摘要:

Mendeleev Communications Electronic Version, Issue 2, 2002 1 Oxidative and anaerobic reactions of benzyl alcohol catalysed by a Pd-561 giant cluster Serhiy S. Hladyi,a Mykhailo K. Starchevsky,*a Yuriy A. Pazdersky,a Michael N. Vargaftikb and Ilya I. Moiseevb a ‘Sintez’ Research Institute, 82300 Borislav, Ukraine. Fax: +380 3248 41369; e-mail: main@insyntez.com.ua b N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 119991 Moscow, Russian Federation.Fax: +7 095 954 1279; e-mail: mvar@igic.ras.ru 10.1070/MC2002v012n02ABEH001568 The unusual redox disproportionation of benzyl alcohol to benzaldehyde and toluene catalysed by the Pd561phen60(OAc)180 giant cluster under anaerobic conditions was found, whereas in an O2 atmosphere the Pd giant cluster catalyses benzyl alcohol oxidation to benzaldehyde and inhibits its further oxidation.Giant cluster Pd561phen60(OAc)180 1 is known to catalyse the polar oxidation of alcohols by dioxygen to the corresponding aldehydes under mild conditions (1 atm O2, 20–60 °C).1,2 In the case of lower aliphatic alcohols, the aldehyde formed is further oxidised into the corresponding carboxylic acid, anhydride and ester.In a parallel route, the aldehyde and starting alcohol produce acetal.3–5 In this work, we found that, unlike aliphatic alcohols, benzyl alcohol is transformed in a solution of cluster 1 under O2 into benzaldehyde and toluene as the major reaction products, and the minor reaction products are benzoic acid, benzene and CO2 (Table 1).† The initial rate of PhCH2OH consumption at 60 °C and [1] = = 4.55×10–5 mol dm–3 was 6.3×10–2 mol dm–3 min–1.After 120 min of the reaction, the conversion of benzyl alcohol reached 40%. As can be seen in Figure 1, the curves for both PhCH2OH consumption and product accumulation have no induction period. Our experiments showed that benzaldehyde undergoes autoxidation by dioxygen with a noticeable rate already at 20 °C when neither initiators nor catalysts are present.Meanwhile, in the presence of cluster 1, benzaldehyde is rather stable in air and even under O2. For instance, benzaldehyde (0.77 mol dm–3 solution in MeCN) was completely oxidised to benzoic acid upon stirring under O2 (1 atm) for 1 h at 60 °C (initial autoxidation rate was 9.0×10–4 s–1). Unlike this, under the same conditions but in the presence of the Pd-561 cluster (7.0×10–5 mol dm–3), the concentration of benzaldehyde remained almost unchanged and O2 was not absorbed during 600 min.In a solution of isopropanol, the autoxidation of benzaldehyde is much slower (initial rate is 1.7×10–5 s–1 at 60 °C), and isopropanol does not undergo oxidation. Meanwhile, when cluster 1 was introduced into the solution after 200 min, the O2 consumption rate increased and PriOH oxidation to acetone and water started.Since that moment, the concentration of benzaldehyde became constant (Figure 2). All these facts point to a parallel rather than consecutive formation of the products of PhCH2OH conversion. In order to clarify the reaction mechanism, we studied the behaviour of benzyl alcohol in the presence of cluster 1 in an Ar atmosphere.When a solution of cluster 1 (4.60×10–5 mol dm–3) in thoroughly degassed benzyl alcohol was stored under Ar for 120 min at 60 °C, ~8% benzyl alcohol was converted into benzaldehyde and toluene. As shown in Figure 3, both of the reaction products were formed in equal amounts. Hence, the Pd-561 cluster causes the redox disproportionation of benzyl alcohol to benzaldehyde and toluene under anaerobic conditions.and at least a fraction of benzaldehyde and toluene that formed during the oxidation of benzyl alcohol can be due to the anaerobic conversion of the alcohol. All these findings point to the fact that cluster 1 not only provides the catalytic polar oxidation and redox disproportionation of benzaldehyde but also retards its free-radical oxidation.It is most likely that the metal core of the cluster can terminate free-radical oxidation chains similarly to other metal complex inhibitors.6 The found synchronism in the accumulation of benzaldehyde and toluene during the contact of benzyl alcohol with the Pd-561 giant cluster implies two parallel reaction pathways, which are originated from two different modes of PhCH2OH coordination by the Pd atoms of the metal core of cluster 1.The first coordination mode is the oxidative addition of the PhCH2OH molecule via C–H bond dissociation [Scheme 1, route (a)], and the second mode occurs via C–OH bond cleavage [Scheme 1, route (b)]. As a result, four coordinated (adsorbed) species occur at the surface layer of the metal core of cluster 1: [PhCH2], [PhCHOH], [H] and [OH].The formation of benzaldehyde and † Experiments were carried out according to published procedures1,3 in a 20 cm3 glass reactor equipped with a sampler, a thermostat, a vibration stirrer (frequency of 200–450 min–1) and a gas burette for the measurement of gas volumes to within 0.1 cm3. Cluster 1 (0.020 g) and the working solution (5.0 cm3) were loaded in the reactor.The reaction solution was rigorously shaken under O2 at 60 °C. The reactants and reaction products were analysed by GLC. The reaction rates were determined by O2 absorption and the GLC analysis of liquid reaction products. Table 1 The products of cluster 1-catalysed benzyl alcohol reactions (neat benzyl alcohol as a solvent, 1 atm O2, 60 °C, [1] = 4.55×10–5 mol dm–3 and reaction time 120 min).Reaction product Concentration/ mol dm–3 Yield based on PhCH2OH consumed (%) PhCHO 3.09 70.2 PhMe 0.96 21.8 PhCOOH 0.27 6.1 PhH 0.084 1.9 CO2 0.08 1.8 4.0 2.0 10.0 8.0 40 80 t/min C/mol dm–3 1 2 3 4 5 C/mol dm–3 Figure 1 Curves for benzyl alcohol consumption and product accumulation in the presence of cluster 1 (4.55×10–5 mol dm–3) under O2 (1 atm) in neat benzyl alcohol at 60 °C: (1) benzyl alcohol, (2) benzaldehyde, (3) toluene, (4) benzene and (5) benzoic acid. 2PhCH2OH ® PhCHO + PhMe + H2O (1)Mendeleev Communications Electronic Version, Issue 2, 2002 2 toluene can be ascribed to the following recombinations of the adsorbed species: This mechanistic scheme allows us to explain the equal yields of benzaldehyde and toluene in the anaerobic reaction [equation (1), Figure 3]: reactions (2) and (3) involve the adsorbed species originated from different coordination routes irrespectively of which of the PhCH2OH adsorption mode, (a) or (b), prevails.Meanwhile, when benzyl alcohol is in contact with cluster 1 under O2, the latter also forms the adsorbed species [O2] and/or [O], switching on an additional reaction pathway such as whereas the adsorbed hydride species [H], which are necessary for reaction (3) are removed thus decreasing the PhCHO:PhMe ratio between the reaction products (Table 1, Figure 1). This work was supported by the Russian Foundation for Basic Research (grant nos. 99-03-32291, 02-03-32853 and 00-15-97429).References 1 M.N. Vargaftik, V. P. Zagorodnikov, I. P. Stolarov, I. I. Moiseev, D. I. Kochubey, V. A. Likholobov, A. L. Chuvilin and K. I. Zamaraev, J. Mol. Catal., 1989, 53, 315. 2 M. N. Vargaftik and I. I. Moiseev, in Catalysis by Di- and Polynuclear Metal Complexes, eds. A. Cotton and R. Adams, Wiley, New York, 1998, pp. 395–442. 3 M. K. Starchevsky, S. L. Hladiy, Yu. A. Pazdersky, M.N. Vargaftik and I. I. Moiseev, J. Mol. Catal., 1999, 146, 229. 4 M. K. Starchevsky, S. L.Gladyi, Ya. V. Lastovyak, Yu. A. Pazdersky, M.N. Vargaftik and I. I. Moiseev, Dokl. Akad. Nauk, 1995, 342, 772 [Dokl. Chem. (Engl. Transl.), 1995, 342, 157]. 5 M. K. Starchevsky, S. L.Gladyi, Ya. V. Lastovyak, P. I. Pasichnyk, Yu. A. Pazdersky, M. N. Vargaftik and I. I. Moiseev, Kinet.Katal., 1996, 37, 408 [Kinet. Catal. (Engl. Transl.), 1996, 37, 383]. 6 G. A. Kovtun and I. I.Moiseev, Metallokompleksnye ingibitory okisleniya (Metal Complex Oxidation Inhibitors), Kiev, Naukova Dumka, 1993, p. 224 (in Russian). 0.8 0.4 100 300 C/mol dm–3 t/min Cluster input 1 2 3 Figure 2 Curves for benzaldehyde oxidation in a solution of isopropanol. T = 60 °C, [1] = 5.65×10–5 mol dm–3; (1) benzaldehyde, (2) acetone and (3) water. PhCH2 OH ~Pd Pd~ ~Pd Pd~ PdCH2 OH ~Pd Pd~ PdCH H OH Scheme 1 (a) (b) [PhCHOH]ads + [OH]ads = PhCHO + H2O, [PhCH2]ads + [H]ads = PhMe. (1) (2) Figure 3 Curves for benzyl alcohol consumption and product accumulation in the presence of cluster 1 (4.6×10–5 mol dm–3) under Ar (1 atm) in neat benzyl alcohol at 60 °C: (1) benzyl alcohol, (2) benzaldehyde and (3) toluene. 0.4 0.2 10.2 9.8 9.4 40 80 t/min C/mol dm–3 C/mol dm–3 1 2 3 [PhCH2]ads + [O]ads ® PhCHO, (4) 2[H]ads + [O]ads ® H2O, (5) Received: 27th February 2002; Com. 01/1894

