摘要:

DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1999, 655–656 655 Ethene and styrene insertion into the Pd–acyl bond of [Pd(COMe)(PŸN)(solv)]O3SCF3 and its role in the copolymerisation of olefins with carbon monoxide Anton Aeby and Giambattista Consiglio * Eidgenössische Technische Hochschule, Laboratorium für Technische Chemie, ETH Zentrum, CH-8092 Zurich, Switzerland. E-mail: consiglio@tech.chem.ethz.ch Received 25th January 1999, Accepted 26th January 1999 Styrene has higher productivity than ethene during copolymerisation with carbon monoxide using [Pd(COCH3)( PŸN)(solv)]O3SCF3 (where PŸN is a phosphanyldihydrooxazole ligand), while ethene, not styrene, is preferentially enchained during the terpolymerisation probably reflecting the different reactivity of the two possible alkyl intermediates toward carbon monoxide insertion.A good deal of attention has been paid to the alternating copolymerisation of olefins with carbon monoxide.1–12 Although the newly developed commercial material, Carilon“, is, indeed, a terpolymer13,14 less emphasis has been placed on terpolymerisation reactions 15–20 and on the factors determining the microstructure of the terpolymers during the catalytic process.To understand the factors that determine the very high enantioface selection in the isotactic copolymerisation of styrene using {(S)-2-[2-(diphenylphosphino-kP)phenyl]-4- benzyl-4,5-dihydrooxazole-kN}diaquapalladium(II) trifluoromethanesulfonate 1 as the catalyst precursor 21,22 we studied the terpolymerisation of styrene, ethene and carbon monoxide.23 Despite the copolymerisation activity shown by 1 being higher by a factor of about 3.5 for styrene than for ethene, in the terpolymerisation experiments using similar concentrations of the two olefins, more ethene is enchained than styrene in the terpolymers.Analogous experiments using (acetonitrile-kN)- {(S)-2-[2-(5H-benzo[b]phosphindol-5-yl-kP)phenyl]-4-benzyl- 4,5-dihydrooxazole-kN}methylpalladium(II) trifluoromethanesulfonate 2 24 as the catalyst precursor give similar results (Table 1).† The terpolymerisation of ethene, styrene and carbon monoxide, using 2 with similar concentrations of ethene and styrene shows a productivity of 38.8 mmol (g Pd h)21 compared to a productivity of 130.0 mmol (g Pd h)21 in the copolymerisation of styrene and carbon monoxide and of 14.8 mmol (g Pd h)21 for the copolymerisation of ethene with the same catalyst precursor.Thus, the rate at which the terpolymer forms is close to that for the ethene copolymer. Furthermore, based on the chiroptical properties, enantioface selection for styrene is similar both in the ter- and co-polymerisation processes. Styrene insertion into the palladium acetyl bond of 3 (the product of CO insertion of 2) was found to take place with essentially complete selectivity and enantioselectivity to 4b (Scheme 1).24 In the reaction of 3 with ethene under atmospheric pressure, 4a forms with the same selectivity, as determined by multinuclear NMR spectroscopy.‡ Using the same technique to determine the rate of the olefin insertion into the Pd–acyl bond of 3, we found that at 0 8C 4a forms about 4–5 times more rapidly than 4b under comparable molar amounts of olefin.§ No further reaction with carbon monoxide is observed for 4a and 4b at normal pressure.25,26 Consistent with the higher insertion rate of ethene into the Pd–acyl bond, an ethene concentration of about 81% was found in the terpolymer chains formed with 2 with similar concentrations of ethene and styrene.The reported results contribute to an understanding of the kinetic role of the various reaction steps in the copolymerisation process (Scheme 2). With the catalyst systems used, coordination of the olefin is favoured for ethene with respect to styrene and does not appear to be completely reversible. Since insertion is more rapid for ethene than for styrene, the turnover frequency of the process must be limited by the successive step from 49 to 39.Both coordination of carbon monoxide and the opening of the chelation ring to form intermediate 5 (the relative order of the two events is not fixed) are expected to be easier for species 49a than for species 49b due to steric and entropic factors respectively. Therefore, the smaller reactivity of ethene compared to styrene most probably reflects a more diYcult insertion of carbon monoxide into a palladium– primary carbon atom bond (5a) than insertion into the palladium–secondary benzylic carbon bond (5b).Scheme 1 P N Pd O C CH3 R H P N Pd L CH3 R *C H2C OC* 3 4a R = H 4b R = C6H5 [O3SCF3] [O3SCF3] R = H or C6H5 P N = P N O CH2C6H5 Table 1 Polymerisation reactions using [(PŸN)Pd(CH3)(CH3CN)][O3SCF3] 2 as the catalyst precursor Styrene/ mmol 435 435 — Ethene/ mmol 0 385 456 CO/bar 320 300 300 Productivity/ mmol (g Pd h)21 130.0 38.8 14.8 Polymer composition C2H4CO:C8H8CO 0 : 100 81:19 100:0 Dea/l mol21 cm21 211.75 213.02 c — Mn b/ g mol21 7500 8000 4500 a From the circular dichroism spectra measured at 282 nm in (CF3)2CHOH–CHCl3 1 : 10.b Estimated from end groups in the 1H NMR spectra. c Extrapolated to 100% styrene units.656 J. Chem. Soc., Dalton Trans., 1999, 655–656 Notes and references † A general procedure for copolymerisation and terpolymerisation reactions is described in ref. 23. ‡ Selected spectroscopic data for 4a: 1H NMR (500 MHz, CD2Cl2, 25 8C): d 0.98–1.04 (m, 1H, CH3 13COCH2CH2), 1.15–1.21 (m, 1H, CH3 13COCH2CH2), 2.38 [d, 2J(C,H) = 5.8, 3H, CH3 13COCH2CH2], 2.72–2.80 (m, 1H, CH3 13COCH2CH2), 2.82–2.89 (m, 1H, CH3 13COCH2CH2). 31P NMR (121.5 MHz, CD2Cl2, 0 8C): d 25.34 [d, 3J(C,P) = 1.6]. 13C NMR (75.5 MHz, CD2Cl2, 0 8C): d 23.2 (s, CH3 13COCH2CH2), 28.0 [dd, 1J(C,C) = 40.0, 4J(P,C) = 2.1, 1C, CH3 13COCH2CH2], 50.7 [d, 1J(C,C) = 40.3, CH3 13COCH2CH2], 235.4 [d, 3J(P,C) = 1.6, CH3 13COCH2CH2].Assignments were made on the basis of HMQC, COSY, NOESY and 31P-{1H} NMR spectroscopic techniques. § The amount of ethene dissolved in the CD2Cl2 solution at 0 8C was determined in preliminary experiments using octamethylcyclotetrasiloxane as an internal standard. Because of the relatively high relaxation time of the protons in ethene, the cycle time was set at 40 s for these quantitative measurements. Scheme 2 P N Pd L GPC P N Pd O C GPC R H R P N Pd GPC R CO P N Pd C R H CO GPC O OC C H2C OC L [O3SCF3] 3' 3'' 4' 5 a R = H b R = C6H5 (GPC = growing polymer chain) [O3SCF3] [O3SCF3] [O3SCF3] 1 A.Sen, Acc. Chem. Res., 1993, 26, 303. 2 E. Amevor, S. Bronco, G. Consiglio and S. Di Benedetto, Macromol. Symp., 1995, 89, 443. 3 E. Drent and P. H. M. Budzelaar, Chem. Rev., 1996, 96, 663. 4 A. Sommazzi and F. Garbassi, Prog. Polym. Sci., 1997, 22, 1547. 5 S. Y. Desjardins, K. J. Cavell, J. L. Hoare, B. W. Skelton, A.N. Sobolev, A. H. White and W. Keim, J. Organomet. Chem., 1997, 544, 163. 6 B. Milani, A. Anzilutti, L. Vicentini, A. Sessanta o Santi, E. Zangrando, S. Geremia and G. Mestroni, Organometallics, 1997, 16, 5064. 7 G. J. P. Britovsek, K. J. Cavell, M. J. Green, F. Gerhards, B. W. Skelton and A. H. White, J. Organomet. Chem., 1997, 533, 201. 8 B. Domhöver, W. Kläui, A. Kremer-Aach, R. Bell and D. Mootz, Angew. Chem., 1998, 110, 3218. 9 M. J. Green, G. J. P. Britovsek, K. J. Cavell, F.Gerhards, B. F. Yates, K. Frankcombe, B. W. Skelton and A. H. White, J. Chem. Soc., Dalton Trans., 1998, 1137. 10 K. Nozaki, M. Yasumoti, K. Nakamoto and T. Hiyama, Polyhedron, 1998, 17, 1159. 11 G. Verspui, G. Papadogianakis and R. A. Sheldon, Chem. Commun., 1998, 401. 12 M. A. Zuideveld, P. C. Kamer, P. W. N. M. van Leeuwen, P. A. A. Klusener, H. A. Stil and C. F. Roobeek, J. Am. Chem. Soc., 1998, 120, 7977. 13 A. Wakker, H. G. Kormelink, P. Verbeke and J. C. M. Jordaan, Kunststoffe, 1995, 85, 1056. 14 H. Seifert, Kunststoffe, 1998, 88, 1154. 15 M. Vincenti and A. Sommazzi, Ann. Chim. (Rome), 1993, 83, 209. 16 A. Sen and Z. Jiang, Macromolecules, 1993, 26, 911. 17 D.-J. Liaw, J.-S. Tsai and B.-F. Lay, Polym. J., 1996, 28, 608. 18 S. Bronco, G. Consiglio and E. L. P. Gindro, Polym. Mater. Sci. Eng., 1997, 76, 106. 19 A. S. Abu-Surrah, G. Eckert, W. Pechhold, W. Wilke and B. Rieger, Macromol. Rapid Commun., 1996, 17, 559. 20 A. S. Abu-Surrah, R. Wursche and B. Rieger, Macromol. Chem. Phys., 1997, 198, 1197. 21 M. Sperrle, A. Aeby, G. Consiglio and A. Pfaltz, Helv. Chim. Acta, 1996, 79, 1387. 22 A. Aeby, A. Gsponer and G. Consiglio, J. Am. Chem. Soc., 1998, 120, 11000. 23 A. Aeby and G. Consiglio, Helv. Chim. Acta, 1998, 81, 35. 24 A. Aeby, F. Bangerter and G. Consiglio, Helv. Chim. Acta, 1998, 81, 764. 25 M. Brookhart, F. C. Rix, J. M. DeSimone and J. C. Barborak, J. Am. Chem. Soc., 1992, 114, 5894. 26 F. C. Rix, M. Brookhart and P. S. White, J. Am. Chem. Soc., 1996, 118, 4746. Communication 9/00668K

ISSN:1477-9226    

DOI:10.1039/a900668k

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1999, 657–658 657 The first alkyl bismuthates: tris(trifluoromethyl)fluoroand tetrakis(trifluoromethyl)-bismuthate Wieland Tyrra,a Dieter Naumann,*a Natalya V. Kirij,b Alexander A. Kolomeitsev b and Yurii L. Yagupolskii b a Institut für Anorganische Chemie, Universität zu Köln, D-50939 Köln, Germany. E-mail: d.naumann@uni-koeln.de b Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 253660 Kiev, Ukraine Received 11th January 1999, Accepted 25th January 1999 Tris(trifluoromethyl)bismuth reacts with fluoride ions and intermediately generated trifluoromethyl anions to form the first representatives of hitherto unknown fluoroalkylbismuthates: tris(trifluoromethyl)fluoro- and tetrakis(tri- fluoromethyl)-bismuthates. Hypervalent bismuthate(III) anions with five electron pairs in the bismuth valence shell are important models for the transition states in nucleophilic substitution reactions at bismuth(III) centers.Therefore, such compounds are of considerable interest. To date some stable bismuthates have been isolated,1–4 but to our knowledge there is no indication in the literature on the synthesis of acyclic hypervalent alkylbismuthate(III) species bearing at least one alkyl group on bismuth. Meanwhile such species have not only theoretical interest, but could be potentially used as precursors to prepare unknown tetra- and pentaalkyl derivatives of Bi(V), which are not available via reactions of trialkylbismuth dihalides with organometallic compounds.The only example of a tetramethylbismuth compound is [Bi(CH3)4]OSO2CF3 as the product of the reaction of Bi(CH3)3 and CH3OSO2CF3.5 Some of us have developed a convenient procedure to synthesize perfluorinated trialkyl bismuthanes.6a,b We suppose that introduction of trifluoromethyl groups to bismuth(III) increases the Lewis acidity of the bismuth compounds which as a result should enhance the interaction of such fluorinated bismuthanes with nucleophiles, stabilizing hypervalent anionic four-coordinated bismuthates and increasing their ability for CF3 group transfer.Successful fluoride induced C6F5 group transfer reactions presumably involving tris(penta- fluorophenyl)fluorobismuthates, [Bi(C6F5)3F]2, have been established in the literature for several years.7a,b The stabilising influence of fluorine and trifluoromethyl groups on phosphoranes is well documented. There are also two reports on stabilisation by fluorine atoms and CF3 groups of phosphites, which can be regarded as the conjugate bases of phosphoranes.8,9 The reaction of Bi(CF3)3 with the fluoride ion proceeds in THF, glyme (H3COCH2CH2OCH3) or diethyl ether.As sources of F2 we used [{N(C2H5)2}3S]1F2, [N(PPh3)2]1F2, [N(CH3)4]1F2 or [N(C2H5)2]3PF2, as shown in eqn. (1), where Bi(CF3)3 1 A1F2 æÆ A1 [Bi(CF3)3F]2 (1) 1 A1 = [{N(C2H5)2}3S]1, [N(PPh3)2]1, [N(CH3)4]1 or [{N(C2H5)2}3- PF]1.The stability of hypervalent bismuthates formed depends on the counter ions and the nature of the fluoride ion source. The most stable solid bismuthate, [N(CH3)4]1[Bi(CF3)3F]2 1,† was prepared using [N(CH3)4]1F2 as a source of the fluoride ion. Surprisingly, tetramethylammonium fluoride was a better fluoride ion source than [{N(C2H5)2}3S]F. Covalent tris(diethylamino) difluorophosphorane, a mild donor of fluoride ion, reacts reversibly with Bi(CF3)3. The tris(diethylamino)fluorophosphonium cation formed in the course of this reaction is electrophilic enough to react reversibly with [Bi(CF3)3F]2 to form [N(C2H5)2]3PF2.This behaviour can be interpreted as a first hint of the fluorinating properties of [Bi(CF3)3F]2, eqn. (2). Bi(CF3)3 1 [N(C2H5)2]3PF2 [{N(C2H5)2}3PF]1 1 [Bi(CF3)3F]2 (2) Tris(trifluoromethyl)bismuth reacts with the intermediately formed CF3 anions (generated from (CH3)3SiCF3 and [N(CH3)4]1F2) in diethyl ether, THF or glyme to form tetrakis(trifluoromethyl)bismuthate [N(CH3)4]1[Bi(CF3)4]2 2,‡ eqn.(3). The reaction proceeds at 270 to 250 8C. An increase Bi(CF3)3 1 (CH3)3SiCF3 1 [N(CH3)4]1F2 æÆ [(CH3)4N]1[Bi(CF3)4]2 1 (CH3)3SiF (3) 2 in temperature causes the formation of [N(CH3)4]1[Bi(CF3)3F]2 1 as a by-product. The formation of 1 in reactions above 250 8C in the presence of (CH3)3SiCF3 indicates that at lower temperatures primarily [(CH3)3Si(CF3)F]2 is formed which undergoes a replacement reaction with Bi(CF3)3 below 250 8C.At elevated temperatures (>250 8C) Bi(CF3)3 appears to be a harder Lewis acid than (CH3)3SiCF3 and reacts preferably with the fluoride ion. Therefore, temperature constancy (270 to 250 8C) is necessary for the preparation of [Bi(CF3)4]2. Hypervalent anionic bismuth species 1,2 are solids, which are stable in a dry nitrogen atmosphere at ambient temperature for some days and can be stored without decomposition in a refrigerator. CF3-containing bismuthates are extremely reactive towards all common aprotic and especially protic solvents. Tri- fluoromethane formation in THF is observed even at 270 8C.The reactivity of both bismuthate anions was studied in reactions with some organic and inorganic electrophilic reagents. To date, only reactions accompanied by a cleavage of the Bi–F or one Bi–CF3 bond have been found. Compound 1 reacts as a fluorinating agent. The interaction of this compound with trimethylchlorosilane and trichloro- fluoromethane leads to chlorine exchange aVording (CH3)3SiF and CCl2F2, respectively, and Bi(CF3)3.We have found, despite the high reactivity with aprotic solvents, that 2 is an excellent source of the trifluoromethyl anion even at 278 8C. Successful trifluoromethylations with this hypervalent bismuthate were carried out with pentafluoropyridine, (CH3)3SnCl and SO2Cl2 to give the trifluoromethylated compounds 4-(trifluoromethyl)tetrafluoropyridine, trimethyl- (trifluoromethyl)tin and trifluoromethylsulfurylchloride, respectively. The bismuthates 1,2 are unambiguously identified by a combination of NMR techniques supported by a satisfactory elemental analysis for all elements. In the 19F NMR spectrum (258 8C, THF-d8) of the [Bi(CF3)3F]2 anion the CF3 group658 J.Chem. Soc., Dalton Trans., 1999, 657–658 resonance is detected as a broad singlet at d 239.84, remarkably shifted to higher field in comparison with the parent molecule Bi(CF3)3 d 233.40, and the fluorine atom as a singlet at d 2106.33.The 13C NMR resonance of the CF3 groups is detected as a quartet at d 183.16 (1JCF = 395.0 Hz). The 19F NMR resonance of the trifluoromethyl groups in [Bi(CF3)4]2 is located at higher field (d 241.21). The quartet of the trifluoromethyl groups in the 13C NMR spectrum is detected at d 167.37 (1JCF = 405 Hz). According to VSEPR theory, both salts should show resonances of two diVerent types of CF3 groups in the 19F NMR spectrum.The fact that only one resonance is observed may be explained by a fast exchange of axial and equatorial CF3 groups in solution (even at low temperature), which is not detectable on the NMR time scale. Acknowledgements We gratefully acknowledge the support and financial assistance of this work by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie. Notes and references † Preparation of 1: tetramethylammonium fluoride (1 mmol) was gradually added under argon to a solution of tris(trifluoromethyl)- bismuth (1 mmol) in 5 ml diethyl ether at 250 8C and the reaction mixture was stirred for 2 h at 240 8C.The solvent was removed in vacuo below 220 8C and the remaining product was washed twice with diethyl ether at 230 8C and finally dried in vacuo. The salt was obtained in nearly quantitative yield and was stable at 230 8C under argon for two weeks. 19F NMR (282.35 MHz, THF-d8, 258 8C, ppm) d 239.84 (CF3, 9F), 2106.33 (F, 1F); 13C NMR (75.48 MHz, THF-d8, 258 8C, ppm) d 183.16 (CF3, q, 1JCF 395), 53.28 (CH3, q, 1JCH 146 Hz) (Found: C, 16.88; H, 2.64; Bi, 40.68; F, 37.20; N, 2.41. C7H12BiF10N requires C, 16.51; H, 2.38; Bi, 41.05; F, 37,31; N, 2.75%).‡ Preparation of 2: to a solution of tris(trifluoromethyl)bismuth (1 mmol) in 5 ml diethyl ether at 270 8C trifluoromethyltrimethylsilane (3 mmol) and tetramethylammonium fluoride (1 mmol) were added. The mixture was stirred at 260 to 265 8C for 1 h.All volatile products were removed in vacuo at 230 8C, the remaining product was washed twice with diethyl ether at 230 8C and dried in vacuo. The salt was obtained in nearly quantitative yield and was stable at 230 8C under argon for 2–3 days. 19F NMR (282.35 MHz, THF-d8; 258 8C, ppm) d 241.21 (CF3); 13C NMR (75.48 MHz, THF-d8, 258 8C, ppm) d 167.37 (CF3, q, 1JCF 405), 55.10 (CH3, q, 1JCH 146 Hz) (Found: C, 16.81; H, 2.45; Bi, 37.72; F, 39.43; N, 2.09. C8H12BiF12N requires C, 17.18; H, 2.16; Bi, 37.37; F, 40.77; N, 2.51%). 1 J.-P. Finet, Chem. Rev., 1989, 89, 1487. 2 G. Faraglia, J. Organomet. Chem., 1969, 20, 99. 3 T. Allman, R. Foel and H. S. Prasad, J. Organomet. Chem., 1979, 166, 365. 4 X. Chen, Y. Yamamoto, K. Akiba, S. Yoshida, M. Yasui and F. Iwasaki, Tetrahedron Lett., 1992, 33, 6656. 5 S. Wallenhauer and K. Seppelt, Angew. Chem., 1994, 106, 1044. 6 (a) D. Naumann and W. Tyrra, J. Organomet. Chem., 1987, 334, 323; (b) D. Naumann, R. Schlengermann and W. Tyrra, J. Fluorine Chem., 1994, 66, 79. 7 (a) H. J. Frohn and H. Maurer, J. Fluorine Chem., 1986, 34, 129; (b) A. O. Miller and G. G. Furin, Russ. Chem. Bull., 1994, 43, 168; Izv. Akad. Nauk, Ser. Khim., 1994, 171. 8 A. A. Kolomeitsev, M. Goerg, U. Dieckbreder, E. Lork and G.-V. Roeschenthaler, Phosphorus, Sulfur, Silicon Relat. Elem., 1996, 109–111, 597. 9 K. O. Christe, D. A. Dixon, H. P. A. Mercier, J. C. P. Sanders, G. J. Schrobilgen and W. W. Wilson, J. Am. Chem. Soc., 1994, 116, 2850. Communication 9/00308H

ISSN:1477-9226    

DOI:10.1039/a900308h

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1999, 659–661 659 Vanadium(V) complexes based on a bis(pyridine)-imine ligand (HL); synthesis and crystal structure of a dioxovanadium(V) complex involving a ligand cyclisation Alette G. J. Ligtenbarg,a Anthony L. Spek,†b Ronald Hage *c and Ben L. Feringa *a a Department of Organic and Inorganic Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands. E-mail: feringa@chem.rug.nl b Bijvoet Center for Biomolecular Research, Crystal and Structural Chemistry, University of Utrecht, Padualaan 8, 3584 CH Utrecht, The Netherlands c Unilever Research Laboratory, Olivier van Noortlaan 120, 3133 AT, Vlaardingen, The Netherlands Received 4th December 1998, Accepted 18th January 1999 Synthesis and characterisation of two novel dioxovanadium( V) complexes based on (2-hydroxybenzylidene)- di(2-pyridin-2-yl)methylamine (HL) and 3-(2-hydroxyphenyl)- 1-pyridin-2-yl-imidazo-[1,5-a]-pyridine (HL9), which is the result of a vanadium-mediated oxidative cyclisation of HL, are reported.The notion that vanadium plays an important role in various biological systems has invoked great interest in the coordination chemistry of vanadium.1 Vanadium(V) complexes have been found to act as catalysts in oxidation reactions of various substrates using peroxides.2 The catalytic oxidation by SchiV- base complexes of vanadium with dioxygen has also been reported.3 During our investigation on the catalytic properties of V(V) complexes, we synthesised novel dipyridylmethyl amine SchiV base dioxovanadium(V) complexes and found a vanadium-mediated oxidative cyclisation.4 In the course of this work, a related iron mediated oxidative cyclisation of a polypyridine ligand has been published by Meunier et al.5 However, in our case the obtained cyclised product was not released from the metal, but remained coordinated resulting in a stable dioxovanadium( V) complex which was completely characterised by X-ray analysis, ES-MS spectrometry, 1H and 51V NMR, UV-Vis and IR measurements.(2-Hydroxybenzylidene)di(2-pyridin-2- yl)methylamine (HL) was prepared starting from dipyridin-2- yl-methylamine 6 and salicylaldehyde (Scheme 1) in 93% yield. Complexation of HL with triisopropoxyvanadium(V) oxide [VO(OiPr)3] in MeOH under reflux aVorded complex 1 in 39% yield.7 Yellow crystals suitable for X-ray analysis were obtained by evaporation of a MeOH–EtOH solution (1: 1) of 1.‡ An ORTEP plot is shown in Fig. 1. Complex 1 contains a dioxovanadium( V) moiety. The vanadium center is pentacoordinated by two nitrogen atoms [2.173(3) and 2.090(3) Å with a bond angle between N(1)–V(1)–N(3) of 72.87(12)8], one oxygen atom of the deprotonated phenolic moiety [1.888(3) Å and a bond angle between N(1)–V(1)–O(1) of 81.448] and two oxo groups [1.610(4), 1.632(4) Å]. The V]] O distances are nearly equal and typical for dioxovanadium(V) complexes in which the oxygens are not involved in hydrogen bonding.8 The bond angle between the oxo groups and the vanadium center is 109.02(16)8. We assumed that initially, upon addition of VO(OiPr)3 to a solution of L in MeOH, complex 2 is formed.In fact, vanadium(V) complex 2 of the uncyclised SchiV base ligand can be obtained in 60% yield when the reaction of L with VO(OiPr)3 is performed in EtOH at 0 8C under an atmosphere of argon. Unfortunately, no crystals suitable for X-ray analysis were obtained.The UV spectrum of 2 in acetonitrile exhibits three bands at † Address correspondence concerning crystallography to this author. 212 nm (e = 1.89 × 104 M21 cm21), 266 (1.23) and 384 (0.23). The spectrum resembles the one recorded in acetonitrile of HL [213 nm (e = 2.43 × 104 M21 cm21), 262 (1.95) and 319 (0.45)]. The UV spectrum of 1 in acetonitrile, however, exhibits four bands at 212 nm (e = 0.89 × 104 M21 cm21), 304 (0.25), 343 (0.36) and 417 (0.24).The distinction between complexes 1 and 2 was further corroborated using electron spray ionisation mass spectrometry (ES-MS), UV-Vis, IR, 1H and 51V NMR measurements. ES-MS spectra for 1 in acetonitrile show peaks at m/z 369.8 and 739.3 which can be attributed to Scheme 1 Synthesis of HL and complexes 1 and 2. Reagents and conditions: (i) salicylaldehyde, rt, MeOH, 93%; (ii) VO(OiPr)3, MeOH, reflux, air, 5 min, 39%; (iii) VO(OiPr)3, EtOH, 0 8C, argon, 2 h, 60%.660 J.Chem. Soc., Dalton Trans., 1999, 659–661 {VO2L9 1 1H} and {2VO2L9 1 1H}, respectively. In addition, electron ionisation mass spectrometry (EI-MS) measurements show, besides the parent peak at m/z 369, a peak at m/z 287 which corresponds to the mass of free HL9. In the ES-MS spectrum of 2 in acetonitrile peaks were observed at m/z 372.0 {VO2L 1 H} and 743.4 {2VO2L 1 H}. Also the 1H NMR spectra of complexes 1 and 2 clearly indicate the diVerence between the two ligand systems.§ Complex 1 lacks two protons compared with 2, i.e.the characteristic imine hydrogen signal (Ha, Scheme 1) has disappeared as well as the signal for the double benzylic proton (Hb). 51V NMR spectra of these two complexes, however, are very similar. Complex 1 dissolved in DMSO-d6 has a single resonance at 2543 ppm (band width, b.w. = 1303 Hz), whereas 2 shows a single resonance at 2540 ppm (b.w. = 965 Hz). This is a strong indication that the coordination sphere around the vanadium(V) center is quite similar in both structures. 9 In the case of 2, the vanadium ion is surrounded by one pyridine nitrogen, the imine nitrogen, the deprotonated phenolic oxygen and two oxo groups as depicted in Scheme 1. As a result, the second pyridine entity is non-coordinating. Heating of a solution of 2 in MeOH results in the formation of 1 as was also shown by 1H NMR measurements. Infrared spectra reveal two V]] O absorptions for both complexes, at 926 and 949 cm21 for 1 and at 918 and 953 cm21 for 2, respectively.These observations correspond to the data known from the literature that stretching frequencies of V]] O bonds with a length of 1.607– 1.621 Å are found in the 930–960 cm21 region.10 The relatively low position of the V]] O stretching band may indicate the existence of intermolecular interactions via O bridges, but no evidence for such interactions was found in the crystal structure. The oxidative cyclisation of the coordinated SchiV base ligand L leads to the formation of an imidazo[1,5-a]pyridine 11 type of ligand (L9).Some imines of di(2-pyridyl)methylamine are known to cyclise spontaneously to imidazo[1,5-a]pyridines by air oxidation.12 However, HL itself remained intact even after refluxing in MeOH solution in the air for 3 h. Therefore, the vanadium(V) ion is likely to play an active role in the cyclisation process. Based on these results, a reaction mechanism is proposed for the ligand cyclisation reaction resulting in the formation of 1 starting from 2 (Scheme 2).13 First the SchiV base ligand is oxidised by vanadium(V) giving a vanadium(IV) species containing one oxo ligand and one hydroxy group (A and B).The radical in resonance structure B then attacks the non-coordinating pyridine nitrogen resulting in the formation of C, which is subsequently oxidised by air to form 1. The involvement of a vanadium(IV) species is supported by results of EPR experiments with crude 1.An EPR signal was observed (g = 1.97) which was attributed to a vanadium(IV) species by comparison with literature data.14 In conclusion, SchiV base ligand HL is found to be eVective in the formation of a dioxovanadium(V) complex. However when HL is heated in the presence of vanadium(V), imidazo- Fig. 1 An ORTEP plot of complex 1 (50% probability level). pyridine type ligand L9 is formed due to an oxidative cyclisation reaction. Catalytic oxidation experiments with these complexes are in progress.We gratefully acknowledge Dr M. Lubben for initial synthesis and Mrs C. M. Jeronimus-Stratingh for performing the ES-MS measurements. This work was supported in part (A. L. S.) by the Netherlands Foundation of Chemical Research (SON) with financial aid from the Netherlands Organisation for Scientific Research (NWO) and in part (A. G. J. L., R. H., B. L. F.) by Unilever Research Vlaardingen, The Netherlands. Notes and references ‡ Crystal data for 1: C18H12N3O3V, Mr = 369.25, yellow needle (0.10 × 0.12 × 0.43 mm), monoclinic, space group P21/c (no. 14) with a = 7.0787(16), b = 16.833(5), c = 13.573(5) Å, b = 115.21(2)8, V = 1463.3(8) Å3, Z = 4, Dc = 1.676 g cm23, F(000) = 752, m(Mo-Ka) = 7.0 cm21, 6346 reflections measured, 3006 independent, R(int) = 0.106, qmax = 26.58, w scan, T = 150 K, Mo-Ka radiation, graphite monochromated, l = 0.71073 Å, Enraf-Nonius CAD4T on rotating anode. Data were corrected for absorption (PLATON/DELABS).The structure was solved by direct methods (SHELXS86) and refined on F 2 using SHELXL97. Hydrogen atoms were taken into account at calculated positions. Convergence was reached at R = 0.0579 for 1984 reflections with I > 2s (I) and 226 parameters. CCDC reference number 186/1318. See http://www.rsc.org/suppdata/ dt/1999/659 for crystallographic files in .cif format. § 1H NMR (300 MHz, DMSO-d6) for 1: d 9.24 (m, 1H), 9.05 (m, 1H), 8.49 (m, 2H), 8.28 (m, 2H), 7.54 (m, 3H), 7.27 (m, 1H), 7.09 (m, 2H); and for 2: 9.22 (s, 1H), 8.86 (s, 2H), 8.06 (m, 2H), 7.70 (m, 3H), 7.57 (m, 3H), 6.93 (m, 3H). 1 D. Rehder, Angew. Chem., Int. Ed. Engl., 1991, 30, 148; A. Butler and C. J. Carrano, Coord. Chem. Rev., 1991, 109, 61. Scheme 2 Proposed mechanism for the formation of complex 1 (R = H, CH3).J. Chem. Soc., Dalton Trans., 1999, 659–661 661 2 K. B. Sharpless and R. C. Michaelson, J. Am. Chem. Soc., 1973, 95, 6136; K. B. Sharpless and T. R. Verhoeven, Aldrichim.Acta, 1979, 12, 63; A. Butler, M. J. Clague and G. E. Meister, Chem. Rev., 1994, 94, 625. 3 K. Yamamoto, K. Oyaizu and E. Tsuchida, J. Am. Chem. Soc., 1996, 118, 12665; K. Oyaizu, K. Yamamoto, K. Yoneda and E. Tsuchida, Inorg. Chem., 1996, 35, 6634. 4 Recently, Dr M. Döring (University of Jena) informed us about the copper mediated cyclisation of L. 5 M. Renz, C. Hemmert, B. Donnadieu and B. Meunier, Chem. Commun., 1998, 1635. 6 E. Niemers and R. Hiltmann, Synthesis, 1976, 593. 7 Complex 1 was stable for several weeks when stored under an atmosphere of dry argon. 8 C. A. Root, J. D. Hoeschele, C. R. Cornman, J. W. Kampf and V. L. Pecoraro, Inorg. Chem., 1993, 32, 3855. 9 V. Conte, F. Di Furia and S. Moro, J. Mol. Catal. A, 1995, 104, 159. 10 G. Asgedom, A. Sreedhara, J. Kivikoski, J. Valkonen and C. P. Rao, J. Chem. Soc., Dalton Trans., 1995, 2459. 11 D. D. Davey, J. Org. Chem., 1987, 52, 1863. 12 A. P. Krapcho and J. R. Powell, Tetrahedron Lett., 1986, 27, 3713; M. T. Edgar, G. R. Pettit and T. S. Krupa, J. Org. Chem., 1979, 44, 396; R. Grigg, P. Kennewell, V. Savic and V. Sridharan, Tetrahedron, 1992, 48, 10423. 13 J. Fossey, D. Lefort and J. Sorba, Free radicals in organic chemistry, John Wiley & Sons, New York, 1995; T. Fukuda, F. Sakamoto, M. Sato, Y. Nakano, X. S. Tan and Y. Fujii, Chem. Commun., 1998, 1391. 14 M. Bonchio, V. Conte, F. Di Furia, G. Modena, S. Moro and J. O. Edwards, Inorg. Chem., 1994, 33, 1631. Communication 8/09476D

