Heterometallic Complexes with Re−Bi Metal Bonds - Organometallics

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Organometallics 2010, 29, 1670–1674 DOI: 10.1021/om100011r

Heterometallic Complexes with Re-Bi Metal Bonds Rafael Schiwon, Christina Knispel, and Christian Limberg* Humboldt-Universit€ at zu Berlin, Institut f€ ur Chemie, Brook-Taylor-Strasse 2, 12489 Berlin, Germany Received January 5, 2010

The reaction of rhenocene hydride with bismuth alkoxides leads to complexes containing Re-Bi metal bonds with concomitant formation of the corresponding alcohols. Hence, compounds of the type [Cp2Re-BiR2] can be obtained from the monoalkoxide [(MeO)Bi(o-tol)2]n and also from the trialkoxide [Bi{OCH(CF3)2}3(thf)]2, for which in principle also multiple substitution reactions would have been possible, but are prohibited by the electron-withdrawing character of the hexafluoroisopropyl groups. Correspondingly, the trialkoxide [Bi(OtBu)3] containing electron-rich tert-butyl groups does lead to multiple substitution events: First of all it reacts with two equivalents of [Cp2ReH] to give the intermediate [(Cp2Re)2Bi(OtBu)], which could not be isolated, since it undergoes an intramolecular alcohol elimination via CpC-H bond cleavage. This results in the complex [CpRe(μ-η5,η1-C5H4)Bi-ReCp2], featuring a bent Bi-C bond so that one deprotonated Cp ligand bridges a Bi-Re metal bond. All compounds have been fully characterized, and their crystal structures are discussed.

Introduction Heterobimetallic oxide compounds receive special attention since two metals with different properties may cooperate electronically, magnetically, or chemically to yield unique applications that cannot be reached with the corresponding homometallic systems.1 One popular element in this context is bismuth, which in combination with other metals has been shown to lead to oxide ion conductors,2 multiferroic materials,3 unique oxidation catalysts,4 photocatalysts,5 high-temperature superconductors,6 etc. So far, there is also a lot of interest in heterometallic molecular compounds as potential single-source

*Corresponding author. Fax: (þ49) 30-2093-6966. E-mail: christian. [email protected]. (1) (a) Setter, N. J. Eur. Ceram. Soc. 2001, 21, 1279–1293. (b) Schmidt, H. Appl. Organomet. Chem. 2001, 15, 331–343. (c) Lucas, E.; Decker, S.; Khaleel, A.; Seitz, A.; Fultz, S.; Ponce, A.; Li, W.; Carnes, C.; Klabunde, K. J. Chem.;Eur. J. 2001, 7, 2505–2510. (d) Hubert-Pfalzgraf, L. G. Inorg. Chem. Commun. 2003, 6, 102–120. (e) Hubert-Pfalzgraf, L. G. J. Mater. Chem. 2004, 14, 3113–3123. (f) Veith, M. J. Chem. Soc., Dalton Trans. 2002, 2405–2412. (g) Chandler, C. D.; Roger, C.; Hampden-Smith, M. J. Chem. Rev. 1993, 93, 1205–1241. (2) (a) Shuk, P.; Wiemh€ ofer, H. D.; Guth, U.; G€ opel, W.; Greenblatt, M. Solid State Ionics 1996, 89, 179–196. (b) Punn, R.; Feteira, A. M.; Sinclair, D. C.; Greaves, C. J. Am. Chem. Soc. 2006, 128, 15386–15387. (3) (a) Choi, T.; Lee, S.; Choi, Y. J.; Kiryukhin, V.; Cheong, S. W. Science 2009, 324, 63–66. (b) Thurston, J. H.; Whitmire, K. H. Inorg. Chem. 2002, 41, 4194–4205. (c) Thurston, J. H.; Whitmire, K. H. Inorg. Chem. 2003, 42, 2014–2023. (4) Hanna, T. A. Coord. Chem. Rev. 2004, 248, 429–440. (5) (a) Feng Yao, W.; Wang, H.; Hong Xu, X.; Feng Cheng, X.; Huang, J.; Xia Shang, S.; Na Yang, X.; Wang, M. Appl. Catal. A: Gen. 2003, 243, 185–190. (b) Liu, H.; Nakamura, R.; Nakato, Y. ChemPhysChem 2005, 6, 2499–2502. (c) Shimodaira, Y.; Kato, H.; Kobayashi, H.; Kudo, A. J. Phys. Chem. B 2006, 110, 17790–17797. (6) Rama Rao, G. V.; Swaminathan, K.; Sreedharan, O. M.; Venkadesan, S.; Mannan, S. L.; Varadaraju, U. V. J. Mater. Sci. 1998, 33, 1511–1516. (7) (a) Thurston, J. H.; Ely, T. O.; Trahan, D.; Whitmire, K. H. Chem. Mater. 2003, 15, 4407–4416. (b) Thurston, J. H.; Trahan, D.; Ould-Ely, T.; Whitmire, K. H. Inorg. Chem. 2004, 43, 3299–3305. (c) Ould-Ely, T.; Thurston, J. H.; Whitmire, K. H. C. R. Chim. 2005, 8, 1906–1921. (d) Veith, M.; Mathur, S.; Mathur, C. Polyhedron 1998, 17, 1005–1034. (8) Mehring, M. Coord. Chem. Rev. 2007, 251, 974–1006. pubs.acs.org/Organometallics