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Synthesis and structure of new triphenylphosphine ¥�-complexes of palladium(0) with p-benzoquinone and their role in the oxidative carbonylation of alkynes Alexander V. Kulik,*a Lev G. Bruk,a Oleg N. Temkin,a Vildar R. Khabibulin,a Vitaly K. Belskyb and Valery E. Zavodnikb a M. V. Lomonosov Moscow State Academy of Fine Chemical Technology 117571 Moscow Russian Federation. Fax +7 095 434 8711; e-mail lbruk@cityline.ru b L. Ya. Karpov Institute of Physical Chemistry 103064 Moscow Russian Federation The complexes [Pd(¥ç2-Q)(PPh3)2]2H2Q and Pd2(¥ì-¥ç2,¥ç2-Q)2(PPh3)2 (where Q and H2Q are p-benzoquinone and hydroquinone respectively) were synthesised and structurally characterised and their catalytic activity in the oxidative carbonylation of phenylacetylene to methyl phenylpropiolate was examined.p-Benzoquinone is widely used as an oxidant in the reactions of unsaturated organic compounds catalysed by palladium compounds. 1¡©3 It can play different roles in the course of a catalytic reaction. In addition to the back oxidation of reduced catalysts p-benzoquinone can participate in the reactions of organometallic intermediates. For example it can contribute to the redox degradation of the allyl ¥�-complexes of palladium without the formation4 or with the formation of intermediate Pd0Q complexes5 (where Q is p-benzoquinone). It can also be responsible for the pathways of intermediate degradation. Thus with the participation of PdCl2 6(a) and [Pd(CO)Cl]n 6(b) in the presence of p-benzoquinone dimethyl oxalate was selectively produced in the oxidative carbonylation of methanol at atmospheric pressure and 40 ¡ÆC and in the oxidative conversion of AcOHgCOOMe (dimethyl carbonate and methyl chloroformate respectively were the reaction products in the absence of p-benzoquinone).6 A number of hypotheses7 were considered in studying the mechanism of the oxidative carbonylation of alkynes at C¡©H bonds in the Pd(OAc)2¡©PPh3¡©Q¡©MeOH system [Pd] (1) RC��CH + CO + MeOH + Q RC��CCOOMe + H2Q 3,8 CO and MeOH.where H2Q is hydroquinone. One of these hypotheses assumes that a Pd0 complex with p-benzoquinone is formed and this complex is active in the carbonylation. In the above system Pd0 complexes can be formed on the reduction of Pd(OAc)2 in reactions with PPh To our knowledge PdII complexes with p-benzoquinone were not obtained previously.For PdI only the complex Pd2SO4¡�Q which was identified by elemental analysis IR and X-ray spectroscopy and thermal analysis is known.9 The Pd0 complexes with p-benzoquinone LPdQ (where L is a bidentate ligand or two monodentate ligands) are well known (L is bipy phen,10 cod or PPh3 11). However the structures of only three compounds with chelate ligands {2,3,4,6-tetra-O-acetyl-1-[(2-diphenylphosphino)- benzylthio]-¥â-D-glucopyranose,12 2,2'-bipyridine,13,14 and 4,5- diazafluoren-9-one (dafo)14} were found recently by X-ray diffraction analysis. H(1m) O(2q) C(4q) C(5q) C(3q) C(6q) C(1q) P(2) H(1h) O(1h) C(1h) C(2h) C(2q) O(1q) C(3h) O(1m) Pd(1) Pd(2) P(1) C(1m) Figure 1 Molecular structure of the [Pd(PPh3)2Q]2(H2Q) methanol solvate complex 1.Selected bond lengths (A) Pd(2)¡©P(2) 2.316(1) Pd(2)¡©P(1) 2.345(2) Pd(2)¡©C(2q) 2.177(4) C(2q)¡©C(3q) 1.410(5) C(5q)¡©C(6q) 1.324(6) O(1q)¡�¡�¡�O(1h) 2.693(5) O(1q)¡�¡�¡�H(1h) 1.79(4) O(1q)¡�¡�¡�O(1m) 2.956(4) O(1q)¡�¡�¡�H(1m) 2.05(3); selected bond angles (¡Æ) O(1q)¡©H(1h)¡©O(1h) 179.3(3) O(1q)¡©H(1h)¡©O(1m) 179.0(1) P(3)¡©Pd(2)¡©P(4) 107.05(5). Mendeleev Communications Electronic Version Issue 2 2002 10.1070/MC2002v012n02ABEH001577 This complex consists of two Pd(PPh Quinone and hydroquinone complexes with palladium and PPh3 with known structures are required for the identification of palladium complexes formed in reaction (1).The aim of this work was to synthesise new Pd0 complexes with PPh3 p-benzoquinone and hydroquinone to characterise them by X-ray diffraction analysis and to examine their catalytic activity in reaction (1). According to 31P NMR spectra several complexes were formed in the reaction of PdL4 (L is PPh3) with p-benzoquinone in a CHCl3 (CDCl3) solution. We failed to prepare single crystals of complexes in this system. However in attempts to synthesise a Pd0 complex with hydroquinone a compound with the L2PdQ unit was formed probably because of slow oxidation of hydroquinone with oxygen of the air. Red crystals of compound 1 with the composition [Pd(PPh3)2Q]2H2Q¡�MeOH (0.049 mmol 48% yield) were formed in the reaction of hydroquinone (0.909 mmol) with Pd(PPh3)4 (0.104 mmol) in methanol (2 ml) at room temperature in air for 12 h.Figure 1 demonstrates the structure of complex 1.¢Ó 3)2Q moieties hydrogen-bonded to a hydroquinone molecule. A palladium atom two phosphorus atoms and two carbon atoms at the palladiumcoordinated double bond of the quinone lie in the same plane. Two double bonds of the quinone are arranged in another plane which is almost perpendicular to the above plane. The quinone molecule is non-planar and the carbonyl groups are out of the plane on the opposite side of palladium. Complex 1 is a solvate complex one methanol solvate molecule is connected by hydrogen bond to the oxygen atom of a quinone. Complex 1 is the O(1) C(6) C(1) C(2) C(4) C(5) C(3) O(2) Pd(2) P(2) Pd(1) O(3) C(7) C(12) C(8) C(9) C(11) C(10) O(4) Figure 2 Molecular structure of the Pd2(PPh3)2(¥ì-¥ç2,¥ç2-Q)2 methanol solvate complex 3.Selected bond lengths (A) Pd(1)¡©C(11) 2.164(5) Pd(1)¡© C(2) 2.181(5) Pd(1)¡©C(3) 2.213(5) Pd(1)¡©C(12) 2.210(5) Pd(1)¡©P(1) 2.360(1) Pd(1)¡©Pd(2) 2.975(1) C(2)¡©C(3) 1.386(7); selected bond angles (¡Æ) P(2)¡©Pd(2)¡©Pd(1) 124.61(4). ¢Ó Crystal data for complex 1 C45.5H39O3.5P2Pd M = 810.11 triclinic a = 12.670(3) b = 18.711(4) and c = 19.220(4) A a = 62.39(3) b = = 71.88(3) g = 78.94(3)¡Æ V = 3831.2(15) A3 T = 293(2) K space group P1 (no. 2) Z = 4 m(MoK¥á) = 0.886mm¡©1 14065 reflections measured on a CAD-4 diffractometer 6791 unique [R(int) = 0.0126] were used in all calculations.The final R(F2) = 0.0243 (all data). P(1) 1 Table 1 Effect of the initial Pd compound on the characteristics of reaction (1).a S (%) t/min R/mol dm¡©3 h¡©1 Catalyst precursor Pd(PPh3)2Cl2 Pd(OAc)2 + 2PPh3 0.000 0.043 0.070 3)4 Pd(PPh [Pd(PPh3)2Q]2H2Q¡�MeOH (1) 0.080 [Pd(PPh3)Q]2¡�1.5MeOH (3) + 2PPh3 0.042 120 200 127 104 184 219 0.031 Pd(dba)2 + 2PPh3 traces 58 54 63 68 72 aThe [Q]:[Pd] ratio is 17; S is the selectivity for methylphenylpropiolate; R is the quasi-steady-state rate of formation of methylphenylpropiolate; t is the reaction time. first complex of this kind. If the above synthesis was performed in a nitrogen atmosphere the solution exhibited no detectable changes over a long period of time.Yellow crystals of compound 2 with the composition Pd(PPh3)3 were formed in an insignificant amount after six months. According to X-ray diffraction data this compound is a new crystalline modification of a previously synthesised complex.15 The structure of compound 2 will be considered elsewhere. After the dissolution of complex 1 in acetone compound 3 of the composition [Pd(PPh3)Q]2¡�1.5MeOH was formed in 76% yield on standing for several days at room temperature. According to X-ray diffraction data compound 3 is a dimer complex containing two Pd(PPh3) units linked by two p-benzoquinone bridging molecules. These bridges are arranged so that both of the double bonds of each p-benzoquinone molecule aomplex 3 is a solvate complex having 1.5 molecules of methanol which are disordered (Figure 2).¢Ô The distance between palladium atoms in complex 3 is 2.975 A which is longer than the Pd¡©Pd bond length in the metal (2.75 A) and the Pd¡©Pd distance in the similar complex Pd2(¥ì-dafo)(¥ì-¥ç2,¥ç2-Q)2 (2.77 A).14 In contrast to known palladium complexes with p-benzoquinone complexes 1 and 3 contain a monodentate triphenylphosphine ligand. Complex 3 is formed from complex 1 which contains a hydroquinone bridge. A comparison of the 1H 13C and 31P NMR spectra of the synthesised complexes with the spectra of the Pd(OAc)2¡©PPh3¡©Q and Pd(PPh3)4¡©Q systems indicates that complex 1 is formed along with other palladium complexes and products of the interaction of PPh3 with p-benzoquinone from Pd(OAc)2 under reaction conditions.Complex 3 is predominant in the Pd(PPh3)4¡©Q system. The signals due to these complexes disappeared after the addition of phenylacetylene to the system. It is likely that the conversion of these compounds into reaction intermediates is responsible for this disappearance. 2] Table 1 compares the catalytic activities of palladium complexes formed in situ from Pd(OAc)2 and Pd(PPh3)4 16 in the oxidative carbonylation of phenylacetylene by reaction (1) with the activities of complexes 1 and 3. It can be seen that all of the used Pd0 compounds exhibited commensurable catalytic activities. This fact may indicate that various Pd0 complexes exhibit similar catalytic activities or various precursors [including Pd(OAc) are converted into the same catalytically active complex.It is most likely that a Pd0 complex with p-benzoquinone is catalytically active. The rate of reaction remained almost unaffected with changes in the pH of the solution (MeCOOH and MeCOONa were added) ¢Ô Crystal data for complex 3 C51H47O5.5P2Pd2 M = 1022.63 monoclinic a = 35.948(6) b = 12.070(2) and c = 23.214(5) A b = 66.84(2)¡Æ V = = 9260.65(3) A3 T = 293(2) K space group C2/c (no. 15) Z = 8 m(MoK¥á) = 0.886 mm¡©1 8916 reflections measured on a CAD-4 diffractometer 4257 unique [R(int) = 0.015] were used in all calculations. The final R(F2) = 0.026 (all data). Atomic coordinates bond lengths bond angles and thermal parameters for 1 and 3 have been deposited at the Cambridge Crystallographic Data Centre (CCDC).For details see ¡®Notice to Authors¡� Mendeleev Commun. Issue 1 2002. Any request to the CCDC for data should quote the full literature citation and the reference number 1135/105. Mendeleev Communications Electronic Version Issue 2 2002 over the range 5.9¡©7.7. An increase in the acidity up to pH 0.4 (a CF3COOH additive) stopped the reaction. In summary the experimental data allowed us to exclude the hypotheses that involved PdII compounds as active species,7,16 steps with the participation of protons and with Pd0 back oxidation by p-benzoquinone (the absence of a sufficient concentration of protons) from consideration. The following tentative mechanism can be proposed for reaction (1) Pd(OAc)2¡©PPh3¡©MeOH¡©Q Complexes 1 3 Q ¡© H2Q PhC��CH ¡© L L2PdQ 4 OH) L2Pd(H)(O LPd(H)(C��CPh)Q 5 7 CO MeOH L LPd(H)2Q 6 PhC��CCO2Me This work was supported in part by the Russian Foundation for Basic Research (grant nos.98-03-32108 02-03-06199 01- 03-32883 and 00-03-32578). We are grateful to Yu. A. Ustynyuk and V. M. Nosova for performing NMR experiments. References 1 I.I.Moiseev ¥�-Kompleksy v zhidkofaznom okislenii olefinov (¥�-Complexes in the Liquid-Phase Oxidation of Olefins) Nauka Moscow 1970 p. 111 (in Russian). 2 P. M. Henry Palladium-Catalyzed Oxidation of Hydrocarbons D. Reidel Publ. Co. Dordrecht 1980. 3 J. E. Backvall Pure Appl. Chem. 1992 64 429. 4 (a) A. P.Belov N. G. Satsko and I. I. Moiseev Kinet. Katal. 1972 13 892 [Kinet. Catal. (Engl. Transl.) 1972 13 802]; (b) A. P. Belov N. G. Satsko and I. I. Moiseev Dokl. Akad. Nauk SSSR 1972 202 81 [Dokl. Chem. (Engl. Transl.) 1972 202 1]. 5 H. Grennberg A. Gogoll and J. E. Backvall Organometallics 1993 12 1790. 6 (a) L. N. Zhir-Lebed¡� and O. N. Temkin Kinet. Katal. 1984 25 316 [Kinet. Catal. (Engl. Transl.) 1984 25 255]; (b) L. N. Zhir-Lebed¡� and O. N. Temkin Kinet. Katal. 1984 25 325 [Kinet. Catal. (Engl. Transl.) 1984 25 263]. 7 L. G. Bruk and O. N. Temkin Inorg. Chim. Acta 1998 280 202. 8 C. Amatore E. Carre A. Jutand and M. A. M¡�Barki Organometallics 1995 14 1818. 9 N. B. Shitova L. N. Kuznetsova E. N. Yurchenko I. A. Ovsyannikova and K. I. Matveev Izv.Akad. Nauk SSSR Ser. Khim. 1973 1453 (Bull. Acad. Sci. USSR Div. Chem. Sci. 1973 22 1414). 10 T. Ukai H. Kawazura Y. Ishii J. J. Bonnet and J. A. Ibers J. Organomet. Chem. 1974 65 253. 11 M. Hiramatsu K. Shiozaki T. Fujinami and S. Sakai J. Organomet. Chem. 1983 246 203. 12 M. Tschoerner G. Trabesinger A. Albinaty and P. S. Pregosin Organometallics 1997 16 3447. 13 B. Milani A. Anzilutti L. Vicentini A. Sessanta o Santi E. Zangrando S. Geremia and G. Mestroni Organometallics 1997 16 5064. 14 R. A. Klein P.Witte Ruud van Belzen J. Fraanje K. Goubitz M. Numan H. Schenk J. M. Ernsting and C. J. Elsevier Eur. J. Inorg. Chem. 1998 319. 15 V. S. Sergienko and M. A. Porai-Koshits Zh. Strukt. Khim. 1987 28 103 [J. Struct. Chem. (Engl. Transl.) 1987 28 548]. 16 L. G. Bruk I. V. Oshanina. V. R. Khabibulin V. M. Nosova O. N. Temkin and Y. A. Ustynyuk Int. Conf. Organometallic Compounds¡©The Material of Future Millennium Nizhni Novgorod 2000 p. 20. Received 13th Mar

