摘要:

Synthesis of Naturally Occurring 5-Allyl-2-aryl-7-methoxybenzofuran and 2-Aryl-5-(3-hydroxypropyl)-7-methoxybenzofurans$ Raghao S. Mali* and Archna Patience Massey Garware Research Centre, Department of Chemistry, University of Pune, Pune-7, India A convenient and general procedure is described for the synthesis of 5-allyl-2-aryl-7-methoxybenzofurans (8a±e) from 2-allyloxy-3-methoxybenzaldehyde (3). The compounds 8a and 8b on hydroboration followed by oxidation provide the naturally occurring benzofurans (1a and 1b).A few compounds, containing the 2-arylbenzofuran nucleus (1a, 1b, 2 and 8a), have been isolated from plants.2±4 Egonol (1a) and homoegonol (1b) were isolated2,3 from the seeds of Styrax japonicum and Styrax o�cinalis L. respect- ively, while (2)-machicendiol 2 was isolated4 from the leaf extracts of Machilus glaucescens, which are used for the treatment of asthma, rheumatism and ulcers. These com- pounds are also reported for their cytostatic activity against human leukemic HL-60 cells.5 In view of the natural occurrence and valuable biological activities associated with 1a, 1b and 2, several methods have been developed for their synthesis.7±9,11 Four approaches are known7±9,11 for egonol 1a and one 8,9 each for homo- egonol 1b and neolignan 8a.We report herein a convenient, general approach (Scheme 1) for the synthesis of egonol 1a, homoegonol 1b and neolignan 8a, starting from 2-allyloxy-3-methoxy- benzaldehyde13 3.When a solution of aldehyde 3 in N,N-dimethylaniline was irradiated in a microwave oven for 10 min, 5-allyl-2-hydroxy-3-methoxybenzaldehyde 4 was obtained in 65% yield along with minor amount (15%) of 2-allyl-6-methoxyphenol. The aldehyde 4 on reduction with sodium tetrahydroborate in ethyl acetate solution, gave the benzyl alcohol 5 as a thick liquid in 76% yield. Reaction of 5 with thionyl chloride in methylene chloride, followed by treatment with triphenylphosphine in benzene solution yielded the phosphonium salt 6, which on reaction with benzoyl chlorides in toluene solution, in the presence of J.Chem. Research (S), 1998, 230±231 J. Chem. Research (M), 1998, 1109±1120 Scheme 1 triethylamine, furnished the 2-arylbenzofurans (8a±e) in 60±89% yields via the intermediacy of phosphonium salts 7a±e. $Dedicated to Professor Dr Dieter Seebach on the occasion of his 60th birthday. *To receive any correspondence (e-mail: rsmali@chem.unipune. ernet.in). 230 J.CHEM. RESEARCH (S), 1998The present work thus describes the total synthesis of neolignan 8a and the related compounds 8b�}e. Conversion of 2-arylbenzofuran 8a into egonol 1a has already been reported8 in the literature using the hydroboration approach. The compound 8b on similar reaction provided homoegonol 1b, mp 121 8C (lit.,3 mp 120�}122 8C) in 70% yield, which is another natural product. We thank Professor N. S. Narasimhan for critical reading of the manuscript and valuable discussions.A.P.M. thanks CSIR, New Delhi for the award of Senior Research Fellowship. Techniques used: IR, 1H NMR, elemental analyses, TLC and column chromatography References: 15 Received, 17th October 1997; Accepted, 14th January 1998 Paper E/7/07498K References cited in this synopsis 2 H. Okada, J. Pharm. Soc. Jpn., 1915, 657. 3 R. Segal, I. M. Goldzweig, S. Sokolo€ and D. V. Zaitschek, J. Chem. Soc. C, 1967, 2402. 4 B. Talaparta, T. Ray and S. Talaparta, Indian J. Chem., Sect. B, 1976, 14, 613. 5 T. Hirano, M. Goto and K. Oka, Life Sci., 1994, 55, 1061. 7 S. Kawai, T. Nakamura and N. Sugiyama, Ber. Dtsch. Chem. Ges., 1939, 72, 1146. 8 E. Ritchie and W. C. Taylor, Aust. J. Chem., 1969, 22, 1329. 9 F. G. Schreiber and R. Stevenson, J. Chem. Soc., Perkin Trans. 1, 1976, 1514. 11 Y. Aoyagi, T. Mizusaki, A. Hatori, T. Asakura, T. Aihara, S. Inaba, K. Hayatsu and A. Ohta, Heterocycles, 1995, 41, 1077. 13 R. S. Mali and A. P. Massey, Indian J. Chem., Sect. B, 1995, 34, 686. J. CHEM. RESEARCH (S), 19

ISSN:0308-2342    

DOI:10.1039/a707498k

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

Nitrenium Ions. Part 3.1 Acid-catalyzed Reactions of 2-tert-Butylindole with Nitrosoarenes. Crystal Structures of 2-tert-Butyl-3-p-tolylimino-3H-indole and 3-tert-Butyl-3-p-tolylamino-1,3-dihydroindol-2-one$ Patricia Carloni,a Lucedio Greci,*a Marco Iacussi,a Monica Rossetti,a Pietro Cozzinib and Paolo Sgarabottob aDipartimento di Scienze dei Materiali e della Terra, Universita¢® , Via Brecce Bianche, I-60131 Ancona, Italy bDipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Universita¢® , Centro di Studio per la Strutturistica Diffrattometrica del CNR, Viale delle Scienze, I-43100 Parma, Italy In the presence of acids nitrosoarenes form nitrenium ions which react with heterocycles such as indoles.J. Chem. Research (S), 1998, 232¡¾233 J. Chem. Research (M), 1998, 1121¡¾1152 Scheme 1 The studies on nitrenium ions are mostly devoted to their potential carcinogenicity.15 Our interest is focused on the reactivity of di€erent heterocycles with nitrosoarenes acti- vated by monochloroacetic acid.The results here described for 2-tert-butylindole support the hypothesis that nitroso- arenes in the presence of acids give rise to the equilibrium (1) and that the formed nitrenium ions react with hetero- cycles such as indoles. Ar0N1O a Ha ¢§4 3¢§¢§¢§¢§ Ar0 Na 0OH O1U The reaction of 2-tert-butylindole 1 with activated nitroso- arenes 2a¡¾d were carried out in dichloromethane in a 1: 2 ratio in the presence of catalytic amounts of monochloro- acetic acid at room temperature.The isolated products are shown in Scheme 1. The structures of compounds 4d and 5d were elucidated by X-ray analysis. The reaction of nitrosoarenes with 2-tert-butylindole in the presence of acids highlights two important results on the reactivity of protonated nitrosoarenes; (a) the formation of azocompounds 3 and (b) the formation of indolenines 4, which are characterised by a new carbon¡¾nitrogen bond.The ¢çrst aspect, together with the detection of the phenyl- aminoxyl signal in the reaction carried out in the EPR cavity, clearly support the involvement of a reductive path- way in these reactions. The problem now is to establish whether an outer or inner-sphere electron transfer is operat- ing. Since the reduction potential Epc of nitrosobenzene in monochloroacetic acid is ¢§1.32 V (vs. Ag¡¾Aga) and the oxidation potential Epa of 1 is a0.57 V (vs. Ag¡¾Aga) it may be argued, on the basis of the general rules,25 that an outer-sphere electron transfer can be ruled out; in fact, the endothermicity of the sole electron transfer based on the redox potentials of the reactions amounts to 43.6 kcal, instead the maximum limiting value is around ca. 10 kcal.25 Thus, the formation of phenylnitroxide could be explained by an homolytic retrogression of the s-complex 14 (inner- sphere electron transfer) forming the phenylaminoxyl 15 and the indole radical cation 16 as shown in Scheme 3.In general, when arylnitrenium ions are generated in the presence of nucleophiles, they react at the conjugated position of the benzene ring,11c,28,29 but in our case the acti- vated nitrosoarenes (N-aryl-N-hydroxynitrenium ions) react Scheme 3 $Dedicated to Professor Dietrich DoE pp on the occasion of his 60th birthday. *To receive any correspondence (e-mail: GRECI@POPCSI. UNIAN.IT). 232 J. CHEM. RESEARCH (S), 1998through the nitrogen, forming a new carbon�}nitrogen bond a€ording the s-complex 14, which leads to compounds 4 by deprotonation and elimination of water, as shown in Scheme 3 and as has been previously observed.20 The formation of compounds 5a�}d could be easily explained by 1,2-addition30 of water to compounds 4 followed by tert-butyl group migration,31 which are both documented processes.In fact, compounds 4 reacted in wet dichloromethane in the presence of monochloroacetic acid to give compounds 5. An alternative mechanism to the radical pathway described before may arise from the di€erent ground states of arylnitrenium ions.These species are mostly ground state singlet,33 which justiRes their reactivity described above. But there are many literature data regarding triplet aryl- nitrenium ions: one of these reports the formation of the parent amine.33 The triplet arylnitrenium ion could promote transfer of an hydrogen atom from indole 1 forming an arylhydroxylamine aArNOHUOH aa radical cation and the indolyl radical 1 .The radical cation ArNOHUOH a may form the arylaminoxyl through the equilibrium (2) and the indolyl radical 1 may be the species responsible for the formation of compound 6. Ar0NOHU0OH a N Ar0NOHU0OH a Ha O2U It is well known that C-centred radicals react with oxygen forming peroxyls34 leading to alkoxyls.35 Therefore in our case, the sequence of reactions shown in Scheme 4 could be invoked in order to explain the formation of compound 6.The results here described clearly demonstrate that nitro- soarenes in acids give rise to the equilibrium (1) involving the formation of arylhydroxynitrenium ions, which lead to compounds characterised by a carbon�}nitrogen bond formation and products deriving from redox processes. The radical pathway attributed to an inner-sphere mechanism or to an hydrogen-atom transfer from 2-tert-butylindole to the nitrenium ion triplet state remains a dicult task to be conRrmed, even if the involvement of the nitrenium ion triplet state in redox processes has also been recently proposed by others.33 Thanks are due to the Italian MURST and to the Consiglio Nazionale delle Ricerche (C.N.R.-Roma) for Rnancial support. Techniques used: Elemental analysis, IR, 1H NMR, 13C NMR, EPR spectroscopy, mass spectrometry, X-ray analysis References: 44 Schemes: 4 Figs. 1 and 2: Perspective views of 4d and 5d Table 1: Yields of the reaction products of 1 with 2a�}d in the pre- sence of monochloroacetic acid Table 2: Bond distances, angles and torsion angles of compounds 4d and 5d Table 3: Crystallographic data for compounds 4d and 5d Appendix: Tables of atomic coordinates and equivalent isotropic displacement parameters, bond lengths and angles, anisotropic displacement parameters, and hydrogen coordinates and isotropic displacement parameters Received, 2nd October 1997; Accepted, 26th January 1998 Paper E/7/07144B References cited in this synopsis 1 P.Carloni, L. Greci, M. Iacussi, M. Rossetti, P. Stipa, C. Rizzoli and P. Sgarabotto, J. Chem. Res. (S), 1996, 350. 11 (c) H. Takeuchi and K. Takano, J. Chem. Soc., Perkin Trans. 1, 1986, 611. 15 (a) S. S. Thorgeirsson, in Biochemical Basis of Chemical Carcino- genesis, ed. H. Greim, R. Jung, M. Kramer, H. Merquardt and F. Oesch, Raven Press, New York, 1984, p. 47; (b) R. C. Garner, C. N. Martin and D. B. Clayson, in Chemical Carcinogenesis, ed. C. E. Searle, American Chemical Society, Washington, DC, 2nd edn., 1984 pp. 175�}276; (c) T. J. Flammang and F. F. Kadlubar, Carcinogenesis, 1986, 7, 919; (d ) C. C. Lai, E. C. Miller, J. A. Miller and A. Liem, Carcinogenesis, 1988, 9, 1295. 20 L. Cardellini, P. Carloni, E. Damiani, L. Greci, P. Stipa, C. Rizzoli and P. Sgarabotto, J. Chem. Soc., Perkin Trans. 2, 1994, 1589. 25 L. Eberson, Electron Transfer Reactions in Organic Chemistry, Springer-Verlag, Heidelberg, 1987, p. 22. 28 G. Kohnstamm, W. A.Pecth and L. H. Williams, J. Chem. Soc., Perkin Trans. 2, 1984, 423. 29 (a) T. Sone, Y. Tokudo, T, Sakai, S. Shinkai and O. Manabe, J. Chem. Soc., Perkin Trans. 2, 1981, 298; (b) T. Sone, K. Hamamoto, Y. Sciji, S. Shinkai and O. Manabe, J. Chem. Soc., Perkin Trans. 2, 1981, 1596. 30 (a) M. Colonna, L. Greci and L. Marchetti, Gazz., 1975, 105, 665; (b) 1975, 105, 985; (c) J. Chem. Soc., Perkin Trans. 2, 1977, 1032; (d ) 1979, 233; (e) L. Eberson and L. Greci, J. Org. Chem. 1984, 49, 2135; ( f ) H. S. Ch'ng and M. Hooper, Tetrahedron Lett., 1969, 1527; (g) S. P. Hiremath and M. Hooper, Adv. Heterocycl. Chem., 1978, 22, 123; (h) J. M. Adam and T. Winkler, Helv. Chim. Acta, 1984, 67, 2186. 31 (a) J. March, Advanced Organic Chemistry, John Wiley and Sons, New York, 3r85, p. 942; (b) C. Berti, L. Greci and M. Poloni, J. Chem. Soc., Perkin Trans. 1, 1981, 1610. 33 S. Srivastava and D. E. Falvey, J. Am. Chem. Soc., 1995, 117, 10 186 and references cited therein. 34 (a) F. E€enberger, W. D. Stoher, K. E. Mack, F. Reisinger, W. Seufert, H. E. A. Kramer, R. Foll and E. Vogelmann, J. Am. Chem. Soc., 1990, 112, 4849; (b) J. F. Nelsen and R. Akaba, J. Am. Chem. Soc., 1981, 103, 2096; (c) J. A. Howard, Rev. Chem. Intermed., 1984, 5, 1. 35 K. U. Ingold, Acc. Chem. Res., 1969, 2, 1 and references cited therein. Scheme 4 J. CHEM. RESEARCH (S), 1998 233