Published on Web 03/01/2010

precursors,7 as small models for aggregated materials,8 or as fascinating subjects for studies in their own right.9 With the background of the oxidation of propene to acrolein, which can be catalyzed by mixed metal oxides nMoO3/Bi2O3,4,10 we and others have developed routes to compounds with Mo-O-Bi units11,12 and with Mo-Bi metal bonds.13-17 We found that Mo-Bi bonds can be created by reactions of molybdocene dihydrides with bismuth alkoxides or siloxides.13,14,16,17 It was also shown that replacement of the bismuth alkoxides in such reactions by tin and antimony halides results in complexes with Mo-Sn and Mo-Sb bonds.18 We were interested in (9) (a) Ould-Ely, T.; Thurston, J. H.; Kumar, A.; Respaud, M.; Guo, W.; Weidenthaler, C.; Whitmire, K. H. Chem. Mater. 2005, 17, 4750–4754. (b) Dikarev, E. V.; Zhang, H.; Li, B. Angew. Chem. 2006, 118, 55745577; Angew. Chem., Int. Ed. 2006, 45, 5448-5451. (c) Nekoueishahraki, B.; Jana, A.; Roesky, H. W.; Mishra, L.; Stern, D.; Stalke, D. Organometallics 2009, 28, 5733–5738. (d) Dikarev, E. V.; Zhang, H.; Li, B. J. Am. Chem. Soc. 2005, 127, 6156–6157. (e) Dikarev, , E. V.; Gray, , T. G.; Li, B. Angew. Chem. 2005 117, 1749-1752. Angew. Chem., Int. Ed. 2005, 44, 1721-1724. (10) Grasselli, R. K. Catal. Today 1999, 49, 141–153. (11) (a) Mendoza-Espinosa, D.; Hanna, T. A. Inorg. Chem. 2009, 48, 7452–7456. (b) Roggan, S.; Limberg, C.; Brandt, M.; Ziemer, B. J. Organomet. Chem. 2005, 690, 5282–5289. (c) Roggan, S.; Limberg, C.; Ziemer, B. Angew. Chem. 2005, 117, 5393-5397; Angew. Chem., Int. Ed. 2005, 44, 5259-5262. (12) Roggan, S.; Limberg, C.; Ziemer, B.; Siemons, M.; Simon, U. Inorg. Chem. 2006, 45, 9020–9031. (13) Roggan, S.; Limberg, C.; Ziemer, B.; Brandt, M. Angew. Chem. 2004, 116, 2906-2910; Angew. Chem., Int. Ed. 2004, 43, 2846-2849. (14) Roggan, S.; Schnakenburg, G.; Limberg, C.; Sandh€ ofner, S.; Pritzkow, H.; Ziemer, B. Chem.;Eur. J. 2005, 11, 225–234. (15) Roggan, S.; Limberg, C. Inorg. Chim. Acta 2006, 359, 4698–4722. (16) Hunger, M.; Limberg, C.; Kaifer, E.; Rutsch, P. J. Organomet. Chem. 2002, 641, 9–14. (17) Knispel, C.; Limberg, C.; Mehring, M. Organometallics 2009, 28, 646–651. (18) (a) Gusev, A. I.; Bulychev, B. M.; Soloveichik, G. L. Koordinat. Khim. 1984, 10, 52. (b) Gusev, A. I.; Kirillova, N. I.; Protsky, A. N.; Bulychev, B. M.; Soloveichik, G. L. Polyhedron 1984, 3, 765–769. (c) Protsky, A. N.; Bulychev, B. M.; Soloveichik, G. L.; Belsky, V. K. Inorg. Chim. Acta 1986, 115, 121–128. (d) Protsky, A. N.; Bulychev, B. M.; Soloveichik, G. L. Inorg. Chim. Acta 1983, 71, 35–39. (e) Knispel, C.; Limberg, C.; Zimmer, L.; Ziemer, B. Z. Anorg. Allg. Chem. 2007, 633, 2278–2284. r 2010 American Chemical Society

