153 V2V3 py-thiolates full IC

153 V2V3 py-thiolates full IC - Inorg. Chem. 1995, 34,...

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Unformatted text preview: Inorg. Chem. 1995, 34, 5745—5752 5745 Synthesis and Characterization of Vanadium(II,III,IV) Complexes of Pyridine-Z-thiolate John G. Reynolds,M Shawn C. Sendlingerf Ann M. Murrayfl‘ John C. Huffman} and George Christen” Department of Chemistry and Molecular Structure Center, Indiana University, Bloomington, Indiana 47405—4001, and Lawrence Livermore National Laboratory, University of California, Mail Stop L—365, P. O. Box 808, Livermore, California 94551 Received March 31, 1995® The synthesis and characterization are reported of vanadium complexes of pyridine-2—thiolate (pyt‘) with the metal in oxidation states 11, III, and IV. The reaction of VOC12(THF)2 with 2 equiv of Na(pyt) in TH_F leads to formation of [V202(pyt)4] (1). Complex 1'2THF-1/3C6H12 crystallizes in hexagonal space group R3 with the following cell dimensions at —171 °C: a = b = 30.888(21) A, c = 8.960(6) A, z = 9, and V = 7402.8 A3. A total of 1310 unique reflections with F > 2.330(F) were employed for structure solution and refinement to R (Rw) values of 0.0613 (0.0563). The structure consists of two VO(pyt)2 units joined to ether by two monoatomic bridges provided by S atoms of two pyt‘ groups. The V' 'V distance is 3.989(2) . The reaction of VClg- (THF)3 with four equivalents of Na(pyt) in THF gives [VNa(pyt)4(THF)2] (2). Complex 2 crystallizes in triclinic space group P1 with the following unit cell dimensions at -171 °C: a = 10.442(2) A, b = 16.476(4) A, c = 9.465(2)A , a = 100.73(4)°, ,6 = 109.20(4)°, y = 87.86(3)°, Z = 2, and V = 1510.3 A3. A total of 3391 unique reflections with F > 2.330(F) were employed for structure solution and refinement to R (Rw) values of 0.0412 (0.0431). The structure is best described as a heterodinuclear complex with the metals monoatomically bridged by S atoms from three pyt' groups. The V is seven-coordinate, and the Na is six-coordinate. The V- -Na distance is 3.516(1) A. The reaction of VClz(tmeda)2 (tmeda = tetramethylethylenediamine) with 2 equiv of Na(pyt) in THF or CH2C12 yields [V(pyt)2(tmeda)] (3). Complex 3 crystallizes in orthorhombic space group B2212 with the following cell dimensions at —170 °C: a = 14.338(5) A, b = 17.755(7) A, c = 7.255(2) A, Z = 4, and V = 1846959. A total of 1192 unique reflections with F > 2.330(F) were employed for structure solution and refinement to R (Rw) values of 0.0220 (0.0261). The complex contains chelating pyt' and tmeda groups with severely distorted octahedral geometry. Complexes 1, 2, and 3 have been characterized by EPR and/or IR spectroscopy. In addition, mass spectral studies are described for 1 and 2, directed toward identifying fragmentation pathways involving C-S bond cleavage within the pyt‘ group; the latter cleavage is detected in the mass spectra of both compounds. Introduction In the conversion of crude oils to transportation fuels, many large-scale refining processes utilize heterogeneous catalysts.1 These catalysts facilitate specialized chemistry, including carbon skeleton cracking and rearrangement, hydrogenation, desulfu- rization, and denitrification. Suspended and solubilized metal complexes in feedstocks lead to deactivation of such heteroge- neous catalysts. The main oil-soluble metal impurities are vanadium and nickel, and crude oils can contain large amounts of soluble vanadyl (VOH) impurities that are believed to possess two types of ligand environment,2 the vanadyl petroporphyrins, which have been well-studied and characterized,3 and the vanadyl non-porphyrins, whose ligand environment is thought to contain S, N, and/or O-donor ligands.4 The presence of these vanadyl impurities leads to the formation of vanadium sulfides (primarily V253 and V384) under the reducing and sulfur-rich hydrotreating conditionsfi’9 These sulfides have deleterious * University of California. i Indiana University. 8 Abstract published in Advance AC5 Abstracts, October 1, 1995. (l) Speight, J . G. The Chemistry and Technology of Petroleum; Chemical Industries 3; Marcel Dekker, Inc.: New York, 1980. (2) Yen, T. F. The Role of Trace Metals in Petroleum; Ann Arbor Science: Ann Arbor, MI, 1975; Chapter 1. (3) Psundararaman, P. Anal. Chem. 1986, 57, 2204. (4) Reynolds, J. G.; Gallegos, E. J.; Fish, R. H.; Komlenic, J. J. Energy Fuels 1987, I, 36. (5) Silbemagel, B. G.', Mohan, R. R.; Singhal, G. H. ACS Symp. Ser. 1984, 248, 91. 0020- 1669/95/13 34-5745$09 .00/0 consequences on the activity and lifetime of the supported heterogeneous catalyst (e.g., Mo/Co/S on alumina) employed for crude oil upgrading by causing pore plugging and surface attrition. To model the progressive reduction, sulfiding, and aggregation of crude oil VO2+ impurities to vanadium sulfide polymers, we have studied a variety of discrete vanadium— sulfur species in the nuclearity range 1—6 and oxidation state range III—V containing a number of thiolate ligands.10‘17 More recently, we have incorporated into these studies the ligand pyridine-2—thiol (pytH) because (i) it contains functional groups common in crude oils (thiolate-S and aromatic-N), and (ii) it (6) Silbernagel, B. G. J. Catal. 1979, 56, 315. (7) Asaoka, S.; Nakata, S.; Takeuchi, C. ACS Symp. Ser. 1987, 344, 275. (8) Rose-Brussin, M.; Moranta, D. Appl. Catal. 1984, 11, 85. (9) Mitchell, P. C. H.; Scott, C. E.; Bonnelle, J.-P.; Grimblot, J. G. J. Chem. Soc, Faraday Trans. 