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Mendeleev Communications Electronic Version, Issue 2, 2002 1 Synthesis and structure of the first platinum(II) pivalato complexes Natalia V. Cherkashina, Natalia Yu. Kozitsyna, Grigory G. Aleksandrov, Michael N. Vargaftik* and Ilya I. Moiseev N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 119991 Moscow, Russian Federation. Fax: +7 095 955 4865; e-mail: mvar@igic.ras.ru 10.1070/MC2002v012n02ABEH001549 The first crystalline platinum(II) complexes with trimethylacetato ligands, K2[Pt(OOCBut)4]¡�3THF and Pt4(OOCBut)4(OOCMe)4¡�2C6H6, were synthesised and structurally characterised by X-ray diffraction analysis.Branched alkylcarboxylate ligands such as trimethylacetate and 2-methylbutyrate are known to endow transition metal complexes with high solubility in low-polarity organic media.1.4 This property is important when using noble metal complexes as starting materials in the syntheses of metal clusters and colloids for homogeneous catalysis in aprotic organic solvents.Phosphine and carbonyl ligands are in common use for these purposes.5,6 Meanwhile, readily removable carboxylato complexes are preferable in many cases.Among VIII Group metals, the chemistry of platinum(II) homoligand carboxylates is restricted to the poorly soluble acetato7,8 and haloacetato complexes.9,10 Although ligand exchange in PtII acido complexes readily occurs, previous attempts produced alkylcarboxylato compounds as an oil or non-crystalline solid. To our knowledge, none of structurally characterised PtII pivalate has been documented so far (see the Cambridge Structure Database, Release 2001).In this work, we synthesised and structurally characterised crystalline platinum(II) pivalato complexes K2[Pt(OOCBut)4]¡�3THF 1 and Pt4(OOCBut)4(OOCMe)4¡�2C6H6 2. We used two exchange reactions for the synthesis of PtII pivalates. Mononuclear crystalline complex 1 was prepared by the metathesis of PtCl2 with potassium pivalate in a THF solution.¢Ó However, the main body of the reaction products is a noncrystalline solid.According to IR and 1H NMR spectra,¢Ô this reaction product contains both bridging and terminal pivalato ligands. Another synthetic approach was based on the reaction of platinum acetate blue [Pt(OOCMe)~2.5]n (see ref. 8) with pivalic acid in benzene.Both ligand substitution and redox transformations of the platinum blue occurred in this system to produce several highly soluble PtII pivalato complexes, from which tetranuclear complex 2 was isolated in a crystalline form.¡× Complex 2 is well soluble in THF, benzene and, to a lesser extent, hexane. Although crystalline complexes 1 and 2 were prepared in low yields, the non-crystalline solids obtained as the main reaction product in both syntheses was found to be very close in composition to complex 2 (based on the IR spectra and elemental analysis data), the main difference being various number of solvate molecules, C6H6 and THF, included. The latter is believed to be the main origin of the non-crystallinity of these reaction products.Meanwhile, preliminary experiments showed that both crystalline complex 2 and the non-crystalline solids behaved identically in reactions with reductants (boron hydrides, alkyllithium, alkylaluminium, etc.), producing virtually the same nanoclusters (based on EXAFS, IR, HREM, SAXS and elemental analysis data) when the same reducing agents were used.11 According to X-ray diffraction data,¢Ò the crystal of complex 1 is built from the [Pt(OOCBut)4]2. anion, K+ cations and solvate THF molecules, which are held by the ionic and van der Waals interactions and C.H¡�¡�¡�O bonds.The central Pt atom in the [Pt(OOCBut)4]2. anion is coordinated with four O atoms of monodentate tert-BuCOO ligands (Figure 1). The monodentate coordination of carboxylato ligands is rare in platinum(II) chemistry.Earlier, such a coordination mode was found in the acetato complexes (PPh3)2Pt2(¥ì-OOCMe)2(OOCMe)2 and ¥ç3-C3H5Pd(¥ì-OOCMe)2Pt(OOCMe).12,13 In complex 1, the square plane of the Pt polyhedron containing the oxygen atoms O(1), O(3), O(5) and O(7) is somewhat tetrahedrally distorted. The displacement of the Pt atom from this plane (~0.1 A) is 0.038 A. The Pt.O bond length (average 2.011 A) is comparable with analogous bond lengths in platinum(II) carboxylato complexes. 7.10 The dihedral angles between the planes of pivalate ligands and square-planar four O atoms are 77.3, 65.8, 65.7 and ¢Ó A typical experimental procedure was as follows: a slurry of PtCl2 (400 mg, 1.50 mmol) and potassium pivalate (420 mg, 3.00 mmol) in 5 cm3 of THF was stirred for 2 h and then stored without stirring for 3 days at room temperature. The crystals formed were separated from the mother liquor by decanting, washed with benzene and dried in air to afford 27 mg (20%) of 1 as light-brown needles, one of which (0.01¡¿0.02¡¿0.5 mm) was used for X-ray diffraction analysis. ¢Ô 1H NMR (CDCl3) d: 1.05 (br.s, ~9H, Me), 1.8 (br. m, ~9H, Me). IR (KBr, n/cm.1): 443 (w), 651 (w), 786 (w), 807 (w), 890 (w), 1023 (w), 1213 (m), 1340 (s), 1397 (s), 1459 (w), 1482 (m), 1568 (m), 1612 (s), 2871 (w), 2928 (m), 2958 (s).¡× In a typical experiment, platinum acetate blue (0.5 g, 1.46 mmol) and pivalic acid (0.7 g, 68.6 mmol) were refluxed in benzene (20 ml) for 1 h. The solvent was evaporated on a rotary evaporator. The excess of pivalic acid was washed off with hexane (4¡¿10 ml) and then evaporated in a vacuum (Fisher¡�s pistol, 78 ¡ÆC, 1 Torr, 5 h).The black residue was dissolved in benzene (10 ml), precipitated with hexane and dried in a vacuum to afford finely crystalline complex 2 in 10% yield. IR (KBr), n(COO)/ cm.1: 1407 (s), 1567 (s); n(COO)as . n(COO)s = 160 cm.1, which is typical of the bridging RCOO group.Found (%): C, 25.71; H, 3.73; Pt, 54.44. Calc. for C28H48O16Pt4 (%): C, 23.66; H, 3.40; Pt, 54.91 (remainder was an amorphous solid with nearly the same elemental composition). Bigger crystals for an X-ray diffraction study (0.2¡¿0.3¡¿0.6 mm) were prepared by the slow diffusion of hexane to a benzene solution of 2 in a 5 mm glass tube. Figure 1 Molecular structure of the complex anion at 1.Selected bond lengths (A): Pt(1).O(1) 2.005(7), Pt(1).O(3) 2.013(6), Pt(1).O(5) 2.022(6), Pt(1).O(7) 2.015(6), O(1).C(1) 1.30(1), O(2).C(1) 1.23(1), O(3).C(6) 1.29(1), O(4).C(6) 1.23(1), O(5).C(11) 1.28(1), O(6).C(11) 1.23(1), O(7).C(16) 1.29(1), O(8).C(16) 1.24(1); selected bond angles (¡Æ): O(1). Pt(1).O(3) 174.4(3), O(1).Pt(1).O(5) 87.3(3), O(1).Pt(1).O(7) 91.8(2), O(3).Pt(1).O(5) 93.5(2), O(3).Pt(1).O(7) 88.0(2), O(5).Pt(1).O(7) 173.9(2), Pt(1).O(1).C(1) 120.9(6), Pt(1).O(3).C(6) 122.1(6), Pt(1).O(5).C(11) 122.5(6), Pt(1).O(7).C(16) 119.5(5), O(1).C(1).O(2) 123.5(8), O(3).C(6).O(4) 124.2(9), O(5).C(11).O(6) 125(1), O(7).C(16).O(8) 126.0(8). C(15) C(13) C(12) C(14) C(11) O(6) O(5) Pt(1) O(1) C(1) O(2) C(2) C(3) C(4) C(5) O(7) C(16) O(8) C(17) C(20) C(19) C(18) O(3) O(4) C(6) C(7) C(8) C(9) C(10)Mendeleev Communications Electronic Version, Issue 2, 2002 2 80.5¡Æ, while the dihedral angles between the trans-pivalate ligands are 17.2 and 18.6¡Æ.The trans-carboxylato groups are mutually oriented in such a way that the non-coordinated O atoms are located above and below the square plane. The atoms O(2) and O(4) are shifted by .2.03 and .1.91 A from the mean square plane O(1).O(3).O(5).O(7), and these values are 1.90 and 2.09 A for the atoms O(6) and O(8), respectively.These atoms form short contacts with the Pt atom: Pt¡�¡�¡�O(2),O(4),O(6),O(8) are 3.097, 3.127, 3.147 and 3.113(7) A, respectively. Two crystallographically independent K+ cations are present in the structure. The nearest environment of the potassium atoms includes six oxygen atoms, and K+¡�¡�¡�O distances are 2.658(7).2.820(9) A.The X-ray diffraction study¢Ó¢Ó of a crystal of complex 2 showed thear complex Pt4(OOCBut)4- (OOCMe)4 and C6H6 solvate molecules associated in the crystal by the C.H¡�¡�¡�O bonds and van der Waals interactions. The molecule Pt4(OOCBut)4(OOCMe)4 (Figure 2) has a .4 crystallographic symmetry, and the inversion four-fold axis passes through the centre of the tetragon formed by four closely spaced platinum atoms.The short Pt.Pt distance [2.487(2) A] is typical of tetranuclear platinum carboxylates.7.10 The platinum tetragon is a tetrahedrally distorted rhomb (the Pt.Pt.Pt angles are 89.53¡Æ) bearing four pivalato and four acetato bridging ligands on its sides.The planes of the pivalato ligands (without regard for tert-butyl groups) are almost coplanar with the mean plane of the platinum tetragon, while the planes of the acetato ligands are nearly perpendicular to the Pt4 plane [the dihedral angle between the Pt4 plane and the Pt(1).Pt(1a).O(3).O(4).C(6) plane is 86.6¡Æ]. According to the .4 symmetry of the molecule, the acetate groups located at the opposite sides of the platinum tetragon are oriented in pairs above and below the Pt4 plane. The opposite Pt2O2CMe planes are approximately parallel to each other (the dihedral angle between these planes is 164.7¡Æ).This work was supported by the Russian Foundation for Basic Research (grant nos. 02-03-32853, 01-03-32553 and 00-15-97429).References 1 I. L. Eremenko, M. A. Golubnichaya, S. E. Nefedov, A. A. Sidorov, I. F. Golovaneva, V. I. Burkov, O. G. Ellert, V. M. Novotortsev, L. T. Eremenko, A. Sousa and M. R. Bermejo, Izv. Akad. Nauk, Ser. Khim., 1998, 725 (Russ. Chem. Bull., 1998, 47, 704). 2 M. A. Golubnichaya, A. A. Sidorov, I. G. Fomina, M. O. Ponina, S. M. Deomidov, S. E. Nefedov, I. L. Eremenko and I.I. Moiseev, Izv. Akad. Nauk, Ser. Khim., 1999, 1773 (Russ. Chem. Bull., 1999, 48, 1751). 3 N. Yu. Kozitsyna, M. V. Martens, I. P. Stolarov, S. E. Nefedov, M. N. Vargaftik, I. L. Eremenko and I. I. Moiseev, Zh. Neorg. Khim., 1999, 44, 1920 (Russ. J. Inorg. Chem., 1999, 44, 1823). 4 A. S. Batsanov, G. A. Timko, Yu. T. Struchkov, N. V. Gerbeleu, K. M. Indirchan and G. A. Popovich, Koord. Khim., 1989, 15, 688 [Sov.J. Coord. Chem. (Engl. Transl.), 1989, 15, 418]. 5 J. S. Bradley, in Clusters and Colloids, ed. G. Schmid, VCH, Weinheim, 1994, p. 459. 6 W. A. Herrmann and B. Cornils, in Applied Homogeneous Catalysis with Organometallic Compounds, eds. B. Cornils and W. A. Herrmann, VCH, Weinheim, 1996, vol. 2, pp. 1167.1197. 7 (a) M. Carrondo and A. C. Skapski, Acta Crystallogr., Sect.B, 1978, 34, 1857; (b) M. Carrondo and A. C. Skapski, Acta Crystallogr., Sect. B, 1978, 34, 3576. 8 R. I. Rudy, N. V. Cherkashina, G. Ya. Mazo, Ya. V. Salyn¡� and I. I. Moiseev, Izv. Akad. Nauk SSSR, Ser. Khim., 1980, 754 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1980, 29, 510). 9 N. V. Gerbeleu, G. A. Timko, K. M. Indrichan, A. S. Batsanov, O. S. Manole and Yu.T. Struchkov, Koord. Khim., 1994, 20, 846 (Russ. J. Coord. Chem., 1994, 20, 799). 10 T. Yamaguchi, Y. Sasaki, A. Nagasawa, T. Ito, N. Koga and K. Morokuma, Inorg. Chem., 1989, 28, 4311. 11 N. V. Cherkashina, M. N. Vargaftik and I. I. Moiseev, Izv. Akad. Nauk, Ser. Khim., in press. 12 N. Yu. Kozitsyna, M. D. Surazhskaya, T. B. Larina, P. A. Koz¡�min, A. S. Kotel¡�nikova and I.I. Moiseev, Izv. Akad. Nauk SSSR, Ser. Khim., 1989, 1894 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1989, 38, 1739). 13 N. Yu. Kozitsyna, L. M. Dikareva, V. I. Andrianov, S. V. Zinchenko, V. A. Khutoryanskii, F. K. Schmidt, M. A. Porai-Koshits and I. I. Moiseev, Izv. Akad. Nauk SSSR, Ser. Khim., 1988, 1894 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1988, 37, 1695). ¢Ò Crystal data for 1: C32H60K2O11Pt, M = 894.09, F(000) = 1824, monoclinic, a = 13.029(3), b = 15.948(4), c = 20.253(5) A, V = 4160(2) A3 at 180 K, space group P21/n, Z = 4, dcalc = 1.428 g cm.3, m = 3.621mm.1. The intensities of 12386 reflections [6889 with I ©ø 2s, of which 5670 (Rint = 0.0395) are independent] were measured using a Bruker AXS SMART 1000 CCD three-circle diffractometer at 180 K (graphite-monochromated MoK¥á radiation, l = 0.7107 A, w-scan, 2 ¡Ì 2q ¡Ì 60¡Æ).The following software was used: SMART (control) and SAINT (integration) (version 5.0, Bruker AXS Inc., Madison, WI., 1997) for collecting frames of data, indexing, integration of intensity of reflections and scaling and SADABS (G. M. Sheldrick, University of Gottingen, 1997, based on the method of R.H. Blessing, Acta Crystallogr., A, 1995, 51, 33) for empirical absorption correction. The structure was solved by the direct method using the SHELXS97 (G. M. Sheldrick, University of Gottingen, 1997) program and refined against F2 in an anisotropic approximation for non-hydrogen atoms using SHELXL97 package (G. M. Sheldrick, University of Gottingen, 1997). The H atoms were located on the difference electron density map and refined in a ¡®ride¡� approximation.The final R1 value was 0.0549 [wR2(F2) = 0.1307] for 5670 reflections, GOOF = 1.019. Figure 2 Molecular structure of complex 2 (positions of the atoms: #1 .y, x, .z; #2 y, .x, .z; #3 .x + 1, .y + 1, z). Selected bond lengths (A): Pt(1).O(3)#1 1.992(13), Pt(1).O(4) 1.998(14), Pt(1).O(2) 2.159(13), Pt(1).O(1)#1 2.160(12), Pt(1).Pt(1)#2 2.4869(16), Pt(1).Pt(1)#1 2.4869(16), O(1).C(1) 1.292(18), O(1).Pt(1)#2 2.160(12), O(2).C(1) 1.235(18), O(3). C(6) 1.240(16), O(3).Pt(1)#2 1.992(13), O(4).C(6) 1.265(17), C(1).C(2) 1.52(3), C(2).C(5) 1.55(3), C(2).C(3) 1.56(3), C(2).C(4) 1.57(4), C(6)- C(7) 1.512(16); selected bond angles (¡Æ): O(3)#1.Pt(1).O(4) 175.8(6), O(3)#1.Pt(1).O(2) 88.2(5), O(4).Pt(1).O(2) 89.1(6), O(3)#1.Pt(1).O(1)#1 85.3(5), O(4).Pt(1).O(1)#1 91.8(5), O(2).Pt(1).O(1)#1 96.5(4), O(3)#1.Pt(1).Pt(1)#2 97.4(4), O(4).Pt(1).Pt(1)#2 85.7(4), O(2).Pt(1).Pt(1)#2 86.8(3), O(1)#1.Pt(1).Pt(1)#2 175.7(3), O(3)#1.Pt(1).Pt(1)#1 86.1(4), O(4).Pt(1).Pt(1)#1 96.8(4), O(2).Pt(1).Pt(1)#1 172.8(4), O(1)#1.Pt(1). Pt(1)#1 87.4(3), Pt(1)#2.Pt(1).Pt(1)#1 89.526(5), C(1).O(1).Pt(1)#2 116.8(11), C(1).O(2).Pt(1) 118.5(11), C(6).O(3).Pt(1)#2 120.3(11), C(6).O(4).Pt(1) 119.0(11), O(2).C(1).O(1) 129.5(18), O(2).C(1).C(2) 114.8(15), O(1).C(1).C(2) 115.8(16), C(1).C(2).C(5) 110(2), C(1).C(2).C(3) 106(2), C(5).C(2).C(3) 111(3), C(1).C(2).C(4) 107(2), C(5).C(2).C(4) 112(3), C(3).C(2).C(4) 111(3), O(3).C(6).O(4) 126.1(15), O(3).C(6).C(7) 116.6(14), O(4).C(6).C(7) 116.9(13).C(1A) O(1A) O(2A) O(4C)C(6C) Pt(1A) Pt(1C) O(2C) C(1C) O(3A) O(4A) C(6A) O(1C) Pt(1B) O(4B) C(6B) O(2B) O(3B) C(1B) O(1B) Pt(1) C(3) O(2) C(2) C(4) C(5) C(1) O(1) O(4) O(3) C(6) C(7) ¢Ó¢ÓCrystal data for 2: C40H60O16Pt, tetragonal at 120 K, a = 13.766(8) and c = 24.157(16) A, V = 4578(5) A3, space group I42d, Z = 4, dcalc = = 2.306 g cm.3, m=12.253 cm.1. The intensities of 10942 reflections [3180 with I ©ø 2s, of which 2484 (Rint = 0.1633) are independent] were measured using Bruker AXS SMART 1000 CCD three-circle diffractometer at 120 K (graphite-monochromated MoK¥á radiation, l = 0.7107 A, w-scan, 2 ¡Ì 2q ¡Ì 60¡Æ). The software used was the same as for complex 1. The structure was solved by direct methods using the SHELXS97 program and refined against F2 in an anisotropic approximation for nonhydrogen atoms using the SHELXL97 package. The final R1 value was 0.0727 [wR2(F2) = 0.193] for 3180 reflections, GOOF = 1.000. Atomic coordinates, bond lengths, bond angles and thermal parameters for 1 and 2 have been deposited at the Cambridge Crystal-lographic Data Centre (CCDC). For details, see ¡®Notice to Authors¡�, Mendeleev Commun., Issue 1, 2002. Any request to the CCDC for data should quote the full literature citation and the reference number 1135/104. Received: 8th January 20