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Chart 1. Recently Synthesized Re-Bi Carbonyl Compounds I and II23

investigating whether also the molybdocene dihydride component can be exchanged by other transition metal hydrides in reactions with bismuth alkoxides and in how far the “hydride-alkoxide” route thus might represent a more general procedure to access transition metal-bismuth systems. Rhenocene hydride19,20 represents a well-defined organometallic hydride, so that it seemed worthwhile to exemplarily investigate its reactions with bismuth alkoxides, especially since hardly any molecular compounds containing Re-Bi bonds were known at the start of this investigation: only [Ph2Bi{Re(CO)5}],21 [ClBi{Re(CO)5}2],22 and [Bi{Re(CO)5}3]22 had been reported, and X-ray data were not available. However, very recently the crystal structures of the carbonyl compounds I and II (Chart 1);synthesized by thermal decomposition of BiPh3 in the presence of an organorhenium carbonyl precursor;were described,23,24 and interestingly I immobilized on silica proved an efficient catalyst for the ammoxidation of 3-picoline to yield nicotinonitrile.24 Starting from I and II further Re-Bi clusters were accessible by pyrolysis.23

Figure 1. Molecular structure of 1. Thermal ellipsoids are shown at 50% probability. Hydrogen atoms are omitted for clarity. Selected bond lengths (A˚) and angles (deg): Re-Bi 2.8468(5), Bi-C11 2.270(12), Bi-C18 2.274(10); Cp-Re-Cp0 148.71(48), Cp-Re-Bi 107.73(2), Cp0 -Re-Bi 101.02(2), C11-Bi-C18 96.71(35), C11-Bi-Re 102.11(23), C18-Bi-Re 105.12(23). Scheme 1. Synthesis of 1 by Reaction of [Cp2ReH] with [(MeO)Bi(o-tol)2]n (III)

Results and Discussion First investigations with rhenocene hydride were undertaken employing [(MeO)Bi(o-tol)2]n, III,12 as the bismuth alkoxide, since it contains only one alkoxide function and thus guarantees a controlled reaction behavior in orienting experiments. On warming of an equimolar solution of [Cp2ReH] and III in hexane from -78 °C to -30 °C, the color changed to bright orange and persisted also on annealing to room temperature. Concentration and subsequent cooling to 4 °C led to orange-red crystals of [Cp2Re-Bi(o-tol)2], 1 (see Scheme 1). The molecular structure as derived from a single-crystal X-ray investigation is shown in Figure 1. A (o-tol)2Bi unit is bound to Cp2Re via a Re-Bi metal bond, whose length (2.8468(5) A˚) is comparable to the corresponding distances found in I (2.8403(3)-2.8422(3) A˚) and II (2.8391(5)-2.8583(5) A˚).23 The angle between the two Cp rings of the Cp2Re unit amounts to 148.71(48)°, which is comparable to that of [Cp2ReCl] (147.58(2)°)25 and thus indicates the absence of any repulsive interactions, whereas the corresponding angles in [Cp2Re-MCp2] (M=Y, 165.6(3)°; (19) (a) Wilkinson, G.; Birmingham, J. M. J. Am. Chem. Soc. 1955, 77, 3421–3422. (b) Paciello, R. A.; Kiprof, P.; Herdtweck, E.; Herrmann, W. A. Inorg. Chem. 1989, 28, 2890–2893. (20) Green, M. L. H.; Pratt, L.; Wilkinson, G. J. Chem. Soc. 1958, 3916–3922. (21) Nesmeyanow, A. N.; Anisimov, K. N.; Kolobova, N. E.; Khandozhko, V. N. Dokl. Akad. Nauk SSSR 1964, 156, 383–385. (22) Compton, N. A.; Errington, R. J.; Fisher, G. A.; Norman, N. C.; Webster, P. M.; Jarrett, P. S.; Nicholls, S. J.; Orpen, A. G.; Stratford, S. E.; Williams, N. A. L. J. Chem. Soc., Dalton Trans. 1991, 669–676. (23) Adams, R. D.; Pearl, W. C. Inorg. Chem. 2009, 48, 9519–9525. (24) Raja, R.; Adams, R. D.; Blom, D. A.; Pearl, W. C.; Gianotti, E.; Thomas, J. M. Langmuir 2009, 25, 7200–7204. (25) Apostolidis, C.; Kanellakopulos, B.; Maier, R.; Rebizant, J.; Ziegler, M. L. J. Organomet. Chem. 1991, 409, 243–254.

