Organometallics 2010, 29, 6165–6168 DOI: 10.1021/om1008204
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A Cobaltocenium Complex of Dibenzo[c,g]fluorenide and Its Structural and Electrochemical Properties Frank Pammer,† Yu Sun,† Monika Sieger,‡ Jan Fiedler,§ Biprajit Sarkar,‡ and Werner R. Thiel*,† †
Fachbereich Chemie, Technische Universit€ at Kaiserslautern, Erwin-Schr€ odinger-Strasse Geb. 54, D-67661 Kaiserslautern, Germany, ‡Institut f€ ur Anorganische Chemie, Universit€ at Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany, and §J. Heyrovsk y Institute of Physical Chemistry, v.v.i., Academy of Sciences of the Czech Republic, Dolej skova 3, CZ-18223 Prague, Czech Republic Received August 26, 2010 Summary: A first cobaltcennium complex of the dibenzo[c,g]fluorenide ligand (Dbf-1) has been prepared and completely characterized by NMR spectroscopy, X-ray diffra0ction, and spectro-electrochemistry. When cobaltocene (Cp2Co) was first isolated independently by Pauson1 and Fischer,2 it immediately became apparent that upon contact with oxidizing agents this uncharged 19e- metallocene forms a stable diamagnetic cation, which is isoelectronic to ferrocene.2 The chemical properties of cobaltocenes and cobaltocenium cations have been intensively studied throughout the past decades and have been thoroughly reviewed.3 Cobaltocene is commonly applied as a *Corresponding author. E-mail:
[email protected]. (1) Wilkinson, G.; Pauson, P. L.; Cotton, F. A. J. Am. Chem. Soc. 1954, 76, 1970–1974. (2) (a) Fischer, E. O.; Jira, R. Z. Naturforsch. 1953, 8b, 1–2. (b) Fischer, E. O.; Jira, R. Z. Naturforsch. 1953, 8b, 327–328. (3) (a) Kemmitt, R. D. W.; Russel, D. R. In Comprehensive Organometallic Chemistry; Abel, E. W.; Stone, F. G. A.; Wilkinson, G., Eds.; Pergamon Press: Oxford, 1982; Vol. 5, pp 1-276. (b) Sweany, R. L. In Comprehensive Organometallic Chemistry II; Abel, E. W.; Stone, F. G. A.; Wilkinson, G., Eds.; Pergamon Press,: Oxford, 1994; Vol. 5, pp 1-115. (c) Sheats, J. F. The Chemistry of Cobaltocene, Cobaltocenium Salts and Other Cobalt Sandwich Compounds. In Journal of Organometallic Chemistry Library (Organomet. Chem. Rev.); 1979; Vol. 7, pp 461-521. (d) Leonova, E. V.; Kochetkova, N. S. Usp. Khimii. 1973, 42, 615–644. (4) (a) Pauson, P. L. In Encyclopedia of Reagents for Organic Synthesis; John Wiley & Sons, Ltd.: Chichester, UK, 2001. (b) Connelly, N. G.; Geiger, W. E. Chem. Rev. 1996, 96, 877–910. (5) Some recent examples of solid-state structures containing Cp2Coþ cations: (a) Jeannin, O.; Clerac, R.; Fourmigue, M. Chem. Mater. 2007, 19, 5946–5954. (b) Yu, R.; Arumugam, K.; Manepalli, A.; Tran, Y.; Schmehl, R.; Jacobsen, H.; Donahue, J. P. Inorg. Chem. 2007, 46, 5131–5133. (c) Ghosh, P.; Stobie, K.; Bill, E.; Bothe, E.; Weyherm€uller, T.; Ward, M. D.; McCleverty, J. A.; Wieghardt, K. Inorg. Chem. 2007, 46, 522– 532. (d) Patra, A. K.; Bill, E.; Weyherm€uller, T.; Stobie, K.; Bell, Z.; Ward, M. D.; McCleverty, J. A.; Wieghardt, K. Inorg. Chem. 2006, 45, 6541–6548. (e) Vaughn, A. E.; Bassil, D. B.; Barnes, C. L.; Tucker, S. A.; Duval, P. B. J. Am. Chem. Soc. 2006, 128, 10656–10657. (f) Bill, E.; Bothe, E.; Chaudhuri, P.; Chlopek, K.; Herebian, D.; Kokatam, S.; Ray, K.; Weyherm€uller, T.; Neese, F.; Wieghardt, K. Chem.;Eur. J. 2005, 11, 204–224. (6) Some recent examples of solid-state structures containing Cp*2Coþ cations: (a) Krinsky, J. L.; Anderson, L. L.; Arnold, J.; Bergman, R. G. Inorg. Chem. 2008, 47, 1053–1066. (b) Nafady, A.; Butterick, R., III; Calhorda, M. J.; Carroll, P. J.; Chong, D.; Geiger, W. E.; Sneddon, L. G. Organometallics 2007, 26, 4471–4482. (c) Jaska, C. A.; Emslie, D. J. H.; Bosdet, M. J. D.; Piers, W. E.; Sorensen, T. S.; Parvez, M. J. Am. Chem. Soc. 2006, 128, 10885–10896. (d) de Carcer, I. A.; DiPasquale, A.; Rheingold, A. L.; Heinekey, D. M. Inorg. Chem. 2006, 45, 8000–8002. (e) Konarev, D. V.; Khasanov, S. S.; Saito, G.; Vorontsov, I. I.; Otsuka, A.; Lyubovskaya, R. N.; Antipin, Y. M. Inorg. Chem. 2003, 42, 3706–3708. (f) Kuroda-Sowa, T.; Lam, M.; Rheingold, A. L.; Frommen, C.; Reiff, W. M.; Nakano, M.; Yoo, J.; Maniero, A. L.; Brunel, L.