1 1985, 81, 1047. (10) Money, J. K.; Huffman, J. C.; Christou, G. Inorg. Chem. 1985, 24, 3297. (11) Money, J. K.; Folting, K.; Huffman, J. C.; Collison. D.; Temperly, J.; Mabbs, F. E.; Christou, G. Inorg. Chem. 1986, 25, 4583. (12) Money, J. K.; Nicholson, J. R.; Huffman, J. C.; Christou, G. Inorg. Chem. 1986, 25, 4072. , (13) Money, J. K.; Huffman, J. C.; Christou, G. J. Am. Chem. Soc. 1987, 109, 2210. (14) Money, J. K.; Folting, K.; Huffman, J. C.; Christou, G. Inorg. Chem. 1987, 26, 944. (15) Money, I. K.', Huffman, J. C.; Christou, G. Inorg. Chem. 1988, 27, 507. (16) Christou, Gs, Heinrich, D. D.; Money, J. K.; Rambo, J. R.; Huffman, J. C.; Folting, K. Polyhedron 1989, 8, 1723. (17) Heinrich. D. D.; Folting, K.; Huffman, J. C.; Reynolds, J. G.; Christou, G. Inorg. Chem. 1991, 30, 300. © 1995 American Chemical Society 5746 Inorganic Chemistry, Vol. 34, No. 23, 1995 has the ability to both chelate and bridge transition metals, potentially allowing access to both mononuclear and Oligo- nuclear products. The pyt‘ ligand has been shown to be capable of binding to transition metals in a number of different ways. Single-crystal X-ray analyses of many complexes have established binding modes I—IV to be those most commonly observed. Of these, Q» @411“, @_ Q» I 11 111 IV the most common is the bidentate, chelating mode I.'3‘32*‘ Several complexes contain 171:771:a-pyt‘ (mode 1033—39 or 77‘: flZZfl-pyt— (mode IV)"'°~41 groups, and there are also examples where two modes are to be found in the same complex.23’26~38~r42v43 (18) (a) Rosenfield, S. G.; Berends, H. P.; Gelmini, L.; Stephen, D. W.; Mascharak, P. K. Inorg. Chem. 1987, 26, 2792. (b) Rosenfield, S. G.; Swedberg, S. A.; Arora, S. K.; Masarak, P. K. Inorg. Chem. 1986, 25, 2109. (19) (a) Block, B.; Ofori-Okai, G.; Kang, H.; Wu, 1.; Zubieta, J. Inorg. Chem. 1991, 30, 4784. (b) Block, E.; Kang, H.; Ofori-Okai, G.; Zubieta, J. Inorg. Chim. Acta 1991, 188, 61. (20) (a) Constable, E. C.; Palmer, C. A.; Tocher, D. A. Inorg. Chim. Acta 1990, 176, 57. (b) Constable, E. C.; Raithby, P. R. Inorg. Chim. Acta 1991, 183,21. (21) Cotton, F. A.; Fanwick, P. E.; Fitch, 1. W., 111. Inorg. Chem. 1978, 17, 3254. (22) Schmidt, W.; Henkel, G.; Krebs, B. Proc. Int. Conf Coord. Chem. 1990, 28, 1. This conference abstract includes the structure of (PPh4)— [V(Pyt)3l. (23) Deeming, A. 1.; Hardcastle, K. 1.; Meah, M. N.; Bates, P. A.; Dawes, H. M.; Hursthouse, M. B. J. Chem. Soc, Dalton Trans. 1988, 227. (24) (a) Kita, M.; Yamanari, K.; Shimura, Y. Bull. Chem. Soc. Jpn. 1989, 62, 3081. (b) Masaki, M.; Matsunami, S.; Ueda, H. Bull. Chem. Soc. Jpn. 1978, 51, 3298. (25) (a) Preut, 11.; Huber, F.; Hengstmann, K.-H. Acta Crystallogr., Sect. C 1988,44, 468. (b) Boualam, M.; Meunier-Piret, 1.; Biesemans, M.; Willem, R.; Gielen, M. Inorg. Chim. Acta 1992, 198, 249. (26) (a) Deeming, A. 1.; Meah, M. N.; Randle, N. F.; Hardcastle, K. I. J. Chem. 506., Dalton Trans. 1989, 2211. (b) Tiekink, E. R. T.; Lobana, T. S.; Singh, R. J. Cryst. Spectrosc. 1991, 21, 205. (27) (a) Mura, F.; Robinson, S. D. Acta Crystallogr. 1984, C40, 1798. (b) Mura, P.; Olby, B. G.; Robinson, S. D. J. Chem. Soc, Dalton Trans. 1985, 2101. (28) Castro, R.; Duran, M.; Garcia-Vazquez, 1.; Romero, A.; Sousa, A.; Castineiras, W.; Hiller, W.; Strahle, 1. J. Chem. Soc, Dalton Trans. 1990, 531. (29) Deeming, A.; Karim. M.; Powell, N. 1. J. Chem. Soc, Dalton Trans. 1990, 2321. (30) Nakatsu, Y.; Nakamura, Y.; Matsumoto. K.; Ooi, S. Inorg. Chim. Acta 1992, 196, 81. (31) Fletcher. S. R.; Skapski, A. C. J. Chem. Soc, Dalton Trans. 1972, 635. (32) (a) Henkel, G.; Krebs, B.; Schmidt, W. Angew. Chem, Int. Ed. Engl. 1992 31, 1366. (b) Tsagkalides, W.', Rodewald, D.', Rehder, D. J. Chem. Soc., Chem. Commun. 1995, 165. (33) (a) Deeming, A. 1.; Meah, M. N.; Dawes, H. M.; Hursthouse, M. B. J. Organomet. Chem. 1986, 299, C25. (b) Kumar, R.; de Mel, V. 5.; Oliver, 1. P. Organometallics 1989, 8, 2488. (34) Ciriano, M. A.; Perez—Torrente, J. 1.; Viguri, F.; Lahoz. F. 1.; Oro, L. A.; Tiripicchio, A.; Tiripicchio—Camellini, M. J. Chem. Soc, Dalton Trans. 1989, 25. (35) Umakoshi, K.; Kinoshita, 1.; Fukui-Yasuba, Y.; Matsumoto, K.; Ooi, S.; Nakai, H.; Shiro, M. J. Chem. Soc, Dalton Trans. 1989, 815. (36) Umakoshi. K.; Kinoshita, 1.; Ichimura, A.; Ooi, S. Inorg. Chem. 1987, 26, 3551. (37) (a) Deeming, A. J. Meah, M. N.; Bates, P. A.; Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1988, 2193. (b) Zhang, N.; Wilson, S. R.; Shapley. P. A. Organometallics 1988, 7, 1126. (38) Umakoshi, K.; Ichimura, A.; Kinoshita, 1.; Ooi, S. Inorg. Chem. 1990, 29, 4005. (39) Yamamoto, J. 11.; Yoshida, W.; Jensen, C. M. Inorg. Chem. 1991, 30. 1353. (40) Hursthouse, M. B.; Khan, 0. F. 2.; Mazid, M.; Motevalli, M.; O’Brien, P. Polyhedron 1990, 9, 541. Reynolds et a1. Some complexes also contain pyt‘ groups binding to more than two metals.3g"”‘44 We herein report the results of an investigation directed toward the preparation of vanadium/pyt‘ complexes spanning the oxidation state range II—IV. We show that complexes at all three oxidation levels have been successfully obtained and describe the results of subsequent spectroscopic and mass spectral analyses. A preliminary account of this work has appeared.45 Experimental Section All syntheses were carried out under a dinitrogen atmosphere employing standard Schlenk glassware and techniques. Air-sensitive samples for spectroscopic study were prepared and handled in either a dinitrogen glovebag (VWR) or 3 Vacuum Atmospheres glovebox. All reagents were obtained from Aldrich, unless otherwise indicated. Spectroanalytical grade (Burdick and Jackson) CH2C12 (0.006% H20), hexanes, and THF were dried over CaHg (Alfa), LiAlHi, and LiA1H4 followed by Na/benzophenone, respectively. Pyridine-Z-thiol (pytH) and N,N,N',N’-tetramethylethylenediamine (tmeda) were used as re— ceived; single crystals of pytH were grown from CH2C12/hexanes. VOC12(THF)246a and VC13(THF)346b were prepared as described; the former was recrystallized from THF/hexanes. VC12(tmeda)z was prepared from [V2C13(THF)6]2[Zn2C16]47 by the method of Edema et al.48 Na(pyt) was prepared by the reaction of NaH with pytH in THF, precipitated with hexanes, and recrystallized from THF/hexanes. [V202(pyt)4] (1). A solution of Na(pyt) (1.89 g, 14.2 mmol) in THF (200 mL) was added to a stirred, blue-green solution of VOC]2(THF)2 (2.00 g, 7.09 mmol) in THF (50 mL). The solution rapidly turned dark brown. After several hours, the solvent was removed in vacuo and the residue dissolved in CH2C12 (100 mL) and filtered. Storage of the filtrate at -10 °C ovemight yielded dark brown crystals. These were collected by filtration, washed with hexanes, and dried in vacuo to give a brown powder