M=Yb, 167.4(1)°)26 or in [Cp2Re-U{N(CH2CH2NSiMe3)3}] (166.7°)27 are much larger. Defining a plane through the Cp centroids and the Re center, it could be expected that the Bi atom is positioned within a second plane perpendicular to the first one and bisecting the Cp-Re-Cp0 unit. However, the Bi atom is located somewhat outside this plane, so that the CpRe-Bi angle amounts to 107.73(2)°, while the Cp0 -Re-Bi angle is 101.02(2)°. In the 1H NMR spectrum only one singlet can be observed for all Cp protons, which indicates a fast rotation both of the Cp rings (around an axis through their centroids and the Re center) and of the (o-tol)2Bi moiety (around the Re-Bi axis). It turned out that low temperatures are essential to the successful synthesis of 1. When the reaction shown in Scheme 1 was carried out at room temperature, the formation of Bi(o-tol)3 was observed already after 5 min. (25%), and after 72 h the yield of Bi(o-tol)3 amounted to 40%, while a black solid had precipitated. In the next step the investigation was extended to bismuth trialkoxides, for which a more complex reaction behavior had to be assumed. First, equimolar reactions between [Cp2ReH] and [Bi(OEt)3]n28 and [Bi(OtBu)3]28 were carried out in various solvents to potentially generate [Cp2Re-Bi(OR)2] (26) Butovskii, M. V.; Tok, O. L.; Wagner, F. R.; Kempe, R. Angew. Chem. 2008, 120, 6569–6572. Angew. Chem., Int. Ed. 2008, 47, 6469-6472. (27) Gardner, B. M.; McMaster, J.; Lewis, W.; Liddle, S. T. Chem. Commun. 2009, 2851–2853. (28) Massiani, M.-C.; Papiernik, R.; Hubert-Pfalzgraf, L. G.; Daran, J.-C. Polyhedron 1991, 10, 437–445.

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Scheme 2. Synthesis of 2 by Reaction of [Cp2ReH] with [Bi{OCH(CF3)2}3(thf)]2

derivatives of 1. While the initial coloration of the reaction mixtures to orange indeed pointed to the formation of such complexes, the solutions were not stable and slowly changed to brown or even black, which was accompanied by the precipitation of dark, pyrophoric solids. This seemed to indicate nonuniform reactions due to multiple exchange of alkoxide ligands, and hence the employment of a less reactive alkoxide was envisaged. The alkoxide ligands in [Bi{OCH(CF3)2}3(thf)]229 contain electron-withdrawing trifluoromethyl groups, which apparently deactivate the bismuth alkoxide for the alcohol elimination reactions with hydrides, and therefore the conversion with molybdocene dihydride led to the formation of only one Mo-Bi bond per Bi atom,16 while Mo-Bi-Mo units were generated employing the more electron-rich [Bi(OtBu)3].13,14 Hence, [Cp2ReH] was added to half an equivalent of the dimer [Bi{OCH(CF3)2}3(thf)]2 dissolved in hexane at room temperature. This led to the precipitation of the desired [Cp2Re-Bi(OR)2] (R = hexafluoroisopropyl), 2, in the form of an orange powder (Scheme 2). During the addition of the [Cp2ReH] it could be observed that a local excess of the hydride led to the formation of black streaks, which vanished again on stirring. As also in the above-mentioned molybdenum chemistry the transition from Mo-Bi to Mo-Bi-Mo units is accompanied by a color change from red to black (due to an increased density of low-lying antibonding orbitals of the metal σ-bonding framework), this finding was interpreted in terms of the (reversible) formation of [(Cp2Re)2Bi(OR)] on contact of the bismuth precursor with excess rhenocene hydride. However, this compound is obviously part of an equilibrium that also includes [Cp2Re-Bi(OR)2], [Cp2ReH], and the HOR generated, and as [Cp2Re-Bi(OR)2] is constantly removed from this equilibrium by precipitation, the reaction is shifted completely in the direction of 2. Overlaying of a concentrated toluene solution of 2 with hexane led to red crystals, which were investigated by single-crystal X-ray diffraction (see Figure 2). In principal the molecular structure is very similar to that of 1. The Cp-Re-Cp0 angle of 149.43(24)° is almost identical to that of 1, and also in 2 the two Cp-Re-Bi angles are not identical (Cp-Re-Bi: 106.82(1)°; Cp0 -Re-Bi: 101.14(1)°). The Re-Bi distance (2.7032(3) A˚) is significantly shorter, though, than the corresponding distances of all other crystallographically characterized Re-Bi compounds (by almost 0.15 A˚, vide supra), which is perhaps indicative of an increased polarity of the bond. Since the course of the reaction yielding 2 had provided hints to an intermediate double substitution, the stoichiometry of subsequent experiments was now altered to Re:Bi = 2:1. Due to the low solubility of the 1:1 complex 2, for these experiments not [Bi{OCH(CF3)2}3(thf)]2 but [Bi(OtBu)3] was employed. (29) (a) Jones, C. M.; Burkart, M. D.; Whitmire, K. H. Angew. Chem. 1992, 104, 466–467. Angew. Chem., Int. Ed. 1992, 31, 451-452. (b) Jones, C. M.; Burkart, M. D.; Bachman, R. E.; Serra, D. L.; Hwu, S. J.; Whitmire, K. H. Inorg. Chem. 1993, 32, 5136–5144.

