Salt Metathesis and Direct Reduction Reactions Leading to Group 3

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Organometallics 2010, 29, 2610–2615 DOI: 10.1021/om1003144

Salt Metathesis and Direct Reduction Reactions Leading to Group 3 Metal Complexes with a N,N 0 -Bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene Ligand and Their Solid-State Structures Tarun K. Panda, Hiroshi Kaneko, Kuntal Pal, Hayato Tsurugi, and Kazushi Mashima* Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan Received April 19, 2010

We successfully prepared and characterized a wide variety of group 3 metal complexes containing a dianionic or monoanionic glyoxal-based N,N0 -bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene (DAD) ligand using a salt metathesis reaction of group 3 metal trichlorides with the dipotassium salt of the DAD ligand or a direct reduction of the DAD ligand with 1:1 mixture of group 3 metal powders and group 3 metal halides. The DAD ligand coordinated to group 3 metal in a σ2-enediamide manner for dimeric complexes of yttrium, ytterbium, and europium complexes, whereas σ2,π-enediamide coordination was observed for the lanthanum complex, due to the different ionic radii of the metal atoms. The reaction of the dipotassium salt of the DAD ligand and ScCl3(thf)3 gave a monomeric scandium complex with the monoanionic DAD ligand.

Introduction

Chart 1. Coordination Modes of 1,4-Diaza-1,3-butadiene Ligands to Transition Metals

1,4-Diaza-1,3-butadiene (DAD) ligands are an important class of redox-active ligands that are able to tune the electronic behavior of coordination compounds throughout the periodic table.1 The coordination modes of DAD ligands are flexible, and all possible modes are described in Chart 1, showing that the ligands coordinate to metals in neutral, monoanionic, and dianionic modes. Although the dianionic DAD ligands preferentially coordinate to early transition metals and alkaline metals in σ2- and σ2,π-coordination modes,2-4 in many cases the DAD ligands coordinate to group 3 metal atoms as a σ2-monoanion,5 and, in addition, both monoanionic and dianionic coordination modes were observed for alkaline-earth metal, group 12, and group 13 metal complexes. 6,7 Recently, several research groups *Corresponding author. E-mail: [email protected]. Fax: 81-6-6850-6245. (1) (a) van Koten, G.; Vrieze, K. Adv. Organomet. Chem. 1982, 21, 151. (b) Vrieze, K. J. Organomet. Chem. 1986, 300, 307. (2) (a) Scholz, J.; Richter, B.; Goddard, R.; Kruger, C. Chem. Ber. 1993, 126, 57. (b) Lorenz, V.; Thiele, K.-H.; Neumuller, B. Z. Anorg. Allg. Chem. 1994, 620, 691. (c) Gardiner, M. G.; Hanson, G. R.; Henderson, M. J.; Lee, F. C.; Raston, C. L. Inorg. Chem. 1994, 33, 2456. (d) Haaf, M.; Schmiedl, A.; Schmedake, T. A.; Powell, D. R.; Millevolte, A. J.; Denk, M.; West, R. J. Am. Chem. Soc. 1998, 120, 12714. (e) Schmidt, E. S.; Jockisch, A.; Schmidbaur, H. J. Am. Chem. Soc. 1999, 121, 9758. (f) Fedushkin, I. L.; Khvoinova, N. M.; Skatova, A. A.; Fukin, G. K. Angew. Chem., Int. Ed. 2003, 42, 5223. (g) Fedushkin, I. L.; Skatova, A. A.; Cherkasov, V. K.; Chudakova, V. A.; Dechert, S.; Hummert, M.; Schumann, H. Chem. Eur. J. 2003, 9, 5778. (h) Fedushkin, I. L.; Skatova, A. A.; Chudakova, V. A.; Fukin, G. K.; Dechert, S.; Schumann, H. Eur. J. Inorg. Chem. 2003, 3336. (i) Fedushkin, I. L.; Skatova, A. A.; Hummert, M.; Schumann, H. Eur. J. Inorg. Chem. 2005, 1601. (j) Fedushkin, I. L.; Morozov, A. G.; Rassadin, O. V.; Fukin, G. K. Chem. Eur. J. 2005, 11, 5749. (k) Fedushkin, I. L.; Skatova, A. A.; Fukin, G. K.; Hummert, M.; Schumann, H. Eur. J. Inorg. Chem. 2005, 2332. (l) Fedushkin, I. L.; Lukoyanov, A. N.; Hummert, M.; Schumann, H. Z. Anorg. Allg. Chem. 2008, 634, 357. (m) Liu, Y.; Yang, P.; Yu, J.; Yang, X.-J.; Zhang, J. D.; Chen, Z.; Schaefer, H. F.; Wu, B. Organometallics 2008, 27, 5830. pubs.acs.org/Organometallics

Published on Web 05/14/2010

reported the preparation of non-Cp group 3 metal complexes with DAD ligands, in which the ligands coordinated to the central metals as σ2,π-dianions.8,9 Because of the limited examples of group 3 metal complexes with dianionic glyoxal-based DAD ligands, we attempted to prepare group 3 metal complexes with a dianionic glyoxal-based DAD ligand to clarify the effect on the DAD ligand coordination mode due to the different ionic radii of the metal atoms. Herein we report complexation of the dianionic glyoxal-based DAD ligand to various group 3 metals and reveal the coordination mode of the DAD ligand to group 3 metals based on X-ray crystallography. We used two different synthetic methodologies: a salt metathesis reaction of group 3 metal trichlorides with the dipotassium salt of the DAD ligand and a direct reduction of the DAD ligand with 1:1 mixture of group 3 metal powders and group 3 metal halides, leading to group 3 metal complexes with DAD and halide ligands. r 2010 American Chemical Society