ISSN:0308-2342    

DOI:10.1039/a707144b

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

Degradation of Concentrated Solutions ofNon-biodegradable Orange II by Photocatalyticand Electrochemical MethodsJayasundera Bandara,a Fernando G. Herrera,a John T. Kiwi*a andCesar O. PulgarinbaInstitute of Physical Chemistry II, Ecole Polytechnique FeÈÍ deÈÍ ral de Lausanne, 1015 Lausanne,SwitzerlandbInstitute of Environmental Engineering, Bioengineering, Ecole Polytechnique FeÈÍ deÈÍ ralde Lausanne, 1015 Lausanne, SwitzerlandThe rate of photodegradation of Orange II was significantly accelerated by the addition of portions of H2O2 atappropriate times based on the monitoring of oxygen content and oxidant consumption; in contrast, mineralisation byelectrochemical treatment was observed to be relatively inefficient.Recent studies have shown that Fenton, photo-Fenton1¡Ó5and electrochemical6 oxidation of organic compounds areecient processes.In this study we plan to show thatthis approach could be applied to degrade concentratedsolutions containing azo-dyestus7 such as Orange II.There is a growing interest in removing dyes from waterreservoirs for health as well as aesthetic reasons. Sincethe photo-Fenton system is catalytic instead of stoichio-metric in iron, it is of interest to see if this approachcould be used with shorter reaction times (in the minutesrange) and compete with the more traditional occulation¡Ócoagulation non-destructive techniques to remove the azo-dye.Irradiation of the solutions as carried out in 60 mlPyrex asks with a cuto at l1290 nm.The light sourcewas a Suntest solar simulator where the radiant ux(90 mW cm£¾2) was measured with a power meter.Fig. 3 shows the total organic carbon (TOC) decrease forconcentrated dye solutions as found in the euents of azo-dye manufacturing at the production site. Fig. 3 indicates aTOC reduction under light from 450 mg C l£¾1 to 38 mg C l£¾1in trace a. This is an 88% reduction within 40 min. Diluteddye solutions shown by traces c and d were seen to minera-lize within shorter times as expected for a lower substrateconcentration.Concentrated solutions of Orange II (2.95 mM or0.118 mM in 40 ml solution) needed 4.4 mmol of H2O2for complete mineralisation.This is an oxidant¡Ópollutantratio of 137:1. Therefore, the mineralisation stoichiometrycan be suggested as shown in eqn. (1).C16H11N2NaO4S+37H2O2 +1=2O2£¾4 16CO2 40H2O NO3£¾ NH4 SO42£¾ H Na 1Fig. 5(a) presents the results for the degradation ofOrange II solutions in dark and light (Suntest simulator)induced reactions at initial pH values of 2, 6 and 10.Theconcentrations of Orange II, Fe3 and H2O2 are the sameas those used in Fig. 3, but adding the H2O2 on an hourlybasis. This allows for a more detailed analysis of the TOCand Orange II concentration reported in Figs. 5(a) and (b).The initial pH has been regulated with an acid (0.1 M HCl)or a base (0.1 M NaOH) in these unbuered systems. For asolution with an initial pH 2, Fig. 5(a) shows mineralisation(TOC decrease vs.time) in the dark to be incomplete andonly reach about 68% of the initial TOC value. It is seenthat during the degradation the Fenton reagent does notfully mineralize the Orange II until 8 h have elapsed. In thedark, the reaction of H2O2 with Fe2 [reaction (2)] competeswith the organic intermediates in solution as the reactionruns its course.Fe2 H2O2 £¾4 Fe3+ OH£¾ OHk1 58 M£¾1 s£¾1 2No kinetic data have been found for the reactionbetween OH radical and Orange II.Conrmation that thereaction (2) producing OH£¾ is involved in the generation ofintermediates during Orange II degradation was obtainedin the following way: a few drops of NaOH (0.1 M) wereadded to a solution containing Orange II (initial pH 13).The initial orange color of the solution changed to red uponNaOH addition. The spectrum of the red compound turnedout to be identical to the spectrum of a solution with aninitial pH 3 irradiated for 1 h. This change is ascribed toreaction (3).The red form undergoes further decompositionduring photo-assisted Fenton reaction.Fig. 5(b) presents the high-pressure liquid chromatog-raphy data for the disappearance of Orange II in the threesolutions used for the results given in Fig. 5(a). The evol-ution of the pH values during the degradation is shownin Fig. 5(c). This gure shows the variation of pH as afunction of time for three unbuered solutions with initialpH values of 2, 6 and 10.The rather complex shape for theJ. Chem. Research (S),1998, 234¡Ó235J. Chem. Research (M),1998, 1153¡Ó1172Fig. 3 Photochemical degradation of a solution of Orange II(2.95 mM), H2O2 (10 mM) and Fe3 (0.92 mM). TOC vs. timeduring dark (filled symbols) and light induced degradation (opensymbols) of concentrated solutions (450 mg C l£¾1) (a,b) anddiluted solutions (60 mg C l£¾1) (c,d) of Orange II. The arrowsindicate the times of H2O2 addition*To receive any correspondence.234 J.CHEM. RESEARCH (S), 1998degradation as a function of time (initial pH 6 and 10) suggests the presence of pH dependent Fe¡¾aqueous com- plexes with di€erent structures and reactivities. The results presented in Fig. 5(c) suggest that only when the pH has reached acidic values is a meaningful reduction of TOC values observed in solution. At higher pH the [Fe(H2O)6]3a species (pKa 2.79) deprotonates rapidly to [Fe(H2O)5(OH)]2a and [Fe(H2O)4(OH)2]a 2,18,19 slowing down the degradation as observed in Fig. 5(c). Recently, adduct formation has been observed between OH and Orange II during dye degradation and the latter process was reported to involve protonated species.19 The disappearance of Orange II at an initial pH of 2.9 by electrolysis via a Pt anode and a Zr cathode (100 mA cm¢§2 at a potential of 3.2 V) was also performed in the presence of Na2SO4 (50 mg l¢§1) electrolyte. The abatement of the Orange II by electrochemistry took twice as long as the Orange II degradation performed by photochemical means in a solution about three times more concentrated in azo- dye.Electrochemical treatment of Orange II solutions close to the solubility limit of 12 g l¢§1 were observed as a func- tion of the electric charge (A h l¢§1) used. The rate of electro- chemical mineralisation [k2, see eqn. (4)] was low when compared to photochemical treatment. Orange II ¢§ k14 organic intermediates ¢§ k24 CO2 where k1 k2 O4U The main organic intermediate observed during the electro- chemical degradation of Orange II was sulfanilic acid.The electrochemical degradation indicates that non- biodegradable abatement is possible with a mass-free reagent and without added oxidant. Support from INTAS 94-0642 and from the European Communities Environmental Program under grant no. EV5V-CT 93-0249 (OFES Contract no.950031, Bern) is duly appreciated. Techniques used: HPLC, UV¡¾VIS spectroscopy, ion¡¾liquid chro- matography References: 24 Figures: 9 Received, 15th November 1997; Accepted, 15th January 1998 Paper E/7/07962A References cited in this synopsis 1 Presented partly in: International Conference on Oxidation Technologies for Water and Wastewater Treatment.Goslar, Germany, May 12¡¾15, 1996. 2 R. Helz, G. Zepp and D. Crosby, Aquatic and Surface Photochemistry, Lewis Publishing Company, Boca Raton, FL, 1994. 3 O. Legrini, E. Oliveiros and A. M. Brown, Chem. Rev., 1993, 93, 67. 4 J. Kiwi, C. Pulgarin, P. Peringer and M. Gratzel, New J. Chem., 1993, 17, 487. 5 C. Morrison, J. Bandara and J. Kiwi, J. Adv Oxidation Technol., 1996, 1, 160. 6 C. Comninellis and C. Pulgarin, J. Appl. Electrochem., 1993, 23, 108. 11 M. Halmann, Photochem. Photobiol. A, 1992, 66, 215. 18 B. Faust and J. HoigneA , Atmos. Environ., 1990, 23, 235. 19 V. Nadtochenko and J. Kiwi, J. Chem. Soc., Faraday Trans., 1997, 93, 2373. Fig. 5 (a) TOC vs. time for three concentrated Orange II unbuffered solutions with different initial pH values. Open symbols are for irradiated solutions and filled symbols refer to dark runs. Other details are seen in the caption inside the figure. (b) disappearance of Orange II under light (open symbols) and in the dark (filled symbols) for the three solutions. (c) Variation of the pH vs. time for reactions in the dark (filled symbols) and light induced (open symbols), for different initial pH values of concentrated solutions of Orange II J. CHEM. RESEARCH (S), 1998 235