ISSN:1477-9226    

DOI:10.1039/a809476d

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1999, 663–666 663 Synthesis and characterisation of the first organotin complex of piroxicam. An extended network system via non-hydrogen, hydrogen bonding linkages and C–H ? ? ?� contacts Sotiris K. Hadjikakou,a Mavroudis A. Demertzis,a John R. Miller b and Dimitra Kovala-Demertzi a* a Inorganic and Analytical Chemistry, Department of Chemistry, University of Ioannina, 45100 Ioannina, Greece. E-mail: dkovala@cc.uoi.gr b Department of Biological and Chemical Sciences, University of Essex, Wivenhoe Park, Colchester, UK CO4 3SQ Received 7th January 1999, Accepted 18th January 1999 The organotin complex, [SnBu2(pir)]n, of the potent and widely used anti-inflammatory drug piroxicam, H2pir, was obtained and a crystal structure determination showed that in this complex the ligand is doubly deprotonated at the oxygen and amide nitrogen atoms.There are two similar molecules in the asymmetric unit. The isolated molecules of Sn(1) or Sn(2) are arranged in polymers in a head to tail fashion with a stacking of alternate parallel chains. Extended networks of Sn–O–Sn, C–H ? ? ? O and C– H? ? ?� contacts lead to aggregation and a supramolecular assembly.Real concentration protonation constants for the zwitterionic form (pyridyl group) and the protonated piroxicam (enolic group) were determined spectrophotometrically in pure aqueous solutions of constant ionic strength. It is the first example where piroxicam is proved to act as a doubly deprotonated tridentate ligand.Piroxicam [4-hydroxy-2-methyl-3-(2-pyridyl carbamoyl)-2H- 1,2-benzothiazine 1,1-dioxide], H2pir, is a potent and extensively used non-steroidal anti-inflammatory (NSDA), anti-arthritic drug with a long biological half-life,1a which acts by inhibiting enzymes involved in the biosynthesis of prostaglandins. To date, piroxicam is among the top ten NSDAs on the market.1 The drug, with four donor atoms and several possible isomers,1 is known to react as a monodentate ligand through the pyridyl nitrogen towards platinum(II) and as a singly deprotonated bidentate chelate ligand, through the pyridyl nitrogen and the amide oxygen, towards copper(II) and cadmium(II).2 Iron(II), cobalt(II), nickel(II) and zinc(II) almost certainly behave similarly to cadmium(II).2 Organotin(IV) compounds form an important series of compounds and have been receiving increasing attention in recent years, not only because of their intrinsic interest, but also owing to the importance of tin-based anti-tumour drugs.3,4 We have developed 5 an interest in the coordination chemistry and anti-inflammatory properties of nonsteroidal anti-inflammatory drugs, and report here the interaction of SnBu2Cl2 with piroxicam (H2pir) † and the crystal structure of the complex [SnBu2(pir)]n.‡ There are two similar molecules in the asymmetric unit.[SnBu2(pir)]n has 1 : 1 Sn : pir stoichiometry and the doubly deprotonated ligand, pir, is coordinated as a tridentate ligand via the enolic oxygen O(1), the amide N(2) and pyridyl N(1) nitrogen atoms.The molecular structure is shown in Fig. 1 which includes some selected bond parameters. The very long Sn–N(pyridyl) bonds are readily explic- Fig. 1 An ORTEP representation of [SnBu2(pir)]n with the atom numbering scheme. Selected bond lengths (Å) [data from the second molecule are in square brackets]; Sn–O 2.083(3) [2.074(2)]; Sn–N(pyridyl) 2.427(3) [2.478(3)]; Sn–N(amide) 2.135(3) [2.176(3)]; Sn(1)–C(16) 2.119(5) [2.120(4)]; Sn(1)– C(20) 2.119(5) [1.238(4)]; C(8)–O(1) 1.313(4) [1.321(4)]; C(6)–O(2) 1.229(5) [1.238(4)]; N(2)–C(5) 1.389(5) [1.388(4)]; N(2)–C(6) 1.375(5) [1.354(4)].664 J.Chem. Soc., Dalton Trans., 1999, 663–666 Table 1 Inter-hydrogen bonding, non-hydrogen intermolecular interactions and C–H ? ? ?p interactions in [SnBu2(pir)]n in Å and degrees. Cg = ring centroid a Donor (D) C(1) C(20) C(36) C(38) C(43) Sn(1) Sn(2) Sn(2) Sn(2) Ha H(1) H(20B) H(36) H(38B) H(43A) Acceptor (A) b O(3)i O(3)i O(3)ii O(4)i O(8)iii O(2)i O(6)iii N(6)iii C(29)iii D? ? ?A 3.238(5) 3.402(5) 3.291(5) 3.521(5) 3.354(5) 3.019(4) 2.611(2) 3.598(3) 3.535(4) H? ? ?A 2.5195 2.4895 2.5278 2.4927 2.4145 D–H? ? ?A 132.55 145.95 137.49 169.18 149.72 C(16)–H(16A) ? ? ? Cg(1) C(21)–H(21A) ? ? ? Cg(1) C(40)–H(40A) ? ? ? Cg(2) C(40)–H(40B) ? ? ? Cg(2) C(44)–H(44B) ? ? ? Cg(2) C(2)–H(2) ? ? ? Cg(3) C(35)–H(35) ? ? ? Cg(4) H? ? ? Cg 2.772 2.760 3.355 2.697 2.438 3.283 2.818 X? ? ? Cg 2.897 3.315 3.151 3.151 3.170 4.059 3.666 C–H? ? ? Cg 86.34 113.51 69.83 106.37 126.58 140.27 113.51 a Cg(1) and Cg(2) are the centroids of the four-membered rings Sn(1)–N(1)–C(5)–N(2) and Sn(2)–N(4)–C(28)–N(5) respectively; Cg(3) and Cg(4) are the six-membered rings N(4)–C(24)–C(25)–C(26)–C(27)–C(28) and C(9)–C(10)–C(11)–C(12)–C(13)–C(14) respectively.b Symmetry operations; i, 1/2 2 x, 1/2 1 y, 1/2 2 z; ii, 1 2 x, 2y, 1 2 z; iii, 3/2 2 x, 21/2 1 y, 1/2 2 z.able in terms of ring strain eVects in the four-membered chelate ring and as a result of the low degree of covalent character of the Sn–N(pyridyl) bond. According to Crow et al.,6c diorganotins with Sn–N bonds longer than 2.39 Å are associated with antitumour activity. On this basis, [SnBu2(pir)]n should be active. Analysis of the shape determining angles using the approach of Reedijk and coworkers 7 yields t ((a 2 b)/60) values of 0.01 and 0.13 for Sn(1) and Sn(2) respectively (t = 0.0 and 1.0 for SPY and TBPY geometries respectively).The metal coordination geometry is therefore described as SPY with the N(2) and N(5) occupying the apical positions for Sn(1) and Sn(2) respectively. The donors N(2) and N(5) are chosen as apices by the simple criterion that neither should be any of the four donor atoms which define the two largest angles, a and b.7 The coordinated part of the ligand is made of three rings, one heterocyclic (I) and two chelates (II and III).The dihedral angles between the planes of the rings I and II, II and III and I and III are 1.5(2), 3.1(2), 4.4(2) and 3.2(2), 5.2(1), 8.0(2)8 for Sn(1) and Sn(2) respectively, indicating that the ligand as a whole deviates from planarity, the largest deviations arising Fig. 2 Packing diagram of the complex [SnBu2(pir)]n viewed along the b axis of the unit cell, showing intra- and inter-molecular hydrogen bonds.from the expected puckering of the sulfonamide rings which contain the pyramidal saturated N atoms, N(3) and N(6). The plane (I) of the first molecule Sn(1) is tilted by 77.92(19)8 with respect to the plane (I) of the second one Sn(2). The di-anionic, tridentate ligand has a EZZ configuration about the bonds C(5)–N(2), N(2)–C(6) and C(6)–C(7) and the corresponding bonds in molecule (2). This type of ligand configuration was found in the ethanolamine salt of piroxicam1b and diVers from the ZZZ isomer only by a 1808 rotation of the pyridyl ring providing an additional internal hydrogen bond of piroxicam.A molecular mechanics analysis 2c showed that the ZZZ con- figuration is more stable than the EZZ one, the deprotonation of amide nitrogen being one of the principal eVects which favour EZZ. The negative charge of the deprotonated amide is delocalized over the three atom fragment C(6)–N(2)–C(5). This is confirmed by an elongation of the C(6)–N(2) bond to 1.375(5) Å and an elongation of the N(2)–C(5) bond to 1.389(5) Å.The bond distances of the five-atom fragment O(1)–C(8)– C(7)–C(6)–O(2) are consistent with the neutral isomer of piroxicam.1c Large thermal parameters are observed in the last two C atoms of the butyl chains; this is considered to arise from disorder in the conformation. Molecules of the same numbering, related by the 21 symmetry axis, are joined into chains by intermolecular bonds between tin and the neighbouring ketonic oxygen atom, with distances Sn(1) ? ? ? O(2)i 3.019(4) and Sn(2) ? ? ? O(6)ii611(2) Å respectively.The range of intermolecular distances, Sn ? ? ?O of 2.61–3.02 Å have been confidently reported for intramolecular bonds, indicate Sn–O bonding.6b Other close interactions, which may cross-link the chains and ensure crystal cohesion, include the possibility of C–H ? ? ? O and C–H ? ? ?p hydrogen bonds.8a These interactions are listed in Table 1 and are shown in the packing diagram in Fig. 2. The isolated molecules of Sn(1) or Sn(2) are arranged in polymers in a head to tail fashion with a stacking of alternate parallel chains. Crystal cohesion is ensured by the hydrogen bonds in and between the two chains. The monomers of Sn(1) are linked through intermolecular hydrogen bonds of C–H? ? ? O type,8a O(3)axial ? ? ? H–C(1) and O(3)axial ? ? ? H– C(20), while the monomers of Sn(2) are linked through O(8)axial ? ? ? H–C(43).Each polymer Sn(1)n is hydrogen bonded to two neighbouring chains of Sn(2)n by C(36)– H? ? ? O(3)axial and C(38)–H ? ? ? O(4)eq respectively, leading to the formation of corrugated layers which are directed along the ac diagonal of the unit cell. Further, C–H ? ? ?p interactions 8b and intramolecular bonds stabilize this structure.J. Chem. Soc., Dalton Trans., 1999, 663–666 665 Although it is remarkable that there are so many contacts, and of so many diVerent types, the interactions themselves are consistent with known guidelines for hydrogen bond formation. 8c In this case molecular recognition of the hydrogen bonds leads to aggregation and a supramolecular assembly. The concentration protonation constants of piroxicam, Ka1 and Ka2, were determined§ and the 95% confidence limits of their logarithms were found to be equal to 5.61 ± 0.01 and 1.97 ± 0.01 (n = 7) with relative standard deviations 0.16% and 0.64%, respectively. The low solubility of piroxicam and its low Ka2 value is the reason for using spectrophotometry to find the protonation constants of the molecule.In aqueous solutions with pH values between 1 and 12 only three independent species of piroxicam (Hpir2, H2pir and H3pir1) become visible as shown by the absorption spectra in Fig. 3. Acknowledgements D. K. D. thanks HELP EPE for the generous gift of piroxicam and J. R. M. acknowledges the use of the EPSRC’s Chemical Database Service at Daresbury.Notes and references † A suspension of H2pir (0.166 g, 0.5 mmol) in methanol (6 cm3) was treated with a standard aqueous 0.1 mol dm23 KOH solution (1 cm3, 1.0 mmol). The resulting colourless solution was stirred while a solution of SnBu2Cl2 (0.152 g, 0.5 mmol) in methanol (6 cm3) was added to give a colourless solution. A quantity of distilled water was added (10 cm3) and the reaction mixture was stirred for 15 min. The white powder was filtered oV, washed with 2–3 ml of cold distilled water and dried in vacuo over silica gel.Crystals of [SnBu2(pir)]n suitable for X-ray analysis were obtained by slow evaporation of a fresh MeOH–MeCN solution. Anal. Calc. for SnC23H29N3O4S: C, 49.14; H, 5.19; O, 11.38; N, 7.47; S, 5.70. Found: C, 49.95; H, 5.00; O, 11.40; N, 7.94; S, 5.66%. IR (–CO– NH–) n(C]] O) 1590s, n(C]] N) 1522s, n(SO2)as 1340s, n(SO2)sym 1180s. Fig. 3 (a) Absorption spectra for piroxicam at 25 8C in the high pH region, where the species Hpir2 (lmax = 356 nm) and H2pir (lmax = 361 nm) are present; (b) absorption spectra for piroxicam at 25 8C in the low pH region, where the species H2pir (lmax = 361 nm) and H3pir1 (lmax = 335 nm) are present.‡ Crystal data for C23H29N3O4SSn: M = 562.28, monoclinic, space group P21/n (no. 14), a = 19.696(7), b = 12.650(3), c = 21.066(7) Å, b = 106.010(10)8, U = 5045(5) Å3, Z = 8, T = 291 K, Dc = 1.480 g cm23, crystal dimensions 0.30 × 0.41 × 0.89, F(000) = 2296, Mo-Ka radiation, l = 0.71073 Å, m(Mo-Ka) = 1.13 mm21. 10854 unique reflections were measured (Rint = 0.013), 8169 observed (Fo > 3.0s(Fo)) with R and Rw 0.037 and 0.050 respectively. CCDC reference number 186/1319. See http://www.rsc.org/suppdata/dt/1999/663/ for crystallographic files in .cif format. § Aqueous piroxicam solutions of constant ionic strength were used to determine protonation constants. All solutions were prepared using distilled water obtained from a borosilicate autostill (Jencons Ltd.). 5 × 1025 M working piroxicam solutions having diVerent hydrogen ion concentrations and constant ionic strength (m = 0.1) were then prepared using standard HCl or KOH and KCl solutions; all measurements were made at 25 8C and the absorption spectra were collected in the range 240–440 nm. A rearrangement9 of the well known equation Ka1 = [H3O1] e(H2pir) 2 eo eo 2 e(Hpir2) (1) or Ka2 = [H3O1] e(H3pir1) 2 eo eo 2 e(H2pir) (2) (where eo, e(H2pir) and e(H3pir1) are the molar absorption coeYcients of the observed solution, negative ionized, molecular and positive charged species, respectively) in the form of eo = e(H2pir) 2 Ka1 eo 2 e(Hpir2) [H3O1] (3) or eo = e(H3pir1) 2 Ka2 eo 2 e(H2pir) [H3O1] (4) was used to determine Ka1 and e(Hpir2) values from (3) as well as Ka2 and e(H3pir1) values from (4). The e(Hpir2) value can be securely obtained from the absorption spectra of piroxicam that completely coincide with each other with pH > 8.By making use of eqn.(1) and (2) only relatively low errors accompany the e(H2pir) and Ka1, but much larger errors result for the e(H3pir1) and Ka2 values, that have to be determined in very strongly acid solutions. 1 (a) G. A. Ando and J. G. Lombardino, Eur. J. Reumatol. Inflam., 1983, 6, 3; (b) J. Bordner, P. D. Hammen and E. B. Whipple, J. Am. Chem. Soc., 1989, 111, 6572; (c) J. Bordner, J. A. Richards, P. Weeks and E .B. Whipple, Acta Crystallogr., Sect. C, 1984, 40, 989. 2 (a) R.Cini, J. Chem. Soc., Dalton Trans., 1996, 111; (b) D. Di Leo, F. Berrettini and R. Cini, J. Chem. Soc., Dalton Trans., 1998, 1993; (c) R. Cini, R. Basosi, A. Donati, C. Rossi, L. Sabadini, L. Rollo, S. Lorenzini, R. Gelli and R. Marcolongo, Met. Bas. Drugs, 1995, 2, 43; (d ) R. Cini, G. Giorgi, A. Cinquantini, C. Rossi and M. Sabat, Inorg. Chem., 1990, 29, 5197. 3 (a) C. J. Evans and S. Karpel, Organotin Compounds in Modern Technology, J. Organomet. Chem. Library vol. 16, Elsevier, New York, 1985; (b) A. J. Crow, in Metal-Based Antitumour Drugs, ed. M. Gielen, Freund, London, 1989, vol. 1, pp. 103–149. 4 (a) P. Tauridou, U. Russo, G. Valle and D. Kovala-Demertzi, J. Organomet. Chem., 1993, 44, C16; (b) D. Kovala-Demertzi, P. Tauridou, J. M. Tsangaris and A. Moukarika, Main Group Met. Chem., 1993, 16, 315; (c) P. Tauridou, U. Russo, D. Marton, G. Valle and D. Kovala-Demertzi, Inorg. Chim. Acta, 1995, 231, 139; (d ) D. Kovala- Demertzi, P. Tauridou, A.Moukarika, J. M. Tsangaris, C. P. Raptopoulou and A. Terzis, J. Chem. Soc., Dalton Trans., 1995, 123; (e) D. Kovala-Demertzi, P. Tauridou, U. Russo and M. Gielen, Inorg. Chim. Acta, 1995, 239, 177; ( f ) N. Kourkoumelis, A. Hatzidimitriou and D. Kovala-Demertzi, J. Organomet. Chem., 1996, 514, 163. 5 (a) D. Kovala-Demertzi, A. Theodorou, M. A. Demertzis, C. Raptopoulou and A. Terzis, J. Inorg. Biochem., 1997, 6, 151; (b) D. Kovala-Demertzi, D. Mentzafos and A. Terzis, Polyhedron, 1993, 11, 1361; (c) D. Kovala-Demertzi, S. K. Hadjikakou, M. A. Demertzis and Y. Deligiannakis, J. Inorg. Biochem., 1998, 69, 223; (d) M. Konstandinidou, A. Kourounakis, M. Yiangou, L. Hadjipetrou, D. Kovala-Demertzi, S. K. Hadjikakou and M. A. Demertzis, J. Inorg. Biochem., 1998, 70, 63. 6 (a) K. C. Molloy, T. G. Purcell, K. Quill and I. W. Nowell, J. Organomet. Chem., 1984, 267, 237; (b) A. R. Forrester, S. J. Garden, R. A. Howie and J. L. Wardell, J. Chem. Soc., Dalton Trans.,666 J. Chem. Soc., Dalton Trans., 1999, 663–666 1992, 2615; (c) A. J. Crow, P. J. Smith, C. J. Cardin, H. E. Parge and F. E. Smith, Canc. Lett., 1984, 24, 45. 7 A. Addison, R. T. Nageswara, J. Reedijk, J. Van Rijn and G. C. Verschoor, J. Chem. Soc., Dalton Trans., 1984, 1349. 8 (a) T. Steiner, B. Lutz, J. van der Maas, A. M. M. Schreurs, J. Kroon and M. Tamm, Chem. Commun., 1998, 171; (b) T. Steiner, M. Tamm, A. Grzegorzewski, N. Schulte, N. Veldman, A. M. M. Schreurs, J. Kroon, J. van der Maas and B. Lutz, J. Chem. Soc., Perkin Trans. 2, 1996, 2441; (c) M. C. Etter, Acc. Chem. Res., 1990, 23, 120; G. R. Desiraju, Acc. Chem. Res., 1991, 24, 290. 9 R.W. Ramette, Chemical Equilibrium and Analysis, Addison-Wesley Publishing Company, London, 1981, p. 432. Communication 9/00227H

ISSN:1477-9226    

DOI:10.1039/a900227h

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 667–675 667 Complexes of new chiral terpyridyl ligands. Synthesis and characterization of their ruthenium(II) and rhodium(III) complexes Marco Ziegler,a Véronique Monney,a Helen Stoeckli-Evans,b Alex Von Zelewsky,*a Isabelle Sasaki,c Gilles Dupic,c Jean-Claude Daran c and Gilbert G. A. Balavoine *c a Institut de Chimie Inorganique et Analytique, Université de Fribourg, Pérolles, CH-1700 Fribourg, Switzerland b Institut de Chimie, Université de Neuchâtel, Av.Bellevaux 51, CH-2000 Neuchâtel, Switzerland c Laboratoire de Chimie de Coordination, CNRS, 205 route de Narbonne, F-31077 Toulouse, France Received 6th January 1999, Accepted 12th January 1999 Enantiomerically pure, chiral terpyridyl-type ligands L1 (‘dipineno’-[5,6:50,60]-fused 2,29:69,20-terpyridine) and L2 (‘dipineno’-[4,5:40,50]-fused 2,29:69,20-terpyridine) have been synthesized in high yields starting from 2,6- diacetylpyridine and enantiopure a-pinene.Complexes of L1 and L2 with RhIII and RuII have been prepared and studied spectroscopically. The complexes [Ru(L)2][PF6]2 (L = L1 or L2) were obtained in high yields using microwave heating in ethylene glycol as solvent. The rhodium(III) and ruthenium(II) complexes of L1 and L2 have a helically distorted terpyridyl moiety, as shown by the considerable optical activity in the ligand centered and metal to ligand charge transfer transitions. Crystal structures of [Rh(L1)Cl3] and [Ru(L1)Cl3] show a considerable out of plane distortion of the terpyridyl moiety, whereas free L2 and [Ru(trpy)(L2)][PF6]2 have a more planar arrangement of the pyridyl units. Introduction Substituted 2,29:69,20-terpyridines are promising building blocks for supramolecular systems 1 and there is great interest in their co-ordination with transition metals,2–7 mainly due to their interesting photophysical properties 8,9 and potential pharmaceutical applications.10,11 We report here the synthesis and characterization of “chiralized” ‘pineno’-fused terpyridyl ligands L1(1) and L1(2) (L1 = ‘dipineno’-[5,6:50,60]-fused 2,29:69,20-terpyridine) and L2(1) and L2(2) (L2 = ‘dipineno’- [4,5:40,50]-fused 2,29:69,20-terpyridine) and their ruthenium(II) complexes, which have predetermined helical twist.† Predetermination of the chirality of metal complexes using chiral ligands is of current interest and has been achieved in our group for bis- and tris-diimine complexes,13–15 and extended to quaterpyridines 16 using our concept.With C2-symmetrical, chiral terpyridyl ligands like L1 or L2 three diVerent stereoisomers are possible in an octahedral mer arrangement: an enantiomeric pair with D2 symmetry and an achiral, S4-symmetrical diastereomer (Scheme 1). In the D2- symmetrical, octahedral complexes a helical twist is induced by the non-planarity of the ligand. The S4-symmetrical complex is an example of a “narcissistic coupling” 17a between two enantiomers giving a meso achiral complex.From a purely geometrical point of view it is also possible to divide such an achiral S4-symmetrical complex by the “coupe du roi” 17b,c into two homochiral halves, cutting through the metal and the central pyridyl moiety of each ligand, which is, however, impossible in a real molecule. † The designation L1(1) refers to the enantiomer obtained from (1)- a-pinene, L1(2) from (2)-a-pinene, L2(1) from (1)-myrtenal and L2(2) from (2)-myrtenal.The locants 5,6 : 50,60 refer to the numbering of the 2,29:69,20-terpyridyl moiety and indicate the fusion sites with the ‘pinene’ moiety. This numbering scheme was introduced for related ligands.12 L1=2,6-Bis(6,6-dimethyl-5,6,7,8-tetrahydro-5,7-methanoquinolin- 2-yl)pyridine, L2 = 2,6-bis(7,7-dimethyl-5,6,7,8-tetrahydro- 6,8-methanoisoquinolin-3-yl)pyridine. Experimental Synthetic methods The enantiomerically pure ligands L1 and L2 have been obtained in an analogous preparation to the “CHIRAGEN” ligand system 15 according to Scheme 2.Complexes were synthesized according to Scheme 3; [Ru(trpy)Cl3] was prepared following literature methods.18,19 Preparations (1S)-(2)-Pinocarvone (6,6-dimethyl-2-methylenebicyclo- [3.1.1]heptan-3-one) I. Following the literature procedure,20 compound I was obtained in 85–100% yields from (1R)-(1)-apinene [enantiomeric excess, e.e.: 98%. a (589 nm, 21 8C) = 50.78] as starting material.(1R)-(1)-Pinocarvone II was obtained Scheme 1 Possible arrangements of octahedral complexes with chiral terpyridyl type ligands.668 J. Chem. Soc., Dalton Trans., 1999, 667–675 from (1S)-(2)-a-pinene [e.e.: 98%. a (589 nm, 21 8C) = 250.18] using the same procedure. (1S)-(1)-Myrtenal (6,6-dimethylbicyclo[3.1.1]hept-2-ene-2- carbaldehyde) III. This was obtained in 32% yield from (1R)- (1)-a-pinene after silica gel chromatography using ethyl acetate–hexane (10 : 90) as the eluent following a literature procedure.21 The pure product was characterized by 1H NMR.(1R)-(2)-Myrtenal is commercially available. 2,6-Bis(pyridinioacetyl)pyridine diiodide IV. To a solution of 3.27 g (20 mmol) of 2,6-diacetylpyridine (Fluka purum) in 15 mL of dry pyridine was added a solution of 10.45 g (41 mmol) of sublimated iodine in 15 mL of dry pyridine. The mixture was heated at 100 8C for 3 h and after cooling, the precipitate is filtered oV, rinsed once with pyridine and dried.Recrystallization from 95% ethanol yielded 9.71 g of a beige powder (91%). 1H NMR (DMSO-d6): d 9.12 [d, 4 H, H(10), 3J(H10H11) = 5.7]; 8.79 [dd, 2 H, H(12), 3J(H12H11) = 7.8]; 8.44 [s, 3 H, H(4), H(5)]; 8.34 [dd, 4 H, H(11), 3J(H11H12) = 7.8, 3J(H11H10) = 5.7 Hz] and 6.71 [s, 4 H, H(8)]. MS(EI): m/z 446 (M1 2 I2 ); 318 (M1 2 2I2 2 H1) and 240 (M1 2 2I2 2 py) (Found: C, 38.08; H, 2.88; N, 6.92. Calc. for C19H17I2N3O2 1 H2O: C, 38.60; H, 3.2; N, 7.10%) Crystal data: C19H17I2N3O2], M = 826.96, orthorhombic, space group Pbca, a = 11.253(4), b = 16.741(4), c = 25.941(7) Å, U = 4887(3) Å3, Z = 8, Dc = 2.249 g cm23, T = 293(2) K, 4687 reflections measured, 3387 unique (Rint = 0.0332) of which all were used in all calculations; final wR(F ) 0.0402, goodness of fit 1.020. L1(2).Compound II (9.0 g, 0.060 mol) 2, 17.2 g (0.030 mol) of IV, and 9.24 g ammonium acetate (0.120 mol, Merck p.a.) were dissolved in 100 mL glacial acetic acid, refluxed overnight, Scheme 2 (i) 1O2, Acetic anhydride, DMAP, [(4-dimethylamino)- pyridine] CH2Cl2, TPP, (5,10,15,20-tetra phenyl porphyrin) 20 8C, 8 h;20 (ii) SeO2, t-BuOOH, CH2Cl2, 35 8C, 48 h;21 (iii) I2/py; (iv) ammonium acetate, acetic acid, 125 8C, 12 h; (v) ammonium acetate, acetic acid, formamide, 100 8C, 12 h.Scheme 3 (i) EtOH–water, 2–12 h, 80 8C; (ii) CH2OHCH2OH, 4 min, microwave heating, 375 W. and 100 mL water added to the ice cold solution. The solution was extracted four times with 150 mL diethyl ether.The extracts were combined and washed first with 70 mL water, then four times with saturated NaHCO3 solution and finally with saturated NaCl. After drying over MgSO4 and filtration over active carbon the product slowly crystallized by evaporation of the solvent (8.84 g, 70%). The compound L1(1) was prepared similarly in 62% yield. 1H NMR (CDCl3): d 8.37 [d, 2 H, H(12), 3J(H12H11) = 7.9]; 8.28 [d, 2 H, H(3), H(5), 3J(H3H4) = 7.7]; 7.88 [dd, 1 H, H(4), 3J(H4H3) = 7.8]; 7.34 [d, 2 H, H(11), 3J(H11H12) = 7.8]; 3.20 [d, 4 H, H(13a/13b), 3J(H13H14) = 2.6]; 2.81 [dd, 2 H, H(16), 3J(H16H15b) = 5.6, 4J16,14 = 5.6]; 2.70 [dd, 2 H, H(15b), 3J(H15bH14) = 5.6, 3J(H15bH16) = 5.6, 2J15b,15a = 9.6]; 2.40 [m sept, 2 H, H(14)]; 1.41 [s, 6 H, H(19)]; 1.31 [d, 2 H, H(15a), 2J15a,15b = 9.6]; and 0.68 [s, 6 H, H(18)]. 13C-{1H} NMR (CDCl3): d 156.3, 153.8, 142.2, 137.6, 133.7, 120.1, 177.9, 46.6, 40.3, 39.6, 36.7, 32.0, 26.1 and 21.3 (Found: C, 81.97; H, 7.59; N, 9.73.Calc. for C29H31N3: C, 82.62; H, 7.41; N, 9.97%). MS(EI): m/z 421 (100, M1); 406 (38, M1 2 CH3); 380 (46, M1 2 H2C = C1–CH3); 334 (26); 167 (61); 128 (20); 77 (22); and 43 (73%). a (330 nm) = 280 8C, a (370) = 265 8C [20 8C, c = 8 × 1025 M (1.68 mg in 50 mL acetonitrile)]. L2(1). To a solution of 2.89 g (5.03 mmol) of compound IV in formamide were added 1.66 g (21.5 mmol) of ammonium acetate and 1.52 g (10.1 mmol) of III. Heating at 80 8C was maintained overnight.The precipitate was filtered oV, rinsed with water and dried. It could be used without purification for the synthesis of the complexes or recrystallized from ethyl acetate (yield = 36%). Compound L2(2) was prepared similarly from (1R)-(2)-myrtenal in 64% yield. 1H NMR (CDCl3): d 8.37 (s, 2 H), 8.34 (d, 2 H, 3J = 7.8), 8.21 (s, 2 H), 7.90 (t, 1 H, 3J = 7.7), 3.11 (d, 4 H, 3J = 2.7), 2.88 (dd, 1 H, 3J = 5.5, 4J = 5.5), 2.68 (ddd, 2 H, 2J = 9.5, 3J = 5.7, 5.4), 2.34 (m sept, 2 H), 1.42 (s, 6 H), 1.25 (d, 2 H, 2J = 9.5 Hz) and 0.67 (s, 6 H). 13C-{1H} NMR (CDCl3): d 155.82, 154.63, 145.49, 145.30, 142.92, 137.70, 120.46, 120.36, 44.51, 40.12, 39.25, 33.03, 31.83, 26.01 and 21.38. IR (KBr): 2923m, 1709 (s), 1554m, 1455m and 1385m (Found: C, 82.72; H, 7.50; N, 9.88. Calc. for C29H31N3: C, 82.62; H, 7.41; N, 9.97%). MS (DCI, NH3): m/z = 422 [M 1 H]1. a (589 nm, 20 8C, 9.6 mg in 2 mL of CHCl3) = 1163.58. [Ru(trpy)2][PF6]2 1. In a 100 mL round flask, 117 mg (0.5 mmol) trpy (Fluka, purum) and 65.5 mg RuCl3?3H2O (0.25 mmol) were suspended in 4 mL ethylene glycol (Fluka, purum) and refluxed for 4 min in a microwave oven (325 W).The salt NH4PF6 (1.0 g) in 25 mL water was added to the orange-brown solution, the precipitate collected in a Buchner funnel, washed with water and a little diethyl ether and recrystallized from acetonitrile–diethyl ether. Yield: 190.5 mg (89%). 1H NMR (CD3CN): d 8.73 [d, 4 H, H(3), 3J(H3H4) = 8.1]; 8.47 [d, 4 H, H(12), 3J(H12H11) = 8.5]; 8.39 [dd, 2 H, H(4), 3J(H4H3) = 8.0]; 7.90 [td, 4 H, H(11), 3J(H11H12) = 7.8, 4J(H11H9) = 1.5]; 7.32 [d, 4 H, H(9), 3J(H9H10) = 5.2]; 7.14 [ddd, 4 H, H(10), 3J(H10H11) = 7.8, 3J(H10H9) = 5.6, 4J(H10H12) = 1.4 Hz].MS(EI): m/z 713 (15, M1 2 PF6); 567 (22, M1 2 2 PF6); 334 (20); 234 (100); and 154 (100%). DC: silica gel; DMF: 8; H2O: 5 EtOH: 3; NaCl: 0.3 M; NH4Cl: 0.2 M; Rf = 0.58.J. Chem. Soc., Dalton Trans., 1999, 667–675 669 [Ru(L1)(2)Cl3 2.The compound L1(2) (84.3 mg, 0.2 mmol) and 48.6 mg RuCl3?3H2O (0.2 mmol) were suspended in 10 mL 1-butanol (Fluka, puriss.) and kept under constant reflux for 12 h. The greenish powder was filtered oV and washed with a little diethyl ether. Drying to constant weight yielded 115 mg of a green-brownish powder (92%). The substance was paramagnetic and contained some [Ru(L1(2))2]Cl2. Recrystallization from acetone yielded small, needle like crystals of 2. Diluted solutions of it in a number of polar solvents (EtOH, DMF, DMSO) all contained dissociated RuIII and free L1(2) as seen from the precipitation of the latter after slow evaporation and from spectroscopic data.MS(EI): m/z 593 (32, M1 2 Cl); 557 (28, M1 2 2 Cl); and 518 (100, M1 2 3 Cl). [Rh(L1(2))Cl3 3. In a 100 mL round flask, 1.60 g (3.80 mmol) L1(2) and 1.00 g RhCl3?3H20 were refluxed for 4 h in 30 mL ethanol. The orange-red precipitate was filtered oV, washed with a little ethanol and recrystallized from dichloromethane– diethyl ether (153 mg, 94%). The complex [Rh(L1(1))Cl3] 4 was obtained similarly from L1(1) in 87% yield. 1H NMR (CDCl3): d 8.03 [s, 3 H, H(3), H(4), (H5)]; 7.83 [d, 2 H, H(12), 3J(H12H11) = 7.8]; 7.44 [d, 2 H, H(11), 3J(H11H12) = 7.8]; 4.46 [m large, 4 H, H(13)]; 2.82 [dd, 2 H, H(16), 3J(H16H15b) = 5.7, 4J(H16H14) = 5.7]; 2.61 [dd, 2 H, H(15b), 3J(H15bH14) = 5.7, 3J(H15bH16) = 5.7, 2J(H15bH15a) = 9.9]); 2.47 [m sept, 2 H, H(14)]; 1.38 [s, 6 H, H(19)]; 1.28 [d, 2 H, H(15a), 2J(H15aH15b) = 9.9 Hz]; and 0.68 [s, 6 H, H(18)].MS(FAB): m/z 594 (100); 595 (34); 596 (69); 597 (22); 598 (14); 599(4) (M1 2 Cl); 559 (100); 560 (34); 561 (37); 562 (11); and 563 (1%) (M1 2 2 Cl). UV-VIS (CH2Cl2, c = 2.00 × 1025 M): l/nm (e/M21 cm21) 242 (42570); 276 (sh, 17000); 312 (21900); 354 (18000) and 376 (sh, 7600). a [404.6 nm, 20 8C, c = 2.00 × 1025 M (0.630 mg in 50 mL dichloromethane] = 112508. [Ru(trpy)(L1(2)][PF6]2 5.The complex [Ru(trpy)Cl3] (147 mg, 0.33 mmol) and 140 mg (0.33 mmol) L1(2) were refluxed in 15 mL ethylene glycol under vigorous stirring for 1 h. The solvent was distilled oV and the black residue dissolved in 100 mL water. After removal of unreacted complex by filtration the product was precipitated upon addition of 0.78 g NH4PF6 and filtered oV. Washing twice with 10 mL CH2Cl2 and once with 10 mL and drying to constant weight yielded 235 mg of an orange powder (67%).Recrystallization from a variety of solvents yielded needle like intense red crystals of 5 that were, however, unsuitable for X-ray measurements. 1H NMR (CD3CN): d 8.71 [d, 2 H, H(3), 3J(H3H4) = 8.2]; 8.63 [d, 2 H, H(39), 3J(H39H49) = 8.2]; 8.48 [ddd, 2 H, H(129), 3J(H129H119) = 8.1, 4J(H129H109) = 0.8, 5J129,99 = 0.6]; 8.39 [t, 1 H, H(49), 3J(H49H39) = 7.9]; 8.34 [t, 1 H, H(4), 3J(H4H3) = 7.9]; 8.24 [d, 2 H, H(12), 3J(H12H11) = 8.0]; 7.93 [td, 2 H, H(119), 3J(H119H109) = 7.9, 4J(H119H99) = 1.5]; 7.58 [d, 2 H, H(99), 3J(H99H109) = 5.8]; 7.43 [d, 2 H, H(11), 3J(H11H12) = 8.0]; 7.27 [ddd, 4 H, H(109), 3J(H109H119) = 7.9, 3J(H109H99) = 5.7, 4J(H109H129) = 1.4]; 2.63 [t, 2 H, H(16), 3J(H16H15b) = 5.7, 4J(H16H14) = 5.7]; 2.31 [ddd, 2 H, H(15b), 2J(H15bH15a) = 9.6, 3J(H15bH14) = 5.3, 3J(H15bH16) = 5.4]; 1.79 [dd, 2 H, H(13b), 2J(H13bH13a) = 16.7, 4J(H13bH14) = 2.9]; 1.71 [m, 2 H, H(14)]; 1.67 [dd, 2 H, H(13a), 2J(H13aH13b) = 16.4, 4J(H13bH14) = 3.0]; 1.13 [s, 6 H, H(19)]; [0.70 (d, 2 H, H(15a), 2J(H15aH15b) = 9.9 Hz]; and 20.14 [s, 6 H, H(18)]. NOE (300 MHz, acetonitrile): d 2.63 (1.9 {1.13}); 2.31 (0.6 {1.71}, 2.61 {1.13}); 1.71 (1.6 {1.13}); 1.13 (0.8 {1.71}); 0.70 (1.0 {1.71}; 20.14 (2.7 {1.13}, 2.0% {1.71}).MS(EI): m/z 902 (20, M1 2 PF6); 756 (38, M1 2 2 PF6); 422 (80); 334 (32); 154 (100); and 136 (91%). a (404.6 nm) = 5208, a (365 nm) = 110008 [20 8C, c = 1.017 × 1024 M (5.32 mg in 50 mL acetonitrile)]. DC: silica gel; DMF: 8; H2O: 5 EtOH: 3; NaCl: 0.3; NH4Cl: 0.2; Rf = 0.72.[Ru(L1(2))2][(PF6]2 6. In a 50 mL round flask, 32.8 mg (0.125 mmol) RuCl3?3H2O and 105.4 mg (0.25 mmol) L1(2) were suspended in 3 mL ethylene glycol (Fluka, purum) and refluxed for 4 min in a microwave oven (325 W). The salt NH4PF6 (0.5 g) in 20 mL water was added to the deep red, brownish solution, the precipitate collected in a Buchner funnel, washed with water and a little diethyl ether and recrystallized from acetonitrile–diethyl ether (153 mg, 99%).In another attempt under the same reaction conditions, 53.4 mg (95%) of [Ru((L1(1))2][BPh4]2 were obtained after recrystallization from acetone–pentane starting with 29.9 mg L1(1) and precipitation with NaBPh4. 1H NMR (CD3CN): d 8.61 [d, 2 H, H(3), H(5), 3J(H3H4) = 7.7]; 8.32 [dd, 1 H, H(4), 3J(H4H3) = 7.8]; 8.25 [d, 2 H, H(12), 3J(H12H11) = 7.9]; 7.46 [d, 2 H, H(11), 3J(H11H12) = 7.8]; 2.69 [dd, 2 H, H(16), 3J(H16H15b) = 5.2, 4J(H16H14) = 5.2]; 2.34 [ddd, 2 H, H(15b), 3J(H15bH14) = 5.6, 3J(H15bH16) = 5.6, 2J(H15bH15a) = 9.6]; 2.01 [d, 4 H, H(13a/13b), 3J(H13H14) = 2.1]; 1.78 [m sept, 2 H, H(14)]; 1.16 [s, 6 H, H(19)]; 0.84 [d, 2 H, H(15a), 2J(H15aH15b) = 9.8 Hz];and 20.14 [s, 6 H, H(18)].NOE (300 MHz, acetonitrile): d 8.61 (25.4 {8.25}, 1.2 {2.01}); 8.25 (0.7 {2.01}); 7.46 (9.4 {8.25}, 12.2 {2.69}, 0.5 {2.01}); 2.34 (1.0 {2.69}); 1.16 (3.6 {2.69}); 0.84 (1.0 {2.69}, 1.6 {2.01}); and 20.14 (0.8 {2.69}, 3.5% {2.01}).MS(EI): m/z 1090 (42, M1 2 PF6); 944 (79, M1 2 2 PF6); 518 (42); 472 (50); 154 (100); 136 (>100%). a (404.6 nm) = 114308, a (365 nm) = 125808 [20 8C, c = 7.29 × 1025 M (4.50 mg in 50 mL acetonitrile)]. DC: silica gel; DMF: 8; H2O: 5 EtOH: 3; NaCl: 0.3; NH4Cl: 0.2; Rf = 0.80. [Ru(trpy)(L2(1))]Cl2 7. The complex [Ru(trpy)Cl3] (74 mg) and 70 mg of L2(1) were refluxed in 20 mL of EtOH–water (1 : 1) for 1 d. The solvent was evaporated and the dark residue dissolved in 2 mL of 95% ethanol.After filtration of insoluble material the filtrate was purified by chromatography on a Sephadex LH20 column. The complex was eluted with 95% EtOH and after evaporation of the solvent the product was recovered as an red-orange powder (yield: 66%). The complex [Ru(trpy)(L2(2))]Cl2 8 has been obtained similarly in 76% yield. 1H NMR (CD3OD): d 8.96 (d, 2 H, 3J = 8.1), 8.88 (d, 2 H, 3J = 8.1), 8.72 (d, 2 H, 3J = 8.1), 8.55 (s, 2 H), 8.46 (t, 2 H, 3J = 8.1), 8.01 (dt, 2 H, 3J = 7.9, 4J = 1.4), 7.49 (dd, 2 H, 3J = 5.4, 4J = 0.6), 7.30 (dt, 2 H, 3J = 6.2, 4J = 1.1), 6.92 (s, 2 H), 3.21 (d, 4 H, 3J = 2.3), 2.62 (m, 2 H), 2.56 (dd, 2 H, 3J = 5.6, 4J = 5.6), 2.28 (m, 2 H), 1.29 (s, 6 H), 0.98 (d, 2 H, 3J = 8.9 Hz) and 0.38 (s, 6 H). 13C-{1H} NMR (CD3OD): d 159.93, 157.80, 157.24, 157.05, 153.32, 149.75, 149.53, 148.31, 139.40, 137.53, 137.14, 129.09, 125.97, 125.55, 125.27, 124.18, 45.82, 41.03, 39.91, 34.19, 31.98, 26.10 and 21.50. FAB (3-nitrobenzyl alcohol): m/z = 791, [M 2 Cl]1; and 756, [M 2 2 Cl]1 (Found: C, 55.46; H, 5.78; N, 8.85.Calc. for C44H42Cl2N6Ru 1 7 H2O: C, 55.46; H, 5.88; N, 8.82%). a (589 nm, 20 8C, 0.146 mg in 2 mL of EtOH) = 12748. [Ru(trpy)(L2(2))][PF6]2 8a was prepared for X-ray analysis. [Ru(L2(1))2]Cl2 9. To 30 mg (0.14 mmol) of RuCl3?3H2O in 20 mL of EtOH–water (1 : 1) were added 130 mg (0.31 mmol) of L2(1) and refluxed for 1 d. After evaporation of the solvent the mixture was purified on Sephadex LH20 as described.The complex [Ru(L1(2))2]Cl2 10 was prepared similarly from L2(2) in 56% yield. Quantitative yields were obtained by microwave heating (4 min, 375 W) in ethylene glycol using the same procedure as for [Ru(L1)2][PF6]2. 1H NMR (CD3OD): d 8.85 (d, 4 H, 3J = 8.1), 8.52 (s, 4 H), 8.41 (t, 2 H, 3J = 8.2), 6.91 (s, 4 H), 3.21 (d, 8 H), 2.64 (m, 4 H), 2.56 (dd, 4 H, 3J = 5.6, 4J = 5.6), 2.29 (m, 4 H), 1.30 (s, 12 H), 1.23 (d, 4 H, 3J = 9.6 Hz) and 0.29 (s, 12 H). 13C-{1H} NMR (CD3OD): d 157.83, 157.13, 149.37, 149.29, 148.08, 137.01, 125.40, 124.14, 41.07, 39.94, 34.19, 31.89, 26.04 and 21.44. FAB (3-nitrobenzyl alcohol): m/z = 979, [M 2 Cl]1; and 944 [M 2 2 Cl]1 (Found: C, 60.66; H, 6.87; N, 7.14. Calc. for C58H62Cl2N6Ru 1 7 H2O: C, 61.05; H,670 J. Chem. Soc., Dalton Trans., 1999, 667–675 Table 1 Shifts of protons of the unsubstituted trpy unit upon complexation in [Ru(trpy)2]21 and in [Ru(trpy)(L1(2))]21. The solvent for the complexes is CD3CN.For free trpy CDCl3 was used as solvent trpy [Ru(trpy)2]21 Dd [Ru(trpy)(L1)]21 Dd 39 8.44 8.73 10.29 8.63 10.19 49 7.94 8.39 10.45 8.39 10.45 99 8.68 7.32 21.36 7.58 21.10 109 7.31 7.14 20.17 7.27 20.04 119 7.84 7.90 10.06 7.93 10.09 129 8.60 8.47 20.13 8.48 20.12 6.66; N, 7.37%). a (589 nm, 20 8C, 0.226 mg in 2 mL of EtOH) = 15048. [Ru(L1(2))(L1(1))][PF6]2 11. This was obtained from [Ru(L1(2))Cl3] by adding L1(1) in equimolar amounts using ethylene glycol and microwave heating. However, the product was obtained as a statistical mixture of [Ru(L1(2))2][PF6]2, [Ru(L1(1))2][PF6]2 and [Ru(L1(2)(L1(1))][PF6]2 (1:1:2).Other solvents with milder conditions (refluxing in EtOH–water) always led to the statistical mixture. Separation of the diastereomers was unsuccessful. 1H NMR (CD3CN): d 8.61 [d, 2 H, H(3)]; 8.31 [dd, 1 H, H(4)]; 8.26 [d, 2 H, H(12)]; 7.48 [d, 2 H, H(11)]; 2.69 [dd, 2 H, H(16)]; 2.35 [ddd, 2 H, H(15b)]; 2.01 [d, 4 H, H(13a/13b)]; 1.78 [m sept, 2 H, H(14)]; 1.15 [s, 6 H, H(19)]; 0.61 [d, 2 H, H(15a)]; and 20.01 [s, 6 H, H(18)].X-Ray crystallography Details of the crystal parameters, data collection and refinement are given in Table 6. The structures were solved by direct methods and refined by the full-matrix least-squares method on all F data, except for [Rh(L1(2))Cl3] which was refined on all F 2 with an extinction correction to all Fc data. No absorption corrections were applied for [Ru(L1(2))Cl3] and [Ru(trpy)- (L2(2))][PF6]2 For [Rh(L1(2))Cl3] no suitable y scans could be measured, and only one equivalent of data was obtained.With m = 1.02 mm21 and a reasonably low residual electron density (1.162/21.011 e A3) no absorption correction was applied. All crystals were stable during the measurements. The H atoms were located on Fourier diVerence maps, but introduced in idealized positions [d(CH) = 0.96 Å] and their atomic coordinates recalculated after each cycle.They were given isotropic thermal parameters 20% higher than those of the carbon to which they are attached. The absolute configurations for all resolved compounds were examined by refining Flack’s parameter x. The absolute configuration cannot be determined reliably for L2(2), whereas for all other compounds the x value is in accord with the absolute configuration expected from the synthetic route. CCDC reference number 186/1310. See http://www.rsc.org/suppdata/dt/1999/667/ for crystallographic files in .cif format. Apparatus and chemicals used For the synthesis of reactants solvents of Fluka purum grade quality were used without further treatment.For spectroscopic purposes, acetonitrile from Aldrich (puriss. for spectroscopy) was used. The compound RuCl3?3H2O (Johnson Matthey) was used as ruthenium source. The NMR spectra were recorded using Bruker AM-250 (250 MHz), Varian Gemini300 (300 MHz) and Bruker DRX500 (500 MHz) spectrometers. The chemical shift values are reported relative to tetramethylsilane.The 2-D COSY and heteronuclear correlation (HETCOR) spectra as well as NOE were obtained according to standard procedures, MS (FAB) spectra on a VG Instruments 7070E spectrometer or with a quadripolar Nermag R10-10H instrument (3-nitrobenzyl alcohol matrix). Elemental analyses were performed by LCC (Laboratoire de Chimie de Coordination) Microanalytical Service. The UV-VIS absorption was determined using a Perkin-Elmer Lambda 5 spectrophotometer with 1 cm quartz cells.Column chromatography purification was performed with 70–200 mm Silica gel or on Sephadex LH20 (Pharmacia). For thin layer chromatography silica gel plates (Merck 60 F254) were used. Optical rotations were measured on a Perkin-Elmer polarimeter 241. The CD spectra were measured on a Dichrograph Mark 5 from Yobin Ivon in a 1 cm quartz cell. Crystal structures were measured on Stoe IPDS and on Stoe-Siemens four-circle AED-2 diVractometers (graphite-monochromated Mo-Ka radiation).Results and discussion Synthesis The Kröhnke condensation 22 of chiral b-unsaturated ketones or aldehydes opens an eYcient way to chiral terpyridines and their metal complexes. Microwave heating aVorded quantitatively bis(terpyridyl)ruthenium(II) complexes of high purity, with typical heating times of only 2–4 min. This procedure shows great advantages over previously reported synthetic methods for the preparation of such complexes in boiling aqueous ethanol.23–25 As an example, for the preparation of [Ru(trpy)2][PF6]2 the yield decreased from 86 (ethylene glycol, 4 min, 375 W) to 65 (ethanol, 3 h) or 21% (DMF, 3 h).It is known that pineno-fused bipyridines can be linked stereoselectively 12,27 by formally substituting H(13). Methylation of L1(2) yields only one diastereoisomer. Ligands of this type are presently being studied and will be reported elsewhere. NMR Table 1 shows relevant protons of the trpy unit with their chemical shifts for the ‘free’ and complexed ligand in [Ru(trpy)2]21 and in [Ru(trpy)(L1(2))]21.The chemical shift of certain protons is highly diagnostic for their environment. In [Ru(trpy)2]21 the proton 99 lies above the plane of the central pyridine ring of the other orthogonal ligand and is thus shifted upfield. In [Ru(trpy)(L1(2))]21 the shielding is less eYcient, which may indicate that proton 99 is pushed away from the face of the opposing central pyridine ring, probably due to the Fig. 1 The NMR signals of a statistical mixture of D2 and S4 symmetric [Ru(L1)2][PF6]2 for the aliphatic protons 15a and 18.J. Chem. Soc., Dalton Trans., 1999, 667–675 671 Table 2 Shifts of protons of free L1(2) as compared with those of [Ru(L1(2))2]21, [Ru(trpy)(L1(2))]21 and [Ru(L1(2)(L1(1))]21; CD3CN was used as solvent L1(2) [Ru(trpy)(L1(2))]21 Dd [Ru(L1(2))2]21 Dd [Ru(L1(2)(L1(1))]21 Dd 3 8.28 8.71 10.43 8.61 10.33 8.61 10.33 4 7.88 8.34 10.46 8.32 10.44 8.31 10.43 13a/b 3.20 1.73 21.47 2.01 21.15 2.01 21.15 14 2.40 1.71 20.69 1.78 20.62 1.78 20.62 15a 1.31 0.70 20.61 0.84 20.57 0.61 20.70 15b 2.70 2.31 20.39 2.34 20.36 2.35 20.35 16 2.81 2.63 20.18 2.69 20.12 2.69 20.12 18 0.68 20.14 20.82 20.14 20.82 20.01 20.69 19 1.41 1.13 20.28 1.16 20.25 1.15 20.26 crowding of the pinene groups of the other ligand.The protons 39 and 49 are slightly shifted downfield upon complexation due to their position in the deshielding plane of the two terminal pyridine rings of the orthogonal ligand.The protons 13a/b, 14, 15a/b, 18 and 19 of L1(2) lie above the plane of the central aromatic pyridine ring and are therefore considerably shifted upfield (Table 2, Fig. 1). In a 1 : 1 complex the protons 13a/b, 15a/b and 19, however, would not be so much shifted as compared to those of the 2 : 1 complex. This is clearly the case for [Rh(L1(2))Cl3]. For the complex [Ru(trpy)(L2(1))]21 the chemical shifts of the aliphatic protons of L2 are much closer to those of free L2 and the upfield shift is less pronounced due to the fact that the pinene group will not come close to the deshielding plane of the orthogonal pyridyl moiety. Electronic spectra The electronic spectra of all complexes (Figs. 2–5, Table 4) are characterized by intense absorptions between 200 and 380 nm attributed to p æÆ p* transitions associated with the aromatic rings of the ligand. Metal to ligand charge transfer (MLCT) Fig. 2 Ligand centered absorption of trpy (a), L1(2) (b), [Ru(trpy)(L1(2))]21 (c), [Ru(trpy)2]21 (d), and [Ru(L1(2))2]21 (e) in acetonitrile (1 × 1025 M). Fig. 3 The CD-spectra of trpy (a), L1(2) (b), [Ru(trpy)(L1(2))]21 (c) and [Ru(L1(2))2]21 (d) in acetonitrile (1 × 1025 M). transitions are observed for the ruthenium complexes at around 450 nm. The absorption spectra of L1(2), [Ru(trpy)2]21, [Ru(trpy)(L1(2))]21 and [Ru(L1(2))2]21 (Fig. 2) show components in the ligand centered absorptions which can be attributed to short and long axis polarized p æÆ p* transitions.For L1(2) C2 symmetry, the long axis transition transforms as A, the short axis transition as B, in trpy as A1 and B1, respectively. ZINDO Calculations (INDO/1 parameterization,27 active space for singlet/triplet CI within 38 orbitals lying below and above the HOMO/LUMO pair) indicate that the lowest lying Fig. 4 The CD spectra of [Ru(L1(1))2]21 (a) and [Ru(L1(2))2]21 (b) in acetonitrile (1 × 1025 M) and of [Ru(trpy)(L2(1))]21 (c) and [Ru(trpy)(L2(2))]21 (d) in Tris buVer.Fig. 5 Absorption (a,b) and circular dichroism spectra (c,d) of the MLCT transition of [Ru(trpy)(L1(2))]21 (dashed line) and [Ru(L1(2))2]21 (full line) in acetonitrile (2 × 1024 M).672 J. Chem. Soc., Dalton Trans., 1999, 667–675 Table 3 Calculated versus experimental transitions for trpy and L1(2). The main single determinants after CI are listed in brackets Trpy L1(2) Short-axis polarized Long-axis polarized Long-axis polarized Calc.(l/nm, f a) 215 (0.32) |1A1;a2(p) æÆ a2(p*)Ò 274 (0.29) |1B1;a2(p) æÆ b2(p*)Ò Measured (l/nm, e/M21 cm21) 236 (38400) 260 (20200) Calc. (l/nm, f a) 297 (0.52) |1A1;a2(p) æÆ a2(p*)Ò 266 (0.58) |1B1;b2(p) æÆ a2(p*)Ò 315 (0.45) |1B1;a2(p) æÆ b2(p*)Ò Measured (l/nm, e/M21 cm21) 289 (sh) 300 (55000) 278 (45000) 258 (34000) 296 (52000) 318 (sh) a f is oscillator strength. Table 4 Possible MLCT and LC transitions in for a D2d symmetrical d6 complex [Ru(trpy)2]21 MLCT LC Transitions b2 æÆ b1 b2 æÆ e b2 æÆ a2 a2 æÆ e a2 æÆ b1 a2 æÆ a2 b1 æÆ e b1 æÆ b1 Corresponding states A1 æÆ A2 A1 æÆ E A1 æÆ B1 A1 æÆ E A1 æÆ B2 A1 æÆ A1 A1 æÆ E A1 æÆ A1 Transitions e æÆ b1 e æÆ e e æÆ a2 b1 æÆ a2 e æÆ e e æÆ b1 e æÆ a2 Corresponding states A1 æÆ E A1 æÆ A1, A2, B1, B2 A1 æÆ E A1 æÆ B2 A1 æÆ A1, A2, B1, B2 A1 æÆ E A1 æÆ E p æÆ p* transitions [260 nm for trpy, 296 nm for L1(2)] are long axis polarized (Table 3).The corresponding MO scheme of [Ru(trpy)2]21 is depicted in Fig. 6.For all metal complexes the LC transitions are shifted to lower energy as compared to those of ‘free;’ ligand due the positive charge of the central metal, which increases the energy of the lowest p orbital of the ligand. This behavior was also observed for complexes of the tris-(bipyridyl) type.28 The MLCT transitions carry large intensities if the electron flow is parallel to the electric dipole moment.29 The electron flow during a MLCT transition is directed along the S4 axis (z axis) which transforms as B2.Therefore, the most intense MLCT transition is attributed to |1B2;e(dxy,dyz) æÆ e(p*)Ò.30,31 Emission properties have not been investigated in detail. At room temperature no emission is detectable as the excited state lifetimes of ruthenium(II) bis(terpyridyl) complexes are expected to be very short, i.e. for [Ru(trpy)2]21 t = 250 ps in water.32 CD Spectra Cotton eVects can be conveniently classified into three types by considering the symmetry properties and the nature of the Fig. 6 Qualitative MO scheme of [Ru(trpy)2]21 (D2d) and trpy (C2v). chromophores and their transitions: (I) from inherently achiral chromophores which are asymmetrically perturbed; (II) from inherently chiral chromophores; (III) due to dipole–dipole interactions between more than two chromophores, the orbitals of which do not mutually overlap. The amplitudes of Cotton eVects of type I are usually very small.Free L1 or L2 is such a case where a chiral substituent imposes a dissymmetric environment. The CD spectrum of L1(2) [Fig. 3(a)] is similar to those of (1)-a-pinene and other pyridines with pinene groups attached.12 However in the case of the reported complexes with L1, stronger CD in the LC absorptions indicates that eVects of type II or III must be present (Fig. 3). All enantiomeric pairs show mirror image CD as exemplified in Fig. 4. As crystal structure analyses of [Rh(L1(2))Cl3] and [Ru(L1(2))Cl3] show (Fig. 7), a helical distortion of the ligand p system occurs upon complexation, which is less pronounced in the complex [Ru(trpy)(L2(2))][PF6]. (Fig. 8). In free L1 the pyridyl moieties have a low energy barrier for rotation around the 2,29 and 29,60 bonds, whereas upon complexation rotation is excluded and the ligand is forced to take a helically distorted geometry. As a result of this helicity, all MLCT transitions show significant CD, which would not be present if the two ligand p systems were planar and strictly perpendicular (even though with chiral substituents) to each other.The sign of the CD bands of MLCT transitions can be derived from symmetry consideration of the orbitals involved. The condition to observe for rotational strength is ·a|m Æ|bÒ·a|mÆ |bÒ � 0. The z-axis directed MLCT transition in D2d |1B2;e(dxy,dyz) æÆ e(p*)Ò that carries most intensity becomes |1B1;b(dxy,yz) æÆ b(p*)Ò in D2 and |1A;b(dxy,yz) æÆ b(p*)Ò in C2, respectively, and in both cases transforms as Rz.Therefore these transitions also have non-zero rotational strengths. The sign of the CD of z-axis polarized transitions being only a function of the helicity of the p orbital involved, one finds that a left handed helical arrangement as in the crystal structure of [Ru(L1(2))Cl3] (Fig. 7) leads to a left handed charge displacement corresponding to a negative CD. This is observed for the strongest MLCT transitions of these complexes, which are therefore tentatively assigned to |1B1;b((dxz,yz) æÆ b(p*)Ò (Fig. 5). The CD activity in the LC transitions of bis(terpyridyl) complexes (Fig. 3) mainly arise from exciton coupling 33 between two intraligand transitions or between two diVerent terpyridyl ligands which have nonorthogonal transition dipole moments d to the out of plane distortion of the terpyridyl moiety. From the CD and UV-VISJ. Chem. Soc., Dalton Trans., 1999, 667–675 673 spectra the exciton splitting is determined to be around 1000 cm21 for the long axis polarized transition at around 315 nm (Fig. 3) of [Ru(L2)2]21. The observed Cotton eVect is consistent with a ligand geometry as found in [Ru(L1(1))Cl3] (Fig. 7). As the terpyridyl ligand L2 is somewhat less distorted in the ruthenium complexes than is the ligand L1, CD values recorded for [Ru(L2)2]21 and [Ru(trpy)(L2)]21 (Fig. 4) are smaller than those of [Ru(L1)2]21 and [Ru(trpy)(L1)]21. Therefore, we conclude that the transitions observed are due to the intrinsic helical arrangement of the ligand fixed at a metal center.Cyclic voltammetry In comparison to [Ru(trpy)2]21, the oxidation potentials of [Ru(trpy)(L1(2))]21 and [Ru(L1(2))2]21 are slightly increased Fig. 7 Molecular views of [Ru(L1(2))Cl3] (with hydrogens) and [Rh(L1(2))Cl3] (without hydrogens) with 50% probability thermal ellipsoids depicted. (Table 5). It is also evident that the first reduction in [Ru(trpy)(L1(2))]21 occurs in the trpy moiety since its reduction potential is equivalent to that of [Ru(trpy)2]21.The ligand L1(2) is a slightly weaker p* acceptor with respect to trpy and it has therefore a slightly lower reduction potential. Crystallographic data Selected bond lengths, angles and dihedral angles of [Rh(L1(2))Cl3] and [Ru(L1(2))Cl3] are given in Table 7, lengths and angles of [Ru(trpy)(L2(2))][PF6]2 in Table 8. The molecular structures of [Rh(L1(2))Cl3] and [Ru(L1(2))Cl3] are shown in Fig. 7. The helical out of plane distortion of the terpyridyl moiety is evident. The twisting angle between the two distant pyridine rings is 32 and 318 for the two complexes and the absolute configuration of these two rings can be denoted as L using the IUPAC designation for a pair of skew lines. The molecular structures of L2(2) and [Ru(trpy)(L2(2))]Cl2 with the atom numbering schemes are shown in Fig. 8. That of L2(2) possesses a twofold axis relating two asymmetric units through N(1) and C(3).The main part of the molecule is planar with the largest deviation being 0.168 Å at N(1). Only the C atoms of the pinene fragment are out of the plane with C(11) and C(13) being away from it by 1.13 and 21.10 Å. The cation [Ru(trpy)(L2(2))]21 adopts a six-coordinate geometry with a mer conformation of the two terpyridyl ligands which make a dihedral angle of 95.28. The distances between Ru and the central N(1) or N(4) atoms, 1.982(6) and 1.957(6) Å respectively, are significantly shorter than the values observed for the other Ru–N bonds, 2.065 Å (mean), and are comparable with the distances in [Ru- (L1(2))Cl3].Conclusion Mono- or bis- 2,29;69,60-terpyridyl complexes of octahedral co-ordination centers have often been considered to be valuable alternatives to bis- or tris-diimine complexes, because the problem of chirality, leading to isomeric mixtures in synthesis, can be avoided.This is due to the fact that terpyridyl ligands can co-ordinate exclusively in a meridional way in an Table 5 Electrochemical data for [Ru(trpy)2]21, [Ru(trpy)(L1(2))]21 and [Ru(L1(2))2]21 Complex [Ru(trpy)2]21 [Ru(trpy)(L1(2))]21 [Ru(L1(2))2]21 E0/V 1.28 (0.09) 1.31 (0.10) 1.34 (0.10) E1/DE 21.27 (0.08) 21.26 (0.08) 21.37 (0.08) E2/V 21.52 (0.10) 21.64 (0.10) 21.67 (0.10) Ia/Ic 0.98 0.95 0.85 Fig. 8 Molecular views of L2(2) and [Ru(trpy)(L2(2))][PF6]2 with 30% probability thermal ellipsoids depicted.674 J.Chem. Soc., Dalton Trans., 1999, 667–675 Table 6 Crystallographic data of L2(2), [Ru(trpy)(L2(2))][PF6]2 8a, [Ru(L1(2))Cl3] 2 and [Rh(L1(2))Cl3] 3 Molecular formula Molecular weight Crystal system Space group a/Å b/Å c/Å V/Å3 ZT /K m/mm21 No. reflections measured No. unique reflections Rint Flack’s parameter Final R values Goodness of fit L2(2) C29H31N3 421.63 Orthorhombic P21221 6.5893(9) 9.080(1) 19.494(4) 1167.0(2) 2 293(2) 0.066 7285 1783 0.032 R(F) = 0.0363 wR(F) = 0.0317 1.054 8a C44H42F12N6P2Ru 1045.91 Orthorhombic P212121 9.508(1) 12.745(2) 37.781(4) 4578(1) 4 293(2) 0.489 16335 4800 0.059 0.03(5) R(F) = 0.0440 wR(F = 0.0499 1.130 2 C32H37Cl3N3ORu 687.10 Orthorhombic P212121 7.9867(7) 15.6250(13) 25.199(2) 3144.6(4) 4 180(2) 0.77 20175 4945 0.0431 20.03(4) R(F) = 0.0217 wR(F) = 0.0244 1.063 3 C29H31Cl3N3Rh 630.85 Orthorhombic P212121 7.9810(10) 15.571(2) 24.630(2) 3060.8(6) 4 193(2) 1.02 3075 3072 0 20.05(5) R(F2) = 0.0396 wR(F 2) = 0.1020 1.101 octahedral complex.Monoterpyridyl complexes therefore have inherently C2V symmetry, bis(terpyridyl) complexes D2d, both achiral symmetry groups. The chiral terpyridyl ligands that are introduced here reduce these symmetries to C2 and D2, respectively (at least for the bis-homochiral terpyridine complex). Since the synthesis of the chiral terpyridyl ligands, derived from that of the earlier published and very versatile method for bipyridine derivatives, yields enantiopure material from natural products, the problem of isomeric mixtures does not occur any more, even though the resulting complexes are chiral.This fact adds a new dimension to the chemistry of octahedral complexes with terpyridyl ligands. For chiral structures, additional spectroscopic information is available from CD spectra. There is also a possibility to study interactions of such complexes with other chiral structures and finally there might be the possibility to build up relatively large linear structures that have a “chiral twist”.The introduction of the chiralized terpyridyl ligands, opens up the already quite varied chemistry of terpyridyl Table 7 Selected bond lengths (Å), angles and angles between the planes of the pyridyl moieties (8) for [Rh(L1(2))Cl3] and [Ru(L1(2))Cl3] where P2 and P3 denote the outer pyridine ring with N(2) and N(3) respectively, P1 the central pyridine ring with N(1) M–Cl(1) M–Cl(2) M–Cl(3) M–N(1) M–N(2) M–N(3) Cl(1)–M–Cl(2) Cl(1)–M–Cl(3) Cl(1)–M–N(1) Cl(1)–M–N(2) Cl–M–N(3) Cl(2)–M–Cl(3) Cl(2)–M–N(1) Cl(2)–M–N(2) Cl(2)–M–N(3) Cl(3)–M–N(1) Cl(3)–M–N(2) Cl(3)–M–N(3) N(1)–M–N(2) N(1)–M–N(3) N(2)–M–N(3) P1/P2 P1/P3 P2/P3 [Ru(L1(2))Cl3] 2.3729(14) 2.3331(16) 2.3365(16) 1.942(5) 2.110(5) 2.111(5) 91.09(6) 92.00(6) 179.66(16) 99.89(14) 100.03(15) 176.82(6) 88.74(16) 89.86(14) 88.97(14) 88.17(16) 90.30(14) 89.80(14) 79.82(21) 80.25(21) 160.07(20) 14.9(3) 18.8(3) 32.0(3) [Ru(L1(2))Cl3] 2.3794(6) 2.3322(7) 2.3504(7) 1.967(2) 2.147(2) 2.139(2) 93.04(2) 92.29(2) 179.70(6) 100.78(6) 100.37(6) 174.66(3) 86.85(6) 89.64(6) 89.05(6) 87.82(6) 89.14(6) 90.21(6) 79.51(9) 79.34(9) 158.85(8) 18.85(13) 13.08(13) 30.72(13) complexes using these ligands which introduce a well defined chiral element.Acknowledgements We thank Dominique Suhr for assistance in the synthesis of ligand L1(1), Dr Catherine Verchère-Béaur for measuring CD spectra of [Ru(trpy)(L2)]Cl2, Professor Peter Belser for advice concerning the synthesis of ruthenium complexes, and Professor R.Chauvin for fruitful discussion. The Swiss National Science Foundation and the Centre National de la Recherche Scientifique are acknowledged for financial support. References 1 J.-P. Collin, P. Gavina, V. Heitz and J.-P. Sauvage, Eur. J. Inorg. Chem., 1998, 1, 1. 2 E. C. Constable and A. W. C. Thompson, J. Chem. Soc., Dalton Trans., 1992, 2947. 3 J. P. Collin, S.Guillerez, J. P. Sauvage, F. Barigelletti, L. D. Cola, L. Flamigni and V. Balzani, Inorg. Chem., 1991, 30, 4230. 4 B. J. Coe, D. W. Thomson, C. T. Culbertson, J. R. Schoonover and T. J. Meyer, Inorg. Chem., 1995, 34, 3385. 5 D. J. Cardenas, P. Gavina and J. P. Sauvage, Chem. Commun., 1996, 1915. 6 G. S. Hanan, C. R. Arana, J. M. Lehn, G. Baum and D. Fenske, Chem. Eur. J., 1996, 2, 1292. 7 L. M. Scolaro, A. Romeo and A. Terracina, Chem. Commun., 1997, 1451. 8 V. Grosshenny, A.Harriman, M. Hissler and R. Ziessel, Platinum Metals Rev., 1996, 40, 72. 9 F. Barigelletti, L. Flamigni, V. Balzani, J.-P. Collin, J.-P. Sauvage and A. Sour, New J. Chem., 1995, 19, 793. 10 H. M. Brothers and N. M. Kostic, Inorg. Chem., 1988, 27, 1761. Table 8 Interatomic distances (Å) and angles (8) for [Ru(trpy)- (L2(2))][PF6]2 Ru(1)–N(1) Ru(1)–N(2) Ru(1)–N(3) N(1)–Ru(1)–N(2) N(1)–Ru(1)–N(3) N(2)–Ru(1)–N(3) N(1)–Ru(1)–N(4) N(2)–Ru(1)–N(4) N(3)–Ru(1)–N(4) N(1)–Ru(1)–N(5) N(2)–Ru(1)–N(5) 1.982(6) 2.066(6) 2.064(6) 78.7(3) 79.7(3) 158.4(3) 177.5(3) 103.9(3) 97.7(2) 101.0(3) 89.4(2) Ru(1)–N(4) Ru(1)–N(5) Ru(1)–N(6) N(3)–Ru(1)–N(5) N(4)–Ru(1)–N(5) N(1)–Ru(1)–N(6) N(2)–Ru(1)–N(6) N(3)–Ru(1)–N(6) N(4)–Ru(1)–N(6) N(5)–Ru(1)–N(6) 1.957(6) 2.073(7) 2.057(6) 95.5(2) 79.0(3) 101.0(3) 92.9(2) 90.3(3) 79.0(3) 157.9(3)J. Chem.Soc., Dalton Trans., 1999, 667–675 675 11 H. Shirai, K. Hanabusa, Y. Takahashi, F. Mizobe and K. Hanada, PCT Int. Appl., WO 94 14440 (Cl. A61K31/44), 7 July 1994, JP Appl. 92/348, 684, 28 Dec 1992, (Chem. Abstr., 121: 195935f). 12 N. C. Fletcher, F. R. Keene, M. Ziegler, H. Stoeckli-Evans, H. Viebrock and A. Von Zelewsky, Helv. Chim. Acta, 1996, 79, 1192. 13 H. Mürner, P. Belser and A. Von Zelewsky, J. Am. Chem. Soc., 1996, 118, 7989. 14 H. Mürner, G. Hopfgartner and A. Von Zelewsky, Inorg. Chim. Acta, 1998, 271, 36. 15 P. Hayoz, A. Von Zelewsky and H. Stoeckli-Evans, J. Am. Chem. Soc., 1993, 115, 5111. 16 E. C. Constable, T. Kulke, M. Neuburger and M. Zehnder, Chem. Commun., 1997, 489. 17 (a) R. Glaser, Chirality, 1993, 5, 272; (b) A. Horeau, personal communication and Collège de France lectures; (c) K. Mislow, Bull. Soc. Chim. Fr., 1994, 131, 534. 18 B. P. Sullivan, J. M. Calvert and T. J. Meyer, Inorg. Chem., 1980, 19, 1404. 19 E. C. Constable, J. Chem. Soc., Dalton Trans., 1985, 2687. 20 E. D. Mihelich and D. J. EickhoV, J. Org. Chem., 1983, 48, 4135. 21 R. K. De Richter, M. Bonato, M. Follet and K. Jean-Marc, J. Org. Chem., 1990, 55, 2855. 22 F. Kröhnke, Synthesis, 1976, 1. 23 D. Rose and G. Wilkinson, J. Chem. Soc., A., 1970, 1791. 24 T. J. Meyer and J. N. Braddock, J. Am. Chem. Soc., 1973, 95, 3158. 25 M. L. Stone and G. A. Crosby, Chem. Phys. Lett., 1981, 79, 169. 26 P. Hayoz and A. Von Zelewsky, Tetrahedron Lett., 1992, 33, 5165. 27 W. P. Anderson, T. R. Cundari, R. S. Drago and M. C. Zerner, Inorg. Chem., 1990, 29, 1. 28 I. Hanazaki and S. Nagakura, Inorg. Chem., 1969, 8, 648. 29 P. Day and N. J. Sanders, J. Chem. Soc. A, 1967, 1536. 30 C. Daul, C. W. Schlaepfer, A. Goursot, E. Penigault and J. Weber, Chem. Phys. Lett., 1981, 78, 304. 31 C. Daul and J. Weber, Chem. Phys. Lett., 1981, 77, 593. 32 J. R. Winkler, T. L. Netzel, C. Creutz and N. J. Sutin, J. Am. Chem. Soc., 1987, 109, 2381. 33 M. Ziegler and A. Von Zelewsky, Chem. Coord. Rev., 1998, in the press. Paper 9/00194H