-C.; Christou, G.; Hendrickson, D. N. Inorg. Chem. 2001, 40, 6469–6480. r 2010 American Chemical Society
one-electron reducing agent in organic, organometallic, and coordination chemistry.4 The weakly coordinating cations Cp2Coþ5 and Cp*2Coþ (Cp*: 1,2,3,4,5-pentamethylcyclopentadienyl)6 serve as well-defined, large counterions for anionic compounds. While the above-mentioned reviews thoroughly cover the chemistry of cobaltocene and its alkylated derivatives, cobalt complexes containing benzannulated Cp derivatives other than indenide (Ind-; e.g., bisindenylcobalt(II), Ind2Co) have been only rarely described in the literature.7 The first presumed cobalt complexes with η5-Flu- ligands (Flu- = fluorenide) onnemann were published by Ingrosso et al. in 19818 and by B€ et al. in 1989.9 However, these compounds had been characterized solely by elemental analysis, mass spectrometry, and infrared spectroscopy. η5-Coordination of Flu- to a cobalt center was finally confirmed in 1992 by the publication of the solid-state structure of (η5-Flu)(η5-carborane)cobaltocene.10 Recent examples of fully characterized cobalt tripledecker complexes containing η5-Flu- ligands were reported by Schneider et al. in 2007.11 Mutseneck et al. were able to transfer the fluorenide anion onto a (tetramethylcyclobutadienyl)cobalt(I) fragment, although the product turned out to be too sensitive to yield satisfactory analytical data.12 To the best of our knowledge, no cobaltocene of an isomer or higher benzannulated homologue of Flu- has been described up to now. Herein we report the first synthesis and complete structural, spectroscopical, and electrochemical analysis of [(η5-Dbf)Co(Cp*)]PF6, a cobaltocenium complex of the dibenzo[c,g]fluorenide ligand (Dbf-). A number of cobalt complexes however, that are closely related to the molecular system we present here, have been prepared by T. J. Katz’s group: Cobaltocenes derived from cyclopentyl-annulated helicenes have been published between 1982 and 1993.13,14 (7) (a) Westcott, S. A.; Kakkar, A. K.; Stringer, G.; Taylor, N. J.; Marder, T. B. J. Organomet. Chem. 1990, 394, 777–794. (b) O'Hare, D.; Green, J. C.; Marder, T.; Collins, S.; Stringer, G.; Kakkar, A. K.; Kaltsoyannis, N.; Kuhn, A.; Lewis, R.; Mehnert, C.; Scott, P.; Kurmoo, M.; Pugh, S. Organometallics 1992, 11, 48–55. (8) Diversi, P.; Giusti, A.; Ingrosso, G.; Lucherini, A. J. Organomet. Chem. 1981, 205, 239–246. (9) B€ onnemann, H.; Goddard, R.; Grub, J.; Mynott, R.; Raabe, E.; Wendel, S. Organometallics 1989, 8, 1941–1958. (10) (a) Lewis, Z. G.; Welch, A. J. Acta Crystallogr., Sect. C 1992, C48, 53–57. (11) Guo, S.; Hauptmann, R.; Schneider, J. J. Z. Anorg. Allg. Chem. 2007, 633, 2332–2337. (12) Mutseneck, E. V.; Loginov, D. A.; Perekalin, D. S.; Starikova, Z. A.; Golovanov, D. G.; Petrovskii, P. V.; Zanello, P.; Corsini, M.; Laschi, F.; Kudinov, A. R. Organometallics 2004, 23, 5944–5957. Published on Web 11/11/2010
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Scheme 1. Synthesis of [(η5-Dbf)Co(η5-Cp*)]PF6 by Formation of (η5-Dbf)Co(η5-Cp*) and Subsequent Oxidationa
a
Overall yield given.