ISSN:0308-2342    

DOI:10.1039/a707962a

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

Chlorination of 20-Oxopregnanes with the Manganese Dioxide±Chlorotrimethylsilane/Acetyl Chloride System: A Simple Approach Towards the Construction of the Corticosteroid Side Chain Parinita Borah, Moinuddin Ahmed and Pritish Chowdhury* Natural Products Chemistry Division, Regional Research Laboratory, Jorhat 785 006, India C-21 chlorination of 20-oxosteroids using the system MnO2 (excess)±TMSCl or MnO2 (excess)±AcCl in acetic acid medium as well as an example of a Wagner±Meerwein rearrangement of 17 -chloro-20-oxopregna-3-yl acetate to 17- -methyl-18-nor-17 -pregn-13-en-3-yl acetate have been demonstrated.C-21 functionalization of 20-oxopregnanes is an important area in the steroid ®eld1, 10±13 as it leads towards the construction of the side chain of the biologically potent cortical hormones and drugs. One widely used method for this transformation is via halogenation of 20-oxosteroids,1 but although a number of bromination techniques have been reported, successful chlorination methods have not been widely reported in the literature.Further, the hitherto known processes for this transformation1±3 involve tedious reaction conditions and toxic chlorinating agents such as chlorine gas and toxic brominating agents such as bromine, hydrogen bromide, pyridinium hydrobromide per- bromide etc. Wuts et al.4 have reported the preparation of 21-chloro-20-oxopregnanes through the chlorination of 21-hydroxysteroids by using the Vilsmeir reagent (involving hazardous phosphorous oxychloride).During our work5 on the process development of 16- dehydropregnenolone acetate, a key intermediate for steroidal drugs from diosgenin in this laboratory, several 20-oxopregnanes, viz., 1±3 were available which persuaded us to carry out some work towards corticosteroid synthesis. In a recent communication,6 we reported stereospeci®c chlorination of several steroidal ole®ns and ketones under mild reaction conditions via MnCl4 species generated in situ from MnO2±TMSCl or MnO2±AcCl systems using MnO2 in stoichiometric amounts.The reagents are non-toxic and easy to handle. Here we describe a simple and single-step room-temperature preparation of 17a,21-dichloro-20-oxo- pregnanes from the respective 20-oxopregnanes in high yield by employing either of the above systems using MnO2 in large excess. This provides a simple and convenient approach towards the construction of the corticosteroid side chain. Thus when the 20-oxopregnanes 1±3 were treated with the reagent system in acetic acid, using MnO2 in large excess, overnight at room temperature, the corresponding 17a,21-dichlorosteroids 4±6 were obtained in more than 80% yield.All these products gave satisfactory IR, NMR, mass spectral and microanalytical data. The C-21 substitution with chlorine was con®rmed from their NMR spectra which displayed a two proton doublet at 4.2 ppm (J à 1.5 Hz) for 21-methylene protons. Further, all these products 4±6 underwent Favorskii rearrangement at room temperature in mild alkaline solution to furnish the corresponding methyl carboxylates 7±9 in excellent yield.The use of a stoichiometric amount of MnO2 in the reaction leads to exclusive formation of 17a-chloro-20-oxopregnanes 14±16 selectively from 1±3 in high yield.6 Further in our attempt towards the preparation of 17-acetoxy-20-oxosteroids, many of which are potent anti- tumor agents.8 from 17a-chlorosteroids, compound 14 was treated with anhydrous sodium acetate in glacial acetic acid.However, from the action of sodium acetate±acetic acid on J. Chem. Research (S), 1998, 236±237 J. Chem. Research (M), 1998, 1173±1180 *To receive any correspondence. 236 J. CHEM. RESEARCH (S), 199814, we isolated a chlorine-free compound 17 (65%) formed apparently through a Wagner�}Meerwein rearrangement, i.e. the migration of the C-18 methyl group to the developing carbonium ion at the C-17 position because of the facile leaving of the chloride ion to furnish Rnally 17b-methyl-18- nor-17a-pregn-13-en-3b-yl acetate 17.An IR spectrum of the compound displayed the bands for the acetate group and ketonic group of the side chain. The mass spectrum did not reveal the presence of any chlorine in the molecule and displayed a molecular ion peak at 358(Ma) corresponding to the structure given as 17. The NMR spectrum did not reveal the presence of any oleRnic proton and one of the angular methyl groups had shifted downReld (1.2 ppm) clearly indicating that the C-18 methyl group has migrated to the C-17 position placing it a to the carbonyl group which caused the observed downReld shift.The b orien- tation of the 17-methyl group was evident from the analo- gous rearrangement reported earlier by Herzog et al.9 in the Lewis-acid catalysed reaction on the 17a-hydroxy group as well as from the 16a,17a-epoxide derivatives of 20-oxopregnanes.However, in the case of compound 4, the major product (70%) isolated was found to be the 16,17-didehydro-21-chloro-20-oxopregnane 10 formed through a simple dehydrohalogenation process. Its NMR spectrum displayed the characteristic two proton singlet at 4.0 ppm for the 21-methylene protons and a multiplet at 6.4 ppm for the 16-oleRnic proton. However, a minor product (yield: 7%) was conRrmed to be the 17-acetoxy- 21-chloro-20-oxopregnane derivative 13 from its spectral analysis. Compounds 5 and 6 furnished compounds 11 and 12 respectively as the major isolable products with sodium acetate.The steroids 10�}12 besides being important inter- mediates for the synthesis of various life-saving steroidal antiin�Pammatory drugs including triamcinolones,10 possess an enone system which has also gained importance in recent years because of its utilization in the preparation of 16a-methoxycarbonylprednisolone13 which Rnds appli- cation in the area of development of local antiin�Pammatory steroids without systemic side e€ects by regio- and facial- selective introduction of the 17a-OH and metabolically labile 16a-methoxycarbonyl functional groups.Techniques used: 1H NMR, IR, MS, elemental analysis, speciRc rotations, mp References: 13 Table 1: Spectroscopic data, speciRc rotations, mps Received, 26th February 1997; Accepted, 22nd January 1998 Paper E/7/01350G References cited in this synopsis 1 C. Djerassi, in Steroid Reactions (An Outline for Organic Chemistry), Holden-Day, San Francisco, 1963. 2 C. Djerassi, I. Fornaguera and O. Mancera, J. Am. Chem. Soc., 1959, 81, 2383. 3 M. Steiger and T. Reichstein, Helv. Chim. Acta., 1937, 20, 1164. 4 P. G. M. Wuts, J. E. Cabaj and K. D. Meisto, Synth. Commun., 1993, 23, 2199. 5 P. K. Chowdhury, M. J. Bordoloi, N. C. Baruah, P. K. Goswami, H. P. Sharma, R. P. Sharma, A. P. Baruah, R. K. Mathur and A. C. Ghosh, US Pat. ( Rled), 08/589, 708; Ind. Pat. ( Rled) 1645/DEL/95. 6 (a) P. Borah and P. K. Chowdhury, J. Chem. Res. (S), 1996, 502; (b) Ind. Pat. ( Rled) NF267/95. 8 (a) M. A. Mitchell and J. W. Wilks, Annu. Rep. Med. Chem. 1992, 27, 143; (b) Drugs of the Future, ed. J. R. Prous, 1993, 18 p. 1178. 9 (a) H. L. Herzog, M. J. Gentles, A. Mitchell, E. B. Hershberg and L. Mandell, J. Am. Chem. Soc. 1959, 81, 6478; (b) E. L. Shapiro, M. Steinberg, D. Gould, M. J. Gentles, H. L. Herzog and M. Gilmore, J. Am. Chem. Soc. 1959, 81, 6483. 10 (a) D. M. Baily Annu. Rep. Med. Chem. 1987, 22, 319, 325; (b) J. A. Bristol, ibid., 1991, 26, 303. 11 D. Taub, R. D. Ho€somer, H. Z. Slates, C. H. Kuo and N. L. Wendler, J. Am. Chem. Soc., 1960, 82, 4012. 12 W. S. Allen, S. Bernstein, L. I. Felder and M. J. Weiss, J. Am. Chem. Soc., 1960, 82, 3696. 13 Z. You, M. A. Khalil, D. H. Ko and H. J. Lee, Tetrahedron Lett., 1995, 36, 3303. J. CHEM. RESEARCH (S),