ISSN:1477-9226    

DOI:10.1039/a900194h

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 677–682 677 Equilibrium and kinetic studies of (2,29:69,20-terpyridine)gold(III) complexes. Preparation and crystal structure of [Au(terpy)(OH)][ClO4]2 Bruno Pitteri,*a Giampaolo Marangoni,a Fabiano Visentin,a Tatiana Bobbo,a Valerio Bertolasi b and Paola Gilli b a Dipartimento di Chimica, Università di Venezia, Calle Larga S. Marta 2137, 30123 Venezia, Italy b Dipartimento di Chimica e Centro di Strutturistica Diffrattometrica, Università di Ferrara, Via Borsari 46, 44100 Ferrara, Italy Received 3rd August 1998, Accepted 23rd December 1998 Kinetic and equilibrium studies of the processes (1) and (2) (terpy = 2,29:69,20-terpyridine) have been carried out in [Au(terpy)Cl]21 1 H2O k1 k21 [Au(terpy)(OH2)]31 1 Cl2 (1) [Au(terpy)(OH2)]31 Ka [Au(terpy)(OH)]21 1 H1 (2) water at 25 8C, I = 0.1 mol dm23 (LiClO4).Owing to the high charge of the metal centre, the [Au(terpy)(OH2)]31 cation behaves as a strong acid (Ka > 0.8 mol dm23) and dissociates completely into the corresponding hydroxo species, which can be isolated in the solid state as its perchlorate.The crystal structure of [Au(terpy)(OH)][ClO4]2 has been determined by the single-crystal X-ray diVraction technique. It consists of SP (square planar) [Au(terpy)- (OH)]21 cations having Au–N distances of 2.009(5), 2.008(4) and 1.949(4) Å and an Au–OH distance, the first experimentally determined, of 2.000(4) Å. The SP geometry is expanded to distorted tetragonal bipyramidal (TBPY) by linking the two perchlorate anions with Au–O distances of 3.023(8) and 3.069(8) Å, which are intermediate between bonding and van der Waals interactions.The secondary co-ordination phenomenon in gold(III) SP complexes is reviewed and a possible reason for its occurrence proposed. Introduction In the last few years there has been much interest in terpy complexes of platinum(II) and palladium(II) (terpy = 2,29:69,20- terpyridine) in connection with the discovery that they show specific interactions with nucleic acids 1 as well as their intriguing spectroscopic and photophysical behaviour.2 Besides, co-ordination compounds of the two metal ions have provided useful substrate for kinetic studies in substitution reactions at planar four-co-ordinate complexes.On the contrary, the chemistry of the related gold(III) complexes has remained undeveloped and the only species to have been reported are [Au(terpy)Cl]Cl2?3H2O and the mixed-valence compound [Au(terpy)Cl]2[AuCl2]3[AuCl4], both of which have been structurally characterized.3 For the former a study of the product distribution in aqueous solution as a function of pH has also been reported.As a continuation of our studies on the synthesis and reactivity of d8 transition-metal complexes containing the terpy ligand 4–7 we have isolated the complex [Au(terpy)(OH)]- [ClO4]2, the crystal structure of which is here reported, together with a kinetic and equilibrium study of the processes (1) and (2) in water, I = 0.1 mol dm23 (LiClO4), at 25 8C.[Au(terpy)Cl]21 1 H2O k1 k21 [Au(terpy)(OH2)]31 1 Cl2 (1) A B [A u(terpy)(OH2)]31 Ka [Au(terpy)(OH)]21 1 H1 (2) B C Experimental Materials The salt KAuCl4?2H2O was prepared according to a standard procedure starting from metallic Au (99.99%). 2,29:69,20- Terpyridine was obtained from Aldrich. Pure reagent grade LiCl, LiClO4 and AgClO4 (Fluka and Aldrich) were dried over P2O5 in a vacuum desiccator and used without further purification.Instruments Infrared spectra (4000–250 cm21, KBr discs and Nujol mulls; 400–150 cm21, polyethylene pellets) were recorded on a Nicolet Magna FT IR 750 spectrophotometer. Electronic spectra and kinetics measurements were obtained on a Perkin-Elmer Lambda 15 spectrophotometer. Proton NMR spectra were taken on a Bruker AC 200 F spectrometer. Conductivity measurements were carried out with a CDM 83 Radiometer Copenhagen conductivity meter and a CDC 334 immersion cell.Elemental analyses were performed by the Microanalytical Laboratory of the University of Padua. Preparation of complexes Chloro(2,29:69,20-terpyridine)gold(III) chloride trihydrate, [Au(terpy)Cl]Cl2?3H2O. The preparation of this compound has been reported 3 but we used KAuCl4?2H2O instead of HAuCl4? 3H2O as starting material. Chloro(2,29:69,20-terpyridine)gold(III) perchlorate, [Au(terpy)- Cl][ClO4]2.The complex [Au(terpy)Cl]Cl2?3H2O (0.591 g, 1 mmol) was dissolved in hot water (40 cm3). After addition of an excess of solid LiClO4, slow cooling of the solution at room temperature resulted in the formation of the ochre crystalline product, which was filtered oV, washed with cold water (2–3 cm3) and dried in vacuo. Yield > 90% (Found: C, 27.2; H, 1.50;678 J. Chem. Soc., Dalton Trans., 1999, 677–682 Cl, 16.1; N, 6.32. C15H11AuCl3N3O8 requires C, 27.1; H, 1.67; Cl, 16.0; N, 6.32%).LM (dmf = dimethylformamide) = 179 W21 cm2 mol21. IR: n& (Au–Cl) = 353 cm21 (polyethylene pellets). Hydroxo(2,29:69,20-terpyridine)gold(III) perchlorate, [Au- (terpy)(OH)][ClO4]2. Silver perchlorate (0.207 g, 1 mmol) was added to a hot aqueous solution (50 cm3) of [Au(terpy)- Cl][ClO4]2 (0.665 g, 1 mmol) and the mixture stirred in the dark for 30 min. The AgCl formed was filtered oV and the warm solution treated with an excess of solid LiClO4. On slow cooling of the solution at room temperature, well formed beige crystals were separated, then filtered oV, washed with the minimum amount of cold water and dried in vacuo. Yield ª 80% (Found: C, 27.8; H, 1.62; Cl, 11.2; N, 6.42.C15H12AuCl2N3O9 requires C, 27.9; H, 1.87; Cl, 11.0; N, 6.50%). LM (dmf) = 160 W21 cm2 mol21. IR: n& (O–H) = 3425 cm21 (Nujol mulls). Kinetics The forward process was followed spectrophotometrically by measuring the changing absorbance at a suitable wavelength (366 nm) as a function of time and initiated by adding 2–20 ml of a 0.015 mol dm23 dmf solution of the substrate complex, [Au(terpy)Cl][ClO4]2, to 3 cm3 of an aqueous solution of 0.1 mol dm23 LiClO4 previously brought to the reaction temperature (25 8C) in a thermostatted cell in the spectrophotometer. The reverse process was followed starting from a l × 1025 mol dm23 aqueous solution of [Au(terpy)(OH)][ClO4]2 with an excess of chloride, in order to provide pseudo-first-order conditions, in the presence of added acid (HClO4). Pseudo-firstorder rate constants (kobs/s21) were obtained either from the gradients of plots of log(Dt 2 D•) vs.time or from a non linear least-squares fit of experimental data from the equation Dt = D• 1 (Do 2 D•)exp(2kobst), where Do, D• and kobs are the parameters to be optimized (Do = absorbance after mixing of reactants, D• = absorbance at completion of reaction). Errors on individual kobs determinations are in the ±5% range.8 1H NMR experiments Experimental conditions: solvent D2O, solvent peak at d 4.65 vs.Me4Si as reference, 25 8C. (a) 0.035 mol dm23 [Au(terpy)- Cl]Cl2?3H2O: d 9.17 (2 H, d, J = 6 Hz; Ha), 8.70 (7 H, m, Hc,d,e,f) and 8.04 (2 H, m, Hb). (b) 0.017 mol dm23 [Au(terpy)- Cl]Cl2?3H2O and 0.1 mol dm23 Cl2: d 9.17 (2 H, d, J = 6 Hz, Ha), 8.70 (7 H, m, Hc,d,e,f) and 8.04 (2 H, m, Hb). (c) 0.004 mol dm23 [Au(terpy)(OH)][ClO4]2: d 8.82 (2 H, d, J = 5.8 Hz; Ha), 8.61 (7 H, m, Hc,d,e,f) and 8.03 (2 H, m, Hb). (d) 0.002 mol dm23 [Au(terpy)(OH)][ClO4]2 and 0.1 mol dm23 Cl2: d 8.82 (2 H, d, J = 5.8 Hz; Ha), 8.61 (7 H, m, Hc,d,e,f) and 8.03 (2 H, m, Hb).(e) 0.002 mol dm23 [Au(terpy)Cl][ClO4]2: signals of both [Au(terpy)Cl]21 and [Au(terpy)(OH)]21 cations in ª2 : 1 ratio. Crystallography X-Ray intensities were collected at room temperature on an Enraf-Nonius CAD4 diVractometer using graphite monochromated Mo-Ka radiation (l = 0.71069 Å) with the w–2q scan technique.Lattice constants were determined by leastsquares fitting of the setting angles of 25 reflections in the range 9 < q < 148. Intensities of three standard reflections were measured every 2 h and did not show significant variations. All N N N X f d e Au 2+ X = Cl,OH a b c intensities were corrected for Lorentz-polarization and absorption eVects (y-scan method, minimum transmission factor 0.37). The structure was solved by Patterson and Fourier methods. All hydrogen atoms were localized in the diVerence synthesis computed after the first refinement cycles.Final full-matrix least-squares refinement was carried out with anisotropic non-hydrogen atoms and isotropic hydrogens, except for the hydrogen bonded to the O(1) atom which, for instability problems during the refinement, was fixed at the position located in the Fourier-diVerence map. However, the hydrogen positions are not completely reliable and in particular that of the hydrogen bonded to O(1) has to be considered highly problematic as far as X-ray diVraction is concerned.The final diVerence map showed a peak of 1.47 e Å23 at 0.92 Å from the Au atom and no other peaks greater than 0.43 e Å23 outside the co-ordination sphere. The programs used and sources of scattering factor data are given in ref. 9. CCDC reference number 186/1296. See http://www.rsc.org/suppdata/dt/1999/677/ for crystallographic files in .cif format. Results and discussion Solution chemistry of (2,29:69,20-terpyridine)gold(III) complexes When complex A is dissolved as its perchlorate salt in water (25 8C, I = 0.1 mol dm23, LiClO4) in the concentration range 2 × 1025–1024 mol dm23 the spectrophotometric changes observed in repetitive scanning of the solution spectrum are characteristic of a single kinetically detectable stage, with well maintained isosbestic points at 341, 352 and 358 nm.Careful examination of the spectral changes and the close similarity of the spectra at the end of reaction to those of authentic samples of C at the same concentration as the starting A demonstrate that, according to the usual associatively activated mechanism for substitution reactions at d8 square planar SP complexes,10 the direct process that has been studied kinetically involves the displacement of co-ordinated chloride by H2O with formation of B, which dissociates rapidly and completely giving the corresponding hydroxo species C.The latter, isolated as its perchlorate, is a non-reactive species.Dissolved either in water or in aqueous chloride solutions in the 0.05–1 mol dm23 range of concentrations, its UV/VIS spectrum does not change even after a long time. This finding is confirmed by 1H NMR spectra [Experimental section, experiments (c), (d)]. The reverse process could then be studied only with an excess of chloride in the presence of added acid (HClO4) which allows the hydroxo species C to be partially converted into the corresponding reactive aqua-complex B by a rapid proton transfer reaction. Under these conditions, the rate law of the overall process, derived by a combination of the kinetic law for the disappearance of A (2d[A]/dt = k1[A] 2 k21[B][Cl2]) with the mass balance (C0 = [A] 1 [B] 1 [C]) and the equilibrium constant (Ka = [H1][C]/[B]), can be expressed as in eqn.(3) (where k1 is kobs = k1 1 (k21[Cl2][H1])/(Ka 1 [H1]) (3) the solvolytic rate constant for the replacement of Cl2 by water, k21 the second-order rate constant for the reverse reaction, and Ka the acidity constant for deprotonation of the co-ordinated H2O in B).For the direct process, in absence of any reagents added, eqn. (3) reduces to kobs = k1, which can be directly determined from the absorbance change vs. time at a convenient wavelength (366 nm); k1 values obtained starting from diVerent concentrations of A are reported in Table 1. As far as the reverse process is concerned, the first-order rate constants, kobs, at diVerent [H1] and [Cl2] values are listed in Table 2.Plots of kobs against [Cl2] at diVerent [H1] concentrations give straight lines for each set of experiments with slopes k21[H1]/(Ka 1 [H1]) and finite intercepts, k1 (Table 3), theJ. Chem. Soc., Dalton Trans., 1999, 677–682 679 mean of which (0.018 s21) is in close agreement with the k1 obtained, with larger accuracy, starting from A (Table 1). As a plot of the slopes against [H1] is linear over the whole examined acidity range (0.003–0.08 mol dm23) (Fig. 1), Ka must be at least ten times greater than the highest [H1], i.e. Ka > 0.8 mol dm23, Table 1 First-order rate constants, kobs = k1, for the reaction [Au(terpy)Cl]21 1 H2O [Au(terpy)(OH2)]31 1 Cl2 in water at 25 8C [I = 0.1 mol dm23 (LiClO4)] 103[Au(terpy)Cl]21/mol dm23 0.025 0.050 0.100 k1/s21 0.0178 ± 0.0005 0.0173 ± 0.0005 0.0179 ± 0.0004 Table 2 First-order rate constants, kobs, for the overall reverse process in water at 25 8C [I = 0.1 mol dm23 (LiClO4, HClO4)] a [H1]/mol dm23 0.003 0.007 0.010 0.020 0.030 0.040 0.060 0.080 103[Cl2]/mol dm23 0.097 0.194 0.291 0.388 0.485 0.097 0.194 0.291 0.388 0.090 0.180 0.225 0.270 0.315 0.450 0.1 0.2 0.3 0.4 0.1 0.2 0.3 0.4 0.10 0.14 0.20 0.26 0.10 0.20 0.30 0.10 0.14 0.20 0.26 102kobs/s21 2.00 2.62 3.12 3.72 4.42 3.00 4.56 6.11 9.00 3.73 5.50 6.50 7.50 8.10 11.8 5.6 9.4 13.8 16.6 7.7 13.8 19.5 26.1 8.0 11.4 14.9 18.3 12.6 23.7 34.2 16.9 25.8 31.2 39.2 a Errors on individual kobs determinations are in the range ± 5% (ref. 8).Substrate concentration: 1 × 1025 mol dm23. Table 3 First-order rate constants, k1, and k21[H1]/(Ka 1 [H1]) values for the overall reverse process in water at 25 8C and diVerent [H1] [I = 0.1 mol dm23 (LiClO4, HClO4)] [H1]/mol dm23 0.003 0.007 0.010 0.020 0.030 0.040 0.060 0.080 k1 a/s21 0.0139 ± 0.0006 0.008 ± 0.006 0.015 ± 0.003 0.020 ± 0.006 0.016 ± 0.003 0.021 ± 0.007 0.019 ± 0.004 0.032 ± 0.003 k21[H1](Ka 1 [H1])21 a/ dm3 mol21 s21 61 ± 2 200 ± 20 220 ± 10 370 ± 20 610 ± 10 630 ± 40 1080 ± 20 1390 ± 20 a Determined starting from [Au(terpy)(OH)]21 as intercepts and slopes of straight lines obtained from plots of kobs against [Cl2] at diVerent [H1] concentrations using the values listed in Table 2.which leads to the conclusion that B behaves as a strong acid in accordance with the high positive charge on the complex. Under these experimental conditions, eqn.(3) can be thus simplified into eqn. (4), which allows one to calculate a series of kobs = k1 1 (k21[Cl2][H1]/Ka) (4) k21/Ka values by dividing the terms k21[H1]/Ka by experimental [H1]. From the mean (20000 ± 3000 dm6 mol22 s21) the k21 rate constant relative to the replacement of co-ordinated water by chloride can therefore be estimated as >16000 dm3 mol21 s21. Consequently, k1/k21, i.e. the equilibrium constant, KH2O, for the reaction A 1 H2O B 1 Cl2, is <1.1 × 1026 mol dm23 and the overall equilibrium constant of the system, as expressed by eqn.(5), is ª8.8 × 1027 mol2 dm26, also in accordance with KH2OKa = [C][Cl2][H1]/[A] (5) the results of the 1H NMR experiments (a)–(e). In particular, under the conditions used in experiments (a), (b), both the spectra correspond to the spectrum of pure [Au(terpy)Cl]21.3 Furthermore, the spectrum of pure [Au(terpy)(OH)]21 [experiment (c)] does not change in the presence of 0.1 mol dm23 Cl2 [experiment (d)].Finally [experiment (e)], the spectrum of a 0.002 mol dm23 [Au(terpy)Cl]21 solution exhibits resonances of both [Au(terpy)Cl]21 and [Au(terpy)(OH)]21 in ª2 : 1 ratio. Structure of [Au(terpy)(OH)][ClO4]2 Crystal data, data collection and refinement details are given in Table 4 and selected bond distances and angles are given in Table 5. An ORTEP11 view of the complex together with its two perchlorate counter anions is shown in Fig. 2.The four positions of the square-planar (SP) co-ordination of the AuIII are occupied by the three nitrogens of the terpy ligand and a further hydroxide group. The ligand is approximately planar, the maximum displacement, D, of a non-hydrogen atom from the mean plane being 0.071 Å. The Au atom lies on this plane (D = 0.046 Å) and the O(1) atom of the hydroxide group is slightly out of it by 0.146 Å. The co-ordination geometry of the gold atom is considerably distorted from the perfect SP geometry, the two N–Au–N Fig. 1 Plot of the k21[H1]/(Ka 1 [H1]) slopes against [H1] (Table 3).680 J. Chem. Soc., Dalton Trans., 1999, 677–682 angles being 81.2(2) and 81.5(2)8 and the N–Au–O ones 100.0(2) and 97.4(2)8. Not even the three Au–N distances are equivalent, the two opposite Au–N(1) and Au–N(3) bonds having rather similar lengths, 2.009(5) and 2.008(4) Å, at variance with the Au–N(2) which is rather shorter (1.949(4) Å). This pattern of distances and angles seems to be typical of all known SP Au(terpy) complexes listed in Table 6, which illustrate another interesting eVect, i.e.the intercorrelation between the Au–N distance and the C–N–C internal angle of the pyridine donor. The shorter Au–N(2) bond [on average 1.940(7) Å] is associated with a wider C–N–C angle of 124.4(8)8, while the longer Au–N(1) and Au–N(3) bonds [on average 2.019(9) Å] meet with a narrower angle of 121.0(5)8. This trend, that is clearly interpretable within the frame of the VSEPR theory 12 as well as by Bent’s rule,13 is confirmed by a number of diVerent measurements of this angle, such as: (a) 116.94(3)8 in the microwave structure of free pyridine; 14 (b) 117(1)8 in the crystal structure of the free terpy ligand; 15 (c) 121(1)8 in a number of SP gold(III) complexes co-ordinating the “free” pyridine ligand at an average AuIII–N distance of 2.03(1) Å; and finally, (d) 124.4(8)8 in the three [Au(terpy)X]21 complexes of Table 6 as far as the “compressed” Au–N(2) bond is concerned.The Au–OH distance of 2.000(4) Å cannot be compared with that of any other gold(III) structure having the same type of bond but only with the AuIII–O in carboxylates which is in the range of 2.00–2.07 Å.16 Figs. 2 and 3 show that the SP complex is able to expand the co-ordination geometry to distorted TBPY (tetragonal bipyramidal) by forming secondary Au]O bonds with the oxygens of the perchlorate anions having distances of 3.023(8) and 3.069(8) Å, longer than normal Au-O bonds but much shorter than the usual non-bonded contacts between these atoms (some 3.6 Å).17 In the present case, two of such distorted TBPYs associate in dimers through two O–H ? ? ?O2 hydrogen bonds [d(O ? ? ? O) = 2.798(9) Å] linking the co-ordinated OH groups to the perchlorate anions.Such a secondary co-ordination of anions is, by itself, interesting because secondary bonding phenomena are known to be possible indicators of incipient chemical reactions since the seminal papers published by Bent (1968) and Alcock (1972).18 A preliminary study19 has shown that secondary co-ordination Fig. 2 An ORTEP11 view of [Au(terpy)(OH)][ClO4]2 showing thermal ellipsoids at 30% probability and the atom numbering scheme. of anions is common in gold(III) SP complexes and gives rise to isolated tetragonal pyramids (TPY) and bipyramids (TBPY ), as well as to m2-anion TPY dimers or infinite TBPY chains. Systematic investigation of the CSD (Cambridge Structural Database) 20 shows that this geometry expansion is largely prevalent for gold(III) SP complexes but is seldom shared by the corresponding compounds of PtII and PdII which prefer to form dimers (or sometimes) chains involving metal–metal interactions.Table 7 reviews, as typical examples, all cases of charged SP gold(III) complexes with nitrogen ligands and TPY or TBPY secondary co-ordination retrievable from CSD. Secondary ligands are, in increasing order of average contact distance, H2O [3.03(1)], ClO4 2 [3.10(9)], Cl2 [3.13(6)], BF4 2 [3.19(2)], NO3 2 [3.21(6)], Br2 [3.24(5)] and AuCl4 2 [3.52(1) Å], that, with the possible exception of the AuCl4 2 anions, are far shorter than van der Waals contact distances (e.g. 4.0 for Au–Cl and 3.6 Å for Au–O).19 This secondary co-ordination in a SP complex of a d8 metal ion, such as AuIII, cannot be interpreted as a co-ordination Table 4 Crystal data and details of data collection and refinement procedure for [Au(terpy)(OH)][ClO4]2 Formula M Space group Crystal system a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 Z Dc/g cm23 F(000) m(Mo-Ka)/cm21 Crystal size/mm Measured reflections Independent reflections Rint Observed reflections (No) qmin 2 qmax/8 hkl ranges RR 9 No.variables (Nv) Goodness of fit [AuC15H12ON3]212[ClO4] 646.15 P1� (no. 2) Triclinic 9.006(1) 12.361(4) 8.790(2) 99.13(2) 102.86(2) 82.93(2) 938.0(4) 2 2.288 616 81.85 0.10 × 0.26 × 0.50 4822 4532 0.027 3882 [I > 3s(I)] 2–28 211, 11; 216, 16; 0, 11 0.032 0.041 315 1.301 Table 5 Selected distances (Å) and angles (8) for [Au(terpy)- (OH)][ClO4]2 Au–N(1) Au–N(2) Au–N(3) Au–O(1) Au ? ? ? O(4) Au ? ? ? O(8) O(1) ? ? ? O(7) N(1)–Au–N(2) N(2)–Au–N(3) N(1)–Au–N(3) N(1)–Au–O(1) N(2)–Au–O(1) N(3)–Au–O(1) N(1)–Au–O(4) N(2)–Au–O(4) N(3)–Au–O(4) O(1)–Au–O(4) N(1)–Au–O(8) N(2)–Au–O(8) N(3)–Au–O(8) O(1)–Au–O(8) 2.009(5) 1.949(4) 2.008(4) 2.000(4) 3.069(8) 3.023(8) 2.798(9) 81.2(2) 81.5(2) 162.6(2) 100.0(2) 176.9(2) 97.4(2) 79.8(4) 87.1(4) 100.4(4) 90.3(5) 78.0(5) 71.2(4) 95.3(4) 111.7(5) N(1)–C(1) N(1)–C(5) N(2)–C(6) N(2)–C(10) N(3)–C(11) N(3)–C(15) C(5)–C(6) C(10)–C(11) O(4)–Au–O(8) Au–N(1)–C(1) Au–N(1)–C(5) C(1)–N(1)–C(5) Au–N(2)–C(6) Au–N(2)–C(10) C(6)–N(2)–C(10) Au–N(3)–C(11) Au–N(3)–C(15) C(11)–N(3)–C(15) N(1)–C(5)–C(6) N(2)–C(6)–C(5) N(2)–C(10)–C(11) N(3)–C(11)–C(10) 1.351(7) 1.359(9) 1.354(8) 1.345(6) 1.351(8) 1.346(9) 1.463(7) 1.489(9) 151.0(5) 125.4(4) 113.2(4) 121.4(5) 117.2(3) 117.4(3) 125.4(4) 113.3(4) 126.0(4) 120.7(5) 115.8(5) 112.7(5) 112.3(4) 115.6(5)J.Chem. Soc., Dalton Trans., 1999, 677–682 681 Table 6 Comparison of the geometries (distances in Å, angles in 8) for some [Au(terpy)X]21 SP complexes (nitrogen labels as in Fig. 2) Complex [Au(terpy)Cl]Cl2?3H2O [Au(terpy)Cl]2[AuCl2]3[AuCl4] [Au(terpy)(OH)][ClO4]2 Average Au–N(1) Au–N(3) 2.018(6) 2.029(6) 2.022(9) 2.030(8) 2.009(5) 2.008(4) 2.019(9) Au–N(2) 1.931(7) 1.941(8) 1.949(4) 1.940(7) C–N(1)–C C–N(3)–C 121.1(7) 121.5(7) 121.0(9) 120.1(9) 121.4(5) 120.7(5) 121.0(5) C–N(2)–C 123.4(7) 124.5(9) 125.4(4) 124.4(8) N(1)–Au–N(2) N(3)–Au–N(2) 81.4(3) 81.4(3) 81.3(4) 81.4(4) 81.2(2) 81.5(2) 81.4(1) Ref. 3 3 This work Table 7 Pseudo-octahedral secondary co-ordination in gold(III) square-planar complexes (distances in Å and e.s.d.s of the averages in square brackets) Refcode This work CAEAUC AEMAUP ZELCAU POPKUA POPKUA POPKUA BUYMOX BENYEY ZENFED DODXID TEMMED JIHGOW AEMAUP BUYMOX BENYEY VEGMEZ FUJFEV VIWKOB FUHLOJ FUHLUP Complex [Au(terpy)(OH)]21 [Au(dien)Cl]21 [Au(dien)Cl]21 [Au(pmpterpy)Cl]21 [Au(tacyd)]31 [Au(tacyd)]31 Average [Au(tacyd)]31 Average [Au(terpy)Cl]21 [Au(py)2Cl2]1 Average [Au(bipy)Cl2]1 Average [Au(dien)Cl]21 [Au(hacytd)]31 [Au(en)2]31 [Au(dien)Cl]21 [Au(terpy)Cl]21 [Au(py)2Cl2]1 [Au(bipy)Cl2]1 Average [Au(tpp)]1 [Au(tdacyn)Cl2]1 Average [Au(phen)(CN)2]1 [Au(phen)(CN)2]1 Average X OOOOOOOOOOOOFF Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Br Br Br Ligand ClO4 2 ClO4 2 ClO4 2 ClO4 2 ClO4 2 ClO4 2 ClO4 2 NO3 2 NO3 2 H2O H2O H2O BF4 2 BF4 2 Cl2 Cl2 Cl2 Cl2 Cl2 Cl2 Cl2 Cl2 AuCl4 2 AuCl4 2 AuCl4 2 Br2 Br2 Br2 Motif TBPY Chain TBPY TBPY TBPY TBPY TBPY TBPY TBPY Chain TBPY TBPY TBPY TBPY TBPY TBPY m2-Cl Chain TPY Chain m2-Br d(Au–X)/Å 3.023(8)/3.069(8) 3.089/3.103 3.102 2.899/3.192 3.194/3.250 3.035 ·3.10[9]Ò 3.150/3.263 ·3.21[6]Ò 3.022 3.045 ·3.03[1]Ò 3.165/3.213 ·3.19[2]Ò 3.121/3.183 3.096/3.096 3.101/3.101 3.05 3.049 3.171 3.211/3.224 ·3.13[6]Ò 3.521/3.521 3.525 ·3.522[2]Ò 3.277/3.277 3.165/3.165 ·3.24[5]Ò terpy = 2,29:69,20-Terpyridine; dien = diethylenetriami; pmpterpy = 49-(p-methoxyphenyl)-2,29:69,20-terpyridine; tacyd = 1,4,8,11-tetraazacyclotetradecane; py = pyridine; bipy = 2,29-bipyridine; hacytd = 1,8-bis(2-hydroxyethyl)-1,3,6,8,10,13-hexaazacyclotetradecane; en = ethylenediamine; tpp = 5,10,15,20-tetraphenylporphyrinate; tdacyn = 1-thia-4,7-diazacyclononane.TBPY = Isolated tetragonal bipyramid; chain = TBPY chain; m2 = TPY (tetragonal pyramid) dimer. Fig. 3 The observed packing motif where two TBPY [Au(terpy)(OH)]- [ClO4]2 dimerize by O–H ? ? ? 2O hydrogen bond formation. expansion because of the great stability of the SP geometry for metal ions of such a configuration having large values of 10 Dq, which is the case of AuIII owing to both its position in the third transition series and its high oxidation number.The interaction is thus to be considered as an electrostatic perturbation of the essentially stable d8 low-spin square-planar complex. Rather paradoxically, such a perturbation is allowed to become the stronger (and the additional bond the shorter) the higher is the 10Dq, because the axial perturbation splits the non-bonding d(z2) metal orbital and the SP complex can remain stable only when the doubly filled d(z2)* molecular orbital so generated is lower in energy than the empty antibonding d(x2 2 y2)* one.This may help to understand why secondary co-ordination in d8 SP complexes is mostly observed for gold(III) compounds. Acknowledgements We thank the Italian Ministry of University and Scientific Research for financial support. References 1 E. C. Constable, Adv. Inorg.Chem. Radiochem., 1986, 30, 69. 2 H.-K. Yip, L.-K. Cheng, K.-K. Cheung and C.-M. Che, J. Chem. Soc., Dalton Trans., 1993, 2933 and refs. therein.682 J. Chem. Soc., Dalton Trans., 1999, 677–682 3 L.S. Hollis and S. J. Lippard, J. Am. Chem. Soc., 1983, 105, 4293. 4 G. Marangoni, B. Pitteri, G. Chessa, V. Ferretti, P. Gilli and V. Bertolasi, Acta Crystallogr., Sect. C, 1992, 48, 814. 5 B. Pitteri, G. Marangoni, L. Cattalini and T. Bobbo, J. Chem. Soc., Dalton Trans., 1995, 3853. 6 G. Annibale, M. Brandolisio and B. Pitteri, Polyedron, 1995, 14, 451. 7 B. Pitteri, G. Marangoni, F. Visentin, L. Cattalini and T. Bobbo, Polyedron, 1998, 17, 475. 8 L. Canovese, L. Cattalini, P. Uguagliati and L. M. Tobe, J. Chem. Soc., Dalton Trans., 1990, 867. 9 MOLEN, An Interactive Structure Solution Procedure, Enraf- Nonius, Delft, 1990; PARST 96, M. Nardelli, J. Appl. Crystallogr., 1995, 28, 659; M. Nardelli, PARSTCIF, Program for Creating a CIF from the Output of PARST, University of Parma, 1991; D. T. Cromer and J. T. Waber, International Tables for X-Ray Crystallography, Kynoch Press, Birmingham, 1974. 10 F. Basolo and R. G. Pearson, Mechanism of Inorganic Reactions, 2nd edn., Wiley, New York, 1967, pp. 410–414. 11 C. K. Johnson, ORTEP II, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. 12 R. J. Gillespie, Molecular Geometry, Van Nostrand-Reinhold, London, 1972; J. Chem. Educ., 1963, 40, 295; 1970, 47, 18. 13 H. A. Bent, J. Chem. Educ., 1960, 37, 616; Chem. Rev., 1961, 61, 275. 14 Landolt-Börnstein, Numerical Data and Functional Relationships in Science and Technology, New Series, ed. K.-H. Hellwege and A. H. Hellwege; vol. 7, Structure Data of Free Polyatomic Molecules, Springer, Berlin, 1976. 15 C. A. Bessel, R. F. See, D. L. Jameson, M. R. Churchill and K. J. Takauchi, J. Chem. Soc., Dalton Trans., 1992, 3233. 16 A. Dar, K. Moss, S. M. Cottrill, R. V. Parish, C. A. McAuliVe, R. G. Pritchard, B. Beagley and J. Sandbank, J. Chem. Soc., Dalton Trans., 1992, 1907; A. G. Orpen, L. Brammer, F. H. Allen, O. Kennard, D. G. Watson and R. Taylor, J. Chem. Soc., Dalton Trans., 1989, S1. 17 G. Nardin, L. Randaccio, G. Annibale, G. Natile and B. Pitteri, J. Chem. Soc., Dalton Trans., 1980, 220. 18 H. A. Bent, Chem. Rev., 1968, 68, 587; N. W. Alcock, Adv. Inorg. Chem. Radiochem., 1972, 15, 1. 19 G. Marangoni, B. Pitteri, V. Bertolasi, V. Ferretti and G. Gilli, J. Chem. Soc., Dalton Trans., 1987, 2235. 20 F. H. Allen, S. Bellard, M. D. Brice, B. A. Cartwright, A. Doubleday, H. Higgs, B. G. Hummelink-Peters, O. Kennard, W. D. S. Motherwell, J. R. Rogers and D. G. Watson, Acta Crystallogr., Sect. B, 1979, 35, 2331; F. H. Allen and O. Kennard, Chem. Des. Autom. News, 1993, 8, 1, 31–37. Paper 8/06098C