ISSN:0959-9436     

出版商:RSC    

年代:2002

数据来源: RSC

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Mendeleev Communications Electronic Version, Issue 2, 2002 1 Synthesis and electrochemical properties of 2-(azahomo[60]fullereno)- 5-nitropyrimidine Irina P. Romanova,*a Vladislav V. Kalinin,a Dmitry G. Yakhvarov,a Adilya A. Nafikova,a Valery I. Kovalenko,a Pavel V. Plekhanov,b Gennady L. Rusinovb and Oleg G. Sinyashina a A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Centre of the Russian Academy of Sciences, 420088 Kazan, Russian Federation. Fax: + 7 8432 75 2253; e-mail: romanova@iopc.knc.ru b Institute of Organic Synthesis, Urals Branch of the Russian Academy of Sciences, 620219 Ekaterinburg, Russian Federation.Fax: + 7 3432 74 1189; e-mail: rusinov@ios.uran.ru 10.1070/MC2002v012n02ABEH001567 2-(Azahomo[60]fullereno)-5-nitropyrimidine was synthesised by the cycloaddition reaction of C60 and 2-azido-5-nitropyrimidine. The practical applications of fullerenes are determined by their solubility and electron affinity.These properties can be modified by the addition of electron-withdrawing organic fragments to fullerenes. However, the number of fullerene derivatives with electron affinities higher than that of parent fullerenes is limited.1–4 In most cases, the opening of fullerene �-bonds leads to a decrease in the electron affinity.For [60]fullerene, the lowest decrease in the electron affinity was observed in homofullerenes; however, the synthesis and identification of such C60 derivatives are difficult to perform. Earlier, we prepared isocyanurato-substituted azahomo[ 60]fullerene.5 Its electrochemical reduction was 80 mV easier than that of C60.Two N-aryl-substituted azahomofullerenes, 3 which are reduced easier than C60, are known. However, the structure of N-aryl-substituted azahomofullerenes was not reliably determined by UV spectroscopy. We described here the synthesis and electrochemical properties of nitropyrimidino-substituted azahomo[60]fullerene.Pyrimidinofullerenes were earlier obtained in a reaction of [60]fullerene with pyrimidine o-chinodimethanes and presented 6,6-closed adducts of C60.6 To introduce an electron-withdrawing nitropyrimidinic fragment to a fullerene molecule, we used the cycloaddition of organic azides to the fullerene, which led to the formation of azahomofullerenes.7 We were the first to use a pyrimidino-substituted azide in this reaction.Azide 2† (0.14 mmol) reacted with [60]fullerene (0.08 mmol) in boiling o-dichlorobenzene. The reaction was monitored by mass spectrometry. After heating for 4.5 h, two peaks (720 and 858) were detected in the mass spectrum of the reaction mixture. The former peak corresponded to C60, and the latter peak corresponded to monoadduct 1. The unreacted fullerene (30%) and monoadduct 1 (18%) were separated by column chromatography (toluene as an eluent).After drying in a vacuum, monoadduct 1 was obtained as brown powder readily soluble in toluene, chloroform and methylene chloride. Its structure was studied by 13C NMR, 1H NMR, UV and IR spectroscopy. In the 13C NMR spectrum‡ of monoadduct 1, signals due to the carbons of a fulleroid sphere and nitropyrimidinic fragment were observed.The positions of signals of fulleroid sphere carbons (d 133–147 ppm), their number (32 signals) and relative intensities (24 signals had intensity 2C, 2 signals had intensity 4C, due to the signals overlapping, and 4 signals had intensity 1C) pointed at azahomo[60]fullerene structure of the molecule with Cs symmetry.This conclusion was proved by the UV spectrum.‡ The bands of a pyrimidine ring, nitro group and a band characteristic of a monoadduct [60]fullerene were observed in the IR spectrum‡ of monoadduct 1. The structure of the nitropirimidine fragment was also confirmed by the 1H NMR spectrum of monoadduct 1.‡ We studied the thermal stability of azahomo[60]fullerene 1 and found that, contrarily to isocyanurate-substituted azahomo- [60]fullerenes, which thermally isomerised to [60]fullereno- [1,2-b]aziridines,5,8 nitropyrimidine-substituted azahomo[60]- fullerene 1 was unusually stable on boiling in a solution of o-dichlorobenzene for 10 h.Only after 20 h heating azahomo- [60]fullerene 1 decomposed to the parent fullerene. The redox-properties of azahomofullerene 1 were studied by cyclic voltammetry.The cyclic voltammogram of C60 exhibited four classically reversible waves of reduction with peak potentials, summarised in Table 1 (Figure 1). At these potentials the reduction of azide 2 also occured (Table 1). Thus, the cyclic voltammogram of azide 2 exhibited four waves of reduction, two of them having the greatest currents were irreversible. All the reduction waves of azide 2 correspond to the reduction of the nitropyrimidine fragment since the azide group was not reduced in the studied range of potentials.5 The relative irreversibility of the reduction waves of the nitro group is explained by carrying out the reduction process at the potential development from –0.7 to –2.5 V, accompanied by the transfer of four electrons to the molecule and its decomposition.The cyclic voltammogram of azahomo[60]fullerene 1 is presented in Figure 1. At the development of potential up to –0.9 V, the first one-electron wave (I) is reversible. Note that the potential of the peak of this reduction wave is 80 mV less negative than the potential of the first peak of reduction of parent C60. Based on the values of potential and reversibility of the wave of reduction, we consider that the first peak in the cyclic volt- † IR spectra were obtained on a Bruker IFS-113V instrument. The 1H and 13C NMR spectra were recorded on a Bruker MSL-400 spectrometer at 250 and 100 MHz, respectively.Chemical shifts were measured with reference to the signals of CDCl3, which was used as a solvent. The mass spectra were measured on a MALDI TOF MS instrument (Dynamo).Compound 2 was obtained by the published method.9 1H NMR (250MHz, CDCl3) d: 9.35 [s, 2H, CH(4,6)]. 13C{1H} NMR (100 MHz, CDCl3) d: 139.06 [C(5)], 155.30 [CH(4,6)], 166.15 [C(2)]. UV-VIS (CH2Cl2, lmax/nm): 290. IR (KBr, n/cm–1): 1571, 1331, 873, 833 (NO2), 1417, 639 (pyrimidine cycle), 2138 (N3). ‡ Compound 1: Rf 0.76 (Silufol; eluent, toluene). 1H NMR (250 MHz, CDCl3) d: 9.38 [s, 2H, CH(4,6)]. 13C NMR (100 MHz, CDCl3) d: 140.17 [d, C(5), 2JCH 1.2 Hz], 155.30 [d, CH(4,6), 1JCH 188.6 Hz], 141.77 [d, C(2), 3JCH 6.7 Hz], 138.06, 138.90, 139.02, 143.71 (C60N, 1C), 134.35, 135.30, 135.87, 137.45, 138.06, 138.75, 140.10, 141.76, 141.82, 142.87, 143.03, 143.10, 143.21, 143.41, 143.66, 143.83, 144.17, 144.35, 144.37, 144.41, 144.52, 145.04, 146.30, 147.34 (C60N, 2C), 144.15, 144.59 (C60N, 4C).UV-VIS (CH2Cl2, lmax/nm): 259, 325, 431 (br.), 539 (br.). IR (KBr, n/cm–1): 526 (C60), 1575, 1332, 849 (NO2), 1456, 645 (pyrimidine cycle). N N N NO2 1 2 3 4 5 6 C60 N3 N N NO2 o-DCB 180 °C, 4.5 h 1 2Mendeleev Communications Electronic Version, Issue 2, 2002 2 ammogram of azahomofullerene 1 corresponds to the transposition of one electron on the fullerene sphere.At a further development of the potential up to .2.5 V, five waves of reduction were observed in the cyclic voltammogram of azahomofullerene 1. In the potential range from .1.00 to .1.50 V, the reduction of both fullerene and pyrimidine fragments takes place, as can be seen in two overlapped reduction waves II and III.Wave II is irreversible, and its potential is in the range of potentials of reduction of azide 2. In this connection, we consider that wave II corresponds to the reduction of the nitropyrimidine fragment in the molecule of azahomofullerene 1. The reversibility of waves III points at the reduction of a fullerene sphere of azahomofullerene 1, and this process occurs easier (.Ep = 20 mV) than the addition of the second electron to initial C60.A comparison of the peak potentials of reduction waves IV, V and VI with the potentials of the reduction waves of C60 and azide 2 allowed us to conclude that reversible waves IV and VI correspond to the reduction of the fullerene sphere and irreversible wave V, to the reduction of the nitropyrimidinic fragment.Thus, we found that 2-(azahomo[60]fullereno)-5-nitropimidine 1 is reduced easier than parent C60. The reduction of fullerene and nitropyrimidine fragments occurs in the same interval of potentials, but the first electron is transfered to the homofullerene fragment of the molecule. The compounds of this type are interesting for the synthesis of complexes with organic donors, which can exhibit ferromagnetic properties.References 1 B. M. Illesca and N. Martin, J. Org. Chem., 2000, 65, 5986. 2 P. Zeng, Y. Liu, D. Zhang, C. Yang, Y. Li and D. Zhu, J. Phys. Chem. Solids, 2000, 61, 1111. 3 J. Zhou, A. Rieker, T. Grosser, A. Skiebe and A. Hirsch, J. Chem. Soc., Perkin Trans. 2, 1997, 1. 4 H. Irngartinger and T. Escher, Tetrahedron, 1999, 55, 10753. 5 O.G. Sinyashin, I. P. Romanova, G. G. Yusupova, A. A. Nafikova, N. M. Azancheev, V. V. Yanilkin, V. I. Kovalenko and Y. G. Budnikova, Mendeleev Commun., 2000, 61. 6 A. C. Tome, R. F. Enes, J. A. S. Cavalero and J. Elguero, Tetrahedron Lett., 1997, 38, 2557. 7 M. Casses, M. Duran, J. Mestres, N. Martin and M. Sola, J. Org. Chem., 2001, 66, 433. 8 O. G. Sinyashin, I. P. Romanova, G.G. Yusupova, A. A. Nafikova, V. I. Kovalenko, N. M. Azancheev, S. G. Fattakhov and V. S. Reznik, Izv. Akad. Nauk, Ser. Khim., 2001, 2064 (Russ. Chem. Bull., Int. Ed., 2001, 50, 2162). 9 V. L. Rusinov and O. G. Chupakhin, Nitroazines, Nauka, Novosibirsk, 1991, p. 133 (in Russian). 3 ¥ìA I II III IV V VI .1.0 .2.0 .E/V 1 2 I Figure 1 Cyclic voltammograms of (1) C60 and (2) azahomo[60]fullerene 1. Table 1 Peak potentials and currents of waves in the cyclic voltammograms of C60, adduct 1 and azide 2 [in a mixture of o-dichlorobenzene and MeCN (3:1) at 25 ¡ÆC].a Compound Ered p / V (Ip /¥ìa) K1 b K2 K3 K4 K5 K6 C60 .0.83 (4.2) .1.24 (3.8) .1.70 (3.9) .2.16 (4.6) 2 .1.11 (24.5)c .1.51 (2.5) .2.02 (25)c .2.20 (4.0) 1 .0.75 (3.5) .1.11 (2.3)c .1.22 (1.3) .1.68 (3.3) .1.88 (3.5)c .2.18 (3.6) I II III IV V VI aSolution concentrations, 1¡¿10.3 mol dm.3; supporting electrolyte, 0.1 M Bu4NBF4; cathode, carbon glass (CG) (Swork = 3.14 mm2; reference electrode, 0.01 M Ag/AgNO3 in MeCN; Vpot = 50mV s.1). bThe reduction waves of substrates observed in cyclic voltammograms. cThe irreversible wave. Received: 25th February 2002; Com. 02/1893

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Mendeleev Communications Electronic Version, Issue 2, 2002 1 Carbocyclic galanthamine analogues: construction of the novel 6H-benzo[a]cyclohepta[hi]benzofuran ring system Matthias Treu, Johannes Frohlich and Ulrich Jordis* Institute of Applied Synthetic Chemistry, Vienna University of Technology, A-1060 Vienna, Austria. Fax: +43 (1) 58 8011 5499; e-mail: ujordis@pop.tuwien.ac.at 10.1070/MC2002v012n02ABEH001557 Unnatural analogues of the anti-Alzheimer drug (.)-galanthamine have been synthesised using K3[Fe(CN)]6 at the key step to construct the novel (¡¾)-6H-benzo[a]cyclohepta[hi]benzofuran ring system via oxidative tandem cyclization.Galanthamine (or galantamine, Reminyl¢ç) is a tertiary alkaloid acetylcholinesterase inhibitor (AChEI), which has been approved in several countries for treating the symptoms of Alzheimer¡�s type senile dementia.1 The key step comprises the K3[Fe(CN)]6 induced oxidative tandem cyclization of suitable norbelladine analogues, whereby the tetracyclic ring system is established in a cascade of radical reactions and Michael addition.We are currently studying this phenol oxidation, which was developed for the synthesis of the galanthamine ring system2,3 and is now performed on an industrial scale.4 We have extended this reaction for the preparation of 6H-benzofuro[3a,3,2-ef][3]benzazepine5 and 12H-[2]benzothiepino[6,5a,5-bc]benzofuran6 ring systems (Figure 1).Here, we report the successful use of this reaction for the synthesis of the novel 6H-benzo[a]cyclohepta[hi]benzofuran ring system starting from diphenol compounds 1a.d.Generally, this type of reaction is successful for the creation of 5-6-6-7 ring systems¢Ó under conditions found to be optimal in the synthesis of galanthamine4 (Scheme 1 and Table 1). For all reactions, the quantitative conversion of diphenol was observed by TLC. These results were rationalised by molecular models generated using the CORINA software7 as described below. A low-energy conformation characterised by the interaction of the bromine atom and the carboxamide moiety show favourable distances between the carbon atoms to be engaged in the radical cyclization.Further attempts to cyclise compounds 3a.d, which were expected to give 5-6-6-6, 5-6-6-8 and unfunctionalised 5-6-6-7 ring systems, were unsuccessful (Scheme 2).These observations were rationalised by the ring tension of 5-6-6-6 ring systems in the case of 3a, as well as 1a, the lack of supportive conformative restriction and the comparatively high flexibility of 3b and 3c, and the formation of coloured decomposition products in the case of 3d (Scheme 2 and Table 2). MeO O OH H N Me (.)-Galanthamine MeO O OH H N Me (4a¥á,6¥â,8aR*)-4a,5,9,10,11,12-Hexahydro- 3-methoxy-10-methyl-6Hbenzofuro[ 3a,3,2-ef]-[3]- benzazepin-6-ol (see ref. 5) MeO O OH H S (4a¥á,6¥â,8aR*)-4a,5,9,10-Tetrahydro- 3-methoxy-11,11-dioxo- 12H-[2]benzothiepino[6,5a,5-bc]- benzofuran-6-ol (see ref. 6) O O Figure 1 Table 1 Tandem cyclization of 1a.d. Compound m n yield of 2 (%) 1a 1 1 0 1b 0 3 8 1c 1 2 19 1d 2 1 6 ¢Ó Representative example of tandem cyclization: (4ab,8ab,12R*)-1-bromo- 4a,5,9,10,11,12-hexahydro-3-methoxy-6-oxa-6H-benzo[a]cyclohepta[hi]- benzofuran-12-carboxamide 2b.K3[Fe(CN)6] (13.2 g, 40.0 mmol) and K2CO3 (7.50 g, 53.1 mmol) in water (75 ml) were added to a suspension of 1b (3.00 g, 7.61 mmol) in CHCl3 (300 ml), and the mixture was stirred vigorously for 45 min at room temperature. The mixture was filtered using diatomaceous earth, and the filtrate was washed with water (3¡¿200 ml) and brine (200 ml), dried over Na2SO4, filtered and concentrated in vacuo.The crude product was obtained as a mixture of diastereomers and purified by flash chromatography (SiO2; CHCl3.MeOH, 96:4). A diastereomer with the higher Rf was formed as colourless crystals (0.24 g, 8%), mp 257.258 ¡ÆC (decomp.), Rf 0.6 (EtOAc). 1H NMR ([2H6]DMSO) d: 7.57 (s, 1H), 7.48 (d, 1H, J 14.5 Hz), 7.14 (s, 2H), 5.89 (d, 1H, J 14.5 Hz), 4.66 (s, 1H), 4.32 (s, 1H), 4.01 (q, 1H, J 7.7 Hz), 3.78 (s, 3H), 3.02 (d, J 19.6 Hz, 1H), 2.79 (d, 1H, J 19.6 Hz), 2.52 (d, 1H, J 16.5 Hz), 2.16 (d, J 16.5 Hz, 1H), 1.96.1.67 (m, 2H), 1.14 (t, 1H, J 7.7 Hz). 13CNMR ([2H6]DMSO) d: 195.6 (s), 174.6 (s), 149.5 (d), 147.9 (s), 144.4 (s), 133.6 (s), 130.6 (s), 126.5 (d), 117.5 (s), 117.1 (d), 88.4 (d), 56.8 (q), 52.1 (s), 51.6 (d), 37.9 (t), 36.6 (t), 33.3 (t), 21.5 (t).Found (%): C, 55.15; H, 4.71; N, 3.38. Calc. for C18H18BrNO4 (%): C, 55.12; H, 4.63; N, 3.57. The diastereomer with the lower Rf which was formed as a minor by-product was detected using TLC and NMR spectroscopy, it was isomerised to the main isomer.Rf 0.45 (EtOAc). Found (%): C, 55.10; H, 4.59; N, 3.46. Calc. for C18H18BrNO4 (%): C, 55.12; H, 4.63; N, 3.57. Table 2 Unsuccessful cyclization attempts. Compound G Ring system expected 3a .N(CHO). 5-6-6-6 3b .N(CHO).(CH2)2. 5-6-6-8 3c .(CH2)2. 5-6-6-7 3d 5-6-6-6-7 CH2 CH2 MeO NH2 O OH Br n m MeO O H O Br CONH2 m n K3[Fe(CN)6]/ K2CO3 1a.d 2a.d Scheme 1 HOMendeleev Communications Electronic Version, Issue 2, 2002 2 In all cases, the starting material was quantitatively consumed under the reaction conditions as observed by TLC.This study was supported by Sanochemia Pharmazeutika AG. References 1 L. J. Scott and K. L. Goa, Drugs, 2000, 60, 1095. 2 (a) B. M. Trost and F. D. Toste, J. Am. Chem. Soc., 2000, 122, 11262; (b) M. Node, S. Kodama, Y. Hamashima, T. Baba, N. Hamamichi and K. Nishide, Angew. Chem., Int. Ed. Engl., 2001, 40, 3060. 3 (a) D. H. R. Barton and G. W. Kirby, Proc. Chem. Soc., 1960, 392; (b) T. Kametani, K. Yamaki, H. Yagi and K. Fukumoto, J. Chem. Soc. C, 1969, 2602. 4 B. Kueenburg, L. Czollner, J. Froehlich and U. Jordis, Org. Process Res. Dev., 1999, 3, 425. 5 A. Poschalko, S.Welzig, M. Treu, S. Nerdinger, K. Mereiter and U. Jordis, Tetrahedron, 2002, 58, 1513. 6 M. Treu, K. Mereiter and U. Jordis, Heterocycles, 2001, 55, 1727. 7 http://www2.organik.uni-erlangen.de/software/corina/index.html. HO OMe Br G OH O O H O Br G K3[Fe(CN)6]/ K2CO3 3a–d Scheme 2 Received: 22nd January 2002; Com. 02/18