ISSN:0308-2342    

DOI:10.1039/a701350g

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

Regioselective Synthesis of Prenylisoflavones. Syntheses of Lupiwighteone, Lupiwighteone Hydrate and Related Compounds Masao Tsukayama,* He Li, Masaki Nishiuchi, Masahumi Takahashi and Yasuhiko Kawamura Department of Chemical Science and Technology, Faculty of Engineering, The University of Tokushima, Minamijosanjima-cho, Tokushima 770, Japan Catalytic hydrogenation and the subsequent dehydration of 8-(3-hydroxy-3-methylbutynyl)isoflavone 12, which was synthesized by the palladium-catalyzed coupling reaction of 4',5,7-tris(benzyloxy)-8-iodoisoflavone 11 with 2-methyl-3- butyn-2-ol, gave a mixture of 8-prenylisoflavone 16 and the isomer [5-acetoxy-8-(3-methyl-3-butenyl)isoflavone] 17, and after the separation of 16 was accomplished by treatment of the mixture with Hg(NO3)2, hydrolysis of 16 afforded 4',5,7-trihydroxy-8-prenylisoflavone (lupiwighteone) 1.Prenyliso�avones and (3-hydroxy-3-methylbutyl)iso�avones are widely distributed in nature and have strong antifungal activity.1 Some of them are known as a phytoalexine such as luteone.1 Prenyliso�avones are useful as precursors of pyranoiso�avones and furanoiso�avones.2 Although tetra- oxygenated prenyliso�avones have been synthesized from suitable iso�avones by acid- and base-catalyzed alkylation, such procedures have resulted in relatively low yields and are not useful for the syntheses of polyhydroxyiso�avones, because O- and di-alkylation, deprotection, and lack of regioselectivity are common problems.3 The reaction of aryl halides with terminal alkynes in the presence of a palladium(0) catalyst is e�cient for formation of C0C bonds and alkylation.4 During the course of our synthetic studies of prenylphenol derivatives, we have recently found that these compounds have been regioselectively synthesized by the palladium-catalyzed method.5 Therefore, this meth- odology seems to be easily applicable to the regioselective synthesis of polyoxygenated prenyliso�avones via the coupling reaction of the corresponding iodoiso�avones with propargyl alcohol. The new iso�avones, lupiwighteone [4',5,7-trihydroxy-8- (3-methyl-2-butenyl)iso�avone] 1 and lupiwighteone hydrate [4',5,7-trihydroxy-8-(3-hydroxy-3-methylbutyl)iso�avone] 2, were isolated from the roots of yellow lupin, Lupinus luteus L., cv.Barpine (Leguminosae).6 We wish to report here on the ®rst syntheses of 1, 2 and angular 4',5-dihydroxy- 20,20-dimethylpyrano[60,50-h]iso�avone (derrone)7 5 by using the palladium-catalyzed coupling reaction, and extend the method to the syntheses of 2'-hydroxy-6-(3-methyl-2- butenyl)-7-methoxy-4',5'-methylenedioxyiso�avone 3, 2'-hy- droxy-6-(3-hydroxy-3-methylbutyl)-7-methoxy-4',5'-methylene- dioxyiso�avone 4 and 2'-acetoxy-6-(3-methyl-2-butenyl)-7- methoxy-4',5'-methylenedioxyiso�avanone 6.The reaction of 4',6'-bis(benzyloxy)-2'-hydroxyaceto- phenone with iodine in the presence of silver tri�uoro- acetate9 gave 4',6'-bis(benzyloxy)-2'-hydroxy-3'-iodoaceto- phenone5a in good yield, which was converted into 4',6'-bis- J.Chem. Research (S), 1998, 238±239 J. Chem. Research (M), 1998, 1181±1196 Scheme 1 Reagents and conditions: i, TTN, MeOH, CHCl3, 408C, 7 h, 10% HCl; ii, THF, EtOH, 10% NaOH, room temperature (79%); iii, PdCl2 (3 mol%), PPh3 (6 mol%), CuI (3 mol%), NEt3, DMF, 80 8C, 2.5 h (82%); iv, Raney Ni, MeOH, THF, 18 8C (82%); v, PhCOCl, K2CO3, acetone, reflux (80%); vi, BF3 OEt2, CH2Cl2, room temperature, 4 h; vii, Ac2O, pyridine, 105 8C (83%); viii, THF, MeOH, 10% NaOH, 50 8C, 50 min (93%) *To receive any correspondence. 238 J. CHEM. RESEARCH (S), 1998(benzyloxy)-3'-iodo-2'-methoxymethoxyacetophenone 7 with chloromethyl methyl ether in the presence of N,N-diiso- propylethylamine. The condensation of 7 with 4-benzyloxy- benzaldehyde gave the corresponding chalcone, and then the methoxymethyl group in the chalcone was cleaved by treatment with hydrochloric acid to a€ord the 2'-hydroxy- chalcone 8.The oxidative rearrangement of the acetate 9, derived from 8, with thallium(III) nitrate trihydrate (TTN) gave the acetal derivative 10, which was converted into the corresponding 8-iodoiso�Pavone 11. The coupling reaction of 11 with 2-methyl-3-butyn-2-ol in the presence of Pd0 gave the desired 8-(3-hydroxy-3-methylbutynyl)iso�Pavone 12. Catalytic hydrogenation of 12 over Raney nickel gave 4',5,7-trihydroxy-8-(3-hydroxy-3-methylbutyl)iso�Pavone 2. The 1H NMR and UV spectral data for 2 were identical with those of natural lupiwighteone hydrate.On the basis of these results, the structure of natural lupiwighteone hydrate was unequivocally established to be 4',5,7-trihydroxy-8-(3- hydroxy-3-methylbutyl)iso�Pavone 2. The 8-alkyltrihydroxyiso�Pavone 2 was converted into the tribenzoate derivative 13. The tribenzoate derivate 13 was dehydrated to give a mixture of the 5-hydroxy-8-(3-methyl- 2-butenyl)iso�Pavone 14 and the isomer 5-hydroxy-8-(3- methyl-3-butenyl)iso�Pavone 15, which was converted into a mixture of 5-acetoxy-8-prenyliso�Pavone 16 and the isomer 5-acetoxy-8-(3-methyl-3-butenyl)iso�Pavone 17.The 1H NMR spectrum of the mixture of the 5-acetate derivatives (16 and 17) showed the ratio of 16 to 17 to be 88:12 [peaks due to CH2CH1C(CH3)2 at d 3.55 (2 H, d) and CH2CH2C(CH3)1CH2 at d 4.72 and 4.77 (each 1 H, s)]. The complete separation of 16 from the mixture (16 and 17) was signiRcantly dicult either by chromatography or recrystallization. A solution to the problem was provided by treatment of the mixture with aqueous mercury(II) nitrate (1.5 equiv.to the isomer 17) in tetrahydrofuran at room temperature to give the terminal alkylmercurinium ion 17' as shown by eqn. (1),5,10 and then the unchanged acetate 16 was quantitatively separated from the mixture by silica gel column chromatography. Hydrolysis of 16 was e€ected to give the desired 4',5,7-trihydroxy-8-(3-methyl-2-butenyl)- iso�Pavone 1, which was converted into 4',5,7-triacetoxy-8- prenyliso�Pavone 18 and the angular 4',5-dihydroxypyrano- iso�Pavone 5.The 1H NMR spectra of 1 and the triacetate 18 were identical with those of natural 8-prenyliso�Pavone (lupiwighteone) and the triacetate. On the basis of these results, the structure of natural lupiwighteone was unequi- vocally established to be 4',5,7-trihydroxy-8-(3-methyl-2- butenyl)iso�Pavone 1.In a similar manner, the 6-prenyliso�Pavone 3, the 6-(3- hydroxy-3-methylbutyl)iso�Pavone 4 and the 6-prenyliso�Pava- none 6 were prepared from the corresponding 6-iodoiso- �Pavone 23. The present palladium-catalyzed coupling reactions of iodoiso�Pavones with 2-methyl-3-butyn-2-ol have been shown to be an ecient and useful procedure for regioselective syntheses of polyhydroxyprenyliso�Pavones. The excellent chemoselectivity of mercury(II) nitrate or benzonitrile oxide to internal and terminal alkenes have been shown to be remarkably useful for the recognition and separation of terminal alkenes. Techniques used: 1H NMR, UV spectroscopy, elemental analysis, chromatography Table 1: 1H NMR data for 1, 18 and 2 Schemes: 2 References: 13 Received, 23rd December 1997; Accepted, 2nd February 1998 Paper E/7/09191E References cited in this synopsis 1 P.M. Dewick, in The Flavonoids: Advances in Research Since 1980, ed. J. B. Harborne, Academic Press, London, 1988; J.L. Ingham, S. Tahara and J. B. Harborne, Z. Naturforsch., Teil C, 1983, 38, 194; M. D. Woodward, Phytochemistry, 1979, 18, 363; J. B. Harborne, J. L. Ingham, L. King and M. Payne, Phytochemistry, 1976, 15, 1485; H. Fukui, H. Egawa, K. Koshimizu and T. Mitsui, Agric. Biol. Chem., 1973, 37, 417. 2 R. Welle and H. Grisebach, Arch. Biochem. Biophys., 1988, 263, 191; S. Tahara, J. L. Ingham and J. Mizutani, Phytochemistry, 1989, 28, 2079; S. Tahara, S. Shibaki, J. L.Ingham and J. Mizutani, Z. Naturforsch., Teil C, 1990, 45, 147; L. Crombie, J. Rossiter and D. A. Whiting, J. Chem. Soc., Chem., Commun., 1986, 352. 3 A. C. Jain, A. Kumar and R. C. Gupta, J. Chem. Soc., Perkin Trans. 1, 1979, 279; A. . Lal and T. R. Seshadri, Tetrahedron, 1970, 26, 1977. 4 K. Sonogashira, Y. Tohda and N. Hagihara, Tetrahedron Lett., 1975, 4467; S. Takahashi, Y. Kuroyama, K. Sonogashira and N. Hagihara, Synthesis, 1980, 627. 5 (a) M. Tsukayama, M. Kikuchi and Y. Kawamura, Chem. Lett., 1994, 1203; (b) M. Tsukayama, M. Kikuchi and Y. Kawamura, Heterocycles, 1994, 38, 1487. 6 Y. Hashidoko, S. Tahara and J. Mizutani, Agric. Biol. Chem., 1986, 50, 1797. 7 J. L. Ingham, in Progress in the Chemistry of Organic Natural Products, ed. W. Herz, H. Grisebach and G. W. Kirby, Springer-Verlag, New York, 1983, vol. 43, p. 71; S. S. Chibber and R. P. Sharma, Phytochemistry, 1980, 19, 1857. 9 D. E. Janssen and C. V. Wilson, Org. Synth., 1967, Coll. Vol. 4, 547. 10 J. L. Wardell, in Comprehensive Organometallic Chemistry, ed. G. Wilkinson, F. G. A. Stone and E. W. Abel, Pergamon Press, New York, 1982, vol. 2, ch. 17, p. 867. 11 S. Kanemasa, M. Nishiuch, A. Kamimura and K. Hori, J. Am. Chem. Soc., 1994, 116, 2324. J. CHEM. RESEARCH (S), 1998 239