Figure 1. Molecular structure of the cation [(η5-Dbf)Co(η5Cp*)]þ in the solid state. Characteristic bond lengths [A˚] and angles [deg]: Co1-C1 2.0684(17), Co1-C2 2.0869(18), Co1C21 2.0349(17), Co1-C12 2.0601(17), Co1-C11 2.1105(17), Co1-C22 2.0579(18), Co1-C23 2.0557(18), Co1-C24 2.0392(18), Co1-C25 2.0373(18) Co1-C26 2.0482(17), Co1Ct1 1.6739, Co1-Ct2 1.6470, H9-H19 1.9558, C3-C4 1.335(3), C13-C14 1.341(3), C10-C1-C11-C20 -13.949(3).
By reaction of the dimeric half-sandwich complex [Cp*CoCl]215 with half an equivalent of DbfLi, (η5-Dbf)Co(Cp*) is formed. This complex can be oxidized in situ with AgPF6 to yield the corresponding cobaltocenium salt [(η5-Dbf)Co(η5Cp*)]PF6 in an overall yield of 26% (Scheme 1). The wellcrystallizing red complex is soluble in dichloromethane and partially soluble in acetone and turned out to be air stable as a solid. The color is rather unusual for cobaltocenium salts, which are generally described to be between pale yellow and amber-colored.16 Katz’s cobalt complexes with polycyclic Cp ligands however exhibit colors ranging from orange to red.13a,b (13) (a) Gilbert, A. M.; Katz, T. J.; Geiger, W. E.; Robben, M. P.; Rheingold, A. L. J. Am. Chem. Soc. 1993, 115, 3199–3211. (b) Katz, T. J.; Sudhakar, A.; Teasley, M. F.; Gilbert, A. M.; Geiger, W. E.; Robben, M. P.; Wuensch, M.; Wards, M. D. J. Am. Chem. Soc. 1993, 115, 3182–3198. (c) Sudhakar, A.; Katz, T. J.; Yang, B.-W. J. Am. Chem. Soc. 1986, 108, 2790– 2791. (d) Sudhakar, A.; Katz, T. J. J. Am. Chem. Soc. 1986, 108, 179–181. (14) For details on an analogue ferrocene complexes see also: (a) Katz, T. J.; Slusarek, W. J. Am. Chem. Soc. 1979, 101, 4259–4267. (b) Katz, T. J.; Pesti, J. J. Am. Chem. Soc. 1982, 104, 345–347. (15) (a) K€ olle, U.; Fuss, B.; Belting, M.; Raabe, E. Organometallics 1986, 5, 980–987. (b) K€olle, U.; Fuss, B. Chem. Ber. 1984, 117, 753–762. (c) K€ olle, U.; Fuss, B. Chem. Ber. 1984, 117, 743–752. (d) K€olle, U.; Khouzami, F.; Fuss, B. Angew. Chem. 1982, 94, 132–132. Angew. Chem., Int. Ed. Engl. 1982, 21, 131-132. (16) Burkey, D. J.; Hays, M. L.; Duderstadt, R. E.; Hanusa, T. P. Organometallics 1997, 16, 1465–1475.