in 40% yield. The product can be recrystallized from CHQClz/ hexanes or THF/hexanes layerings. The crystallographic sample was obtained by filtering the initial reaction mixture through a fine frit and layering the filtrate with hexanes; the resultant crystals of 1-2THF-1/3C6H12 lose solvent extremely rapidly when removed from their mother liquor. A vacuum-dried sample analyzed as solvent-free. Anal. Calcd (found) for C20H16N402$4sz C, 41.81 (42.19); H, 2.81 (3.18); N, 9.75 (9.92); S, 22.32 (22.95). Selected IR data, cm“: 1585 (s), 1552 (m), 1450 (s), 1407 (s), 1269 (m), 1141 (s), 972 (vs), 901 (b). [VNa(pyt)4(THF)2] (2). A solution of Na(pyt) (2.85 g, 21.4 mmol) in THF (200 mL) was added to a stirred, red solution of VC13(THF)3 (2.00 g, 5.35 mmol) in THF (100 mL). The solution rapidly turned deep blue-black, and then slowly converted to a deep blood-red over the course of 6 h. The next day, the solution was filtered through a fine frit and the filtrate stored at -10 °C for 3 days. The resultant black crystals were collected by filtration and recrystallized from THF/ hexanes or CH2C12/hexanes layerings at — 10 °C. Yields were typically ~60%. Anal. Calcd (found) for C23H32N402S4NaV: C, 51.05 (50.93); H, 4.90 (4.82); N, 8.50 (8.32)%. Selected 1R data, cm“: 1577 (s), 1549 (m), 1444 (s), 1416 (s), 1254 (m), 1138 (s), 1055 (m), 902 (b). (41) (a) Cockerton, B.; Deeming, A. 1.; Karim, M.; Hardcastle. K. I. J. Chem. Soc, Dalton Trans. 1991, 431. (b) Deeming, A. 1.; Karim, M.; Powell, N. 1.; Hardcastle, K. 1. Polyhedron 1990, 9, 623. (42) Oro, L. A.; Ciriano, M. A.; Viguri, F.; Tiripicchio, A.; Tiripicchio- Camellini. M.; Lahoz, F. 1. Now. J. Chim. 1986, 10, 75. (43) (a) Deeming, A. 1.; Meah, M. N.; Bates, P. A.; Hursthouse, M. B. J. Chem. Soc, Dalton Trans. 1988, 235. (b) Kiroshita, T.; Yasuba, Y.; Matsumoto. K.; Ooi, S. Inorg. Chim. Acta 1983. 80, L13. (44) Kitagawa, 5.; Munakata, M.; Shimono, 11.; Matsuyama, S.; Masuda, H. J. Chem. 500., Dalton Trans. 1990, 2105. (45) Reynolds, 1. G.; Sendlinger, S. C.; Murray, A. M.; Huffman, J. C.; Christou, G. Angew. Chem, Int. Ed. Engl. 1992, 31, 1253. (46) (a) Kern. R. J. J. Inorg. Nucl. Chem. 1962, 24, 1105. (b) Manzer, L. E. Inorg. Synth. 1982, 21, 135. (47) Canish,1. A. M.; Cotton, F. A.; Duraj, S. A.; Roth, W. J. Polyhedron 1987, 6, 1433. (48) Edema, J. J. H.; Stauthamer, W.; Bolhuis, F.; Gambarotta. 5.; Smeets, W. J. 1.; Spek. A. L. Inorg. Chem. 1990, 29, 1302. Vanadium Complexes of Pyridine-2-thiolate Table 1. Crystallographic Data for Complexes 1-2THF-1/3C5H12, 2, 3, and pytH l-2THF- 1/3C6H12 2 3 pytH formula“ C30H36N4- C23H32N4- C15H24N4- CsHsNS OaS4V2 02S4NaV SzV fw 373.38 658.76 387.45 111.16 space group R3 Fl 82212 P21/c a, 30.888(2l) 10.442(2) 14.338(5) 6.044(1) 12, A 30.888(2l) l6.476(4) 17.755(7) 6.273(1) c, A 8.960(6) 9.465(2) 7.255(2) l4.146(2) CL, deg 90 100.73(4) 9O 90 [3, deg 90 109.20(4) 90 101.93 y, deg 120 8786(3) 90 90 V, A3 7402.84 1510.33 1846.86 524.77 Z 9 2 4 4 T, °C --171 —171 —l7l —157 radiation” 0.71069 0.71069 0.71069 0.71069 pcalc, g/cm3 1.508 1.449 1.393 1.407 [.t, cm‘1 8.337 6.290 7.405 4.476 no. of obsd data 1310 3391 1192 631 (F > 30(5) R (RWY 6.13 (5.63) 4.12 (4.31) 2.20 (2.61) 2.46 (3.05) “Including solvate molecules. ’7 Graphite monochromator. “R ZIIFul — chH/ZIFOI. Rw = [Zwum e chl)2/2wchl2]”2 where w 1/02(iFoi)~ [V(pyt)2(tmeda)] (3). VC12(tmeda)2 (0.500 g, 1.41 mmol) and Na- (pyt) (0.380 g, 2.85 mmol) were dissolved with stirring in THF (45 mL) to give a deep purple-red solution. The reaction mixture was stirred overnight and the solvent removed in vacuo. The purple residue was dissolved in CH2C12 (20 mL), filtered to remove NaCl, and the solvent removed in vacuo to give a deep purple solid in essentially quantitative yield. Black crystals suitable for crystallography were obtained from a THF solution layered with hexanes (3:4 v/v). Repeated attempts to obtain an elemental analysis were unsuccessful, the results being highly variable even on the same sample, and we assign this to the extreme sensitivity of the complex. Selected IR data, cm“: 1576 (s), 1549 (m). 1443 (s), 1416 (s), 1254 (m), 1138 (m), 1126 (m), 1053 (m), 901 (b). X-ray Crystallography. Data were collected using a Picker four- circle diffractometer; details of the diffractometry, low-temperature facilities, and computational procedures employed by the Molecular Structure Center are available elsewhere.49 Suitable crystals were located. affixed to the end of a glass fiber using silicone grease, and transferred to the goniostat where they were cooled for characterization and data collection. Inert-atmosphere handling techniques were employed. Data collection parameters are summarized in Table 1. The structures were solved using the standard combination of direct methods (MULTAN) and Fourier techniques, and refined by full-matrix least- squares methods. No absorption corrections were performed. For complex 1-2THF'1/3C5H12, a systematic search of a limited hemisphere of reciprocal space yielded a set of reflections whose Laue symmetry indicated the space group to be either R3 or R3. Choice of the centrosymmetric space group R3 was confirmed by subsequent successful solution and refinement of the structure. The positions of the V and S atoms were obtained from an initial E—map, and the remainder of the non-hydrogen atoms were found in subsequent iterations of least-squares refinement and difference Fourier map calculations. The structure consists of a V202(pyt)4 molecule lying on an inversion center, a THF molecule in a general position and displaying disorder of one C atom (C(21)), and a C(3ng molecule lying on a 3 site (occupancy 0.33). For complex 2, a systematic search of a limited hemisphere of reciprocal space located a set of diffraction maxima with no symmetry or systematic absences, indicating a triclinic space group. Subsequent structure_solution and refinement confirmed the centrosymmetric space group P1. All non-hydrogen atoms were readily located and refined anisotropically; there was no sign of any disorder problems. Hydrogen (49) Chisholm, M. H; Folting, K.; Huffman, J. C; Kirkpatrick, C. C. Inorg. Chem. 1984, 23, 1021. Inorganic Chemistry, Vol. 34, No. 23, 1995 5747 atoms were clearly visible in a difference Fourier map phased on the non-hydrogen atoms, and they were allowed to vary in the final refinement cycles with isotropic thermal parameters. A final difference map was featureless, the largest peak being 0.43 e/A3. For complex 3, a systematic search of a limited hemisphere of reciprocal space located a set of diffraction maxima with systematic absences and symmetry corresponding to the unique orthorhombic space group 8212 (an alternate setting of C2221). Subsequent solution and refinement confirmed this choice. All non-hydrogen atoms were readily located and showed no signs of disorder. They were refined with anisotropic thermal parameters. All hydrogen atoms were visible in a difference Fourier map phased on the non-hydrogen atoms, and they were included in the final least-squares cycles and refined isotropically. The reported structure is the correct absolute structure, on the basis of examination of the final residuals after changing the signs of the anomalous dispersion terms. A final difference Fourier map was featureless, the largest peak being 0.21 e/A3. For pytH (4), a systematic search of a limited hemisphere of reciprocal space revealed symmetry and systematic absences consistent with space group P21/c, which was confirmed by the successful solution of the structure. After the non-hydrogen atoms had been located and partially refined, a difference Fourier map revealed all of the hydrogen positions. In the final cycles of least-squares refinement, the non- hydrogen atoms were refined with anisotropic thermal parameters and the hydrogen atoms were refined with isotropic thermal parameters. The final difference map was essentially featureless, the largest peak being 0.2 e/A3. Other Measurements. IR spectra were recorded as KBr pellets or Nujol mulls on a Mattson Polaris Model 10410 FTIR, a Nicolet 5101> FTIR, or a Perkin-Elmer 283 IR spectrometer. Electronic spectra were recorded on CH2C12 or THF solutions using a Hewlett—Packard Model 8452A diode-array spectrophotometer and Spectrocell R-2010-T quartz anaerobic cells. Mass spectra were recorded on a VG 7070E mass spectrometer in the electron-impact positive ion mode. EPR spectra were recorded on a Bruker ESP 300 spectrometer. Elemental analyses were performed by Galbraith Laboratories. Results Syntheses. A number of synthetic procedures have been employed in the past to access M/pyt complexes, including the use of (i) the free ligand with or without added base,”33 (ii) the Na(pyt) salt in a metathesis reaction with the metal chloride,”39 and (iii) the disulfide version 2,2’-dithiobis— (pyridine) in an oxidative addition reaction.24~30~50 We chose the reaction of Na(pyt) with Cl‘-containing V reagents as being the most convenient for our purposes. 2V0Cl2(THF)2 + 4Na(pyt) —» V202(pyt)4 + 4NaCl + 4TI-IF (1) Addition of Na(pyt) to VOC12(THF)2 gives a dark brown solution from which can be isolated V202(pyt)4 (l) in good yield (eq 1). Crystals isolated from CH2C12/hexanes and THF/hexanes are brown and green, respectively, but both lose solvent rapidly to give the same pea green powder, and the different crystal colors are therefore a result of different lattice solvent content. IR spectra of crystals and powder are identical except for solvent bands. In a similar fashion, the reaction of Na(pyt) with VC13(THF)3 gives an intense blood-red color from which can be isolated [VNa(pyt)4(THF)2] (2) (eq 2). The reaction gives the same VC13(THF)3 + 4Na(pyt) —> [VNa(pyt)4(THF)2] + 3NaCl + THF (2) product in lower yield and purity when only 3 equiv. of Na— (50) Mura, P.; Olby, B. G.; Robinson, S. D. Inorg. Chim. Acta 1985, 98, L21. 5748 Inorganic Chemistry, Vol. 34, N0. 23, I995 (pyt) are employed. Dissolution of complex 2 in CH2C12 gives a red solution that slowly deposits :1 white powder identified as Na(pyt) by IR. This suggests that in this solvent the tris—chelate complex forms (eq 3), but its isolation was not pursued; it is [VNa(Pyt)4(THF)2] ’* V(PYUs + Na(Pyt) (3) likely to be structurally very similar to the anion in the V11 complex (PPh4)[V(pyt)3] reported by othersnv323 Extending our efforts to V", we explored the reaction of Na- (pyt) with VClg(tmeda)2. This gave a deep purple-red solution, and an extremely air- and moisture-sensitive dark purple solid was isolated, which proved to be V(pyt)z(tmeda) (3) after recrystallization from THF/hexanes (eq 4). Addition of a third VC12(tmeda)2 + 2Na(pyt) —> V(pyt)2(tmeda) + 2NaC1 + tmeda (4) equivalent of Na(pyt) had no effect. Complex 3 is an extremely rare example of a V11 thiolate, the only other examples being (PPh4)[V(pyt)3] mentioned above and V(L—S4)(tmeda) (L-S4 = a tetradentate S-based ligand).32b The 02 sensitivity of complexes 2 and 3 was further explored in THF solution. For both complexes, addition of stoichiometric amounts of 02 at room temperature produced a lighter green- brown color; layering of the solutions with hexanes gave green products identified as complex 1 by IR. The transformations are summarized in eqs 5 and 6. Apparently similar reactions 2[VNa(pyt)4(THF)2l + 02 e V202(pyt)4 + 2Na(pyt) + (pyt)2 + 4THF (5) 2V(pyt)2(tmeda) + 02 —’ V202(pyt)4 + 2tmeda (6) in THF occur with elemental sulfur, rapidly with 3 but less so with 2; the latter reaction had to be refluxed to ensure complete reaction. The solutions turn an orange-red color, and addition of hexanes causes precipitation of orange-red microcrystalline solids whose IR spectra are identical to each other and very similar to that of 1, except that the band at 972 cm‘1 assignable to the vanadyl [V0]2+ stretch is absent, and a new band is observed at 582 cm‘1 characteristic of the thiovanadyl [VS]2+ unit. The data are consistent with the products being V282- (pyt)4, the thiovanadyl version of 1, formed in a manner analogous to the reactions in eqs 5 and 6. However, a crystal structure is required for confirmation of the precise metal nuclearity and structure, and we have been unable to—date to obtain suitable single crystals. Description of Structures. ORTEP plots of complexes 1—3 are shown in Figures 1—3. Fractional coordinates and selected structural parameters for 1-4 are listed in Tables 2—9. Complex 1 lies on an inversion center and contains two [V0]2+ units monoatomically bridged by two S atoms 5(3) and S(3’) from two pyt' groups whose N atoms are terminally ligated in an equatorial coordination site. These two pyt' groups are thus bound in mode IV, but the S atoms bridge very asymmetrically, and this is an extremely rare variation of mode IV binding.