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Organometallics, Vol. 29, No. 11, 2010

Results and Discussion The reaction of 2 equiv of elemental potassium with N,N0 -bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene ligand (1) in THF produced the corresponding dipotassium salt of 2 (eq 1), which was highly air- and moisture-sensitive and a useful reagent for the synthesis of group 3 metal complexes. Compound 2 was characterized by spectroscopic data, combustion analysis, and single-crystal X-ray crystallography (Figure S1). The solid-state structure of 1 was basically similar to the dilithium salt of N,N0 -bis(4-methylphenyl)-1,4-diaza2,3-diphenyl-1,3-butadiene,2a except for the presence of the bridging thf molecule. In the 1H NMR spectrum of 2 in THF-d8, a broad singlet was observed at δ 4.00, assignable to olefinic protons of the ligand backbone, and a broad multiplet signal and broad resonance appeared at δ 3.46 and 1.20, respectively, due to the isopropyl groups of the ligand.

When in situ generated 2 was reacted with MCl3(thf)3 (M = Y, Yb) or LaCl3 in THF, the salt metathesis reaction proceeded to afford chloride-bridged dinuclear complexes 3-5 in good yield after the elimination of potassium chloride (Scheme 1). All complexes 3-5 were isolated as air- and moisturesensitive crystals. The molecular structures are shown in Figure 1 for 3 and Figure 2 for 5 (Figure S2 for 4 in Supporting Information). Each complex has a dimeric structure (3) (a) Latesky, S. L.; McMullen, A. K.; Niccolai, G. P.; Rothwell, I. P. Organometallics 1985, 4, 1986. (b) Borcarsly, J. R.; Floriani, C.; ChiesiVilla, A.; Guastini, C. Organometallics 1986, 5, 2380. (c) Chamberlain, L. R.; Durfee, L. D.; Fanwick, P. E.; Kobringer, L. M.; Latesky, S. L.; McMullen, A. K.; Steffey, B. D.; Rothwell, I. P.; Folting, K.; Huffmann, J. C. J. Am. Chem. Soc. 1987, 109, 6068. (d) Hessen, B.; Bol, J. E.; de Boer, J. L.; Meetsma, A.; Teuben, J. H. J. Chem. Soc., Chem. Commun. 1989, 1276. (e) tom Dieck, H.; Rieger, H. J.; Fendesak, G. Inorg. Chim. Acta 1990, 177, 191. (f) Scholz, J.; Dlikan, M.; Str€ohl, D.; Dietrich, A.; Schumann, H.; Thiele, K.-H. Chem. Ber. 1990, 123, 2279. (g) Scholz, J.; Dietrich, A.; Schumann, H.; Thiele, K.-H. Chem. Ber. 1991, 124, 1035. (h) Berg, F. J.; Peterson, J. L. Organometallics 1991, 10, 1599. (i) Berg, F. J.; Petersen, J. L. Tetrahedron 1992, 48, 4749. (j) Bol, J. E.; Hessen, B.; Teuben, J. H.; Smeets, W. J. J.; Spek, A. L. Organometallics 1992, 11, 1981. (k) Herrmann, W. A.; Denk, M.; Scherer, W.; Klingan, F.-R. J. Organomet. Chem. 1993, 444, C21. (l) Richter, B.; Scholz, J.; Sieler, J.; Thiele, K.-H. Angew. Chem., Int. Ed. Engl. 1995, 34, 2649. (m) Aoyagi, K.; Gantzel, P. K.; Kalai, K.; Tilley, T. D. Organometallics 1996, 15, 923. (n) Scholz, J.; G€orls, H. Inorg. Chem. 1996, 35, 4378. (o) Aoyagi, K.; Gantzel, P. K.; Tilley, D. T. Polyhedron 1996, 15, 4299. (p) Kloppenburg, L.; Petersen, J. L. Organometallics 1997, 16, 3548. (q) Spaniel, T.; G€ orls, H.; Scholz, J. Angew. Chem., Int. Ed. 1998, 37, 1862. (r) Kawaguchi, H.; Yamamoto, Y.; Asaoka, K.; Tatsumi, K. Organometallics 1998, 17, 4380. (s) Amor, F.; Gomez-Sal, P.; Royo, P.; Okuda, J. Organometallics 2000, 19, 5168. (t) Galindo, A.; Ienco, A.; Mealli, C. New J. Chem. 2000, 24, 73. (u) Daff, P. J.; Etienne, M.; Donnadieu, B.; Knottenbelt, S. Z.; McGrady, J. E. J. Am. Chem. Soc. 2002, 124, 3818. (v) Stanciu, C.; Jones, M. E.; Fanwick, P. E.; Abu-Omar, M. M. J. Am. Chem. Soc. 2007, 129, 12400. (w) Kreisel, K. A.; Yap, G. P. A.; Theopold, K. H. Inorg. Chem. 2008, 47, 5293. (x) Ghosh, M.; Sproules, S.; Weyherm€uller, T.; Wieghardt, K. Inorg. Chem. 2008, 47, 5963. (y) Ghosh, M.; Weyhermuller, T.; Wieghardt, K. Dalton Trans. 2008, 5149. (4) (a) Mashima, K.; Matsuo, Y.; Tani, K. Chem. Lett. 1997, 767. (b) Mashima, K.; Matsuo, Y.; Tani, K. Organometallics 1999, 18, 1471. (c) Matsuo, Y.; Mashima, K.; Tani, K. Angew. Chem., Int. Ed. 2001, 40, 960. (d) Mashima, K.; Nakamura, A. J. Organomet. Chem. 2001, 621, 224. (e) Matsuo, Y.; Mashima, K.; Tani, K. Organometallics 2002, 21, 138. (f) Tsurugi, H.; Ohno, T.; Yamagata, T.; Mashima, K. Organometallics 2006, 25, 3179. (g) Tsurugi, H.; Ohno, T.; Kanayama, T.; Arteaga-M€ uller, R. A.; Mashima, K. Organometallics 2009, 28, 1950–1960.