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Mendeleev Communications Electronic Version, Issue 2, 2002 1 Synthesis of mono- and bisphthalocyanine complexes using microwave irradiation Evgeniya G. Kogan,a Aleksey V. Ivanov,a Larisa G. Tomilova*b and Nikolai S. Zefirovb a Institute of Physiologically Active Compounds, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russian Federation. Fax: +7 095 785 7024 b Department of Chemistry, M.V. Lomonosov Moscow State University, 119992 Moscow, Russian Federation. Fax: +7 095 939 0290; e-mail: tom@org.chem.msu.su 10.1070/MC2002v012n02ABEH001558 Starting with phthalic and 4-tert-butylphthalic acid derivatives, the bisphthalocyanines of rare earth elements and hafnium and zirconium were prepared using microwave irradiation. Phthalocyanines are of interest not only as model compounds for biologically important porphyrins but also because of their outstanding physical properties, including semiconductive, liquid crystalline and non-linear optical behaviour.1–4 Generally, the published methods of phthalocyanine synthesis, rely on the interaction of phthalogens (anhydrides of phthalic acids or phthalodinitriles) with metals or their salts at high temperatures.5–8 These methods require long-term heating (for 2.5–5 h) of a reaction mixture in a melt (fusion) or high-boiling solvent.In more recent publications,9,10 it was proposed to use alcohols as solvents and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as the base in order to decrease the temperature of the synthesis. However, the synthesis takes 12–14 h, and the range of phthalogens is limited to phthalodinitrile.Recently, the synthesis of metal-containing (Cu, Co, Ni and Fe) phthalocyanines has been reported using microwave irradiation, 11 which simplified the synthesis in the absence of solvents and shortened its duration from several hours to few minutes. However, Shaabani11 restricted his studies to complex formation from phthalic anhydride in the presence of urea.We investigated the synthesis of phthalocyanine complexes using microwave irradiation with different phthalogens: phthalodinitrile 1a, phthalimide 1b, phthalic anhydride 1c, and phthalic acid 1d. tert-Butyl-substituted phthalocyanines were synthesised from 4-tert-butyl phthalodinitrile 2a or 4-tert-butyl phthalimide 2b. The reaction mixtures were irradiated in a microwave oven (Samsung, model 1714R) for 5–10 min at 450–850 W.Following these experiments, we were able to select optimal conditions for the production of planar and sandwich-like complexes, depending on the nature of starting reagents and their ratio. The interaction of phthalodinitrile or 4-tert-butyl phthalodinitrile with lithium methylate (taken in a 2:1 ratio of nitrile to lithium methylate) for 3–5 min at the irradiation power 700 W resulted in the formation of di-lithium complexes of the corresponding phthalocyanines in yields of as high as 70%. Treating the reaction mass with a 3% HCl solution gave the quantitative yields of free phthalocyanines, since the complexes of alkali metals are unstable and lithium is rapidly removed from complexes even with trace water.12 The other phthalogens used for the synthesis of lithium phthalocyanines and free phthalocyanine were found to be less active in the complex formation reactions. When we carried out the synthesis of divalent metal (Co, Zn, Cu and Ni) phthalocyanines, we observed that the activity of phthalogens increased in the order phthalic acid < phthalic anhydride < phthalimide < phthalodinitrile; tert-butyl phthalocyanines were produced in better yields than unsubstituted phthalocyanines.The highest yield (70–80%) was attained with the use of 4-tert-butyl phthalodinitrile as the initial reagent under microwave irradiation at 650–700 W for 6–10 min. To synthesise manganese and chromium phthalocyanines, MnCl2 or Mn(OAc)2 and chromium hexacarbonyl Cr(CO)6 served as the initial reagents. Unsubstituted Mn- and Cr-containing phthalocyanines were produced from precursors 1a–b.As in the case of divalent metals, the yield of phthalocyanines was lowest after synthesis from phthalic acid, while the use the other phthalogens ensured similarly good production of metal-containing phthalocyanines. Therewith, phthalimide and phthalodinitrile have some advantages for the synthesis of Cr and Mn phthalocyanines, respectively.As the described for the divalent metals studied, tert-substituted phthalocyanines of Cr and Mn were produced in greater yield (52% and 30%, respectively) than their unsubstituted analogues after 6–10 min exposure to microwave irradiation (650– 700 W). Of particular interest was the synthesis of the phthalocyanines of rare-earth elements, which are capable of forming both planar and sandwich-like complexes.13 In our work, rare-earth elements phthalocyanines were produced from tetrahydrated Tb, Dy and Lu acetates and different phthalogens.Inasmuch as we found previously14 that the formation of bisphthalocyanines proceeds via planar phthalocyanines, our attempts were focused on the production of individual mono- and bisphthalocyanines by varying the phthalogen : salt ratio (4:1, 8:1, 12:1) and the time of synthesis.Indeed, with increasing time of synthesis, the proportion between mono- and bisphthalocyanine yields was shifted toward the bisphthalocyanine. The activity of 1b–d as phthalogens slightly increased in the order: phthalic acid < phthalic anhydride < phthalimide, but the main final product was mono-phthalocyanine even if the reagents were taken in the ratio optimal for bisphthalocyanine synthesis.However, the reaction with 1a as a precursor gave bisphthalocyanine as the main final product, which was formed even at the phthalodinitrile : salt ratio equal to 4:1. Thus, depending upon the nature of the phthalogen, its proportion to the metal salt, and the duration of microwave irradiation, it was possible to control the yield of final products.Unexpectedly, the yield of the tert-butyl-substituted phthalocyanines of rare earth elements under microwave irradiation was much smaller than that of unsubstituted phthalocyanine analogues. Thus, the yield of unsubstituted bisphthalocyanines synthesised from rare-earth acetates was 7–10 times higher than that of tert-butyl phthalocyanines and accounted for more than 70%.Earlier, we found that the heating of the reaction mixture consisting of phthalodinitrile and hafnium and zirconium salts at 250–280 °C for several hours was necessary for the formation of sandwich-like complexes of these metals.15 In this work, this reaction was accomplished over a few minutes under exposure to 650–700 W microwave irradiation and the amount of side products was lower, which make final purification simpler.Thus, a single purification procedure with the use of column chromatography gives the individual compounds with a high degree of purity, as is evident from TLC, elemental analysis and the UV and visible spectra.Hence, the proposed method of phthalocyanine synthesis allows one to avoid lengthy heating of the reaction mass at high temperatures, which is undesirable for some of phthalodinitriles in view of their possible destruction. This work was supported by the Russian Foundation for Basic Research (grant no. 00-03-32658) and the International Science and Technology Centre (grant no. 1526).Mendeleev Communications Electronic Version, Issue 2, 2002 2 References 1 P. N. Moskalev and I. S. Kirin, Zh. Fiz. Khim., 1972, 46, 1778 (Russ. J. Phys. Chem., 1972, 46, 1019). 2 D. Walton, B. Ely and G. Elliot, J. Electrochem. Soc., 1981, 128, 2479. 3 Y. Li, K. Shigehara, M. Hara and A. Yamada, J. Am. Chem. Soc., 1991, 113, 440. 4 G. Corker, B.Grant and N. Clecak, J. Electrochem. Soc., 1979, 126, 1339. 5 R. P. Linsted, J. Chem. Soc., 1934, 1016. 6 C. E. Dent, J. Chem. Soc., 1938, 1. 7 A. B. P. Lever, The Phthalocyanines. Adv. in Inorg. Chem. and Radiochem., 1965, 7, 27. 8 I. S. Kirin, P. N.Moskalev and Yu. A.Makashev, Zh. Neorg. Khim., 1965, 10, 1951 (Russ. J. Inorg. Chem., 1965, 10, 1065). 9 J. Jiang, R. Lin, W. Mak, N. Chan and D. Ng, Polihedron, 1997, 16, 515. 10 T. Toupance, P. Bassoul, L. Mineau and J. Simon, J. Phys. Chem., 1996, 100, 11704. 11 A. Shaabani, J. Chem. Res. (S), 1998, 672. 12 B. D. Beresin, Koordinatsionnye soedineniya porfirinov i ftalotsianinov (Coordination Compounds of Porphirines and Phthalocyanines), Nauka, Moscow, 1978, p. 23 (in Russian). 13 I. S. Kirin, P. N. Moskalev and Yu. A. Makashev, Zh. Neorg. Khim., 1967, 12, 707 (Russ. J. Inorg. Chem., 1967, 12, 369). 14 L. G. Tomilova, E. V. Chernykh and E. A. Luk’yanets, Zh. Obshch. Khim., 1985, 55, 2631 [J. Gen. Chem. USSR (Engl. Transl.), 1985, 55, 2339]. 15 N. A. Ovchinnikova, L. G. Tomilova, N. B. Seregina, V. V. Minin, G. M. Larin and E. A. Luk’yanets, Zh. Obshch. Khim., 1992, 62, 1631 (Russ. J. Gen. Chem., 1992, 62, 1340). Received: 25th January 2002; Com. 02/1884

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Mendeleev Communications Electronic Version, Issue 2, 2002 1 Formation and absorption spectra of X3 – ions upon the radiation-chemical oxidation of Cl– in the presence of Br– (Cl, Br = X) in aqueous solution Boris G. Ershov,*a Eberhard Janata,b Manfred Kelmc and Andrei V. Gordeeva a Insititute of Physical Chemistry, Russian Academy of Sciences, 119991 Moscow, Russian Federation. Fax: +7 095 335 1778; e-mail: ershov@ipc.rssi.ru b Hahn-Meitner-Institut, D-14109 Berlin, Germany c Institut für Nukleare Entsorgungstechnik, Forschungszentrum Karlsruhe, PO Box 3640, 76021 Karlsruhe, Germany 10.1070/MC2002v012n02ABEH001561 The formation of Cl3 –, Cl2Br– and ClBr2 – in the radiation-chemical oxidation of Cl– ions in an aqueous solution (1–5 M) containing Br– (10–6–10–3 M) ions was studied by pulse radiolysis.The radiation-chemical oxidation of Cl– ions in aqueous acid solutions is due to OH radicals, and it results in the formation of Cl2 – radical anions. The oxidation mechanism was studied in most detail by Jayson et al.1 using a pulse-radiolysis technique. It includes the following reactions: It is believed that Cl2 – disappears in the reaction The reaction products Cl2 and Cl3 – are in the equilibrium The aim of this work was to detect the formation of the Cl3 – ion as a result of the radiation-chemical oxidation of Cl– ions and to study the effect of Br– ions on this process.For this purpose, we examined weakly acidic ([H+] = 5×10–4 M) aqueous solutions of NaCl and NaBr saturated with N2O with the use of pulse radiolysis.The pulse radiolysis assembly based on a Van de Graaf accelerator with an energy of 3.8 MeV and the computer data processing were described elsewhere.2–4 Experimental conditions and dosimetry were discussed previously.5 Hydrated electrons eaq – in solutions saturated with N2O are converted into OH radicals by the following reaction (k6 = 9.1×109 dm3 mol–1 s–1):6 We used concentrated NaCl solutions (� 1 M) to shift the equilibrium of reaction (5) to the right and thereby to produce favourable conditions for observing the absorption of Cl3 – .Figure 1(a) demonstrates changes in the absorbance of a 5 M NaCl solution saturated with N2O (pH 3.3) with time after the action of an electron pulse. After 1 µs, the characteristic absorption band of Cl2 – with a maximum at 340 nm was observed (eCl2 – = 8800 dm3 mol–1 cm–1).1 The disappearance of Cl2 – was accompanied by the appearance of a new band at 220±2 nm, which can be attributed to the formation of the Cl3 – ion.The absorbance at 220 nm reached a maximum and stable value 0.3 ms after a pulse; this fact indicates that the equilibrium of reaction (5) was rapidly attained. As the concentration of NaCl was decreased from 5 to 1 M, the band intensity at 340 nm on a dose-per-pulse basis remained almost constant.The radiationchemical yield of Cl2 – in 1–5 M solutions was 5.3±0.2 ion/100 eV. The optical density (D) at 220 nm decreased in the order 0.24; 0.20; 0.17; 0.13 and 0.007 for 5, 4, 3, 2 and 1 M NaCl solutions, respectively, at a dose per pulse of 7.4×1016 eV cm–3.That is, the equilibrium of reaction (5) was shifted to the left as the concentration of Cl– ions was decreased. The presence of Br– ions in 1–5 M NaCl solutions even in a very low concentration (� 10–6 M) considerably affected the absorbance in the UV region. A new band with a maximum at 230±2 nm appeared upon the disappearance of Cl2 – . Its intensity increased with Br– concentration and reached a maximum at ~10–5 M NaBr. In this case, the rate of appearance of the absorbance increased.Figure 2(a) illustrates this process. In the absence of Br–, the absorbance at 230 nm was very low (< 10%). It is well known7 that the mixed ion Cl2Br– (lmax = 232 nm) results from the interaction of Cl2 molecules with Br– in acidified aqueous solutions. This circumstance allowed us to assign the band observed at 230 nm to the above species.Note that in the case of a 1 M NaCl solution containing 10–3 M NaBr a new band with a maximum at 245 nm was formed in the UV region. According to Wang et al.,7 this band was attributed to ClBr2 –. The absorbance of Cl2 at 220 nm is negligibly small as compared with the absorbance of Cl3 – .7 Therefore, it is believed that OH + Cl– ClOH– ClOH– + H+ Cl + H2O Cl + Cl– Cl2 – (1) (2) (3) Cl2 – + Cl2 – Cl2 + 2Cl– or Cl2 – + Cl2 – Cl3 – + Cl– (4a) (4b) Cl2 + Cl– Cl3 – (5) eaq – + N2O + H2O OH + N2 + OH– (6) 0.06 0.04 0.02 0.00 200 250 300 350 400 Absorbance l/nm (a) (b) 0.05 0.10 0.15 0.20 0.25 t/ms 1 2 3 4 Absorbance 0.06 0.04 0.02 0.00 Figure 1 (a) Absorption spectra of a 5 M NaCl solution saturated with N2O (pH 3.3) (1) 1, (2) 35, (3) 80 and (4) 250 µs after the action of an electron pulse.Pulse duration, 20 ns. Absorbed dose, 7.4×1016 eV cm–3. (b) Kinetics of changes in the absorbance at 220 nm in a 5 M NaCl solution saturated with N2O (pH 3.3) after the action of an electron pulse. Pulse duration, 60 ns. Absorbed dose, 1.7×1017 eV cm–3. Points: experimental data.Curves: computer simulation at k5f = 1.1×105 s–1, k5b = 2.0×104 dm3 mol–1 s–1 and e220 = 1.35×104 dm3 mol–1 cm–1. Solid line 1: Cl2 – decay by reaction (4a). Dashed line 2: Cl2 – decay by reaction (4b) with a rate constant of 1.5×109 dm3 mol–1 s–1. 4 3 2 1 1 2Mendeleev Communications Electronic Version, Issue 2, 2002 2 the value of D220 is proportional to the concentration of Cl3 –.Then, we can write K5 = [Cl3 –] /[Cl2][Cl–] = Dx/(D0 – Dx)[Cl–], where Dx and D0 are the optical densities of Cl3 – at 220 nm for a given concentration of Cl– ions and a Cl– concentration that approaches infinity, respectively. The use of the experimental dependence of D220 on the concentration of Cl– ions for 1–5 M solutions allowed us to calculate K5 = 0.18 dm3 mol–1 and e220 = = 1.35×104 dm3 mol–1 cm–1 (±20%).The value of K5 is consistent with the constant measured previously in a study of equilibrium (5) in acidic chloride solutions containing chlorine. 7 The value of e was found to be somewhat higher than 1.04×104 dm3 mol–1 cm–1.7 The kinetics of disappearance of Cl2 – and formation of Cl3 – were fit with the results of computer calculations.In the course of fitting, the values of k4, k5f and k5b were varied. The decay of Cl2 – was adequately described by a second-order reaction rate equation, and the value of t1/2 decreased proportionally to dose per pulse. The value of k4 for a 5 M NaCl solution was calculated to be equal to 1.5×109 dm3 mol–1 s–1. The kinetics of the appearance of the Cl3 – signal depends on dose per pulse only slightly, and it is inconsistent with the disappearance of Cl2 –.This fact indicates that the slower step of equilibration by reaction (5) rather than the decay of Cl2 – is the rate-limiting step in the appearance of the Cl3 – signal. The kinetic curves of the appearance of absorbance at 220 nm in NaCl solutions can be adequately described [Figure 1(b), curve 1] if we take into account that a Cl2 molecule is formed upon the disappearance of two Cl2 – ; that is, reaction (4a) takes place and then equilibrium is attained by reaction (5).If reaction (4b) is assumed, the appearance of an optical signal at 220 nm cannot be described at the initial time interval [Figure 1(b), curve 2]. Note that we concluded previously8 that the Br3 – ion is formed by an analogous mechanism upon the decay of Br2 –.It is likely that charges prevent radical anions from approaching and the reaction occurs via electron transfer according to scheme . The best fit was attained at k5f = 1.1×105 s–1 and k5b = 2.0×104 dm3 mol–1 s–1 [Figure 1(b)]; that is, indeed, at K5 = k5b/k5f equal to 0.18 dm3 mol–1. We propose the scheme given below for the formation of Cl2Br– in the oxidation of Cl– in solutions containing Br– ions.First, it includes the above reactions, which result in the formation of Cl2 and Cl3 –. Second, it is supplemented with the reactions that, in accordance with published data,7 take into account the formation of mixed chlorine and bromine compounds by the interaction of Cl2 molecules with Br–.The rate constant of the reaction of Cl2 with Br– ions in a 1 M HCl solution (k7f) was measured previously with a pulsedaccelerated- flow spectrophotometer (PAF).7 It was found to be equal to (7.7±1.3)×109 dm3 mol–1 s–1. In the optimisation of our experimental data, the best results were obtained with the use of k7f = (6.0±1.0)×109 dm3 mol–1 s–1 and K7 = k7f /k7b = (6.7±1.3)× ×105 dm3 mol–1.The ratio between the rate constants of forward and backward reactions (8) was taken on a basis of the known K8 = k8f /k8b equal to (6.0±0.3) dm3 mol–1.7 The partial transformation of Cl2Br– in the reaction with the Br– ion to form ClBr2 – (at 230 nm, e is 1.8×104 dm3 mol–1 cm–1) was also taken into consideration.7 The rates of ClBr2 – dissociation into ClBr + Br – and Br2 + Cl– were taken to be low, and they were ignored in the time interval under discussion.The proposed scheme adequately describes the appearance of absorbance at 230 nm in a 1 M NaCl solution in the presence of (1–10)×10–6 M Br– ions at k8b = = 1.7×105 s–1, k8f = 1.0×106 dm3 mol–1 s–1 and k9 = 3.0×108 dm3 mol–1 s–1 [Figure 2(b)]. The value of e for Cl2Br– was found to be equal to (3.6±0.4)×104 dm3 mol–1 cm–1.It is consistent with the published7 value 3.27×104 dm3 mol–1 cm–1. The mechanism of ClBr2 – formation is much more complicated, and it is beyond the scope of this communication. In addition to Cl2 –, the radical anions ClBr– and Br2 – take part in its formation.9 References 1 G. G. Jayson, B. J. Parsons and A. J. Swallow, J. Chem. Soc., Faraday Trans. 1, 1973, 69, 1579. 2 E. Janata, Radiat. Phys. Chem., 1992, 40, 437. 3 E. Janata, Radiat. Phys. Chem., 1994, 44, 449. 4 E. Janata and W. Gutsch, Radiat. Phys. Chem., 1998, 51, 65. 5 B. G. Ershov, M. Kelm and E. Janata, Radiat. Phys. Chem., 2000, 59, 309. 6 E. Janata and R. H. Schuler, J. Phys. Chem., 1982, 86, 2078. 7 T. X. Wang, M. D. Kelley, J. N. Cooper, R. C. Beckwith and D.W. Margerum, Inorg. Chem., 1994, 33, 5872. 8 B. Ershov, A. Gordeev, E. Janata and M. Kelm, Mendeleev Commun., 2001, 149. 9 B. G. Ershov, A. V. Gordeev, M. Kelm and E. Janata, Phys. Chem. Chem. Phys., 2002, 4, in press. 0.06 0.04 0.02 0.00 200 250 300 350 400 Absorbance l/nm (b) 0.05 0.10 0.15 0.20 0.25 1 2 3 4 Absorbance 0.06 0.04 0.02 0.00 4 3 2 1 (a) 5 6 5 6 t/ms Figure 2 (a) Absorption spectra of a 1 M NaCl solution containing 1×10–5 M NaBr and saturated with N2O (pH 3.3) (1) 1, (2) 8, (3) 24, (4) 50, (5) 100 and (6) 250 µs after the action of an electron pulse. Pulse duration, 20 ns. Absorbed dose, 5.4×1016 eV cm–3. (b) Kinetics of changes in the absorbance at 230 nm in a 1 M NaCl solution containing 1×10–5 M NaBr and saturated with N2O (pH 3.3) after the action of an electron pulse. Pulse duration, 20 ns. Absorbed dose, 7.5×1016 eV cm–3. Points: experimental data. Curves: computer simulation at k7f = 6.0×109 dm3 mol–1 s–1, k7b = 9.0×103 s–1, k8f = = 1.0×106 dm3 mol–1 s–1, k8b = 1.7×105 s–1; k9 = 3.0×108 dm3 mol–1 s–1 and eCl2Br– = 3.6×104 dm3 mol–1 cm–1. Cl2 + Br– Cl2Br– Cl2Br– Cl2 + Br– Cl2Br– ClBr + Cl– ClBr + Cl– Cl2Br– Cl2Br– + Br– ClBr2 – + Cl– (7f) (7b) (8b) (8f) (9) Received: 20th January 2002; Com. 02/1887