“ Atom S(3), for example, occupies an equatorial site at V(l’) but an axial site at V(1), and the two resultant bond lengths (V(1’)—S(3) = 2.457(4) A, V(l)-S(3) = 2.798(3) A) are significantly different, the lengthening of the latter being (51) To our knowledge, only one example of this ligation mode has been reported. See: Castano, M. V.; Macias, A.; Castineiras, A.; Gonzalez, A. S.; Martinez, E. M.; Casas, J. St, Sordo, S.; Hiller, W.; Castellano, E. E. J. Chem. Soc. Dalton Trans. 1990, 1001. Reynolds et a1. Figure l. ORTEP representation of [V202(Pyt)4] (1) at the 50% probability level. Primed and unprimed atoms are related by the inversion center. Figure 2. ORTEP representation of [V(pyt)4Na(THF)z] (2) at the 50% probability level. Figure 3. ORTEP representation of [V(pyt)g(tmeda)] (3) at the 50% probability level. assignable to the strong trans influence of the multiply-bonded [VO]2+ unit. A bidentate, chelating pyt‘ (mode I) completes a highly distorted octahedral geometry at each metal center. The [V0]2+ bond (1.583(6) A) is typical for this unit, and indicates no noticeable lengthening from the presence of a trans S atom. The molecule has crystallographically—imposed Ci symmetry. Complex 2 (Figure 2) contains a rare example of a seven- coordinate VIII center52‘55; there are three chelating pyt‘ groups attached to the V, and a seventh bond to the S atom, S(23), which is part of the fourth pyt‘ group. The latter is chelating (52) Vuletic, N.; Djordjevic, C. J. Chem. Soc, Dalton Trans. 1973, 1137. (53) Drew, R. E.; Einstein, F. W. B. Inorg. Chem. 1973, 12, 829. (54) Levenson, R. A.; Dominguez, R. J. G.; Willis, M. A.; Young, F. R., 111. Inorg. Chem. 1974, I3, 2761. (55) Begin, D.; Einstein, F. W. B.; Field, J. Inorg. Chem. 1975, I4, 1785. Vanadium Complexes of Pyridine-Z-thiolate Table 2. Selected Fractional Coordinates (x104) and Equivalent Isotropic Thermal Parameters (x10)" for [V202(pyt)4l'2THF"/3C6H12 atom x y z Beq, A2 V(l) 5611(1) 172(1) 6189(2) 13 5(2) 5523(1) 730(1) 7910(2) 16 5(3) 5265(1) 502(1) 3808(2) 14 0(4) 5856(2) — 101(2) 7041(7) 18 N(5) 6216(2) 899(3) 6046(7) 12 N(6) 5722(3) —13(3) 4017(8) 15 C(7) 6113(3) 1135(3) 7140(9) 16 C(8) 6444(3) 1630(4) 7492(10) 20 C(9) 6881(4) 1870(3) 6722(11) 24 C(10) 6999(3) 1630(4) 5621(11) 23 C(11) 6655(3) 1145(3) 5312(9) 18 C(12) 5552(3) 194(3) 3004(9) 16 C(13) 5609(3) 141(3) 1482(9) 20 C(14) 5830(3) —l3l(3) 1028(10) 22 C(15) 5998(3) —340(3) 2076(10) 21 C(16) 5947(3) —272(4) 3573(10) 20 ” Beq = 4/3ZZBVIIKII‘. Table 3. Selected Fractional Coordinates (x104) and Equivalent Isotropic Thermal Parameters (><10)a for VNa(pyt)4(THF)2 (2) atom x y z Beq, A2 V(l) 6376(1) 2804.2(4) 7816(1) 11 S(Z) 4093(1) 3281(1) 6303(1) 16 C(3) 4173(4) 3691(2) 8159(5) 16 C(4) 3190(4) 4159(3) 8628(5) 21 C(5) 3436(5) 4439(3) 10152(6) 25 C(6) 4646(5) 4266(3) 11197(5) 22 C(7) 5583(4) 3803(3) 10676(5) 19 N(8) 5348(3) 3522(2) 9191(4) 14 5(9) 7240(1) 1884(1) 9830(1) 15 C(10) 5894(4) 1275(2) 8528(4) 15 C(11) 5511(4) 475(3) 8555(5) 19 C(12) 4454(4) 72(3) 7373(5) 20 C(13) 3766(4) 478(3) 6189(5) 20 C(14) 4164(4) 1265(3) 6236(5) 18 N(15) 5205(3) 1666(2) 7390(4) 14 S(l6) 8651(1) 3465(1) 9533(1) 15 C(17) 8320(4) 4019(2) 8067(4) 15 C(18) 9177(4) 4597(3) 7879(5) 19 C(19) 8688(5) 5002(3) 6678(5) 22 C(20) 7381(5) 4828(3) 5671(5) 22 C(21) 6605(4) 4238(3) 5889(5) 18 N(22) 7061(3) 3840(2) 7074(4) 14 S(23) 7104(1) 1884(1) 5823(1) 14 C(24) 8375(4) 2371(2) 5382(4) 14 C(25) 8062(4) 2723(3) 4094(5) 18 C(26) 9092(4) 3068(3) 3760(5) 18 C(27) 10409(4) 3048(3) 4715(5) 19 C(28) 10639(4) 2694(3) 5970(5) 18 N(29) 9656(3) 2348(2) 6327(3) 14 Na(30) 9535(2) 1849(1) 8507(2) 17 0(31) 9888(3) 460(2) 8302(3) 22 C(32) 8816(5) — 130(3) 8045(5) 29 C(33) 9266(6) -948(3) 7417(6) 39 C(34) 10183(6) —711(3) 6614(6) 42 C(35) 10872(5) 73(3) 7648(6) 31 0(36) 11759(3) 2167(2) 10077(3) 26 C(37) l2991(5) 2003(3) 9721(5) 27 C(38) 14002(5) 1865(3) 11177(6) 31 C(39) 13583(5) 2466(3) 12384(5) 33 C(40) l217l(5) 2700(3) 11549(5) 27 " Beq = 4/3ZZBgaiaj. to the Na+ ion, which is also attached to two S atoms of the pyt‘ chelates on the V. Two terminal THF groups complete six-coordination for the Na ion. The initial temptation to describe 2 as an intimate ion-pair between [Na(THF)2]" and [V(pyt)4]' is resisted; the mode of binding of the pyt‘ ligand containing S(23) and N(29) suggests the best description of 2 is as a molecular, triply-bridged, heterobimetallic complex. As Inorganic Chemistry, Vol. 34, N0. 23, 1995 5749 Table 4. Selected Fractional Coordinates (x10‘)” and Equivalent Isotropic Thermal Parameters (x10)b for [V(pyt)2(tmeda)] (3) atom x y z Beq, A2 V(l) 8345.5(4) 5000* 0* 12 5(2) 7977.0(5) 5785.3(4) 2846(1) 17 C(3) 7342(2) 6240(2) 1129(4) 15 C(4) 6837(2) 6908(2) 1324(4) 18 C(5) 6405(2) 7216(2) —185(5) 22 C(6) 6465(2) 6854(2) —1869(5) 21 C(7) 6966(2) 6196(2) — 1995(4) 18 N(8) 7392(1) 5890(1) —533(3) 14 N(9) 9534(2) 5704(1) — 1071(3) 15 C(10) 10369(2) 5417(2) —97(5) 21 C(11) 9646(3) 5594(2) —3o76(5) 25 C(12) 9466(3) 6517(2) —718(6) 26 " Parameters marked by an asterisk were fixed by symmetry. 