Crown Ether Palladacycles as Metalloligands: Suitable Precursors for

Organometallics 2009, 28, 6657–6665 DOI: 10.1021/om900390a

6657

Crown Ether Palladacycles as Metalloligands: Suitable Precursors for Tetranuclear Mixed Transition/Non-Transition Metal Complexes Samuel Castro-Juiz,† Alberto Fernandez,† Margarita L opez-Torres,† † † ,‡ Digna V azquez-Garcı´ a, Antonio J. Suarez, Jose M. Vila,* and Jes us J. Fernandez*,† †

Departamento de Quı´mica Fundamental, Universidade da Coru~ na, E-15071 A Coru~ na, Spain and Departamento de Quı´mica Inorg anica, Universidad de Santiago de Compostela, E-15782 Santiago de Compostela, Spain

‡

Received May 13, 2009

Reaction of Pd(OAc)2 with the Schiff base ligands 2,3,4-(MeO)3C6H2C(H)dN-[9,10-(C8H16O5)C6H3] (a) and 2,3,4-(MeO)3C6H2C(H)dN[9,10-(C10H20O6)C6H3] (b) leads to the cyclometalated compounds [Pd{2,3,4-(MeO)3C6HC(H)dN-[9,10-(C8H16O5)C6H3]-C6,N}( μ-O2CMe)]2 (1a) and [Pd{2,3,4-(MeO)3C6HC(H)dN[9,10-(C10H20O6)C6H3]-C6,N}( μ-O2CMe)]2 (1b), respectively, via CH activation. The metathesis reaction of 1a with aqueous tetrabutylammonium chloride gave the corresponding cyclopalladated dimer with bridging chloride ligands, 2a. Treatment of the dimer compounds with NaClO4, KClO4, NH4PF6, Pb(SCN)2, RbClO4, and Ba(ClO4)2 gave the corresponding products in which the cation (Naþ, Kþ, NH4þ, Pb2þ, Rbþ, Ba2þ) was coordinated to the crown ether moiety. The structures of compounds 1a and 6a (a complex with one Naþ cation coordinated to each crown ether group) have been determined by X-ray single-crystal diffraction analysis. Introduction The most salient property of crown ethers is their ability to form complexes selectively with ionic species, such as alkali metal and alkaline-earth metal cations; the different crown ether cavity size can be chosen to bind selectively with a given cation.1 The stability of the resulting complexes depends on the relative size of the metal ion with respect to the crown ether cavity size, the charge on the metal, conformation of the ether ring, the particular structure of the designed ligands, and the solvent; it is also possible to tailor-make different types of molecules for specific uses.2 The particular ability of crown ethers to complex cations3 has been used to study a large number of applications such as the production of sensors and the selective extraction of cations or the ionic *Corresponding authors. (J.M.V.) Fax: þ34/981-595012. E-mail: [email protected]. (J.J.F.) Fax: þ34/981-167065 E-mail: lujjfs@ udc.es.

transport in membranes.4 The design of functionalized crown ethers is an intensively studied area of tremendous potential significance because of the new properties that can be generated. For example, a common approach in this area is the organometallic functionalization of the classic crown ethers in order to obtain photochemical controlled and electrochemical active receptors5 or compounds with promising anticancer properties.6 Furthermore, metalloligands may be defined as compounds with potential coordination sites possessing a metal center in their structure, and they have recently attracted much attention in supramolecular chemistry because the physical and chemical properties of the metal center as well as the characteristic structure of the complex are very useful in obtaining a stronger and more selective recognition, as well as the formation of a stable supramolecular system.7

(1) (a) Izatt, R. M.; Bradshaw, J. S.; Nielsen, S. A.; Lamb, J. D.; Christensen, J. J.; Sen, D. Chem. Rev. 1985, 85, 271. (b) Inoue, Y.; Gokel G. W., Eds. Cation Binding by Macrocycles; Marcel Dekker: New York, 1990. (2) (a) Lehn, J. M.; Montavon, F. Helv. Chim. Acta 1978, 61, 67. (b) Izatt, R. M. Christensen, J. J., Eds. Synthetic Multidentate Macrocyclic Compounds; Academic Press: London, 1978. (c) V€ogtle, F.; Weber, E., Eds.; Host-/Guest Complex Chemistry: Macrocycles; Springer-Verlag: Berlin, 1985. (d) Izatt, R. M.; Christensen, J. J., Eds. Synthesis of Macrocycles: The Design of Selective Complexing Agents. In Progress in Macrocyclic Chemistry, Vol. 3; Wiley: New York, 1987. (e) Gokel, G. W. Crown Ethers and Cryptands. In Monographs in Supramolecular Chemistry; The Royal Society of Chemistry: Cambridge, 1991. (f) Cooper, S. R., Ed. Crown Compounds: towards Future Applications,; Wiley Interscience: New York, 1992. (g) Yordanov, A. T.; Roundhill, D. M. Coord. Chem. Rev. 1998, 170, 93. (3) (a) Pedersen, C. J. J. Am. Chem. Soc. 1967, 89, 2495. (b) Pedersen, C. J. Science 1988, 241, 536. (c) Steed, J. W. Coord. Chem. Rev. 2001, 215, 171.

(4) (a) Xiaotian, Q.; Zaide, Z.; Minggui, X.; Yongchang, Z.; Ying, T. Talanta 1998, 46, 45. (b) Rosa, D. T.; Young, V. G.; Coucouvanis, D. Inorg. Chem. 1998, 37, 5042. (c) Dillon, R. E. A.; Stern, C. L.; Shriver, D. F. Solid State Ionics 2000, 133, 247. (d) Yam, V. W. W.; Tang, R. P. L.; Wong, K. M. C.; Lu, X. X.; Cheung, K. K.; Zhu, N. Chem.;Eur. J. 2002, 8, 4066. (e) Breccia, P.; Van Gool, M.; Perez-Fernandez, R.; Martín-Santamaría, S.; Gago, F.; Prados, P.; de Mendoza, J. J. Am. Chem. Soc. 2003, 125, 8270. (f) Siu, P. K. M.; Lai, S. W.; Lu, W.; Zhu, N.; Che, C. M. Eur. J. Inorg. Chem. 2003, 2749. (5) (a) Ohshita, J.; Uemura, T.; Inoue, T.; Hino, K.; Kunai, A. Organometallics 2006, 25, 2225. (b) Liu, W.; Chen, Y.; Wang, R.; Zhou, X. H.; Zuo, J. L.; You, X. Z. Organometallics 2008, 27, 2990. (c) Perekalin, D. S.; Babak, M. V.; Novikov, V. V.; Petrovskii, P. V.; Lyssenko, K. A.; Corsini, M.; Zanello, P.; Kudinov, A. R. Organometallics 2008, 27, 3654. (6) Kelly, M. E.; Dietrich, A.; Gomez-Ruiz, S.; Kalinowski, B.; Kaluderovic, G. N.; Muller, T.; Paschke, R.; Schmidt, J.; Steinborn, D.; Wagner, C.; Schmidt, H. Organometallics 2008, 27, 4917. (7) (a) Lehn, J. M. Supramolecular Chemistry, Concepts and Perspectives; VCH: Weinheim, 1995. (b) Nabeshima, T. Coord. Chem. Rev. 1996, 148, 151. (c) Nabeshima, T.; Akine, S.; Saiki, T. Rev. Heteroat. Chem. 2000, 22, 219. (d) Albrecht, M. Chem. Rev. 2001, 101, 3457.

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On the other hand, cyclometalated compounds constitute a well-researched8 and developed9 area of organometallic chemistry, and they have been proved to be generally rather stable and relatively easy to characterize, showing a large number of applications.10 They may also provide a novel and interesting route to the preparation of metalloligands containing a crown ether ring systems, capable of further coordination to metal cations, producing mixed transition metal/main group metal species. These results are presented herein, where we describe the synthesis of crown ether palladacycles, complexes functionalized with benzo-15crown-5 and benzo-18-crown-6 groups, and their coordinative capability toward different cations, which puts forward their behavior as cyclometalated metalloligands toward metal cations; hitherto crystal structures of such compounds were still outstanding, and thus, the first crystal structure of a crown ether palladacycle with coordinated sodium cations is also described.