ISSN:0308-2342    

DOI:10.1039/a709191e

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

Hydrothermal Synthesis of Co(pdc) 2H2O (pdc à 3,5-Pyridinedicarboxylate). A Two-dimensional Coordination Polymer M. John Plater,* Alexander J. Roberts and R. Alan Howie Department of Chemistry, Aberdeen University, Meston Walk, Aberdeen AB24 3UE, UK A hydrated coordination polymer is formed by heating the tecton 3,5-pyridinedicarboxylic acid (H2pdc) with cobalt(II) acetate. Metal-ion directed assembly of organic molecular building blocks known as tectons is giving access to new open frame- work solid-state materials with fascinating technological potential and scienti®c interest.1 Supramolecular chemistry has frequently centered on the synthesis of hosts with convergent functional groups to form binding cavities which mimic enzyme active sites and can show homogeneous catalytic activity.2 The synthesis of 1D, 2D and 3D coordination polymers, which are structurally analogous to important minerals such as quartz and zeolites,3 and have the potential for heterogeneous catalysis, requires rigid tectons which possess divergent functional groups.Methods for the assembly of crystalline lattices from organic tectons and metal ions which may show stability to guest or template desorption/adsorption are of considerable current interest. Here we report the hydrothermal synthesis and X-ray single-crystal structure characterisation of Co(pdc) H2O. 3,5-Pyridinedicarboxylic acid (100 mg) and a stoichiometric quantity of Co(OAc)2 4H2O in water (10 ml) were heated to 180 8C and allowed to cool slowly.Pink crystals of Co(pdc)2H2O were obtained in 90% yield which are insoluble in boiling water. Hydrothermal synthesis is essential to obtain good quality crystals. If the same quantities of reagents are re�uxed in water (200 ml) for 2 h complete dissolution does not occur but a pink microcrystal- line material identical with the above material does slowly form. The structure shown in Fig. 1 consists of in®nite layers of alternating CoII cations and 3,5-pyridinedicarboxy- late dianions.Each cobalt ion is seven-coordinate and is coordinated by two identical bidentate carboxylate groups, one pyridine nitrogen and two water molecules. The CoII ions coordinate to the pdc tectons along the crystallographic a axis with Co0O(1) and Co0O(2) bond lengths of 2.157(4) and 2.432(4) A Ê respectively. Although the Co0O(2) bond length is quite long it is shorter than the estimated cobalt±oxygen van der Waals distance of 2.562 A Ê .This is calculated as the sum of the Co single bond metallic radius of 1.161 A Ê and the van der Waals radius of an oxygen atom of 1.400 A Ê .5 The carboxylate anions form a dihedral angle of 13.3(7)8 to the pyridine ring. The pyridine nitrogens coordinate to each cobalt ion along the crystallographic b axis forming a Co0N distance of 2.206(7) A Ê . Hence in the ab plane the structure consists of a 2D coordination polymer. The layers are not chemically bonded together in the c axis direction but are interleaved with water molecules coordinated to each cobalt ion with a cobalt±oxygen bond length of 2.072(4) A Ê .The hydrogen atoms of the water molecules form interlayer hydrogen bonds to the carboxylate groups. Adjacent 2D layers are related by crystallographic centres of symmetry with parallel pyridine rings stacked 3.7 A Ê apart in a zigzag arrangement almost on top of each other along the c axis. The zigzag arrangement of pyridine rings occurs parallel to the b axis.The half thickness of an aromatic ring is 1.85 A Ê 6 so the pyridine rings are stacked at the optimum van der Waals distance. The layers are neutral, interleaved with water molecules and might be easily cleaved apart. In this respect the compound J. Chem. Research (S), 1998, 240±241 J. Chem. Research (M), 1998, 1001±1013 Fig. 1 A view down c of the cation/anion layer with z/c close to 1/4 for all atoms shown. The water molecules and hydrogen atoms have been omitted for clarity.Atoms are shown as 40% probability elipsoids Fig. 2 The coordination of Co. Atoms are shown as 40% probability ellipsoids *To receive any correspondence (e-mail: m.j.plater@abdn.ac.uk). 240 J. CHEM. RESEARCH (S), 1998can be described as an `organic clay' crudely resembling the inorganic layer silicates.7 This analogy is supported by the plate-like morphology of the crystals and the observation of preferred orientation in its experimental X-ray powder di€raction pattern (Fig. 3A) as compared with the calculated pattern (Fig. 3D). This is compatible with ready cleavage of the crystals parallel to the planes of cobalt cations and pdc anions which in turn are parallel to the 001 planes. In the original hydrated compound, as explained above, the distance between adjacent cation/anion layers is determined by the van der Waals thickness of the aromatic rings of the pdc anions and cannot be reduced further upon the loss of water.Further studies on crystalline lattices formed from larger tectonic building blocks are in progress. Techniques used: IR, X-ray crystallography, powder di€raction, thermal gravimetric analysis References: 10 Figs: 3 Tables: 6 (crystal data and structure reRnement, atomic coordinates and Ueq values, interatomic distances and angles, anisotropic displacement parameters, hydrogen coordinates and isotropic displacement parameters) Received, 4th July 1997; Accepted, 22nd December 1997 Paper E/7/04747I References cited in this synopsis 1 M.J. Zaworotko, Chem. Soc. Rev., 1994, 23, 283; R. Robson and B. F. Hoskins, J. Am. Chem. Soc., 1990, 112, 1546; R. Robson, B. F. Abrahams, S. R. Batten, R. W. Gable, B. F. Hoskins and J. Liu, Supramolecular Architecture, ACS, Washington, DC, 1992, ch. 19; G. R. Desiraju, Crystal Engineering, The Design of Organic Solids, Elsevier, Amsterdam, 1989; D. Venkataraman, G. B. Gardner, S. Lee and J.S. Moore, Nature, 1995, 374, 792; R. Robson, S. R. Batten and B. F. Hoskins, J. Am. Chem. Soc., 1995, 117, 5385. 2 For example, see, R. Breslow, X. J. Zhang, R. Xu, M. Maletic and R. Merger, J. Am. Chem. Soc., 1996, 118, 11678; R. Breslow and W. H. Chapman, ibid., 1995, 117, 5462; R. Breslow and J. M. Desper, ibid., 1994, 116, 12081; R. Breslow, J. Mol. Cat., 1994, 91, 161. 3 S. W. Keller, Angew. Chem., 1997, 109, 295; Angew. Chem., Int. Ed. Engl., 1997, 36, 247; A. Dyer, An Introduction to Zeolite Molecular Sieves, Wiley, Chichester, 1988. 5 L. Pauling, in The Nature of the Chemical Bond, 3rd edition, Cornell University Press, 1960, pp. 256�}257. 6 CRC Handbook of Chemistry and Physics, 58th edition, CRC Press, 1977, p. D178. 7 A. F. Wells, Structural Inorganic Chemistry, 4th edition, Oxford University Press, 1975, p. 818; A. Muller, H. Reuter and S. Dillinger, Angew. Chem., 1995, 107, 2505; Angew. Chem., Int. Ed. Engl., 1995, 34, 2328. Fig. 3A Powder diffraction pattern for Co(pdc) 2H2O Fig. 3D Calculated powder diffraction pattern for Co(pdc) 2H2O J. CHEM. RESEARCH (S), 1998

ISSN:0308-2342    

DOI:10.1039/a708520f

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

Alkene Epoxidation and Alkane Hydroxylation withPeriodate Catalysed by Manganese(III) PorphyrinSupported on Poly(4-vinylpyridine)$Shahram Tangestaninejad* and Majid MoghadamDepartment of Chemistry, Esfahan University, Esfahan 81744, IranSulfonated manganese(III) tetraphenylporphyrin supported on poly(4-vinylpyridine), Mn(tpps)¡ÓPVP, can act as an efficientheterogeneous catalyst for alkene epoxidation and alkane hydroxylation by sodium periodate.So far a great variety of metalloporphyrin-based systems forthe catalytic oxidation of hydrocarbons using various single-oxygen-atom donors, such as PhIO,1,2 ClO£¾ 3,4 and IO4£¾ 5,6have been described.The attachment of metalloporphyrincatalysts to insoluble polymer supports appears to be agood way to render them more practicable and improvetheir catalytic activity and selectivity.7¡Ó9 In this report wedescribe a new periodate-heterogenized metalloporphyrinsystem for alkene epoxidation and alkane hydroxylation.In the absence of imidazole, the Mn(tpps)¡ÓPVP/NaIO4system is less ecient for oxidation of hydrocarbons[H2tpps =5,10,15,20-tetra(sulfonato)phenylporphyrin, PVP=poly(4-vinylpyridine)].Reactions were performed at roomtemperature under air in CH3CN/H2O medium contain-ing the alkene, oxidant, imidazole and Mn(tpps)¡ÓPVP in1 : 2 : 0.2 : 0.0145 ratio, respectively. This catalytic system ledto the epoxidation of various alkenes (Table 1) with goodyields (40¡Ó95%). In the case of stilbenes, trans-stillbene isconverted only into the trans-epoxide and cis-stilbene into a70 : 2 mixture of cis and trans-epoxide.The regioselectivityobserved for epoxidation of (R)-()-limonene with theMn(tpps)¡ÓPVP/NaIO4 system is comparable to that onmoderately hindered Mn(tmpp)Cl and Mn(tdcpp)Cl withNaOCl and PhIO or H2O2.10,11 In this case the ratio of8,9-epoxide to 1,2-epoxide was 0.8:1 in epoxidation onMn(tpps)¡ÓPVP by NaIO4 in the presence of imidazole.Alkanes were oxidized with NaIO4 by Mn(tpps)¡ÓPVP tothe corresponding alcohols and ketones only in the presenceof imidazole (Table 2).In the absence of the supportedmetalloporphyrin catalyst, cyclooctene and cyclooctaneremained almost unchanged by NaIO4 in CH3CN/H2O after24 h.In conclusion, the Mn(tpps)¡ÓPVP/NaIO4 systemseems to have some advantages in comparison to the homo-geneous Mn(tppcl)/NaIO4 system.5 The manganese pro-phyrin remains stable and strongly bonded to poly(4-vinylpyridine) during the reaction and is easily recovered bysimple ltration at the end of the reactions. This supportedcatalyst can be used in other solvents such as acetone¡Ówater. The heterogenized metalloporphyrin system hasshown a considerable selectivity in oxidation reactions.ExperimentalThe porphyrin H2tpps, was prepared and metallated according tothe literature procedures.12,13 The Mn(tpps) immobilized on cross-linked poly(4-vinylpyridine) (Fluka) was prepared according to thereported procedure14 [100mg of Mn(tpps) were immobilized on500mg of the resin].Typical Reaction Procedure.A 25cm3ask was charged withalkene or alkane (1 mmol), Mn(tpps)¡ÓPVP (158 mg), imidazole(0.2 mmol) and CH3CN (10 cm3).After addition of sodium period-ate solution (2 mmol in 10 cm3 H2O), the mixture was stirred by amagnetic stirrer at room temperature for 3.5¡Ó8 h. The progressof the reaction was monitored by GLC. The reaction mixturewas diluted with CH2Cl2 (20 cm3) and ltered. The resin wasthoroughly washed with CH2Cl2 and the combined washings andltrates were puried on silica gel plates or a silica gel column.The identities of the products were conrmed by IR and 1H NMRspectral data.Partial support of this work by the Esfahan UniversityResearch Council is gratefully acknowledged.Received, 11th November 1997; Accepted, 18th December 1997Paper E/7/08106EReferences1 J.T. Groves and T. E. Nemo, J. Am. Chem. Soc., 1983, 105,5786.2 A. J. Appleton, S. Evans and J.R. Lindsay Smith, J. Chem.Soc., Perkin Trans. 2, 1996, 281.3 O. Bortolini and B. Meunier, J. Chem. Soc., Perkin Trans. 2,1984, 1967.4 B. Meunier, E. Guilmet, M. E. De Carvalho and R. Poilblane,J. Am. Chem. Soc., 1984, 106, 6668.5 D. Mohajer and S. Tangestaninejad, J. Chem. Soc., Chem.Commun., 1993, 240.6 D. Mohajer and S. Tangestaninejad, Tetrahedron Lett., 1994, 35,945.J. Chem. Research (S),1998, 242¡Ó243$Table 1 Epoxidation of alkenes with NaIO4 catalysed byMn(tpps)¡ÓPVP in the presence of imidazoleAlkeneConversion(%)aEpoxide yield(%)aReactiontime/hCyclooctene 100 95 4Cyclohexene 100 93 4Styrene 96 75 4a-Methylstyrene 90 85 4()-Camphene 60 60 4Oct-1-lene 55 40 8trans-Stilbene 40 40 (trans) 8cis-Stilbene 72 70 (cis)b 82 (trans)(R)-()-Limonene 45 25 (1,2-epoxide)b 3.520 (8,9-Epoxide)aGLC yield based on the starting olefin.bBoth 1H NMR and GLCdata confirmed the reported yields.Table 2 Hydroxylation of alkanes with NaIO4catalysed by Mn(tpps)¡ÓPVP in the presence ofimidazole; reaction time 8 hAlkane Ketone (%)a Alcohol (%)aCyclooctane 20 36Ethylbenzene 60 ¡ÓFluorene 25 ¡ÓDiphenylmethane 18 ¡ÓaGLC yield based on the starting alkane.$This is a Short Paper as dened in the Instructions for Authors,Section 5.0 [see J.Chem. Research (S), 1998, Issue 1]; there is there-fore no corresponding material in J. Chem. Research (M).*To receive any correspondence.242 J. CHEM. RESEARCH (S), 19987 D. R. Leanord and J. R. Lindsay Smith, J. Chem. Soc., Perkin Trans. 2, 1991, 25. 8 T. Mori, T. Santa and M. Hirobe, Tetrahedron Lett., 1985, 26, 5555. 9 D. R. Leanord and J. R. Lindsay Smith, J. Chem. Soc., Perkin Trans. 2, 1990, 1917. 10 N. Mizuno, M. Tateshi, T. O. Hirose and M. Iwamoto, Chem. Lett., 1993, 1985. 11 P. Battioni, J. P. Renaud, J. F. Bartoli, M. Reina-Artiles, M. Fort and D. Mansuy, J. Am. Chem. Soc., 1988, 110, 8462. 12 C. A. Busby, R. K. DiNello and D. Dolphin, Can. J. Chem., 1975, 53, 1554. 13 A. Harriman and G. Porter, J. Chem. Soc., Faraday 2, 1979, 75, 1532. 14 S. Campestrini and B. Meunier, Inorg. Chem., 1992, 31, 1999. J. CHEM. RESEARCH (S), 1998 243