Figure 2. Molecular structure of 2. Thermal ellipsoids are shown at 50% probability. Hydrogen atoms are omitted for clarity. Selected bond lengths (A˚) and angles (deg): Re-Bi 2.7032(3), Bi-O 2.144(4), Bi-O0 2.214(4); Cp-Re-Cp0 149.43(24), Cp-Re-Bi 106.82(1), Cp0 -Re-Bi 101.14(1), O-Bi-O0 86.09(15), O-Bi-Re 101.79(11), O0 -Bi-Re 104.01(10). Scheme 3. Synthesis of 3 by Reaction of 2 equiv of [Cp2ReH] with [Bi(OtBu)3]

When a hexane solution of [Cp2ReH] was added at ambient temperatures to a hexane solution containing half an equivalent of [Bi(OtBu)3], the originally colorless solution turned orange within 10 min and then quickly changed color to brown. After one hour the solution was brown-violet and after a further 2 days of stirring black-violet. Storing of such a solution for 24 h led to the precipitation of needle-shaped dark violet crystals, which were identified as [CpRe(μ-η5,η1C5H4)Bi-ReCp2], 3, by elemental analysis and 1H as well as 13 C{1H} NMR spectroscopy. The formation of 3 can be explained assuming that [(Cp2Re)2Bi(OtBu)], 4, was generated in a first reaction step (Scheme 3) and that due to its structure hydrogen atoms of the Cp rings are located in close proximity to the O atom of the remaining alkoxide ligand. These C-H bonds would then get activated via “complexinduced proximity effects”, and they may well be cleaved in solution during a vibration of the molecule under elimination of alcohol. This should yield 3, containing a μ-η5,η1C5H4 ligand that bridges a Re and a Bi center, which are additionally linked by a metal-metal bond. A similar reaction behavior had been observed before for the system

Article

Figure 3. Molecular structure of 3. Thermal ellipsoids are shown at 50% probability. Hydrogen atoms are omitted for clarity. Selected bond lengths and distances (A˚) and angles (deg): Re-Bi 2.8652(6), Re0 -Bi 2.8934(6), Bi-C1 2.242(3), Re-Bi-Re0 113.236(18), Cp1-Re-Cp2 156.40(12), Cp1-Re-Bi 117.04(2), Cp2-Re-Bi 83.80(2), Cp3-Re0 -Cp4 149.90(17), Cp3-Re0 -Bi 103.11(2), Cp4-Re0 -Bi 102.47(2), C1-Bi-Re 49.70(8), Cp2-C1-Bi 136.24(12).

Cp2MoH2/Bi(OtBu)3:13,14,17 In the first reaction steps [Cp2Mo{μ-Bi(OtBu)}2MoCp2] was formed, which subsequently underwent intramolecular alcohol eliminations to yield [CpMo(μ-η5,η1-C5H4Bi)2MoCp]. To confirm this hypothesis, the 2:1 reaction of [Cp2ReH] with [Bi(OtBu)3] in C6D6 was monitored with the aid of 1H NMR spectroscopy. This showed that after mixing of the reagents all [Bi(OtBu)3] is consumed instantaneously to yield [Cp2Re-Bi(OtBu)2], 5, which quickly (within 5 min) reacts further to yield [(Cp2Re)2Bi(OtBu)], 4. At the same time formation of 3 sets in. After 3 h all 5 was consumed and only 4 was present in solution besides small amounts of 3. After 24 h the ratio 4:3 amounted to 5:1. As 3 is not soluble in hexane (note that the NMR experiment was carried out in C6D6), it is precipitated from this equilibrium, which is thus constantly shifted in the direction of 3. The crystals of 3 were also investigated by means of X-ray diffraction, and the result is shown in Figure 3 (the corresponding molecular structure occurs in two split sites within the crystal packing; see Supporting Information). While the Cp2Re0 -Bi unit can be described as “normal” as compared to the structures of 1 and 2 (Cp3-Re0 -Cp4 amounts to 149.90(17)°, Cp3-Re0 -Bi to 103.11(2)°, and Cp4-Re0 -Bi to 102.47(2)°), the second rhenocene unit is significantly distorted to allow for a bonding of Cp2 both to the Re center in a η5 fashion and to the Bi atom. This expresses itself in an enlarged Cp2-Re-Cp1 angle of 156.40(12)°, and in fact the Re-Bi bond is now significantly bent out of the bisecting plane (perpendicular to the plane defined by the Cp centroids and the Re atom) by a respective 18.0(1)° in the direction of Cp2. The resulting Bi-C1 distance of 2.242(3) A˚ can be described as typical for Bi-C bonds (2.20-2.34 A˚), but it has to be considered that the straight line drawn between these atoms is bent out of the Cp2 plane by 43.76(12)°, which is indicative of a bent bond (“banana bond”) between them.14 Not surprisingly, the Re-Bi bond is somewhat shorter (2.8652(6) A˚) than the Re0 -Bi bond (2.8934(6) A˚). The 1H NMR spectrum of 3 dissolved in d8-toluene (see Supporting Information) is more complex than the spectra of 1 and 2. Still, the Cp2Re0 unit gives rise to only one singlet (HR), which shows that it freely rotates around the Re0 -Bi bond, and the Cp1 ring leads to a further singlet (Hβ).