Experimental Section General Remarks. Safety Note: CAUTION: Perchlorate salts of metal complexes with organic ligands are potentially explosive. Only small amounts of these materials should be prepared and handled with great caution. Solvents were purified by standard methods.11 Chemicals were reagent grade and were purchased from Aldrich-Chemie and Alfa Aesar. Microanalyses were carried out using a Carlo Erba elemental analyzer, model 1108. The FAB mass spectra were recorded using a FISONS Quatro mass spectrometer with a Cs ion gun; 3-nitrobenzyl alcohol was used as the matrix. IR spectra were recorded as Nujol mulls or polythene discs Nujol mulls or KBr discs on a Perkin-Elmer model 1330. NMR spectra were obtained as CDCl3 solutions and referenced to SiMe4 (1H, 13 C{1H}) and were recorded on a Bruker AVANCE-300 spectrometer. All chemical shifts were reported downfield from standards. Synthesis of the Ligands. 2,3,4-(MeO)3C6H2C(H)dN-[9,10(C8H16O5)C6H3] (a). 2,3,4-Trimethoxybenzaldehyde (0.86 g, 4.33 mol) and 40 -aminobenzo-15-crown-5 (1.33 g, 4.69 mol) (8) Kleinmann, J. P.; Dubeck, M. J. Am. Chem. Soc. 1963, 86, 1544. (9) (a) Dehand, J.; Pfeffer, M. Coord. Chem. Rev. 1976, 18, 327. (b) Bruce, M. I. Angew. Chem., Int. Ed. Engl. 1977, 16, 73. (c) Omae, I. Coord. Chem. Rev. 1982, 42, 245. (d) Constable, E. C. Polyhedron 1984, 3, 1037. (e) Rothwell, I. P. Polyhedron 1985, 4, 177. (f) Wu, Y.; Huo, S.; Gong, J.; Cui, X.; Ding, L.; Ding, K.; Du, C.; Liu, Y.; Song, M. J. Organomet. Chem. 2001, 637-639, 27. (g) Albrecht, M.; van Koten, G. Angew. Chem., Int. Ed. 2001, 40, 3750. (h) Omae, I. Coord. Chem, Rev. 2004, 248, 995. (i) Mohr, F.; Priver, S. H.; Bhargava, S. K.; Bennett, M. A. Coord. Chem. Rev. 2006, 250, 1851. (10) (a) Marcos, M. In Metallomesogens. Synthesis, Properties and Applications; Serrano, J. L., Ed.; VCH: Weinheim, 1996. (b) Wild, S. B. Coord. Chem. Rev. 1997, 166, 291. (c) Gomez-Quiroga, A.; NavarroRanninger, C. Coord. Chem. Rev. 2004, 248, 119. (d) Slagt, M. Q.; van Zwieten, D. A. P.; Moerkerk, A. J. C. M.; Klein Gebbink, R. J. M.; van Koten, G. Coord. Chem. Rev. 2004, 248, 2275. (e) Dupont, J.; Consorti, C. S.; Spencer, J. Chem. Rev. 2005, 105, 2527. (f) Ghedini, M.; Aiello, I.; Crispini, A.; Golemme, A.; La Deda, M.; Pucci, D. Coord. Chem. Rev. 2006, 250, 1373. (g) Gagliardo, M.; Rodríguez, G.; Dam, H. H.; Lutz, M.; Spek, A. L.; Havenith, R. W. A.; Coppo, P.; De Cola, L.; Hartl, F.; van Klink, G. P. M.; van Koten, G. Inorg. Chem. 2006, 45, 2143. (h) Ruiz, J.; Lorenzo, J.; Sanglas, L.; Cutillas, N.; Vicente, C.; Villa, M. D.; Aviles, F. X.; Lopez, G.; Moreno, V.; Perez, J.; Bautista, D. Inorg. Chem. 2006, 45, 6347. (i) Pucci, D.; Barneiro, G.; Bellusci, A.; Crispini, A.; Ghedini, M. J. Organomet. Chem. 2006, 691, 1138. (j) Kui, S. C. F.; Sham, I. H. T.; Cheung, C. C. C.; Ma, C.-W.; Pan, B.; Zhu, N.; Che, C. M.; Fu, W.-F. Chem.;Eur. J. 2007, 13, 417. (k) Johansson, R.; Wendt, O. L. Dalton Trans. 2007, 488. (l) Tang, L.; Zhang, Y.; Ding, L.; Li, Y.; Mok, K.-F.; Yeo, W.-C.; Leung, P.-H. Tetrahedron Lett. 2007, 48, 33. (m) Dupont, J.; Pfeffer, M., Eds. Palladacycles; Wiley-VCH: Weinheim, 2008. (11) Armarego, W. L. F.; Chai, C. L. L. Purification of Laboratory Chemicals, 5th ed.; Butterworth-Heinemann: Bodmin, 2003.

Castro-Juiz et al. were added to 20 cm3 of dry chloroform. The mixture was heated under reflux in a Dean-Stark apparatus for 4 h. After cooling to room temperature, the solution was filtered, the solvent evaporated under vacuum, and the residue recrystallized in chloroform/n-hexane to give pale yellow microcrystals. Yield: 95%. Anal. Found (%): C, 62.3; H, 6.9; N, 3.0. C24H31NO8 requires: C, 62.5; H; 6.8; N, 3.0. MS-FAB: m/z 461 [M]þ. IR: ν(CdN) 1621s cm-1. 1H NMR (300 MHz, CDCl3, δ ppm, J Hz): δ 8.73 [s, 1H, Hi]; 7.86 [d, 1H, H6, 3J(H5H6) = 8.8]; 6.88 [d. 1H, H11, 3J(H11H12) = 8.8]; 6.82 [dd, 1H, H12, 3J(H11H12) = 8.8, 4J(H8H12) = 2.0,]; 6.76 [d, 1H, H5, 3 J(H5H6) = 8.8]; 6.70 [d, 1H, H8, 4J(H8H12) = 2.0]; 3.93, 3.90, 3.78 [s, 9H, 2,3,4-(OMe)3]. 13C{1H} NMR (125 MHz, CDCl3, δ ppm, J Hz): δ 156.3, 154.4 [s, C2/C4]; 154.3 [s, CdN]; 149.4, 147.4, 146.5 [s, C7/C9/C10]; 141.7 [s, C3]; 122.9 [s, C1]; 122.3 [s, C6]; 114.6, 112.7, 107.9, 107.7 [s, C5/C8/C11/C12]; 62.0, 60.8, 56.0 [s, 2,3,4-(OMe)3]. 2,3,4-(MeO)3C6H2C(H)dN[9,10-(C10H20O6)C6H3 (b). 2,3,4Trimethoxybenzaldehyde (0.30 g, 1.53 mmol) and 40 -aminobenzo-18-crown-6 (0.50 g, 1.53 mmol) were added to 20 cm3 of dry chloroform. The mixture was heated under reflux in a DeanStark apparatus for 5 h. After cooling to room temperature, the solution was filtered through Celite, the solvent evaporated under vacuum, the resultant dark oil triturated with diethyl ether, and the residue filtered to give a gray solid. Yield: 95%. Anal. Found: C, 61.7; H, 6.9; N, 2.7. C26H35NO9 requires: C, 61.8; H, 7.0; N, 2.8. MS-FAB: m/z 506 [M]þ. IR: ν(CdN) 1613 m cm-1. 1H NMR (300 MHz, CDCl3, δ ppm, J Hz): δ 8.73 [s, 1H, Hi]; 7.86 [d. 1H, H6, 3J(H5H6) =8.6]; 6.89 [d, 1H, H11, 3J(H11H12) = 8.3]; 6.83 [dd, 1H, H12, 3J(H11H12) = 8.3, 4J(H8H12)=2.4]; 6.77 [d, 1H, H5, 3J(H5H6)=8.8]; 6.74d, 1H, H8, 4J(H8H12) = 2.4]; 3.97, 3.93, 3.90 [s, 9H, 2,3,4-(OMe)3]. 13 C{1H} NMR (125 MHz, CDCl3, δ ppm, J Hz): δ 156.3, 154.5 [s, C2/C4]; 154.4 [s, CdN]; 149.4, 147.3, 146.6 [s, C7/C9/C10]; 141.8 [s, C3]; 123.0 [s, C1]; 122.4 [s, C6]; 114.7, 112.9, 108.1, 107.8 [s, C5/ C8/C11/C12]; 62.0, 60.9, 56.1 [s, 2,3,4-(OMe)3]. Synthesis of the Complexes. [Pd{2,3,4-(MeO)3C6HC(H)d N-[9,10-(C8H16O5)C6H3]-C6,N}( μ-O2CMe)]2 (1a). A pressure tube containing ligand a (0.63 g, 1.30 mmol), palladium(II) acetate (0.30 g, 1.30 mmol), and 10 cm3 of dry toluene was sealed under argon. The mixture was heated for 4 h at 60 °C. The hot solution was filtered through Celite to remove the black palladium formed, and the solvent removed under vacuum to give a brown oil, which was triturated with acetone, filtered, and recrystallized in chloroform/n-hexane to give pale orange microcrystals. Yield: 85%. Anal. Found: C, 49.8; H, 5.4; N, 2.3. C52H66N2O20Pd2 requires: C, 49.9; H, 5.3; N, 2.2. MS-FAB: m/z 1252 [M]þ, 743 [(L-H)Pd2(OAc)]þ, 567 [(L-H)Pd]þ, 461 [(L-H)]þ. IR: ν(CdN) 1605sh,m; νas(COO) 1560s; νs(COO) 1416s cm-1. 1H NMR (300 MHz, CDCl3, δ ppm, J Hz): δ 7.76 [s, 1H, Hi]; 6.96 [d, 1H, H8, 4J(H8H12) = 2.4]; 6.57 [d, 1H, H11, 3J(H11H12) = 8.3]; 5.88 [dd, 1H, H12, 3J(H11H12) = 8.3, 4J(H8H12) = 2.4]; 5.77 [s, 1H, H5]; 3.86, 3.77, 3.50 [s, 9H, 2,3,4-(OMe)3]; 1.91 [s, 3H, MeCO2]. 13C{1H} NMR (125 MHz, CDCl3, δ ppm, J Hz): δ 180.0 [s, MeCO2]; 167.3 [s, CdN]; 154.9, 151.8 [s, C2/C4]; 151.4, 147.8, 147.6 [s, C7/C9/C10]; 141.2 [s, C3]; 137.5 [s, C6]; 130.6 [s, C1]; 112.6, 112.3, 110.3, 110.0 [s, C5/C8/C11/C12]; 62.0, 60.8, 55.5 [s, 2,3,4-(OMe)3]; 24.2 [s, O2CMe]. [Pd{2,3,4-(MeO)3C6HC(H)dN[9,10-(C8H16O5)C6H3]-C6,N}( μ-Cl)]2 (2a). A solution of 1a (0.20 g, 0.16 mmol) in 10 cm3 of acetone was treated with 50 cm3 of a solution (∼10-2 M) of tetrabutylammonium chloride in water. The mixture was stirred for 12 h, and the yellow precipitate formed was filtered off, washed with water, and dried under vacuum. Yield: 85%. Anal. Found: C, 47.6; H, 5.0; N, 2.3. C48H60N2O16Cl2Pd2 requires: C, 47.8; H, 5.0; N, 2.3. MSFAB: m/z 1204 [M]þ, 1169 [MH - Cl]þ, 566 [(L-H)Pd]þ, 461 [(L-H)]þ. IR: ν(CdN) 1600 m cm-1, ν(Pd-Cltrans-N) 330 m, ν(Pd-Cltrans-C) 295 m cm-1. 1H NMR (300 MHz, CDCl3, δ

