Chemistry and catalysis advances in organometallic chemistry and catalysis
, 45 , 3940 39. Moonen, N. N. P.; Thilgen, C.; Echegoyen, L.; Diederich, F. Chem. Commun. 2000
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2009, 45 , 3940 39. Moonen, N. N. P.; Thilgen, C.; Echegoyen, L.; Diederich, F. Chem. Commun. 2000, 36 , 335 40. Kessinger, R.; Crassous, J.; Herrmann, A.; R¨uttimann, M.; Echegoyen, L.; Diederich, F. Angew. Chem. Int. Ed. 1998, 37 , 1919. 41. Lukoyanova, O.; Cardona, C. M.; Aaltable, M.; Filippone, S.; Domenech, A. M.; Martin, N.; Echegoyen, L. Angew. Chem. Int. Ed. 2006, 45 , 7430. 42. Mart´ın, N.; Altable, M.; Filippone, S.; Mart´ın-Domenech, A.; Echegoyen, L.; Cardona, C. M. Angew. Chem. Int. Ed. 2006, 45 , 110. 43. Filippone, S.; Barroso, M. I.; Martin-Domenech, A.; Osuna, S.; Sola, M.; Martin, N. Chem. Eur. J. 2008, 14 , 5198. 44. Brunetti, F. G.; Herrero, M. A.; De, M. J.; Giordani, S.; Diaz-Ortiz, A.; Filippone, S.; Ruaro, G.; Meneghetti, M.; Prato, M.; Vazquez, E. J. Am. Chem. Soc. 2007, 129 , 14580. 45. Martin, N.; Altable, M.; Filippone, S.; Martin-Domenech, A.; Martinez-Alvarez, R.; Suarez, M.; Plonska-Brzezinska, M. E.; Lukoyanova, O.; Echegoyen, L. J. Org. Chem. 2007, 72 , 3840. 46. Delgado, J. L.; Oswald, F.; Cardinali, F.; Langa, F.; Martin, N. J. Org. Chem. 2008, 73 , 3184. 47. Ettl, R.; Chao, I.; Diederich, F.; Whetten, R. L. Nature, 1991, 353 , 149. 48. Thilgen, C.; Gosse, I.; Diederich, F. Top. Stereochem. 2003, 23 , 1. 49. C. Thilgen, F. Diederich, Chem. Rev. 2006, 106 , 5049–5135. 50. (a) Friedman, S. H.; Ganapathi, P. S.; Rubin, Y.; Kenyon, G. L. J. Med. Chem. 1998, 41 , 2424; (b) Zhu, Z.; Schuster, D. I.; Tuckerman, M. E. Biochemistry 2003, 42 , 1326. 51. Nishimura, T.; Tsuchiya, K.; Ohsawa, S.; Maeda, K.; Yashima, E.; Nakamura, Y.; Nishimura, J. J. Am. Chem. Soc. 2004, 126 , 11711. 52. Hizume, Y.; Tashiro, K.; Charvet, R.; Yamamoto, Y.; Saeki, A.; Seki, S.; Aida, T. J. Am. Chem. Soc. 2010, 132 , 6628. 53. Filippone, S.; Maroto, E. E.; Mart´ın-Domenech, ´ A.; Suarez, M.; Mart´ın, N. Nat. Chem. 2009, 1 , 578. 54. Maggini, M.; Scorrano, G.; Prato, M. J. Am. Chem. Soc. 1993, 115 , 9798 55. Prato, M.; Maggini, M. Acc. Chem. Res. 1998, 31 , 519. 56. Lian-He, S.; Guan-Wu, W.; Shi-Hui, W.; Hou-Ming, W.; Xia-Fei, L. Tetrahedron Lett. 1995, 36 , 3871. 57. Wu, S.-H.; Sun, W.-Q.; Zhang, D.-W.; Shu, L.-H.; Wu, H.-M.; Xu, J.-F.; Lao, X.-F. J. Chem. Soc. Perkin Trans. 1998, 1 , 1733. 58. Maroto, E. E.; Filippone, S.; Martin-Domenech, A.; Suarez, M.; Mart´ın, N. J. Am. Chem. Soc. 2012, 134 , 12936. 59. Wilson, S. R.; Lu, Q.; Cao, J.; Wu, Y.; Welch, C. J.; Schuster, D. I. Tetrahedron 1996, 52 , 5131. 60. Maroto, E. E.; de C´ozar, A.; Filippone, S.; Mart´ın-Domenech, ´ A.; Suarez, M.; Coss´ıo, F. P.; Mart´ın, N. Angew. Chem. Int. Ed. 2011,
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35 ORGANOMETALLIC COMPLEXES OF SUMANENE Toru Amaya and Toshikazu Hirao* Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Osaka, Japan 35.1 INTRODUCTION Complexation of metals to curved carbon π surfaces has attracted continuous interest since the discovery of fullerenes. So far, fullerenes have been found to act as an η 2
π-surface [1, 2]. Other coordination modes in exo complexes were reported in the modified fullerene π systems [3], such as “buckyferrocene” [4] Fe(C