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bearing the DAD ligand, two thf molecules, and two bridged chloride atoms, with a distorted octahedral geometry. One of the two nitrogen atoms of the DAD ligand and one solvated thf molecule occupy the apical position in each complex. The mean M-N distance (Y-N 2.24, La-N 2.34, and Yb-N 2.21 A˚) is close to that of the M-N covalent bond.10 In contrast to the salt-contacted DAD yttrium compound, (DAD)Y(THF)2(μ-Cl)2Li(THF)2, reported by Trifonov et al.,8b reaction of lanthanide trihalides and dipotassium salt of the DAD ligand gave chloride-bridged dinuclear complexes without incorporation of an alkaline metal salt. Notably, the structures of 3 and 4 are different from that of 5, although all of these complexes have a five-membered diazametallacyclopentene structure. Complexes 3 and 4 possess an almost planar metallacycle, whereas in 5 the metallacycle is folded. The dihedral angle between the N1-M-N2 and N1-C1-C2-N2 planes of 5 is 130.1°, and the distances between the lanthanum atom and the C1dC2 moiety are short enough for contact, as in the σ2,π-enediamide mode (La-C1 2.795(3) A˚; La-C2 2.781(4) A˚).8 The geometries around the metallacycle for 3-5 are consistent with dianionic DAD ligation, in which two N-C bonds are elongated (mean N-C distance: 1.41 A˚ for 3; 1.41 A˚ for 4; 1.40 A˚ for 5) and the C-C bond is shortened (1.35 A˚ for 3; 1.34 A˚ for 4; 1.39 A˚ for 5), i.e., a long-short-long sequence, compared to the neutral DAD ligands.2-4 Such a different coordination mode of the DAD ligand to group 3 metal atoms is presumably due to the different ionic radii of the central element; the larger ionic radius (5) (a) Cloke, F. G. N.; de Lemos, H. C.; Sameh, A. A. J. Chem. Soc., Chem. Commun. 1986, 1344. (b) Recknagel, A.; Noltemeyer, M.; Edelmann, F. T. J. Organomet. Chem. 1991, 410, 53. (c) Bochkarev, M. N.; Trifonov, A. A.; Cloke, F. G. N.; Dalby, C. I.; Matsunaga, P. T.; Andersen, R. A.; Schumann, H.; Loebel, J.; Hemling, H. J. Organomet. Chem. 1995, 486, 177. (d) Scholz, A.; Thiele, K.-H.; Scholz, J.; Weimann, R. J. Organomet. Chem. 1995, 501, 195. (e) Trifonov, A. A.; Kirillov, E. N.; Bochkarev, M. N.; Schumann, H.; Muehle, S. Russ. Chem. Bull. 1999, 48, 382. (f) Trifonov, A. A.; Kirillov, E. N.; Dechert, S.; Schumann, H.; Bochkarev, M. N. Eur. J. Inorg. Chem. 2001, 2509. (g) Trifonov, A. A.; Kurskii, Y. A.; Bochkarev, M. N.; Muehle, S.; Dechert, S.; Schumann, H. Russ. Chem. Bull. 2003, 52, 601. (h) Trifonov, A. A.; Fedorova, E. A.; Ikorskii, V. N.; Dechert, S.; Schumann, H.; Bochkarev, M. N. Eur. J. Inorg. Chem. 2005, 2812. (i) Moore, J. A.; Cowley, A. H.; Gordon, J. C. Organometallics 2006, 25, 5207. (j) Walter, M. D.; Berg, D. J.; Andersen, R. A. Organometallics 2007, 26, 2296. (k) Cui, P.; Chen, Y.; Wang, G.; Li, G.; Xia, W. Organometallics 2008, 27, 4013. For lanthanide complexes having μ-dianionic DAD ligands: (l) Trifonov, A. A.; Zakharov, L. N.; Bochkarev, M. N.; Struchkov, Y. T. Russ. Chem. Bull. 1994, 43, 148. (m) G€orls, H.; Neum€uller, B.; Scholz, A.; Scholz, J. Angew. Chem., Int. Ed. Engl. 1995, 34, 673. (n) Scholz, J.; G€orls, H.; Schumann, H.; Weimann, R. Organometallics 2001, 20, 4394. (o) Trifonov, A. A.; Fedorova, E. A.; Fukin, G. K.; Baranov, E. V.; Druzhkov, N. O.; Bochkarev, M. N. Chem. Eur. J. 2006, 12, 2752. (6) (a) Richter, S.; Daul, C.; Aelewsky, A. V. Inorg. Chem. 1976, 15, 943. (b) Geoffrey, F.; Cloke, N.; Dalby, C. I.; Henderson, M. J.; Hitchcock, P. B.; Kennard, C. H.; Lamb, R. N.; Raston, C. L. J. Chem. Soc., Chem. Commun. 1990, 1394. (c) Henderson, M. J.; Kennard, C. H. L.; Raston, C. L.; Smith, G. J. Chem. Soc., Chem. Commun. 1990, 1203. (d) Kaim, W.; Matheis, W. J. Chem. Soc., Chem. Commun. 1991, 597. (e) Gardiner, M. G.; Hanson, G. R.; Henderson, M. J.; Lee, F. C.; Raston, C. L. Inorg. Chem. 1994, 33, 2456. (f) Clyburne, J. A. C.; Culp, R. D.; Kamepalli, S.; Cowley, A. H.; Decken, A. Inorg. Chem. 1996, 35, 6651. (g) Rijnberg, E.; Boersma, J.; Jastrzebski, J. T. B. H.; Lakin, M. T.; Spek, A. L.; van Koten, G. Organometallics 1997, 16, 3158. (h) Rijnberg, E.; Richter, B.; Thiele, K.-H.; Boersma, J.; Veldman, N.; Spek, A. L.; van Koten, G. Inorg. Chem. 1998, 37, 56. (i) Mair, F. S.; Manning, R.; Pritchard, R. G.; Warren, J. E. Chem. Commun. 2001, 1136. (j) Baker, R. J.; Davis, A. J.; Jones, C.; Kloth, M. J. Organomet. Chem. 2002, 656, 203. (k) Baker, R. J.; Farley, R. D.; Jones, C.; Kloth, M.; Murphy, D. M. J. Chem. Soc., Dalton Trans. 2002, 3844. (l) Baker, R. J.; Jones, C.; Kloth, M.; Mills, D. P. New J. Chem. 2004, 28, 207. (m) Baker, R. J.; Jones, C.; Murphy, D. M. Chem. Commun. 2005, 1339. (n) Baker, R. J.; Jones, C.; Kloth, M. Dalton Trans. 2005, 2106. (o) Yang, X.-J.; Yu, J.; Liu, Y.; Xie, Y.; Schaefer, H. F.; Liang, Y.; Wu, B. Chem. Commun. 2007, 2363. (p) Jones, C.; Stasch, A.; Woodul, W. D. Chem. Commun. 2009, 113.

