yu.G. Gololobov and L. I. Nesterova, Zh. Obshch. Khim., 1977, 47, 1422 [J. Gen. Chem. USSR (Engl. Transl.), 1977, 47, 1303]; (b) A. M. Kibardin, T. Kh. Gazizov, K. M. Enikeev and A. N. Pudovik, Izv. Akad. Nauk SSSR, Ser. Khim., 1983, 432 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1983, 32, 390). 4 L. I. Belenkii and N. D. Chuvylkin, Khim. Geterotsikl. Soedin., 1996, 1535 [Chem.Heterocycl. Compd. (Engl. Transl.), 1996, 1319] and references therein. 5 (a) E. Regel, K.-H. Büchel, Liebigs Ann. Chem., 1977, 145; (b) E. Anders, H.-G. Boldt, R. Fuchs and T. Gassner, Tetrahedron Lett., 1984, 1715. 6 (a) G. V. Oshovsky, A. A. Tolmachev, A. S. Merkulov and A. M. Pinchuk, Khim. Geterotsikl. Soedin., 1997, 1422 [Chem. Heterocycl. Compd. (Engl. Transl.), 1997, 1242]; (b) A.A. Tolmachev, A. A. Yurchenko, M. G. Semenova and N. G. Feschenko, Zh. Obshch. Khim., 1993, 63, 714 [J. Gen. Chem. USSR (Engl. Transl.), 1993, 63, 714]. 7 (a) L. D. Quin and J. H. Sommers, J. Org. Chem., 1972, 37, 1217; (b) D. B. Cooper, I. D. Inch and G. L. Lewis, J. Chem. Soc., Perkin Trans. 1, 1974, 1043; (c) G. D. Macdonnel, K. D. Berlin, J. R. Baker, S. E. Ealick, D.van der Helm and K. L. Marsi, J. Am. Chem. Soc., 1978, 100, 4535. N P N P N N X Y X Y R R R R a b g d t e a a a b b b g g g d d d e t C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(11) C(12) C(13) C(14) C(15) C(16) C(17) C(18) C(19) C(20) C(21) C(22) C(23) C(24) C(25) C(26) C(27) C(28) C(29) C(30) C(31) C(32) C(33) C(34) N(1) N(2) N(3) N(4) N(5) P(1) P(2) S(1) S(2) Figure 1 Crystal structure of 1,4,2,5-diazadiphosphorinane 5a'. Selected bond lengths (Å): P(1)–S(1) 1.924(3), P(2)–S(2) 1.915(3), P(1)–N(1) 1.643(7), P(1)–N(2) 1.712(6), P(2)–N(4) 1.706(6), P(2)–N(6) 1.638(7), P(1)–C(5) 1.856(8), P(2)–C(6) 1.828(8); selected bond angles (°): N(2)– P(1)–C(5) 101.1(3), N(4)–P(2)–C(6) 102.0(3), C(5)–N(3)–C(13) 122.2(7), C(6)–N(5)–C(25) 125.9(7). The C(5)–P(1)–N(2)–C(6) and C(5)–N(4)– P(2)–C(6) groups are planar to within 0.06 Å, and the dihedral angle between these planes is 39.5°. N(6) Received: Moscow, 20th July 1998 Cambridge, 26th November 1998; Com. 8/06223D

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摘要:

Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) Recyclization of 2-amino- and 2-methylamino-2-trifluoromethyl-5,5-dimethyltetrahydro- 4-pyrone oximes to 5-amino- and 5-methylamino-5-trifluoromethyl- 3-(2-hydroxy-1,1-dimethylethyl)- 2-isoxazolines Vyacheslav Ya. Sosnovskikh,* Mikhail Yu. Mel’nikov and Andrei V. Zaitsev Department of Chemistry, A. M. Gor’ky Urals State University, 620083 Ekaterinburg, Russian Federation.Fax: +7 343 261 5978; e-mail: Vyacheslav.Sosnovskikh@usu.ru The reactions of hydroxylamine with 2-amino- and 2-methylamino-2-trifluoromethyl-5,5-dimethyltetrahydro-4-pyrones yield 2-aminoand 2-methylamino-2-trifluoromethyl-5,5-dimethyltetrahydro-4-pyrone oximes, which can be converted to 5-amino- and 5-methylamino- 5-trifluoromethyl-3-(2-hydroxy-1,1-dimethylethyl)-D2-isoxazolines, respectively, by