ISSN:0308-2342    

DOI:10.1039/a708106e

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

Non-linear Optical Properties of Squarate Esters and Amides$ Michael G. Hutchings,*a Ian Ferguson,b Simon Allen,c Joseph Zyssd and Isabelle Ledouxd aBASF plc, PO Box 4, Earl Road, Cheadle Hulme, Cheshire SK8 6QG, UK bZeneca Specialties Research Centre, Blackley, Manchester M9 8ZS, UK cICI plc, Wilton Research Centre, P.O. Box 90, Middlesbrough TS90 8JE, UK dFrance Te�Ê le�Ê com, CNET, Centre Paris B, Laboratoire de Bagneux, 196 Avenue Henri Ravera, F-92220 Bagneux, France In agreement with theoretical prediction, a squaric acid diamide shows appreciable quadratic non-linear optical (NLO) activity in solution, and because of their transparency such amides may be attractive materials for second harmonic generation of blue light, although all crystalline derivatives measured were essentially NLO inactive.A major potential use of organic non-linear optical (NLO) materials is frequency doubling, or second harmonic generation (SHG), of laser-generated light.1,2a Near-infrared radiation of wavelength 830 nm from a semiconductor laser can in principle be converted into blue light of wavelength 415 nm by a suitable NLO material.One particular appli- cation of a device based on such a material is in optical data storage, where four times as much information could be stored per unit area of optical disc by writing the infor- mation with the SH radiation, compared with the funda- mental wavelength. While this application of NLO materials has been much discussed, there are few materials which combine the desirable high NLO activity to bring about SHG with the transparency essential to allow passage of the shorter wavelength SH radiation.In fact, these properties are to a certain extent mutually incompatible, leading to the so-called transparency�}non-linearity trade- o€.2b Consequently a major goal in the research of new organic NLO materials has been the design, synthesis, and optical characterisation of speculative materials having properties consistent with these fundamental requirements.Recent theoretical studies3 on oxocarbon derivatives of generic structure 1 have been reported. Squarate (1; n a 2), croconate (1; n a 3), and rhodizonate (1; n a 4) esters and amides (1; Xa OR or NRR') were predicted to have relatively high NLO activity, especially considering their small molecular volumes, combined with transparency in the important blue region of the visible spectrum. In this paper, we report on experimental follow-up studies of the theoretical work, centred on the most easily accessible members of this series, a squarate diester 2a, mixed amide esters 3, and diamides 4 (Scheme).These molecules can be considered typical conjugated donor�}acceptor systems, where alkoxy and/or amino donor groups are connected to the dicarbonyl acceptor unit by the unsaturated cyclobutene skeleton. NLO results have been published on cyclobutenediones substituted by either a hydroxy or amino substituent in combination with a 4-N,N-dimethylaminophenyl group attached directly to the ring nucleus.4 However, these have absorbances bathochromic relative to the molecules reported in this study, and are unsuitable for SHG from a funda- mental wavelength near 830 nm.The commercially available diethyl diester of squaric acid (2a) was used as starting material for the preparation of the amides (Scheme). Reaction between the diester 2a and one equivalent of amine led to the monoester mono- amides 3, and with further amine to the diamide 4.Characterisation of products was unexceptional. The main problem encountered was the relative insolubility of some of the derivatives thus prepared, inhibiting recrystallisation as well as meaningful solution measurements. However, by inclusion of either relatively polar or long-chain hydro- phobic substituents in the amines, several derivatives of sucient solubility were ultimately prepared.The ester amide 3a was intentionally based on homochiral prolinol as amine, ensuring that the homochiral product must crystallise in a non-centrosymmetric space group. Such a packing arrangement is a necessary (although not sucient) condition for NLO activity in the crystal. Furthermore, the pendant hydroxy functionality could act as a source of attachment to a polymer backbone. One of the attractive features predicted for squarate derivatives by MO calculations3 is their relative trans- parency. This is particularly signiRcant for blue SHG.There is reasonable agreement between theoretical (gas phase) values calculated by the CNDOVSB method5 and exper- iment (Table 1); the absorption maxima of the squarate derivatives are indeed well into the UV. However, for practi- cal purposes, the concentration of active chromophore in any NLO device will be much higher than that of the dilute solutions used for spectral measurements, so spectra of saturated solutions were also measured in order to determine the transparency cut-o€ wavelengths. The values found are far more bathochromic than might be antici- pated from the dilute solution spectra (Table 1).However, they are still below the SH wavelengths of interest (ca. J. Chem. Research (S), 1998, 244�}245$ Scheme $This is a Short Paper as deRned in the Instructions for Authors, Section 5.0 [see J. Chem. Research (S), 1998, Issue 1]: there is there- fore no corresponding material in J.Chem. Research (M). *To receive any correspondence. 244 J. CHEM. RESEARCH (S), 1998410 nm), and so the squarate esters and amides are potential materials for SHG of blue light. The experimental hyperpolarisability values, b0, at zero ¢çeld strength are determined by the EFISH technique at 1.06 mm,6 b0 being deduced from the experimental b value using a two-level dispersion model.6 These data are recorded for 2a, 3a and 4d in Table 1, alongside experimentally deter- mined ground-state dipole moments, m0.For comparison, the theoretical results3 on comparable structures are also given in Table 1. The b0 values for the diester and the ester amide are both low in comparison with calculated values. However, the value of 1210¢§30 esu for the diamide 4d is close to the value calculated for the comparable diamide 4f (b0=1110¢§30, b1.17=2110¢§30 esu). The magnitude of the hyperpolarisability is comparable with that measured for typical benzenoid donor¡¾acceptor NLO materials such as 4-dimethylaminonitrobenzene [b0=1010¢§30, b1.06= 2610¢§30 esu; lmax(EtOH) a 388 nm].7 The latter material is yellow and thus of no use for SHG of blue wavelengths. Furthermore, the hyperpolarisability per unit molecular volume is higher for the squaramide than for the nitro- aniline.Crystalline materials 3a, 3b and 4a¡¾4e were colourless as expected. They were screened for SHG activity by the Kurtz¡¾Perry powder method,8 but disappointingly most of the materials are NLO inactive (<10¢§3urea standard).The two exceptions are the bis(dodecylamide) 4c and the mixed esteramide 3b. However, activity for each of these is only ca. 0.03 times that of the urea standard, and thus they are of no practical interest. The crystalline derivative 3a containing the homochiral prolinol substituent is forced to pack in a non-centrosymmetric space group, but despite this it is NLO inactive implying the chromophore dipoles must still align more or less antiparallel in the crystal.A crystal structure determination of the squarate diamide 4d revealed a centrosymmetric packing motif, with adjacent squarate chromophores oriented antiparallel with respect to one another.9 We conclude that squarate diamides have intrinsic quad- ratic NLO activity and transparency high enough for them to be technically useful materials for SHG. However, this is counterbalanced by our failure to ¢çnd a suitable non- centrosymmetric crystalline form.Poled polymer ¢çlms based on the diamides would be alternative synthetic targets. Experimental Synthetic routes followed a published procedure10 and gave products with satisfactory microanalytical and spectroscopic properties.11 Molecular hyperpolarisabilities and dipole moments were determined shed technique.6,12 Received, 8th December 1997; Accepted, 7th January 1998 Paper E/7/08794B References 1 H. S. Nalwa and S.Miyata, in Nonlinear Optics of Organic Molecules and Polymers, CRC Press, Boca Raton, FL, 1994. 2 (a) J. Zyss (editor), Molecular Nonlinear Optics, Materials, Physics and Devices, Academic Press, Boston, 1994; (b) J. Zyss, I. Ledoux and J.-F. Nicoud, in ref. 2(a), p. 129. 3 M. Dory, J.-M. AndreA , J. Delhalle and J. O. Morley, J. Chem. Soc., Faraday Trans., 1994, 90, 2319. 4 L. S. Pu, ACS Symp. Ser., 1991, 455, 331. 5 V. J. Docherty, D. Pugh and J. O. Morley, J. Chem. Soc., Faraday Trans. 2, 1985, 81, 1179. 6 J.-L. Oudar, J. Chem. Phys., 1977, 67, 446. 7 M. Barzoukas, D. Josse, J. Zyss, P. F. Gordon and J. O. Morley, Chem. Phys., 1989, 139, 359. 8 S. K. Kurtz and T. T. Perry, J. Appl. Phys., 1968, 39, 3798. 9 J. Delhalle and M. Dory, personal communication. 10 A. H. Schmidt, Synthesis, 1980, 961. 11 Melting point/8C (crystallisation solvent): 3a 102¡¾105 (toluene); 3b 156¡¾161 (ethanol) (lit.,10 154¡¾157; 156); 4a 133 (water); 4b 320¡¾323 (ethanol); 4c 173¡¾174 (toluene) (lit.,10 174¡¾178); 4d 275¡¾277 (water) (lit.,10 272¡¾275); 4e 129¡¾133 (ethanol). 12 M. G. Hutchings, I. Ferguson, D. J. McGeein, J. O. Morley, J. Zyss and I. Ledoux, J. Chem. Soc., Perkin Trans. 2, 1995, 171. Table 1 NLO and other solution properties of squarate derivatives UV/VIS spectra (nm) Dipole moments (D) and hyperpolarisability (10¢§30 esu) Experimentala Calculatedb Experimental Calc.b No. lmax lcut-off lcalc m0 b0 b1.17 m0 b0 Squarate diesters 2b 302 2.92 6.68 10.7 2a 338 400 5.3 1.6 Squarate monoester, monoamide 3a 281 390 319 6.09 8.44 13.59 6.3 2.4 Squarate diamides 4f 356 7.57 10.56 20.77 4d 304 400 7.0 12.0 aChloroform solution. bRef. 3. J. CHEM. RESEARCH (S), 1998 245