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Figure 1. Molecular structure of yttrium complex 3. All hydrogen atoms and solvent molecules are omitted for clarity. Selected bond distances (A˚) and angles (deg): Y1-N1 2.254(3), Y1-N2 2.232(3), Y-Cl1 2.7695(11), Y-Cl1* 2.7300(14), Y1-O1 2.391(3), Y-O2 2.369(2), N1-C1 1.416(4), N2-C2 1.419(5), C1-C2 1.352(5), N1-Y1-N2 77.12(10), N1-Y1-O1 86.76(10), N1-Y1-O2 99.72(10), N1-Y1-Cl1 177.31(8), N2-Y1-O1 162.39(10). Scheme 1

of the lanthanum atom favored the σ2,π-enediamide coordination of 5. Upon treating 2 with ScCl3(thf)3 in a similar manner, another type of complex (6) was obtained as red crystals (eq 2). In sharp contrast to the diamagnetic complex 5, no resonance was observed in the 1H NMR spectrum of 6. The room-temperature solution EPR spectrum of 6 displayed a 14-line hyperfine resonance (g=2.003) (Figure 3a). Since the DAD ligand-localized radical was observed as seven hyperfine lines,6a,e,g,h the spectrum was simulated by taking into account the hyperfine coupling with virtually identical value (about 5 G) for one scandium atom, two equivalent nitrogen atoms, and two equivalent hydrogen atoms of the DAD ligand (Figure 3b). The g value was close to free organic radicals, indicating that the unpaired electron in 6 might be localized mainly at the DAD ligand. The EPR spectrum of the mainly DAD ligand localized radical with small spin density on the metal center was similar to aluminum and gallium complexes.6b,d The molecular structure of 6 is clarified by X-ray

Panda et al.

Figure 2. Molecular structure of lanthanum complex 5. All hydrogen atoms and solvent molecules are omitted for clarity. Selected bond distances (A˚) and angles (deg): La1-N1 2.343(3), La1-N2 2.316(3), La-C1 2.795(3), La-C2 2.781(4), La1-O1 2.604(3), La1-O2 2.599(3), La1-Cl1 2.8616(10), La1-Cl1* 2.9299(12), N1-C1 1.404(4), N2-C2 1.404(4), C1-C2 1.385(5), N1-La1N2 77.81(10), N1-La1-O1 92.40(9), N1-La1-O2 108.99(9), N1-La1-Cl1 94.87(7), N1-La1-Cl1* 171.05(7), N2-La1O1 169.36(9).

crystallography (Figure 4). The geometry around the scandium atom can best be described as a slightly distorted octahedron, where two chlorides occupy the apical position and the two oxygen atoms of the thf molecules and two nitrogen atoms of the DAD ligand are in a square plane. The distances of two C-N and one C-C bond are significantly different from those of the other group 3 metal complexes 3-5, but are identical to the previously reported group 3 metal complexes with monoanionic DAD ligands.5b-e,g-k The shortened C-N bond lengths (1.3380(16) and 1.3373(16) A˚) and elongated C-C bond length (1.3986(17) A˚) compared with those of 3-5 are consistent with the monoanionic radical character of the DAD ligand.