60 Me 5 )Cp (Cp = cyclopentadienyl). Fullerenes are also known to form the endohedral metal complexes to provide potential materials in carbon chemistry [5, 6]. On the other hand, fullerene fragments, termed as π bowls (we use this term in the present chapter, whereas they have been also called open geodesic polyarenes [7] or buckybowls [8]), also possess curved carbon π surfaces. π Bowls have attracted interest in the science of nonplanar π-conjugated carbon systems [9–14]. From the viewpoint of coordination chemistry, such molecules are quite unique because they can provide not only a convex surface but also an open concave surface for binding (a schematic illustration is shown in Fig. 35.1), which was first addressed by the computational study of hemifullerene (C 30 H
) in 1993 [15]. As polar end-cap structural motifs of fullerene or carbon nanotube, there are two representative key subunits for π bowls. One is a C 5v symmetric “corannulene” (2, C 20 H
) and the other is a C 3v symmetric “sumanene” (1, C 21 H 12 ) (Fig. 35.2). Corannulene (2) was first synthesized in 1966 [16]. More practical synthetic methods of 2 have been developed since then [17–19], which made a breakthrough in the coordination chemistry of the π bowl. On the other hand, research based on sumanene (1) started with our first synthesis in 2003 [20], besides some earlier synthetic and theoretical studies [21, 22]. The characteristic structural feature of 1 is three sp 3 -hybridized carbon atoms at the benzylic positions. It is in sharp contrast to the structure of 2, the rim of which is covered with five aromatic rings. The bowl depth of 1 (1.11 ˚ A) [23] is larger than that of 2 (0.89 ˚ A) [24] which may cause the effect attributed to the bowl structure in metal coordination. In this chapter, we describe the synthesis of organometallic complexes of 1, including organolithium and η 6 -coordination complexes with RCpM
+ (M = Fe and Ru). 35.2 ORGANOLITHIUM COMPLEXES OF SUMANENE Organolithium compounds are one of the widely used reagents in organic synthesis. Another use of organolithium reagents is in the preparation of various organometallic compounds, usually by reaction with metal halides. Therefore, the preparation of organolithium is important even in π-bowl chemistry. The study on the coordination chemistry of π bowls started from the lithiation of corannulene in 1992 [25]. Treatment of
35.3). More specifically, the doubly degenerate lowest unoccupied molecular orbital (LUMO) levels of 2 allow it to accept Advances in Organometallic Chemistry and Catalysis: The Silver/Gold Jubilee International Conference on Organometallic Chemistry Celebratory Book, First Edition. Edited by Armando J. L. Pombeiro. © 2014 John Wiley & Sons, Inc. Published 2014 by John Wiley & Sons, Inc.
474 ORGANOMETALLIC COMPLEXES OF SUMANENE π Bowl Metal
Convex complex Concave complex or
Schematic illustration of convex and concave bindings of a metal to a π bowl.
Sumanene (1) and corannulene (2). up to four electrons to form an aromatic Cp anion (6e/5C) suspended by five radial bonds within the hole of an aromatic 18e/l5C annulenyl trianion. Interestingly, such a tetraanion 3 assembles to form the sandwich dimer complex with some lithium cations inside [26]. Recently, the supercharged dimer structure was confirmed using X-ray crystallographic analysis and
7 Li NMR spectroscopy [27] as a sandwich 4, consisting of five lithium cations jammed between two corannulene tetraanions (Fig. 35.3).