ISSN:0308-2342    

DOI:10.1039/a708794b

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

Synthesis of Clusters containing the MRuCoS(M M or W) Cores$Er-Run Ding,a Shu-Lin Wu,a Yuan-Qi Yin*a and Jie SunbaState Key Laboratory for Oxo Synthesis and Selective Oxidation,Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, ChinabShanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032,ChinaThe new clusters [fMRuCo(CO)8(3-S)g2f5-C5H4C(O)C6H4C(O)C5H4-5g] (M Mo 2 or W 3) have been isolatedfrom the reaction of [RuCo2(CO)9(3-S)] 1 and [fM(CO)3gf5-C5H4C(O)C6H4C(O)C5H4-5g]2£¾ (M Mo or W), andthe structure of cluster 3 has been established by single-crystal X-ray diffraction methods.Clusters with unique structural features and unusual reac-tivities have been obtained by using chalcogen atomsas bridging ligands.1 Chalcogen ligands display a widevariety of bonding modes when these are incorporated intransition-metal carbonyl cluster frameworks.The com-pound [RuCo2(CO)9(m3-S)] is a useful procluster, whichwas rst reported in 1984 by Roland and Vahrenkamp.2Here the new novel double tetrahedral clusters[{MRuCo(CO)8(m3-S)}2{Z5-C5H4C(O)C6H4C(O)C5H4-Z5}](M= Mo 2 or W 3) have been obtained from the reactionof Na2[{M(CO)3}2{Z5-C5H4C(O)C6H4C(O)C9H4-Z5}] (M =Mo or W) with the cluster 1 in reuxing THF (Scheme 1).The clusters 2 and 3 are air-stable red solids. They aresoluble in polar solvents like THF, toluene and chloro-form.Satisfactory C,H analyses were obtained for allcompounds.The similar spectral characterization of compounds 2and 3 suggests the same conguration for these clusters.The infrared spectra of cluster 2 and 3 showed intenseterminal carbonyl absorption bands in the range 1899¡Ó2085 cm£¾1, and also the corresponding carbonyl bands forthe acyl at 1650 and 1661 cm£¾1, which were much lowerthan that of RC1O in known clusters [FeCoM(CO)8(m3-S)-{C5H4C(O)R}].3 This is because of the conjugative eectof the aromatic ring in these complexes.The 1H NMRresonances of the substituted cyclopentadienyls appeareddowneld relative to that of unsubstituted cyclopenta-dienyls,4 due to the shielding eect of the p system ofthe C(O)C6H4C(O) group.It should be mentioned that themoleculer structure of 2 and 3 is achiral containing asymmetric center. However, the cyclopentadienyl protons of2 and 3 show an A2BB' instead of an A2B2 pattern, becauseof the presence of a chiral tetrahedral subcluster SRuCoM.5The structural features of this new series of mixed-metalclusters have been established by X-ray diraction analysisof a suitable crystal of 3.The structure contains twoindependent centrosymmetric molecules in a unit cell, eachof which has two tetrahedral skeletons (SRuCoW) con-nected through a C5H4C(O)C6H4C(O)C5H4 bridge (Fig. 1).The slightly distorted triangular RuCoW is capped by am3-sulde ligand. The Ru and Co atoms are co-ordinatedby three two-electron carbonyl ligands, the W atom by twocarbonyl ligands and one ve-electron carbonylcyclo-pentadienyl ligand.The capping sulde atom bonds to Ru,Co, and W with bond lengths of 2.325(4), 2.191(4) and2.376(4) A , respectively. The W atom¡ÓC5H4 ring centroiddistance is 1.790 A . Since the p system of the COC6H4CObridge would be quite well conjugated with that of the C5H4ring, the bond lengths C(5)0C(6) (1.46 A ) and C(6)0C(7)(1.47 A ) become much shorter than a normal C0C singlebond (1.54 A ), but longer than a C1C double bond(1.34 A ).Cluster 3 contains a total of 482 electrons and iselectronically saturated.ExperimentalAll reactions were performed under an atmosphere of pure nitro-gen by using standard Schlenk or vacuum-line techniques. Columnchromatography was carried out by using silica gel of 300¡Ó400mesh. The compounds [Mo(CO)6] and [W(CO)6] were purchasedfrom Fluka and Aldrich Chem. Co. Infrared spectra were recordedon a Nicolet FT-IR 10 DX spectrophotometer; 1H NMR spectra ona Bruker AM-300 MHz spectrometer; analyses (C, H) were per-formed on a 1106-type analyzer.J.Chem. Research (S),1998, 246¡Ó247$Scheme 1 Synthesis of complexes 2 and 3Preparation of Na2[{M(CO)3}2{5-C5H4C(O)C6H4C(O)C5H4-5}][M=Mo or W ].The compound Na(C5H5) (88 mg, 1.0 mmol)and dimethyl terephthalate (194 mg, 0.5 mmol) were dissolved inTHF (50 cm3). After the mixture was reuxed for 8 h, [M(CO)6]Fig. 1 Crystal structure of the cluster 3. Selected bonddistances (A ) and angles (8): W(1)0Ru(1) 2.873(1),W(1)0Co(1) 2.750(1), W(1)0S(1) 2.376(4), Ru(1)0Co(1)2.633(3), Ru(1)0S(1) 2.325(4), Co(1)0S(1) 2.191(4),C(5)0C(6) 1.46(2) and W(1)0Cp 1.790; Ru(1)0W(1)0Co(1)55.80(6), Ru(1)0W(1)0S(1) 51.52(10), Ru(1)0S(1)0Co(1)71.3(1), Co(1)0W(1)0S(1) 50.0(1), Ru(1)0Co(1)0S(1)56.1(1), Ru(1)0Co(1)0W(1) 64.47(6), Ru(1)0S(1)0W(1)75.4(1), W(1)0S(1)0Co(1) 73.9(1), W(1)0Ru(1)0Co(1)59.73(5), W(1)0Ru(1)0S(1) 53.13(9) andCo(1)0Ru(1)0S(1) 52.0(1)$This is a Short Paper as dened in the Instructions for Authors,Section 5.0 [see J.Chem. Research (S), 1998, Issue 1]: there is there-fore no corresponding material in J. Chem. Research (M).*To receive any correspondence.246 J. CHEM. RESEARCH (S), 1998(1.0 mmol) was added and reuxed for 12 (for Mo) or 24 h (for W).The solvent was removed under reduced pressure and then theresidue was washed with pentane; it can be used directly in thefollowing reactions.Preparation of [{MoRuCo(CO)8(3-S)}2{5-C5H4C(O)C6H4C(O)-C5H4-5}] 2.The cluster [RuCo2(CO)9(3-S)] 1 (503 mg, 1.0 mmol)and Na2[{Mo(CO)3}2{5-C5H4C(O)C6H4C(O)C5H4-5}] (305 mg,0.5 mmol) were dissolved in THF (50 cm3).After the mixture wasreuxed, 3 h, the red-brown solution was evaporated to dryness.The residue was extracted with CH2Cl2 (5 cm3) and then theextracts were subjected to column chromatography. The main pro-duct 2 was obtained in 315 mg (49%) yield. IR(KBr disc): 2085vs,2042vs, 2009vs, 1907m and 1650m cm£¾1 (C1O). 1H NMR (CDCl3,300 MHz); 5.32¡Ó6.03 (m, 8 H, 2C5H4) and 7.94 (s, 4H, C6H4). 13CNMR(CDCl3, 300 MHz): 215.2 and 208.15 (terminal CO), 193.40and 188.34 (C1O), 140.87 and 128.40 (C6H4), 94.41, 93.61, 91.73,87.71 and 86.66 (C5H4).Preparation of [{WRuCo(CO)8(3-S)}2{5-C5H4C(O)C6H4C(O)-C5H4-5}] 3.The synthetic method for cluster 3 was the same asthat for 2. Yield: 327 mg (42%). IR(KBr disc): 2083vs, 2040vs,2002vs, 1899m and 1661m cm£¾1 (C1O). 1H NMR (CDCl3,300 MHz): 5.35¡Ó6.01 (m, 8 H, 2C5H4) and 7.92 (s, 4 H, C6H4).Crystal data of 3.A crystal of compound 3 (C34H12Co2O18-Ru2S2W2, Mr=1460.28) was grown from a CH2Cl2 solution.Thespace group was P1. The cell parameters were determined ona Rigaku AFC7R diractometer with graphite-monochromatedMo-K radiation: as a= 12.688(4); b=20.290(7); c =9.429(3) A ,= 99.78(3); = 90.64(2); = 78.28(3)8, Z =2; V=2341(1) A 3;Dc=2.071 g cm£¾3, =63.73 cm£¾1, 2max=45.08, and F(000)=1364.00. Crystal size 0.200.200.40 mm. Of the 6460 reectionscollected, 6123 were unique (Rint=0.031). The intensities of threerepresentative reections were measured every 200. Renementconverged at nal R=0.042, Rw=0.063. Minimum and maximumnal electron densities £¾0.79 and 1.28 e A £¾3. The calculations wereperformed using the TEXSAN crystallographic software package ofMolecular Structure Corporation. The non-hydrogen atoms wererened anisotropically. Hydrogen atoms were included but notrened.We are grateful to the Laboratory of OrganometallicChemistry at Shanghai Institute of Organic Chemistry,Chinese Academy of Sciences for the nancial support ofour work.Received, 3rd November 1997; Accepted, 13th January 1998Paper E/7/07891IReferences1 L. C. Roof and J. W. Kolis, Chem. Rev., 1993, 93, 1037.2 E. Roland and H. Vahrenkamp, Chem. Ber., 1984, 117, 1039.3 Er-Run Ding, Xing-Min Liu, Yuan-Qi Yin and Jie Sun,Polyhedron, 1997, 16, 3273.4 R. Blumhofer, K. Fischer and H. Vahrenkamp, Chem. Ber., 1986,119, 194.5 H. Beurich and H. Vahrenkamp, Angew. Chem., Int. Ed. Engl.,1978, 17, 86.J. CHEM. RESEARCH (S), 1998 247