ISSN:1477-9226    

DOI:10.1039/a806098c

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 683–689 683 Anion interactions with (polypyridyl)ruthenium complexes, and their importance in the cation-exchange chromatographic separation of stereoisomers of dinuclear species † Nicholas C. Fletcher and F. Richard Keene * School of Biomedical and Molecular Sciences, James Cook University, Townsville, Queensland 4811, Australia. E-mail: Richard.Keene@jcu.edu.au Received 4th December 1998, Accepted 13th January 1999 The separation of the ligand-bridged dinuclear complex cation [{(Me2bpy)2Ru}2(m-bpm)]41 (Me2bpy = 4,49-dimethyl- 2,29-bipyridine; bpm = 2,29-bipyrimidine) into its two diastereoisomeric forms, meso and rac, by cation-exchange chromatography has been investigated, using a wide range of organic counter anions (aromatic and aliphatic) in the aqueous eluents. 1H NMR titration studies not only confirm association between the complex cation and the counter anions in solution, but also reveal diVerential associations with the two diastereoisomers of [{(Me2bpy)2Ru}2- (m-bpm)]41.Analogous interactions are also evident with mononuclear species, [Ru(pp)3]21, where pp is a bidentate ligand such as Me2bpy, 1,10-phenanthroline (phen) or 2,29-bipyridine (bpy): from 1H NMR titration studies, the first association with a number of organic anions has a stability constant in the order of 100 dm3 mol21 in aqueous solution. This association also aVects the emission from the MLCT excited state of the monomers, with up to a 10% enhancement in the luminescence.Introduction Octahedral tris(bidentate)-ruthenium(II) and -osmium(II) complexes involving polypyridyl ligands such as 2,29-bipyridine (bpy) and 1,10-phenanthroline (phen) have been extensively studied, primarily because of their unique combination of chemical inertness, redox properties and photophysical characteristics. 1,2 They have found application within diverse areas of chemistry such as photo-catalysis,3 molecular recognition,4,5 and artificial photosynthesis/charge separation schemes,6–10 and exhibit specific interactions with polynucleotides such as DNA.11–13 These coordination centers are inherently chiral, and any supramolecular assembly composed of such moieties may exhibit a number of possible stereoisomers, a complication which has until recently received only tacit attention.14–16 In our stereochemical investigations of mono- and oligonuclear ruthenium complexes with a,a9-diimine ligands, the cation-exchange support SP Sephadex C-25 has proved remarkably successful in the separation of individual geometric isomers, diastereoisomers and enantiomers of mixtures typically produced in structurally-uncontrolled syntheses.15–23 This material had been extensively used in the separation of stereoisomers of various octahedral cobalt(III) species,24–26 but surprisingly it appears not to have been widely applied to ruthenium(II) complexes containing polypyridyl ligands until our recent studies.SP SephadexTM is composed of a cross-linked dextran matrix functionalised with strongly acidic propylsulfonate groups.25 The separation of cationic species is achieved as a result of the † Supplementary data available: NMR titration curves plotted for the sequential addition of sodium 4-toluate to diastereoisomers of [{(Me2bpy)2Ru}2(m-bpm)]Cl4 and for the sequential addition of [Ru(Me2bpy)3]Cl2 to sodium toluene-4-sulfonate; relative 1H NMR signal perturbations observed on the protons of [Ru(Me2bpy)3]Cl2 on the addition of organic anions; relative photoemission of the complex [Ru(Me2bpy)3]Cl2 upon the addition of organic sodium salts of organic anions.For direct electronic access see http://www.rsc.org/suppdata/dt/ 1999/683/, otherwise available from BLDSC (No. SUP 57484, 6 pp.) or the RSC Library. See Instructions for Authors, 1999, Issue 1 (http:// www.rsc.org/dalton). diVerential equilibria between the absorbed cations and the cations in the mobile eluent phase (typically Na1) with the anionic stationary phase. The lowest-charged cations move faster relative to the other species introduced onto the column, with coulombic forces (charge densities and polarities of the cations) dominating the equilibria leading to the separation.The initial application of this cation-exchange chromatographic technique to the separation of ruthenium(II) complexes containing polypyridyl ligands utilised aqueous sodium toluene- 4-sulfonate solution as eluent.21 It became apparent that the anion of the eluent was not innocent in the process and associated with the complex cations, eVectively reducing their overall charge and causing increased rate of travel down the column.27 The diVerent geometries of the stereoisomers of the cations and the choice of anion had a profound eVect on the strength of these anion interactions, facilitating the separations: the present paper elucidates factors giving rise to these observations.Unless they occupy a formal coordination site on the metal centre, anions have classically been considered as isolated from the complex in a polar environment, being part of a secondsphere solvent “cage”. However, the recent work of Beer et al. has shown that a variety of anions can strongly associate with a cationic ruthenium complex containing amide-functionalised polypyridyl ligands.4,5,28 Such specific interactions rely heavily upon hydrogen bonding, in addition to electrostatic factors which facilitate the association.Photophysical studies of ruthenium polypyridyl complexes with anionic micelles,29–31 polyelectrolytic anions, 29–35 and DNA11,12,36–39 have indicated a distinct interaction manifested as an increase in luminescence. In this paper we illustrate the significant association of anions with both mono- and di-nuclear complexes of ruthenium(II) containing polypyridyl ligands, the connotations of which spread well beyond the chromatographic process.Experimental Instrumentation NMR spectra were recorded on a Varian Unity Inova-500 spectrometer using the solvent as the internal reference. Electronic684 J. Chem. Soc., Dalton Trans., 1999, 683–689 and emission spectra were recorded on Varian CARY 5E and Perkin-Elmer LS 50B spectrophotometers, respectively. Materials Sodium chloride (Ajax; AR) was used without further purifi- cation.Sodium toluene-4-sulfonate (Aldrich; 95%) and sodium butyrate (butanoate) (Aldrich) were recrystallised from ethanol. All other sodium salts were prepared by the neutralisation of the corresponding acids (Fluka/Aldrich) with aqueous sodium hydroxide solution until a pH of 8–9 was obtained. The solutions were filtered, and the water was removed under reduced pressure. The resulting white solids were recrystallised from ethanol and dried in vacuo prior to use. The complexes [Ru(bpy)3]Cl2, [Ru(Me2bpy)3]Cl2 (Me2bpy = 4,49-dimethyl-2,29-bipyridine) and [Ru(phen)3]Cl2 were prepared according to literature procedures.1 [{(Me2bpy)2Ru}2- (m-bpm)]Cl4 (bpm = 2,29-bipyrimidine) was prepared according to previously described methods, and the two diastereoisomers (meso and rac) were isolated using cation-exchange chromatography on SP Sephadex C-25, with aqueous 0.25 mol dm23 sodium toluene-4-sulfonate solution as eluent.27 Quantitative column chromatography A small perspex column (Model K9; Amrad Pharmacia Biotech; dimensions 9 × 600 mm), fitted with an external water-jacket was maintained at a constant temperature of 30 8C by a thermostatted circulating water-bath (Talabo F10).SP Sephadex C-25 was equilibrated in the eluent solution at an electrolyte concentration of 0.25 mol dm23 to overcome problems of contraction of the support on changes of electrolyte concentration, and allowed to settle in the column at a constant eluent flow rate of approximately 0.5 ml min21, regulated by a Gilson Minipulse 2 peristaltic pump.Once equilibration was achieved, the head of solution was lowered to the level of the top of the chromatographic support and the compound to be separated was introduced (dissolved in the appropriate eluent; 0.25 mg of each isomer in 250 ml), taking extreme care that the surface of the Sephadex was undisturbed during the process. To ensure standardised results, the rate of flow was monitored and the data standardised to give the volume of eluent solution required to move the individual bands by unit length (ml cm21). 1H NMR titration studies The 1H NMR titrations on the dinuclear species were performed by the sequential addition of 0.2 equivalents of the sodium salt of the anions contained in 20 ml of D2O to 2.5 × 1026 mol of the meso or rac diastereoisomer of [{(Me2bpy)2- Ru}2(m-bpm)]Cl4 in 0.5 ml of D2O. The titrations with the mononuclear species [Ru(Me2bpy)3]Cl2, [Ru(bpy)3]Cl2 and [Ru(phen)3]Cl2 were performed at twice the concentration of complex to provide comparable results.The stability constants were obtained by the application of the program EQNMR,40 coded in Fortan90 and compiled to execute on Apple Power- Mac systems.41 However, the parameter refinement routines were based on a constrained quasi-Newton–Rapson procedure which made the optimisation less sensitive to selection of the starting parameters than the original code. Photophysical titrations The UV/visible spectra and emission spectra (excitation at 455 nm) were recorded in aqueous solutions at a concentration of 5 × 1025 mol dm23 for [{(Me2bpy)2Ru}2(m-bpm)]Cl4 and 1 × 1024 mol dm23 for [Ru(Me2bpy)3]Cl2.The titrations were performed by the sequential addition of the sodium salt of the anion (1 equivalent in 5 ml) to 2.5 ml of the above solutions. Dilution eVects were corrected by the subtraction of a blank titration. Results In an achiral synthesis of the ligand-bridged dinuclear species [{(Me2bpy)2Ru}2(m-bpm)]41, the two diastereoisomers {meso DL (]] ] LD) and rac (DD and LL); Fig. 1} were obtained in approximately equal proportions and were readily separated by cation-exchange chromatography on SP Sephadex C-25 with aqueous sodium toluene-4-sulfonate solution as the eluent.27 A study of this chromatographic process as a function of eluent concentration and temperature revealed a surprisingly strong association between the cation to be separated and the anion in the eluent.27 The rate of travel of the meso diastereoisomer was considerably faster, indicating its shape led to a preferential interaction of the anion.To elucidate the nature of this interaction, and identify factors controlling its strength, the chromatographic processes were investigated as a function of the variation of the anion in the aqueous eluent (Fig. 2). Quantitative column chromatography studies A series of quantitative experiments, similar to those previously described,27 were undertaken on small columns using a mixture of the two diastereoisomers of the dinuclear cation [{(Me2bpy)2- Ru}2(m-bpm)]41.The relative rates of movement of the two bands down the column of SP Sephadex C-25 cation exchanger were measured using a constant eluent concentration of 0.25 mol dm23, but varying the organic anion in the solution. The relative rates of passage of the two diastereoisomers down the column with a variety of anions are displayed in Fig. 3, giving the data for two forms (meso and rac), as well as the average for the combined bands. Several trends are apparent. Slight movement of the cation down the column (shown by the average movement) was observed with chloride as the eluent anion, although there was very poor separation of the two diastereoisomers. With acetate as the eluent anion no movement was detected, but as the chain length of the aliphatic carboxylate anion was extended the rate of travel down the column dramatically increased (Fig. 3a). Further, the relative diVerence in rate of movement of the two diastereoisomers (meso: rac) increased with the chain length of the aliphatic anions (1 : 0.66 for butanoate compared with 1: 0.41 for octanoate). Generally, better separation of the two forms was observed for these simple longer chain aliphatic anions than Fig. 1 Schematic view of the isomeric possibilities of the general dinuclear species [{M(pp)2}2(m-BL)]41 {pp is an a,a9-diimine ligand, and BL a di-bidentate bridging ligand}.Ru Ru Ru Ru rac meso D D L L D L (or DL) Ru RuJ. Chem. Soc., Dalton Trans., 1999, 683–689 685 had previously been observed with sodium toluene-4-sulfonate (1 : 0.66).27 The rate of travel of the two diastereoisomers down the column was not enhanced by the presence of branched chains (e.g. trimethylacetate and cyclohexanoate). A series of aromatic anions were investigated in an analogous fashion.While it was observed that the behaviour of sodium benzoate closely resembled that of sodium cyclohexanoate, para-substituted aromatic carboxylates gave significantly enhanced rates of travel down the column when compared with the aliphatic anions, as illustrated in Fig. 3b. This did not appear to be a function of the diVerence in electronic character of the appended group, but rather the hydrophobicity (with the possible exception of 4-nitrobenzoate). If the aromatic anion was substituted in the position ortho to the carboxylate group (e.g. 2-toluate and mesitoate), the rate of travel was significantly decreased: this may arise from the diVerence in shape between these two anions and the 4-substituted species, but it may also indicate that the hydrogen atoms in the ortho position are significant in the interaction. For these two aromatic anions, the relative rates of travel of the two diastereoisomers (meso: rac) proved to be very similar (1 : 0.46 to 0.56).Notably, no separation was observed for 4-hydroxybenzoate. Clearly the identity of the anion in the eluent greatly influences the rate of movement of the complex cations by diminution of their eVective charges: there must be diVerences in the association between the tetravalent species [{(Me2bpy)2Ru}2- (m-bpm)]41 and the various anions used in the eluting electrolyte. The association appears greatest for the aromatic anions, Fig. 2 The organic anions used in these studies.which induce a faster rate of travel down the column. The separation of the two diastereoisomers is brought about by diVerences in the association between the two forms (meso/rac). 1H NMR Studies In recent years, NMR has proved an extremely successful tool in elucidating interactions within host–guest chemistry.42 In the present case, a series of 1H NMR titrations were carried out in an attempt to observe perturbations in the signals of the cation (host) as the chloride salt (for which the associations are weak) with the sequential addition of sodium salts of the anions (guest) illustrated in Fig. 2. All of the titrations were carried out in D2O at 30 8C, in order to maintain the environment as similar as possible to that used in the chromatographic experiments. The series of anions used with the quantitative columns described above were titrated against the complex [{(Me2bpy)2- Ru}2(m-bpm)]41. Upon the sequential addition of the organic anions as their sodium salts, standard titration curves (such as those provided in SUP 57484 Fig. S1) could be plotted for the small but significant perturbations for the majority of protons on the cation.In most of the curves, the intersection of the initial and final slopes occurred at ca. 4 equivalents of the anion, indicating a stoichiometry of 1 : 4 which is consistent with the ratio of the magnitude of the charges of the cation and anion. Fig. 3 Plots of relative rates of travel of the diastereoisomers of [{(Me2bpy)2Ru}2(m-bpm)]41, down a 9 mm (internal diameter) column as a function of (a) aliphatic organic sodium salts, (b) aromatic organic sodium salts as eluent (Concentration: 0.25 mol dm23, at 30 8C.) {black ]] ] meso; white ]] ] rac; hatched ]] ] mixture of meso 1 rac}.686 J.Chem. Soc., Dalton Trans., 1999, 683–689 Fig. 4 shows the perturbations (D ppm) observed after the addition of ten equivalents of the respective anion for three protons {Me2bpy-H69, Me2bpy-H3 and bpm-H4/6} of both diastereoisomers, selected from three distinct regions of the cation.Several observations can be made from the data. The two diastereoisomers gave essentially similar results, although the magnitude of the observed shifts were signifi- cantly less with the rac form. While the magnitude of the shift is not necessarily directly related to the strength of an associ- Fig. 4 The relative 1H NMR signal perturbations observed on the protons: bpm-H4/6 (black), Me2bpy-H3 (white) and Me2bpy-H69 (hatched), respectively, with (i) meso-[{(Me2bpy)2Ru}2(m-bpm)]Cl4, (ii) rac-[{(Me2bpy)2Ru}2(m-bpm)]Cl4 on the addition of 10 equivalents of the organic anions.ation, it can be assumed that larger shifts are caused by more intimate interactions of the anions with the meso than the rac diastereoisomer, reflecting diVerences in structure between the two forms. This was particularly noticeable with the aliphatic anions.Another very obvious trend is that the aliphatic species all induced down-field shifts in the protons of the dinuclear complex, while the aromatic anions generally gave rise to an up-field shift under the same conditions. The approach of a negative charge has been observed previously to cause down-field shifts in the 1H NMR spectrum of a complex cation, as a result of second sphere interactions,28 in accordance with the present results for the aliphatic anions. However, the presence of the aromatic anions gave rise to up-field shifts indicating this interaction must have an additional dimension.It is apparent that the aromatic anions occupy a position suYciently proximate to the protons on the cation that they experience a ring current (anisotropy) from the associated p-electron rich anions, giving rise to the up-field perturbation. Such ring anisotropy implies that the nature of such aromatic associations probably arises from a p-stacking eVect.43 In both the meso and rac forms, as the chain length of the aliphatic anions increased greater shifts were observed and by implication there were larger associations. Branched aliphatic species did not improve this eVect, and if anything reduced it.At a first glance, the size of the observed shifts for the aromatic anions correlates with the respective rates of passage through cation-exchange support. A comparison of cyclohexanoate and benzoate reveals that in the latter the shifts have inverted, and increased considerably in magnitude.Thus while the column data imply a similar behaviour of these two anions, the observed shift perturbations imply a diVering mechanism of association. The para-substituted benzoates each produced significant shifts (up to 0.15 ppm with 4-tert-butylbenzoate and 4-trifluoromethylbenzoate) on the majority of the terminal ligand protons of both diastereoisomers. Surprisingly, the size of the shifts does not correlate to the electronic character of the substituted groups, again implying the eVects are not a consequence of the basicity of the carboxylate.By placing the substituents at the ortho-position to the carboxylate (2-toluate and mesitoate) the shift is greatly reduced or even turned down- field, indicating that the aromatic interaction is being blocked. As discussed above, this observation may arise from diVerences in the shapes of the respective anions, or it implies that the H2/6 protons on the aromatic anion play an important role in the association, in which case it emphasises that the association probably relies on an edge-to-face p-stacking.43 The protons on the bridge (bpm) show somewhat diVerent behaviour to those on the terminal ligands.The shifts can vary greatly, from extremely large with 4-trifluoromethylbenzoate to an extremely small down-field shift with 4-nitrobenzoate. Hence it is postulated that this para-substituent on the aromatic anionJ.Chem. Soc., Dalton Trans., 1999, 683–689 687 lies over (or below) the bridge. These diVerences are more pronounced for the meso than for the rac form, implying the geometry over the bridge is more favourable to the association in the meso isomer. To reinforce the observations, the cation was titrated against sodium toluene-4-sulfonate to examine whether the anion also experienced similar perturbations in the proton behaviour (Fig. 5). The change in peak positions of the anion were larger than those observed in the cation, and the titration curves (Dd vs.equivalents of complex added) indicated a 4 : 1 stoichiometry. The shifts were all in an up-field direction indicating the anion is not only being brought into an electron-rich area (shielding environment), but also that the aromatic system of the anion experiences the ring currents of the polypyridyl ligands. There are some pronounced diVerences in the behaviour of the protons with the two diVerent diastereoisomers (Fig. 5). While the H2/6 protons of the toluene-4-sulfonate anion do not experience much diVerence for the two diastereoisomeric forms, the H3/5 and H-Me protons both show greater perturbations with the meso form. While the diVerence in structure of the two diastereoisomers must contribute to their respective diVerences in behaviour, the complexes both interacted in a 1 : 4 ratio with the anions. It is unlikely that such associations would only involve the region between the two metal centres (in the vicinity of the bridge), so that the interactions must also involve the terminal ligands.If this were the case, similar patterns should be observed with mononuclear polypyridyl complexes of ruthenium. Accordingly, a similar series of titrations were made with the complex [Ru(Me2bpy)3]21 in order to judge the strength of its associations with the same anions. The titration curves obtained indicated a 2 : 1 stoichiometry. Additionally, a titration of the cation against the anion indicated very similar-sized shifts to those observed for the dinuclear isomers, described above (SUP 57484 Fig.S2). Fig. 5 1H NMR titration curves plotted for the sequential addition of (a) meso-[{(Me2bpy)2Ru}2(m-bpm)]Cl4, (b) rac-[{(Me2bpy)2Ru}2- (m-bpm)]Cl4 to sodium toluene-4-sulfonate [H-Me (m), H2/6 (j) and H3/5 (d)]. Generally the shifts observed on the addition of five equivalents of the anions to the complex [Ru(Me2bpy)3]21 revealed a similar magnitude and pattern to the addition of ten equivalents to the rac diastereoisomer of [{(Me2bpy)2Ru}2- (m-bpm)]41, showing that they both behave in a similar manner (SUP 57484 Fig.S3). From the titration data obtained by the 1H NMR titrations, the program EQNMR40,41 was used to estimate the stability constants for the association of the first (kstab1) and then the second (kstab2) anion with the mononuclear target. Not all of the anions provided suYciently large shifts on the sequential addition of the anion to the complex cation, but using data for several of the aromatic anions and the octanoate ion it was possible to determine the stability constants (Table 1).The errors in the values are approximately ±50%, but the majority of the values for the first association constant (kstab1) fell into the range of 50 to 130 dm3 mol21 (with the exception of 4-trifluoromethylbenzoate, which indicated anomalous behaviour).While these values are small they are nevertheless significant, especially in aqueous solution where the polarity of the solvent eVectively negates the electrostatic attractions. As expected, the second stability constants are an order of magnitude smaller. Such data would have proved invaluable in the case of the dinuclear species, but the number of independent variables proved to be too extensive to allow the EQNMR software to provide meaningful answers. Similar behaviour was observed with the mononuclear complexes [Ru(bpy)3]21 and [Ru(phen)3]21 as for the complex [Ru(Me2bpy)3]21 upon the sequential addition of both sodium octanoate and sodium benzoate.The perturbations observed typically were not as large as those observed with [Ru(Me2bpy)3]21 (Fig. 6), however it provided strong evidence that this eVect is not simply limited to complexes containing Me2bpy. It is noted that recent structural studies of the complex L-(1)-[Ru(phen)3]L?8H2O {L= (1)-O,O9-di-4-toluoyl-Dtartrate} showed the [Ru(phen)3]21 cations formed layers which alternated with layers containing water molecules.44 For L = (1)-O,O9-di-4-toluoyl-D-tartrate the anions were positioned such that the tartrate backbone (containing the two carboxylate functionalities) resided in the water layer (hydrophilic), while the toluoyl rings penetrated into a virtually hydrophobic region in the complex cations where they underwent p-stacking with the phenanthroline rings.While this observation was made in the solid state, the interaction is analogous to the present proposal for the mode of association of similar anions and complexes in solution. Absorption/emission spectra Studies of the photophysical properties of the mononuclear and dinuclear targets in the presence of the various anions were Table 1 Stability constants obtained using EQNMR40,41 from 1H NMR titration data for the mononuclear tris(a,a9-diimine)- ruthenium(II) complexes Complex [Ru(Me2bpy)3]Cl2 [Ru(phen)3]Cl2 Anion (introduced as Na1 salt) Octanoate Toluene-4-sulfonate (tosylate) Benzoate 4-Chlorobenzoate 4-tert-Butylbenzoate 4-Nitrobenzoate 4-Hydroxybenzoate 4-Trifluoromethylbenzoate 4-Toluate Benzoate Kstab1 (±50%)/ dm3 mol21 250 120 125 55 75 64 130 16 75 160 Kstab2 (±50%)/ dm3 mol21 46 10 31 14 14 7 15 14 9688 J.Chem. Soc., Dalton Trans., 1999, 683–689 carried out in aqueous solution to investigate whether the associations could be detected by other methods.Unfortunately, there was no indication of any form of interaction in the UV/visible absorption spectra of the ruthenium complexes even up to the addition of a 100-fold excess of the aliphatic or aromatic anions. The studies in the latter case were somewhat hindered by the absorption of the anions themselves which prevented an examination of the sensitive p–p* transition at 280 nm. The characteristic emission behaviour of the mononuclear species gave more satisfactory evidence. A strong quenching eVect was observed for the addition of sodium 4-nitrobenzoate to a 1024 mol dm23 solution of [Ru(Me2bpy)3]Cl2 in (nondeaerated) water at room temperature.It is known that nitrated aromatic species are capable of accepting an electron from an excited state species, indicated here by the quenching of the emission,45 although no indication of an association was observed. The presence of the majority of other organic anions listed in Fig. 2 produced no eVective change in the emission. However, on the sequential addition of the anions 4-tert-butylbenzoate, 4-trifluoromethylbenzoate, 4-toluate or octanoate, there was a small increase (5–10%) in the emission from the initial value upon the addition of 50 equivalents of the anion (SUP 57484 Fig. S4). All of these particular anions demonstrated good associations with both the dinuclear complex on the chromatography column and in the 1H NMR studies (see above), and are thus assumed to be the most likely to cause a change in the emission behaviour.This increase can be rationalised in terms of the displacement of a layer of solvent molecules surrounding the excited state cation by a protective layer of the anions, held there by the association described above. This would render the excited state complex less susceptible to solvent collision and the resultant radiationless decay, and hence an increase in the emission is observed. Similar behaviour has been observed by the inclusion of complexes such as [Ru(phen)3]21 and [Ru(bpy)3]21 in polyelectrolytes, 32,35 micelles 29–31 and DNA.38 While the change in environment is considerably greater upon the addition of these large polyanionic species, the same eVect can be brought about by considerably smaller anions, presumably by discrete associations.Discussion We have had particular success with the separation on the cation-exchange support SP Sephadex C-25 of stereoisomers of polynuclear complexes of ruthenium containing bidentate a,a9-diimine ligands.The present work provides an understanding of the mechanism of the separation process, which relies Fig. 6 The relative 1H NMR signal perturbations observed with [Ru(Me2bpy)3]Cl2, [ Ru(bpy)3]Cl2 and [Ru(phen)3]Cl2 on the addition of 5 equivalents of the organic anions octanoate and benzoate: H3 (Me2bpy and bpy) and H5/6 (phen) {black}, H-Me (Me2bpy), H4 (bpy) and H4/7 (phen) {grey}; H5 (Me2bpy and bpy) and H3/8 (phen) {white}; H6 (Me2bpy and bpy) and H2/9 (phen) {hatched}.heavily on a “host–guest” association of an organic anion of the eluent with the complex cation. A variety of anions have been used to explore the nature of these interactions, and these studies indicate that there are several factors involved. While there is inevitably a certain electrostatic attraction between the cation and the anion, it would not be exected to be large or specific in a highly polar solvent such as water.Ruthenium(II) complexes containing polypyridyl ligands exist as rigid structures with well-defined clefts between the ligands which provide hydrophobic cavities into which the organic entities present in the bulk polar solvent environment may insert. The resultant specific associations cause changes in the 1H NMR spectra of both the complex (host) and anion (guest), and give rise to the behaviour of the complex cations on the cation exhange chromatographic support.While the use of aromatic anions such as 4-toluate are driven by such hydrophobicity, with the polar carboxylate grouping probably pointing away from the cation, there are additional possibilities arising from the formation of energetically favourable edge-to-face and face-to-face p-stacking interactions or aromatic anions with the pyridyl rings.43 By the inclusion of para-substituted hydrophobic substituents to the aromatic rings of the anions, the binding is enhanced.However ortho-functionalised groups inhibit the association, reducing possibilities of the aromatic p-stacking. From our studies, it is clear that the relative shapes of the two diastereoisomers of the complex [{(Me2bpy)2Ru}2(m-bpm)]41 give rise to the chromatographic separation by virtue of diVerential associations with certain anions. The structural features of the cation determine the access by the aliphatic or aromatic anions for either hydrophobic binding or p-stacking interactions, as demonstrated both in the NMR studies and by the rate of passage of the diastereoisomers down the cation exchange column.The meso form has a cleft above and below the bridge, formed by the orthogonal orientation of the terminal ligands, as indicated in Fig. 1. From simple molecular models, this cleft is of an appropriate size to accept an aromatic moiety. In the rac form the terminal ligands lie parallel to each other above and below the plane of the bridging ligand, and do not provide such a well-defined cleft, and consequently do not allow as good an association with the organic anions (Fig. 7). The implications of such “host–guest” associations are of much wider significance than the chromatographic separations. It has been known for several decades that polypyridyl complexes of ruthenium(II) interact with DNA,46 although there remains conjecture regarding the actual mode of bonding; i.e. whether the complexes intercalate and form a p-stacking interaction into the aromatic base pairs of the right-handed helix, or rely upon hydrophobicity to the surface of the helix, or the attraction is merely electrostatic.11,12,37,38,47 From the present studies, it is apparent that both hydrophobic and p-stacking interactions are possible between anions Fig. 7 Schematic illustration of the possible diVerence in association of the meso and rac forms of the dinuclear species.J. Chem. Soc., Dalton Trans., 1999, 683–689 689 and complexes of this type, and the two types of association are of a similar order of magnitude for the simple complex [Ru(Me2bpy)3]21.However, the 1H NMR signal perturbations are in opposite directions for the two interactions, a characteristic which could prove invaluable in the investigation of the actual mode of binding of similar complexes with the larger biological anions. Acknowledgements This work was supported by the Australian Research Council. The authors wish to thank Dr Ian Atkinson for valuable discussions, and assistance with the stability constant calculations.The involvement of Mr David Reitsma in the early stages of the project is acknowledged. References 1 A. Juris, S. Barigelletti, S. Campagna, V. Balzani, P. Belser and A. von Zelewsky, Coord. Chem. Rev., 1988, 84, 85 and refs. therein. 2 V. Balzani and F. Scandola, Supramolecular Photochemistry, Ellis Horwood, Chichester, 1991, p. 427. 3 P. Frediani, M.Bianchi, A. Salvini, R. Guarducci, L. C. Carluccio and F. Piacenti, J. Org. Chem., 1995, 498, 187. 4 P. D. Beer, N. C. Fletcher and T. Wear, Polyhedron, 1996, 15, 1339. 5 F. Szemes, D. Hesek, Z. Chen, S. W. Dent, M. G. B. Drew, A. J. Goulden, A. R. Graydon, A. Grieve, R. J. Mortimer, T. Wear, J. S. Weightman and P. D. Beer, Inorg. Chem., 1996, 35, 5868. 6 L. F. Cooley, S. L. Larson, C. M. Elliott and D. F. Kelley, J. Phys. Chem., 1991, 95, 10694. 7 J. D. Petersen, S. L.Gahan, S. C. Rasmussen and S. E. Ronco, Coord. Chem. Rev., 1994, 132, 15. 8 E. Zahavy, M. Seiler, S. Marx-Tibbon, E. Joselevich, I. Willner, H. Durr, D. O’Connor and A. Harriman, Angew. Chem., 1995, 107, 1012; Angew. Chem., Int. Ed. Engl., 1995, 34, 1005. 9 J.-P. Collin, S. Guillerez, J.-P. Sauvage, F. Barigelletti, L. Flamigni, L. De Cola and V. Balzani, Coord. Chem. Rev., 1991, 111, 291. 10 R Argazzi, C. A. Bignozzi, T. A. Heimer, F. N. Castellano and G. J. Meyer, J. Am. Chem.Soc., 1995, 117, 11815. 11 A. Kirsch-De Mesmaeker, J.-P. Lecomte and J. M. Kelly, Top. Curr. Chem., 1996, 177, 25. 12 A. M. Pyle and J. K. Barton, Prog. Inorg. Chem., 1990, 38, 413. 13 C. Turro, S. Niu, J. K. Barton and N. J. Turro, Inorg. Chim. Acta, 1996, 252, 333. 14 A. von Zelewsky, Chimia, 1994, 48, 331. 15 F. R. Keene, Coord. Chem. Rev., 1997, 166, 121. 16 F. R. Keene, Chem. Soc. Rev., 1998, 27, 185. 17 T. J. Rutherford and F. R. Keene, Inorg. Chem., 1997, 36, 3580. 18 T.J. Rutherford, O. Van Gijte, A. Kirsch-De Mesmaeker and F. R. Keene, Inorg. Chem., 1997, 36, 4465. 19 T. J. Rutherford and F. R. Keene, Inorg. Chem., 1997, 36, 2872. 20 T. J. Rutherford, M. G. Quagliotto and F. R. Keene, Inorg. Chem., 1995, 34, 3857. 21 D. A. Reitsma and F. R. Keene, J. Chem. Soc., Dalton Trans., 1993, 2859. 22 B. T. Patterson and F. R. Keene, Inorg. Chem., 1998, 37, 645. 23 T. J. Rutherford, PhD Thesis, James Cook University, 1997. 24 G. H. Searle, Aust. J. Chem., 1977, 30, 2625. 25 Y. Yoshikawa and K. Yamasaki, Coord. Chem. Rev., 1979, 28, 205. 26 H. Yoneda, J. Chromatogr., 1984, 313, 59. 27 N. C. Fletcher, P. C. Junk, D. A. Reitsma and F. R. Keene, J. Chem. Soc., Dalton Trans., 1998, 133. 28 P. D. Beer, Chem. Commun., 1996, 689. 29 B. L. Hauenstein, W. J. Dressick, T. B. Gilbert, J. N. Demas and B. A. DeGraV, J. Phys. Chem., 1984, 88, 1902. 30 S. W. Snyder, S. L. Buell, J. N. Demas and B. A. DeGraV, J. Phys. Chem., 1989, 93, 5265. 31 K. R. Gopidas, A. R. Leheny, G. Caminati, N. J. Turro and D. A. Tomalia, J. Am. Chem. Soc., 1991, 113, 7335. 32 J. W. Park, M.-H. Kim, S. H. Ko and Y. H. Paik, J. Phys. Chem., 1993, 97, 5424. 33 D. Y. Chu and J. K. Thomas, J. Phys. Chem., 1985, 89, 4065. 34 D. Meisel and M. S. Matheson, J. Am. Chem. Soc., 1977, 6577. 35 G. L. Duveneck, C. V. Kumar, N. J. Turro and J. K. Barton, J. Phys. Chem., 1988, 92, 2028. 36 C. Turro, A. Evenzahav, S. H. Bossmann, J. K. Barton and N. J. Turro, Inorg. Chim. Acta, 1996, 243, 101. 37 J. P. Rehmann and J. K. Barton, Biochemistry, 1990, 29, 1701. 38 A. M. Pyle, J. P. Rehmann, R. Meshoyrer, C. V. Kumar, N. J. Turro and J. K. Barton, J. Am. Chem. Soc., 1989, 111, 3051. 39 J. K. Barton, J. M. Goldberg, C. V. Kumar and N. J. Turro, J. Am. Chem. Soc., 1986, 108, 2081. 40 M. J. Hynes, J. Chem. Soc., Dalton Trans., 1993, 311. 41 I. M. Atkinson, unpublished work. 42 C. S. Wilcox, Frontiers in Supramolecular Organic Chemistry and Photochemistry, ed. H.-J. Schneider and H. Dürr, VCH Verlagsgesallschaft, Weinheim, 1991, p. 123. 43 C. A. Hunter and J. K. M. Sanders, J. Am. Chem. Soc., 1990, 112, 5525. 44 T. J. Rutherford, P. A. Pellegrini, J. Aldrich-Wright, P. C. Junk and F. R. Keene, Eur. J. Inorg. Chem, 1998, 1677. 45 G. J. Kavarnos, Fundamentals of Photoinduced Electron Transfer, VCH, New York, 1993. 46 A. Shulman and F. P. Dwyer, Chelating Agents and Metal Chelates, ed. F. P. Dwyer and D. P. Mellor, Academic Press, New York, 1964, pp. 383–439. 47 P. Lincoln, A. Broo and B. Nordén, J. Am. Chem. Soc., 1996, 118, 2644. Paper 8/09481K