Article ppm, J Hz): δ 8.04 [s, 1H, Hi]; 7.01 [d, 1H, H8, 4J(H8H12)=2.0]; 6,81 [b, 2H, H11/H12]; 6.57 [s, 1H, H5]; 3.77, 3.76, 3.75 [s, 9H, 2,3,4-(OMe)3]. 13C{1H} NMR (125 MHz, CDCl3, δ ppm, J Hz): δ 170.1 [s, CdN]; 155.3, 152.1 [s, C2/C4]; 149.8, 148.6, 148.5 [s, C7/C9/C10]; 143.1 [s, C3]; 138.2 [s, C6]; 131.5 [s, C1]; 114.4, 113.6, 113.3, 110.2 [s, C5/C8/C11/C12]; 61.8, 60.9, 56.5 [s, 2,3,4-(OMe)3]. [Pd{2,3,4-(MeO)3C6HC(H)dN[9,10-(C10H20O6)C6H3]-C6,N}( μ-O2CMe)]2 (1b). A pressure tube containing ligand b (0.40 g, 0.80 mmol), palladium(II) acetate (0.18 g, 0.80 mmol), and 10 cm3 of dry toluene was sealed under argon. The mixture was heated for 5 h at 60 °C. The hot solution was filtered through Celite to remove the black palladium formed, the solvent removed under vacuum, and the residue triturated with acetone and filtered to give a yellow solid. Yield: 91%. Anal. Found: C, 49.8; H, 5.5; N, 2.0. C56H74N2O22Pd2 requires: C, 50.2; H, 5.6; N, 2.1. MS-FAB: m/z 1340 [MH]þ, 1281 [MH - (OAc)]þ, 670 [(L-H)Pd(OAc)]þ, 505 [(LH)]þ. IR: ν(CdN) 1593 m; νas(COO) 1571s; νs(COO) 1420 m cm-1. 1H NMR (300 MHz, CDCl3, δ ppm, J Hz): δ 7.76 [s, 1H, Hi]; 6.96 [d, 1H, H8, 4J(H8H12) = 2.4]; 6.54 [d, 1H, H11, 3 J(H11H12) = 8.3]; 5.86 [dd, 1H, H12, 3J(H11H12) = 8.3, 4 J(H8H12) = 2.4]; 5.74 [s, 1H, H5]; 3.94, 3.86, 3.50 [s, 9H, 2,3,4-(OMe)3]; 1.91 [s, 3H, MeCO2]. 13C{1H} NMR (125 MHz, CDCl3, δ ppm, J Hz): δ 180.1 [s, MeCO2]; 167.3 [s, CdN]; 155.0, 151.8 [s, C2/C4]; 151.4, 147.6, 147.4 [s, C7/C9/C10]; 142.0 [s, C3]; 137.6 [s, C6]; 130.7 [s, C1]; 112.5, 112.0, 110.3, 109.8 [s, C5/ C8/C11/C12]; 62.0, 60.9, 55.5 [s, 2,3,4-(OMe)3]; 24.2 [s, O2CMe]. [(1a)Na2(ClO4)2] (3a). A solution of compound 1a (30 mg, 0.024 mmol) and sodium perchlorate (5.9 mg, 0.048 mmol) in 5 cm3 of dry acetonitrile was stirred at room temperature for 12 h. The solvent was removed under vacuum, and the residue was recrystallized in acetone/dichloromethane, filtered, and washed with diethyl ether to give a yellow solid. Yield: 72%. Anal. Found: C, 39.1; H, 4.1; N, 1.9. C52H66N2O28Cl2Pd2Na2(CH2Cl2)2 requires: C, 38.9; H, 4.2; N, 1.7. MS-FAB: m/z 649 [(L-H)2Pd2(OAc)2Na2]þ2. IR: ν(CdN) 1600 m; νas(COO) 1569 m; νs(COO) 1422 m; νas(Cl-O) 1127s, 1109s, 1090s cm-1. 1H NMR (300 MHz, CDCl3, δ ppm, J Hz): δ 7.73 [s, 1H, Hi]; 6.92 [d, 1H, H8, 4J(H8H12) = 2.3]; 6.52 [d. 1H, H11, 3 J(H11H12) = 8.2]; 5.82 [dd, 1H, H12, 3J(H11H12) = 8.2, 4 J(H8H12) = 2.3]; 5.72 [s, 1H, H5]; 3.87, 3.75, 3.50 [s, 9H, 2,3,4-(OMe)3]; 1.91 [s, 3H, O2CMe]. [(1a)K2(ClO4)2] (4a). A solution of compound 1a (30 mg, 0.024 mmol) and potassium perchlorate (6.6 mg, 0,048 mmol) in 5 cm3 of dry acetonitrile was stirred at room temperature for 12 h. Addition of diethyl ether produces the precipitation of a yellow solid, which was filtered, washed with diethyl ether and water, dried under reduced pressure, and recrystallized in dichloromethane/n-hexane. Yield: 66%. Anal. Found: C, 39.8; H, 4.2; N, 1.6. C52H66N2O28Cl2Pd2K2(CH2Cl2) requires: C, 39.4; H, 4.2; N, 1.7. MSFAB: m/z 664 [(L-H)2Pd2(OAc)2K2]þ2. IR: ν(CdN) 1605 m; νas(COO) 1571s; νs(COO) 1411sh,m; νas(Cl-O) 1121s, 1108s, 1087s cm-1. 1H NMR (300 MHz, CDCl3, δ ppm, J Hz): δ 7.80 [s, 1H, Hi]; 6.99 [d, 1H, H8, 4J(H8H12) = 2.3]; 6.54 [d. 1H, H11, 3 J(H11H12) = 8.2]; 5.83 [dd, 1H, H12, 3J(H11H12) = 8.2, 4 J(H8H12) = 2.3]; 5.79 [s, 1H, H5]; 3.86, 3.77, 3.52 [s, 9H, 2,3,4-(OMe)3]; 1.90 [s, 3H, O2CMe]. [(1a)Pb2(SCN)4] (5a). A solution of compound 1a (30 mg, 0.024 mmol) and lead thiocyanate (15.5 mg, 0,048 mmol) in a mixture of 4 cm3 of dry acetonitrile and 1 cm3 of dimethylformamide was stirred at room temperature for 12 h. The resultant suspension was filtered, washed with diethyl ether, and dried under reduced pressure to give a yellow solid. Yield: 68%. Anal. Found: C, 36.1; H, 3.5; N, 5.1. C56H66N6O20S4Pd2Pb2(CH3CN) requires: C, 35.9; H, 3.6; N, 5.0. MSFAB: m/z 729 [(L-H)2Pd2(OAc)2Pb]þ2. IR: ν(CN)SCN 2140s; ν(CdN) 1601 m νas(COO); 1538 m; νs(COO) 1401sh,m cm-1. 1 H NMR (300 MHz, CDCl3, δ ppm, J Hz): δ 7.76 [s, 1H, Hi]; 6.95 [d, 1H, H8, 4J(H8H12) = 2.3]; 6.54 [d, 1H, H11,