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However, the Re(μ-η5,η1-C5H4)Bi unit is rigid and highly asymmetric, so that all four protons show individual signals. The protons nearest the C atom connected to Bi (i.e., the protons located at C2 and C5 in Figure 3) are designated Hδ and Hχ, while the remaining two are designated Hε and Hj. While Hδ and Hχ should resonate in the form of doublets, pseudotriplets should be observed for Hε and Hj. Hence, two doublets occurring at 5.34 and 5.21 ppm could be assigned to Hδ and Hχ, though it was not possible to distinguish between them. A pseudotriplet is found at 5.13 ppm, which can thus be assigned to either Hε or Hj. Surprisingly, the second pseudotriplet appeared substantially shifted into the high-field region: It is masked by the signal of the Cp1 protons (Hβ) at 4.23 ppm but could be identified at 4.23 ppm with the aid of a 1H-13C{1H} COSY NMR spectrum (see Supporting Information). The reasons for this marked chemical shift difference between Hε and Hj are not quite clear, and it is not paralleled in the 13C{1H} NMR spectrum: resonances at 85.3, 74.5, and 62.4 ppm can be assigned to the three carbon atoms bound to the protons absorbing at low field in the 1H NMR spectrum, and the signal of the fourth C atom belonging to the “high-field proton” is positioned closely beside those at 61.4 ppm. 3 is a very reactive compound, as one might suspect looking at its structure. It is very sensitive to moisture and O2, and in contact with air it is pyrophoric. Nevertheless, it is readily accessible in good yields, the crystals isolated directly from the reaction mixture are already pure by elemental analysis, and they are readily soluble in toluene and benzene. These are ideal prerequisites for further investigations concerning its reactivity in the future.

Conclusions We have successfully applied the “alkoxide-hydride” route for the targeted synthesis of di- and trinuclear compounds containing Re-Bi metal bonds. The hydride/Cp2Re exchange proceeds in a clean and controlled manner, with the degree of substitution depending on the number of alkoxide functions offered as well as on the electronic properties of the alkoxide ligands involved. As observed before for Mo/Bi systems, also within Re/Bi alkoxides complex-induced proximity effects can lead to C-H activation and intramolecular alcohol elimination with formation of Bi-C banana bonds. Current research now focuses on the exploration of conditions that might lead to the triply substituted compound [(Cp2Re)3Bi] and opening of the bent bonds for the further functionalization of such compounds (compare lit.17), as well as on their utilization as single-source precursors in MOCVD processes for the preparation of Re/Bi compounds showing interesting properties, for instance in catalysis.

Experimental Section General Procedures. All manipulations were carried out in a glovebox or by means of Schlenk-type techniques involving the use of a dry and oxygen-free argon atmosphere. The 1H and 13 C{1H} NMR spectra were recorded on a Bruker AV 400 NMR spectrometer (1H, 400.1 MHz; 13C{1H}, 100.6 MHz; 19F, 282.4 MHz) in dry deoxygenated benzene-d6 or toluene-d8 as solvent. The spectra were calibrated against the internal residual proton and natural abundance 13C resonances of the deuterated solvent (benzene-d6 δH 7.15 ppm, δC 128.0 ppm; toluene-d8 δH 2.09 ppm, δC 20.4 ppm). Microanalyses were performed on a HEKAtech Euro EA 3000 elemental analyzer. Infrared (IR) spectra