1 H NMR spectra were recorded in acetone-d6 and CD2Cl2. For better comparability with literature values, in the following the measurements in acetone-d6 are discussed. The values for CD2Cl2 are given in parentheses. In the 1H NMR spectrum the methyl groups of the Cp moiety yield a singlet at 1.21 ppm (acetone-d6, CD2Cl2: 1.10 ppm) and thus appear shifted to higher field by 0.6 ppm as compared to [Cp*2Co]PF6 in the same solvent (1.78 ppm in acetone-d6).17 We attribute this observation to the influence of the aromatic ring current of the Dbf ligand. Similar effects have been observed before on Dbf-ferrocenes18 and (η3-allyl)(η5-Dbf)M(CO)2 complexes (M = Mo, W).19 The remaining proton of the five-membered ring of the Dbf ligand is detected at 6.52 ppm (acetone-d6, CD2Cl2: 5.90 ppm) and appears slightly broadened. The signals of the CH groups in the 8- and 80 positions appear separated from the other aromatic resonances as a doublet at 9.12 ppm (3JHH = 7.8 Hz, acetone-d6, CD2Cl2: 8.95 ppm; the 8,80 -CH groups correspond to C9, H9 and C19, H19 in the solid-state structure; see Figure 1). By HH-COSY NMR spectroscopy the remaining resonances of the terminal phenylene rings can then be identified: The 6,60 and 7,70 -protons yield a superimposed multiplet between 7.87 and 7.98 ppm; the 5,50 -CH groups are detected at 8.16 ppm and appear to be superimposed with one doublet of the 3,30 - or 4,40 -protons, to yield a pseudo triplet. The second doublet of the 3,30 - and 4,40 -protons is observed at 7.57 ppm. The signal of the 9-CH group is detected in the 13C NMR spectrum at 74.74 ppm (acetone-d6, CD2Cl2: 77.60 ppm), while the remaining resonances of the quaternary carbons of the aromatic η5-C5H ring are allocated at 99.89 and 90.44 ppm (acetone-d6, CD2Cl2: 98.98, 89.82 ppm). The 13C NMR spectrum shows only seven further aromatic resonances for the Dbf unit when recorded in CD2Cl2, presumably due to superimposition of two signals. In acetone-d6 the signals of all eight remaining aromatic carbon atoms of the Dbf unit are resolved individually. The methyl groups of the Cp* moiety give one resonance at 7.95 ppm (acetone-d6, CD2Cl2: 7.51 ppm). By HMBC NMR spectroscopy a signal at 95.59 ppm (acetone-d6, CD2Cl2: 94.75 ppm) can be assigned to the corresponding quaternary Cp ring atoms. Single crystals suitable for X-ray diffraction analysis were obtained by overlaying a solution of the complex in CH2Cl2 with Et2O, which yielded [(η5-Dbf)Co(η5-Cp*)]PF6 as red prismatic needles crystallizing in the space group P21/c.
(17) Robbins, J. L.; Edelstein, N.; Spencer, B.; Smart, J. C. J. Am. Chem. Soc. 1982, 104, 1882–1893. (18) Pammer, F.; Sun, Y.; Pagels, M.; Weismann, D.; Sitzmann, H.; Thiel, W. R. Angew. Chem. 2008, 120, 3315–3318. Angew. Chem., Int. Ed. 2008, 47, 3271-3274. (19) Pammer, F.; Sun, Y.; Thiel, W. R. Organometallics 2008, 27, 1015–1018.
Communication
As the packing diagram shows, the PF6- anions arranged in channels. The two Cp ligands assume an almost ideally staggered conformation, as judged by the angle H21-C21C25-C30 = -35.389(1)°. Due to this, the C27 methyl group is positioned almost exactly between to two naphthyl arms. The twist of the binaphthyl system, described by the angle C10-C1-C11-C20, amounts to -13.949(3)°, while the leastsquares planes defined by the naphthyl residues intersect at an angle of 19.535(0)°. Thus the torsion of the ligand is reduced compared to the free ligand DbfH (-23.9657(2)° and 29.0°),20 but lies at the upper end of the range as yet observed for η5-Dbf complexes (min.: (η5-Dbf)Mn(CO)3: 10.7(5)° and 17.1°, 21 max.: (η 3 -allyl)(η 5 -Dbf)Mo(CO)2 : 15.6(13)° and 23.0°19). As has already been observed for other Dbf complexes, metal coordination leads to a more localized aromatic system in the Dbf- anion22 accompanied by a decreased conjugation of the double bonds in the positions 3,4 and 30 ,40 . This leads to bond lengths close to those of isolated double bonds (C3dC4: 1.335(3) A˚, C13dC14: 1.341(3) A˚). The Dbf- ligand assumes a slightly unsymmetrical coordination to the metal center. The C11-Co1 bond is lengthened to 2.1105(17) A˚, because the corresponding naphthyl arm is twisted away from the Co core, while the three remaining quaternary η5-C5-ring carbon atoms undergo coordination to the cobalt site with distances between 2.0601(17) A˚ (C12) and 2.0869(18) A˚ (C2). The carbon-metal bond to C21 is found to be distinctly shortened (2.0349(17) A˚) due to some charge concentration at this position. The coordination mode of the Cp*- ligand is also affected by the binaphthyl system: The bonds of the cobalt atom to the three carbon cores positioned underneath the Dbf- ligand (C22, C23, and C26) amount to 2.0579(18), 2.0557(18), and 2.0482(17) A˚, respectively, and are found to be about 0.01-0.02 A˚ longer than the distances to C24 and C25 (2.0392(18) and 2.0373(18) A˚). These slight shifts also distort the coordination sphere around the metal center, so that the five-membered-ring planes diverge by 4.790° from coplanarity and the ring centers form an angle of 176.948(1)° with the cobalt core. With a Co-Ct2 distance of only 1.647 A˚ the electron-rich Cp*- ligand is found slightly closer to the cobalt core than in [Cp*2Co]PF6 (between 1.6548(12)23a and 1.6520(1) A˚23b), while C5H ring of the Dbf- fragment is found 1.6739 A˚ from the metal site. Cyclic voltammetry was carried out in dichloromethane solution in the presence of (n-Bu4N)(PF6) as the conducting salt to evaluate the redox properties of [(η5-Dbf)Co(η5Cp*)]PF6 (Figure 2). A glassy carbon electrode was used as the working electrode, a Ag wire as the pseudo reference electrode, and a Pt wire as the counter electrode. There is one reversible redox process at E1/2 = -1363 mV vs ferrocene (Epc = -1426 mV, ΔE = 125 mV, Epa = -1301 mV, determined in situ by the addition of ferrocene after the CV experiment), the electrochemically generated reduced species (20) Pammer, F. Ph.D. thesis, TU Kaiserslautern, 2009. (21) Pammer, F.; Sun, Y.; May, C.; Wolmersh€auser, G.; Kelm, H.; Kr€ uger, H.-J.; Thiel, W. R. Angew. Chem. 2007, 119, 1293–1296. Angew. Chem., Int. Ed. 2007, 46, 1270-1273. (22) Pammer, F.; Sun, Y.; Weismann, D.; Sitzmann, H.; Thiel, W. R. Chem.;Eur. J. 2010, 16, 1265–1270. (23) (a) Braga, D.; Benedi, O.; Maini, L.; Grepioni, F. J. Chem. Soc., Dalton Trans. 4, 2611-2618. (b) Heise, H.; K€ ohler, F. H.; Herker, M.; Hiller, W. J. Am. Chem. Soc. 2002, 124, 10823–10832.
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Figure 2. Cyclic voltammogram of [(η5-Dbf)Co(η5-Cp*)]PF6.
is stable on the time scale of the CV experiment, and there is no oxidative redox process within the window of the solvent. Since there is almost no dependence of the potentials Epc and Epa as well as of the peak currents ipc and ipa with respect to variations of the scan rates, this indicates a noninhibited electron transfer between the electrode and the substrate. By comparison with literature values (see below), the redox process around 1363 mV can be attributed to the reduction/oxidation of the Co3þ/Co2þ redox couple. Therefore [(η5-Dbf)Co(η5-Cp*)]PF6 shows a similar electron affinity to Cp2Coþ (E1/2 = -1340 mV, NCMe, 0.1 M n-Bu4N(PF6))13a,24 and the (Cp*)Co(helicenyl-Cp) complexes published by Katz (E1/2 between -1410 and -1460 mV, NCMe, 0.1 M n-Bu4N(PF6)).13a Though literature values vary, bisindenylcobalt(III) ((η5-Ind)2Coþ) exhibits a distinctly higher electron affinity (E1/2 = -920 mV, NCMe, no conducting salt given,13b E1/2 = -530 mV, DMF, 0.2 M NaClO425). To obtain further information on the nature of the product generated by reducing [(η5-Dbf)Co(η5-Cp*)]PF6, spectroelectrochemical investigations were carried out. A combined electrochemistry/UV-vis study clearly proved the direct electrochemical generation of the reduced product. For this, [(η5-Dbf)Co(η5-Cp*)]PF6 was electrolytically reduced in an OTTLE cell (rt, CH2Cl2, n-Bu4N(PF6), Figure 3).26 The reduction of [(η5 -Dbf)Co(η5 -Cp*)]PF6 results in pronounced changes of the UV-vis spectrum. A strong absorption at 380 nm is shifted to 330 nm, while a series of new absorptions appear at 420, 500, and 820 nm. Katz et al. reported strong bands at 598 and 957 nm for a cobaltocene complex bearing a CpMe5 and a Cp-helicene ligand.13a The combination of electrochemistry and EPR spectroscopy allowed to further characterize the reduced species. The in situ generated one-electron reduced species [(η5-Dbf)Co(η5-Cp*)] in CH2Cl2/0.1 M n-BuN(PF6) is EPR silent at room temperature. This corroborates with the behavior of many other Co(II) systems, where fast spin-lattice relaxation (24) Geiger, W. E. J. Am. Chem. Soc. 1974, 96, 2632–2634. (25) Hsiung, H.-S.; Brown, G. H. J. Electrochem. Soc. 1963, 110, 1085–1086. (26) Krejcik, M.; Danek, M.; Hartl, F. J. Electroanal. Chem. Interfacial Electrochem. 1991, 317, 179–187.
