Microwave-assisted synthesis of cyclopentadienyl-cobalt sandwich complexes from diaryl acetylenes

Organometallics

Volumn 27, Issue 7, 2008, Pages 1653-1656

  Harcourt, Emily M ^a   Yonis, Shifra R ^a   Lynch, Daniel E ^b   Hamilton, Darren G ^a  

^a MOUNT HOLYOKE COLLEGE   (United States)

^b Institute for Clean Growth and Future Mobility   (United Kingdom)

Author keywords

[No Author keywords available]

Indexed keywords

DIARYL ACETYLENES; MICROWAVE DIELECTRIC HEATING;

COBALT COMPOUNDS; DIELECTRIC HEATING; METAL COMPLEXES; MICROWAVE HEATING; SYNTHESIS (CHEMICAL);

ORGANOMETALLICS;

EID: 42449129660     PISSN: 02767333     EISSN: None     Source Type: Journal    
DOI: 10.1021/om7011634     Document Type: Article

References (30)

1. (a) For a comprehensive overview see: Microwaves in Organic Synthesis; Loupy, A., Ed.; Wiley-VCH: Weinheim, 2002.
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9. Taylor, C. J.; Motevalli, M.; Richards, C. J. Organometallics 2006, 25, 2899-2902.
10. 4, thus allowing full investigation of its chemistry, especially its aromatic reactivity.
11. (b) Selected cyclobutadienyl-CoCp complexes may also be obtained via a more complex route, but one that avoids acetylene cyclodimerization: Yamazaki, H.; Wakatsuki, Y. J. Organomet. Chem. 1978, 149, 377-384.
12. For diverse examples of the preparation and utility of these classes of complex see: (a) Nguyen, H. V.; Butler, D. C. D.; Richards, C. J. Org. Lett. 2006, 8, 769-772(asymmetric organic synthesis).
13. (b) Waybright, S. M.; Singleton, C. P.; Wachter, K.; Murphy, C. J.; Bunz, U. H. F. J. Am. Chem. Soc. 2001, 123, 1828- 1833(oligonucleotide chemistry).
14. (c) Johannessen, S. C.; Brisbois, R. G.; Fischer, J. P.; Grieco, P. A,; Counterman, A. E.; Clemmer, D. E. J. Am. Chem. Soc. 2001, 123, 3818-3819(supramolecular chemistry).
15. Harrison, R. M.; Brotin, T.; Noll, B. C.; Michl, J. Organometallics 1997, 16, 3401-3412.
16. Decalin was investigated, as this was the solvent employed for the previously reported microwave-assisted preparations of cyclopentadienone cobalt metallocenes (see ref 3).
17. DME was investigated, as this solvent has proven particularly effective in reactions involving cobalt-mediated acetylene cycloadditions: Boñaga, L. V. R.; Zhang, H.-C.; Gauthier, D. A.; Reddy, I.; Maryanoff, B. E Org. Lett. 2003, 24, 4537-4540.
18. Reactions in DME were maintained at temperatures of no more than 120°C for reasons of safety. Inevitably rates of production of the desired metallocenes would be reduced at this temperature when compared with reactions in either p-xylene or Decalin. However, lengthier reaction times did not produce comparable yields to reactions conducted in either of these hydrocarbon solvents.
19. For a critical overview of the origin of differences in reaction outcome between microwave and traditional heating approaches, see: De la Hoz, A.; Díaz-Ortiz, Á.; Moreno, A. Chem. Soc. Rev. 2005, 34, 164-178.
20. (a) Stevens, A. M.; Richards, C. J. Organometallics 1999, 18, 1346-1348.
21. (b) Uno, M.; Ando, K.; Komatsuzaki, N.; Tsuda, T.; Tanaka, T.; Sawada, M.; Takahashi, S. J. Organomet. Chem. 1994, 473, 303-311.
22. All quoted yields are the average of a minimum of three independent runs and are based on conversion of the respective starting acetylene to complexes 2 and 3. These reactions also typically produced very small amounts of hexasubstituted benzene derivatives, the products of metal-catalyzed cyclotrimerization of the parent acetylene, and non-cobalt-complexed tetraarylcyclopentadieneones. The presence of these materials was confirmed by TLC comparison with, where available, authentic samples, but the amounts were generally too small for practical isolation.
23. Complexes 2a and 3a have long been known (see ref 4a), while 2b and 3b have also been previously prepared (see ref 6). All other materials reported are new, with the exception of cyclobutadiene complex 2c, which has previously been prepared by an alternative route: Wang, H.; Tsai, F.-Y.; Nakajima, K.; Takahashi, T. Chem. Lett. 2002, 6, 578-579.
24. Rausch, M. D.; Westover, G. F.; Mintz, E.; Reisner, G. M.; Bernal, I.; Clearfield, A.; Troup, J. M. Inorg. Chem. 1979, 18, 2605-2615.
25. 1 = 0.0614. CCDC entry 643536.
26. 6-DMSO, 140°C). Preparative TLC did not allow for separation of any individual isomer, but did allow two components to be isolated from the remainder (see Supporting Information).
27. 2 under microwave conditions, lending credence to the view that 1-naphthyl substituents are at the upper limit of those aryl groups that may be successfully incorporated.
28. The small amount of complex 2f produced in this reaction could be isolated by column chromatography and corresponded to a yield of 1-2%. While TLC analysis also indicated the presence of complex 3f, this material could not be separated from a number of additional products of similar polarity.
29. He, H.; Wu, Y.-J. Tetrahedron Lett. 2004, 45, 3237-3239.
30. 2 (162 mg, 120 μL, 0.9 mmol); the mixture was heated, with stirring, at 175°C for an additional 10 min. After final cooling the reaction mixture was worked up and purified according to the example preparative procedure to afford complex 2a (50 mg, 21%) and complex 3a (30 mg, 12%). Yields quoted in Scheme 3 are the average of three independent runs at this scale. No attempt was made to fully optimize solvent or temperature conditions, nor reaction times.