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J(H11H12) = 8.1]; 5.85 [dd, 1H, H12, 3J(H11H12) = 8.1, J(H8H12) = 2.3]; 5.70 [s, 1H, H5]; 3.86, 3.79, 3.55 [s, 9H, 2,3,4-(OMe)3]; 1.90 [s, 3H, O2CMe]. [(2a)Na2(ClO4)2] (6a). A 50 mL two-necked round-bottomed flask was equipped with a mechanical stirrer, a 25 mL pressureequalizing addition funnel, and a condenser. The flask was charged with 30 mg (0.025 mmol) of compound 2a in 10 cm3 of methanol, and the addition funnel with 6.1 mg (0.050 mmol) of sodium perchlorate in 10 cm3 of methanol, which was added dropwise. The resultant mixture was stirred and refluxed for 30 min, and the hot solution filtered and cooled to room temperature. A yellow precipitate was filtered and recrystallized in dichloromethane/n-hexane to give a crystalline powder. Yield: 78%. Anal. Found: C, 38.3; H, 4.1; N, 1.8. C48H60N2O24Cl4Pd2Na2(CH2Cl2) requires: C, 38.4; H, 4.1; N, 1.8. MSFAB: m/z 1226 [(L-H)2Pd2Cl2Na]þ, 625 [(L-H)2Pd2Cl2Na2]þ2. IR: ν(CdN) 1605 m; νas(Cl-O) 1133s, 1108s, 1088s cm-1, ν(Pd-Cltrans-N) 325 m, ν(Pd-Cltrans-C) 290 m cm-1. 1H NMR (300 MHz, CDCl3, δ ppm, J Hz): δ 8.00 [s, 1H, Hi]; 7.00 [d, 1H, H8, 4J(H8H12) = 2.0]; 6.80 [b, 2H, H11/H12]; 6.61 [s, 1H, H5]; 3.79, 3.76, 3.75 [s, 9H, 2,3,4-(OMe)3]. [(2a)K2(ClO4)2] (7a). A suspension of 2a (30 mg, 0.025 mmol) in 5 cm3 of acetonitrile was treated with 6.9 mg (0.050 mmol) of potassium perchlorate and stirred for 24 h. Addition of diethyl ether produces the precipitation of a yellow solid, which was filtered, washed with diethyl ether and water, dried under vacuum, and recrystallized in dichloromethane/n-hexane. Yield: 67%. Anal. Found: C, 36.3; H, 3.9; N, 1.7. C48H60N2O24Cl4Pd2K2(CH2Cl2)2 requires: C, 36.4; H, 3.9; N, 1.7. MSFAB: m/z 1243 [(L-H)2Pd2Cl2K]þ, 641 [(L-H)2Pd2Cl2K2]þ2. IR: ν(CdN) 1605 m; νas(Cl-O) 1130s, 1109s, 1088s cm-1, ν(Pd-Cltrans-N) 330 m, ν(Pd-Cltrans-C) 290 m cm-1. 1H NMR (300 MHz, CDCl3, δ ppm, J Hz): δ 8.01 [s, 1H, Hi]; 7.05 [d, 1H, H8, 4J(H8H12) = 2.1]; 6,85 [b, 2H, H11/H12]; 6.52 [s, 1H, H5]; 3.78, 3.77, 3.72 [s, 9H, 2,3,4-(OMe)3]. [(2a)(NH4)2(PF6)2] (8a). A suspension of 2a (30 mg, 0.025 mmol) in 10 cm3 of methanol was treated with 8.2 mg (0.050 mmol) of ammonium hexafluorophosphate and refluxed for 1/2 h. After cooling to room temperature, a yellow crystalline precipitate was filtered, dried under vacuum, and recrystallized in dichloromethane/n-hexane. Yield: 69%. Anal. Found: C, 37.7; H, 4.5; N, 3.7. C48H68N4O16P2F12Cl2Pd2 requires: C, 37.5; H, 4.5; N, 3.7. MS-FAB: m/z 1223 [(L-H)2Pd2Cl2(NH4)]þ. IR: ν(CdN) 1600 m cm-1, ν(Pd-Cltrans-N) 320 m, ν(Pd-Cltrans-C) 295 m cm-1. 1H NMR (300 MHz, CDCl3, δ ppm, J Hz): δ 8.07 [s, 1H, Hi]; 7.08 [d, 1H, H8, 4J(H8H12) = 2.0]; 6.89 [b, 2H, H11/H12]; 6.58 [s, 1H, H5]; 3.78, 3.75, 3.74 [s, 9H, 2,3,4-(OMe)3]. 31P{1H} NMR (300 MHz, CDCl3, δ ppm, J Hz): δ -146.55 [h, J(PF) = 712.9]. [(1a)Pb2(SCN)4] (9a). A suspension of 2a (30 mg, 0.025 mmol) in 10 cm3 of methanol was treated with 20.3 mg (0.050 mmol) of lead thiocyanate and refluxed for 0.5 h. After cooling to room temperature, a yellow precipitate was filtered, dried under vacuum, and recrystallized in dichloromethane/n-hexane. Yield: 66%. Anal. Found: C, 28.5; H, 3.2; N, 1.4. C48H60N2O32Cl4Pd2Pb2(CH2Cl2) requires: C, 28.0; H, 3.0; N, 1.3. MSFAB: m/z 1511 [(L-H)2Pd2Cl2Pb(ClO4)]þ, 705 [(L-H)2Pd2Cl2Pb]þ2. IR: ν(CN)SCN 2138s; ν(CdN) 1603 m cm-1, ν(PdCltrans-N) 325 m, ν(Pd-Cltrans-C) 295 m cm-1. 1H NMR (300 MHz, CDCl3, δ ppm, J Hz): δ 8.09 [s, 1H, Hi]; 7.10 [d, 1H, H8, 4 J(H8H12)=1.9]; 6,84 [b, 2H, H11/H12]; 6.55 [s, 1H, H5]; 3.78, 3.75, 3.73 [s, 9H, 2,3,4-(OMe)3]. [(1b)K2(ClO4)2] (2b). A suspension of 1b (30 mg, 0.022 mmol) in 5 cm3 of acetonitrile was treated with 6.2 mg (0.044 mmol) of potassium perchlorate and stirred for 12 h. A yellow solid was filtered, washed with diethyl ether and water, and dried under vacuum. Yield: 76%. Anal. Found: C, 40.2; H, 4.6; N, 1.6. C56H74N2O30Cl2Pd2K2(H2O)3 requires: C, 40.3; H, 4.8; N, 1.7. MS-FAB: m/z 1377 [(L-H)2Pd2(OAc)2K)]þ, 709 [(L-H)2Pd2(OAc)2K2]þ2. 4