5 Beq = 4/3ZZBiJ-aiaj. Table 5. Fractional Coordinates (x104) and Equivalent Isotropic Thermal Parameters (x10)“ for pytH (4) atom x y z Beq, A2 C(1) 6631(4) 2652(4) 6139(1) 16 C(2) 7356(4) 4423(4) 6745(2) 18 C(3) 5899(4) 6015(4) 6858(2) 21 C(4) 3621(4) 5936(4) 6387(2) 21 C(5) 2919(4) 4222(4) 5817(2) 18 N(6) 4395(3) 2656(3) 5706(1) 16 5(7) 8346(1) 640(1) 5923.4(4) 19 a ch = 4/32EBij-aibj. Table 6. Selected Interatomic Distances (A) and Angles (deg) for [V202(Pyt)4l'2THF’l/3C6H12 V(1)---V(l’) 3.989(2) V(1)—N(5) 2.088(7) V(1)—S(2) 2.427(3) V(1)—N(6) 2.106(7) V(1)—S(3) 2.457(4) S(2)—C(7) 1.756(8) V(1)—S(3’) 2.798(3) S(3)—C(12) 1.746(9) V(l)—O(4) 1.583(6) S(2)-V(1)-S(3) 9165(10) 5(3)—V(1)—N(5) 158.1 1(19) S(2)—V(1)—S(3’) 9776(9) S(3)—V(1)—N(6) 9174(21) 8(2)—V(1)—0(4) 108.92(24) S(3’)—V(1)—N(6) 6235(21) S(2)—V(1)—N(5) 6851(19) O(4)—V(1)-—N(5) 101.13(28) S(2)—V(1)—N(6) 150.68(21) 0(4)—V(1)—N(6) 96.7(3) S(3)-V(1)-S(3’) 8135(9) N(5)—V(1)-N(6) 93.15(27) S(3’)—V(1)—O(4) 158.99(24) V(l)—S(2)—C(7) 79.2(3) S(3)—V(1)—O(4) 9947(22) V(1)-—S(3)—V(1’) 98.65(9) 5(3’)—V(1)—N(5) 82.07(18) for complex 1, the pyt‘ groups in 2 comprise binding modes I and IV, the latter again in the highly asymmetric form. Complex 3 (Figure 3) is a six-coordinate, distorted octahedral mononuclear VII species with two chelating pyt‘ groups (mode I) and a chelating tmeda group. The molecule has crystallo- graphically-imposed C2 symmetry; the S(2)—V-S(2') angle is only 156.05(4)° and the N(8)—V—N(9’) angle is only 164.27- (8)°, emphasizing the large distortion of the molecule away from octahedral geometry. The bonds to pyridine-type N atoms (V— N(8) = 2.1244(23) A) are noticeably shorter than the bonds to tmeda N atoms (v—N(9) = 2.2524(23) A). The low-temperature crystal structure of the free ligand in its protonated form was obtained for comparison with the pyt‘ groups in 1—3. The pytH molecule exists as a tautomeric equilibrium between the thiol (A) and thione (B) forms shown. N SH N s 11 A B Room-temperature diffraction experiments56 have previbusly 5750 Inorganic Chemistry, Vol. 34, N0. 23, 1995 Table 7. Selected Interatomic Distances (A) and Angles (deg) for [VNa(Pyt)4(THF)2] (2) V(l)—S(2) 2.526(1) V(1)—N(22) 2.187(3) V(l)—S(9) 2.567(1) S(2)—C(3) 1.737(4) V(1)~S(16) 2.543(1) S(9)C(10) 1.734(4) V(1)—S(23) 2.495(1) S(16)—C(17) 1.735(4) V(l)—N(8) 2.121(3) S(23)—C(24) 1.774(4) V(1)—N(15) 2.178(3) V(l)- ~Na(30) 3.516(1) S(2)-V(1)-—N(8) 6658(9) S(9)—V(1)-N(22) 140.1104) 5(2)—v0)—5(9) 136.09(9) S(16)—V(1)—S(23) 100.06(9) S(2)-V(l)-N(15) 81.4604) N(22)—V(l)-S(23) 8676(9) S(2)-V(l)—S(l6) 137.24(9) S(9)—Na(30)—S(16) 6393(9) S(2)—V(l)-N(22) 81.1104) S(9)—Na(30)—S(23) 7742(9) S(2)-V(l)-S(23) 102.76(9) S(9)-Na(30)-N(29) 130.6804) N(8)-V(1)—S(9) 89.45(14) S(9)—Na(30)-0(31) 96.8004) N(8)—V(1)—N(15) 96.05(12) S(9)—Na(30)—O(36) 120.9904) N(8)—V(1)—S(16) 9158(9) S(16)—Na(30)—S(23) 8281(9) N(8)—V(1)—N(22) 96.3202) S(16)-Na(30)-N(29) 87.8404) N(8)-V(1)—S(23) 168.16(9) S(l6)—Na(30)—O(3l) 159.3004) S(9)-V(l)-N(15) 64.3904) S(16)—Na(30)-0(36) 91.8204) S(9)-V(l)-S(l6) 7587(9) S(9)—V(l)—S(23) 9555(9) N(15)—V(l)—S(l6) l39.35(9) S(23)—Na(30)—N(29) 58.6304) N(15)—V(l)—N(22) 152.5302) S(23)-Na(30)-O(3l) 101.0404) N(15)—V(l)-S(23) 7659(9) S(23)-Na(30)-O(36) 156.0904) S(l6)—V(l)-N(22) 6457(9) V(1)—S(9)—Na(30) 77.15(9) N(29)—Na(30)—O(3l) 111.6504) V(l)—S(l6)—Na(30) 8044(9) N(29)-Na(30)—O(36) 98.0304) V(l)—S(23)—Na(30) 7996(9) O(3l)-Na(30)—O(36) 92.2004) Table 8. Selected Interatomic Distances (A) and Angles (deg) for [V(P)'t)2(tmeda)l (3) V(1)—S(2) 2.546(1) V(l)—N(9) 2.252(2) V(l)—N(8) 2.124(2) 5(2)—C(3) 1.741(3) S(2)—V(1)—S(2’) 156.05(4) N(8)—V(1)—N(8’) 99.8903) S(2)—V(1)—N(8’) 9724(6) N(8)—V(1)—N(9) 9065(9) S(2)—V(1)—N(8) 6685(6) N(8)—V(1)—N(9’) l64.27(8) S(2)—V(1)—N(9) 9763(6) N(9)-V(1)-N(9’) 81.6402) S(2)—V(l)—N(9’) 100.4505) v0)—S(2)—C(3) 77.43( 10) Table 9. Interatomic Distances (A) and Angles (deg) for pytH (4)” S(7)—C(1) 1.700(2) C(2)*C(3) 1.363(3) N(6)—C(1) 1.364(3) C(3)—C(4) 1.401(3) N(6)—C(5) 1.357(3) C(4)—C(5) 1.359(3) C0)—C(2) 1.416(3) C(1)—N(6)—C(5) 124.3200) C(2)—C(3)—C(4) 120.92(23) 3(7)vc0)4(6) 120.3506) C(3)—C(4)—C(5) 117.79(23) S(7)-C(l)—C(2) 124.5507) N(6)—C(5)~C(4) 120.5802) N(6)—C(1)—C(2) 115.10(20) C(1)—C(2)—C(3) 121.29(22) r——‘—1 “ Numbering scheme: S(7)—C(l)—C(2)-C(3)-C(4)—-C(5)-N(6)—. indicated that the H atom is located on the N atom and that the thione tautomer is a major contributor to the tautomeric equilibrium. This conclusion is confirmed by our own low- temperature (-157 °C) study, which also shows insignificant changes to the structural parameters (i.e., to the tautomeric composition) as a function of temperature. The salient features of the structure of pytH (4) are as follows: (i) the angle at the N atom (124.32(20)°) is consistent with the protonated form; for pyridine rings, protonated and nonprotonated N atoms possess angles greater or less than 120°, respectively;57 (ii) owing to the low-temperature data set, the observation of the H atom on the N is reliable, all the H atoms being located in a difference Fourier map and refined; (iii) the six-membered ring shows the variation in C—C bond lengths expected for thione form B rather than the equivalence expected for A, which is aromatic; and (iv) the C—S bond length (1.700(2) A) is (56) Ohms, U.; Guth, H9, Kutoglu, A.; Scheringer, C. Acta Crystallogr. 1982, B38, 831. (57) Kvick, A.; Booles, S. S. Acta Crystallogr. 1972, 328, 3405. Reynolds et a1. 3 300 ' M-S 2'5 W 25° -< ._'._.§ ‘5 . Q— —§3—— 13 5 2 DE ‘9 @— c.s — 200 a g 0600—0-00—°~—e<»————<> 3, ° 15 C-N - 150 3 ;' x-x—>o<—-x-3$<--><---->o<-~~-EEK-X ‘% _ . M._. _':_ . as: 1 A—Aflg -a A —AA— A‘ 100 % +4.1; 4-40.. Jr... +1. . .SrMiN.