(7) Acenaphthene-based DAD complexes: (a) Fedushkin, I. L.; Skatova, A. A.; Chudakova, V. A.; Fukin, G. K.; Dechert, S.; Schumann, H. Eur. J. Inorg. Chem. 2003, 3336. (b) Fedushkin, I. L.; Khvoinova, N. M.; Skatova, A. A.; Fukin, G. K. Angew. Chem., Int. Ed. 2003, 42, 5223. (c) Fedushkin, I. L.; Skatova, A. A.; Chudakova, V. A.; Khvoinova, N. M.; Baurin, A. Y.; Dechert, S.; Hummert, M.; Schumann, H. Organometallics 2004, 23, 3714. (d) Feduchkin, I. L.; Khvoinova, N. M.; Baurin, A. Y.; Fukin, G. K.; Cherkasov, V. K.; Bubnov, M. P. Inorg. Chem. 2004, 43, 7807. (e) Fedushkin, I. L.; Chudakova, V. A.; Skatova, A. A.; Khvoinova, N. M.; Kurskii, Y. A.; Glukhova, T. A.; Fukin, G. K.; Dechert, S.; Hummert, M.; Schumann, H. Z. Anorg. Allg. Chem. 2004, 630, 501. (f) Fedushkin, I. L.; Skatova, A. A.; Hummert, M.; Schumann, H. Eur. J. Inorg. Chem. 2005, 1601. (g) Fedushkin, I. L.; Chudakova, V. A.; Skatova, A. A.; Fukin, G. K. Heteroat. Chem. 2005, 16, 663. (h) Schumann, H.; Hummert, M.; Lukoyanov, A. N.; Fedushkin, I. L. Organometallics 2005, 24, 3891. (i) Lukoyanov, A. N.; Feduchkin, I. L.; Schumann, H.; Hummert, M. Z. Anorg. Allg. Chem. 2006, 632, 1471. (j) Fedushkin, I. L.; Makarov., V. M.; Rosenthal, E. C. E.; Fukin, G. K. Eur. J. Inorg. Chem. 2006, 827. (k) Fedushkin, I. L.; Hummert, M.; Schumann, H. Eur. J. Inorg. Chem. 2006, 3266. (l) Schumann, H.; Hummert, M.; Lukoyanov, A. N.; Fedushkin, I. L. Chem. Eur. J. 2007, 13, 4216. (m) Feduchkin, I. L.; Skatova, A. A.; Eremenko, O. V.; Hummert, M.; Schumann, H. Z. Anorg. Allg. Chem. 2007, 633, 1739. Fedushkin, I. L.; Skatova, A. A.; Ketkov, S. Y.; Eremenko, O. V.; Piskunov, A. V.; Fukin, G. K. Angew. Chem., Int. Ed. 2007, 46, 4302. (n) Fedushkin, I. L.; Tishkina, A. N.; Fukin, G. K.; Hummert, M.; Schumann, H. Eur. J. Inorg. Chem. 2008, 483. (o) Fedushkin, I. L.; Lukoyanov, A. N.; Hummert, M.; Schumann, H. Z. Anorg. Allg. Chem. 2008, 634, 357. (p) Feduchkin, I. L.; Morozov, A. G.; Hummert, M.; Schumann, H. Eur. J. Inorg. Chem. 2008, 1584. (q) Fedushkin, I. L.; Nikipelov, A. S.; Skatova, A. A.; Maslova, O. V.; Lukoyanov, A. N.; Fukin, G. K.; Cherkasov, A. V. Eur. J. Inorg. Chem. 2009, 3742. (r) Fedushkin, I. L.; Morozov, A. G.; Chudakova, V. A.; Fukin, G. K.; Cherkasov, V. K. Eur. J. Inorg. Chem. 2009, 4995. (s) Fedushkin, I. L.; Eremenko, O. V.; Skatova, A. A.; Piskunov, A. V.; Fukin, G. K.; Ketkov, S. Y.; Irran, E.; Schumann, H. Organometallics 2009, 28, 3863.

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Figure 4. Molecular structure of scandium complex 6. All hydrogen atoms are omitted for clarity. Selected bond distances (A˚) and angles (deg): Sc1-N1 2.2259(12), Sc1-N2 2.2245(11), Sc1-O1 2.2236(11), Sc1-O2 2.2246(10), Sc1-Cl1 2.4336(12), Sc1-Cl2 2.4416(12), N1-C1 1.3380(16), N2-C2 1.3373(16), C1; C2 1.3986(17), N1-Sc1-N2 74.78(4), N1-Sc1-O1 167.58(4), N1-Sc1-O2 91.82(4), N1-Sc1-Cl1 96.57(3), N1-Sc1-Cl2 97.01(3), N2-Sc1-O1 92.80(4), N2-Sc1-O2 166.52(4), Cl1Sc1-Cl2 163.751(16).

Figure 3. EPR spectrum of (DAD)ScCl2(thf)2 (6) in toluene at 298 K: (a) experimental; (b) simulated for 1 45Sc, 2 14N, and 2 1H atoms with 5 G hyperfine coupling.

Several groups recently reported the direct reaction of the DAD ligand by group 3 metal vapor to form bis- or tris(DAD) metal complexes, in which the DAD ligands were coordinated to the metal center as monoanions or dianions.5a,11 Although we examined the reaction of finely divided yttrium, lanthanum, and ytterbium metal powders with the DAD ligand, direct metalation of the DAD ligand was not observed. Jones et al. reported a preparation of aluminum complexes with the DAD ligand from a mixture of aluminum metal powders, AlI3, and the DAD ligand.6k This reaction prompted us to use a mixture of yttrium metal powders, YCl3(thf)3, and the DAD ligand to synthesize a yttrium complex without preactivation of the DAD ligand by alkaline metals. The chloride-bridged yttrium complex 3 was formed in good yield under the reaction conditions (Scheme 2). (8) (a) Trifonov, A. A.; Borovkov, I. A.; Fedorova, E. A.; Fukin, G. K.; Larionova, J.; Druzhkov, N. O.; Cherkasov, V. K. Chem. Eur. J. 2007, 13, 4981. (b) Mahrova, T. V.; Fukin, G. K.; Cherkasov, A. V.; Trifonov, A. A.; Ajellal, N.; Carpentier, J.-F. Inorg. Chem. 2009, 48, 4258. (9) For group 3 metal complexes with acenaphthene-based R-diimine ligands: (a) Schumann, H.; Hummert, M.; Lukoyanov, A. N.; Chudakova, V. A.; Fedushkin, I. L. Z. Naturforsch. 2007, 62b, 1107. (b) Vasudevan, K.; Cowley, A. H. Chem. Commun. 2007, 3464. (c) Fedushkin, I. L.; Maslova, O. V.; Baranov, E. V.; Shavyrin, A. S. Inorg. Chem. 2009, 48, 2355. (d) Fedushkin, I. L.; Maslova, O. V.; Hummert, M.; Schumann, H. Inorg. Chem. 2010, 49, 2901. (10) (a) Aspinall, H. C.; Bradley, D. C.; Hursthouse, M. B.; Sales, K. D.; Walker, N. P. C.; Hussain, B. J. Chem. Soc., Dalton Trans. 1989, 623. (b) Sesterhausen, M.; Hartmann, M.; Pfitzner, A.; Schwarz, W. Z. Anorg. Allg. Chem. 1995, 621, 837. (c) Evans, W. J.; Ansari, M. A.; Ziller, J. W.; Khan, S. I. Inorg. Chem. 1996, 35, 5435. (d) Collin, J.; Giuseppone, N.; Jaber, N.; Domingos, A.; Maria, L.; Santos, I. J. Organomet. Chem. 2001, 628, 271. (e) Niemeyer, M. Z. Anorg. Allg. Chem. 2002, 628, 647. (f) Meermann, C.; Gerstberger, G.; Spiegler, M.; T€ornroos, K. W.; Anwander, R. Eur. J. Inorg. Chem. 2008, 2014. (11) Cloke, F. G. N. Chem. Soc. Rev. 1993, 22, 17.