In contrast to corannulene (2), sumanene (1) has three methylene carbons at the benzylic positions, which enables facile formation of organolithium species. The stepwise generation of the mono-, di-, and trianions was observed by NMR experiments (Fig. 35.4) [23]. Benzylic protons are kinetically deprotonated by the treatment of t-BuLi. Careful control of the amount of t-BuLi selectively led to the formation of the monoanion 5. In the 1 H NMR spectrum, the signals of 1 disappeared with the appearance of the signals for 5. In addition, a singlet peak around 6.0 ppm, assignable to the benzyl anion species, was observed. Additional treatment with t-BuLi provided another set of the signals assigned to the dianion 6. The difference in chemical shifts between the exo/endo-benzylic protons increased in the order of the number of anions (dianion 6 > monoanion 5 > 1). Further addition of t-BuLi afforded only two singlets in the 1 H NMR, assignable to the protons at the anion-generated carbons and aromatic rings. Such a simple spectrum is consistent with the symmetrical trianion 7. Because of charge localization, trapping the anion with an electrophile leads to selective substitution at the desired benzylic positions. The reaction of 7 with Me 3 SiCl gave the exo-introduced tris(trimethylsilyl) derivative 8 as a sole isomer quantitatively (Scheme 35.1). The observed stereoselectivity is probably due to the steric demand. Synthetic approaches via the benzylic anions can be applied for the facile preparation of various sumanene derivatives [28–30]. 3 6 π 18 π Li Li Li Li Li 4 4Li
+ 3Li
Figure 35.3 Corannulene tetraanion 3 and sandwich 4 consisting of five lithium cations jammed between two corannulene tetraanion. ORGANOLITHIUM COMPLEXES OF SUMANENE 475 ppm
3 4 5 6 7 X X X X H endo
H endo
H endo
H exo
H exo
H exo
H anion
H anion
H anion
H arom
H arom
H arom
H arom
Li + 2Li + 3Li
+ 5 6 7 THF-d 8
H endo H exo
1 H endo H exo
H anion
H anion
H endo
H exo
H anion
t-BuLi t-BuLi Figure 35.4 Stepwise generation of mono-, di-, and trianions 5–7 from 1 and their 1 H NMR spectra. Me 3 SiCl quant. 8 SiMe
3 SiMe
3 Me 3 Si 7 Below
−80 °C to rt Scheme 35.1 Synthesis of tris(trimethylsilyl)sumanene 8. 35.2.2 Bowl-to-bowl Inversion of Sumanene’s Benzylic Anion Species Bowl-to-bowl inversion is one of the characteristic behaviors for some flexible π bowls such as corannulene (2) and sumanene (1) (Fig. 35.5). The bowl-to-bowl inversion of the corannulene derivative 9 (Fig. 35.6) occurs rapidly with an activation barrier of 10–11 kcal/mol [31]. The close relationship between the inversion energy barrier and the bowl depth was investigated using corannulene derivatives [32]. An equation between the bowl depth x and the energy barrier E a (E a = Cx 4 )
barrier of 1 was estimated by a variable-temperature NMR study [20]. More detailed investigation was carried out by 2D 476 ORGANOMETALLIC COMPLEXES OF SUMANENE Bowl-to-bowl inversion
Schematic representation of bowl-to-bowl inversion of π bowl.
OH
D D
Figure 35.6 Corannulene derivative 9 and trideuteriosumanene 10. exchange spectroscopy (EXSY) NMR experiments using trideuteriosumanene 10 (Fig. 35.6), showing an inversion barrier of approximately 20 kcal/mol [29, 33]. In this molecule, the bowl-to-bowl inversion is equivalent to the isomerization between the diastereomers. Accordingly, estimation of the isomerization rate quantified by the cross peaks in a 2D EXSY NMR spectrum gives the inversion rate. The dynamic behaviors of the mono- and dianion were investigated using trideuteriosumanene 10 as a starting material. Treatment of 10 with the requisite amount of t-BuLi generated 12 and 13. The inversion behavior was first studied using 2D EXSY NMR experiments in THF-d 8 . However, no cross peak was observed in either of them. It suggests that the anions 12 and 13 maintain a relatively rigid bowl shape in this timescale [29]. So, we planned to monitor the equilibration of exo-deutrated 12a and 13a by simple 1 H NMR measurement to investigate such a slow inversion. Selective deuteration of the trianion 7 was achieved to give 11 (Fig. 35.7) by precipitation with CH 3 OD at approximately −100 ◦ C. Keeping 11 as a solid at room temperature did not induce the bowl-to-bowl inversion. To generate monoanion 12a and dianion 13a, 11a was treated with the requisite amount of t-BuLi at approximately −100 ◦