+ ‘P 0.5 50 o o 0.55 0.6 0.55 0.7 0.75 0.8 0.85 0.9 Iomc Radius, A Figure 4. Relationship of M—S, M—N, C—S, and C—N bond lengths and S—C-N and S-M-N bond angles to six-coordinate metal ionic radii for pyt“ ligands in binding mode I from forty-two transition metal/ pyt single-crystal X-ray structures. Complexes 1, 2, and 3 are indicated by arrows. significantly shorter than the C—S single bond value typical of the unbound PhS' group (1.770(5) A in (PPh4)(PhS)).58a The neutral pytH group is often seen as a ligand to soft metals where it functions as an S-bound monodentate ligand.59 On depro- tonation to pyt‘ and incorporation into a metal complex, the thiolate form A becomes more significant, and the ligand may be approximately and quite adequately described as being deprotonated form A, i.e., a thiolate. Restricting further discussion to the present complexes 1-3, the predominantly thiolate (A) character of pyt‘ is supported by (i) the C—S bonds (1.734(4)—1.774(4) A), which approach those in VHMV/SPh complexes (1 .77—1.80 119,581”C and (ii) the smaller range of C—C and C—N bond distances within the six-membered rings, which now look more typical of aromatic rings. This shift of the tautomeric equilibrium toward form A is as expected for attachment of strongly Lewis acidic M centers, because total electron donation to the latter is facilitated by form A, which provides greater electron density at the better 0- and n—donating S atom. In Figure 4 are compared M—S, M-N, C-S and C-N bond lengths, and S-M-N and S—C-N angles for 42 terminal, chelating (type I) pyt‘ ligands in various M/pyt~ complexes (including 1—3) as a function of metal ionic radii for six- coordination.60 The M—S and M—N bond lengths show the expected slight increase with M radius, but it is interesting that the C-S and C—N values are essentially invariant, indicating little if any influence of the M identity on the tautomeric nature (equilibrium) of the ligand. The S-M—N angles become slightly smaller as the ionic radii increase, but this is just strain within the four-membered chelate ring as the M—N/M—i bonds shorten. The average values for the bonds (A) and angles (deg) are as follows: M—S, 2.445 :1: 0.086; M—N, 2.116 :b 0.101; C—S, 1.741 i 0.015; C—N, 1.351 i 0.018; S—M—N, 67.62 :1: 2.46, and S-C—N, 111.11 :1: 3.18. The V—S bond lengths for 2 are a bit longer than expected but this is due to the metal being seven-coordinate, ionic radii for six-coordination having been employed. (58) (a) Huffman, J. C.; Christou, G. Unpublished results. (b) Nicholson, J. R.; Huffman, J. C.; Ho, D. M.; Christou, G. Inorg. Chem. 1987, 26, 3030. (c) Dean, N. S.; Bartley, S. L.; Streib, W. En, Lobkovsky, E. B.; Christou, G. Inorg. Chem, in press. (59) For recent references, see: (a) Guochen, J .; Puddephatt, R. E.; Vittal, J. J. Polyhedron 1992. 11, 2009. (b) Hadjikalou, S. K.; Aslanidis, Pu, Karagiannidis, P.; Aubry, A.; Skoulika, S. Inorg. Chim. Acta 1992, 193, 129. (c) Povey, D. C.; Smith, G. W.; Lobana, T. S.‘, Bhatia, P. K. J. Cryst. Spectrosc. 1991, 21, 9. (60) Shannon, R. D.; Prewitt, C. T. Acta Crystallogr. 1970, 326, 1076. Vanadium Complexes of Pyridine-Z—thiolate 298 x l I 3050 a 4050 e 77 K I 1 2550 G 4250 G l i l 1000 c 5000 G Figure 5. EPR spectra of (A) complex 1 in THF at 298 K, (B) complex 1 in THF at 77 K, and (C) complex 3 in toluene at 115 K. EPR Spectroscopy. Figure 5a shows the room-temperature X-band EPR spectum of complex 1 in THF solution. The spectrum is a typical eight-line isotropic signal characteristic of mononuclear VO2+ species (51V, 1 = 7/2, ~100%), suggesting the dinuclear structure in the solid state is not retained in solution or the metal centers are negligibly interacting. The isotropic parameters, giso and A150, calculated using the second-order Zeeman correction, are 1.972 and 97 G, respectively. These values are in the range typical for VO2+ square-pyramidal complexes. More detailed relationships between the isotropic parameters of square-pyramidal VO2+ complexes and the atoms in the first coordination sphere (N, S, and/or 0) have been suggested.“62 Compilations of isotropic parameters for V02+ complexes with 04, S4, S202, N202, and N4 show, in most cases, an approximately linear relationship between the giso and Aiso . values. For an N252 first-coordination sphere, the giso and A150 values are predicted from this relationship to be approximately 1.979 and 92 G, respectively, similar but nevertheless different from those for 1. One of the few examples of a VO2+ complex with an N2S2 first-coordination sphere, VO(SCH2CH(NH2)CO2— CH3)2,63~64 has isotropic parameters that also do not agree with those predicted by the above relationship. [VO]2+ complexes with minor distortions from square-pyramidal to trigonal- bipyramidal geometry also show deviation from this linear relationship.65 It is unclear whether this behavior is due to the particular ligands employed or S2N2 coordination in general; that it is likely the latter is suggested by 34 GHz EPR studies of 12 VOS2N2 complexes (unspecified structures) that indicate that there is no relationship between the giso and Aiso values.66 The relatively small bite distance and angle of the pyt‘ ligand should have some noticeable effect on the M/pyt bonds compared with metal complexes containing bidentate ligands with larger bites. The degree of M—L covalency in the S2N2 complexes can be estimated from the EPR parameters. The (61) Yen, T. F.; Boucher, L. 1.; Dickie, l. P.; Tynan, E. C.; Vaughan, G. B. J. Inst. Pet. 1969, 55, 87. (62) Dickson, F. E.; Kunesh, C. .I.; McGinnis, E. L.; Petrakis, L. Anal. Chem. 1969, 44, 978. (63) Sakurai, H.; Taira, Z.-E.; Sakai, N. Inorg. Chim. Acta 1988, 151, 85. (64) Sakurai, H.; Hamada, Y.; Shimomura, S.; Yamashita, S. Inorg. Chim. Acta 1980, 46, L119. (65) Shiro, M.; Fernando, Q. Anal. Chem. 1971, 43, 1222. (66) Malhotra, V. M.; Buckmaster, H. A. Fuel 1985, 64, 335. Inorganic Chemistry, Vol. 34, No. 23, 1995 5751 Table 10. Principal Ions and their Intensities in EIMS Examination of [V202(pyt)4l (1) and [VNa(pyt)4(THF)2l (2) species 1 (M = V0)“ 2 (M = V)“ A na 380 (100) B 287 (100) 271 (80) C 254 (4) 238, 239 (35) D 208, 209 (10) 192, 193 (22) E 223 (38) 207 (5) F 177 (47) 161 (14) G 145 (13) 129 (5) H 99(2) 83 (9) ‘1 M/z (relative intensity). na = not applicable. Fermi contact term K (the higher the value of K, the less covalent character in the M—L bonds) can be related to the gist) and Am, values and the dipolar term P through eq 7.67 Using the P value K = [Am + (2.002 — giso)P]/P (7) of +117 G for VO(8-mercaptoquinoline)2,68 the K values are 0.86 for 1 and 0.69 for VO(SCH2CH(NH2)CO2CH3)2, suggesting a significantly higher degree of covalency in the latter. Figure 5b shows the X—band EPR spectrum at 77 K of a frozen THF solution of 1. The spectrum is a typical V02+ anisotropic spectrum, exhibiting only partial resolution of the expected 16 lines of an axial system. The spectral parameters are: 3“ = 1.983, g)_ = 1.966, A“ = 181 G, and A) = 54 G. These values are typical for V02+ complexes with N, S, and/or 0 in the first coordination sphere. In comparison with other N2S2 complexes, they are very close to those of VO(8- mercaptoquinoline)2,68 but show a much lower g1) and much higher A“ than VO(SCH2CH—NH2COOCH3)2.63‘64 The room-temperature X-band EPR spectrum of complex 3 in toluene solution shows a very broad signal centered in the g z 2 region. In frozen toluene solution at 115 K (Figure 5c), additional broad and ill-defined features become apparent at higher g values. There is some faint indication of hyperfine structure in the upfield signals. The signal is clearly not that of a S = 1/2 spin system and in that respect is consistent with a S = 3/2 system in rhombic symmetry, as expected for 3, but little other useful information can be extracted. Mass Spectrometry. Complexes 1 and 2 have been studied by electron ionization mass spectrometry (EIMS) to determine gas-phase fragmentation pathways and to probe possible C—S bond cleavage reactions. Figure 6 shows the principal fragments for 1 (M = V0), and 2 (M = V). Table 10 lists the m/z and relative intensities for structures A—H in Figure 6, normalized to the parent ion of the complex. Both complexes have very similar fragmentation patterns; smaller ions are formed from the loss of S, pyridine, or pyt“ during the fragmentation process. For 2, ML3+ is the highest intensity ion, which is not the expected ion for the formula VNa(pyt)4(THF)2. This suggests that Na(pyt) and THF are readily lost from 2, as also suggested by its behavior in CH2Cl2 described earlier. For 1, ML2+ is the highest intensity ion, which also is not expected from the dinuclear structure of 1 in the solid state. Dissociation into mononuclear units is obviously facile under these conditions. The next highest, intensity ion for 2 is the ML2+ fragment, which is the highest intensity ion for 1. Other fragments of both complexes are similar, differing only by M = V or V0. (67) Boucher, L. J.; Tynan, E. C.; Yen, T. F. In Electron Spin Resonance of Metal Complexes, Proceedings; Yen, T. F., Eds.; Plenum Press: New York, 1969. (68) Jezierski, A.; Jezowska—Trzebiatowska, B. Bull. Pol. Acad. Sci, Chem. 1985, 33, 85. 5752 Inorganic Chemistry, Vol. 34, No. 23, I995 E\”0 7 \@ ON—M + fi+ G Figure 6. EIMS fragmentation patterns for complexes 1 and 2. Fragment m/z values and relative intensities are listed in Table 10. The intensities of these fragments, however, differ markedly depending on whether they are from 1 or 2. For example, 1 exhibits a prominent ion with only one ligand (structure F). The analogous fragment for 2 is not nearly as intense. Frag- ments C and D for 2 are reasonably intense, but fragments E and F are not. For 1, the relative intensities of these fragments are reversed; fragments C and D are not intense, while fragments E and F are. Thus, complexes 1 and 2 show noticeable differences in the fragmentation behaviors that can reasonably be attributed to the main difference between the complexes, namely, the presence of a multiply-bonded [VO] unit. Its presence appears to facilitate/stabilize the smaller fragments E and F whereas these are too unstable and short—lived for 2. This suggests that the oxidation state of the metal center and strong ancillary ligation can be important in controlling the fragmenta- tion pathways of 1 and 2; similar effects have been seen in the fragmentation pathways of other vanadium complexes studied by EIMS.69~70 (69) MacDonald. C. 6.; Shannon, J. S. Aust. J. Chem. 1986, 19, 1545. Reynolds et al. The above study was undertaken with the belief that the results might be of utility as a model system for some of the high-energy reactions occurring during hydrodemetalation (HDM)-hydrodesulfurization (HDS) petroleum processes. Clearly, under normal ionization conditions, both compounds 1 and 2 show one or more fragmentation pathways involving C-S bond cleavage, as previously detected in [V(SBu‘)4] where the C-S bonds are more easily cleaved.17 For example, [VO(C5H4NS)2]+ (B) gives fragment ions assigned to [VO(C5H4— NS)(C5H4N)I+ (C), [V0(C5H4N)2l+ (E), and [V0(C5H4NS)S]+ (D) that appear to form through a one- or two-step process involving C—S bond cleavage. The ion [V(C5H4NS)3]+ re— sponds similarly under the same conditions, producing [V(C5H4- NS)2]+ (B) which gives [V(C51-I4NS)(C51-I4N)]+ (C), [V(C5H4- N)2]+ (E), and [V(C5H4NS)S]+ (D) via the same C-S bond cleavage processes. Extrapolating the gas-phase fragmentations observed in this study to the similarly high-energy conditions of HDS/HDM provides a credible pathway for the conversion of (i) molecular V/organosulfur impurities in crude oils into V/S polymer deposits (V233/V384) and/or (ii) the binding of free organosulfur molecules onto the surface V atoms of a V253/ V384 solid followed by V-catalyzed C—S bond cleavage providing new S atoms for the growing V283/V3S4 phase. Acknowledgment. The work at Lawrence Livermore Na— tional Laboratory was performed under the auspices of the US Department of Energy under Contract No. W-7405-ENG-48. Work at Indiana University was supported by the Office of Basic Energy Sciences, Division of Chemical Sciences, U.S. Depart— ment of Energy, Grant DE-FG02—87ER13702. We thank Norman S. Dean for assistance with EPR spectroscopy. Supporting Information Available: Text detailing the structure refinement, figures showing the basic structure and unit cell, and complete listings of atomic coordinates, isotropic and anisotropic thermal parameters, bond distances and angles (40 pages). Ordering information is given on any current masthead page. Listings of observed and calculated structure factors for 1—4 are available from the author on request. Complete MSC structure reports (Nos. 91014 for 1, 91150 for 2, 92011 for 3, and 89020 for 4) are available on request from the Indiana University Chemistry Library. IC9503702 (70) Charalambous, J. J. In Mass Spectrometry of Metal Compounds; Charalambous, 1., Ed.; Butterworths: London, 1975; pp 45-60. ...
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