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Mendeleev Communications Electronic Version, Issue 2, 2002 1 Alkylation of malonic and acetoacetic esters in an ionic liquid Galina V. Kryshtal, Galina M. Zhdankina and Sergei G. Zlotin* N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 119991 Moscow, Russian Federation. Fax: +7 095 135 5328; e-mail: zlotin@ioc.ac.ru 10.1070/MC2002v012n02ABEH001563 1-Butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) has been used as a recyclable medium in the alkylation of malonic and acetoacetic esters with alkyl, benzyl and prenyl halides.The alkylation of malonic and acetoacetic esters is widely used for the synthesis of polyfunctional compounds.1(a)–(c) Classical alkylation procedures,1(a)–(c) alkylations in dipolar aprotic solvents2( a),(b) and under phase-transfer catalysis conditions3(a)–(f) are often complicated by using flammable organic solvents and difficulties in their regeneration, as well as in the regeneration of phase-transfer catalysts and in the isolation of reaction products.These problems can be solved by performing reactions in organic ionic liquids, which are of interest as an alternative to common organic solvents.4(a),(b) These melts, of which 1,3-dialkylimidazolium tetrafluoroborates and hexafluorophosphates containing poorly coordinating ion pairs have received most attention,5(a)–(c) are good solvents for both organic and inorganic compounds. They are moisture stable, not flammable and, what is very important, can be easily recovered and reused.4(a),(b) Due to the ionic nature, they can serve as polar solvents and phasetransfer catalysts simultaneously.Many applications of these melts in C–C coupling reactions, for instance, in the Friedel–Crafts,6 Diels–Alder,7(a)–(c) Wittig,8 Horner–Emmons,9 Knoevenagel10 and Heck11(a)–(c) have been reported. To the best of our knowledge, there is only one example of the C-alkylation of carbanions in ionic liquids, the base-promoted cycloalkylation of phenylacetonitrile with 1,4- dibromobutane in 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]).12 It is unclear whether the reaction can be used for the monoalkylation of phenylacetonitrile.12 There is no information on the base-promoted alkylation of ambident carbanions in ionic liquids; only Pd2(dba)3-catalysed C-allylation of dimethylmalonate with (E)-1,3-diphenyl-3-acetoxyprop- 1-ene was published.13 Here, we report the first example of the base-promoted alkylation of malonic 1 and acetoacetic 2 esters in an ionic liquid.We found that malonic ester 1 regioselectively reacts with alkyl, benzyl and prenyl halides 3a–f (1:3 ratio £ 1.5) in [bmim][PF6] in the presence of K2CO3 to afford monosubstituted malonates 4a–f in 53–80% yield.The reactions were carried out at 85–130 °C for 5–20 h (until starting compound 1 disappeared; TLC monitoring). Two substituents can be introduced into diethyl malonate 1 if an excess of an alkylating agent is used. Indeed, the reaction of 1 with 2.5 equiv. of benzyl chloride 3e under the same conditions afforded dibenzyl derivative 5 (yield 64%) as the only isolated product (Table 1).The K2CO3-promoted reactions of the ambident anion of acetoacetic ester 2, with 3a,d,e in [bmim][PF6] proceeded in a less selective manner to give, along with C-alkylation products 6a,d,e, vinyl ethers 7a,d,e. The ratio 6:7 varied from 88:12 to 60:40 depending on the alkylating agent. The fraction of O-alkylation products 7a,d,e in [bmim][PF6] was generally higher than those obtained under classical1(a),(b) and phase-transfer catalysis14,15 conditions (Table 2).This fact may be explained by a higher polarity of [bmim][PF6] than that of the most commonly used organic solvents16 and, consequently, by a higher likelihood of the SN1 mechanism of alkylation in the ionic liquid. Unlike 3e, more reactive benzyl bromide 3e' reacted with 2 in [bmim][PF6] under milder conditions to afford C-alkylation product 6e (yield 50%), which, according to 1H NMR spectra, was not contaminated with ether 7 (there are no vinyl protons in the d range 4.8–5.2 ppm).This difference in the behaviour of 3e and 3e' is not unexpected because less electrone-withdrawing leaving groups (particularly, Br compared to Cl) usually reduce the portion of O-alkylation.17(a),(b) The reaction of 2 with prenyl chloride 3f in [bmim][PF6] gave only C-alkylation product 6f, which was also obtained under classical1(a),(b) and phase-transfer catalysis14,15 conditions (Table 2).Tables 1 and 2 indicate that the yields of compounds 4–7 obtained in [bmim][PF6], as well as under the classical and phasetransfer catalysis conditions, are similar.Reactions in ionic liquids are preferable besause of the simplicity of product isolation and solvent regeneration.9,18 Compounds 4–7 can be isolated by evaporation at a reduced pressure (2 torr) from their solutions in the non-volatile ionic liquid.5(c) This procedure is technologically attractive but inconvenient in small-scale preparations (~10 mmol) owing to the irregularity of boiling of the reaction mixture.In laboratory conditions, it seems reasonable to use the extraction of alkylation products with diethyl ether (which is immiscible with [bmim][PF6]) followed by distillation. The ionic liquid was recovered by filtration from inorganic salts followed by the removal of volatile impurities at 40–60° (2 torr). In all cases, Table 1 K2CO3-Promoted alkylation of diethylmalonate in [bmim][PF6].Compound R Hal t/h T/°C Yield of 4a–f, 5 (%)a aYield of distilled compounds. b1:3:EtONa = 1:2:2.1(a) c1:3:NaOHaq:PTC = 1:1:2:1, CH2Cl2, 40 °C, 1 h.3(e),(f) d1:3:K2CO3:BTEA-Cl = 1:1.5:1.5:0.1, DMF, 50–65 °C, 6–9 h.2(b) e1:3:NaOHaq:BTEA-Cl = 1:1:2:0.1, 40–45 °C, 2 h.2(a) Reported yield of 4a–f, 5 (%) EtONa/EtOH (1:3:EtONa = 1:1:1) Phase-transfer catalysis (PTC) 4a Bu Br 12 85–90 80 80–901(a) 85c 4b Pri Br 20 85–90 54 65-801(a) 45c 4c cyclopentyl Br 15 120–130 57 701(a) 21d 4d Ami Br 15 110–120 70 801(a) 72d 4e PhCH2 Cl 5 120–130 72 51–571(b) 70e 4f (Me)2C=CHCH2 Cl 5 90–95 53 501(a) 46e 5 PhCH2 Cl 7 120–130 64 84b — RCH(COOEt)2 CH2(COOEt)2 (PhCH2)2C(COOEt)2 i ii Reagents: i, 1,5 equiv.RHal (3a–f), 2 equiv.K2CO3, 6 equiv. [bmim][PF6]; ii, 2.5 equiv. PhCH2Cl (3e), 2 equiv. K2CO3, 6 equiv. [bmim][PF6]. 4a–f 1 5Mendeleev Communications Electronic Version, Issue 2, 2002 2 we were able to recover 97–98% of the starting [bmim][PF6]. The recovered melt can be reused several times either in the same alkylation reaction (Table 3, items 2 and 3) or in the alkylation of another carbanion (Table 3, item 5) without a decrease in the yield and purity of compounds 4, 6, 7.† As a result, we have developed a recyclable procedure for the alkylation of malonic and acetoacetic esters, which is a good alternative to classical and phase-transfer catalysis methods.References 1 (a) A. C. Cope, H. L. Holmes and H. O. House, Organic Reactions, New York, 1957, vol. 9, p. 107; (b) H. Henecka, in Houben-Weyl, 1952, 8, 600; (c) S. Banetty, R. Romagnoli, C. De Risi, G. Spalluto and V. Zanirato, Chem. Rev., 1995, 95, 1065. 2 (a) A. Jonczyk, M. Ludwikow and M. Makosza, Rocz. Chem., 1973, 47, 89; (b) N. N. Sukhanov, L. N. Trappel, V. P. Chetverikov and L. A. Yanovskaya, Zh. Org. Khim., 1985, 21, 2503 [J. Org. Chem. USSR (Engl. Transl.), 1985, 21, 2341]. 3 (a) E. V. Dehmlow and S. S. Dehmlow, Phase-Transfer Catalysis, 3rd edn., Verlag Chemie, Weinheim, 1993; (b) C. M. Starks, C. L. Liotta and M. Halpern, Phase-Transfer Catalysis, Fundamentals, Applications and Industrial Perspectives, Chapman & Hall, London, 1994; (c) M. Makosza and M. Fedorynski, Adv. Catal., 1987, 35, 375; (d) M. Fedorynski, K. Wojciechowski, Z. Matacz and M.Makosza, J. Org. Chem., 1978, 43, 4682; (e) A. Brandstrom and U. Junggren, Acta Chem. Scand., 1969, 23, 2204; (f) A. Brandstrom and U. Junggren, Acta Chem. Scand., 1969, 23, 3585. 4 (a) M. J. Earle and K. R. Seddon, Pure Appl. Chem., 2000, 72, 1391, and references therein; (b) T. Welton, Chem. Rev., 1999, 99, 2071. 5 (a) P. A. Z. Suarez, J. E. L. Dullius, S. Einloft, R. F. de Souza and J.Dupont, Polyhedron, 1996, 15, 1217; (b) S. Chun, S. V. Dzyuba and R. A. Bartsch, Anal. Chem., 2001, 73, 3737; (c) R. Hagiwara and Y. Ito, J. Fluorine Chem., 2000, 105, 221. 6 C. J. Adams, M. J. Earle, G. Roberts and K. R. Seddon, Chem. Commun., 1998, 2097, and references therein. 7 (a) C. W. Lee, Tetrahedron Lett., 1999, 40, 2461; (b) M. J. Earle, P. B. McCormac and K.R. Seddon, Green Chem., 1999, 1, 23; (c) T. Fisher, A. Sethi, T. Welton and J. Woolf, Tetrahedron Lett., 1999, 40, 793. 8 V. le Boulaire and R. Gree, Chem. Commun., 2000, 2195. 9 T. Kitazume and G. Tanaka, J. Fluorine Chem., 2000, 106, 211. 10 D. W. Morrison, D. C. Forbes and J. H. Davis, Tetrahedron Lett., 2001, 42, 6053. 11 (a) A. J. Carmichael, M. J. Earle, J. D. Holbrey, P. B.McCormac and K. R. Seddon, Org. Lett., 1999, 1, 997; (b) W. Chen, L. Xu, C. Chatterton and J. Xiao, Chem. Commun., 1999, 1247; (c) L. Xu, W. Chen, J. Ross and J. Xiao, Org. Lett., 2001, 3, 295. 12 C. Wheeler, K. N.West, C. L. Liotta and C. A. Eckert, Chem. Commun., 2001, 887. 13 S. Toma, B. Gotov, I. Kmentova and E. Solcaniova, Green Chem., 2000, 2, 149. 14 P. Tundo, P. Venturello and E.Angeletti, J. Chem. Soc., Perkin Trans. 1, 1987, 2159. 15 H. D. Durst and L. Liebeskind, J. Org. Chem., 1974, 39, 3271. 16 S. N. V. K. Aki, J. F. Brennecke and A. Samanta, Chem. Commun., 2001, 413. 17 (a) A. L. Kurts, N. K. Genkina, A. Macias, I. P. Beletskaya and O. A. Reutov, Tetrahedron, 1971, 54, 4777; (b) O. A. Reutov, I. P. Beletskaya and A. L. Kurts, Ambident Anions, Consultants Bureau, New York, 1983. 18 S. V. Dzyuba and R. A. Bartsch, J. Heterocycl. Chem., 2001, 38, 265. † General procedure. To a vigorously stirred solution of 1 or 2 (10 mmol) in [bmim][PF6] (60 mmol) prepared according to known method5(b) were added successively 3a–f (10–25 mmol) and K2CO3 (20 mmol). The reaction mixture was stirred for 5–20 h at 65–130 °C (reaction conditions are given in Tables 1 and 2), cooled to 20 °C and extracted with Et2O (4×20 ml).The combined ether extracts were dried over anhydrous MgSO4. The solvent was evaporated, and products 4–7 were distilled. Boiling points, n20 D and 1H NMR spectra of compounds 4–7 were in accordance with reported data. Reaction conditions were not optimised. The remaining ionic liquid was filtered from inorganic salts and kept at 40–60 °C (2 torr) for 2 h to afford 58.8 mmol (98%) of [bmim][PF6].The 1H NMR spectrum of thus recovered melt was identical to that of freshly prepared [bmim][PF6].5(b) Table 2 K2CO3-Promoted alkylation of acetoacetic ester in [bmim][PF6]. Compound R Hal t/h T/°C Yield of 6 + 7 (%)a (Ratio 6:7)b aYield of distilled compounds. b6:7 ratio was determied from 1H NMR spectra.c2:3:K2CO3:Carbowax 6000 = 1:1.5:2.5:0.05, GLC conditions.14 d2:3:NaH: Aliquat 336 = 2:1:2:0.1, PhH, 80 °C, 8 h.15 Reported yield of 6+7 (%) (Ratio 6:7) EtONa/EtOH (2:3:EtONa = 1:1:1) Phase-transfer catalysis 6a + 7a Bu Br 12 115–120 51 (88:12) 651(b) (>99:1) 52c (75:25) 6d + 7d Ami Br 12 115–120 75 (60:40) 701(a) (>99:1) — 6e + 7e PhCH2 Cl 12 120–125 52 (80:20) 551(b) (>99:1) 72d (>99:1) 6e PhCH2 Br 12 65–70 50 (>99:1) — — 6f (Me)2C=CHCH2 Cl 6 90–95 66 (>99:1) 471(a) (>99:1) 30d (>99:1) EtOOCCH2COMe EtOOCCHCOMe + EtOOCCH=C–Me i Reagents: i, 1–1.5 equiv. RHal (3a,d,e,e',f), 2 equiv. K2CO3, 6 equiv. [bmim][PF6]. R OR 2 6a, d,e,f 7a, d,e Table 3 K2CO3-Promoted alkylation of malonic and acetoacetic esters 1 and 2 in recovered [bmim][PF6]. Item no. Cycle no. Starting compound RHal Product Yield of 4a, 4d, 6d+7d (%) Recovered [bmim][PF6] (%) 1 1 1 BuBr 4a 80 98 2 2 1 BuBr 4a 78 98 3 3 1 BuBr 4a 79 97 4 1 1 AmiBr 4d 70 98 5 2 2 AmiBr 6d + 7d (60:40) 75 98 Received: 25th January 2002; Com. 02/1889