heating in ethanol.Previously1 we described the interaction of 6-trifluoromethyl- 3,3-dimethyl-2,3-dihydro-4-pyrone 1 with hydroxylamine hydrochloride and hydroxylamine base. We found that the reaction with NH2OH·HCl in the presence of Et3N in methanol proceeded at the C(6) atom and was accompanied by ring opening to form monoxime 2.This compound exists as cyclic isoxazoline species 3 in the solid state and in CDCl3 solution or as a mixture of monoxime 2 and isoxazoline 3 (in the ratio 40:60) in DMSO solution. Dihydropyrone 1 with an excess of hydroxylamine base yielded 5-hydroxyamino-D2-isoxazoline 4. To explain the formation of 4, we suggested that the reaction proceeds simultaneously at two electrophilic sites via a step of formation of 2-trifluoromethyl-2-hydroxyamino-5,5-dimethyltetrahydro- 4-pyrone oxime 5, which immediately undergoes recyclization to isoxazoline 4 under the reaction conditions.To test this hypothesis, we decided to examine the interaction of hydroxylamine with 2-amino- and 2-methylamino-2-trifluoromethyl- 5,5-dimethyltetrahydro-4-pyrones 6a,b prepared by reactions of dihydropyrone 1 with ammonia2 and methylamine.† Because tetrahydropyrone 6a is a cyclic form of 5-amino-6,6,6-trifluoro-1-hydroxy-2,2-dimethylhex-4-en-2-one 7, which was synthesised previously by condensation of 4-hydroxy-3,3-dimethyl-2-butanone with trifluoroacetonitrile,2 it was also of interest to compare the behaviour of aminoenone 7 and its cyclic isomer 6a in reactions with hydroxylamine.Note that 7 cannot transform into 6a either spontaneously or in the presence of bases. We found that tetrahydropyrones 6a,b with hydroxylamine base in methanol at room temperature formed oximes 8a,b‡ in high yields. These oximes undergo recyclization to thermodynamically more stable 5-amino- and 5-methylamino-D2-isoxazolines 9a,b§ on heating in ethanol.The transformation 8 ® 9 † 2-Trifluoromethyl-2-methylamino-5,5-dimethyltetrahydro-4-pyrone 6b: yield 84%, mp 87–88 °C. 1H NMR (250 MHz, CDCl3) d: 1.01 (s, 3H, Me), 1.30 (s, 3H, Me), 1.58 (br. s, 1H, NH), 2.27 (d, 1H, CHeH, JAX 15.0 Hz), 2.42 (s, 3H, NMe), 2.97 (d, 1H, CHHa, JAX 15.0 Hz), 3.72 (AB system, Dd 0.22, 2H, CH2–O, JAB 11.0 Hz). IR (Vaseline oil, n/cm–1): 3390 (NH), 1720 (C=O).Found (%): C 48.00; H 6.49; N 6.14. Calc. for C9H14F3NO2 (%): C 48.00; H 6.27; N 6.22. supports a scheme that was suggested previously1 for the formation of isoxazoline 4 and makes it possible to prepare 5-amino derivatives of 5-trifluoromethyl-D2-isoxazolines. This transformation can be considered as a new example of ring–ring isomerisation (see ref. 3 and references therein) that proceeds via unstable open-chain imino-oxime species 10, which cannot be detected in 1H NMR spectra. Note that a mixture of compounds 8b and 9b in the ratio 55:45 was formed when deuterioacetic acid was added to an oxime 8b solution in CDCl3, whereas oxime 8a remained unchanged under similar conditions (according to 1H NMR spectral data). Tetrahydropyrone 6a reacted with NH2OH at