On the basis of the controlled experimental observation that (DAD)YCl3 was not observed in the mixture of the DAD ligand and YCl3(thf)3 and the reported examples of coordination of the neutral DAD ligand to trivalent group 13 metal atoms,6f,j,k we hypothesized that the formation of 3 proceeded through formation of the transient yttrium species (DAD)YCl3, which was then reduced by the yttrium metal powders. Thus, the presence of both group 3 metal powders and group 3 metal halides was necessary for the formation of (DAD)MX complexes (M = group 3 metals, X=halide) via the direct reduction pathway. We previously reported the synthesis of lanthanide complexes of dienes and cyclooctatetraene from the reaction of lanthanide metal powders with dienes and cyclooctatetraene in the presence of iodine.12 Under the reaction conditions, lanthanide metal powders and lanthanide metal halides were present in the reaction mixture. Thus, we examined the reaction of lanthanide metal powders and the DAD ligand in the presence of iodine. Treatment of finely divided europium metal, 0.5 equiv of iodine, and the DAD ligand in THF gave 7 as a green precipitate. Recrystallization of 7 in THF at -35 °C afforded dark green crystals in 50% yield. Similarly, the neodymium complex 8 was isolated as green-yellow crystals (Scheme 3). All of these lanthanide complexes were characterized using X-ray crystallography. The molecular structure of 7 is essentially the same as those of complexes 3 and 4, except for the bridging element, chloride or iodide; however, the quality of the data is not enough due to the highly disordered thf molecules. On the other hand, the neodymium complex 8 is monomeric and the neodymium atom is coordinated by two nitrogen atoms of the DAD ligand, one iodide ligand, and three thf molecules (Figure 5). The long-short-long sequence of the DAD ligand (two C-N distances: 1.419(10) and 1.409(9) A˚, and CdC distance: 1.343(10) A˚) indicates a dianionic coordination mode of the DAD ligand. The folding (12) (a) Mashima, K.; Takaya, H. Tetrahedron Lett. 1989, 30, 3697. (b) Mashima, K.; Sugiyama, H.; Nakamura, A. J. Chem. Soc., Chem. Commun. 1994, 1581. (c) Mashima, K.; Nakayama, Y.; Nakamura, A.; Kanehisa, N.; Kai, Y.; Takaya, H. J. Organomet. Chem. 1994, 473, 85. (d) Mashima, K.; Nakamura, A. J. Chem. Soc., Dalton Trans. 1999, 3899.

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Scheme 2

Scheme 3

Figure 5. Molecular structure of scandium complex 8. All hydrogen atoms are omitted for clarity. Selected bond distances (A˚) and angles (deg): Nd-N1 2.297(6), Nd-N2 2.267(6), Nd-I 3.2448(10), Nd-C1 2.670(8), Nd-C2 2.649(8), Nd-O1 2.487(6), Nd-O2 2.582(5), Nd-O3 2.470(6), N1-C1 1.419(10), C1-C2 1.343(10), C2-N2 1.409(9), N1-Nd-N2 79.3(2), N1-Nd-I 116.30(16), N1-Nd-O1 106.7(2), N1-Nd-O2 154.3(2), N1;NdO3 85.4(2).

angle (121.39°) between the N1-Nd-N2 and N1-C1-C2N2 planes and the distances (2.670(8) A˚ for Nd-C1 and 2.649(8) A˚ for Nd-C2) between the neodymium atom and the C1dC2 moiety of the DAD ligand are in accordance with the σ2,π-enediamide coordination mode, as observed in the dimeric complex 5.2-4 Such a monomeric lanthanide complex with the DAD ligand in σ2,π-enediamide coordination has been found in related complexes, Cp*Yb(DAD)(THF)8a and (DAD)Tm[Ga{N(Ar)CHdCHNAr}](TMEDA).6p In summary, we successfully prepared a wide variety of group 3 metal complexes containing a dianionic or monoanionic DAD ligand using two different synthetic methodologies. A salt metathesis reaction of the dipotassium salt of the DAD ligand with the trichloride of group 3 metals was effective for the formation of several group 3 metal complexes with a monoanionic or dianionic DAD ligand. A second synthetic method, treatment of the DAD ligand with a mixture of group 3 metal powders and group 3 metal halides, produced (DAD)MX complexes (M = group 3 metal, X = halide). The DAD ligand coordinated to the group 3 metal in a σ2-enediamide manner for dimeric complexes of yttrium, ytterbium, and europium complexes, whereas σ2,π-enediamide coordination was observed for the lanthanum complex, due to the different ionic radii of the metal atoms. In addition, a monoanionic radical coordination mode of the DAD ligand was observed for the monomeric scandium complex 6. Direct reduction of various redox-active ligands by a mixture of group 3 metal powders and group 3 metal halides leading to group 3 metal complexes is ongoing in our laboratory.