8 (Fig. 35.7); then the equilibration was monitored. The 1 H NMR spectra are shown in Fig. 35.7a and b. Growth of the exo-benzylic protons (4.46 and 3.88 ppm for 12b and 13b, respectively) was observed in both spectra (Fig. 35.7a and b) [29]. The half-life times were 2755 s for 12a at 283 K and 7580 s for 13a at 273 K. The rate constants (k’s) for the reversible equilibration of 12 and 13 were 9.10
× 10 – 5
s −1 at 283 K and 3.40 × 10 –5 s −1 at 273 K, respectively, determined by regression analysis using the equation 2kt = ln[a/(a—2x)], where a is the initial concentration of 12a (or 13a) and x is the concentration of 12b (or 13b) at time t. Correlation coefficients of the linear regressions were 0.999 and 0.978. G ‡ ’s were 21.8 and 21.5 kcal/mol for 12 and 13, respectively, calculated from the Eyling equation. Monoanion 12 and dianion 13 possess 1.5 and 1.2 kcal/mol higher barrier than 10, respectively. 35.3 η
-COORDINATION COMPLEXES OF SUMANENE Transition-metal complex of π bowls have attracted much attention [12, 34, 35]. Controlled positioning of metal centers inside the bowls is expected to provide a direct route to the inclusion complexes of fullerenes and nanotubes. On the other hand, the coordination of metal centers to the outside of the bowls should permit applications in the field of surface activation and functionalization of fullerenes and nanotubes. To date, some π bowl (mainly corannulene or its derivatives) complexes with several coordination modes have been synthesized [12, 34, 35]. In addition to the conventional liquid phase synthesis, a microscale gas-phase coordination method was introduced [36] to prepare η 1 - and/or η 2 -binding complexes, which is based on co-deposition of volatile complementary building units such as Rh 2 (O
CCF 3 ) 4 , Ru
2 (O 2 C(3,5-CF 3 ) 2 C 6 H 3 ) 2 (CO)
5 , and
Ru 2 (O 2 CCF
3 ) 2 (CO) 4 under reduced pressure. Among several coordination modes, some η 6 -arene complexes have been prepared and characterized. In 1997, the first
η 6 -arene complex of 2, [Cp*Ru(corannulene)]CF 3 SO 3 (14a) (Cp* = pentamethylcyclopentadienyl) (Fig. 35.8), was η 6 -COORDINATION COMPLEXES OF SUMANENE 477 11 D D D 12a D or H
D or H 13a t-BuLi (1 equiv), 3.0 4.0
12b D or H
H exo
D H exo D D or H
D H endo D H endo 30 min 60 min
90 min 150 min
210 min 283 K
Residual THF THF-d 8
ca.
−100 °C (a)
(b) 2.5
3.5 Residual THF 30 min 90 min
150 min 300 min
480 min t-BuLi (2 equiv), 11 THF-d 8
ca.
−100 °C D H endo 273 K
D or H D or H
H exo
D 13b ΔG ‡ = 21.8 kcal/mol ΔG ‡ = 21.5 kcal/mol ppm ppm
Figure 35.7 (a) Generation of monoanion 12a and selected 1 H NMR spectra for the equilibration at 283 K. (b) Generation of dianion 13a and selected 1 H NMR spectra for the equilibration at 273 K. Ru X
3 SO
14b: X = SbF 6
[(C 5
5 )Ru(corannulene)]X (X = CF 3
3 : 14a, X = SbF 6
478 ORGANOMETALLIC COMPLEXES OF SUMANENE Fe PF
15 Ferrocene (10 equiv), Al (2 equiv), AlCl 3 (10 equiv) 120 ° C, 19 h 91% 1 Sat. NH
4 PF 6 aq Scheme 35.2 Synthesis of [CpFe(sumanene)]PF 6 (15). 15 Fe H H H H b c d endo d exo e endo
e exo
f 3.0% 2.6% NOEs from Cp protons to endo-benzylic protons a
NOEs from Cp protons to endo-benzylic protons in 15. synthesized; however, the face selectivity of the coordination was not confirmed at that time [37]. Eight years later, the convex binding of [Cp*Ru(corannulene)]SbF 6 (14b) (Fig. 35.8) was finally revealed by X-ray crystallographic analysis [38]. Both convex and concave binding complexes [(Cp*Ru) 2 ( μ 2 - η 6 : η 6 -corannulene)][X] 2 (X = PF 6 or SbF
6 ) were also reported, where significant flattening of the bowl structure is induced [38, 39]. In addition to Cp*Ru, some η 6 -corannulene complexes bearing Cp*Ir 2 +
2 Ir + (COE = cyclooctene) [41], (COE) 2 Rh
[41], (C 6 Me 6 )Ru
2 + [42], and (cymene)Os 2 + [42] were prepared, and all of them showed the convex coordination. Theoretical studies of corannulene complexes using DFT calculation were also carried out, which indicated the preferential convex binding to transition metals [43–45]. Download 11.05 Mb. Do'stlaringiz bilan baham: 
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