the carbonyl group with the retention of the cyclic structure; this fact suggests that this compound is reasonably stable despite the hemiaminal character of the C–O bond.In contrast, open-chain species 7 exhibited a much different behaviour in this reaction. Aminoenone 7 underwent a nucleophilic attack on the carbon atom adjacent to the CF3 group and, via a transamination step, resulted in monoxime 2, which exists predominantly as isoxazoline 3, which was prepared previously from dihydropyrone 1.1 Judging from the 1H NMR spectral data for oximes 8a,b (only a single set of signals was observed in the spectra), the reaction resulting in these compounds is highly stereoselective and leads to products with the E-configuration of the C=N bond.A comparison between the 1H NMR spectra for compounds 6b and 8b indicates that replacing a carbonyl oxygen by an oxime functional group primarily affected the positions of doublets of ‡ 2-Amino-2-trifluoromethyl-5,5-dimethyltetrahydro-4-pyrone oxime 8a: yield 63%, mp 126–127 °C. 1H NMR (250 MHz, CDCl3) d: 1.11 (s, 3H, Me), 1.29 (s, 3H, Me), 1.80 (s, 2H, NH2), 2.43 (d, 1H, CHeH, JAX 15.0 Hz), 3.34 (d, 1H, CHHa, JAX 15.0 Hz), 3.46 (d, 1H, CHH–O, JAX 11.2 Hz), 3.93 (d, 1H, CHH–O, JAX 11.2 Hz), 8.43 (s, 1H, OH).IR (Vaseline oil, n/cm–1): 3425, 3385, 3280 (br.), 3120 (OH, NH2), 1660, 1625 (C=N, NH2). Found (%): C 42.40; H 5.82; N 12.09. Calc. for C8H13F3N2O2 (%): C 42.48; H 5.79; N 12.38. 2-Trifluoromethyl-2-methylamino-5,5-dimethyltetrahydro-4-pyrone oxime 8b: yield 70%, mp 129–130 °C. 1H NMR (250 MHz, CDCl3) d: 1.08 (s, 3H, Me), 1.28 (s, 3H, Me), 1.58 (br. s, 1H, NH), 2.39 (d, 1H, CHeH, JAX 15.1 Hz), 2.41 (s, 3H, NMe), 3.31 (d, 1H, CHHa, JAX 15.1 Hz), 3.56 (AB system, Dd 0.22, 2H, CH2–O, JAB 11.2 Hz), 8.49 (s, 1H, OH). IR (Vaseline oil, n/cm–1): 3420, 3250 (br.), 3150 (OH, NH), 1675 (C=N). Found (%): C 44.82; H 6.43; N 11.64. Calc.for C9H15F3N2O2 (%): C 45.00; H 6.29; N 11.66. § 5-Amino-5-trifluoromethyl-3-(2-hydroxy-1,1-dimethylethyl)-D2-isoxazoline 9a: yield 74%, mp 73–74 °C. 1H NMR (250 MHz, CDCl3) d: 1.17 (s, 3H, Me), 1.19 (s, 3H, Me), 2.54 (br. s, 3H, NH2, OH), 2.90 (dq, 1H, CHH, JAB 18.3 Hz, 4JH,F 1.1 Hz), 3.33 (d, 1H, CHH, JAB 18.3 Hz), 3.58 (AB system, Dd 0.02, 2H, CH2–O, JAB 11.0 Hz). IR (Vaseline oil, n/cm–1): 3465, 3390, 3320 (OH, NH), 1615 (C=N).Found (%): C 42.56; H 6.02; N 12.04. Calc. for C8H13F3N2O2 (%): C 42.48; H 5.79; N 12.38. 5-Trifluoromethyl-5-methylamino-3-(2-hydroxy-1,1-dimethylethyl)-D2- isoxazoline 9b: yield 82%, mp 41–42 °C. 1H NMR (250 MHz, CDCl3) d: 1.18 (s, 6H, 2Me), 2.30 (br. s, 2H, NH, OH), 2.40 (s, 3H, NMe), 3.06 (dq, 1H, CHH, JAB 18.6 Hz, 4JH,F 1.1 Hz), 3.18 (d, 1H, CHH, JAB 18.6 Hz), 3.59 (s, 2H, CH2–O).IR (Vaseline oil, n/cm–1): 3435 (br.), 3310 (OH, NH), 1625 (C=N). Found (%): C 44.93; H 6.30; N 11.36. Calc. for C9H15F3N2O2 (%): C 45.00; H 6.29; N 11.66. D O O Me Me CF3 1 N F3C O OH Me Me HO N O F3C O OH Me Me H O NOH Me Me F3C NHOH N O NHOH CF3 OH Me Me NH2OH 2 3 5 4Mendeleev Communications Electronic Version, Issue 1, 1999 (pp. 1–44) the AX system of CH2(3) group protons, of which a downfield doublet of the axial proton and an upfield doublet of the equatorial proton exhibited paramagnetic shifts by 0.34 and 0.12 ppm, respectively.