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were recorded in the region 4000-400 cm-1 using samples prepared as KBr pellets with a Shimadzu FTIR-8400s spectrometer. Materials. Solvents were purified, dried, and degassed prior to use. [Cp2ReH] has been prepared according to a procedure developed by Green and Pratt.20 [(MeO)Bi(o-tol)2]n, III,12 [Bi(OEt)3]n,28 [Bi(OtBu)3],28 and [Bi{OCH(CF3)2}3(thf)]229 were prepared according to the literature procedures. Syntheses. [Cp2Re{Bi(o-tol)2}] (1). A yellow solution of [Cp2ReH] (185 mg, 0.58 mmol, 1 equiv) in 15 mL of hexane was added to a stirred colorless suspension of [(MeO)Bi(o-tol)2]n, III (245 mg, 0.58 mmol, 1 equiv), dissolved in the same solvent (10 mL) at -78 °C, and the reaction mixture was warmed to room temperature. This resulted in an intensely orange solution within 1 h, which was filtered off from unreacted III. Subsequently, the solvent was evaporated under vacuum, resulting in a red, oily residue, which was freeze-dried to yield 322 mg of a crude red powder. Cooling a hexane solution of the red residue to 4 °C yielded orange-red crystals of pure 1 (yield: 223 mg, 0.32 mmol, 54%). 1H NMR (C6D6): δ 7.90 (pd, 2H, o-tolCH), 7.23 (pt, 2H, m-tolCH), 7.195 (pd, 2H, m-tolCH), 7.04 (pt, 2H, p-tolCH), 3.98 (s, 10H, CpCH), 2.49 (s, 6H, CCH3). 13 C{1H} NMR (C6D6): δ 144.0 (tolCCH3), 141.9/128.8/128.5/ 127.7 (tolCH), 67.5 (CpCH), 27.7 (tolCCH3). IR (KBr): ν [cm-1] 3101, 3043, 3016, 2979, 2959, 2907, 2849, 2727, 1913, 1575 1458, 1444, 1420, 1395, 1373, 1348, 1263, 1199, 1152, 1109, 1099, 1060, 1043, 1011, 977, 912, 900, 865, 832, 810, 791, 751, 742, 668, 586, 535, 435, 430, 419. Anal. Calcd for C24H24BiRe: C 40.74, H 3.42. Found: C 40.90, H 3.46. [Cp2ReBi{OCH(CF3)2}2] (2). A yellow solution of [Cp2ReH] (51.4 mg, 0.16 mmol, 1 equiv) in 15 mL of hexane was added dropwise to a stirred colorless solution of [Bi{OCH(CF3)2}3(thf)]2 (124.7 mg, 0.08 mmol, 0.5 equiv) dissolved in the same solvent (10 mL) at ambient temperature. During the addition the color changed from colorless to orange, and an orange solid precipitated. After complete addition the resulting orange suspension was stirred for 3 h at ambient temperature. The solvent was evaporated under vacuum to yield 129.6 mg of a crude orange powder. Slow diffusion of hexane at room temperature into a concentrated toluene solution of the orange residue resulted in the precipitation of orange-red crystals of pure 2 within 7 days (yield: 84.8 mg, 0.09 mmol, 61%). 1H NMR (C7D8): δ 5.04 (sept, 2H, 3JFH = 6.40 Hz, CH), 3.99 (s, 10H, Cp CH). 13C{1H} NMR (C7D8): δ 125.0 (q, 4C, 1JFC = 282.55 Hz, CF3), 76.05 (sept, 3JFC = 31.17 Hz, CH), 68.8 (CpCH). 19F NMR (C7D8): δ -74.9 (d, 12F, 3JHF = 6.70 Hz, CF3). IR (KBr): ν [cm-1] 3098, 3089, 1616, 1420, 1399, 1369, 1277, 1263, 1205, 1174, 1129, 1097, 889, 854, 804, 740, 685. Anal. (%) Calcd for C16H12BiF12O2Re: C 22.36, H 1.41. Found: C 22.60, H 1.15. [CpRe(μ-η5,η1-C5H4)Bi-ReCp2] (3). A yellow solution of [Cp2ReH] (200 mg, 0.63 mmol, 1 equiv) in 15 mL of hexane was added to a stirred colorless solution of [Bi(OtBu)3] (135 mg, 0.32 mmol, 0.5 equiv) dissolved in the same solvent (5 mL) at ambient temperature. After complete addition the color changed within 10 min from yellow via orange, to brown, and finally within 1 h to brown-violet. The reaction mixture was stirred for 2 days at ambient temperature, resulting in a black-violet solution, which was stored at room temperature without further stirring. After 24 h black needles of 3 precipitated (yield: 110 mg, 0.13 mmol, 41%). 1H NMR (300 MHz, C6D6): δ 5.43 (d, 1H, 3 JHH = 1.87 Hz, CHδχ), 5.32 (d, 1H, 3JHH = 2.08 Hz, CHδχ), 5.16 (pt, 1H, 3JHH = 2.07 Hz, CHεj), 4.26 (s, 5H, CHβ), 4.25 (1H, CHεj), 4.20 (s, 10H, CHR). 13C{1H} NMR (75 MHz, C6D6): δ 85.0 (CHδχ), 74.7 (CHδχ), 67.0 (10C, CHR), 65.1 (5C, CHβ), 61.8 (CHεj), 61.0 (CHεj). 1H NMR (400 MHz, C7D8): δ 5.34 (d, 1H, 3JHH = 1.71 Hz, CHδχ), 5.21 (d, 1H, 3JHH = 2.02 Hz, CHδχ), 5.13 (pt, 1H, 3JHH = 2.02 Hz, CHεj), 4.23 (s, 5H, CHβ), 4.23 (1H, CHεj), 4.20 (s, 10H, CHR). 13C{1H} NMR (100 MHz, C7D8): δ 85.4 (CHδχ), 74.5 (CHδχ), 66.6 (10C, CHR), 64.9 (5C, CHβ), 62.4 (CHεj), 61.4 (CHεj); the signal of the C atom