Experimental Section General Conditions. All manipulations involving air- and moisture-sensitive organometallic compounds were carried

out under argon using the standard Schlenk technique or an argon-filled glovebox. Potassium metal, lanthanide metals, and anhydrous LnCl3 were purchased, and LnCl3(THF)3 (Ln = Y,13 Yb14) and 1,4-diaza-1,3-butadiene ligand 115 were prepared according to the literature procedures. Tetrahydrofuran, pentane, and toluene were dried and deoxygenated twice by distillation over sodium benzophenone ketyl under argon and distilled and dried over CaH2 prior to storage in a glovebox. Benzene-d6, toluene-d8, and THF-d8 were dried over Na/K alloy and stored in a glovebox. 1H NMR (300 MHz, 400 MHz) and 13 C NMR (75 MHz, 100 MHz) spectra were measured on Varian UNITY INOVA-300 and Bruker AVANCEIII-400 spectrometers. The elemental analyses were recorded by using a Perkin-Elmer 2400 at the Faculty of Engineering Science, Osaka University. The EPR spectrum was recorded at 298 K on a Bruker EMX-10/12 spectrometer in toluene. Synthesis of [(DAD)K2(μ-THF)(THF)4] (2). To a 25 mL Schlenk were placed 376 mg (1.0 mmol) of 1 and 80 mg (2.0 mmol) of potassium metal, and 15 mL of THF was added. The color of the solution immediately turned deep red. The solution was stirred for 6 h, and then the solvent was evaporated under reduced pressure to leave an orange oily residue, which was washed with pentane. The pentane was removed and the residue was placed for crystallization from THF/pentane at -35 °C. After one week deep red crystals were obtained (200 mg, 0.245 mmol, 25%). This was performed only once, and for further reaction the in situ preparation of [(DAD) K2(μ-THF)(THF)4] was done without isolation. 1H NMR (THFd8, 300 MHz, 25 °C): δ 7.82 (br, 2H, Ph), 7.09-6.89 (m, 4H, Ph), 4.00 (s, 2H, CH2), 3.62-3.57 (m, THF), 3.46 (sept, 4H, CH), 1.781.71 (m, THF), 1.20 (br, 24H, CH3). Anal. Calcd for C46H76K2N2O5: C, 67.76; H, 9.39; N, 3.43. Found: C, 67.36; H, 9.01; N, 3.27. Synthesis of [(DAD)Y(μ-Cl)(THF)2]2 (3). To a suspension of YCl3(THF)3 (1.0 mmol) in THF (5 mL) was added a solution of freshly prepared 1 (1.0 mmol) in THF (10 mL) at room temperature. The disappearance of the white suspension indicated the initiation of the reaction. The mixture was stirred for 12 h, and then the solvent was evaporated. Toluene (15 mL) was added, and the (13) Wu, J.; Boyle, T. J.; Shreeve, J. L.; Ziller, J. W.; Evans, W. J. Inorg. Chem. 1993, 32, 1130. (14) Deacon, G. B.; Feng, T.; Nickel, S.; Skelton, B. W.; White, A. H. J. Chem. Soc., Chem. Commun. 1993, 1328. (15) (a) Kliegman, J. M.; Barnes, R. K. Tetrahedron 1970, 26, 2555. (b) Kliegman, J. M.; Barnes, R. K. J. Org. Chem. 1970, 35, 3140.