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Mendeleev Communications Electronic Version, Issue 2, 2002 1 Superacidic cyclisation.lipase-mediated kinetic resolution as a short route from achiral linear isoprenoid alcohols to scalemic cyclic isomers Edward P. Serebryakov,*a Galina D. Gamalevich,a Veacheslav N. Kulcitki,b Nicon D. Ungurb and Pavel F. Vlad*b a N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 119991 Moscow, Russian Federation.Fax: +7 095 135 5328 b Institute of Chemistry, Academy of Sciences of Republic of Moldova, MD 2028 Kishinev, Republic of Moldova. Fax: + 373 2 73 9775 10.1070/MC2002v012n02ABEH001566 (¡¾)-¥á-Cyclogeraniol and (¡¾)-drim-7-en-11-ol acetates obtained via the FSO3H-induced cyclisation of geraniol and (E)-farnesol and subsequent acetylation were hydrolysed in the presence of hog pancreas lipase (PPL) to afford (R)-(+)-¥á-cyclogeraniol (ee ~30% at the optimal conversion C = 20¡¾2%) and (5R,9R,10R)-(+)-drim-7-en-11-ol (ee 78.5% at C = 30%), respectively; (¡¾)-15-acetoxyisoagath- 12-ene, obtained similarly from all-E-geranylgeraniol, is resistant to PPL-mediated hydrolysis, but is hydrolysed in the presence of lipase from Candida cylindracea to afford (10S,14R)-(.)-isoagath-12-en-15-ol of 69.80% ee in ~3% yield.Cyclic isoprenoids with a common structure and common relative configuration can occur in the nature in both enantiomeric forms. Typically, the species abundant in one or another enantiomer belong to rather remote taxons. To study the biomedical properties of enantiomeric terpenoids and, all the more so, to convert the latter into chiral building blocks, considerable amounts of both enanitomers are needed, but it is not always easy to obtain each of the two from natural sources or by chemical synthesis.However, both enantiomers of certain cyclic isoprenoids could be obtained in only three steps via a stereodivergent protocol that includes (i) the stereospecific superacid-induced cyclisation of geometrically pure achiral alcohols of the type H[CH2C(Me)= CHCH2]nOH into racemic cyclic isomers, (ii) the acetylation of the latter to produce the corresponding (¡¾)-acetates, and (iii) the subsequent lipase-mediated kinetic resolution of the acetates into differently functionalised (+)- and (.)-enantiomers by partial hydrolysis.Cyclisation of the lower members of the above type (n = 2.4) is well known,1 while enzymatic optical resolution of chiral alcohols or esters is such an obvious solution,2 that one can only wonder, (or just not wonder) why this protocol has not been actuated so far.¢Ó This work demonstrates the feasibility of stereodivergent transformation of geraniol 1 and (E,E)-farnesol 2 into scalemic ¥á-cyclogeraniols [(R)-3, (S)-3] and drim-7-en-11-ols [(all-R)-4, (all-S)-4].Similar transformation of all-E geranylgeraniol 5 into (.)-isoagath-12-en-15-ol [(10S,14R)-6] is also reported. By means of superacidic cyclisation alcohols 1, 2 and 5 were converted into corresponding cyclic isomers (¡¾)-3, (¡¾)-4, and (¡¾)-6,¢Ô from which acetates (¡¾)-3a, (¡¾)-4a and (¡¾)-6a were prepared¡× and subjected to partial hydrolysis in the presence of hog pancreas lipase (PPL) or lipase from Candida rugosa (�� C.cylindracea, CCL). In order to attain the highest possible ee of scalemic alcohols 3 and 4 without sacrificing too much the yield, conversions of (¡¾)-3a and (¡¾)-4a were arrested at C ¡Ì 30%. Acetate (¡¾)-6a could not be hydrolysed in the presence of PPL even upon repetitive addition of the enzyme up to a twofold excess (w/w).The scalemic form of alcohol 6 was obtained only using CCL as the catalyst.¢Ò The PPL-mediated hydrolysis of (¡¾)-3a proceeded with low enantioselectivity. In the best variant (C = 20% in 32 h), it afforded in a 20% yield a specimen of (+)-¥á-cyclogeraniol [(R)-3] with [a]D 20 +34.6¡Æ (c 0.96, EtOH), which corresponds to ~30% ee.For the specimens of 3 with ee ~100%, [a]D 25 +122¡Æ (EtOH)4(a) for the R enantiomer and .116¡Æ or .109.2¡Æ (EtOH) for its S antipode were reported.4(b),(c) Mild alkaline hydrolysis of the fraction of unconverted acetate gave a specimen of alcohol (S)-3 with [a]D 20 .10.4% (c 1.05, EtOH), which corresponds to ee ~10%. The hydrolysis of (¡¾)-4a was quicker (C = 30% in 22 h) and more selective.The isolated drim-7-en-11-ol with all-R configuration [(R)-4] had [a]D 21 +13.1¡Æ (c 1.1, PhH), which corresponds to ee 78.5%. Lit., [a]D 25 +15.8¡Æ (PhH)5(a) for a specimen of (R)-4 with ee 88% and [a]D rt .18¡Æ or .18.2¡Æ (PhH)5(a),(b) for the specimens of all-S drim-7-en-11-ol [(S)-4] of ~100% ee. The fraction of unconverted acetate upon alkaline hydrolysis gave alcohol (S)-4 with [a]D 20 .5.81¡Æ (c 0.89, PhH), which corresponds to ee ~32% (Scheme 1).The enhanced hydrolysis enantioselectivity in the case of (¡¾)-4a was considered earlier.6 The transition from (¡¾)-4a to (¡¾)-6a resulted in a dramatical deceleration of the PPL-catalysed hydrolysis, the recovery of acetate (¡¾)-6a after 96 h of incubation being almost quantitative. The hydrolysis of (¡¾)-6a in the presence of CCL was also very slow (C ~10% after 148 h). The reaction mass was workedup as usual and chromatographed twice, first on SiO2 and then on Florisil¢ç, to give an alcohol in 3% yield with [a]D 21 .7.2¡Æ (c 0.23, CHCl3).It was identical to the (.)-enantiomer of 6 with the 10S,14R configuration in 1H and 13C NMR spectra, GC MS data7(a),(b) and the sign of [a]D. Specimens of the latter with ~100% ee, obtained earlier from natural sources7(a),(b) or by partial synthesis from grindellic acid7(a) and sclareol7(c), displayed [a]D rt .9 to .10.5¡Æ (CHCl3).7 Consequently, the ee of this speci- ¢Ó A conceptually similar approach to Ambrox¢ç.from farnesyl acetate via lipase-mediated kinetic resolution of (¡¾)-drimane-8,10-diol3 is unsuitable for obtaining unsaturated cyclic alcohols with unambiguously positioned double bonds. ¢Ô Starting alcohols 1.3 were cyclised on treatment with fluorosulfonic acid (20 equiv.) in 2-nitropropane at .78¡ÆC, the reaction mass was neutralised with NEt3, washed with water, extracted with Et2O, dried (Na2SO4), and concentrated. The remainder was subjected to column chromatography on SiO2 using hexane.Et2O gradient elution (80:20 ¢ç 0:100) to give, in agreement with known procedures, (¡¾)-¥á-cyclogeraniol [(¡¾)-3, yield 73%],1(a) (¡¾)-drim-7-en-15-ol [(¡¾)-4, yield 71%]1(b) and (¡¾)-isoagath-12-en-15-ol [(¡¾)-6, yield 72%].1(c) ¡× The solutions of (¡¾)-4, (¡¾)-5 and (¡¾)-6 (0.25 mmol in hexane) were treated with Ac2O.Py (1:1, v/v; ~20 ¡ÆC, 12.18 h) in the presence of 4-DMAP (4.5 mg). After standard work-up the acetates were purified by column chromatography on SiO2 to give (¡¾)-3a, (¡¾)-4a and (¡¾)-6a in 92, 94 and 79% yields, respectively. ¢Ò Powdered PPL (48 units per mg protein, Olainfarm, Latvia) or CCL (type VII with lactose, 1200 units per mg solid, Sigma) and a substrate (1:2, w/w) were suspended in a 0.1 M aqueous phosphate buffer solution [pH 6.5 for PPL or 7.0 for CCL, 1.3 ml per 0.25 mmol of (¡¾)-acetate] and vigorously stirred at 20.22 ¡ÆC.The duration of stirring for (¡¾)-3a, (¡¾)-4a and (¡¾)-6a was 28.32 and 22 h (using PPL), or 148 h (using CCL), respectively. After standard work-up the only products of PPLmediated hydrolysis, the required alcohol and acetate (TLC monitoring), were separated by column chromatography on SiO2 [in the case of Cdiated hydrolysis of (¡¾)-6a this was followed by additional chromatography on Florisil¢ç] and identified spectroscopically.The enantioselectivity of hydrolysis was estimated by comparing the signs and magnitudes of [a]D of chromatographically pure alcohols obtained at C ¡Ì 30% with those reported in the literature for the same alcohols of ~100% ee.The fractions of unconverted acetates left after the hydrolysis of (¡¾)-3a or (¡¾)-4a were saponified (1 N NaOH/MeOH.H2O, ~20 ¡ÆC, 2.4 h) to give alcohols with the opposite signs of [a]D.Mendeleev Communications Electronic Version, Issue 2, 2002 2 men of (R)-6 is 69�C80%. The unconverted acetate afforded ¡®entisoagath- 7-en-11-ol¡� [(10R,14S)-6] with only ~1.5% ee {[a]D 21 +0.13¡ã (c 0.4, CHCl3)} upon alkaline hydrolysis.Attempts to enhance the enantioselectivity of enzymatic resolution of alcohols (¡À)-3 and (¡À)-4 by acylating them in the Ac2O�CPPL/hexane or vinyl acetate�CCCL/Et2O systems were unsuccessful. The PPL-mediated acylation of alcohol (¡À)-3 to 15% conversion gave acetate (R)-3a with only ~1.3% ee. When CCL was used, the fractions of unconverted alcohols recovered at C 55�C75% [predominantly (S)-3 and (S)-4] were contaminated by ¦Â-cyclogeraniol and drim-8-en-12-ol, respectively, and had ~9�C13% ee (as estimated by correlating the observed [a]D values with the respective 1H and 13C NMR data).8 Our results suggest that the superacidic cyclisation�Cacetylation �Cenzymatic hydrolysis protocol is synthetically useful.Its optimisation by lipase screening and/or by other known biocatalytic methods2,9 seems to be a feasible task. This work was supported by the Russian Foundation for Basic Research and the Federal Programme of Supporting Leading Scientific Schools of Russia (grant nos. 96-03-33396, 99-03-32992 and 96-15-97461) and by INTAS (grant no. 96-1109). References 1 (a) P.F. Vlad, N. D. Ungur, V. H. Nguen and V. B. Perutsky, Izv. Akad. Nauk, Ser. Khim., 1995, 2494 (Russ. Chem. Bull., 1995, 44, 2390); (b) P. F. Vlad, N. D. Ungur and V. B. Perutsky, Khim. Prir. Soedin., 1986, 793 [Chem. Nat. Compd. (Engl. Transl.), 1986, 12, 737]; (c) P. F. Vlad, N. D. Ungur and V. B. Perutsky, Khim. Prir. Soedin., 1986, 514 [Chem. Nat. Compd. (Engl. Transl.), 1986, 12, 485]; (d) P.F. Vlad, Pure Appl. Chem., 1993, 65, 1329. 2 (a) Enzyme Catalysis in Organic Synthesis, eds. K. Drauz and H.Waldmann, VCH, Weinheim, 1995, vol. 1, pp. 178�C261; (b) C. H. Wong and G. M. Whitesides, Enzymes in Synthetic Organic Chemistry, 2nd edn., Pergamon Press, Throwbridge, 1995, pp. 9�C13, 60�C130; (c) K. Faber, Biotransformations in Organic Chemistry.A Textbook, 2nd edn, Springer, Berlin, 1995, pp. 1�C23, 24�C144; (d) E. P. Serebryakov, Izv. Akad. Nauk, Ser. Khim., 2001, 1986 (Russ. Chem. Bull., Int. Ed., 2001, 50, 1984). 3 H. Tanimoto and T. Oritani, Tetrahedron: Asymmetry, 1996, 7, 1695. 4 (a) R. Buchecker, R. Egli, H. Regel-Wild, C. Tscharner, C. H. Eugster, G. Uhde and G. Ohloff, Helv. Chim. Acta, 1973, 56, 2544; (b) K.Mori, M. Amiake and M. Itou, Tetrahedron, 1993, 49, 1871; (c) H. Meyer and A. R��ttimann, Helv. Chim. Acta, 1980, 63, 1451. 5 (a) H. Akita, M. Nozawa, A. Mitsuda and H. Ohsawa, Tetrahedron: Asymmetry, 2000, 11, 1375; (b) H. H. Appel, C. J. Brooks and K. H. Overton, J. Chem. Soc., 1959, 3322. 6 E. P. Serebryakov and G. D. Gamalevich, Mendeleev Commun., 1996, 221. [There, due to erroneous assignment of ligands seniority at the atom C(9) in molecules (R)-4 and (S)-4a, the configurations of the dextrorotatory alcohol and ¡®unconverted acetate¡� were denoted wrongly]. 7 (a) G.Cimino, D. de Rosa, S. de Stefano and L. Minale, Tetrahedron, 1974, 30, 645; (b) K. Gustafson and R. J. Andersen, Tetrahedron, 1985, 41, 1101; (c) D. K. Manh Duc, M. Fetizon and M. Kone, Bull. Soc. Chim. Fr., 1975, 2351. 8 G. D. Gamalevich and E. P. Serebryakov, Izv. Akad, Nauk, Ser. Khim., 1997, 175 (Russ. Chem. Bull., 1997, 46, 171). 9 F. Theil, Tetrahedron, 2000, 56, 2905. Scheme 1 Reagents and conditions: i, FSO3H (20 equiv.)/Me2CHNO2, �C75 ¡ãC; ii, Ac2O�CPy (1:1, v/v)/4-DMAP (cat.), room temperature; iii, H2O (pH 6.5)/PPL (substrate:enzyme = 2:1, w/w), room temperature; iv, KOH�C MeOH (aqueous), room temperature; v, H2O (pH 7.0)/CCL (substrate: enzyme = 2:1, w/w), room temperature, 148 h. OH 1 OR (¡À)-3 H (¡À)-3a ii (92%) i (73%) iii (C ¡Ö 20%) OH H OR H R S (R)-(+)-3 ee ¡Ö 30% (S)-3a (R = Ac) (S)-(�C)-3 (R = H) ee ¡Ö 10% iv OH OAc H i (71%) ii (94%) 2 (¡À)-4a iii (C = 30%) OH H OR H R R R S S S (R)-(+)-4 ee 78.5% (S)-4a (R = Ac) (S)-(�C)-4 (R = H) ee ¡Ö 32% iv H i (72%) ii (79%) 5 (¡À)-6a v (3%) (C ¡Ö 10%) OH H OAc H H OH H R S (10S,14R)-6 ee 69�C80

