Dicarbonyl(cyclopentadienyl)(isobutene)iron Tetrafluoroborate

[41707-16-8]  · C11H13BF4FeO2  · Dicarbonyl(cyclopentadienyl)(isobutene)iron Tetrafluoroborate  · (MW 319.87)

(exchange reagent for synthesis of Fp-alkene+ and Fp-alkyne+ complexes; Fp+ protecting group for alkenes; cycloadditions of alkenes and alkynes)

Physical Data: yellow-orange crystalline solid.

Solubility: sol CH2Cl2, THF; insol Et2O, benzene, hexane; decomposes at varying rates in DMSO, MeNO2, MeCN, acetone, and other coordinating solvents.

Analysis of Reagent Purity: 1H NMR (CD3CN): d 5.52 (Cp), 3.81 (=CH2), 1.84 (CH3). 13C NMR (CD3CN): d 209 (CO), 118 (=CMe2), 87 (Cp), 51 (=CH2), 26 (Me).2 NMR shifts are highly solvent dependent.

Preparative Method: by reaction of NaFp (Fp = CpFe(CO)2) with methallyl chloride followed by protonation of the resulting alkyl complex with HBF4 (eq 1).1

Handling, Storage, and Precautions: stable indefinitely under Ar or N2 at 0 °C.

Alkene Exchange.3

Isobutene-Fp+ BF4- is a convenient reagent for the synthesis of Fp-alkene+ complexes. Exchange reactions occur readily in 1,2-dichloroethane (65-70 °C) or CH2Cl2 (at reflux) to form p-complexes with a wide variety of alkenes,4 dienes,5 allenes,6 and alkynes,7 and to form s-complexes with heteroatomic donors (eq 2).8

Protecting Group for Alkenes.

Isobutene-FpBF4 has also been used successfully to protect alkenes from hydrogenation3 and halogenation (eq 3).9

Activation of Alkynes and Allenes; Ring Formation.10

Reaction of isobutene-FpBF4 with homopropargylic alcohols or hydroxyallenes gives substituted dihydrofurans, as their Fp complexes (eq 4).

Isobutene-FpBF4 has also been reported to catalyze the cycloaddition of alkynic esters to alkenes to give cyclobutenes and lactones (eq 5).11 The complex Fp-THF+ BF4- has been used in a similar fashion.12

1. (a) Giering, W. P.; Rosenblum, M. JOM 1970, 25, C71. (b) Rosenblum, M.; Giering, W. P.; Samuels, S-B. Inorg. Synth. 1990, 28, 207.
2. Faller, J. W.; Johnson, B. V. JOM 1975, 88, 101.
3. Rosenblum, M. ACR 1974, 7, 122.
4. (a) Giering, W.; Rosenblum, M. JCS(D) 1971, 441. (b) Cutler, A.; Ehntholt, D.; Lennon, P.; Nicholas, K.; Marten, D. F.; Madhavarao, M.; Raghu, S.; Rosan, A.; Rosenblum, M. JACS 1975, 97, 3149. (c) Cutler, A.; Ehntholt, D.; Giering, W. P.; Lennon, P.; Raghu, S.; Rosan, A.; Rosenblum, M.; Tancrede, J.; Wells, D. JACS 1976, 98, 3495. (d) Weinberg, E. L.; Burton, J. T.; Baird, M. C.; Herberhold, M. ZN(B) 1981, 36, 485.
5. Boyle, P. F.; Nicholas, K. M. JOC 1975, 40, 2682.
6. Foxman, B. M.; Marten, D.; Rosan, A.; Raghu, S.; Rosenblum, M. JACS 1977, 99, 2160.
7. Samuels, S-B.; Berryhill, S. R.; Rosenblum, M. JOM 1979, 166, C9.
8. (a) Foxman, B. M.; Klemarczyk, P. T.; Liptrot, R. E.; Rosenblum, M. JOM 1980, 187, 253. (b) Boudjouk, P.; Woell, J. B.; Radonovich, L. J.; Eyring, M. W. OM 1982, 1, 582. (c) Goodrich, J. D.; Nickias, P. N.; Selegue, J. P. IC 1987, 26, 3424. (d) Shaver, A.; Butler, I. S.; Gao, J. P. OM 1989, 8, 2079.
9. Nicholas, K. M. JACS 1975, 97, 3254.
10. (a) Benaim, J.; L'Honore, A. JOM 1980, 202, C53. (b) Marten, D. F. CC 1980, 341. (c) Bates, D. J.; Rosenblum, M.; Samuels, S-B. JOM 1981, 209, C55.
11. Rosenblum, M.; Scheck, D. OM 1982, 1, 397.
12. Schmidt, E. K. G.; Thiel, C. H. JOM 1981, 220, 87.

Mark M. Turnbull

Clark University, Worcester, MA, USA

Copyright 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.