ISSN:0308-2342    

DOI:10.1039/a707891i

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

Mechanistic Studies on the Reaction ofPentaaquahydroxochromium(III) Ion withOxalic Acid$Deng Wenjie,*a Ye Xiaolan,b Wang Huatonga and Hu KechengbaDepartment of Chemistry, Hangzhou Teachers College, Hangzhou 310012, P. R. ChinabDepartment of Chemistry, Hangzhou University, Hangzhou 310028, P. R. ChinaThe substitution of aqua ligands from pentaaquahydroxochromium(III) ion by oxalic acid occurs through a mechanisminvolving the formation of an ion pair followed by an associative interchange (Ia) process.Previous studies1¡Ó6 have shown that the anation reactions of[Cr(H2O)5(OH)]2 with incoming ligands containing N,Odonor centres occur through an associative interchange(Ia) mechanism, while those with ligands containing N,Ndonor centres proceed through a dissociative mechanism.To our knowledge, the mechanism of the anation of[Cr(H2O)5(OH)]2 by ligands containing O,O donor centreshas not been studied, though the reactions of [Cr(H2O)6]3with oxalate ions have been reported previously.7,8Compared with [Cr(H2O)6]3, the co-ordinated OH in[Cr(H2O)5(OH)]2 facilitates a dissociative mechanismthrough its p-bonding ability, but it seems that the liganddonor power has an important inuence on mechanism.Thepresent investigation is concerned with the mechanism ofanation of [Cr(H2O)5(OH)]2 by a ligand containing a O,Odonor centre (oxalic acid) and the inuence of the liganddonor power.ExperimentalHexaaquachromium(III) perchlorate was prepared by the litera-ture method.9 Pentaaquahydroxochromium(III) was prepared in situby adjusting the pH of a solution of [Cr(H2O)6]3 to 5.0 {the per-centage of [Cr(H2O)5(OH)]2 is estimated to be 85% at 25 8C andpH 5.0 from the acid dissociation constants10} and was veriedfrom the absorption spectrum, lmax at 430 (log E=1.422) and590nm (log E=1.121).All the chemicals used were of AR grade.The composition of the product in solution was determined bychanging the molar ratios of the two reactants and by Job's methodof continuous variation.The metal to ligand ratio was found to be1:1. The reaction course was monitored with a UV-265 spectro-photometer (Shimadzu, Japan) at 315nm where the molar absorp-tion coecients of the reactant complex and product dierappreciably. The pH was adjusted by NaOH/HClO4 using a pHS-3digital pH meter, and the ionic strength of the reaction medium byadding NaClO4. The [ligand] was always maintained high so that apseudo-rst-order rate law would be obeyed.All data were treatedby a least-squares procedure.Results and DiscussionAt xed [ligand] (0.1 mol dm£¾3), pH 5.0, ionic strength I(0.2 mol dm£¾3) and at dierent [Cr(H2O)5(OH)]2 concen-trations (0.005, 0.00625, 0.0075 mol dm£¾3), the kobs valuesare 3.4910£¾4, 3.4110£¾4 and 3.3210£¾4 s£¾1 respectivelyat 35 8C. Thus the rate of reaction showed a rst-orderdependence on [Cr(H2O)5(OH)2].The rate of reaction was found to increase with increasingpH of the medium (Table 1).This can be explained byconsidering the pK values of the incoming ligand and thereactant complex. According to the following equilibriaH2C2O4 HC2O4£¾ C2O42£¾pK1 1:27; pK2 4:27 at 25 8Cit is obvious that the percentage of the dinegative anionicform C2O42£¾, which can be calculated to be 84% at 25 8Cand pH 5.0 by using the pK1 and pK2 values, will increasewith the increase in pH and it has a higher donor power.Thus, the rate of reaction increases with pH. Consideringthe acid dissociation equilibriumCrH2O63 CrH2O5OH2 HpK 4:0 at 25 8Cthe percentage of the more reactive pentaaquahydroxospecies increases with increasing pH.The enhanced reac-tivity of this species is due to the well known labilising eectof the hydroxide ion adjacent to the water molecule throughits lone pair of electrons exerting a strong electromericeect. Hydroxide ion is also a strong p donor which facili-tates the formation of very reactive hydroxo intermediatesand thus inceases the rate.The results of the variation of [ligand] on the reactionrate at 27, 30, 35, 38 and 40 8C are illustrated in Fig. 1. Therate of reaction increases with increase in [ligand] and athigh [ligand] approaches a limiting value due to completionof ion-pair formation.11 The following mechanism is pro-posed to explain the variation of rate with [ligand].CrH2O5OH2 C2O42£¾KE£¾£¾£¾£¾£¾* )£¾£¾£¾£¾£¾CrH2O5OH2C2O42£¾1CrH2O5OH2C2O42£¾ £¾£¾4kaslowCrH2O3OHC2O4 2H2O 2Based on reactions (1) and (2) and considering the ion-pairequilibrium and rate-determining step, the following ratelaw can be derived:dCrH2O3OHC2O4dt kaKECrH2O5OH2TC2O42£¾1 KEC2O42£¾ kobsCrH2O5OH2T 3where KE is the ion-pair equilibrium constant, ka theanation rate constant and [Cr(H2O)5(OH)2]T representsJ.Chem. Research (S),1998, 248¡Ó249$Table 1 Influence of pH on kobs (308 K)apH 4.4 4.6 4.8 5.0 5.2104 kobs/s£¾1 1.75 1.80 2.03 3.49 4.40a[Cr(H2O)5(OH)2] 0.005mol dm£¾3, [ligand] 0.10 mol dm£¾3,I 0.2mol dm£¾3.$This is a Short Paper as dened in the Instructions for Authors,Section 5.0 [see J.Chem. Researh (S), 1998, Issue 1]; there is there-fore no corresponding material in J. Chem. Research (M).*To receive any correspondence.248 J. CHEM. RESEARCH (S), 1998the total unreacted complex concentration in solution. So, kobs a kaKEaC2O4 2¢§a 1 a KEaC2O4 2¢§a O4U or 1 kobs a 1 ka a 1 kaKEaC2O4 2¢§a O5U eqn. (5) suggests that plots of 1/kobs versus 1/[C2O4 2¢§] at a constant pH should be linear with an intercept = 1/ka and slope =1/kaKE, and this is indeed evidenced in Fig. 2. The ka values are 2.3710¢§4, 3.1010¢§4, 4.8310¢§4, 6.9810¢§4 and 8.9110¢§4 s¢§1 at 27, 30, 35, 38 and 40 8C respectively, The KE values are found to be 21 to 26 dm3 mol¢§1 in the temperature range studied. Activation parameters were calculated from the linear Eyring plot of log ka/T versus 1/T and the values of DH% and DS% found to be 76.2 kJ mol¢§1 and ¢§60.7 JK¢§1 mol¢§1 respectively.The high ion-pair equilibrium constant indicates the interaction between a bipositive cation [Cr(H2O)5(OH)]2a and a binegative anion C2O4 2¢§. Compared to the rate of isotopic water exchange, the high anation rate constant suggests the associative character of the interchange process, i.e. bond formation by the incoming ligand plays a signi¢çcant role in the interchange step, which is evidenced by the low value of DH%. Moreover, the considerably negative DS% suggests the acti- vated complex formation through outer-sphere association is stabilised by hydrogen bonding between a water molecule of the inner-sphere complex and the negative end of the oxalate ion, which leads to the formation of a stable and compact activated state.Based on the above discussion, we propose that the reaction occurs through an associative interchange (Ia) process. This is consistent with the anation of [Cr(H2O)5(OH)]2a by ligands containing N,O donor centres.1¡¾5 The complex [Cr(H2O)5(OH)]2a and the incoming ligands (N,O or O,O) form an ion-pair ¢çrst. In the following slow step the O¢§ in the ligands replace the co-ordinated water molecule.The ion pair is stabilised by hydrogen bonding and the interaction between two reactants having opposite charges. We note however that the anation of [Cr(H2O)5(OH)]2a by ligands containing N,N donor centres occurs through a dissociative mechanism.6 Compared with O¢§,N has a weaker donor power and the incoming ligands are neutral molecules.It is di.cult to form an ion pair between a complex ion and a neutral molecule containing N,N centres which has a lower donor power. Moreover, due to the s- and p-bonding abilities of the hydroxo-group in [Cr(H2O)5(OH)]2a, the OH group labilises the aqua ligand, producing a stable ¢çve-co-ordinate intermediate rather than an ion pair between two reactants. This leads to the con- clusion that the nature of the incoming ligands has an important e€ect on the mechanism of the anation of [Cr(H2O)5(OH)]2a, although the co-ordinated OH facilitates a dissociative mechanism.The increase in donor power of the incoming ligands is favorable to the Ia mechanism. Received, 11th February 1997; Accepted, 8th December 1997 Paper E/7/00973I References 1 H. G. M. Mustofy and G. S. De, J. Indian Chem. Soc., 1986, 63, 1040. 2 H. G. M. Mustofy and G. S. De, Proc. Indian Acad. Sci. (Chem. Sci.), 1987, 98, 255. 3 H. G. M. Mustofy and G. S. De, J. Indian Chem. Soc., 1988, 65, 81. 4 B. K. Niogy and G. S. De, Proc. Indian Acad. Sci. (Chem. Sci.), 1983, 92A, 153. 5 B. K. Niogy and G. S. De, J. Indian Chem. Soc., 1984, 61, 389. 6 H. G. M. Mustofy and G. S. De, Transition Met. Chem., 1988, 13, 196. 7 R. E. Hamm and R. E. Davis, J. Am. Chem. Soc., 1953, 75, 3085. 8 D. L. Huizenga and H. M. Patterson, Anal. Chim. Acta, 1988, 206, 263. 9 P. Moore and F. Basolo, Inorg. Chem., 1965, 4, 1670. 10 K. B. Kladnitskaya, A. I. Zayats and V. S. Kulbanovskii, Zh. Fiz. Khim., 1974, 48, 3034. 11 R. B. Jordan, Reaction Mechanisms of Inorganic and Organo- metallic Systems, Oxford University Press, New York, 1991, p. 31. Fig. 2 Plots of 1/kobs versus 1/[C2O4 2¢§] at different temperatures: (A) 27, (B) 30, (C) 35, (D) 38 and (E) 40 8C Fig. 1 Variation of kobs with [C2O4 2¢§] at different temperatures. (A) 27, (B) 30, (C) 35, (D) 38 and (E) 40 8C; [Cr(H2O)5(OH)2a] a 0.005 mol dm¢§3, pH 5.0, I a 0.2 mol dm¢§3 J. CHEM. RESEARCH (S), 1998 249

ISSN:0308-2342    

DOI:10.1039/a700973i

出版商:RSC    

年代:1998

数据来源: RSC