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年代:2002

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Novel aromatic borafluorole, fluoraborabenzene and diborafluorabenzene heterocyclic systems: an ab initio study Ruslan M. Minyaev,* Tatyana N. Gribanova, Alexei A. Milov, Andrei G. Starikov and Vladimir I. Minkin Institute of Physical and Organic Chemistry, Rostov State University, 344090 Rostov-on-Don, Russian Federation. Fax: +7 8632 43 4667; e-mail: minyaev@ipoc.rsu.ru The ab initio [MP2(fu)/6-311+G**] and DFT (B3LYP/6-311+G**) calculations predict aromatic stabilization of the planar structures of borafluorole, fluoraborabenzene and diborafluorabenzenes, boron-containing heterocycles with hypercoordinated fluorine centres.Aromaticity is among the most important concepts of theoretical chemistry1,2 designed to predict and explain the stability and chemical properties of various, in particular, heterocyclic compounds.We have previously considered a simple method to design novel heteroaromatic systems by substituting CH units or CC bonds in the ring of the archetype aromatic system of benzene by equal numbers of isoelectronic (e.g., BH¡©, N, O+ and F2+) or 2¥�-electronic (NH, O and S) centres, respectively. The efficiency of the approach was demonstrated by the prediction of a significant stability of six-membered oxaboraheterocycles and oxa-1,8-diboranaphthalene.3 In a similar way, novel stable nonclassic molecular systems 1¡©3 can be produced starting from another aromatic system.Here, we report on the computational study of five-membered boron-containing heterocycles with hypercoordinated fluorine centres in the ring, which are derived from the aromatic cyclopentadienide anion.In addition, %+ ) ) &Y Method Structure, symmetry 1, C2v 2, Cs 12, Cs 4, C2v 5, Css 6, C 7, C2v 8, C2v 9, C2v 10, Cs 11, Cs 15, Cs &V MP2(fu)/6-311+G** B3LYP/6-311+G** MP2(fu)/6-311+G** B3LYP/6-311+G** MP2(fu)/6-311+G** B3LYP/6-311+G** MP2(fu)/6-311+G** B3LYP/6-311+G** MP2(fu)/6-311+G** B3LYP/6-311+G** MP2(fu)/6-311+G** MP2(fu)/6-311+G** B3LYP/6-311+G** MP2(fu)/6-311+G** B3LYP/6-311+G** MP2(fu)/6-311+G** B3LYP/6-311+G** MP2(fu)/6-311+G** B3LYP/6-311+G** MP2(fu)/6-311+G** B3LYP/6-311+G** MP2(fu)/6-311+G** B3LYP/6-311+G** a E¡ª ¡ª0 05.5 3.2 ¡ª ¡ª0 0 76.2 41.3 37.2 0 0 126.9 117.0 75.8 72.2 42.8 41.2 11.7 10.2 (kcal mol¡©1) are the relative enthalpy and relative Gibbs free energy at standard conditions (P = 1 atm and T = 298.1 K).w1 437.7 423.8 359.5 276.4 129.6 152.1 239.0 252.4 217.8 239.3 185.7 121.1 138.9 245.7 271.8 188.7 179.1 123.6 217.9 164.5 143.3 77.3 86.9 Etot (a.u.) is the total energy (1 a.u.= 627.5095 kcal mol¡©1); ZPE (a.u.) is the harmonic zero-point correction; w1 (cm¡©1) is the smallest harmonic vibration frequency; E (kcal mol¡©1) is the relative energy; EZPE (kcal mol¡©1) is the relative energy including the harmonic zero-point correction; H and G calculations of a series of the six-membered fluorine- and boroncontaining heterocyclic cations 4¡©7 and electrically neutral diborafluorabenzenes 8¡©11, which are isoelectronic to benzene, have been performed to demonstrate the applicability of the method to the construction of nonclassic aromatic systems. Table 1 The ab initio and DFT data for compounds 1¡©2, 4¡©12, 15.a Mendeleev Communications Electronic Version, Issue 2, 2002 ) &V ¡©253.733629 ¡©254.326792 ¡©240.819808 ¡©241.402386 ¡©240.809152 ¡©241.396040 ¡©291.846694 ¡©292.522902 ¡©279.203663 ¡©279.863714 ¡©279.080603 ¡©279.135828 ¡©279.801776 ¡©266.300209 ¡©266.949997 ¡©266.094547 ¡©266.759355 ¡©266.176852 ¡©266.832591 ¡©266.229763 ¡©266.881886 ¡©266.277945 ¡©266.930541 4, C HB8, C %+ All calculations of compounds 1¡©11 and other possible positional isomers have been carried out with the help of ab initio [MP2(fu)/6-311+G**] and density function theory (B3LYP/6- 311+G**) methods.4 The principal questions to be solved by calculations are: (i) whether the designed (4n + 2)¥�-electron systems remain stable to possible distortions of the planar structures and (ii) what is the magnitude of the additional stabilization of the cyclic systems, which is due to the ¥�-electronic cyclic delocalization.To answer these questions, we have considered possible out-of-plane distortions of the planar structures of 1¡©11 and estimated the aromatic character of these compounds using the approach3 similar to that used for calculations of the Dewar resonance energies.1,2 ZPE E E tot ¡ª ¡ª0 0 0.066714 0.065893 0.062942 0.062162 6.7 4.0 ¡ª ¡ª 0.061069 0.060910 0.083322 0.082448 0 0 77.2 42.6 38.9 0.081574 0.081236 0.079992 0.079495 0.078517 0 0 129.1 119.6 0.078446 0.078003 0.075042 0.073749 77.4 73.7 44.2 42.7 0.075937 0.075685 0.076241 0.075542 14.0 12.2 0.074911 0.074884 10.1070/MC2002v012n02ABEH001576 F+ F 2+ F + F + BH BH BH 7, C 6, C 5, C 2v s s 2v F F F F BH BH BH BH BH HB BH 9, C 11, C 10, C s s s 2v G H ZPE ¡ª ¡ª0 0 ¡ª ¡ª0 0 4.5 2.4 ¡ª ¡ª 6.2 3.8 ¡ª ¡ª 0 0 76.2 41.3 36.7 0 0 76.3 41.5 37.6 0 0 126.7 116.5 0 0 127.2 117.4 74.9 71.6 42.0 40.1 76.2 72.5 43.2 41.7 9.7 8.4 12.8 11.2 1According to the calculations, the molecules of 1,2,4,5,7¡©11 possess planar structures and correspond to deep minima on the respective potential energy surfaces (PES). Their geometric and energy characteristics are listed in Table 1 and shown in Figures 1 and 2.Other conceivable positional isomers are unstable in cyclic forms and do not correspond to minima on the PES. As for furan, their isoelectronic analogues fluorole cation 1 and the most stable positional isomer of 1,2-borafluorole 2 have relatively low aromatic character displayed by the substantial alternation in the CC bond lengths (Figure 1), and the long BF distance (1.670 A, MP2 and 1.683 A, DFT) in 2 which is considerably longer than the standard length of an ordinary BF bond (~1.35 A).7,8 This conclusion is consistent with previous calculations.1,5,6 To evaluate the thermodynamic stability of cyclic system 2 and the role of ¥�-electronic cyclic delocalization, we compared it with isomeric polyene 12 as the reference structure.According to the calculations, the latter is 4.0 (DFT) and 6.7 (MP2) kcal mol¡©1 less energy favourable than 2. MP2(fu)/6-311+G** B3LYP/6-311+G** F+ 106.8 106.1 1.489 1.517 106.1 105.6 110.5 111.4 1.328 1.317 1.461 1.464 1, C2v 1.350 1.357 122.7 123.7 F 1.339 1.332 1.457 1.453 12, Cs Figure 1 Geometry parameters of structures 1, 2 and 12 calculated by ab initio and DFT methods.The bond lengths and angles are indicated in angstrom units and degrees, respectively. MP2(fu)/6-311+G** B3LYP/6-311+G** F2+ 1.462 1.486 124.8 124.8 121.0 121.5 1.352 1.338 115.4 114.7 122.5 122.9 1.417 1.422 4, C2v F 1.510 1.523 108.4 108.1 B B1.529 1.522 119.2 1.342 1.347 125.8 125.9121.1 121.4 1.460 1.454 113.3 112.9125.3 125.6 120.9 120.4 F 1.405 1.404 8, C2v Figure 2 Geometry parameters of isomers 4, 5, 8 and 15 calculated by ab initio and DFT methods.The bond lengths and angles are indicated in angstrom units and degrees, respectively. Mendeleev Communications Electronic Version, Issue 2, 2002 F 1.670 1.683 1.439 1.468 106.6 106.1 100.5 B 100.4 114.3 115.3 1.434 1.428 1.339 1.334 1.450 1.445 2, Cs 1.396 1.387 B 176.7 176.8 F+ 1.521 1.527 1.458 1.484 B 124.9 125.0 112.2 111.7 116.1 115.2 1.496 1.492 1.329 1.319 120.5 123.5 120.9 124.0 122.8 123.1 1.369 1.361 1.453 1.455 5, Cs B 1.450 1.445 127.3 120.7 129.2 178.3 177.7 125.6 1.362 126.0 1.359 1.400 1.391 15, Cs + + + + ) ) +% +% % ++ ) & &V + + & The length of the double BC bond in polyene 12 (1.387 A, DFT and 1.396 A, MP2) is close to that of a double BC bond in organoboron compounds.7,8 To evaluate the stabilization determined by &ectronic cyclic delocalization (Earom) in 2, we used the equation Earom(2) = E(2¡©12) ¡© EBF, (1) where E(2¡©12) is the difference between the total energies of 2 and 12, EBF (1.8, DFT and 3.9 kcal mol¡©1, MP2) corresponds to the energy of the BF bond in 2 calculated as the difference between the total energies of cyclic 13 and open chain 14 structures.The stereochemical surrounding of the BF bond in 13 is nearly the same as in 2, the dihedral angle between the CF and CB bonds in 13 equals 17.3¡Æ (DFT) and 3.5¡Æ (MP2).However, in contrast to 2, 13 does not embody a property of ¥�-electronic cyclic delocalization. As can be seen in Table 1, the Earom values (2.2, DFT and 2.8 kcal mol¡©1, MP2) for 2 are considerably lower than those (23¡©75 kcal mol¡©1) for ¥�-electronic cyclic delocalization of benzene as obtained by the use of various methods and different reference systems.2 Analogously, ¥�-electronic cyclic delocalization energy in 8 is calculated according to the equation Earom(8) = E(8¡©15) ¡© EBF, (2) where E(8¡©15) is the difference of the total energies of 8 and 15, EBF is the BF bond energy in 8 estimated as the difference of the total energies of 16 and 17.The values of Earom(8) obtained in such a way, 13.1 (DFT) and 13.6 (MP2) kcal mol¡©1, are twice larger than the values of Earom(2), even though they remain lower than the cyclic ¥�-electron delocalization energy of benzene. ) + + +% %+ ) ) +% +% ++ %+ %+ + + & &V References + + & In conclusion, the above calculations demonstrated the generality of an approach to the computational design of nonclassic aromatic systems based on replacing CH or CHCH units in parent aromatic hydrocarbons by hypercoordinated ¥�-isoelectronic heteroatomic fragments.Hypothetical compounds 2, 5 and 8, containing hypercoordinated fluorine were found to have stable planar structures with weak aromatic stabilization. This work was supported by the Russian Foundation for Basic Research (grant no. 01-03-32546) and the US Civilian Research and Development Foundation (grant no. RC1-2323-RO-02). 1 V. I. Minkin, M. N. Glukhovtsev and B. Ya. Simkin, Aromaticity and Antiaromaticity: Electronic and Structural Aspects, Wiley, New York, 1994.2 T. M. Krygowski, M. K. Cyranski, Z. Czarnocki, G. Hafelinger and A. R. Katritzky, Tetrahedron, 2000, 56, 1783. 3 R.M.Minyaev, V. I.Minkin, T. N. Gribanova and A. G. Starikov, Mendeleev Commun., 2001, 43. 4 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, V. G. Zakrzewski, J.A. Montgomery, Jr., R. E. Stratmann, J. C. Burant, S. Dapprich, J.M.Millam, A. D. Daniels, K. N. Kudin, M. C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi, R. Cammi, B.Mennucci, C. Pomelli, C. Adamo, S. Clifford, J. Ochterski, G. A. Petersson, P. Y. Ayala, Q. Cui, K.Morokuma, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. Cioslowski, J. V. Ortiz, A. G. Baboul, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R. L.Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe, 27 P. P. Power, Inorg. Chim. Acta, 1992, 198–200, 443. 8 W. J. Grigsby and P. P. Power, Chem. Eur. J., 1997, 3, 368. P.M.W. Gill, B. Johnson,W. Chen, M.W.Wong, J. L. Andres, C. Gonzalez, M. Head-Gordon, E. S. Replogle and J. A. Pople, Gaussian 98, Revision A.9, Gaussian, Inc., Pittsburgh PA, 1998. 5 R. M. Minyaev, G. V. Orlova and V. I. Minkin, Zh. Org. Khim., 1989, 25, 2033 [J. Org. Chem. USSR (Engl. Transl.), 1989, 25, 1837]. 6 E.Uggerud, J. Chem. Soc., Perkin Trans. 2, 1976, 1857. Received: 13th March 2002; Com. 02/1902 3 Mendeleev Communications Electronic Version, Iss

ISSN:0959-9436     

出版商:RSC    

年代:2002

数据来源: RSC