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Figure 4. EPR spectrum of [(η5-Dbf)Co(η5-Cp*)]PF6 recorded at 110 K and simulated spectrum.
Figure 3. Generation of [(η5-Dbf)Co(η5-Cp*)] by electrolysis of [(η5-Dbf)Co(η5-Cp*)]PF6 followed by UV/vis spectroscopy.
pathways make signal recording at room temperature difficult.27 After cooling to 110 K this compound shows a strong rhombic signal that could be simulated by considering a S = 1/2 system and hyperfine coupling to 59Co (I = 7/2). The parameters resulting from the simulation (Figure 4) are g1 = 2.102, g2 = 2.010, g3 = 1.880 and A1 = 133 G, A2 = 35 G, A3 = 64 G. For the D5d symmetric cobaltocenium with a 2E1g ground state (electronic configuration (e2g)4(a1g)2(e1g)1) very fast spin-lattice relaxations owing to orbital degeneracy allow observing the EPR signal only at 4 K. For the Jahn-Teller active cobaltocenium case, the signal is strongly anisotropic with all g-values significantly lower than the free electron gvalue.27 Moving from the highly symmetric cobaltocenium to systems such as (Cp)Co(acac) or (Cp*)Co(acac) (acac = acetylacetonato) with a much lower ligand field symmetry leads to a larger splitting of the e1g pair and an increase of the relaxation times as well as the g-values.28 The present case (27) (a) Ammeter, J. H.; Swalen, J. D. J. Chem. Phys. 1972, 57, 678– 698. (b) Weber, J.; Goursot, A.; Penigault, E.; Ammeter, J. H.; Bachmann, J. J. Am. Chem. Soc. 1982, 104, 1491–1506. (28) Smith, M. E.; Anderson, R. A. J. Am. Chem. Soc. 1996, 118, 11119–11128.
is certainly more similar to a half-sandwich compound such as [(Cp)Co(acac)] than to cobaltocene itself. Hence the ganisotropy observed in the present case (Δg = g1 - g3 = 0.222) is much lower than cobaltocene, with one g-value above, one close to, and one below the free electron g-value. Similar results have been recently observed for an ansacobaltocene.29 In summary we were able to isolate and completely characterize the first cobalt complex of the polycyclic ligand dibenzo[c,g]fluorenide. The complex is stable and shows, when reduced to the corresponding Co(II) system, the typical spectroscopic features of cobaltocenes bearing extended π-ligands. Supporting Information Available: Tables and figures giving X-ray structure data and NMR spectra. This material is available free of charge via the Internet at http://pubs.acs.org. Crystallographic data (excluding structure factors) for the structure reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as Supplementary Publication No. CCDC-798212 ([(η5-Dbf)Co(η5-Cp*)]PF6) and No. CCDC798211 (DbfH). Copies of the data can be obtained free of charge on application to the CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (fax, (þ44)1223-336-033; e-mail,
[email protected]. ac.uk). (29) Braunschweig, H.; Breher, F.; Kaupp, M.; Gross, M.; Kupfer, T.; Nied, D.; Radacki, K.; Schinzel, S. Organometallics 2008, 27, 6427– 6433.