ISSN:1477-9226    

DOI:10.1039/a809481k

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 691–698 691 Oxidatively induced isomerisation of vinylidene ligands to alkynes: ESR spectra of paramagnetic vinylidene and alkyne arene metal complexes Ian M. Bartlett,a Neil G. Connelly,a Antonio J. Martín,a A. Guy Orpen,a Timothy J. Paget,a Anne L. Rieger b and Philip H. Rieger b a School of Chemistry, University of Bristol, Bristol, UK BS8 1TS. E-mail: neil.connelly@bristol.ac.uk b Department of Chemistry, Brown University, Rhode Island, RI 02912, USA Received 3rd December 1998, Accepted 27th January 1999 UV irradiation of [M(CO)3(h-arene)] and Me3SiC]] ] CSiMe3 gives [M(CO)2{C]] C(SiMe3)2}(h-arene)] (M = Cr, arene = C6H2Me4-1,2,3,5 2V, C6H3Me3-1,2,3 3V or C6H6 4V; M = Mo, arene = C6Me6 5V or C6H3Me3-1,3,5 6V).The crystal structure of [Cr(CO)2{C]] C(SiMe3)2}(h-C6H6)] 4V confirms the presence of the vinylidene ligand; the complex has approximate Cs symmetry with the C(SiMe3)2 plane orthogonal to the arenecentroid–Cr–Ca–Cb plane.Voltammetry and IR and NMR spectroscopy show that in solution [Mo(CO)2{C]] C(SiMe3)2}(h-C6H3Me3-1,3,5)] 6V thermally equilibrates with the alkyne isomer [Mo(CO)2(h-Me3SiC]] ] CSiMe3)(h-C6H3Me3-1,3,5)] 6A. The vinylidene complexes [M(CO)2{C]] C(SiMe3)2}(h-arene)] 2V–6V undergo one-electron oxidation to the alkyne cations [M(CO)2- (h-Me3SiC]] ] CSiMe3)(h-arene)]1 2A1–6A1 via fast, redox-induced vinylidene-to-alkyne isomerisation. These cations are reduced to the neutral alkyne complexes [M(CO)2(h-Me3SiC]] ] CSiMe3)(h-arene)] 2A–6A which slowly isomerise thermally to the neutral vinylidene complexes 2V–6V.Paramagnetic vinylidene and alkyne complex cations have been characterised by ESR spectroscopy; unpaired electron density is extensively delocalised from the metal centre to the C2 ligand, in agreement with the results of EHMO calculations. Introduction We have recently presented 1 the results of a detailed study of the mechanism of the redox-induced isomerisation processes linking the vinylidene complex [Cr(CO)2{C]] C(SiMe3)2}- (h-C6Me6)] 1V with the alkyne cation [Cr(CO)2(h-Me3SiC]] ] CSiMe3)(h-C6Me6)]1 1A1, quantifying the kinetics of the conversion of 1V1 into 1A1 and of 1A into 1V.We have also noted that related alkyne cations [Cr(CO)2(h-RC]] ] CR)(h-C6Me6)]1 (R = Ph, C6H4OMe-4, etc.) can be made directly from the neutral complexes [Cr(CO)2(h-RC]] ] CR)(h-C6Me6)],2,3 and have made a brief comparison of the structures of the redox-related pair [Cr(CO)2(h-PhC]] ] CPh)(h-C6Me5H)]z (z = 0 or 1).4 We now describe the characterisation of a wider series of vinylidene complexes, [M(CO)2{C]] C(SiMe3)2}(h-arene)] (M = Cr, arene = C6H2Me4-1,2,3,5 2V, C6H3Me3-1,2,3 3V or C6H6 4V; M = Mo, arene = C6Me6 5V or C6H3Me3-1,3,5 6V), including the crystal structure of [Cr(CO)2{C]] C(SiMe3)2}(h-C6H6)] 4V, and their oxidative isomerisation to the corresponding alkyne cations. Moreover, ESR spectroscopic analysis and EHMO calculations have provided insight into the electronic structure of a unique set of paramagnetic vinylidene and alkyne complex isomers.Results and discussion Synthesis of [M(CO)2{C]] C(SiMe3)2}(Á-arene)] (M 5 Cr or Mo) The chromium and molybdenum complexes [M(CO)2- {C]] C(SiMe3)2}(h-arene)] [M = Cr, arene = C6H2Me4-1,2,3,5 2V, C6H3Me3-1,2,3 3V or C6H6 4V; M = Mo, arene = C6Me6 5V or C6H3Me3-1,3,5 6V) (Chart 1) were prepared by a method analogous to that previously described 1 for [Cr(CO)2- {C]] C(SiMe3)2}(h-C6Me6)] 1V, namely by the UV irradiation of a mixture of [M(CO)3(h-arene)] and Me3SiC]] ] CSiMe3 in solution; the tungsten complexes [W(CO)3(h-arene)] (arene = C6H3Me3-1,3,5 and C6Me6) did not react with Me3SiC]] ] CSiMe3 under the same conditions.The solvent used for the photolysis reaction influences both the yield and reaction time. Thus, complex 2V was prepared in good yield by irradiation in thf whereas the use of this solvent for the less stable complexes 3V, 4V and 6V resulted in extensive decomposition and n-hexane was found to give higher yields.The molybdenum complex [Mo(CO)3(h-C6Me6)] reacted very slowly with Me3SiC]] ] CSiMe3 in n-hexane or thf (ca. 10% conversion in thf after 15 h) but the reaction rate was significantly increased in benzene or toluene (ca. 70% conversion in benzene after 15 h). During the preparation of the vinylidene complex [Mo(CO)2{C]] C(SiMe3)2}(h-C6H3Me3-1,3,5)] 6V the formation of a second product, shown below to be the alkyne isomer [Mo(CO)2(h-Me3SiC]] ] CSiMe3)(h-C6H3Me3-1,3,5)] 6A, was observed; pure samples of 6V were, however, isolated by slow crystallisation from n-hexane at 220 8C.M OC C C O C SiMe3 SiMe3 M OC C O CSiMe C SiMe3 Rn Rn V A Complex M Rn 1V/1A Cr Me6 2V/2A Cr 3V/3A Cr 4V/4A Cr 5V/5A 6V/6A Mo Mo Me6 H2Me4–1,2,3,5 H3Me3–1,2,3 H6 H3Me3–1,3,5 Chart 1 Numbering of vinylidene and alkyne complexes.692 J. Chem.Soc., Dalton Trans., 1999, 691–698 Table 1 Analytical, electrochemical and IR spectroscopic data for chromium and molybdenum arene vinylidene complexes Yield Analysis a (%) IRb/cm21 Complex [Cr(CO)2{C]] C(SiMe3)2}(h-C6Me6)] e 1V [Cr(CO)2{C]] C(SiMe3)2}(h-C6H2Me4-1,2,3,5)] 2V [Cr(CO)2{C]] C(SiMe3)2}(h-C6H3Me3-1,2,3)] 3V [Cr(CO)2{C]] C(SiMe3)2}(h-C6H6)] 4V [Mo(CO)2{C]] C(SiMe3)2}(h-C6Me6)] 5V [Mo(CO)2{C]] C(SiMe3)2}(h-C6H3Me3-1,3,5)] 6V Colour Orange Orange Orange Red Orange Orangered (%) — 39 38 22 27 19 C — 58.3 (58.2) 57.4 (57.3) 54.0 (53.9) 54.5 (54.5) 51.3 (51.6) H — 7.7 (7.8) 7.8 (7.6) 7.2 (6.8) 7.5 (7.5) 6.9 (6.9) n(CO) 1925, 1872ms 1933, 1881ms 1913, 1849ms d 1937, 1886ms 1918, 1855ms d 1949, 1900ms 1929, 1869ms d 1928, 1871ms 1905, 1834ms d 1940, 1884ms 1917, 1848ms d 1915w, 1851w f 1898w, 1818w f,d n(C]] C) 1567m 1576m 1575 d 1576m 1576 d 1586m 1585 d 1567m 1566 d 1578m 1578 d —— Ec,d/V 0.18 (20.24) 0.25 (20.13) 0.28 (20.13) 0.34 (20.03) 0.35 (20.01) 0.44 (0.13) a Calculated values in parentheses.b Strong (s) absorptions in n-hexane unless otherwise stated, m = medium, w = weak. c Peak potential, Epk, of the irreversible oxidation wave; potential for the reversible product wave in parentheses. d In CH2Cl2. e From ref. 1. f Bands for the isomeric alkyne complex [Mo(CO)2(h-Me3SiC]] ] CSiMe3)(h-C6H3Me3-1,3,5)] 6A. Table 2 Proton and 13C-{1H} NMR spectroscopic data for arene chromium and molybdenum complexes a Compound 2V 1H 0.35 (18H, s, SiMe3), 1.60 (3H, s, Me2 or Me5), 1.75 (3H, s, Me2 or Me5), 1.78 (6H, s, Me1,3), 4.55 (2H, s, H4,6) 13C-{1H} 2.7 (SiMe3), 14.7 (Me5), 19.6 (Me1,3), 19.8 (Me2), 98.5 (CH4,6), 105.7 (Cb), 107.7 (CMe5), 110.8 (CMe2), 112.4 (CMe1,3), 239.5 (CO), 349.2 (Ca) 3V 0.38 (18H, s, SiMe3), 1.63 (3H, s, Me2), 1.77 (6H, s, Me1,3), 4.65 (2H, d, JH4H5 and JH5H6 6, H4,6), 4.75 (1H, t, JH4H5 and JH5H6 6, H5) 2.6 (SiMe3), 14.9 (Me2), 19.6 (Me1,3), 96.6 (CH5), 97.2 (CH4,6), 106.4 (Cb), 110.1 (CMe2), 112.0 (CMe1,3), 239.3 (CO), 348.3 (Ca) 4V 0.36 (18H, s, SiMe3), 4.66 (6H, s, C6H6) 2.2 (SiMe3), 96.0 (C6H6), 107.7 (Cb), 238.7 (CO), 347.5 (Ca) 5V 0.41 (18H, s, SiMe3), 1.89 (18H, s, C6Me6) 2.4 (SiMe3), 17.8 (CMe), 101.8 (Cb), 114.2 (CMe), 231.4 (CO), 331.8 (Ca) b 6V 0.39 (18H, s, SiMe3), 1.79 (9H, s, CMe), 4.79 (3H, s, CH) 2.5 (SiMe3), 20.5 (CMe), 98.8 (CH), 100.2 (Cb), 116.4 (CMe), 229.4 (CO), 333.4 (Ca) 6A 0.41 (18H, s, SiMe3), 1.71 (9H, s, CMe), 4.68 (3H, s, CH) 1.7 (SiMe3), 20.2 (CMe), 93.5 (CH), 107.1 (CSiMe3), 110.1 (CMe), 237.4 (CO) a Chemical shift (d) in ppm, J values in Hz, spectra in C6D6 unless stated otherwise.b In CDCl3. There is an extensive array of complexes of the type [Cr(CO)2L(h-arene)] (e.g. L = PR3, RC]] ] CR, R2C]] CR2, RCN, py, CS, N2, thf, etc.),5 but 5V and 6V are rare examples of the molybdenum analogues [Mo(CO)2L(h-arene)]. Generally, carbonyl substitution does not occur when [Mo(CO)3(h-arene)] is treated with L, either thermally or photochemically, mainly because the Mo–Carene bonds are easily cleaved.Indeed, replacement of the arene in [Mo(CO)3(h-arene)] by L provides a convenient and general route to fac-[Mo(CO)3L3].6 Characterisation of the vinylidene complexes 2V–6V Complexes 2V–6V are orange to red crystalline solids the air stability of which decreases from chromium to molybdenum and with decreasing substitution at the arene; solutions of 4V and 6V decompose in air over several minutes.The complexes were characterised by elemental analysis and by IR (Table 1) and NMR spectroscopy (Table 2). The IR spectra show two strong carbonyl bands (between 1834 and 1949 cm21) and a third, weaker, band at lower energy (1566 to 1586 cm21); the last is assigned to n(C]] C) and is typical of a vinylidene complex.7 Both n(CO) and n(C]] C) for 1V–6V move to lower energy as methylation at the arene is increased although changing the metal from Cr to Mo has little eVect.Increased methylation causes the arene to become a better electron donor so that back donation from M to p* CO and C]] CR2 orbitals increases. The vinylidene ligand is generally considered to be a good, essentially single-faced p-acceptor 8 and the vinylidene ligand of [Mn(CO)2(C]] CHPh)(h-C5H5)] has been classified as a better p acceptor than CO.9 The carbonyl bands of 1V–6V are considerably lower in energy than those of [Cr(CO)2(C]] CR2)(h-arene)] (R = Me or Ph) 10 (e.g. 1980 and 1930 cm21 for [Cr(CO)2(C]] CPh2)(h-C6H6)]). Thus the p-accepting ability of the vinylidene ligands follows the order: C]] CPh2 > C]] CMe2 @ C]] C(SiMe3)2. Since b-silyl groups can stabilise carbocations,11 this stabilising eVect may also decrease the electrophilicity of Ca of the vinylidene, so reducing the acceptor ability of the ligand. Uniquely, the IR spectrum of pure 6V in CH2Cl2 changed with time, two extra bands appearing at 1898 and 1818 cm21.These bands continued to grow for ca. 1 h at which point equilibrium appeared to be reached (see below). The new bands are lower in energy than those of 6V (1917, 1848 cm21), consistent with the formation of the alkyne isomer [Mo(CO)2(h-Me3SiC]] ] CSiMe3)(h-C6H3Me3)] 6A. A similar diVerence was noted 1 between the bands of [Cr(CO)2{C]] C(SiMe3)2}(h-C6Me6)] 1V (1901, 1834 cm21) and those of [Cr(CO)2(h-Me3SiC]] ] CSiMe3)- (h-C6Me6)] (1A) (1874 and 1799 cm21).NMR spectroscopy The 1H NMR spectra of 2V–6V (Table 2) do not allow a distinction to be made between the presence of vinylidene or alkyne ligands. Each complex shows a single resonance for the methyl protons of the SiMe3 groups and the expected signals for the arene protons and methyl substituents. However, the diVerent C2 ligands can be distinguished by the characteristic 13C-{1H} NMR resonances of the vinylidene fragment. Thus Ca, the highly deshielded carbon atom bonded directly to the metal, is typically observed between d 258 and 382 7 whereas Cb, much less deshielded, is typically observed between d 87 and 143.For the chromium complexes 2V–4V Ca appears as a weakJ. Chem. Soc., Dalton Trans., 1999, 691–698 693 resonance between d 347 and 350; in the molybdenum complexes 5V and 6V, Ca is slightly less deshielded, at d 332 and 334 respectively. The signal for Cb is also very weak but is observed between d 105 and 108 in 2V–4V and at d 102 and 100 in 5V and 6V respectively.Similar shifts for Ca and Cb were reported for [Cr(CO)2(C]] CR2)(h-C6H6)]; Ca is at d 313 (R = Me) and 328 (R = Ph), and Cb is at d 134 (R = Me) and 132 (R = Ph).10 The room temperature 1H and 13C-{1H} NMR spectra of 6V also show the presence of the alkyne isomer [Mo(CO)2(h-Me3- SiC]] ] CSiMe3)(h-C6H3Me3)] 6A (Table 2); integration of the alkyne and vinylidene peaks in the 1H spectrum provides an estimated ratio of 5 : 1 for the vinylidene to alkyne isomers.The crystal structure of [Cr(CO)2{C]] C(SiMe3)2}(Á-C6H6)] 4V The 13C NMR and IR spectra provide strong evidence for the formulation of 1V–6V as vinylidene complexes. However, the crystal structure of 4V was determined in order to verify the structure and compare the structural parameters with those of other vinylidene complexes. Crystals of [Cr(CO)2{C]] C(SiMe3)2}(h-C6H6)] 4V were grown from a concentrated n-hexane solution cooled to 220 8C for 16 h.The molecular structure of 4V is shown in Fig. 1 and Fig. 1 The molecular structure of [Cr(CO)2{C]] C(SiMe3)2}(h-C6H6)] 4V showing the atom labelling scheme. Hydrogen atoms have been omitted for clarity. Table 3 Selected bond lengths (Å) and angles (8) for [Cr(CO)2- {C]] C(SiMe3)2}(h-C6H6)] 4V Cr–C(1) Cr–C(2) Cr–C(3) Cr–C(4) Cr–C(5) Cr–C(6) ave. Cr–Carene a Si(1)–C(11) Si(1)–C(12) Si(1)–C(13) Si(2)–C(14) Si(2)–C(15) Si(2)–C(16) Cr–C(9)–C(10) C(9)–C(10)–Si(1) C(9)–C(10)–Si(2) Cr–C(7)–O(1) Cr–C(8)–O(2) 2.229(6) 2.204(7) 2.206(8) 2.230(8) 2.215(7) 2.228(6) 2.216(8) 1.848(7) 1.854(7) 1.834(9) 1.832(8) 1.814(11) 1.810(10) 176.5(4) 119.3(4) 117.1(4) 179.5(7) 177.1(6) Cr–C(7) Cr–C(8) ave.Cr–CO Cr–C(9) C(9)–C(10) C(10)–Si(1) C(10)–Si(2) ave. C(10)–Si(Me) C(7)–O(1) C(8)–O(2) Si(1)–C(10)–Si(2) C(7)–Cr–C(8) C(7)–Cr–C(9) C(8)–Cr–C(9) 1.837(7) 1.838(9) 1.838(9) 1.854(5) 1.297(7) 1.872(5) 1.883(5) 1.878(5) 1.155(7) 1.145(8) 123.6(3) 85.9(3) 90.5(3) 86.2(3) a The error given for the mean values is the largest individual standard deviation in the set of values averaged.important bond lengths and angles are listed in Table 3. The benzene ligand eVectively occupies three co-ordination sites of a pseudo-octahedral geometry; the Cr–Carene distances are in the range 2.204–2.230 Å. The metal–carbonyl angles are essentially linear and the Cr–C(O) lengths [average 1.838(9) Å] are similar to those of other neutral arene chromium complexes such as [Cr(CO)3(h-C6H6)] (1.844 Å).12 The almost linear Cr–C(9)–C(10) angle [176.5(4)8] and the short distances Cr– C(9) [1.854(5) Å] and C(9)–C(10) [1.297(7) Å] are consistent with the presence of metal–carbon and carbon–carbon double bonds, as observed in other vinylidene complexes.7 The geometry around C(10) (Cb) is essentially trigonal (angles 117.1– 123.68), consistent with sp2 hybridisation. The large size of the SiMe3 group is reflected in the Si(1)–C(10)–Si(2) angle [123.6(3)8].The silyl atoms of the SiMe3 substituents of the vinylidene ligand lie in a plane perpendicular to an approximate mirror plane lying through AR–Cr–Ca-Cb (AR = centre of the arene), the orientation observed for the isoelectronic complex [Mn- (CO)2(C]] CMe2)(h-C5H5)].13 Molecular orbital studies on [Mn- (CO)2(C]] CR2)(h-C5H5)] have been carried out by HoVmann14 and Fenske.15 The valence orbitals in the metal fragment [Mn(CO)2(h-C5H5)] are derived from those of [Mn(CO)3- (h-C5H5)]; the two most important orbitals involved in bonding to the vinylidene ligand are shown in Fig. 2a. Two symmetrical orientations are possible for the vinylidene, coinciding with the symmetry plane (vertical, the xz plane in Fig. 2b) or bisecting the symmetry plane (horizontal, the yz plane in Fig. 2c). In the horizontal orientation the p and p* orbitals on the vinylidene interact with the metal-based orbitals of a9 symmetry, and the vacant vinylidene C(p) orbital interacts with the metal orbitals of a0 symmetry. In the vertical orientation the combinations are reversed.Thus, the C–C p and p* orbitals overlap with the metal orbitals a0 and the C(p) orbital overlaps with the metal a9 orbitals. For the complexes [M(CO)2(C]] CR2)(h-C5H5)]z1 (M = Fe, z = 1; M = Mn, z = 0) the interaction of the p orbital on Ca with the metal a0 orbital sets the ground state orientation as horizontal (Fig. 2a). However, this orientation is only marginally lower in energy than the vertical orientation and the energy barrier to rotation of the vinylidene ligand is ca. 17 kJ mol21 for [Mn(CO)2(C]] CR2)(h-C5H5)].15 The horizontal orientation appears to be similarly favoured in the arenechromium complex 4V. Electrochemistry The CVs of 2V–6V, at a platinum electrode in CH2Cl2 and at a scan rate of 200 mV s21, are similar to that of 1V,1 showing an irreversible oxidation wave, in the range 0.18 to 0.44 V, (Table 1) accompanied by a reversible product wave, between 20.24 and 0.13 V.Decreasing methylation of the arene increases the potential of both the irreversible oxidation wave and the Fig. 2 (a) Important orbitals of the M(CO)2(h-C5H5) fragment; (b) horizontal and (c) vertical orientations for complexes [M(CO)2- (C]] CR2)(h-C5H5)]z (M = Mn, z = 0; M = Fe, z = 1).694 J. Chem. Soc., Dalton Trans., 1999, 691–698 reversible product wave, by ca. 30 mV per methyl substituent, reflecting the reduced electron density at the metal.The molybdenum complexes are significantly more diYcult to oxidise than their chromium analogues (by ca. 170 mV). The irreversible oxidation wave corresponds to the formation of the cationic vinylidene complex [M(CO)2{C]] C(SiMe3)2}- (h-arene)]1 and its isomerisation to the cationic alkyne complex [M(CO)2(h-Me3SiC]] ] CSiMe3)(h-arene)]1. That the product wave is reversible shows that the isomerisation of [M(CO)2- (h-Me3SiC]] ] CSiMe3)(h-arene)] to [M(CO)2{C]] C(SiMe3)2}- (h-arene)] is slow on the CV timescale.The more positive potential for the oxidation of the vinylidene complex (cf. that for the alkyne complex) reflects a more electron-deficient metal centre. As noted above, NMR and IR spectroscopy suggested that the vinylidene complex [Mo(CO)2{C]] C(SiMe3)2}(h-C6H3Me3- 1,3,5)] 6V slowly equilibrates with the alkyne isomer [Mo(CO)2- (h-Me3SiC]] ] CSiMe3)(h-C6H3Me3-1,3,5)] 6A. The voltammetry of 6V provides conclusive evidence that thermally induced vinylidene-to-alkyne isomerisation does occur in solution (as well as the oxidatively-induced isomerisation process). Fig. 3a shows the CV of 6V ran immediately following the addition of a pure solid sample to the electrochemical cell; it is similar to those observed for the other vinylidene complexes 2V–5V. However, over ca. 20 min a second oxidation wave appears at a potential associated with the oxidation wave of the alkyne complex 6A (Fig. 3b). At this point the IR spectrum of the solution in the electrochemical cell showed the two new bands, at 1898 and 1818 cm21, assigned to the alkyne isomer.The formation with time of the alkyne complex 6A was also studied by using a rotating platinum electrode. Fig. 4a shows the rotating platinum electrode voltammogram (rpev) ca. 45 s after adding 6V to the electrochemical cell; there is only one wave, corresponding to the oxidation of the vinylidene complex. After 5 min a second wave, at the potential anticipated for Fig. 3 CV of [Mo(CO)2{C]] C(SiMe3)2}(h-C6H3Me3-1,3,5)] 6V, (a) after ca. 30 s, (b) after 20 min. Fig. 4 Voltammograms of [Mo(CO)2{C]] C(SiMe3)2}(h-C6H3Me3- 1,3,5)] 6V, from 20.2 to 0.6 V, at a rotating platinum electrode (a) after 45 s, (b) after 2 h. the alkyne complex 6A, begins to appear; Fig. 4b shows the rpev after 2 h by which time equilibrium had been reached. The relative wave heights provide an estimated vinylidene : alkyne ratio at equilibrium of 5 : 1, in good agreement with the results of 1H NMR spectroscopy.For the majority of alkyne and vinylidene complexes, the interconversion of the two bonding modes of the C2 fragment is not observed although in some syntheses of vinylidene complexes from terminal alkynes and a d6 metal centre an intermediate alkyne complex has been detected.16,17 Where isomerisation has been reported, alkyne-to-vinylidene rearrangements are far more common than the reverse vinylidene-to-alkyne isomerisation and the equilibrium between alkyne and vinylidene usually favours one isomer outright.However, the terminal alkyne complex [Re(PPh3)(h-ButC]] ] CH)(NO)(h-C5H5)]1, when heated to 80 8C for 2 h, undergoes alkyne-to-vinylidene isomerisation to give mostly [Re(PPh3)(C]] CHBut)(NO)(h- C5H5)]1; a small amount (ca. 14% by 1H NMR spectroscopy) of [Re(PPh3)(h-ButC]] ] CH)(NO)(h-C5H5)]1 remained even after 7 h. The vinylidene complex [Re(PPh3)(C]] CHBut)(NO)(h- C5H5)]1 has also been made by protonating the alkynyl complex [Re(PPh3)(C]] ] CBut)(NO)(h-C5H5)] with H[BF4] at 278 8C where no alkyne complex is formed.However, heating this cation to 80 8C for 2 h resulted in the same ratio of vinylidene and alkyne isomers, confirming that thermal equilibrium occurs at 80 8C.18 The vinylidene complexes 2V–6V are favoured over the alkyne complexes 2A–6A in that the repulsive interactions between the t2g orbitals (assuming octahedral symmetry) of the d6 metal and the filled alkyne p^ orbital are alleviated.Given the (unique) thermal isomerisation of 6V to 6A, the repulsive interaction appears to be alleviated by reducing the number of methyl groups on the arene and by replacing chromium by molybdenum. Chemical redox reactions The chemical oxidation of 2V–4V was readily eVected by adding one equivalent of [Fe(h-C5H5)2][PF6] to a CH2Cl2 solution of the chromium complexes at 0 8C. In each case, the IR spectrum of the resulting yellow solution shows two new carbonyl Table 4 IR spectroscopic and electrochemical data for alkyne complexes IRa/cm21 Complex 1Ab 1A1b 2A 2A1 3A 3A1 4A 4A1 5A 5A1 6A 6A1 7Ad 7A1 8Ad 8A1 9Ad 9A1 n(CO) 1874, 1799ms 2015ms, 1950 1891, 1817ms 2027ms, 1961 1898, 1826ms 2040ms, 1959 1911, 1841ms 2046ms, 1981 1879, 1802ms 2001, 1941 1898, 1818 2013, 1957 1937, 1861 2060, 2010 1889, 1811 2011, 1965 1894, 1821 2034, 1976 n(C]] ] C) — 1764w — 1785w — 1791w — 1810w — 1736w ———————— E89/V 20.24 c 20.13 c 20.13 c 20.03 c 20.01 c 0.13 c 0.12 20.24, 0.89 20.18 a Strong absorptions (s) in CH2Cl2 unless otherwise stated, m = medium, w = weak.b From ref. 1. c Potential data taken from the reversible product wave observed in the cyclic voltammogram of the isomeric vinylidene complex, in CH2Cl2. d [Cr(CO)2(h-RC]] ] CR9)- (h-C6Me6)] R =R9 =O2CEt 7A, R = R9 = C6H4OMe-4 8A, R = Ph, R9 = H 9A.J. Chem. Soc., Dalton Trans., 1999, 691–698 695 bands shifted to higher energy (by ca. 90 cm21) (Table 4), consistent with the formation of a cationic complex. Furthermore, as in the oxidation of 1V, the n(C]] C) band in 2V–4V is replaced by a much weaker band at higher energy (1785 to 1810 cm21) assigned to n(C]] ] C), indicating the formation of the cationic alkyne complexes [Cr(CO)2(h-Me3SiC]] ] CSiMe3)(h-arene)][PF6] (arene = 1,2,3,5-Me4H2C6 2A1, 1,2,3-Me3H3C6 3A1 or C6H6 4A1). The chemical oxidation of the molybdenum complexes 5V and 6V was carried out in a similar manner to that of the chromium complexes 2V–4V, reaction with one equivalent of [Fe(h-C5H5)2][PF6] resulting in an immediate colour change from orange to pale yellow.With 5V, the IR spectrum showed two new carbonyl bands at 2001 and 1941 cm21 and a weak n(C]] ] C) band at 1736 cm21 consistent with the formation of the cationic alkyne complex [Mo(CO)2(h-Me3SiC]] ] CSiMe3)(h-C6- Me6)]1 5A1. However, the oxidation of 6V did not proceed as cleanly and the IR spectrum of the product solution contained five peaks, at 2050, 2013, 1988, 1957 and 1895 cm21.The strongest two peaks, at 2013 and 1957 cm21, are assigned to n(CO) for the alkyne complex [Mo(CO)2(h-Me3SiC]] ] CSiMe3)- (h-C6H3Me3-1,3,5)][PF6] 6A1 by comparison with those of 5A1 but the other peaks remain unidentified. Attempts to isolate 2A1–6A1 were unsuccessful; their stability decreases with decreasing methylation of the arene and, more strikingly, on changing the metal from chromium to molybdenum.In order to study the stability of the neutral alkyne complexes 2A–6A, solutions of the cations 2A1–6A1 were generated at 0 8C from the neutral vinylidene complexes 2V–6V as described above. Addition of one equivalent of the mild reducing agent [NBun 4][BH4] then resulted in an immediate colour change from yellow to orange. The IR spectrum of each solution showed four new carbonyl bands at lower energy than those of 2A1– 6A1. Two of the bands correspond to those of the neutral vinylidene complexes 2V–4V.The other peaks, at slightly lower energy (ca. 25 cm21) than those of the vinylidene complex, are assigned to the neutral alkyne complexes [Cr(CO)2(h-Me3SiC]] ] CSiMe3)(h-arene)] (arene = C6H2Me4-1,2,3,5 2A, C6H3Me3- 1,2,3 3A or C6H6 4A). Over ca. 20 min the peaks due to the alkyne complexes 2A–4A are replaced by those of the corresponding vinylidene complexes as the alkyne-to-vinylidene isomerisation slowly occurs.The reduction of the molybdenum complex 5A1 with one equivalent of [Co(h-C5H5)2] gave an immediate colour change from yellow to orange, the resulting solution showing only two IR carbonyl bands, at 1879 and 1802 cm21, assigned to the alkyne complex [Mo(CO)2(h-Me3SiC]] ] CSiMe3)(h-C6Me6)] 5A. These bands were then replaced by those of the neutral vinylidene complex 5V over the next hour. Although the oxidation of [Mo(CO)2{C]] C(SiMe3)2}(h-C6H3Me3-1,3,5)] 6V with [Fe(h-C5H5)2][PF6] does not proceed cleanly, as noted above, addition of approximately one equivalent of [Co(h-C5H5)2] to the reaction mixture resulted in the replacement of the carbonyl bands assigned to 6A1 by four bands which can be assigned to the neutral alkyne complex 6A and the vinylidene complex 6V.The oxidation and reduction sequences described above are similar to those observed for [Cr(CO)2{C]] C(SiMe3)2}(h-C6- Me6)] 1V and likewise can be represented by a square scheme (Scheme 1).The qualitative chemical oxidation and reduction studies noted above allow the identification of three members of the square scheme (the vinylidene cations have not been detected by IR spectroscopy, but their ESR spectra are described below). Moreover, it is clear that isomerisation of the neutral alkyne complexes to the vinylidene isomers is much slower than that of the cationic vinylidene to the alkyne containing cation. This has been quantified for 1V1 but the present qualitative study suggests that alkyne-to-vinylidene isomerisation is slower for the d6 molybdenum complexes 5A and 6A than for the chromium complexes 2A–4A.ESR spectroscopic studies of the paramagnetic vinylidene and alkyne complex cations The electronic structures of the paramagnetic vinylidene and alkyne complexes described above have been probed by ESR spectroscopy. At low temperatures the vinylidene-to-alkyne isomerisation is retarded and the cationic vinylidene complexes [M(CO)2{C]] C(SiMe3)2}(h-arene)]1 can be detected by ESR spectroscopy.The complexes 2V1–6V1 were generated in situ by adding solid [Fe(h-C5H5)2][PF6] to frozen CH2Cl2 solutions of 2V–6V at 77 K. The frozen solution was transferred to the cavity of the ESR spectrometer and allowed to warm to 190 K; after ca. 10 min, a spectrum assignable to the vinylidene cation was observed. These spectra consist of a relatively broad line, ·gÒ ª 2.014–2.015, usually accompanied by one or more satellites assigned to coupling to 53Cr (I = 3/2, 9.5% abundance) or 95,97Mo (I = 5/2, 25.5% abundance). A sharper line, also accompanied by satellites, is observed at higher field and assigned to the alkyne complex, [M(CO)2(h-Me3SiC]] ] CSiMe3)(h-arene)]1 2A1–6A1.(Fig. 5 shows the ESR spectrum of 4V1 accompanied by a small amount of 4A1.) At 190 K, the alkyne lines are much weaker than those assigned to the vinylidene complex, but at higher temperatures, they increase in intensity at the expense of the vinylidene lines, and at 250 K or above, only the spectrum of the alkyne complex is observed.ESR parameters for 1V1– 6V1 and 1A1–6A1 are given in Table 5. For comparison, parameters for [Cr(CO)2(h-RC]] ] CR9)(h-C6Me6)]1 (R = R9 = CO2Et 7A1, C6H4OMe-4 8A1; R = Ph, R9 = H 9A1),2 generated directly from the neutral alkyne complexes 7A–9A by oxidation with [Fe(h-C5H5)2][PF6], are given in Table 6, and g components, measured from frozen CH2Cl2–thf solution spectra of 1V1,1 1A1, 7A12 and 8A1, are given in Table 7.The 53Cr or 95,97Mo satellites observed in the spectra of 1A1– 9A1 exhibit a dependence of line width on mI, the nuclear spin quantum number, with the high-field lines substantially broader than those at low field. The lowest-field feature is usually Scheme 1 Square scheme for redox-induced vinylidene–alkyne isomerisations. M OC C C R R C O Men M OC C C R R C O Men + –e– +e– M OC C O Men M OC C O Men + –e– +e– CR CR CR CR Fig. 5 The ESR spectrum of [Cr(CO)2{C]] C(SiMe3)2}(h-C6H6)]1 4V1 in CH2Cl2 at 190 K. The asterisk (*) marks the spectrum of [Cr(CO)2- (h-Me3SiC]] ] CSiMe3)(h-C6H6)]1 4A1.696 J. Chem. Soc., Dalton Trans., 1999, 691–698 Table 5 Isotropic ESR parameters for [M(CO)2{C]] C(SiMe3)2}(h-arene)]1 and [M(CO)2(h-Me3SiC]] CSiMe3)(h-arene)]1 in CH2Cl2 M Cr Cr Cr Cr Mo Mo arene C6Me6 C6H2Me4-1,2,3,5 C6H3Me3-1,3,5 C6H6 C6Me6 C6H3Me3-1,3,5 Complex 1V1a 2V1 3V1 4V1 5V1 6V1 ·gÒ 2.0139(2) 2.0155(2) 2.0150(1) 2.0140(2) 2.0412(1) 2.0436(6) ·aMÒ/G 13.1(1) 12.8(1) 13.15(3) 13.09(6) 18.1(3) 18.5(4) Complex 1A1 2A1 3A1 4A1 5A1 6A1 ·gÒ 1.9983(1) 1.9991(1) 1.9989(1) 1.9980(1) 2.0140(1) 2.0160(1) ·aMÒ/G 16.77(1) 16.8(3) 16.79(2) 17.02(1) 29.65(3) 29.74(4) ·aHÒ/G — 1.50(5) (2 H) — 1.418(5) (6 H) — 2.2(1) (3 H) a From ref. 1. sharper than the central line and, in some spectra of alkyne complexes, e.g. that of [Cr(CO)2(h-Me3SiC]] ] CSiMe3)(h-C6H6)]1 4A1 (Fig. 6), arene proton hyperfine coupling is resolved comparable to that observed in the spectra of the sandwich complexes [M(h-arene)2]1 (M = Cr, Mo),19,20 anisotropic ESR parameters for which are given in Table 7.Extended Hückel MO calculations were performed on [Cr- (h-C6H6)2]1, [Cr(CO)2(h-HC]] ] CH)(h-C6H6)]1, and [Cr(CO)2- (C]] CH2)(h-C6H6)]1 using idealised coordinates derived from the crystal structures of the Cr(0) complexes [Cr(h-C6H6)2],21 [Cr(CO)2(h-PhC]] ] CPh)(h-C6Me5H)] 4 and 4V respectively, and parameters collated by Alvarez.22 The results for [Cr(h-C6H6)2]1 are essentially identical to those reported by Muetterties et al.23 The a1g SOMO is nearly purely metal dz2, and the e2g pair, largely metal dx2 2 y2 and dxy, lies at slightly lower energy.Metal dxz and dyz mainly contribute to weakly anti-bonding, empty MOs. The frontier orbitals for the alkyne and vinylidene complexes show family resemblances to those of [Cr(h-C6H6)2]1 although the lower symmetry allows considerable d-orbital hybridisation; the principal interactions for the Cr(CO)2(h-C6- Fig. 6 The ESR spectrum of [Cr(CO)2(h-Me3SiC]] ] CSiMe3)(h-C6H6)]1 4A1 in CH2Cl2 at 250 K, showing hyperfine coupling to the arene protons and the variation in line width of the 53Cr satellites. Table 6 Isotropic ESR parameters for [Cr(CO)2(h-RC]] ] CR9)(h-C6- Me6)]1 in CH2Cl2 Complex 7A1a 8A1 9A1 R CO2Et C6H4- OMe-4 Ph R9 CO2Et C6H4- OMe-4 H ·gÒ 1.9936(1) 1.9956(1) 1.9964(1) ·aCrÒ/G 16.78(3) 14.38(2) 16.12(2) ·aXÒ/G 9.1(1) (2 C) — 4.17(5) (1 H) a From ref. 2. Table 7 Anisotropic ESR parameters for arene metal complexes Complex [Cr(h-C6H6)2]1 [Mo(h-C6H6)2]1 1V1 1A1 7A1 8A1 gx 1.978 1.977 1.993 1.994 1.995 1.996 gy 1.978 1.977 2.020 1.986 1.979 1.983 gz 2.002 1.998 2.030 2.017 2.007 2.009 Ref. 19 20 1 This work 2 This work H6) vinylidene complex are similar to those shown in Fig. 2 for the isoelectronic [Mn(CO)2(h-C5H5)]1 fragment. For both the alkyne and vinylidene complexes, the a9 SOMO is significantly delocalised into ligand p orbitals and the metal contribution is a dz2/dx2 2 y2/dxz hybrid: 28, 12 and 2% for the vinylidene complex, 43, 11 and 0.3% for the alkyne complex; in either case, the metal contribution is best described as dz2 2 x2.The next two filled MOs, related to the e2g pair for [Cr(h-C6H6)2]1, are an a9 MO with metal dx2 2 y2/dz2/dxz character (34, 16 and 3% for the vinylidene complex, 44, 11 and 0.4% for the alkyne complex, in either case best described as dy2) and an a0 MO with metal dxy/dyz character (44 and 2% for the vinylidene complex, 45 and 6% for the alkyne complex), similar to the a0 orbital of Fig. 2. These orbitals are very similar in shape to those found by HoVmann14 for [Mn(CO)2(HC]] ] CH)(h-C5H5)] and [Mn(CO)2- (C]] CH2)(h-C5H5)], but the energy order of the two a9 molecular orbitals is inverted. The dz2 character of the SOMO is confirmed for the alkyne complexes by the appearance of hyperfine coupling to the arene ring protons.The proton couplings observed in the ESR spectra of [Cr(h-C6H6)2]1 (3.46 G),19 [Mo(h-C6H6)2]1 (4.45 G),20 and related species are positive in sign 24 and have been interpreted as resulting from direct delocalisation of the predominantly metal dz2 SOMO into the s-orbitals of the arene; 25 the usual mechanism whereby proton couplings in arene radical ions arise from spin polarisation by p spin density is of negligible importance in these systems.If we assume that the arene proton coupling is proportional to the metal dz2 character, the observed 3.46 G coupling for [Cr(h-C6H6)2]1, together with the EHMO calculations, suggests a coupling of 1.6 G for [Cr(CO)2(h-HC]] ] CH)(h-C6H6)]1 and 1.4 G for [Cr(CO)2(C]] CH2)(h-C6H6)]1. This prediction is in reasonable agreement with the observed couplings for 2A1 and 4A1. No proton coupling could be resolved for the vinylidene complexes, in part because the isotropic spectra could be observed only at relatively low temperatures where lines are too broad to resolve the proton coupling.The larger proton coupling found for 6A1 is consistent with the larger coupling observed for [Mo(h-C6H6)2]1. Spin–orbit coupling of the dz2 SOMO with dxz and dyz for [Cr(h-C6H6)2]1 leads to g^ < ge, g|| = ge. In addition to similar contributions for the alkyne and vinylidene model complexes, coupling of the dx2 2 y2 SOMO contribution with dxy leads to gz slightly larger than the free-electron value. For the alkyne complex, the dxz contributions to empty MOs still dominate so that gy remains less than ge, but for the vinylidene complex, the dxz contributions to the SOMO and to the filled MOs lead to gy slightly larger than ge.In general, these results are in good agreement with the experimental results and allow us to make tentative assignments of the g-matrix components: for the alkyne complexes, gz > gx > gy; for the vinylidene complexes, gz > gy > gx.The mI-dependence of the satellite line widths is similar to that observed in the spectra of [Cr(h-C6H6)2]1 and related species.26 Line widths can be expressed by eqn. (1) where Width = a 1 bmI 1 gmI2 (1) the parameters a, b and g are related to the anisotropies of theJ. Chem. Soc., Dalton Trans., 1999, 691–698 697 g- and metal-hyperfine matrices.27 In the case of [Cr(h-C6H6)2]1, it is known that ·aCrÒ is positive so that the observed increase in width with increasing magnetic field implies that b is negative.(The nuclear magnetic moments of 53Cr and 95,97Mo are negative so that a spin polarisation mechanism is expected to lead to positive isotropic coupling constants.) For w0tr @ 1, |·AÒ|/w0 ! 1, the parameter b is given by eqn. (2), where tr is the b = 4– 15 B0(b Dg 1 4c dg) tr (2) rotational correlation time, w0 is the angular microwave frequency, and the other parameters are given by eqns.(3a–d). For b = 2 3 – [Az 2 ��� (Ax 1 Ay)] (3a) c = 1– 4 (Ax 2 Ay) (3b) Dg = 2pmB h [gz 2 ��� (gx 1 gy)] (3c) dg = pmB h (gx 2 gy) (3d) [Cr(h-C6H6)2]1, c = dg = 0, Dg > 0 and, for the dz2 SOMO, we expect Az, and thus b, to be negative, consistent with the observed line widths. Assuming ·ACrÒ is also positive for the alkyne and vinylidene cations, we again have b < 0. With the g-component assignments given in Table 7, Dg > 0 for both alkyne and vinylidene complexes, dg > 0 for alkyne complexes, and dg < 0 for vinylidene complexes.If we describe the metal SOMO contribution as dz2 2 x2, we expect a dipolar contribution 1Q to Ay, 2Q/2 to Ax and Az; thus b = 2Q/2, c = 23Q/8. Substituting numbers in eqn. (3c), (3d) and (2), we find balkyne ! bvinylidene < 0, consistent with the experimental results. Coupling to a single proton was observed in the ESR spectrum of [Cr(CO)2(h-PhC]] ] CH)(h-C6Me6)]1 9A12 and to two 13C nuclei in the spectrum of [Cr(CO)2(EtCO2C]] ] CCO2Et)(h- C6Me6)]1 7A1.Lines in the spectra of [Cr(CO)2(h-4-MeOC6- H4C]] ] CC6H4OMe-4)(h-C6Me6)]1 8A1 are significantly broader than those of 7A1 and are noticeably non-Lorentzian, suggesting unresolved hyperfine coupling to the phenyl ring protons. These results are consistent with the extensive delocalisation of the SOMO into the alkyne p-orbitals predicted by EHMO calculations. Indeed, the EHMO results suggest a carbon 2pp spin density of 0.074, nearly large enough to explain the proton coupling for 9A1 in terms of the usual indirect polarisation mechanism.Since the 53Cr or 95,97Mo couplings arise primarily through polarisation of inner-shell s-orbitals by 3d or 4d metal spin density, it is tempting to use these couplings as measures of the metal d-orbital character in the SOMOs. Since ·aCrÒ = 18.1 G for [Cr(h-C6H6)2]1,19 this measure would suggest a SOMO with nearly as much Cr 3d character for the alkyne complexes and only slightly smaller values for the vinylidene complexes.Unfortunately, in all cases the SOMOs belong to totally symmetric representations and metal 4s character is permitted. This leads to a negative contribution to ·aCrÒ, 2267 r4s G,28 cancelling part of the dominant polarisation contribution. EHMO calculations suggest that metal 4s SOMO character is suf- ficiently variable that the metal coupling cannot be used as a reliable measure of metal 3d SOMO character. Conclusions UV irradiation of [M(CO)3(h-C6Me6 2 nHn)] (M = Cr, Mo) with the alkyne Me3SiC]] ] CSiMe3 generally gives the vinylidene complexes [M(CO)2{C]] C(SiMe3)2}(h-C6HnMe6 2 n)] rather than the alkyne complexes [M(CO)2(h-Me3SiC]] ] CSiMe3)(h- C6HnMe6 2 n)].However, the molybdenum complex [Mo(CO)2- {C]] C(SiMe3)2}(h-C6H3Me3-1,3,5)] reaches thermal equilibrium with the alkyne complex [Mo(CO)2(h-Me3SiC]] ] CSiMe3)- (h-C6H3Me3-1,3,5)] in solution. By contrast, for the more substituted arene complexes such as [Mo(CO)2{C]] C(SiMe3)2}- (h-C6Me6)], no vinylidene-to-alkyne isomerisation is observed.One-electron oxidation of the vinylidene complexes [M(CO)2{C]] C(SiMe3)2}(h-C6HnMe6 2 n)] (M = Mo, Cr) gives the cationic alkyne complexes [M(CO)2(h-Me3SiC]] ] CSiMe3)- (h-C6HnMe6 2 n)]1 via a fast redox-induced vinylidene-to-alkyne isomerisation. However, on reduction the neutral alkyne complex [M(CO)2{C]] C(SiMe3)2}(h-C6HnMe6 2 n)] is formed which slowly isomerises to the neutral vinylidene complex.Analysis of the ESR spectra of [M(CO)2{C]] C(SiMe3)2}- (h-C6HnMe6 2 n)]1 and [M(CO)2(h-Me3SiC]] ] CSiMe3)(h-C6Hn- Me6 2 n)]1 shows the unpaired electron to be extensively delocalised on to the alkyne, in agreement with the results of EHMO calculations. Experimental The preparation, purification and reactions of the complexes described were carried out under an atmosphere of dry dinitrogen using dried, distilled and deoxygenated solvents; reactions were monitored by IR spectroscopy where necessary.The compounds [M(CO)3(h-arene)] (M = Cr29 or Mo30), [Cr(CO)2- {C]] C(SiMe3)2}(h-C6Me6)],1 [Cr(CO)2(h-RC]] ] CR9)(h-C6Me6)] (R = R9 = Ph, 4-MeOC6H4C]] ] CC6H4OMe-4, CO2Et; R = Ph, R9 = H)3 and [Fe(h-C5H5)2][PF6] 31 were prepared by published methods. IR spectra were recorded on a Nicolet 5ZDX FT spectrometer. 1H and 13C NMR spectra were recorded on JEOL GX270, l300 or GX400 spectrometers with SiMe4 as internal standard.X-Band ESR spectra were recorded using a Bruker ESP-300E spectrometer equipped with a Bruker variabletemperature accessory and a Hewlett Packard 5350B microwave frequency counter. The field calibration was checked by measuring the resonance of the diphenylpicrylhydrazyl (dpph) radical. Cyclic voltammetry was carried out as previously described; 32 for rpev the platinum electrode was rotated at 600 r.p.m. Under the conditions used for voltammetry, E89 for the one-electron reduction of [Co(h-C5H5)2][BF4], added to the test solutions as an internal calibrant, is 20.87 V.(On this scale, the one-electron oxidation of ferrocene occurs at 0.47 V.) Microanalyses were carried out by the staV of the Microanalytical Service of the School of Chemistry, University of Bristol. Syntheses [Cr(CO)2{C]] C(SiMe3)2}(Á-C6H2Me4-1,2,3,5)] 2V. A stirred solution of [Cr(CO)3(h-C6H2Me4-1,2,3, 1.85 mmol) and Me3SiC]] ] CSiMe3 (2 cm3, 8.90 mmol) in thf (70 cm3) was irradiated under UV light for 5 h while a slow purge of nitrogen (ca. 1 bubble per second) was passed through the mixture. The resulting brown-orange solution was evaporated to dryness in vacuo and the residue extracted into n-hexane (70 cm3). After filtration through Celite, the orange solution was reduced in volume to ca. 20 cm3 and then stored at 220 8C for 18 h giving the product as orange needles, yield 0.30 g (39%). The solid complex is stable in air for several weeks.It dissolves in most organic solvents to give moderately air-sensitive solutions. The complexes [Cr(CO)2{C]] C(SiMe3)2}(h-C6H3Me3-1,2,3)] 3V and [Cr(CO)2{C]] C(SiMe3)2}(h-C6H6)] 4V were prepared similarly; UV irradiation was carried out in n-hexane (for 6 h and 27 h respectively) and the reaction mixture was filtered, evaporated to low volume in vacuo and cooled to induce crystallisation. Air stability, both in the solid state and in solution, decreases with decreasing methylation of the arene ligand.[Mo(CO)2{C]] C(SiMe3)2}(Á-C6Me6)] 5V. A stirred solution of [Mo(CO)3(h-C6Me6)] (0.50 g, 1.46 mmol) and Me3SiC]] ] CSiMe3 (2 cm3, 8.90 mmol) in benzene (120 cm3), purged with a stream of N2, was irradiated under UV light for 16 h to give an698 J. Chem. Soc., Dalton Trans., 1999, 691–698 orange solution which was evaporated to dryness in vacuo. The residue was extracted into diethyl ether (180 cm3) and filtered through Celite to give an orange solution which was treated with n-hexane (80 cm3).Removal of the diethyl ether in vacuo and cooling to 220 8C for 5 h gave the product as orange needles, yield 0.19 g (27%). The solid complex is stable in air for ca. 1 d and soluble in most organic solvents (sparingly in nhexane, insoluble in MeCN) to give solutions which decompose in air in minutes. The complex [Mo(CO)2{C]] C(SiMe3)2}(h-C6H3Me3-1,3,5)] 6V was prepared similarly, in n-hexane. The reaction mixture also contains small amounts of [Mo(CO)2(h-Me3SiC]] ] CSiMe3)- (h-C6H3Me3-1,3,5)] but crystallisation of the filtered solution at 220 8C gave pure orange-red needles of [Mo(CO)2- {C]] C(SiMe3)2}(h-C6H3Me3-1,3,5)].The solid is stable in air for a few hours; solutions in organic solvents are air-sensitive. Structure determination of [Cr(CO)2{C]] C(SiMe3)2}(Á-C6H6)] 4V Many of the details of the structure analysis of [Cr(CO)2- {C]] C(SiMe3)2}(h-C6H6)] 4V are presented in Table 8. Crystal decay of ca. 35% was observed over the period of data collection; an appropriate correction was made. CCDC reference number 186/1336. Acknowledgements We thank the EPSRC for a Postdoctoral Research Associateship (to T. J. P.), the Spanish Ministerio de Educacion y Ciencia for an FPU (Becas en el extranjero) grant (to A. J. M.) and the University of Bristol for a Postgraduate Scholarship (to I. M. B.). References 1 N. G. Connelly, W. E. Geiger, M. C. Lagunas, B. Metz, A. L. Rieger, P.H. Rieger and M. J. Shaw, J. Am. Chem. Soc., 1995, 117, 12202. Table 8 Crystal and refinement data for complex 4V Formula M Crystal system Space group (no.) a/Å b/Å c/Å b/8 T/K U/Å3 Z m/mm21 Reflections collected Independent reflections (Rint) Goodness-of-fit on F2 Final R indices [I > 2s(I)]: R1, wR2 C16H24CrO2Si2 356.53 Monoclinic C2/c (15) 34.627(7) 6.8137(14) 16.501(3) 94.67(3) 293(2) 3880.3(14) 8 0.714 3441 3373 (0.0468) 1.138 0.0662, 0.1419 2 N. G. Connelly, A. G. Orpen, A.L. Rieger, P. H. Rieger, C. J. Scott and G. M. Rosair, J. Chem. Soc., Chem. Commun., 1992, 1293. 3 N. G. Connelly and G. A. Johnson, J. Organomet. Chem., 1974, 77, 341. 4 I. M. Bartlett, N. G. Connelly, A. G. Orpen, M. J. Quayle and J. C. Rankin, Chem. Commun., 1996, 2583. 5 R. Davis and L. A. P. Kane-Maguire, in Comprehensive Organometallic Chemistry, eds. G. W. Wilkinson, F. G. A. Stone and E. W. Abel, Pergamon Press, Oxford, 1982, vol. 3, 1035. 6 R. Davis and L. A.P. Kane-Maguire, in Comprehensive Organometallic Chemistry, eds. G. W. Wilkinson, F. G. A. Stone and E. W. Abel, Pergamon Press, Oxford, 1982, vol. 3, 1218. 7 M. I. Bruce, Chem. Rev., 1991, 91, 197. 8 M. I. Bruce and A. G. Swincer, Adv. Organomet. Chem., 1983, 22, 59. 9 A. B. Antonova, N. E. Kolobova, P. V. Petrovsky, B. V. Lokshin and N. S. Obezyuk, J. Organomet. Chem., 1977, 137, 55. 10 U. Schubert and J. Grönen, Chem. Ber., 1989, 122, 1237; U. Schubert, U. Kirchgässner, J. Grönen and H. Piana, Polyhedron, 1989, 8, 1589. 11 P. D. Magnus, T. Sarkar and S. Djuric, in Comprehensive Organometallic Chemistry, eds. G. W. Wilkinson, F. G. A. Stone and E. W. Abel, Pergamon Press, Oxford, 1982, vol. 7, 515. 12 B. Rees and P. Coppens, Acta Crystallogr., Sect. B, 1973, 29, 2516. 13 H. Berke, G. Huttner and J. von Seyerl, J. Organomet. Chem., 1981, 218, 193. 14 J. Silvestre and R. HoVmann, Helv. Chim. Acta, 1985, 68, 1461. 15 N. M. Kostic and R. F. Fenske, Organometallics, 1982, 1, 974. 16 K. R. Birdwhistell, T. L. Tonker and J. L. Templeton, J. Am. Chem. Soc., 1987, 109, 1401. 17 R. M. Bullock, J. Chem. Soc., Chem. Commun., 1989, 165. 18 J. J. Kowalczyk, A. M. Arif and J. A. Gladysz, Organometallics, 1991, 10, 1079. 19 R. Prins and F. J. Reinders, Chem. Phys. Lett., 1969, 3, 45. 20 K. H. Hausser, Naturwissenshaften, 1961, 48, 426. 21 E. Keules and F. Jellinek, J. Organomet. Chem., 1966, 5, 490. 22 S. Alvarez, Tables of Parameters for Extended Huckel Calculations, University of Barcelona, Barcelona, 1989. 23 E. L. Muetterties, J. R. Bleeke, E. J. Wucherer and T. A. Albright, Chem. Rev., 1982, 82, 499. 24 A. D. Krivospitskii and G. K. Chirkin, Zh. Strukt. Khim., 1974, 15, 25. 25 S. E. Anderson, Jr. and R. S. Drago, Inorg Chem., 1972, 11, 1564. 26 W. Karthe and W. Kleinwächter, Ann. Phys. (Leipzig), 1968, 21, 137; B. G. Gribov, B. I. Kozyrkin, A. D. Krivospitskii and G. K. Chirkin, Dokl. Akad. Nauk SSSR, 1970, 193, 91. 27 R. Wilson and D. Kivelson, J. Chem. Phys., 1966, 44, 4445. 28 J. R. Morton and K. F. Preston, J. Magn. Reson., 1978, 30, 577. 29 B. Nicholls and M. C. Whiting, J. Chem. Soc., 1959, 551. 30 A. Pidcock, J. D. Smith and B. W. Taylor, J. Chem. Soc. A, 1967, 872. 31 N. G. Connelly and W. E. Geiger, Chem. Rev., 1996, 96, 877; J. C. Smart and B. L. Pinsky, J. Am. Chem. Soc., 1980, 102, 1009. 32 N. C. Brown, G. B. Carpenter, N. G. Connelly, J. G. Crossley, A. Martin, A. G. Orpen, A. L. Rieger, P. H. Rieger and G. H. Worth, J. Chem. Soc., Dalton Trans., 1996, 3977. Paper 8/09451I