Article insoluble powders were removed by filtration. After evaporation of the solvent, the remaining residue was washed with pentane (10 mL). The resulting powder was recrystallized from THF/ pentane (2:1) in -35 °C to give yellow crystals (500 mg, 0.757 mmol, 75%). 1H NMR (C6D6, 400 MHz, 35 °C): δ 7.22-7.10 (m, 6H, Ph), 5.47 (s, 2H, CH2), 3.67 (br, 4H, CH(CH3)2), 3.67 (br, 8H, R-CH2, THF),1.36 (d, 24H, 3JHH = 4.5 MHz, CH(CH3)2), 1.27 (br, 8H, β-CH2, THF). 13C NMR (C6D6, 75 MHz, 35 °C): δ 152.8 (ipso-C), 143.4 (o-C), 123.4 (Ph), 122.7 (Ph), 112.7 (CHdCH), 69.0 (THF), 28.7 (CH3), 25.6 (CH3). Anal. Calcd for C35H55ClN2O2Y: C, 63.68; H, 8.40; N, 5.37. Found: C, 63.43; H, 8.21; N, 4.98. Compounds 4 and 5 were prepared as described for 3. Synthesis of [(DAD)Yb(μ-Cl)(THF)2]2 (4). Yield: 77%. Anal. Calcd for C35H55ClN2O2Yb: C, 56.48; H, 7.45; N, 3.76. Found: C, 56.32; H, 7.19; N, 3.67. Synthesis of [(DAD)La(μ-Cl)(THF)2]2 (5). Yield: 85%. 1H NMR (C6D6, 300 MHz, 35 °C): δ 7.22-7.01 (m, 6H, Ph), 5.47 (br s, 2H, CH2), 3.60 (br, 4H, CH), 1.33 (d, 12H, CH3, 2J = 4.5 MHz), 1.23 (br, 12H, CH3). 13C NMR (C6D6, 75 MHz, 35 °C): δ 152.8 (ipso-C), 143.4 (o-C), 123.4 (Ph), 122.7 (Ph), 112.7 (CHdCH), 69.0 (THF), 28.7 (CH3), 25.6 (CH3). Anal. Calcd for C35H55ClN2O2La, C, 59.19; H, 7.81; N, 4.99. Found: C, 58.87; H, 7.49; N, 4.82. Synthesis of [(DAD)ScCl2(THF)2] (6). To a suspension of anhydrous ScCl3 (151.5 mg, 1.0 mmol) in THF (5 mL) was added a solution of freshly prepared 1 (1.0 mmol) in THF (10 mL) at room temperature. The reaction mixture was stirred for another 12 h, and then the solvent was evaporated. Toluene (15 mL) was added, and the insoluble powders were removed by filtration. After evaporation of the solvent, the remaining residue was washed with pentane (10 mL). Toluene (15 mL) was introduced, and the compound was extracted through filtration. The resulting powder was recrystallized from THF/pentane (2:1) in -35 °C to give yellow crystals (500 mg, 0.785 mmol, 78%). Anal. Calcd for C34H52Cl2N2O2Sc: C, 64.14; H, 8.23; N, 4.40. Found: C, 63.97; H, 8.17; N, 4.15. Synthesis of [(DAD)Y(μ-Cl)(THF)2]2 (3) from YCl3(thf)3 and Yttrium Metal. To a 20 mL vial containing finely divided yttrium metal (30.0 mg, 0.337 mmol), YCl3(thf)3 (138.8 mg, 0.337 mmol), and 1 (126.9 mg, 0.337 mmol) was added THF (10 mL) at room temperature. The suspension was stirred for 3 days. After removal of insoluble products by filtration, the solvent was evaporated to give a yellow powder (225 mg, 0.175 mmol, 52%). Synthesis of [(DAD)Eu(μ-I)(THF)2]2 (7). To a mixture of finely divided europium metal (149.9 mg, 0.986 mmol) and 1 (371.3 mg, 0.986 mmol, 1.0 equiv) in THF (5.0 mL) was added iodine (124.8 mg, 0.493 mmol, 0.5 equiv) at room temperature. The reaction mixture was stirred for 13 h at room temperature. The color of the suspension turned deep red. After removal of insoluble products by filtration, all volatiles were removed in vacuo to give 7 as a brown powder (793.8 mg, 0.493 mmol, 50% yield). Anal. Calcd for C60H88I2N4O2Eu2: C, 49.53; H, 6.10; N, 3.85. Found: C, 49.79; H, 5.90; N, 3.79. The analytical value was fitted to [(DAD)Eu(μ-I)(THF)]2, and the loss of two thf molecules was due to the dryness of the brown powder of 7. Compound 8 was prepared as described for 7. (16) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl. Crystallogr. 1999, 32, 115.

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Synthesis of [(DAD)NdI(THF)3] (8). Yield: 84%. Anal. Calcd for C38H60IN2O3Nd: C, 52.82; H, 7.00; N, 3.24. Found: C, 53.28; H, 6.66; N, 3.32. X-ray Crystallographic Studies. Single crystals of 2-6 and 8 were grown from THF/pentane (1:3) or a THF solution at -35 °C. A suitable crystal was mounted on a CryoLoop (Hampton Research Corp.) with a layer of light mineral oil and placed in a nitrogen stream at 113(1) K. Measurements were made on a Rigaku R-AXIS RAPID imaging plate area detector or a Rigaku AFC7R/Mercury CCD detector with graphite-monochromated Mo KR (0.71075 A˚) radiation. All structures were solved using SIR-9716 and refined using SHELXL-97.17 Crystal structures were viewed using ORTEP-III.18 The remaining non-hydrogen atoms were located from successive difference Fourier map calculations. The refinements were carried out by using full-matrix leastsquares techniques on F, minimizing the function (Fo Fc)2, where the weight is defined as 4Fo2/2(Fo2) and Fo and Fc are the observed and calculated structure factor amplitudes using the program SHELXL-97. In the final cycles of each refinement, all non-hydrogen atoms in 2-6 and 8 were assigned anisotropic temperature factors. Carbon-bound hydrogen atom positions were calculated and allowed to ride on the carbon to which they are bonded assuming a C-H bond length of 0.95 A˚. The hydrogen atom contributions were calculated, but not refined. The final values of refinement parameters are given in Tables S1. The locations of the largest peaks in the final difference Fourier map calculation as well as the magnitude of the residual electron densities in each case were of no chemical significance. For compound 2, the addititional pseudosymmetry was checked by PLATON (CALC ADD SYMM EXACT); no additional symmetry was found. Complex 2 formed as a racemic twin crystal. The data were twinned by incorporation of the TWIN instruction in SHELXL. This complex contains one major component, as indicated by the batch scale factor (BASF) of 0.56. For compounds 3 and 8, a poorly defined region of residual electron density was tentatively identified as one THF molecule, but could not be refined satisfactorily. The program SQUEEZE (A. L. Spek, University of Utrecht, The Netherlands)19 was therefore used to remove mathematically the effects of the solvent.

Acknowledgment. We are thankful for the JSPS Fellowship to T.K.P. and K.P. H.K. is thankful for the GrobalCOE Fellowship. H.T. acknowledges financial support from a Grant-in-Aid for Young Scientists(B) and The Sumitomo Foundation. This work was supported by the Core Research for Evolutional Science and Technology (CREST) program of the Japan Science and Technology Agency (JST), Japan. Supporting Information Available: Molecular structures of 2 and 4, crystallographic data for 2-6 and 8, and their CIF files. This material is available free of charge via the Internet at http://pubs. acs.org. (17) Sheldrick, G. M. Program for the Refinement of Crystal Structures; University of G€ottingen: G€ottingen, Germany, 1997. (18) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837. (19) Sluis, P. v. d.; Spek, A. L. Acta Crystallogr., Sect. A 1990, 46, 194.