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IR: ν(CdN) 1595 m; νas(COO) 1568s; νs(COO) 1421 m; νas(Cl-O) 1122s, 1100s, 1098s cm-1. 1H NMR (300 MHz, CDCl3, δ ppm, J Hz): δ 7.79 [s, 1H, Hi]; 6.96 [d, 1H, H8, 4J(H8H12)=2.4]; 6.55 [d, 1H, H11, 3J(H11H12) = 8.3]; 5.88 [dd, 1H, H12, 3J(H11H12) = 8.3, 4J(H8H12) = 2.4]; 5.70 [s, 1H, H5]; 3.96, 3.82, 3.51 [s, 9H, 2,3,4-(OMe)3]; 1.91 [s, 3H, O2CMe]. [(1b)Pb2(SCN)4] (3b). A suspension of 1b (30 mg, 0.022 mmol) in 5 cm3 of methanol was treated with 14.5 mg (0.044 mmol) of lead thiocyanate and stirred for 12 h. A yellow solid was filtered, washed with diethyl ether, dried under vacuum, and recrystallized in chloroform/n-hexane. Yield: 62%. Anal. Found: C, 33.0; H, 3.4; N, 4.0. C60H74N6O22S4Pd2Pb2(CHCl3)2 requires: C, 33.4; H, 3.4; N, 3.8. MSFAB: m/z 772 [(L-H)2Pd2(OAc)2(Pb)]þ2. IR: ν(CdN) ν(CN)SCN 2148s; ν(CdN) 1592 m; νas(COO) 1571s; νs(COO) 1404 m cm-1. 1 H NMR (300 MHz, CDCl3, δ ppm, J Hz): δ 7.72 [s, 1H, Hi], 6.92 [d, 1H, H8, 4J(H8H12) = 2.4]; 6.52 [d, 1H, H11, 3 J(H11H12) = 8.2]; 5.87 [dd, 1H, H12, 3J(H11H12) = 8.2, 4 J(H8H12) = 2.4]; 5.75 [s, 1H, H5]; 3.94, 3.87, 3.50 [s, 9H, 2,3,4-(OMe)3]; 1.91 [s, 3H, O2CMe]. [(1b)Rb2(ClO4)2] (4b). A suspension of 1b (30 mg, 0.022 mmol) in 5 cm3 of methanol was treated with 8.3 mg (0.044 mmol) of rubidium perchlorate and stirred for 12 h. Addition of diethyl ether produces the precipitation of a yellow solid, which was filtered, washed with diethyl ether, dried under vacuum, and recrystallized in dichloromethane/n-hexane. Yield: 65%. Anal. Found: C, 36.8; H, 4.0; N, 1.4. C56H74N2O30Cl2Pd2Rb2(CH2Cl2) requires: C, 37.1; H, 4.2; N, 1.5. MSFAB: m/z 1610 [(L-H)2Pd2(OAc)2Rb2(ClO4)]þ, 1425 [(LH)2Pd2(OAc)2(Rb)]þ, 755 [(L-H)2Pd2(OAc)2Rb2]2þ. IR: ν(CdN) 1593 m; νas(COO) 1571 m; νs(COO) 1421 m; νas(Cl-O) 1111s, 1096s, 1080s cm-1. 1H NMR (300 MHz, CDCl3, δ ppm, J Hz): δ 7.72 [s, 1H, Hi]; 6.99 [d, 1H, H8, 4J(H8H12) = 2.3]; 6.59 [d, 1H, H11, 3J(H11H12) = 8.2]; 5.82 [dd, 1H, H12, 3J(H11H12) = 8.2, 4 J(H8H12) = 2.3]; 5.77 [s, 1H, H5]; 3.99, 3.87, 3.52 [s, 9H, 2,3,4-(OMe)3]; 1.90 [s, 3H, O2CMe]. [(1b)Ba2(ClO4)4] (5b). A suspension of 1b (30 mg, 0.022 mmol) in 5 cm3 of methanol was treated with 14.8 mg (0.044 mmol) of barium perchlorate and stirred for 24 h. Addition of diethyl ether produces the precipitation of a yellow solid, which was filtered, washed with diethyl ether, dried under vacuum, and recrystallized in dichloromethane/n-hexane. Yield: 65%. Anal. Found: C, 32.4; H, 3.6; N, 1.2. C56H74N2O38Cl4Pd2Ba2(CH2Cl2) requires: C, 32.6; H, 3.6; N, 1.3. MSFAB: m/z 739 [(L-H)2Pd2(OAc)2(Ba)]þ2. IR: ν(CdN) 1590 m; νas(COO) 1569 m; νs(COO) 1417 m; νas(Cl-O) 1109s, 1085s cm-1. 1H NMR (300 MHz, CDCl3, δ ppm, J Hz): δ 7.74 [s, 1H, Hi]; 6.90 [d, 1H, H8, 4J(H8H12) = 2.2]; 6.51 [d, 1H, H11, 3 J(H11H12) = 8.1]; 5.90 [dd, 1H, H12, 3J(H11H12) = 8.1, 4 J(H8H12) = 2.2]; 5.79 [s, 1H, H5]; 3.96, 3.83, 3.53 [s, 9H, 2,3,4-(OMe)3]; 1.92 [s, 3H, O2CMe]. X-ray Crystallographic Study. Three-dimensional, roomtemperature X-ray data were collected on a Bruker Smart 1K CCD diffractometer using graphite-monochromated Mo KR radiation. All the measured reflections were corrected for Lorentz and polarization effects and for absorption by semiempirical methods based on symmetry-equivalent and repeated reflections. The structures were solved by direct methods and refined by full matrix least-squares on F2. Hydrogen atoms were included in calculated positions and refined in riding mode. Large disorder was found in one of the crown ether rings of complex 6a; the O(7) and C(22) atoms were disordered and, consequently, refined in two complementary positions with occupancies of 80% and 20%. Disorder also affected the O(5)oxygen atom; the refinement was carried out taking into account two components with occupancies of approximately 62% and 38%. Other models were used to treat the disorder with less satisfactory results. Refinement converged with allowance for thermal anisotropy of all non-hydrogen atoms. The structure solution

Castro-Juiz et al. and refinement were carried out using the program package SHELX-97.12