¶ At the same time, the chemical shifts ¶ According to our unpublished data, in compounds related to tetrahydropyrone 6b, such as 2-trifluoromethyl-2-hydroxy-5,5-dimethyltetrahydro- 4-pyrone and 2-amino-2-trichloromethyl-5,5-dimethyltetrahydro- 4-pyrone, it is the downfield doublet of the AX system of CH2(3) group protons that split into a doublet of doublets and a doublet of triplets with JAX ~ 15.0 Hz and 4J 1.8 and 1.6 Hz, respectively.This is due to longrange spin–spin coupling of a downfield proton with the protons of OH and NH2 groups.This fact is indicative of a rigid chair conformation with the trans-diaxial position of these groups and the downfield proton. At this arrangement, the W-conformation, which is required for the observed stereospecific long-range coupling through four s bonds,6 becomes possible. of methyl groups changed insignificantly: the d values are 1.01 and 1.08 ppm for the equatorial methyl or 1.30 and 1.28 for the axial methyl in compounds 6b and 8b, respectively.4 These data count in favour of the E-configuration such that protons of the CH2(3) group spatially approach the oxime hydroxyl to result in a downfield shift primarily due to an electrostatic deshielding effect5 (this is particularly true for the axial proton).As distinct from the CH2(3) group protons forming the AX system with JAX ~ 15.0 Hz, hydrogen atoms of the CH2(6) group appear as the AB spectrum with JAB ~ 11.0 Hz and are shifted to higher field by 0.16 ppm on going from tetrahydropyrone 6b to oxime 8b.Note that in the 1H NMR spectra of both isoxazolines 9a,b, the upfield signal of the AB quartet due to the CH2 group of the isoxazoline ring (JAB ~ 18.5 Hz) was further split into quartets with 4JH,F = 1.1 Hz.This is due to long-range spin–spin coupling of a proton from this group with fluorine atoms of the trifluoromethyl substituent. This work was supported by the Russian Foundation for Basic Research (grant no. 96-03-33373). References 1 V. Ya. Sosnovskikh, S. A. Pogozhikh and M. Yu. Mel’nikov, Izv. Akad. Nauk, Ser. Khim., in press. 2 V. Ya. Sosnovskikh and M. Yu. Mel’nikov, Zh. Org. Khim., 1998, 34, 303 (Russ. J. Org. Chem., 1998, 34, 280). 3 K. N. Zelenin, Org. Prep. Proced. Int., 1995, 27, 519. 4 S. Bory, M. Fetizon, P. Laszlo and D. H. Williams, Bull. Soc. Chim. Fr., 1965, 2541. 5 B. L. Shapiro, M. D. Johnston, Jr. and T. W. Proulx, J. Am. Chem. Soc., 1973, 95, 520. 6 C. A. Kingsbury, R. S. Egan and T. J. Perun, J. Org. Chem., 1970, 35, 2913. 6a,b NH2 CF3 O OH Me Me O O Me Me F3C NHR N O NHR CF3 OH Me Me NH2OH 2 3 10 7 NH2OH 8a,b O N Me Me F3C NHR OH EtOH D NR F3C NOH OH Me Me 9a,b a R = H b R = Me Received: Moscow, 28th September 1998 Cambridge, 17th November 1998; Com. 8/07880G

ISSN:0959-9436     

出版商:RSC    

年代:1999

数据来源: RSC