ISSN:1477-9226    

DOI:10.1039/a809451i

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 699–710 699 Supramolecular networks via hydrogen bonding and stacking interactions for adenosine 59-diphosphate. Synthesis and crystal structure of diaqua(2,29:69,20-terpyridine)copper(II) [adenosine 59-diphosphato(32)](2,29:69,20-terpyridine)cuprate(II) adenosine 59-diphosphate(12) hexadecahydrate and density functional geometry optimization analysis of copper(II)- and zinc(II)- pyrophosphate complexes Renzo Cini * and Claudia PiVeri Dipartimento di Scienze e Tecnologie Chimiche e dei Biosistemi, Università di Siena, Pian dei Mantellini 44, I-53100 Siena, Italia. E-mail: cini@cuces.unisi.it Received 7th October 1998, Accepted 12th January 1999 Single crystal X-ray diVraction showed that crystals of [Cu(TERPY)(H2O)2][Cu(TERPY)(ADP)][H2ADP]?16H2O [TERPY = 2,29:69:20-terpyridine; ADP = adenosine 59-diphosphate(3-)] belong to the triclinic system, space group P1 (no. 1) and contain free nucleotide molecules, nucleotide molecules linked to the metal centre of Cu(TERPY)21 units, [Cu(TERPY)(H2O)2]21 complexes and free water molecules. The molecules of free nucleotide, [Cu(TERPY)- (ADP)]2 and [Cu(TERPY)(H2O)2]21 are clustered together and interact via the phosphate moieties and the Cu(H2O)2 21 group.An extensive web of hydrogen bonds holds the three molecules oriented in such a way that the most hydrophobic regions (TERPY) occupy the perimeter of a pocket which contains the pyrophosphate systems.Stacking interactions between the adenine rings and the TERPY ligands stabilize the supramolecular aggregates. Owing to the high content of cocrystallized water molecules the nucleotides have an environment similar to the aqueous phase. The analysis of the Fourier-diVerence map and of the geometrical parameters of the molecules is consistent with a model in which the free nucleotide molecule is protonated at N(1) and phosphate(b), whereas the copper-bound nucleotide molecule is fully deprotonated as regards the N(1) and phosphate oxygen atoms.The phosphate(b) of the copper-bound nucleotide behaves as a better ligand than phosphate(a) [Cu–O, 1.919(8) and 2.244(10) Å, respectively]. The chelation to the metal of the pyrophosphate moiety causes a lengthening of 0.040(9) Å of the P(b)–OP bond with respect to P(a)–OP. A density functional analysis at the B3LYP/LANL2DZ level was carried out on P2O7 42, HP2O7 32, [Cu(O,O-PO4)]2, [Cu{O(a),O(b)-P2O7}]22, [Zn{O(a),O(b)-P2O7}]22, [Zn{O(a),O(b)-HP2O7}(H2O)(OH)]22, [Cu{O(a),O(b)-HP2O7}(NH3)3]2 and [Zn{O(a),O(b)-HP2O7}(NH3)2]2?NH3.The computational procedure was able to reproduce the overall conformation (bond and torsion angles) of the pyrophosphate group as well as the structure of the co-ordination ring found in the solid state. The computed fully optimized structure for [Cu{O(a),O(b)-P2O7}]22 has a Cu–O bond distance of 1.837 Å and the co-ordination ring has a boat-envelope conformation, in agreement with the experimental structure found for the metal-bound nucleotide molecule.The structural characterization via diVraction techniques of metal-nucleoside polyphosphate complexes is a diYcult task because of the problems encountered in growing suitable single crystals. In spite of the significant improvements in experimental devices for data collection, like high power sources and reliable fast detecting tools, the number of accurate crystal structure analyses for metal–nucleoside polyphosphates so far reported is quite small.1a The presence of many complex species in the mother-solution, of diVerently protonated forms, of conformation equilibria, and the occurrence of hydrolytic processes on the phosphate chain catalysed by the metal ions are some of the causes of frustration.The enormous scientific interest about nucleoside 59-diphosphate and -triphosphate arises because the most important bioenergetic processes involve ATP (adenosine 59-triphosphate), ADP, AMP (adenosine 59-monophosphate), phosphate and pyrophosphate (or diphosphate).1b,c A general feature of enzymes which catalyse the hydrolysis of phosphoanhydride bonds is the requirement of divalent metal ions for activation.1d These enzymes recognize divalent cation (usually magnesium)–nucleotide complexes as substrates, rather than free nucleotide molecules.1e The investigation of metal–nucleoside, -nucleotide linkages is also of importance to understand metal–nucleic acid interactions and the biological mechanism of certain metal based drugs.1f–l Moreover, nucleotide and nucleoside analogues are investigated as drugs, mostly for their antiviral activities.1m,n The knowledge of accurate geometrical parameters from diffraction studies in the solid state of nucleoside 59-diphosphate and -triphosphate molecules as well as those of the relevant metal complexes is very important for understanding the coordinating ability, hydrogen bond formation and base pairing schemes, and the conformation of flexible moieties such as ribose and phosphates.What can be learnt from such studies throws light on many biochemical processes and helps in interpreting the Fourier maps calculated from diVraction data of crystals containing enzyme–nucleotide adducts. To cite a few examples, in the work by Löwe and Amos2 on the structure of a 1 : 1 adduct between FtsZ protein (a GTPase in eubacteria; after filamenting temperature-sensitive mutant Z genes) and GDP (guanosine 59-diphosphate), by Davies et al.3 on the structure of a 1 : 1 adduct between 3-phosphoglycerate kinase from a procaryotic cell and ADP, and by Janin and co-workers 4 on700 J.Chem. Soc., Dalton Trans., 1999, 699–710 the structure of a nucleoside diphosphate kinase–ADP-Mg21 complex, the authors stress how the conformation of the phosphate chain and ribose, the method of linking of the nucleotide to metal ions, the hydrogen-bond formation to the base, sugar and phosphate moieties are the basis of molecular recognition, self-assembly and catalytic activity of the protein also in the particular cases of nucleoside diphosphates as substrates.The concepts of self-assembly, molecular recognition and supramolecular chemistry 5,6 are strictly related and have been noted and emphasized in a growing number of scientific reports.7,8 Metal–ligand co-ordination, electrostatic forces, hydrogen bonds, stacking interactions, cation p system 9 and (R)H–p system interactions,10 and torsional equilibria control the selfassembly processes.In biological systems all these components are interconnected and chemists have only a very poor understanding of the ways through which they relate to one another to give self-assembly and dynamic eVects. In all the cases of biological importance water molecules and protonation/ deprotonation processes play an important role for influencing the conformation of biomolecules and the method of assembling molecular aggregates.In turn the success in growing crystals depends in general on the process through which molecular subunits spontaneously aggregate (i.e. chemical selfassembly). EVorts devoted to understanding metal–nucleoside and –nucleotide co-ordination have continued in this laboratory 11–14 and attention was recently focused on three aspects: (1) the choice of a second ligand which can occupy up to three coordination sites so reducing the number of donors from the nucleotide ligand;14 (2) the supramolecular structures organized in highly hydrated crystals; (3) the ability of accessible (also for an inorganic chemistry laboratory) theoretical approaches to simulate the covalent metal–ligand systems and the noncovalent complex–ligand interactions.Here we report on the preparation and structural characterization of highly hydrated single crystals containing adenosine 59-diphosphate and copper(II) ions with the stoichiometry [Cu(H2O)2(TERPY)]- [Cu(TERPY)(ADP)] [H2ADP]?16H2O, and on the density functional geometry optimization of model systems.The existence of supramolecular aggregates of complex molecules, H2ADP2 molecules and water molecules is deeply analysed and discussed. Experimental Materials Di(cyclohexylammonium)adenosine 59-diphosphate 2.5 hydrate [MCHA]2[HADP] was purchased from Sigma, 2,29:69,20-terpyridine from Fluka, copper(II) sulfate pentahydrate, analytical grade, from Carlo Erba and 96% EtOH from Merck.All the chemicals and solvents were used without any other purification. Synthesis of [Cu(TERPY)(H2O)2]21 [Cu(TERPY)(ADP)]2- [H2ADP]2?16 H2O The salt [MCHA]2[HADP] (25 mg, 3.7 × 1022 mmol) was added to a clear solution of TERPY (8.7 mg, 3.7 × 1022 mmol) and 96% EtOH (1.5 mL). Water (20 drops) was added to the suspension to obtain the complete dissolution of [MCHA]2- [HADP]. Copper sulfate pentahydrate (9 mg, 3.6 × 10 22 mmol) was dissolved in water (1 mL).The two solutions were mixed at room temperature. The final blue solution was heated for a few minutes at 70 8C. Single crystals suitable for X-ray diVraction were obtained by slowly evaporating the aqueous solution in an air atmosphere at room temperature. The crystals grew within 3 d from the mixing. They were collected, washed twice with cold water (5 mL each), twice with EtOH (3 mL each) and then stored in a sealed vessel at 5 8C.Yield 60%. Found: C, 34.02; H, 4.83; N, 12.8; P, 6.94. Calc. for C25H42CuN8O19P2: C, 33.96; H, 4.79; N, 12.67; P, 7.01%. Infrared spectroscopy The infrared spectra from KBr pellets were recorded on a Perkin-Elmer 1800 spectrometer. X-Ray diVraction X-Ray powder diVraction data were taken with Cu-Ka radiation (l = 1.5418 Å, graphite monochromatized) on a Siemens D500 diVractometer. The generator was operated at 40 kV, 20 mA. Selected lines are (d, interplanar distance Å; relative intensity): 6.46, s (strong); 5.31, s; 3.38, s; 2.00, m (medium); 1.84, m; 1.76, m; 1.72, s.Single crystal X-ray diVraction was performed on a blue plate (0.30 × 0.30 × 0.05 mm) chosen at the polarizing microscope and mounted on a glass fiber. Preliminary oscillation and Weissenberg photograms indicated that the crystal belonged to the triclinic system. The data collection was performed on a Siemens P4 diVractometer operating at 293 K.Crystallographic data are reported in Table 1. Unit cell parameters were obtained by least-squares refinement of the angles of 28 randomly selected reflections (10 < 2q < 358). The intensities were corrected for Lorentz-polarization eVects; absorption correction was performed through the y-scan technique. Reflections were considered observed [I > 2s(I)]. The copper atoms and most of the atoms of the diphosphate chains of the nucleotide molecules were located through the direct methods of SHELXS 86.15 A sequence of Fourier-diVerence analysis showed all the non-hydrogen atoms.The Fourier-diVerence map computed after an isotropic full-matrix least-squares refinement (10 cycles) of all the non-hydrogen atom positions allowed the location of H[C(2)], H2[N(6A)], H[C(8)] for the adenine system of the metal-bound nucleotide molecule as well as H[N(1B)], H[C(2B)], H2[N(6B)] and H[O(7)] for H2ADP2. The positions Table 1 Crystal data and structure refinement for [Cu(TERPY)- (H2O)2]21[Cu(TERPY)(ADP)]2[H2ADP]2?16H2O Empirical formula MT /K l/Å Crystal system, space group a/Å b/Å c/Å a/8 b/8 g/8 V/Å3 Z Dc/Mg m23 Reflections collected Refinement method Data/restraints/parameters Goodness of fit on F2 Final R1, wR2 [I > 2s(I)] (all data) Absolute structure parameter Largest diVerence peak and hole/e Å23 C50H84Cu2N16O38P4 1768.3 293(2) 0.71073 Triclinic, P1 (no. 1) 12.171(2) 13.098(2) 14.221(3) 100.740(10) 104.32(2) 115.380(10) 1870.7(6) 1 1.570 6470 (Rint = 0.025) Full-matrix least squares on F2 6440/0/1019 1.108 0.0628, 0.1429 0.0909, 0.2062 20.01(2) 1.026 and 21.135J. Chem.Soc., Dalton Trans., 1999, 699–710 701 of these H atoms were freely refined in the subsequent leastsquares cycles. All the other H atoms of the adenosine diphosphate molecules and TERPY molecules were located and refined through the HFIX and AFIX options of SHELXL 93.16 The H atoms of the H2O ligand and H2O free molecules were not located.The last stage of refinement consisted of full-matrix least-squares cycles (10) at the anisotropic level for the Cu, P, O, N, and C atoms. The H atoms were refined as isotropic with their thermal parameter restrained to 1.2 Ueq of the atom to which they are bound. The choice of the absolute configuration was based on the value of the Flack parameter.17 All the calculations were carried out on Pentium personal computers via SHELXS 86, SHELXL 93 and PARST 9518 programs.Molecular graphics was performed with ZORTEP19 and ORTEP 3 for Windows.20 Selected bond distances and angles are given in Tables 2 and 3. CCDC reference number 186/1309. See http://www.rsc.org/suppdata/dt/1999/699/ for crystallographic files in .cif format. Computational procedure All calculations have been performed by using the GAUSSIAN 94/DFT package.21 Geometries, energetics and the population analysis reported were obtained using the B3LYP method.22 We have mainly used the LANL2DZ basis set 21 which consists of the 6-31G like functions for non-transition metal ions and a valence double-zeta basis set for 3s, 3p, 3d and 4s electrons and orbitals along with an eVective core potential (Hay and Wadt) 23 for the metals. In one case, namely P2O7 42, the cc-pVDZ 24 basis set (correlation consistent polarized valence) was used.The aim of the present density functional computation was the simulation of the general conformation of diphosphate groups and Table 2 Bond lengths (Å) for [Cu(TERPY)(H2O)2]21[Cu(TERPY)- (ADP)]2?[H2ADP]2?16H2O Cu(1)–O(3A) Cu(1)–O(6A) Cu(1)–N(11) Cu(1)–N(21) Cu(1)–N(31) P(1A)–O(59A) P(1A)–O(2A) P(1A)–O(3A) P(1A)–O(4A) P(2A)–O(4A) P(2A)–O(5A) P(2A)–O(6A) P(2A)–O(7A) O(29A)–C(29A) O(39A)–C(39A) O(49A)–C(19A) O(49A)–C(49A) O(59A)–C(59A) C(19A)–C(29A) C(29A)–C(39A) C(39A)–C(49A) C(49A)–C(59A) N(1A)–C(2A) N(1A)–C(6A) N(3A)–C(2A) N(3A)–C(4A) N(6A)–C(6A) N(7A)–C(5A) N(7A)–C(8A) N(9A)–C(4A) N(9A)–C(8A) N(9A)–C(19A) C(4A)–C(5A) C(5A)–C(6A) 2.244(10) 1.919(8) 2.020(10) 1.938(10) 2.029(10) 1.594(9) 1.466(10) 1.478(11) 1.591(9) 1.632(10) 1.511(8) 1.501(9) 1.499(8) 1.39(2) 1.407(13) 1.40(2) 1.454(13) 1.441(13) 1.512(15) 1.53(2) 1.51(2) 1.50(2) 1.347(14) 1.359(14) 1.328(15) 1.358(14) 1.326(15) 1.391(14) 1.317(15) 1.379(14) 1.380(13) 1.460(13) 1.387(14) 1.401(15) Cu(2)–O(1W2) Cu(2)–O(2W2) Cu(2)–N(12) Cu(2)–N(22) Cu(2)–N(32) P(1B)–O(59B) P(1B)–O(2B) P(1B)–O(3B) P(1B)–O(4B) P(2B)–O(4B) P(2B)–O(5B) P(2B)–O(6B) P(2B)–O(7B) O(29B)–C(29B) O(39B)–C(39B) O(49B)–C(19B) O(49B)–C(49B) O(59B)–C(59B) C(19B)–C(29B) C(29B)–C(39B) C(39B)–C(49B) C(49B)–C(59B) N(1B)–C(2B) N(1B)–C(6B) N(3B)–C(2B) N(3B)–C(4B) N(6B)–C(6B) N(7B)–C(5B) N(7B)–C(8B) N(9B)–C(4B) N(9B)–C(8B) N(9B)–C(19B) C(4B)–C(5B) C(5B)–C(6B) 2.194(12) 1.939(8) 2.021(11) 1.950(9) 2.042(11) 1.592(7) 1.484(9) 1.494(9) 1.616(10) 1.602(8) 1.483(9) 1.483(9) 1.539(11) 1.401(14) 1.411(12) 1.404(15) 1.448(13) 1.454(13) 1.526(15) 1.532(13) 1.52(2) 1.52(2) 1.351(15) 1.363(14) 1.324(15) 1.373(13) 1.314(14) 1.403(14) 1.314(14) 1.378(13) 1.375(13) 1.471(13) 1.361(14) 1.39(2) metal–diphosphate complexes.The goal could be reached also by the simpler LANL2DZ basis set (see below, Results and Discussion). It should be noted that the inclusion of polarization functions for P and O (cc-pVDZ) improved the agreement between computed and experimental P–O bond distances but the P–O–P bond angle (160.58) is far from the computed value Table 3 Bond angles (8) for [Cu(TERPY)(H2O)2]21[Cu(TERPY)- (ADP]2[H2ADP]2?16H2O O(3A)–Cu(1)–O(6A) O(3A)–Cu(1)–N(11) O(3A)–Cu(1)–N(21) O(3A)–Cu(1)–N(31) O(6A)–Cu(1)–N(11) O(6A)–Cu(1)–N(21) O(6A)–Cu(1)–N(31) N(11)–Cu(1)–N(21) N(11)–Cu(1)–N(31) N(21)–Cu(1)–N(31) P(1A)–O(3A)–Cu(1) P(2A)–O(6A)–Cu(1) C(211)–N(11)–Cu(1) C(611)–N(11)–Cu(1) C(221)–N(21)–Cu(1) C(621)–N(21)–Cu(1) C(231)–N(31)–Cu(1) C(631)–N(31)–Cu(1) O(2A)–P(1A)–O(3A) O(2A)–P(1A)–O(4A) O(2A)–P(1A)–O(59A) O(3A)–P(1A)–O(4A) O(3A)–P(1A)–O(59A) O(4A)–P(1A)–O(59A) O(5A)–P(2A)–O(4A) O(6A)–P(2A)–O(4A) O(6A)–P(2A)–O(5A) O(7A)–P(2A)–O(4A) O(7A)–P(2A)–O(5A) O(7A)–P(2A)–O(6A) P(1A)–O(4A)–P(2A) C(59A)–O(59A)–P(1A) C(2A)–N(1A)–C(6A) C(2A)–N(3A)–C(4A) C(5A)–N(7A)–C(8A) C(4A)–N(9A)–C(8A) C(4A)–N(9A)–C(19A) C(8A)–N(9A)–C(19A) N(3A)–C(2A)–N(1A) N(3A)–C(4A)–C(5A) N(9A)–C(4A)–C(5A) N(9A)–C(4A)–N(3A) C(4A)–C(5A)–C(6A) C(4A)–C(5A)–N(7A) N(7A)–C(5A)–C(6A) N(6A)–C(6A)–N(1A) N(6A)–C(6A)–C(5A) N(1A)–C(6A)–C(5A) N(7A)–C(8A)–N(9A) C(19A)–O(49A)–C(49A) O(49A)–C(19A)–N(9A) O(49A)–C(19A)–C(29A) N(9A)–C(19A)–C(29A) O(29A)–C(29A)–C(19A) O(29A)–C(29A)–C(39A) C(19A)–C(29A)–C(39A) O(39A)–C(39A)–C(49A) O(39A)–C(39A)–C(29A) C(49A)–C(39A)–C(29A) O(49A)–C(49A)–C(39A) O(49A)–C(49A)–C(59A) C(39A)–C(49A)–C(59A) O(59A)–C(59A)–C(49A) 93.7(4) 94.9(4) 100.9(4) 92.7(4) 95.3(4) 164.9(4) 103.1(4) 79.7(4) 159.5(4) 80.2(4) 121.8(5) 134.5(5) 114.9(8) 126.0(8) 119.2(8) 119.3(10) 114.3(9) 128.4(9) 118.1(6) 111.4(5) 106.5(6) 109.9(5) 109.2(5) 100.2(5) 103.3(5) 106.1(5) 113.2(6) 106.2(5) 114.9(5) 112.1(5) 131.0(5) 119.9(9) 118.5(9) 110.7(9) 104.6(9) 105.3(9) 125.8(8) 128.8(9) 129.3(10) 126.2(10) 106.6(9) 127.0(9) 117.6(10) 109.8(9) 132.4(9) 119.4(10) 122.9(11) 117.5(9) 113.4(10) 108.7(9) 108.5(10) 107.1(9) 114.9(9) 114.2(10) 116.9(10) 100.9(9) 112.2(9) 106.5(11) 103.0(9) 107.0(10) 108.6(9) 114.1(10) 109.6(11) O(1W2)–Cu(2)–O(2W2) O(1W2)–Cu(2)–N(12) O(1W2)–Cu(2)–N(22) O(1W2)–Cu(2)–N(32) O(2W2)–Cu(2)–N(12) O(2W2)–Cu(2)–N(22) O(2W2)–Cu(2)–N(32) N(12)–Cu(2)–N(22) N(12)–Cu(2)–N(32) N(22)–Cu(2)–N(32) C(212)–N(12)–Cu(2) C(612)–N(12)–Cu(2) C(222)–N(22)–Cu(2) C(622)–N(22)–Cu(2) C(232)–N(32)–Cu(2) C(632)–N(32)–Cu(2) O(2B)–P(1B)–O(3B) O(2B)–P(1B)–O(4B) O(2B)–P(1B)–O(59B) O(3B)–P(1B)–O(4B) O(3B)–P(1B)–O(59B) O(4B)–P(1B)–O(59B) O(5B)–P(2B)–O(4B) O(6B)–P(2B)–O(4B) O(6B)–P(2B)–O(5B) O(7B)–P(2B)–O(4B) O(7B)–P(2B)–O(6B) O(7B)–P(2B)–O(5B) P(1B)–O(4B)–P(2B) C(59B)–O(59B)–P(1B) C(2B)–N(1B)–C(6B) C(2B)–N(3B)–C(4B) C(5B)–N(7B)–C(8B) C(4B)–N(9B)–C(8B) C(4B)–N(9B)–C(19B) C(8B)–N(9B)–C(19B) N(3B)–C(2B)–N(1B) N(3B)–C(4B)–C(5B) N(9B)–C(4B)–C(5B) N(9B)–C(4B)–N(3B) C(4B)–C(5B)–C(6B) C(4B)–C(5B)–N(7B) N(7B)–C(5B)–C(6B) N(6B)–C(6B)–N(1B) N(6B)–C(6B)–C(5B) N(1B)–C(6B)–C(5B) N(7B)–C(8B)–N(9B) C(19B)–O(49B)–C(49B) O(49B)–C(19B)–N(9B) O(49B)–C(19B)–C(29B) N(9B)–C(19B)–C(29B) O(29B)–C(29B)–C(19B) O(29B)–C(29B)–C(39B) C(19B)–C(29B)–C(39B) O(39B)–C(39B)–C(49B) O(39B)–C(39B)–C(29B) C(49B)–C(39B)–C(29B) O(49B)–C(49B)–C(39B) O(49B)–C(49B)–C(59B) C(39B)–C(49B)–C(59B) O(59B)–C(59B)–C(49B) 94.7(4) 96.9(5) 95.7(4) 93.0(5) 96.2(4) 169.3(5) 101.9(4) 80.0(4) 158.5(4) 80.1(4) 114.1(9) 127.2(9) 117.9(9) 118.1(8) 113.1(9) 126.2(9) 116.3(6) 110.7(6) 106.8(4) 111.5(5) 109.6(5) 100.7(4) 108.5(5) 109.7(5) 116.8(5) 110.8(5) 100.7(5) 109.0(6) 127.3(6) 118.8(7) 123.6(10) 112.0(9) 103.7(8) 105.3(8) 126.1(8) 127.6(8) 124.8(11) 126.1(10) 106.9(9) 126.9(9) 119.7(10) 110.4(9) 129.9(10) 120.1(10) 125.9(10) 113.6(9) 113.6(9) 107.8(9) 108.0(9) 106.4(8) 113.7(8) 109.9(8) 114.7(9) 100.0(8) 111.8(8) 107.4(8) 103.2(9) 107.5(9) 108.1(9) 116.1(9) 106.6(9)702 J.Chem. Soc., Dalton Trans., 1999, 699–710 (1808) 25a at the 6-31G ** 25b level. As the overall conformation of free and metal-bound diphosphates is reproduced at the more economic LANL2DZ level, we used this latter basis set for all the systems reported in this work.All the geometrical parameters have been fully optimized. The system [Zn(HP2O7)(NH3)2]2?NH3 was optimized to the convergence criteria of the Gaussian 94/DFT package for maximum force, rms force, and rms displacement. The maximum displacement was 0.0062 Å (limiting value for GAUSSIAN 94/DFT package, 0.0018); the total energy did not change more than 0.07 kcal in the last ten cycles (out of a total of 80). The structure was considered optimized at this stage. The [Cu(HP2O7)(NH3)3]2 molecule was optimized to the convergence criteria for maximum force and rms force.The maximum displacement was 0.0089 Å and the rms displacement 0.0022 (limiting value for GAUSSIAN 94/DFT package, 0.0012); the total energy did not change more than 0.10 kcal in the last ten cycles (out of a total of 80). The geometry was considered optimized at this stage. All the other molecules or aggregates were fully optimized on the basis of the criteria implemented in the GAUSSIAN 94/DFT package.Results and discussion X-Ray crystallography The asymmetric unit consists of [Cu(TERPY)(H2O)2] [Cu- (TERPY)(ADP)][H2ADP]?16H2O. The two copper atoms have diVerent co-ordination spheres: Cu(1) is surrounded by two phosphate groups from an ADP32 molecule and by three nitrogen atoms from a TERPY molecule; Cu(2) is co-ordinated to two water molecules and to three nitrogen atoms from a TERPY molecule. Both Cu(1) and Cu(2) have a pseudo-square pyramidal co-ordination environment.The H2ADP2 anion has no covalent linkage to the metal centres. The ORTEP drawings are in Figs 1–3. Diphosphate geometry and conformation. The bridging P–O bond lengths are 1.591(9) [P(a)–O] and 1.632(10) Å [O–P(b)] for copper-bound ADP32 whereas they measure 1.616(10) and 1.602(8) for the non-coordinated H2ADP2 molecule. An ADP–metal species studied via X-ray diVraction at a good accuracy contains K1 cations.26 For this latter case the H2ADP2 molecule has mostly electrostatic interactions to the cations, and the P–O bridging distances [1.626(8), P(a)–O; 1.609(8) Å, O–P(b)] are very similar to that of H2ADP2 of the present structure.Another good accuracy structure of H2ADP2 contains (HOCH2)3(CH3)N1, Tris, cations.27 In this case P(b)–O [1.627(5) Å] is longer than P(a)–O [1.585(6) Å]. The P–O–P bond angle is 131.0(5)8 and 127.3(6)8 for [Cu- (ADP)(TERPY)]2 and H2ADP2, respectively. The P(a) ? ? ? P(b) distance is 2.933(7) and 2.884(7) for the same molecules.Rele- Fig. 1 Drawing of the [Cu(TERPY)(ADP)]2 complex molecule with the labeling scheme. The ellipsoids enclose 30% probability. vant values found for ATP complexes are equal or larger than 2.90 Å (see refs. 12 and 28 and refs. therein). In the structure KH2ADP?2H2O26 the P(a) ? ? ? P(b) distance is 2.947(8) Å and [(HOCH2)2(CH3)N][H2ADP]?2H2O27 it is 2.916(8) Å. Angles of 131.3(4) and 130.5(3)8 were reported for KH2ADP?2H2O and [(HOCH2)3(CH3)N][H2ADP]?2H2O. The angles around P(a) which involve the terminal oxygen atoms [namely O(2) and O(3)] are larger than the idealized tetrahedral value of 109.5, i.e. 118.1(6)8 for [Cu(ADP)(TERPY)]2 and 116.3(6) for H2ADP2.All the other values are close to 109.58, except for O(59)–P(a)–O(4) which is 100.2(5) and 100.7(4)8 for [Cu(ADP)(TERPY)]2 and H2ADP2 respectively. The angles around P(b) have also significant deviations from the idealized values. The largest deviations are that of O(4)–P(2)–O(6) 103.3(5)8 for [Cu(ADP)(TERPY)]2 and that of O(4)–P(2)–O(7) 100.7(5)8 for H2ADP2.It should be noted that the O(5A)– P(2A)–O(6A) angle for [Cu(ADP)(TERPY)]2 is 113.2(6)8, O(6A) being strongly bound to copper (see below). The P(a)–O–P(b)–O(6) torsion angle values are -38(1) and 24(1) for the copper-bound and free H2ADP2 molecules, respectively. Therefore the conformation around the diphosphate chain is in the gauche and cis domain respectively on the basis of spectroscopic and crystallographic notations.29 The nucleoside molecule co-ordinated to the metal is reported as fully deprotonated, ADP32, whereas the free nucleoside molecule is protonated, H2ADP2, on the phosphate( b) and on the N(1) purine atom on the basis of several observations.The diVerent protonation of the terminal phosphate group is related to the P–O bond distances. For the metal bound molecule the terminal P–O distances have almost the same value, 1.511(8) [P(2A)–O(5A)], 1.501(9) [P(2A)–O(6A)] and 1.499(8) Å [P(2A)–O(7A)].The linkage of O(6A) to the metal does not influence much the value of P(2A)–O(6A). For the free nucleotide molecule the P(2B)–O bond distances are: P(2B)–O(5B) 1.483(9); P(2B)–O(6B) 1.483(9); P(2B)–O(7B) 1.539(11) Å. These values are consistent with monoprotonation Fig. 2 Drawing of the H2ADP2 molecule with the labeling scheme. The ellipsoids enclose 30% probability. Fig. 3 Drawing of the [Cu(TERPY)(H2O)]21 complex molecule with the labeling scheme. The ellipsoids enclose 30% probability.J.Chem. Soc., Dalton Trans., 1999, 699–710 703 of the terminal phosphate [namely O(7B)] of the free nucleotide molecule but not of the metal-bound nucleotide. The diVerence between the P(2B)–O(7B) distance and the lengths of the other two P(2B)–O(terminal) vectors is only 5.6 times the estimated standard deviation; however, the Fourier-diVerence map showed the hydrogen atom on O(7B) but not any hydrogen atom on the O(5A) or O(7A) atoms (see above, Experimental Section).Further observations on the protonation status of the nucleotide molecules are discussed below (see Hydrogen bonds, Interaggregate interactions and conclusion). Metal co-ordination to diphosphate. The Cu(1) atom is coordinated to the diphosphate chain of a fully deprotonated ADP32 molecule through one oxygen donor from both phosphate( a) [Cu(1)–O(3A) 2.24(1) Å] and phosphate(b) [Cu(1)– O(6A) 1.919(8) Å]. The metal centre is also linked to three nitrogen atoms from one TERPY ligand. The geometry of the co-ordination sphere can be described as square pyramidal. The equatorial donors are the three nitrogens from TERPY and O(6A); the apical donor is O(3A).The four equatorial donors are almost coplanar, deviations ranging from 20.07(1) [N(21)] to 0.07(1) Å [N(31)], whereas the metal centre deviates 0.1846(4) Å from the plane, towards O(3A). The angles formed by the apical Cu(1)–O(3A) vector with the equatorial Cu–N/O vectors are 93.7(4) [O(6A)], 94.9(4) [N(11)], 100.9(4) [N(21)] and 92.78 [N(31)].The conformation of the six-membered co-ordination ring at the pyrophosphate chain can be described as boat with the O(4A) and Cu(1) atoms out of the plane defined by O(3)/P(1)/P(2)/O(6) by 0.467(9) and 0.2942(3) Å, respectively. A Cremer and Pople 30 conformation analysis of the same ring gives a total puckering amplitude QT 0.513(8) Å (0.630 Å for cyclohexane), a boat component q 98.2(4)8 (90 for pure boat, 0/1808 for pure chair) and a skewing component f 227.4(8)8 (0 for pure boat, 290/908 for pure skewed boat).It is interesting that the a/b and b/g chelate rings for [M(HATP)2]42 anions have chair and skew boat conformation respectively.12,31 The chelate ring of KH2ADP26 has a distorted chair conformation. The handedness of the co-ordination can be designed as D (see ref. 31 and refs. therein) for the present structure.Geometry and conformation of the nucleoside moiety. The adenine system of the [Cu(ADP)(TERPY)]2 anion is deprotonated at N(1), whereas the H2ADP2 anion is protonated at the same position. This finding came from the analysis of the Fourier-diVerence map which showed a peak attributable to a proton for N(1) only in the case of the free nucleotide molecule. It is confirmed by the value of the C(2)–N(1)–C(6) angle which is 118.5(9) and 123.6(10)8, for the co-ordinated and free nucleotide molecules, respectively. It should be noted that Singh 32 reported an analysis of geometrical parameters for N(1)- protonated and non-protonated purine systems and concluded that C(2)–N(1)–C(6) angles are in the range 125 ± 3 and 116 ± 38 for the two cases, respectively.The N(1)–C(2)–N(3) angle is 129(1) and 125(1)8 for metal-bound ADP32 and free H2ADP2 . Endocyclic N(6) angles diVer by 3.9(9)8, the largest value being that for metal-bound nucleotide.The other corresponding angles diVer by 3(1)8 or less. Corresponding bond distances for the two adenine systems are almost equal, the largest diVerence being that relevant to C(4)–C(5) [1.39(1) and 1.36(1) Å for metal-bound ADP32 and free H2ADP2, respectively]. The nine endocyclic atoms of the purine systems define good least-squares planes, the largest deviations being that of C(6B) [0.05(1) Å]. Atom N(6A) deviates slightly [0.087(2) Å] from the purine. Small deviations are also found for C(19A) [0.06(2)] and C(19B) [0.14(1) Å].The conformations around the glycosidic bond N(9)–C(19) for the nucleoside moieties of this structure are unusual. They are measured by the C(4)–N(9)–C(19)–O(49) (c) torsion angle; c is 284(1)8 for the copper bound nucleotide molecule and 294(1)8 for the free H2ADP2 anion. So the conformation can be described as high-anti, -sc 33 and anti, -ac for metal-bound ADP32 and H2ADP2, respectively. The extreme position described as high-anti is not frequent for nucleoside and it has never been found before for solid state structures of ATP and ADP nucleotides.The conformation of the ribose ring can be described on the basis of the pseudo-rotation phase angle P calculated from the endocyclic sugar torsion angles;34 P is 161(1) and 151(1)8 for metal-bound ADP32 and H2ADP2, respectively so that the conformation of the sugar is pure C(29)- endo (2E, envelope) and C(29)-endo with a small component of C(19)-exo for the metal-bound and free nucleotide molecules, respectively.In fact the C(19), C(39), C(49) and O(49) atoms define a good least-squares plane for both the nucleotides [maximum deviation 0.005(11) Å for C(49A)]. It should be noted that the pure C(29)-endo conformation has never been found for ATP metal complexes, whereas it is very common for ADP metal complexes or ADP salts.31 It would be interesting to crystallize a larger number of nucleoside diphosphate complexes to see if this conformation is the favorite one for this class of nucleotide.It was previously reported that the c value is larger for C(29)-endo than for a C(39)-endo sugar conformation. 