Schiwon et al. Table 1. Crystal Data and Experimental Parameters for the Crystal Structure Analyses of 1, 2, and 3

formula weight, g mol-1 temp, K cryst syst space group a, A˚ b, A˚ c, A˚ R, deg β, deg γ, deg V, A˚3 Z density, g cm-3 μ(Mo KR), mm-1 F(000) GoF R1 [I > 2σ(I)] wR2 [all data] ΔFmin/ΔFmax, e A˚-3

1

2

3

C24H24BiRe 707.61 100(2) monoclinic P21/c 13.6349(3) 16.8562(4) 17.6871(5) 90 89.964(3) 90 4065.07(17) 8 2.312 14.601 2608 1.048 0.0501 0.1402 3.554/-4.553

C16H12BiF12O2Re 859.44 100(2) orthorhombic Pbca 14.6191(3) 17.5119(4) 15.7302(3) 90 90 90 4027.06(15) 8 2.835 14.854 3120 1.023 0.0341 0.0800 2.074/-4.092

C20H19BiRe2 840.73 100(2) monoclinic P21/c 20.0540(8) 7.6906(3) 10.8238(5) 90 92.596(3) 90 1667.61(12) 4 3.349 25.004 1488 1.217 0.0455 0.0901 2.201/-2.334

bound to Bi was not observed due to the high quadrupole moment of the 209Bi-isotope (Q = -0.4  10-28 m2, I = 9/2, 100% abundance). IR (KBr): ν [cm-1] 3090, 3073, 3065, 1407, 1392, 1369, 1339, 1318, 1261, 1088, 1059, 1020, 1012, 995, 899, 877, 856, 825, 816, 792, 668, 640, 583. Anal. (%) Calcd for C21H23BiRe2: C 28.57, H 2.28. Found: C 28.15, H 2.32. 1 H NMR Data for [(Cp2Re)2Bi(OtBu)] (4). 1H NMR (300 MHz, C6D6): δ 4.27 (s, 20H, CpCH), 1.41 (s, 9H, C(CH3)3). 1 H NMR Data for [Cp2Re-Bi(OtBu)2] (5). 1H NMR (300 MHz, C6D6): δ 4.24 (s, 10H, CpCH), 1.45 (s, 18H, C(CH3)3). Crystal Structure Determinations. Suitable single crystals of 1 were obtained by cooling a concentrated hexane solution to 4 °C. Suitable single crystals of 2 were obtained by slow diffusion of hexane into a concentrated toluene solution of 2. Crystals of 3 suitable for X-ray crystallography could be obtained by storing of the reaction mixture in hexane for 24 h at room temperature. The crystal data were collected on a Stoe IPDS I or Stoe IPDS 2T diffractometer using Mo KR radiation, λ = 0.71073 A˚. In all cases, the structures were solved by direct methods (SHELXS97)30 and refined versus F2 (SHELXL-97)31 with anisotropic temperature factors for all non-hydrogen atoms. All hydrogen atoms were added geometrically and refined by using a riding model. Relevant crystallographic data are collected in Table 1. Structural information of the reported structures 1 (759185), 2 (759186), and 3 (759187) has been deposited at the CCDC database.

Acknowledgment. We are grateful to the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie, the BMBF, and the Humboldt-Universit€ at zu Berlin for financial support. We also would like to thank Dr. B. Ziemer for helpful discussions concerning crystal structure analyses, as well as Prof. R. Kempe for valuable information concerning the synthesis of [Cp2ReH]. Supporting Information Available: CIF files containing full details of the structural analysis of complexes 1, 2, and 3, 1H and 1 H-13C{1H} COSY NMR spectrum of 3, and a comment describing the split sites of 3 and 30 . This material is available free of charge via the Internet at http://pubs.acs.org. (30) (a) Sheldrick, G. M. SHELXS-97, Program for Crystal Structure Solution; University of G€ottingen, 1997. (b) Sheldrick, G. Acta Crystallogr. A 2008, 64, 112–122. (31) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Refinement; University of G€ottingen, 1997.