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Organometallics 2004, 23, 3548-3551
Notes Copper(I)-Catalyzed Synthesis of Ferrocenyl Aryl Ethers Markus R. an der Heiden, Guido D. Frey, and Herbert Plenio* Institut fu¨ r Anorganische Chemie, TU Darmstadt, Petersenstr. 18, 64287 Darmstadt, Germany Received March 24, 2004 Summary: Ferrocenyl aryl ether can be synthesized in good yields by CuI/2,2,6,6-tetramethylheptane-3,5-dione (TMHD)-catalyzed coupling reactions from iodoferrocene or 1,1′-diiodoferrocene and various phenols in NMP solvent using Cs2CO3 or K3PO4 bases. Ferrocenes constitute an important class of organometallic compounds, which has found numerous applications as ligands in homogeneous catalysis,1 for molecular recognition,2 in polymer sciences,3 and as biolabels,4 sensors,5 NLO materials,6 and molecular switches.7 Nonetheless, several deficits in the preparative chemistry of ferrocenes are still obvious. As an example, the synthetic availability of heteroatom (oxygen, nitrogen)substituted ferrocenes is rather limited, as the synthetic routes traditionally used to introduce such heteroatoms on benzenes are not suitable for ferrocenes. The main entries into this chemistry are 1,1′-diaminoferrocene and 1,1′-dihydroxyferrocene or the respective monosubstituted ferrocenes, which can be functionalized via simple nucleophilic substitutions with alkyl halides to result in secondary or tertiary ferrocenylamines or in ferrocenyl alkyl ethers.8 Related compounds with additional substituents on ferrocene are less easily obtained. Basically, substituted ferrocenyl alkyl ethers are accessible primarily via the stable trialkylsilyl-protected hydroxyferrocenes, which can be obtained in good yields from the respective lithiated cyclopentadienyl silyl ethers and FeCl2.9 On * Corresponding author. E-mail:
[email protected]. (1) (a) Colacot, T. J. Chem. Rev. 2003, 103, 3101. (b) Blaser, H.-U. Adv. Synth. Catal. 2002, 344, 17. (c) Ferrocenes; Togni, A., Hayashi, T., Eds.; VCH: Weinheim, 1995. (d) Dai, L. X.; Tu, T.; You, S. L.; Deng, W. P.; Hou, X. L. Acc. Chem. Res. 2003, 36, 659. (2) Beer, P. D.; Gale, P. A.; Chen, G. Z. Coord. Chem. Rev. 1999, 186, 3. (3) Manners, I. Macromol. Symp. 2003, 196, 57. (4) (a) Salmain, M.; Jaouen, G. C. R. Chim. 2003, 6, 249. (b) Nakayama, M.; Ihara, T.; Nakano, K.; Maeda, M. Talanta 2002, 56, 857. (5) Luk, Y. Y.; Abbott, N. L. Science 2003, 301, 623. (6) Whittall, I. R.; McDonagh, A. M.; Humphrey, M. G.; Samoc, M. Adv. Organomet. Chem. 1999, 43, 349. (7) Plenio, H.; Aberle, C. Chem. Eur. J. 2001, 7, 4438. (8) (a) Herberhold, M. In Ferrocenes; pp 219-279, ref 1c. (b) Shafir, A.; Power, M. P.; Whitener, G. D.; Arnold, J. Organometallics 2000, 19, 3978. (c) Herberhold, M.; Brendel, H.-D.; Hofmann, A.; Hofmann, B.; Milius, W. J. Organomet. Chem. 1998, 556, 173. (d) Bildstein, B.; Malaun, M.; Kopacka, H.; Wurst, K.; Mitterbo¨ck, M.; Ongania, K.-H.; Opromolla, G.; Zanello, G. Organometallics 1999, 18, 4325. (9) (a) Plenio, H.; Aberle, C. Organometallics 1997, 16, 5950. (b) Plenio, H.; Aberle, C. Chem. Commun. 1996, 2123.