Results and Discussion Cyclopalladated Dimer Complexes. For the convenience of the reader the compounds and reactions are shown in Scheme 1. The compounds described in this paper were characterized by elemental analysis (C, H, N), mass spectrometry, and IR and 1H and (in part) 13C{1H} NMR spectroscopy (data in Experimental Section). The Schiff base ligands a and b were prepared by condensation between 2,3,4-trimethoxybenzaldehyde and 40 -aminobenzo-15-crown-5 and 40 -aminobenzo-18-crown-6, respectively, in chloroform, and isolated as air-stable solids, which were fully characterized (see data in Experimental Section). Reaction of ligands a and b with palladium(II) acetate in toluene at 60 °C gave [Pd{2,3,4-(MeO)3C6HC(H)dN-[9,10(C8H16O5)C6H3]-C6,N}( μ-O2CMe)]2 (1a) and [Pd{2,3,4-(MeO)3C6HC(H)dN[9,10-(C10H20O6)C6H3]-C6,N}( μ-O2CMe)]2 (1b), respectively, as yellow solids, after C-H activation at the 6-position. The microanalytical data and the MS-FAB spectra were consistent with the proposed empirical formula. The 1H NMR spectra for 1a and 1b showed a singlet assigned to the H5 proton; the H6 resonance was absent upon metalation at C6. The 13C{1H} NMR spectra confirmed the proposed structures, showing a strong downfield shift of the HCdN and C6 carbon resonances ca. 13 and ca. 15 ppm, respectively, from those for the free Schiff base spectra, consequent upon metalation (see Experimental Section).13 In the IR spectra of complexes 1a and 1b the ν(CdN) stretch appeared at lower frequency, ca. 15 cm-1, than the corresponding free imines, in accordance with nitrogen coordination to the metal center.14 This was supported by the upfield shift of the HCdN resonance in the 1H NMR spectra, ca. 1.0 ppm.15 The νas(COO) and νs(COO) values were consistent with bridging acetato groups.16 A singlet resonance at ca. 2.0 ppm in the 1H NMR spectra and two singlets at ca. 180 and 24 ppm in the 13C{1H} NMR were assigned to the equivalent methyl acetate groups, (CH3COO) and (CH3COO, CH3COO), respectively, consistent with an anti geometry of the cyclometalated moieties in an “open book” arrangement linked by two acetate bridging ligands between the palladium atoms.17 The crystal structure of compound 1a has been determined by X-ray diffraction (vide infra). (12) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112. (13) (a) Vila, J. M.; Gayoso, M.; Pereira, M. T.; L opez, M.; Alonso, G.; Fernandez, J. J. J. Organomet. Chem. 1993, 445, 287. (b) Dotta, P.; Kumar, P. G. A.; Pregosin, P. S.; Albinati, A.; Rizatto, S. Organometallics 2004, 23, 4247. (14) Onoue, H.; Moritani, I. J. Organomet. Chem. 1972, 43, 431. (15) Ustinyuk, Y. A.; Chertov, V. A.; Barinov, I. V. J. Organomet. Chem. 1971, 29, C53. (16) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds, 5th ed.; Wiley & Sons: New York, 1997. (17) (a) Navarro-Ranninger, C.; L opez-Solera, I.; Gonzalez, V. M.; Perez, J. M.; Alvarez-Valdes, A.; Martin, A.; Raithby, P. R.; Masaguer, J. R.; Alonso, C. Inorg. Chem. 1996, 35, 5181. (b) Herrman, W. A.; Brown, V. P. M.; Reisinger, C. P. J. Organomet. Chem. 1999, 576, 23. (c) Mosteiro, R.; Perille, E.; Fernandez, A.; Lopez-Torres, M.; Vila, J. M.; Suarez, A.; Ortigueira, J. M.; Pereira, M. T.; Fernandez, J. J. Appl. Organomet. Chem. 2000, 14, 634. (d) Evans, P. G.; Brown, N. A.; Clarkson, G. J.; Newman, C. P.; Rourke, J. P. J. Organomet. Chem. 2006, 691, 1251.

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Scheme 1a

a (i) Pd(OAc)2, toluene; (ii) NBu4Cl, acetone/water; (iii) NaClO4, acetonitrile (3a); KClO4, acetonitrile (4a); Pb(SCN)2, acetonitrile/dimethylformamide (5a); (iv) NaClO4, methanol (6a); KClO4, acetonitrile (7a); NH4PF6, methanol (8a); Pb(SCN)2, methanol (9a); (v) KClO4, acetonitrile (2b); Pb(SCN)2, methanol (3b); RbClO4, methanol (4b); Ba(ClO4)2, methanol (5b).

Treatment of 1a with aqueous tetrabutylammonium chloride gave [Pd{2,3,4-(MeO)3C6HC(H)dN[9,10-(C8H16O5)C6H3]-C6,N}( μ-Cl)]2 2a, with exchange of the acetate bridging groups by chloride bridging ligands, which was fully characterized (see Experimental Section). The use of a bulky cation is paramount in obtaining the chloride-bridged dimer

2a pure, preventing coordination of the crown ether group; the traditional metathesis reaction,18 via reaction with aqueous sodium chloride, afforded a mixture of two products: (18) Teijido, B.; Fernandez, A.; L opez-Torres, M.; Suarez, A.; Vila, J. M.; Mosteiro, R.; Fernandez, J. J. Organometallics 2002, 21, 1304.

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the chloro-bridged dimer 2a and the related dimer 3a, containing coordinated sodium (vide infra). The MS-FAB spectrum of 2a showed, among others, the peaks assigned to [M]þ and [MH - Cl]þ ions, thereby confirming the dinuclear nature of the complex.19 The IR and 1H NMR data were in agreement with the absence of the acetate bands, and in the IR spectra the appearance of two ν(Pd-Cl) bands was consistent with an asymmetric Pd2Cl2 bridging unit.20 The phenyl proton signals were shifted to higher frequency, in comparison with the spectrum for compound 1a, due to the planar arrangement in 2a, as opposed to the “open-book” geometry of 1a, which prevents aromatic ring shielding of the resonances.21 Crown Ether Palladacycles As Metalloligands. Complexes 1a, 1b, and 2a are potential receptors to be used for selective coordination of metal cations, owing to the presence of crown ether rings; accordingly, several adducts with nontransition metals have been isolated pure (see Scheme 1), without disruption or modification of the characteristic dimer structure, as shown by elemental analysis and by the 1 H NMR spectra; these were similar to the corresponding starting materials and were in agreement with the proposed formulations (see Experimental Section). Treatment of 1a and 2a with NaClO4 in 1:2 molar ratio in acetonitrile or methanol, as appropriate, yielded 3a and 6a, respectively, via complexation of one Naþ ion to each crown ether group. Sodium was chosen as the alkaline cation because its radius best fits the 15-crown-5 ether moiety.3a,22 The 1H NMR spectra showed only one set of signals, those corresponding to the anti isomer, as opposed to related compounds where a mixture of syn and anti isomers had been observed, with an increase in the stability of the syn complex.23 The MSFAB spectra showed, among others, the corresponding peaks assigned to [(L-H)2Pd2Cl2Na]þ and/or [(L-H)2Pd2Cl2Na2]þ2 (L-H = cyclometalated ligand), which were characteristic clusters of isotopic peaks covering about 10 m/z units, due to the presence of the numerous palladium isotopes.19 The IR spectra show three absorptions ca. 1100 cm-1, assigned to the perchlorate group, which displays a bidentate coordination (C2v symmetry).16 This suggests a tight association of the perchlorate anions to the cationic complex through two oxygen atoms of the perchlorate ligand to the sodium cation. Coordination of sodium by perchlorate finds support in various X-ray structures reported in the literature,24 and the molecular structure of complex 6a, vide infra, confirms this assumption. A similar derivative of complex 1b with Naþ could not be obtained because the 18-crown-6 group is too large to coordinate optimally to the Naþ cation, although in some cases a partial coordination to the oxygen atoms of a larger crown ether group allows binding of sodium atoms.25 (19) (a) Tusek-Bozic, L.; Curic, M.; Traldi, P. Inorg. Chim. Acta 1997, 254, 49. (b) Tusek-Bozic, L.; Komac, M.; Curic, M.; Lycka, A.; Dalpaos, M.; Scarcia, V.; Furlani, A. Polyhedron 2000, 19, 937. (20) Vila, J. M.; Gayoso, M.; Fernandez, A.; Bailey, N. A.; Adams, H. J. Organomet. Chem. 1993, 448, 233. (21) (a) Vila, J. M.; Gayoso, M.; Pereira, M. T.; Ortigueira, J. M.; Fern andez, A.; Bailey, N. A.; Adams, H. Polyhedron 1993, 12, 171–180. (b) Zhao, G.; Wang, Q. G.; Mak, T. C. W. J. Chem. Soc., Dalton Trans. 1998, 1241. (22) (a) Gokel, G. W.; Leevy, W. M.; Weber, M. E. Chem. Rev. 2004, 104, 2723. (b) Brown, M. D.; Dyke, J. M.; Ferrante, F.; Levason, W.; Ogden, J. S.; Webster, M. Chem.;Eur. J. 2006, 12, 2620. (23) Arias, J.; Bardajı´ , M.; Espinet, P. J. Organomet. Chem. 2006, 691, 4990. (24) Owen, J. D. Dalton Trans. 1981, 1066, and references therein. (25) Baylies, C. J.; Harding, L. P.; Jeffery, J. C.; Riis-Johannessen, T.; Rice, C. R. Angew. Chem., Int. Ed. 2004, 43, 4515.

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Figure 1. Molecular structure of [Pd{2,3,4-(MeO)3C6HC(H)d N[9,10-(C8H16O5)C6H3]-C6,N}(μ-Cl)Na(O2ClO2)]2 (6a), with labeling scheme. Hydrogen atoms have been omitted for clarity.