35 That finding is confirmed by the present work. The degree of pucker of the ribose ring based on the q2 parameter 30 is similar for the two nucleotide molecules in the present structures [0.35(1) and 0.38(1) Å for metal-bound and free nucleotide, respectively]. The conformation around the C(49)–C(59) vector (Table 4) is gauche-, gauche1 (1sc) for both the nucleotide molecules of the present structure on the basis of the yOO [268(1) and 275(1)8 for A and B, respectively] and yOC [51(1) (A) and 46(1)8 (B)] torsion angles.The rotations around C(59)–O(59) (f) and O(59)–P(a) (w) are trans and gauche- for both metal-bound ADP3 and H2ADP2, respectively. Structure of [Cu(TERPY)(H2O)2]21. The TERPY ligand acts as tridentate at three equatorial sites. One of the H2O ligands occupies the fourth equatorial position and the other molecule is at the apical position.The Cu–N bond distance relevant to the central pyridine ring of TERPY is 1.950(9) Å, shorter than the Cu–N bond lengths for the peripheral pyridine rings [average, 2.025(10) Å] in agreement with the values for [Cu(ADP)(TERPY)]2 [Cu(1)– N(21) 1.938(10); Cu(1)–N(11) 2.020(10); Cu(1)–N(31) 2.029(10) Å]. The equatorial Cu–O(2W2) vector, 1.939(8) Å, is much shorter than the apical one, Cu–O(1W2) 2.194(12) Å.The Table 4 Selected torsion angles (8) defining the ribose and the phosphate chain conformations f C(49)–C(59)–O(59)–P(1) w C(59)–O(59)–P(1)–O(4) yOC C(39)–C(49)–C(59)–O(59) yOO O(49)–C(49)–C(59)–O(59) y C(59)–C(49)–C(39)–O(39) c C(4)–N(9)–C(19)–O(49) t0 C(49)–O(49)–C(19)–C(29) t1 O(49)–C(19)–C(29)–C(39) t2 C(19)–C(29)–C(39)–C(49) t3 C(29)–C(39)–C(49)–O(49) t4 C(39)–C(49)–O(49)–C(19) C(59)–O(59)–P(1)–O(2) C(59)–O(59)–P(1)–O(3) O(59)–P(1)–O(4)–P(2) O(2)–P(1)–O(4)–P(2) O(3)–P(1)–O(4)–P(2) P(1)–O(4)–P(2)–O(5) P(1)–O(4)–P(2)–O(6) P(1)–O(4)–P(2)–O(7) Molecule A, [Cu(TERPY)(ADP)]2 170.3(9) 261(1) 51(1) 268(1) 147(1) 284(1) 223(1) 35(1) 233(1) 21(1) 1(1) 2177.6(1) 54(1) 174.7(8) -73(1) 60(1) 2157.3(9) 238(1) 81(1) Molecule B, H2ADP2 2154.1(9) 62(1) 46(1) 275(1) 142(1) 294(1) 229(1) 39(1) 233(1) 18(1) 7(1) 2177.9(9) 55(1) 160.6(8) 287(1) 44(1) 2104.5(9) 24(1) 141.0(9)704 J.Chem. Soc., Dalton Trans., 1999, 699–710 four equatorial donors define a good plane, the largest deviation from the mean least-squares plane being that of N(22), 0.001(14) Å.The metal atom deviates 0.174(3) Å towards the apical position. The O(1W2)–Cu(2)–N angles are in the range 93.0(5)–96.9(5)8; whereas O(1W2)–Cu(2)–O(2W2) is 94.78. The equatorial bond angles N–Cu–N(cis) are 80.0(4)8 (average), whereas O(2W2)–Cu(2)–N(cis) are 96.2(4) and 101.9(4)8. Bond distances and angles relevant to the Cu(TERPY) moieties in this work are in agreement with the values previously reported for copper(II)–TERPY complexes with analogous co-ordination environments.36,37 Supramolecular aggregates.Molecules of [Cu(ADP)- (TERPY)]2, [Cu(TERPY)(H2O)2]21, H2ADP2 build supramolecular aggregates in 1:1:1 ratio (Fig. 4). Each superstructure is stabilized by a complicated web of electrostatic and hydrogen bonding interactions which mostly act at the central region of the unit. Stacking interactions between the aromatic rings co-operate to strengthen each aggregate.Free water molecules are mostly distributed around the hydrophilic regions of the nucleotides (pyrophosphate and sugar moieties) and around the Cu–OH2 group. The triplets are connected to each other via stacking and hydrogen bonding interactions. Hydrogen bonds and electrostatic interactions. Hydrogen bonds are listed in Table 5. The pyrophosphate groups of H2ADP2 and [Cu(ADP)(TERPY)]2 face each other and both Fig. 4 Drawing of the [Cu(TERPY)(H2O)]21 [Cu(TERPY)(ADP)]2 H2ADP2 self-assembly.Fig. 5 All the atoms within a sphere (radius 6 Å) centred on O(2W2). Hydrogen bonds are represented by dashed lines. face the Cu(H2O)2 region of [Cu(TERPY)(H2O)2]21 (Fig. 5). Selected hydrogen bonds which link the three molecules are: O(2A) ? ? ? H–O(7B) [d(O ? ? ? O) 2.65(1)]; O(7A) ? ? ? H–O(2W2) [2.60(1)]; O(6B) ? ? ? H–O(2W2) [2.63(1)] and O(6B) ? ? ? H– C(632) [d(O ? ? ? C), 3.35(1) Å]. The short O(2A) ? ? ? O(7B) contact distance is in agreement with the presence of a hydrogen bond and hence with the protonation of O(7B), as O(2A) can be protonated only at a very low pH.The short O(7A) ? ? ? O(2W2) contact distance can be explained with the presence of a hydrogen bond in which O(2W2) is the hydrogen donor but it does not exclude that O(7A) is protonated and O(2W2) is the hydro- Table 5 Selected contact distances (Å) indicative of possible hydrogen bonds O(2A) ? ? ? O(7B) O(7A) ? ? ? H–O(2W2) O(6B) ? ? ? H–O(2W2) O(6B) ? ? ? C(632) O(4W) ? ? ? O(5A) O(4W) ? ? ? O(1W2) O(8W) ? ? ? C(312) O(7W) ? ? ? C(512) O(3W) ? ? ? O(9W) O(5W) ? ? ? O(13W) O(8W) ? ? ? O(10W) O(8W) ? ? ? O(15W) O(9W) ? ? ? O(15W) O(10W) ? ? ? N(1A) O(10W) ? ? ? O(12W) O(11W) ? ? ? O(14W) O(1W) ? ? ? C(8A) N(7B) ? ? ? N(6A) O(3B) ? ? ? N(1B) O(6B) ? ? ? N(6B) N(7A) ? ? ? N(6B) O(3A) ? ? ? O(8W) O(29A) ? ? ? O(12W) O(13W) ? ? ? O(16W) O(29A) ? ? ? O(5W) O(29B) ? ? ? O(7A) O(2A) ? ? ? O(1W) O(6B) ? ? ? O(1W) O(39A) ? ? ? N(3B) O(6W) ? ? ? C(632) O(7W) ? ? ? O(14W) O(13W) ? ? ? O(14W) O(39B) ? ? ? N(3A) O(3B) ? ? ? O(9W) O(5B) ? ? ? O(6W) O(5B) ? ? ? O(5W) O(11W) ? ? ? O(15W) N(6A) ? ? ? O(2W) O(3W) ? ? ? O(1W2) O(39A) ? ? ? O(5W) O(2B) ? ? ? O(1W) O(2B) ? ? ? O(2W) O(2B) ? ? ? O(4W) O(3W) ? ? ? O(6W) O(3W) ? ? ? O(16W) O(10W) ? ? ? O(16W) O(39B) ? ? ? O(6W) O(1W) ? ? ? O(12W) O(7W) ? ? ? O(12W) 2.65(1) 2.60(1) 2.63(1) 3.35(1) 2.71(2) 2.72(2) 3.27(3) 3.24(2) 2.74(2) 2.92(3) 2.93(3) 2.68(2) 2.75(4) 2.80(3) 2.67(2) 2.88(3) 3.26(2) 2.97(1) 2.66(2) 2.79(1) 2.93(1) 2.74(2) 3.00(2) 2.72(3) 2.88(1) 2.70(1) 2.77(2) 3.33(2) 2.94(1) 3.28(2) 2.85(2) 2.81(2) 2.78(1) 2.79(1) 2.77(2) 2.74(2) 2.76(3) 2.92(1) 2.72(1) 2.92(1) 2.77(2) 2.82(2) 2.81(2) 2.76(3) 2.92(3) 3.09(4) 2.76(2) 2.75(3) 2.69(3) Equivalent position x, y, z x 2 1, y, z x, y 1 1, z x, y 2 1, z x 1 1, y, z x 2 1, y, z 2 1 x 1 1, y, z 1 1 x 1 1, y 1 1, z x, y, z 2 1 x 1 1, y, z x 1 2, y, z 1 1 x 2 1, y 2 1, zJ.Chem. Soc., Dalton Trans., 1999, 699–710 705 gen acceptor. Some free water molecules, particularly O(1W), O(3W), O(4W) and O(6W), also play an important role in stabilizing the triplet. Selected bonding distances are: O(1W) ? ? ? O(2A) [d(O ? ? ? O) 2.77(2)]; O(1W) ? ? ? O(6B) [3.33(2)]; O(1W) ? ? ? H–C(8A) [d(O ? ? ? C) 3.26(2)]; O(4W) ? ? ? O(5A) [d(O ? ? ? O) 2.71(2)]; O(4W)? ? ?O(1W2) [2.72(2)]; O(6W) ? ? ?O(5B) [2.77(2)] and O(6W) ? ? ? H–C(632) [d(O ? ? ? C) 3.28(2)].Stacking interactions. The adenine system of [Cu(TERPY)- (ADP)]2 and the TERPY ligand of [Cu(TERPY)(H2O)2]21 are connected by stacking interactions (Fig. 6 and Table 6) which reinforce the supramolecular aggregate. Selected short contact distances are: N(7A) ? ? ? N(12) [3.56(2)]; C(5A) ? ? ? C(212) [3.64(2)] and N(6A) ? ? ? C(222) [3.38(2) Å] (note the strong eVect at 3.38 Å in the X-ray diVraction powder diagram; see above, Experimental Section).The dihedral angle between the N(12)/C(212)/C(312)/C(412)/C(512)/C(612) and the leastsquares planes of the adenine system of metal-bound ADP32 is 1.4(5)8. Fig. 6 Aromatic systems involved in the stacking interactions and in the adenine–adenine base pairing. Adenine B is at x, y 2 1, z. Table 6 Significant stacking distances (Å) between adenine A (copperbound ADP32), adenine B (free H2ADP2) and the TERPY ligand of [Cu(TERPY)(H2O)2]21 Adenine A N(1A) ? ? ? C(312) C(2A) ? ? ? C(312) C(2A) ? ? ? C(412) N(3A) ? ? ? C(412) N(3A) ? ? ? C(512) C(4A) ? ? ? C(512) C(4A) ? ? ? C(612) C(5A) ? ? ? N(12) C(5A) ? ? ? C(212) C(6A) ? ? ? C(212) C(6A) ? ? ? C(312) N(6A) ? ? ? N(22) N(6A) ? ? ? C(222) N(6A) ? ? ? C(322) N(7A) ? ? ? N(12) C(8A) ? ? ? C(612) N(9A) ? ? ? C(612) 3.48(3) 3.57(3) 3.63(3) 3.51(3) 3.70(2) 3.51(2) 3.64(2) 3.52(1) 3.64(2) 3.46(2) 3.65(3) 3.53(2) 3.38(2) 3.57(3) 3.56(2) 3.67(3) 3.67(2) Adenine B (x, y 2 1, z) N(1B) ? ? ? C(532) N(1B) ? ? ? C(632) C(2B) ? ? ? C(532) N(3B) ? ? ? C(432) N(3B) ? ? ? C(532) C(4B) ? ? ? C(332) C(4B) ? ? ? C(432) C(4B) ? ? ? C(532) C(5B) ? ? ? N(32) C(5B) ? ? ? C(232) C(5B) ? ? ? C(632) C(6B) ? ? ? N(32) C(6B) ? ? ? C(632) N(7B) ? ? ? C(232) N(9B) ? ? ? C(332) 3.55(3) 3.51(3) 3.40(3) 3.52(3) 3.52(2) 3.64(2) 3.48(3) 3.64(2) 3.55(2) 3.65(2) 3.65(2) 3.64(2) 3.45(2) 3.55(2) 3.62(2) Interaggregate interactions and base pairing.The aggregates interact with each other via hydrogen bonds and stacking interactions.The adenine system from metal-bound ADP32(A) and free H2ADP2(B) (this latter is from an outer aggregate) are paired via N(6A)H2 ? ? ? N(7B) [d(N ? ? ? N) 2.97(1) Å] and N(6B)H2 ? ? ? N(7A) [d(N ? ? ? N) 2.93(1) Å], see Fig. 6. It is interesting that the same adenine–adenine base-pairing scheme was previously found by one of us for the structure of [Mg(H2O)6]- [HDPA][Mg(HATP)2]?12H2O (HDPA = protonated 2,29- dipyridylamine) 12 and related compounds.28,38 Atom N(1B) has a strong and interaggregate interaction with O(3B) [d(N ? ? ? O) 2.66(1) Å].This short contact distance is consistent with the protonation of N(1B) of the free nucleotide molecule as the terminal oxygen atoms of the phosphate(a) can be protonated only at very low pH. The two paired adenine systems are anchored to the same [Cu(TERPY)(H2O)2]21 molecules via stacking interactions. Some short stacking contacts which connect two aggregates are: N(1B) ? ? ? C(632) 3.514(9); C(2B) ? ? ? C(532) 3.404(9); C(5B) ? ? ? C(232) 3.65(2) Å.Infrared spectroscopy The infrared spectrum has a band at 1649 cm21 (strong, broad), which can be related to the scissoring mode of NH2 proximal to deprotonated N(1).12 The corresponding band for N(1) deprotonated Na2HADP is located at 1663 cm21. The absence of an intense band at around 1700 attributable to the N(1)- protonated adenine NH2 group can be related to the hydrogen bonds which involve NH2 as well as N(1)H, see above, hydrogen bonding network.The bands relevant to the PO2 stretching modes occur at around 1230 and 1100 cm21 as for adenosine 59-triphosphate complexes.12 Molecular orbital calculations Geometry. The selected geometrical parameters for all the molecules optimized in this work are shown in Table 7. The structures of P2O7 42, HP2O7 32, [Cu(O,O-PO4)] 2, [Cu{O(a),O(b)- P2O7}]22, [Zn{O(a),O(b)-HP2O7}(H2O)(OH)]22, [Zn{O(a),O(b)- HP2O7}(NH3)2]2?NH3 and [Cu{O(a),O(b)-HP2O7}(NH3)3]2 are shown in Figs. 7–13. P2O7 42. The optimized structure for P2O7 42 (Fig. 7) has a linear P–O–P bridge and the two PO3 groups are staggered. The P–O(b) (b = bridge) and P–O(t) (t = terminal) distances are 1.793 and 1.659 Å, respectively. The computed bond distances are significantly longer than the corresponding ones found in the solid state for a variety of hydrogen orthophosphates, pyrophosphates, triphosphates and linear and cyclic metaphosphates [P-O(b) 1.61; P-O(t) 1.52].39 It is interesting that some divalent cobalt (Co2P2O7 40a), nickel (Ni2P2O7 40b) and magnesium [Nb2Mg(P2O7)3 40c] diphosphates have linear P–O–P bridges in the solid state.A certain overestimation of bond distances produced by the level of theory and basis set used for this work appears also from comparison with more sophisticated basis sets used recently for computations on magnesium Fig. 7 Drawing of the fully optimized P2O7 42 molecule at the B3LYP/ LANL2DZ level.706 J.Chem. Soc., Dalton Trans., 1999, 699–710 Table 7 Selected bond lengths (Å) and angles (8) (t, terminal; b, bridging; d, donor) of molecules calculated at the B3LYP/LANL2DZ level System H2O OH2 NH3 PO4 32 P2O7 42 HP2O7 32 [Cu(PO4)]2 [Cu(P2O7)]22 [Zn(P2O7)]22 [Cu(HP2O7)(NH3)3]2 [Zn(HP2O7)(H2O)(OH)]22 [Zn(HP2O7)(NH3)2]2?NH3 O–H 0.977 1.005 1.096 0.982 0.996 1.004 (H2O) 1.027 (HP2O7 32) 0.982 N–H 1.088 1.033 1.042 1.027 (free NH3) P(1)–O(t) 1.695 1.659 1.631 1.663 1.607 1.603 1.606 1.610 1.607 P(1)–O(d) 1.686 1.760 1.760 1.694 1.700 1.686 P(1)–O(b) 1.793 1.824 1.766 1.846 1.828 1.833 1.856 P(2)–O(b) 1.793 1.756 1.766 1.844 1.698 1.707 1.698 P(2)–O(t) 1.659 1.627 1.607 1.603 1.624 1.588 1.599 P(2)–O(H) 1.723 1.720 1.713 1.723 P(2)–O(d) 1.760 1.760 1.678 1.656 M–O(P) 2.031 1.837 1.894 1.934 2.003 1.992 M–OH 1.924 2.727 (H2O) M–NH3 2.070 2.092 P–O–P 179.7 133.0 158.6 177.1 138.7 138.3 132.7 P–O–H 109.7 110.2 112.7 110.1 O(P)–M–O(P) 79.7 148.8 160.7 100.0 99.0J.Chem. Soc., Dalton Trans., 1999, 699–710 707 and calcium pyrophosphates.25a Some enlarging eVects (ca. 0.08 Å) for computed Zn–OH2 bond distances in the gas phase when compared with experimental solid state ones for four-coordinate zinc(II) complexes were also noted in a previous work.41 HP2O7 32. An optimized structure with a strong intramolecular hydrogen bond between the two PO3 groups was computed in this work (Fig. 8). The conformation of the PO3 groups is almost eclipsed [O(t)P ? ? ? PO(t), ca. 38]. The P–O(t) bond distances for the P(1) and P(2) atoms average 1.629 Å. The P(1)–O(b) and P(2)–O(b) distances are 1.824 and 1.756 Å, respectively. The last values are significantly diVerent, and the trend is in agreement with the findings previously reported.25a,42 The P–O–P angle is 133.08. A comparison of the computed structures of pyrophosphates from this work and those of previous molecular orbital calculations 25a,42 performed through the 6-31G ** basis set as well as those from experimental solid state studies shows that our computational procedure reproduces well the general conformation of the ligand moiety, i.e.bond angles and torsion angles. The agreement for bond distances is not excellent (e.g. diVerences of some 0.10 Å for P2O7 42) but it increases when the overall charge of the molecule decreases. For these reasons we may conclude that the B3LYP/LANL2DZ level is accurate enough (see above, computational procedure for the inclusion of polarization functions) for the purpose of computing bond angles and torsion angles of complex molecules such as [MII{O(a),O(b)-P2O7}]22 and [MII{O(a),O(b)-HP2O7}(NH3)3]2 which can be considered models also for some metal–nucleoside 59-diphosphate co-ordination compounds.Furthermore, relative eVects on computed bond lengths such as protonation and metal co-ordination can be discussed even though absolute values are overestimated.[Cu(O,O-PO4)]2. The optimization of the [Cu–O–PO3]2 molecule did not reach convergence. On the contrary the [Cu(O,O–PO4)]2 chelate molecule nicely converged to C2v symmetry (Fig. 9). The Cu–O bond lengths are 2.031 Å, whereas the P–O(d) (d = donor) and P–O(t) bond lengths are 1.689 and 1.663 Å, respectively. The O–Cu–O bond angle is 79.78. [Cu {O(a),O(b)-P2O7 }]22. The starting structure had the two PO3 groups eclipsed and the geometry optimization converged to the structure (whose symmetry is Cs) in Fig. 10. The Cu–O bond lengths are 1.837 Å, shorter than those for [Cu(O,O-PO4)]2, consistent with a smaller tension for the Fig. 8 Drawing of the fully optimized HP2O7 32 molecule at the B3LYP/LANL2DZ level. Fig. 9 Drawing of the fully optimized [Cu(O,O-PO4)]2 chelate at the B3LYP/LANL2DZ level. six-membered chelate ring when compared to a four-membered one. The P–O(d) distances are 1.760 Å whereas the P–O(t) are 1.607 Å. The P–O(b) lengths are 1.766.The metal co-ordination to the two PO3 groups slightly decreases the P–O(b) distances (some 0.03 Å) as well as the P–O(t) distances (some 0.06 Å). The P–O(d) distances increase by some 0.10 Å when compared to those of P2O7 42. The P–O–P angle for computed [Cu- {O(a),O(b)-P2O7}]22 is 158.68, much larger than the value found for [Cu(TERPY)(ADP)]2 [131.0(5)8]. The discrepancy can be related to the diVerence in the co-ordination spheres. The conformation of the chelate ring for the computed structure is boat-envelope (QT 0.210 Å, f 179.98, q 65.58 q 908 for pure boat, 458 for pure envelope).[Zn {O(a),O(b)-P2O7 }]22. The optimized structure of [Zn{O(a),O(b)-P2O7}]22 has some significant diVerences when compared to [Cu{O(a),O(b)-P2O7}]22. The P–O–P bridge [angle, 177.18; O(b) displaced towards Zn] is almost linear as for P2O7 42 and the chelate ring is very flat. The Zn–O distances (1.894 Å) are longer than the Cu–O ones (1.837 Å). The P–O(b) distance for the zinc species (1.845 Å) is much longer than the corresponding value for the copper species (1.766 Å).It is noteworthy that for [Zn{O(a),O(b)-P2O7}]22 the Zn–O(b) distance is 2.042 Å and the O–Zn–O angle is 160.78, in agreement with a Zn–O(b) bonding interaction. [Zn {O(a),O(b)-HP2O7 }(H2O)(OH)]22. An initial structure for [Zn{O(a),O(b)-P2O7}(H2O)2]22 where the zinc ion has a pseudo-C2v co-ordination environment was submitted to geometry optimization. During the refinement one of the coordinated water molecules lost a H atom which passed to P2O7.Thus, the final co-ordination sphere consists of a O(a),O(b)- HP2O7 32 chelating ligand, a OH2 anion and a H2O molecule (Fig. 11). The Zn–OH and Zn–OH2 bond distances are 1.924 and 2.272 Å, respectively; i.e. the water molecule is very weakly Fig. 10 Drawing of the fully optimized [Cu{O(a),O(b)-P2O7}]22 chelate at the B3LYP/LANL2DZ level. Fig. 11 Drawing of the fully optimized [Zn{O(a),O(b)-HP2O7}- (H2O)(OH2)]22 chelate at the B3LYP/LANL2DZ level.708 J.Chem. Soc., Dalton Trans., 1999, 699–710 co-ordinated. The protons of the H2O ligand interact with the oxygen donors from pyrophosphate. The P–O(d) distances average 1.700 Å whereas P(1)–O(b) and P(2)–O(b) are 1.833 and 1.707 Å, respectively. The conformation of the coordination ring is chair (QT 0.812 Å; f 6.88; q 29.88). [Zn{O(a),O(b)-HP2O7 }(NH3)2]2?NH3. A structure for [Zn{O(a),O(b)-HP2O7}(NH3)3]2 with pseudo-Cs symmetry was submitted to geometry optimization. The final partially optimized (see above, computational procedure) system (Fig. 12) has a four-co-ordinate zinc atom linked to two ammonia molecules and to two oxygen atoms from pyrophosphate. The co-ordination sphere is pseudo-tetrahedral. One of the ammonia molecules initially bound to zinc escaped the coordination sphere and linked to one co-ordinated ammonia molecule and to the two oxygen donors via hydrogen bonds. The P–O–P bond angles for both [Zn{O(a),O(b)-HP2O7}- (H2O)(OH)]22 (138.38) and [Zn{O(a),O(b)-HP2O7}(NH3)2]2? NH3 (132.78) are in agreement with the solid state structure of [Cu(TERPY)(ADP)]2 [131.0(5)8].[Cu {O(a),O(b)-HP2O7 }(NH3)3]2. A structure for [Cu- {O(a),O(b)-HP2O7}(NH3)3]2 with pseudo-Cs symmetry was submitted to geometry optimization. The partially optimized geometry (see above, computational procedure) is a four-coordinate, almost square planar, (Fig. 13), the metal atom being linked to three NH3 molecules and to one oxygen atom of phosphate(1) [Cu–O(3), 1.934 Å]. The protonated phosphate escapes the co-ordination sphere and makes hydrogen bonds with the two trans NH3 ligands.The P–O(b) bond distances are 1.828 [P(1)] and 1.698 Å [P(2)], and the P–O–P bond angle is 138.78. The Cu–N bond distances are 2.03, 2.08, and 2.09 Å for N cis, cis, and trans to the O donor. Metal-ligand binding energy. The calculated energies of some protonation and metal–ligand bond formation are in Table 8.It is evident that the formation energy for the [Cu(O,O-PO4)]2 chelate (2962.22 kcal mol21) is much smaller than the corre- Fig. 12 Drawing of the partially optimized (see computational procedure) structure of the [Zn{O(a),O(b)-HP2O7}(NH3)2]2?NH3 aggregate at the B3LYP/LANL2DZ level. Fig. 13 Drawing of the partially optimized (see computational procedure) structure of the [Cu{O(a),O(b)-HP2O7}(NH3)3]2 complex molecule at the B3LYP/LANL2DZ level.sponding binding energy for [Cu{O(a),O(b)-P2O7}]22 (-1071.66 kcal mol21). This is consistent with a higher strain energy for a four-membered chelate ring when compared to a six-membered one. The formation of the 1 : 1 chelate system for zinc(II) is less favored than for copper(II). In fact the geometry optimization of [Zn(O,O-PO4)]2 did not converge, whereas the binding formation energy for [Zn{O(a),O(b)-P2O7}]22 is 21017.88 kcal mol21, some 54 kcal smaller than the corresponding one for the copper(II) species.Atomic charges. The atomic charges calculated through the Mulliken population analysis are shown in Table 9. The atomic charge of P in P2O7 42 (1.442 e) is, as expected, higher than in PO4 32 (1.330). The protonation of one of the PO3 groups, as in HP2O7 32, produces a decrease of the charge for both the phosphorus atoms (1.405, 1.418 e), even though P from protonated PO3 is slightly more positive than the other. The eVect of metal chelation does not influence much the charge of P: 1.448 e for [Cu{O(a),O(b)-P2O7}]22 and 1.399 for [Cu(O,O-PO4)]2.The chelation of Zn21 by P2O7 42 causes a small decrease of charge on P (down to 1.411 from 1.442). The atomic charge of copper is decreased to 0.361 e upon chelation by PO4 32 and to 0.478 upon chelation by P2O7 42. The electron donation to zinc by P2O7 42 is much smaller than that to copper (charge of Zn, 1.00 e). Vibrational frequencies. Selected normal frequencies, IR intensities and diagonal elements of the force constant matrix for P2O7 42 and [Cu{O(a),O(b)-P2O7}]22 calculated at the B3LYP/LANL2DZ level are listed in Table 10.A detailed discussion of the absolute values of vibrational frequencies for the stretching modes is not appropriate because bond distances are often overestimated at this level. However, a brief comparative analysis is reported mostly to understand the eVect of complexation. Upon complexation to copper the computed n[P–O(t)] stretching frequency of P2O7 42 is blue shifted by some 80 cm21 in agreement with a significant shortening (0.052 Å) of the P–O(t) bond distance.The n[P–O(b)] frequency is red shifted by some 40 cm21 even though the computed P–O(b) bond distance undergoes a small shortening (0.028 Å). It should be noted that n[P–O(b)] and n[Cu–O] stretching modes are coupled in the case of [Cu{O(a),O(b)- P2O7}]22. Conclusion This is the first structure of a nucleoside 59-diphosphate (and -triphosphate) which contains covalently metal-bound and free nucleotide molecules.This allows a fine comparative analysis of the eVects by metal co-ordination on the nucleotide. A copper(II) promoted dephosphorylation of ADP in aqueous solution has been previously presented.43 It has been postulated that the dephosphorylation process proceeds via the formation of dimers which contain self-stacked adenine bases bound to metal centres through N(7). The present work confirms the formation of aggregates which contain two metal centres and two nucleotide molecules.The presence of a strong co-ordinating agent, TERPY in this work, makes only the coordination at the diphosphate possible; adenine nitrogen atoms are not involved. The TERPY–adenine stacking interaction and adenine–adenine base pairing play a very important structuring role to held diphosphates and copper(II) centres directly linked or bound via Cu–OH2 ? ? ? O(phosphate) bridges.Free water molecules are near the P(b) atom for the free nucleotide [P(2B) ? ? ? O(6W) 3.91(1) Å] and P(a) atom of the copper(II)-bound nucleotide [P(1A) ? ? ? O(1W) 3.80(1)]; the sum of the van der Waals radii for O and P is 3.35 Å.44 The copper(II)-bound O(2W2) water molecule is at 3.60(1) Å from P(b) of the copper(II)-bound nucleotide. Interestingly, theJ. Chem. Soc., Dalton Trans., 1999, 699–710 709 Table 8 Bond formation energies (kcal mol21) for formal reactions calculated at the B3LYP/LANL2DZ level Reaction P2O7 42 1 H1 æÆ HP2O7 32 Cu21 1 PO4 32 æÆ [Cu(O,O-PO4)]2 Cu21 1 P2O7 42 æÆ [Cu{O(a),O(b)-P2O7}]2 Zn21 1 P2O7 42 æÆ [Zn{O(a),O(b)-P2O7}]2 Zn21 1 HP2O7 32 1 OH2 1 H2O æÆ [Zn{O(a),O(b)-HP2O7}(H2O)(OH)]22 Zn21 1 HP2O7 32 1 3NH3 æÆ [Zn{O(a),O(b)-HP2O7}(NH3)2]2?NH3 Cu21 1 HP2O7 32 1 3NH3 æÆ [Cu{O(b)-HP2O7}(NH3)3]2 DE 2636.48 2962.22 21071.66 21017.88 2876.88 2879.88 a 2927.08 a a The systems were geometry optimized without reaching the full convergence criteria of the GAUSSIAN 94/DFT package.Table 9 Atomic charges (e) from the Mulliken population analysis calculated at the B3LYP/LANL2DZ level System H2O OH2 Cu21 Zn21 NH3 PO4 32 P2O7 42 HP2O7 32 [Cu(PO4)]2 [Cu(P2O7)]22 [Zn(P2O7)]22 [Cu(HP2O7)(NH3)3]2 [Zn(HP2O7)(H2O)(OH)]22 [Zn(HP2O7)(NH3)2]2?NH3 O(H) 20.711 21.144 20.864 20.740 20.770 20.895 (OH2) 20.788 (H2O) 20.733 O(t) 21.083 20.993 20.902 20.620 20.756 20.781 20.777 20.837 20.763 O(b) 20.926 20.863 20.892 20.979 20.853 20.825 20.832 O(d) 20.760 20.728 20.862 20.789 20.853 20.895 (OH2) 20.798 (H2O) 20.866 N 20.893 20.909 21.016 20.983 (free NH3) P 1.330 1.442 1.405 1.399 1.448 1.411 1.452 1.426 1.427 P(OH) 1.418 1.488 1.480 1.447 Cu 2 0.361 0.478 0.546 Zn 2 1.003 0.909 1.044 H(O) 0.356 0.144 0.416 0.401 0.421 0.393 (OH2) 0.424 (H2O) 0.399 H(N) 0.298 0.372 0.374 0.347 (free NH3) Table 10 Selected normal vibrational wavenumbers (n, stretching; d, bending) in cm21.Intensities: w, weak; m, medium; s, strong; with the values in km mol21.The diagonal elements of the force constant matrix are in square brackets in mdyne Å21 or mdyne rad21 Molecule P2O7 42 n[P–O(t)] 912.5 m(558.6) [10.380] n]P–O(b)] 721.5 s(1385.1) [5.738] n(Cu–O) d[O(t)–P–O(t)] 464.0 m(304.0) [2.429] d(Cu–O–P) d(O–Cu–O) [Cu(P2O7)]22 994.9 s(126.0) [11.890] n[P–O(b)]/ n(Cu–O) 681.5 w(12.0) [4.727] n(Cu–O)/ n[P–O(b)] 662.1 w(0.4) [4.954] 398.2 m(28.7) [1.831] 211.4 m(10.2) [0.545] 157.8 m(13.4) [0.431] O(5B)–P(2B)–O(6B) angle [116.8(5)8], which is in front of O(6W), and the O(5A)–P(2A)–O(7A) angle [114.9(5)8], which is faced to O(2W2), are larger than the idealized tetrahedral value.Even though no linking interaction seems to exist on the basis of the O ? ? ? P contact distances, this analysis suggests that a certain activation for nucleophilic attack by water on the phosphate groups of both the free and metal-bound nucleotide molecules occurs in this structure.The protonation status of the nucleotides formulated as H2ADP2 and ADP32 for the free and metal-bound molecules, respectively, was inferred from the following series of observations. (1) The Fourier-diVerence map shows peaks on N(1B) and O(7B); no peaks were detected around N(1A) and O atoms from phosphate groups of the metal-bound nucleotide. (2) The P–O bond distances for the nucleotide molecules are consistent with protonation of the terminal phosphate of free nucleotide molecule only.(3) The values of the C(2)–N(1)–C(6) angles confirm the protonation of N(1B) only, on the basis of the Singh rule.32 (4) A strong linkage of copper to a ligand molecule can increase significantly the acidity of the ligand protons especially in the portion of the molecule close to metal ligation. In this work the crystals were obtained from a mother-liquor composed of ethanol (ca. 50%) and water and no acid was added to increase the acidity. (5) Atoms N(1B) and O(3B) at x,y 1 1,z have a contact distance of 2.66(2) Å [angle at H(N1B) 166(3)8] which is indicative of a hydrogen bond.It is not reasonable that an alpha-phosphate oxygen [like O(3B)] is protonated. So, only N(1B) can be a hydrogen donor, of the latter pair of atoms. In conclusion N(1B) is protonated. (6) Atoms O(7B) and O(2A) both at x,y,z have a contact distance of 2.65(1) Å [angle at H(O7B) 152(3)8] which is indicative of a possible hydrogen bond. Again, O(2A) is very reasonably not protonated; O(7B) is probably protonated.All this evidence converges towards the formulation given in this work even though it is clear that each single observation alone is not strong enough to make the assumption reliable. A sound answer could come from a very accurate diVraction analysis carried out on larger single crystals possibly investi-710 J. Chem. Soc., Dalton Trans., 1999, 699–710 gated at low temperature and through a neutron beam. The authors recall that the best quality crystal used for the present data collection came after very many crystal growth attempts.Finally, this work proves that density functional analysis, at least at the B3LYP/LANL2DZ level, is able to reproduce the copper(II)–pyrophosphate linkage and to give important physico-chemical parameters relevant to the copper(II)– and zinc(II)–nucleotide interactions. The positive charge on phosphorus atoms of phosphate and pyrophosphate ligands increases, even though slightly, upon co-ordination to copper(II).This eVect and the computed distortion from the tetrahedral environment around phosphorus caused by the CuII–O(P) bond formation [for instance, the O(t)–P–O(t) angle for the computed [Cu{O(a),O(b)-P2O7}]22 molecule is 120.78) is in accord with the catalytic role copper(II) ions play in hydrolytic processes of nucleotides. Acknowledgements The authors thank Professor G. Sabatini, director, and Mr A. Scala for the collection of X-ray powder diVraction data at Istituto di Mineralogia e Petrografia, Università di Siena.Mr F. Berrettini, at Centro Interdipartimentale di Analisi e Determinazioni Strutturali, Università di Siena, is acknowledged for X-ray data collection. Università di Siena, Ministero dell9Università e della Ricerca Scientifica e Tecnologica (Roma), through grant COFIN.MURST 97-CIFSB, and Consiglio Nazionale delle Ricerche (Roma) are acknowledged for funding. References 1 (a) K.Aoki, in Metal Ions in Biological Systems, eds. A. Sigel and H. Sigel, Marcel Dekker, Basel, 1996, vol. 32, ch. 4; (b) L. Stryer, Biochemistry, W. H. Freeman and Co., New York, 1991; (c) M. Ronaghi, M. Uhlén and P. Nyrén, Science, 1998, 281, 363; (d ) D. A. Suhy and T. V. O’Halloran, in Metal Ions in Biological Systems, eds. A. Sigel and H. Sigel, Marcel Dekker, Basel, 1996, vol. 32, ch. 16; (e) T. Steitz, S. J. Smerdon, J. Jäger and C. M. Joyce, Science, 1994, 266, 2022; ( f ) J.P. Whitehead and S. J. Lippard, in Metal Ions in Biological Systems, eds. A. Sigel and H. Sigel, Marcel Dekker, Basel, 1996, vol. 32, ch. 20; (g) R. K. O. Sigel, E. Freisinger and B. Lippert, Chem. Commun., 1998, 219; (h) M. Sabat, in Metal Ions in Biological Systems, eds. A. Sigel and H. Sigel, Marcel Dekker, Basel, 1996, vol. 32, ch. 15; (i) M. J. Bloemink, J. P. Dorenbos, R. J. Heetebrij, B. K. Keppler and J. Reedijk, Inorg. Chem., 1994, 33, 186; ( j) N. Farrell, in Metal Ions in Biological Systems, eds.A. Sigel and H. Sigel, Marcel Dekker, Basel, 1996, vol. 32, ch. 18; (k) M. Coluccia, A. Nassi, F. Loseto, A. Boccarelli, M. A. Mariggio, D. Giordano, F. P. Intini and G. Natile, J. Med. Chem., 1993, 36, 510; (l) T. P. Kline, L. G. Marzilli, D. Live and G. Zon, J. Am. Chem. Soc., 1989, 111, 7057; (m) B. Song, A. Holý and H. Sigel, Gazz. Chim. Ital., 1994, 124, 387; (n) G. B. Helion, Angew. Chem., 1989, 101, 893. 2 J. Löwe and L. A. Amos, Nature (London), 1998, 391, 203. 3 G. J. Davies, S. J. Gamblin, J. A. Littlechild, Z. Dauter, K. S. Wilson and H. C. Watson, Acta Crystallogr. Sect. D, 1994, 50, 202. 4 S. Morera, I. Lascu, C. Dumas, G. LeBras, P. Briozzo, M. Véron and J. Janin, Biochemistry, 1994, 33, 459. 5 J.-M. Lehn, Supramolecular Chemistry; Concepts and Perspectives, VCH, Weinheim, 1995. 6 J.-M. Lehn, Science, 1993, 260, 1762. 7 S. H. Gellman (Guest editor), Chem. Rev., 1997, 97. 8 L. J. Barbour, G. W. Orr and J.L. Atwood, Nature (London), 1998, 393, 671. 9 J. C. Ma, D. A. Dougherty, Chem. Rev., 1997, 97, 1303. 10 A. Cavaglioni and R. Cini, J. Chem. Soc., Dalton Trans., 1997, 1149. 11 R. Cini, R. Bozzi, A. Karaulov, M. B. Hursthouse, A. M. Calafat and L. G. Marzilli, J. Chem. Soc., Chem. Commun., 1993, 889. 12 R. Cini, M. C. Burla, A. Nunzi, G. P. Polidori and P. F. Zanazzi, J. Chem. Soc., Dalton Trans., 1984, 2467. 13 P. Orioli, R. Cini, D. Donati and S. Mangani, Nature (London), 1980, 283, 691. 14 R. Cini and R. Bozzi, J. Inorg. Biochem., 1996, 61, 109. 15 G. M. Sheldrick, SHELXS 86, Program for Crystal Structure Determination, University of Göttingen, 1986. 16 G. M. Sheldrick, SHELXL 93, Program for Refinement of Crystal Structure, University of Göttingen, 1993. 17 H. D. Flack, Acta Crystallogr., Sect. A, 1983, 39, 876. 18 M. Nardelli, PARST 95, A System of Computer Routines for Calculating Molecular Parameters from Results of Crystal Structure Analyses, University of Parma, 1995. 19 L. Zsolnai, ZORTEP, An Interactive ORTEP program, University of Heidelberg, 1994. 20 L. J. Farrugia, ORTEP 3 for Windows, Version 1.01 Beta, University of Glasgow, 1997. 21 M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, J. Cioslowski, B. B. Stefanov, A. Nanayakkara, M. Challacombe, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez and J. A. Pople, Gaussian Inc., Pittsburgh, PA, 1995. 22 A. D. Becke, J. Chem. Phys., 1988, 88, 1053; C. Lee, W. Yang and R. G. Parr, Phys. Rev. B, 1988, 37, 785. 23 P. J. Hay and W. R. Wadt, J. Chem. Phys., 1985, 82, 299. 24 D. E. Woon and T. H. Dunning, Jr., J. Chem. Phys., 1993, 98, 1358 and refs. therein. 25 (a) H. Saint-Martin, L. E. Ruiz-Vicent, A. Ramírez-Solís and I. Ortega-Blake, J. Am. Chem. Soc., 1996, 118, 12167; (b) A. J. H Wachters, J. Chem. Phys., 1970, 52, 1033. 26 P. Swaminathan and M. Sundaralingam, Acta Crystallogr., Sect. B, 1980, 36, 2590. 27 Z. Shakked, M. A. Viswamitra and O. Kennard, Biochemistry, 1980, 19, 2567. 28 M. Sabat, R. Cini, T. Haromy and M. Sundaralingam, Biochemistry, 1985, 24, 7827. 29 W. Sanger, Principles of Nucleic Acid Structure, Springer, New York, 1984. 30 D. Cremer and J. A. Pople, J. Am. Chem. Soc., 1975, 97, 1354. 31 R. Cini, Comments Inorg. Chem., 1992, 13, 1. 32 C. Singh, Acta Crystallogr., 1965, 19, 861. 33 P. Prusiner and M. Sundaralingam, Acta Crystallogr., Sect. B, 1972, 28, 2148. 34 C. Altona and M. Sundaralingam, J. Am. Chem. Soc., 1972, 94, 8205. 35 O. Kennard, N. W. Isaacs, W. D. S. Motherwell, J. C. Coppola, D. L. Wampler, A. C. Larson and D. G. Watson, Proc. R. Soc., London, Ser. A, 1971, 325, 401. 36 J. V. Folgado, R. Ibáñez, E. Coronado, D. Beltrán, J. M. Savariault and J. Galy, Inorg. Chem., 1988, 27, 19. 37 M. C. Muñoz, R. Ruiz, M. Julve, F. Lloret and X. Solans, Acta Crystallogr., Sect. C, 1993, 49, 674. 38 R. Cini and L. G. Marzilli, Inorg. Chem., 1988, 27, 1855. 39 A. F. Wells, Structural Inorganic Chemistry, Clarendon Press, Oxford, 1975. 40 (a) D. Kobashi, S. Kohara, J. Yamakawa and A. Kawahara, Acta Crystallogr., Sect. C, 1997, 53, 1523; (b) R. Masse, J. C. Guitel and A. Durif, Mater. Res. Bull., 1979, 14, 337; (c) M. T. Averbruch- Pouchot and A. Durif, Z. Kristallogr., 1987, 180, 195. 41 R. Cini, D. G. Musaev, L. G. Marzilli and K. Morokuma, J. Mol. Struct. (Theochem.), 1997, 392, 55. 42 B. Ma, C. Meredith and H. F. Schaefer III, J. Phys. Chem., 1995, 99, 3815. 43 H. Sigel and B. Song, in Metal Ions in Biological Systems, eds. A. Sigel and H. Sigel, Marcel Dekker, Basel, 1996, vol. 32 and refs. therein. 44 A. Bondi, J. Phys. Chem., 1964, 68, 441. Paper 8/07793B