the contrary, ferrocenyl aryl ethers are almost unknown; the only synthesis of such compounds dates back to the early 1960s when Rausch10 and Nefedova11 described Ullmann type coupling reactions at elevated temperatures to produce ferrocenyl phenyl ethers in modest yields of around 10-25%. Consequently, we wish to describe here a reliable and high-yielding synthesis of ferrocenyl aryl ethers from bromo- or iodoferrocenes and phenols mediated by copper(I)-based catalysts.12 To synthesize ferrocenyl aryl ethers, we first tested the Pd-catalyzed Buchwald-Hartwig ether synthesis13 using various phenols and iodo- or bromoferrocenes. Unfortunately, all our attempts using different phosphine ligands and palladium sources as catalysts did not lead to the formation of the desired products. Following this, we evaluated several copper-based catalysts,14 which were demonstrated to work efficiently for the synthesis of aryl ethers by Buchwald et al. (CuI/ 1,10-phenanthroline, Cs2CO3),15 Venkataraman et al. [Cu(neocup)(PPh3) and Cu(PPh3)3Br],16 and Song et al. [CuCl/THMD].17 Among these, the CuI/1,10-phenanthroline catalyst (Table 1, entries 1-4) and the Cu(PPh3)3Br complex resulted in the formation of modest amounts of ferrocenyl aryl ethers. In test reactions of iodoferrocene and 1,4-tert-butylphenol up to 16% yield of coupling products were formed with the CuI/1,10phenanthroline system (10 mol % CuI and 20 mol % phen) after 24 h at 110 °C. Significantly improved yields were obtained with the Venkataraman catalyst Cu(PPh3)3Br. However, instead of using a preformed copper-phosphine complex, we considered it more practical to in situ generate the respective catalyst. Consequently, we evaluated the (10) Rausch, M. D. J. Org. Chem. 1961, 26, 1802. (11) Nefedov, V. A.; Nefedova, M. N. Zh. Obs. Khim. 1966, 36, 122. (12) Ley, S. V.; Thomas, A. W. Angew. Chem. 2003, 115, 5585. (13) (a) Mann, G.; Shelby, Q.; Roy, A. H.; Hartwig, J. F. Organometallics 2003, 20, 2775. (b) Torraca, K. E.; Huang, X.; Parrish, C. A.; Buchwald, S. L. J. Am. Chem. Soc. 2001, 123, 10770. (c) Aranyos, A.; Old, D. W.; Kiyomori, A.; Wolfe, J. P.; Sadighi, J. P.; Buchwald, S. L. J. Am. Chem. Soc. 1999, 121, 4369. (14) Cristau, H.-J.; Cellier, P. P.; Hamada, S.; Spindler, J.-F.; Taillefer, M. Org. Lett. 2004, 6, 913. (15) Wolter, M.; Nordmann, G.; Job, G. E.; Buchwald, S. L. Org. Lett. 2002, 4, 973. (16) (a) Gujadhur, R. K.; Bates, C. M.; Venkataraman, D. Org. Lett. 2001, 3, 4315. (b) Gujadhur, R. K.; Venkataraman, D. Synth. Commun. 2001, 31, 2865. (17) Buck, E.; Song, Z. J.; Tschaen, D.; Dorner, P. G.; Volante, R. P.; Reider, P. J. Org. Lett. 2002, 4, 1623.
10.1021/om0497893 CCC: $27.50 © 2004 American Chemical Society Publication on Web 06/10/2004
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Organometallics, Vol. 23, No. 14, 2004 3549
Table 1. Ligand Screening for the Coupling of Iodoferrocene and 1,4-tert-Butylphenola
Table 2. Ligand/Base Screening for the Coupling of Iodoferrocene and Phenols in NMPa
entry
entry 1 2 3 4 5 6 7 8 9 10 11 12 13
solvent
ligand
base
yielde [%]
toluene toluene toluene toluene toluene toluene toluene toluene toluene NMP NMP NMP toluene
1,10-phenb
Cs2CO3 K3PO4 DABCO Et3N Cs2CO3 Cs2CO3 Cs2CO3 Cs2CO3 K3PO4 Cs2CO3 Cs2CO3 Cs2CO3 Cs2CO3
9 16 95 >95 86 33 >95
42 81 86 30 77 89 87 65 24 90 40 65 27 30 22 none none none
75 70 60