Treatment of 1a, 2a, and 1b with KClO4 in a 1:2 molar ratio in acetonitrile yielded compounds 4a, 7a, and 2b, respectively, with complexation of one Kþ ion to each crown ether group. Potassium forms, according to its cation size, the most stable complexes with 18-crown-6 derivatives,26 but the 15-crown-5 group is also capable of easily coordinating this cation.27 In contrast to other reported ortho-palladated precursors,26e the 1H NMR spectra showed one set of resonances assigned to the anti isomer, and the presence of the syn isomer was not detected. The MS-FAB spectra showed peaks assigned to the [(L-H)2Pd2(X)2K)]þ and [(L-H)2Pd2(X)2K2]þ2 (X = OAc or Cl) fragments. The IR spectra showed three bands assigned to the ν(Cl-O) stretches of the perchlorate group, in accordance with a bidentate coordination to the Kþ cation, in a similar way to that in the sodium derivatives. Stable complexes of ammonium cations, with an ionic radius close to that of potassium, have been described with functionalized 18-crown-6 ring derivatives.28 Thus, the reaction of 2a with ammonium hexafluorophosphate in methanol gave 8a. Elemental analyses and mass spectra were consistent with the formula [(2a)(NH4)2(PF6)2]. Similar reactions of complexes 1a and 1b yielded a mixture of products, regardless of the reaction conditions, presumably of the (26) (a) Takeda, Y.; Yano, H.; Ishibashi, M.; Isozumo, H. Bull. Chem. Soc. Jpn. 1980, 53, 72. (b) Koritsanszky, T.; Buschmann, J.; Luger, P.; Kn€ochel, A.; Patz, M. J. Am. Chem. Soc. 1994, 116, 6748. (c) Kuate, A. C. T.; Reeske, G.; Schurmann, M.; Costisella, B.; Jurkschat, K. Organometallics 2008, 27, 5577. (d) Coronado, E.; Galan-Mascaros, J. R.; MartGastaldo, C.; Waerenborgh, J. C.; Gaczynski, P. Inorg. Chem. 2008, 47, 6829. (e) Coco, S.; Cordovilla, C.; Espinet, P.; Gallani, J. L.; Guillon, D.; Donnio, B. Eur. J. Inorg. Chem. 2008, 1210. (27) (a) Yam, V. W.; Tang, R. P.; Wong, K. M.; Ko, C.; Cheung, K. Inorg. Chem. 2001, 40, 571. (b) Sureshan, K. M.; Shashidhar, M. S.; Varma, A. J. J. Org. Chem. 2002, 67, 6884. (28) (a) Nelsen, D. L.; White, P. S.; Gagne, M. R. Organometallics 2005, 24, 5479. (b) Endicott, C.; Strauss, H. L. J. Phys. Chem. A 2007, 111, 1236.

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Figure 2. Other view of the molecular structure of [Pd{2,3,4-(MeO)3C6HC(H)dN[9,10-(C8H16O5)C6H3]-C6,N}(μ-Cl)Na(O2ClO2)]2 (6a).

starting material and the corresponding adduct, which could not be isolated. Treatment of 1a, 2a, and 1b with Pb(SCN)2 in acetonitrile yielded 5a, 9a, and 3b, respectively (see Scheme 1 and Experimental Section). As for the coordination of the thiocyanate anion, it has been observed that hard metals and soft metals tend to be N- and S-bonded, respectively, with lead(II) showing an intermediate behavior giving rise to both types of complexes, a subject that continues to be a matter of debate. In fact, lead(II) complexes of crown ethers with Nbonded,29 S-bonded,30 or even both N- and S-bonded31 thiocyanate ligands have been reported. In the present case, the IR spectra showed the ν(CdN)SCN stretch at higher frequency, ca. 2140 cm-1, than the corresponding one in KSCN, 2040 cm-1, suggesting sulfur coordination to the metal center.32 Reactions of 1a and 2a with different Rbþ and Ba2þ salts were tested, but as expected, no stable adduct could be isolated due to the differing sizes of the metal cation and of the 15-crown-5 ring. However, the corresponding complexes derived from 1b could be isolated in pure form, as a consequence of the better adaptation of the metal to the 18-crown-6-ring size,22b,25,33 by reaction with RbClO4 and Ba(ClO4)2 in methanol, which gave 4b and 5b, respectively. Elemental analyses and mass spectra were in accordance with the proposed 1:2 adducts. The IR spectra of 4b and 5b showed two and three absorptions, respectively, assigned to the perchlorate group (see Experimental Section), indicating a monodentate coordination in the case of the rubidium complex and a bidentate coordination for the barium one. Crystal Structure of Complex 6a. Suitable crystals of complex 6a were grown by recrystallization from a dichloromethane/n-hexane solution. The labeling schemes are shown in Figure 1 and 2. Crystallographic data and selected interatomic distances and angles are listed in Tables 1 and 2. (29) Nazarenko, A. Y.; Rusanov, E. B. J. Coord. Chem. 1995, 34, 265. (30) Metz, B.; Weiss, R. Acta Crystallogr. Sect. B 1973, 29, 1088. (31) Nazarenko, A. Y.; Rusanov, E. B. Polyhedron 1994, 13, 2549. (32) Costero, A. M.; Villarroya, J. P.; Gil, S.; Aurell, M. J.; Ramı´ rez de Arellano, M. C. Tetrahedron 2002, 58, 6724. (33) Nuss, H.; Jansen, M. Angew. Chem., Int. Ed. 2006, 45, 4369.

Table 1. Crystal and Structure Refinement Data for Complexes 6a and 1a 6a 3 2CH2Cl2 3 2H2O empirical formula fw temperature/K wavelength (A˚) cryst syst space group unit cell dimens a (A˚) b (A˚) c (A˚) β (deg) Z 2θmax (deg) indep reflns S R [I > 2σ(I )] wR (F2, all data)

1a

C50H68Cl8N2Na2O26Pd2 1655.44 293(2) 0.71073 monoclinic P21/c

C52H68N2O20Pd2 1253.88 293(2) 0.71073 monoclinic P21/c

18.8417(3) 8.8127(1) 21.3286(3) 111.315(1) 2 56.76 8.176 (Rint = 0.0643) 0.979 0.0610 0.1681

14.2604(2) 23.7058(2) 16.5549(3) 99.740(1) 4 56.54 13.524 (Rint = 0.0186) 1.111 0.0311 0.0785

Table 2. Selected Bond Distances (A˚) and Angles (deg) for Complex 6a C(1)-Pd(1) N(1)-Pd(1) Cl(1)-Pd(1) Cl(1)-Pd(1)#1 C(1)-C(6) C(6)-C(7) C(7)-N(1) O(4)-Na(1) O(5)-Na(1) O(6)-Na(1) O(7)-Na(1) O(8)-Na(1) Na(1)-O(4S) Na(1)-O(2S) Cl(1S)-O(1S) Cl(1S)-O(3S) Cl(1S)-O(2S) Cl(1S)-O(4S)

1.979(4) 2.052(3) 2.3332(11) 2.4717(11) 1.405(6) 1.436(6) 1.291(5) 2.364(3) 2.389(4) 2.368(4) 2.482(4) 2.381(4) 2.506(6) 2.556(5) 1.398(5) 1.417(5) 1.421(4) 1.422(6)

C(1)-Pd(1)-N(1) C(1)-Pd(1)-Cl(1) Cl(1)-Pd(1)-Cl(1)#1 N(1)-Pd(1)-Cl(1)#1 C(6)-C(1)-Pd(1) C(1)-C(6)-C(7) N(1)-C(7)-C(6) C(7)-N(1)-Pd(1) O(4)-Na(1)-O(5) O(6)-Na(1)-O(5) O(6)-Na(1)-O(7) O(8)-Na(1)-O(7) O(4)-Na(1)-O(8) O(4S)-Na(1)-O(2S) O(2S)-Cl(1S)-O(4S) O(1S)-Cl(1S)-O(3S)

81.17(16) 94.46(13) 84.65(4) 99.56(10) 112.7(3) 115.1(4) 117.1(4) 113.7(3) 69.33(11) 70.05(13) 68.72(14) 67.75(14) 66.89(12) 52.99(16) 105.2(3) 109.7(4)

The asymmetric unit for complex 6a comprises a halfmolecule, a dichloromethane, and a water solvent molecule and presents a crystallographic inversion center located at the center of the Pd( μ-Cl)2Pd moiety. The molecules are