ISSN:1477-9226    

DOI:10.1039/a807793b

出版商:RSC    

年代:1999

数据来源: RSC

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DALTON PERSPECTIVE J. Chem. Soc., Dalton Trans., 1997, Pages 701–705 701 Co-ordination complexes as organic–inorganic layer magnets Peter Day Davy Faraday Research Laboratory, The Royal Institution of Great Britain, 21 Albemarle Street, London W1X 4BS, UK Examples are given of transition-metal co-ordination complexes that give rise to alternating layers of organic and inorganic moieties in the solid state exhibiting finite zero-field magnetisation at low temperature. The mechanisms of magnetic exchange included are ferromagnetism, ferrimagnetism and canted antiferromagnetism.When inorganic chemistry finally emerged as a distinct discipline in the 1950s one of the driving forces was the application of physical methods to determine the fine detail of molecular electronic structure, and hence provide the basis for correlations between structure and properties. Among the methods that came especially into prominence at that time was the measurement of bulk magnetic susceptibility.In his seminal book ‘The Nature of the Chemical Bond’ Pauling,1 in the 1930s, devoted a whole chapter to what he called ‘the magnetic criterion for bond type’, by which he meant the distinction between what we now know as high-spin and low-spin electron configurations. In the 1950s and 1960s it was Nyholm, with Figgis and Lewis,2 who pioneered the field that became known as magnetochemistry, but since then, until the last few years, inorganic chemists have moved away from bulk magnetic studies in favour of more direct structural probes like magnetic resonance. However, there is now a distinct field of study developing around the directed synthesis of new compounds (often based on coordination complexes) that show varieties of long-range magnetic order.From some points of view, ordered magnets have been considered as closer to the concerns of physicists, and the key examples have tended to be, if not simple metals and alloys, then binary or ternary oxides: in short, continuous lattices.The purpose of this Perspective is to survey some of the more novel forms of magnetism that have arisen from synthetic inorganic chemistry, using mainly examples from the work of my group, and with an emphasis on molecular lattices with strongly developed layer structures. Strategies towards Spontaneous Magnetism A major force driving synthesis in the field of magnetism is to try and create lattices which not only show long-range magnetic order, but exhibit ‘spontaneous’ magnetisation, i.e.a non-zero net moment in the absence of an applied field. To reach this goal a variety of strategies have been tried. The large majority of materials showing spontaneous magnetisation at finite temperatures have crystal lattices continuous in three dimensions, either close-packed structures or oxides, chalcogenides and halides. 3 Of these many are metals and insulating magnets are quite rare. Indeed, all the molecular-based magnets prepared up to now are insulators (Table 1).Physical mechanisms of ferromagnetic exchange coupling between localised moments are based on the notion of ‘orthogonal magnetic orbitals’,4 a situation that is very difficult to achieve in a three-dimensionally continuous lattice. Many years ago it was shown5,6 that a co-operative Jahn–Teller lattice distortion provided a suitable means of creating ‘orbital ordering’ in two dimensions, such that singly occupied 3d orbitals on a given metal ion are made orthogonal to the corresponding ones on all the nearest-neighbour ions.The metals concerned are CrII, MnIII and CuII (Table 1). Halide and cyanide complexes of these elements generate genuine ferromagnets, but still they are small in number. Given the difficulty of engineering near-neighbour ferromagnetic exchange in the absence of conduction electrons, alternative strategies for inducing finite zero-field magnetisation are worth considering.One route lies in exploiting ferrimagnetism. A ferrimagnet contains two different magnetic ions with near-neighbour antiferromagnetic exchange coupling. Since the antiparallel moments do not cancel there is a net resultant moment in zero field below the ordering temperature Tc. The most famous examples are the ferro-spinels, including the oldest magnetic material of all, magnetite (Fe3O4), but some molecular-based examples are discussed below. Finally a third strategy, less exploited than the other two, consists of building lattices containing only one magnetic ion, but in which (because of competition with single-ion anisotropy induced by a lowsymmetry ligand field and second-order spin–orbit coupling) the moments on neighbouring ions are not exactly antiparallel.This is called canted antiferromagnetism or ‘weak ferromagnetism’ because the resultant of two vectors that are nearly, but not quite, antiparallel is a small vector at right angles. Some examples will be given of all three approaches, based on synthetic co-ordination chemistry.Transparent Insulating Ferromagnets One of the most intensively studied of the ferromagnets based on the principle of orthogonal magnetic orbitals is the A2CrX4 series since they have relatively high Curie temperatures.7–9 Their properties have been comprehensively reviewed so only a few salient points will be mentioned here. The structure consists of a two-dimensionally infinite square lattice of CrII bridged by halide ions, the A+ being situated between the layers (Fig. 1). An important characteristic of these compounds is that they are relatively transparent in the visible and also at microwave frequencies. The intensity of the optical absorption of such materials, which is due to spin-forbidden ligand-field transi- Table 1 Some insulating ferromagnets with mono- and poly-atomic ligands Tc/K Tc/K CrBr3 EuO K2[CuF4] Cs[MnF4] [(RNH3)2][CuCl4] Tb(OH)3 Fe4[Fe(CN)6]3?14H2O 33 69 6.3 18.9 7–11 3.7 5.5 [Mn(pc)] [Fe(phen)2Cl2] GdCl3 A2CrX4 [Fe(h-C5Me5)2]?tcne [Mn(tpp)]?tcne Cs[Cr2(CN)6] [Cr5(CN)12]?10H2O 8.6 5 2.2 50–60 4.8 18 90 220 pc = Phthalocyaninate; phen = 1,10-phenanthroline; tcne = tetracyanoethylene; tpp = 5,10,15,20-tetraphenylphorphyrinate.702 J.Chem. Soc., Dalton Trans., 1997, Pages 701–705 tions, is extremely sensitive to the onset of the magnetic ordering.10 This is because the transitions become allowed by coupling the electronic excitation with annihilation of thermally populated spin deviations, a mechanism which has been validated in great detail by a combination of optical and neutron experiments. As well as exciting spin deviations thermally, they can also be excited by irradiating the compound with microwaves, and it has been demonstrated 11 that microwave pumping changes the magnetisation and hence the optical absorption intensity.Thus one could envisage using this kind of material to modulate a beam of optical frequency at a microwave frequency for communications purposes. The A+ separating the layers are not confined to monoatomic Group 1 ions, but can be a wide range of organic cations, principally of the RNH3 + type.12 This leads to the unusual situation of a magnetic material containing molecular entities, but in which the latter do not participate directly in the exchange mechanism.However, they do participate indirectly, because the ferromagnetic state must show long-range order in all three dimensions and the organic molecular cations separate the ([CrX4]22)• layers.By changing R (especially the length of an alkyl chain CnH2n+1) one can vary the interlayer spacing by a factor of more than two. This kind of chemistry makes accessible a structural change much larger than would be possible in a purely inorganic non-molecular lattice. The variation of Curie temperature with interlayer spacing in the series is shown in Fig. 2. Fig. 1 The ([CrCl4]22)• layer in [H3N(CH2)3NH3][CrCl4] 8 Fig. 2 Variation of the Curie temperature of A2CrCl4 with interlayer spacing Canted Antiferromagnets When a paramagnetic ion is surrounded by a low-symmetry ligand environment, spin–orbit coupling results in a small component of excited states being mixed into the ground state giving a zero-field splitting of the lowest electronic levels. This splitting mimics the effect of a large static magnetic field, along the principal axis of the local ligand field.13 The moments are therefore constrained to that direction and we find a single-ion anisotropy. Should the local distortion axes on neighbouring sites not be parallel, in the presence of near-neighbour antiferromagnetic exchange the moments will not be aligned in an exactly parallel fashion, but will make an angle to each other.Consequently the moments do not cancel in the antiferromagnetically ordered state, and there is a small net moment, hence weak ferromagnetism.14 A few years ago we examined15 the series of alkylphosphonate salts Mn(CnH2n+1PO3)2?H2O which have layer structures quite similar to the ternary phosphates MIMIIPO4?H2O.16 The metal ion is again surrounded by a very low-symmetry coordination of oxygen (site group C2), five from phosphonate groups and one from H2O. Neighbouring metal ions are connected by exchange paths through O]P]O linkages of the anions into a nearly square two-dimensional lattice almost identical to that of the phosphates, while the P]C bonds of the phosphonate groups are directed perpendicular to the planes defined by the metal ions (Fig. 3). Exchange within the layers is antiferromagnetic and the susceptibilities also pass through a broad maximum around 20 K characteristic of a lowdimensional antiferromagnet. Near 15 K the susceptibility increases abruptly, finally saturating at low temperature at a value which varies markedly with the length of the alkyl chain, being smallest for CH3 and largest for C4H9.The limiting low- field magnetisation at low temperature yields a direct estimate of the canting angle between the moments. For example that for C4H9 is 2.98. Close examination shows that the onset temperature of the canted state also changes with the alkyl group, those of the C2H5 and C4H9 compounds being higher than those of CH3 and C3H7 (Fig. 4). Alternation effects are a well known structural feature of crystals containing aliphatic hydrocarbon chains, for example the interplanar spacing in the layer perovskite halide salts [CnH2n+1NH3]2[MX4] when plotted against n is not a straight line but a zigzag.17 Put another way, the increase in interlayer spacing caused by adding one CH2 group to the chain is larger from an even to an odd number of C atoms than vice versa.The difference arises from the contrasting ways in which the terminal CH3 groups mesh together in the two cases: the terminal C]C bond of a C2n chain is nearly parallel to the layer while that of a C2n+1 chain is nearly perpendicular.Fig. 4 shows the first example of an alternation effect in magnetic properties. Fig. 3 The layer structure of Mn(CH3PO3)?H2OJ. Chem. Soc., Dalton Trans., 1997, Pages 701–705 703 Although full crystal structures are not available for the four compounds, one must suppose that the different packing of the chain ends causes a small change in the orientation of the PO3 group.That would change the M]O]P bond angle, affecting the superexchange pathway and hence TN. Thus we have a clear case of intervention of an organic substituent far from the magnetic site in influencing the ordering process. Varying the chain length of the alkylphosphonate group leads to a much larger variation in the interlayer spacing than changing the Group 1 ion in the ternary phosphates. For example in Mn(CH3PO3)?H2O it is 8.82 Å and in Mn(C4H9- PO3)?H2O in 14.71 Å.This makes the phosphate and phosphonate salts a very attractive series in which to monitor the transition from two- to three-dimensional order by measuring the critical exponent of the magnetisation b as TN is approached from lower temperatures. Thus the critical behaviour of [NH4][Mn(PO4)]?H2O and its deuteriated analogue was studied 18 by neutron diffraction and bulk magnetometry, finding that b underwent a crossover from a value of 0.20 when the reduced temperature e = (TN 2 T)/TN was >0.03–0.07 to a much higher value (0.39–0.40) on approaching TN.Then the alkylphosphonates were examined19 to see whether there is a corresponding crossover and if so how it varies with interlayer spacing. Data more remote from TN obey the relationship Me = M0eb with b in the region of 0.20 for Mn(CnH2n+1PO3)?H2O (n = 2–4). However, as TN is approached from below the exponential relationship changes and a much higher exponent b9 becomes evident.The value of b is close to that found in MI[Mn- (PO4)]?H2O (MI = NH4, ND4 or K) and far from any of the estimates of two- or three-dimensional magnetic models. Thus in three dimensions the Ising, XY and Hesienberg models predict respectively 0.31, 0.33 and 0.35 while the two-dimensional Ising model predicts 0.125. The related compound Mn(HCO2)2? 2D2O, also a quadratic layer Heisenberg antiferromagnet, gives b = 0.22(1), with a crossover to b9 = 0.31(2) at e ª 0.02. Recently, Bramwell and Holdsworth 20 have shown how b values in the region of 0.23 can arise from a two-dimensional model.Whilst the measured b9 are larger than predicted for any of the threedimensional models the crossover clearly demonstrates evolution from two- to three-dimensional behaviour. The reduced temperatures eX0 at which the cross-overs occur also vary significantly from one compound to another within the manganese phosphate (phosphonate) hydrate series. Among the metal(I) compounds eX0 is a little larger in K[Mn(PO4)]?H2O [0.09(1)] than in the NH4 compound [0.07(1)], no doubt to be correlated with the smaller interlayer separation in the former.For the alkylphosphonates eX0 decreases as the interlayer separation increases, corresponding to a decrease in the ratio of inplane to out-of-plane exchange constants. This was the first systematic study of the critical exponents and crossover Fig. 4 Magnetic ordering temperatures of Mn(n-CnH2n+1PO3)?H2O as a function of n (ref. 15) temperatures for a series of two-dimensional weak ferromagnets. Ferrimagnets In the previous section non-zero spontaneous magnetisation was achieved in compounds where there was only one type of metal-ion site. When two different metal ions (or two oxidation states of the same metal) are coupled antiferromagnetically ferrimagnetism provides an alternative route to the same end. Ferrimagnetic bulk magnetic properties of metal–organic compounds can be sensitive to very small changes in the organic substituents, and hence the molecular packing.Compounds with general formula AMIIMIII(C2O4)3 constitute a very extensive series, formed by a wide range of organic cations A+ as well as di- and tri-valent M both from transition metal and B-subgroup ions.21 Cross-linking of the [MIII(C2O4)3]32 by MII in two dimensions produces a honeycomb structure in which both metal ions occupy sites of trigonally distorted octahedral geometry, with all near-neighbour MII, MIII pairs bridged by oxalate ions (Fig. 5). Many compounds in this series therefore have approximately hexagonal crystal structures with basal-plane unit-cell constants that vary only slightly with A+, though with strongly varying interlayer separation. Some unit-cell constants are listed in Table 2, which shows that a factor of 2 in interlayer Fig. 5 Honeycomb layer structure of AIMIIMIII(C2O4)3 Table 2 Intralayer (d1) and interlayer MIIFeIII separation (d2) in AMIIFeIII(C2O4)3 in Å (ref. 23) MII = Fe MII = Mn A d1 d2 d1 d2 [N(n-C3H7)4]+ [N(n-C4H9)4]+ [N(n-C5H11)4]+ [P(n-C4H9)4]+ [As(C6H5)4]+ [N(CH2C6H5)(n-C4H9)3]+ [(C6H5)3PNP(C6H5)3]+ 4.667 4.701 4.703 4.735 4.683 4.690 4.690 8.218 8.990 10.233 9.317 9.655 9.633 14.433 4.686 4.731 4.728 4.760 4.722 4.735 4.707 8.185 8.937 10.158 9.525 9.567 9.433 14.517704 J. Chem. Soc., Dalton Trans., 1997, Pages 701–705 separation is easily achievable. In fourteen compounds with MII = Mn or Fe and MIII = Fe the spacing between the metal ions in the plane decreases from Mn to Fe by 0.026 Å, in line with the decrease in ionic radius expected from ligand-field considerations, while the interplanar spacing increases by an average of 0.083 Å, most probably because the organic groups which enter the hexagonal cavities are slightly extended as the cavity becomes smaller. One example is [N(n-C5H11)4][MnFe- (C2O4)3] the crystal structure of which consists of alternate layers of [MnFe(C2O4)3]2 and [N(n-C5H11)4]+, the former comprising honeycomb networks of alternating Mn and Fe bridged by C2O4 22 (Fig. 6).22 Thus both metal ions are co-ordinated by six O originating from three bidentate oxalate ions forming a trigonally distorted octahedron.Similar networks have been observed in [P(C6H5)4][MnCr(C2O4)3] 24 and [N(n-C4H9)4]- [MnCr(C2O4)3] 25 though in the latter case none of the C atoms of the cation was located, and the N was arbitrarily placed on a three-fold axis.In the [P(C6H5)4]+ compound, too, one P]C bond lies parallel to a three-fold axis and the unit cell is also rhombohedral. In the [N(n-C5H11)4]+ compound the deviation of the 3d ions from a hexagonal array is implicit in the orthorhombic space group: the angles Fe]Mn]Fe and Mn]Fe]Mn are respectively 112 and 1388 instead of 1208. The site symmetry of the metal ions, which would be D3 if the cell were rhombohedral, is reduced to C2 and the metal–oxygen bond lengths are not all equal. One index of the distortion of the MO6 units is the deviation of the trans O]M]O bond angles from 1808: at the iron site two such angles are 163 and 1708. The ‘bite angle’ O]M]O for bidentate chelating oxalate groups averages 78.08 around the iron site and 798 around the Mn, similar to those found in other oxalato-complexes of FeIII and MnII.26 Since the mean O]M]O angle for O atoms on adjacent oxalate groups exceeds 908 (99.48 at the iron site and 98.68 at Mn) both MO6 octahedra are elongated perpendicular to the plane of the [MnFe(C2O4)3]2 layer.Alternate layers have opposite chirality [i.e. Mn(L) and Fe(D) in one layer, and Mn(D), Fe(L) in the next]. The ferrimagnetism of the MII = Mn compounds is a rather unusual kind in that the ground states of the two metal ions are both 6A1 in D3 symmetry. The near-neighbour exchange interaction is strongly antiferromagnetic, as indicated by the large negative Weiss constants, which do not vary much with A.Existence of strong antiferromagnetic spin correlations within the layers is confirmed by a broad maximum in the susceptibil- Fig. 6 Crystal structure of [N(n-C5H11)4][MnFe(C2O4)3] projected along the b axis ity at 55 K, again independent of A. The short-range magnetic order therefore mimics that of a two-dimensional antiferromagnet. However, with the onset of three-dimensional order at 27 K (nearly independent of A) the susceptibility increases abruptly (Fig. 7), to reach a value which does vary strongly with A, being smallest for [N(n-C4H9)4]+ and largest for [(C6H5)3- PNP(C6H5)3]+ at 5 K.23 As in the manganese alkylphosphonates 15 this is due to canted antiferromagnets. Furthermore, the magnitude of the uncompensated moment is determined by an organic group which not only takes no part in the exchange mechanism, but is far removed from the site of the magnetic moment. Clearly, this phenomenon has no analogue among conventional magnetic materials.When MII = Fe in the bimetallic tris(oxalato)ferrate(III) series the two magnetic ions have S = 2 and 5 2 – , giving rise to a conventional ferrimagnet. However, depending on the nature of the organic cation A, one either has a normal magnetisation at low temperature that increases monotonically from zero at Tc to a limiting value at T = 0, or one that increases below Tc but reaches a maximum. At lower temperatures the magnetisation then falls again, passing through zero and becoming strongly negative 27 (Fig. 8). This behaviour is highly unusual but finds a precedent among ferrimagnetic mixed-valent iron oxides with spinel and garnet structures, which were widely studied in the 1950s because they were among the first materials with nonzero spontaneous magnetisation which were not metallic.28 The origin of the apparently bizarre situation that the net magnetisation of a sample should be antiparallel to the applied measurement field was rationalised by Néel 29 on the basis of molecular field theory.In a ferrimagnet the net magnetisation at a given temperature is the sum of the magnetisations of each sublattice. If the temperature dependences of the sublattice Fig. 7 Variation of the magnetisation of [N(n-C5H11)4][MnFe(C2O4)3] measured at 10 mT with temperature Fig. 8 Temperature dependence of the magnetisation of AIFeIIFeIII- (C2O4)3 measured at 10 mT: ‘normal’ behaviour, AI = As(C6H5)4; ‘negative’ behaviour, AI = (C6H5)3PNP(C6H5)3J.Chem. Soc., Dalton Trans., 1997, Pages 701–705 705 magnetisations are similar the resultant is a monotonic increase from Tc to absolute zero as shown in Fig. 8 for [As(C6H5)4]- [FeIIFeIII(C2O4)3]. On the other hand, if the temperature derivatives of sublattice magnetisation dMFeII/dT and dMFeIII/dT vary differently with temperature, the resultant d(MFeII 2 MFeIII)/dT may change sign (Fig. 9). It may also happen (as shown in Fig. 9) that the magnetisations of the two sublattices cancel at some temperature called the ‘compensation temperature’. However, the feature distinguishing the bimetallic tris(oxalato) compounds from the oxides is that the drastically varying magnetic behaviour comes about by changing organic groups situated quite far away in the lattice from the magnetic centres. Conclusion This Perspective has used examples from transition-metal coordination chemistry to illustrate how it is possible to construct layer lattices, interleaved with organic molecular moieties, that exhibit spontaneous magnetisation.All the magnetic exchange mechanisms known to quantum mechanics, i.e. ferromagnetic, ferrimagnetic and canted antiferromagnetic, are found among organic–inorganic layer compounds, but with features unique to the molecular solid state. Apart from the obvious, that one can synthesize materials showing spontaneous magnetisation from solution at room temperature (in contrast to high temperatures needed to obtain halide and chalcogenide magnets), there are other features common to metal–organic magnets that distinguish them from more conventional magnetic materials.30 Among these are optical transparency, opening up the possibility of unusual magneto-optical behaviour, and extreme sensitivity to small changes in the packing of organic groups between the layers that contain the magnetic ions. Such features enable lattice engineering to be exploited to design compounds with optical and magnetic properties capable of being switched by temperature, pressure and applied fields.If we can achieve this goal not only will the science of inorganic chemistry be enlarged, but many applications lie in waiting. Acknowledgements The work described was made possible principally by the Fig. 9 Schematic temperature dependence of the sublattice magnetisations in a MIIMIII ferrimagnet and the resulting measured magnetisation enthusiastic efforts of the people whose names are recorded in References.Financial support came from EPSRC and the EU Human Capital and Mobility Programme (Network on Molecular-based Magnets). References 1 L. Pauling, The Nature of the Chemical Bond, Cornell University Press, Ithaca, 1948. 2 See, for example, B. N. Figgis and J. Lewis, in Modern Coordination Chemistry, eds. J. Lewis and R. G. Wilkins, Interscience, New York, 1960, ch. 6. 3 See, for example, J. B. Goodenough, Magnetism and the Chemical Bond, Interscience, New York, 1963. 4 A. Ginsberg, Inorg. Chim. Acta Rev., 1971, 5, 45. 5 P. Day, A. K. Gregson, D. H. Leech and M. J. Fair, J. Chem. Soc., Dalton Trans., 1975, 1306. 6 P. Day, J. Magn. Magn. Mater., 1986, 54 and 57, 1442. 7 P. Day, Acc. Chem. Res., 1979, 12, 236. 8 C. Bellitto and P. Day, J. Mater. Chem., 1992, 2, 265. 9 P. Day, Chem. Soc. Rev., 1993, 22, 51. 10 C. Bellitto, M. J. Fair, T. E. Wood and P. Day, J. Chem. Soc., Faraday Trans. 2, 1980, 1579. 11 P. J. Fyne, P. Day, M. T. Hutchings, S. Depinna, B. C. Cavenett and R. Pynn, J. Phys. C., 1984, 17, L245. 12 P. Day, Philos. Trans. R. Soc. London, Ser. A, 1985, 314, 145. 13 See, for example, R. L. Carlin, Magnetochemistry, Springer, Berlin, 1986, p. 30. 14 T. Moriya, Phys. Rev., 1960, 117, 635; 120, 91. 15 S. G. Carling, P. Day and D. Visser, J. Solid State Chem., 1993, 106, 111. 16 S. G. Carling, P. Day and D. Visser, Inorg. Chem., 1995, 34, 3917. 17 H. Arend, W. Haber, F. H. Mischgvorsky and G. K. Richter-van Leeuwen, J. Cryst. Growth, 1978, 42, 213. 18 S. G. Carling, P. Day and D. Visser, Solid State Commun., 1992, 88, 135. 19 S. G. Carling, P. Day and D. Visser, J. Phys.: Condens. Matter, 1995, 7, L109. 20 S. T. Bramwell and P. C. W. Holdsworth, J. Phys.: Condens. Matter, 1992, 5, L53. 21 H. I. Tamaki, Z. J. Zhong, N. Matsumoto, S. Kida, M. Koikawa, N. Achiwa, Y. Hashimoto and H. Okawa, J. Am. Chem. Soc., 1992, 114, 6974. 22 S. G. Carling, C. Mathoniere, P. Day, K. M. A. Malik, S. J. Coles and M. B. Hursthouse, J. Chem. Soc., Dalton Trans., 1996, 1839. 23 C. Mathoniere, C. J. Nuttall, S. G. Carling and P. Day, Inorg. Chem., 1996, 35, 1201. 24 S. Descurtins, H. W. Schmalle, H. R. Oswald, A. Linden, J. Enslig, P. Gütlich and A. Hauser, Inorg. Chim. Acta, 1994, 216, 65. 25 L. O. Atovmyan, G. V. Shilov, R. N. Lyubovskaya, E. I. Zhilyaeva, N. S. Ovanesyan, S. I. Piramova and I. G. Gusakovskaya, JETP Lett., 1993, 58, 766. 26 M. Julve, J. Faus, M. Verdaguer and A. Gleizes, J. Am. Chem. Soc., 1984, 106, 8306. 27 C. Mathoniere, S. G. Carling, Y. Dou and P. Day, J. Chem. Soc., Chem. Commun., 1994, 1551. 28 J. B. Goodenough, Magnetism and the Chemical Bond, Interscience, New York, 1963. 29 L. Néel, Ann. Phys., 1948, 1, 137. 30 P. Day, in Magnetism: a Supramolecular Function, ed. O. Kahn, Kluwer, Dordrecht, 1996, p. 467. Received 21st October 1996; Paper 6/07182A

ISSN:1477-9226    

DOI:10.1039/a607182a

出版商:RSC    

年代:1997

数据来源: RSC