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Table 3. Selected Bond Distances (A˚) and Angles (deg) for Complex 1a Pd(1)-C(1) Pd(1)-N(1) Pd(1)-O(9) Pd(1)-O(10) N(1)-C(7) C(1)-C(6) C(6)-C(7) Pd(1)-Pd(2) Pd(2)-C(29) Pd(2)-N(2) Pd(2)-O(12) Pd(2)-O(11) N(2)-C(35) C(29)-C(34) C(34)-C(35)

1.960(2) 2.0456(19) 2.0540(16) 2.1493(16) 1.2973(19) 1.416(2) 1.4314 2.9146(2) 1.958(2) 2.0361(18) 2.0425(16) 2.1514(17) 1.3035(19) 1.408(2) 1.4315

C(1)-Pd(1)-N(1) C(1)-Pd(1)-O(9) O(9)-Pd(1)-O(10) N(1)-Pd(1)-O(10) C(7)-N(1)-Pd(1) N(1)-C(7)-C(6) C(1)-C(6)-C(7) C(6)-C(1)-Pd(1) C(29)-Pd(2)-N(2) C(29)-Pd(2)-O(12) O(12)-Pd(2)-O(11) N(2)-Pd(2)-O(11) C(35)-N(2)-Pd(2) N(2)-C(35)-C(34) C(29)-C(34)-C(35) C(29)-C(30)-C(31)

81.28(8) 90.58(8) 89.30(7) 98.38(7) 113.83(11) 116.85(8) 114.58(9) 113.15(13) 81.39(8) 91.71(8) 88.58(7) 98.31(7) 113.85(11) 116.50(8) 114.75(10) 119.67(10)

dimeric, with the cyclometalated ligands in a relative anti disposition and the [Na(ClO4-O,O] fragments situated on opposite faces of the molecule. The fragment [(C-N)Pd( μ-X)2Pd(C-N)] (C-N = cyclometalated ring) adopts a planar configuration, with an angle between the coordination planes of the palladium atoms and the Pd2X2 ring of 6.2°, a similar situation to that observed in related species,34 in contrast with compounds in which the Pd( μ-Cl)2Pd bridging ring is not planar and is hinged about the Cl-Cl axis.35 Except for the methoxy and the benzo-15-crown-5 groups, the cyclopalladated moiety is essentialy planar. The mean deviations from the least-squares planes determined for the metalated phenyl ring (C1, C2, C3, C4, C5, C6; plane 1) and the metallacycle (Pd1, C1, C6, C7, N1; plane 2) are 0.0211 and 0.0178 A˚, respectively, and the angle between these planes is 4.7°. The oxygen atoms of the crown ether group (O(4), O(5), O(6), O(7), O(8); plane 3) are almost planar (rms 0.2066 A˚), and the sodium atom shows a displacement from this plane of ca. 0.74 A˚. The sodium atom is coordinated to the five oxygen atoms of the crown ether group, with a Na-O bond distances of 2.36-2.48 A˚ (see Table 3), and to two oxygen atoms of the perchlorate anion, acting as a bidentate chelating ligand [Na(1)-O(4S), 2.506(6); Na(1)-O(2S), 2.556(5) A˚]. Crystal Structure of Complex 1a. Crystals of complex 1a, obtained from a dichloromethane/n-hexane solution, were monoclinic. The labeling scheme is shown in Figure 3. Crystallographic data and selected interatomic distances and angles are listed in Tables 1 and 3. The asymmetric unit for 1a comprises one molecule in a dimeric form with the cyclopalladated moieties in an “open book” arrangement linked by two acetate bridging ligands, (34) (a) Vila, J. M.; Gayoso, M.; Pereira, M. T.; Romar, A.; Fernandez, J. J.; Thronton-Pett, M. J. Organomet. Chem. 1991, 401, 385. (b) NavarroRanninger, C.; L opez-Solera, I.; Alvarez-Valdes, A.; Rodríguez, J. H.; Masaguer, J. R.; García-Ruano, J. L. J. Organomet. Chem. 1994, 476, 19. (c) Fernandez, A.; Pereira, E.; Fernandez, J. J.; Lopez-Torres, M.; Suarez, A.; Mosteiro, R.; Pereira, M. T.; Vila, J. M. New J. Chem. 2002, 26, 895. (d) Chen, Ch.L.; Liu, Y.-H.; Peng, Sh.-M.; Liu, S.-T. J. Organomet. Chem. 2004, 689, 1806. (35) (a) Crispini, A.; De Munno, G.; Ghedini, M.; Neve, F. J. Organomet. Chem. 1992, 427, 409. (b) Kleij, A. W.; Kleijn, H.; Jastrzebski, J. T. B. H.; Spek, A. L.; van Koten, G. Organometallics 1999, 18, 277. (c) Kleij, A. W.; Gebbink, R. J. M. K.; van den Nieuwenhuijzen, P. A. J.; Kooijman, H.; Lutz, M.; Spek, A. L.; van Koten, G. Organometallics 2001, 20, 634. (d) Kok-Peng, J.; Tan Liu, G.-K.; Vittal, J. J.; Leung, P.-H. Inorg. Chem. 2003, 42, 7674. (e) Naya, L.; Vazquez-García, D.; LopezTorres, M.; Fernandez, A.; Vila, J. M.; Gomez-Blanco, N.; Fernandez, J. J. J. Organomet. Chem. 2008, 693, 685.

Figure 3. Molecular structure of [Pd{2,3,4-(MeO)3C6HC(H)d N[9,10-(C8H16O5)C6H3]-C6,N}(μ-O2CMe)]2 (1a), with labeling scheme. Hydrogen atoms have been omitted for clarity.

with the cyclometalated ligands in a relative anti disposition.36 As a result of Pd(1) and Pd(2) being bridged by two mutually cis μ-acetate ligands, the chelating C,Nbonded Schiff bases are forced to lie above one another in the dimeric molecule. This leads to interligand repulsions on the “open” side of the molecule and results in the coordination planes of the palladium atoms being tilted at an angle of 51.0°. Each palladium atom is in a slightly distorted squareplanar coordination environment, bonded to the nitrogen atom of the imine group, the ortho carbon C(1) of the phenyl ring, and two oxygen atoms from the bridging acetate ligands; the most noticeable distortion of the ideal coordination sphere corresponds to the C-Pd-N bite angle of ca. 81.3°.

Conclusions We have shown that Schiff base crown ether palladacycles may be prepared as acetate- or chloride-bridged dimer compounds in the anti form, with 15-crown-5 or 18-crown6 rings. The ensuing complexes may accommodate two non-transition metals per dimer molecule without substantial changes in the palladacycle structure to yield mixed transition/non-transition metal complexes. Alkaline and alkaline-earth metal cations, as well as lead(II) and (owing to its size) the ammonium cation, have been tested; the corresponding counteranion is bonded to the coordinated metal cation. The first crystal structure of this type of mixed (36) (a) Navarro-Ranninger, C.; Zamora, F.; L opez-Solera, I.; Monge, A.; Masaguer, J. R. J. Organomet. Chem. 1996, 506, 149. (b) Pereira, M. T.; Vila, J. M.; Gayoso, E.; Gayoso, M.; Hiller, W.; Str€ahle, J. J. Coord. Chem. 1988, 18, 245. (c) Teijido, B.; Fernandez, A.; LopezTorres, M.; Castro-Juiz, S.; Suarez, A.; Ortigueira, J. M.; Vila, J. M.; Fernandez, J. J. J. Organomet. Chem. 2000, 598, 71.

Article

metal complexes is reported, as definitive proof of the molecular arrangement.

Acknowledgment. We thank the Ministerio de Educaci on y Ciencia (Projects CTQ2006-15621-C02-02/BQU, UDC, and CTQ2006-15621-C02-01/BQU, USC) and the Xunta de Galicia (ref PGIDIT04PXI10301IF, INCITE07PXI103083ES, and INCITE08ENA209044ES) for financial support.


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Supporting Information Available: This material is available free of charge via the Internet at http://pubs.acs.org. Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. 718094 (1a) and no. 718095 (6a). Copies of the data can be obtained free of charge on application to The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK. E-mail: deposit@ ccdc.cam.ac.uk.

Crown Ether Palladacycles as Metalloligands: Suitable Precursors for

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