Triphenylmethyl Hexafluorophosphate

[437-17-2]  · C19H15F6P  · Triphenylmethyl Hexafluorophosphate  · (MW 388.31)

(catalyst for Michael additions,1 aldol reactions,2 photooxygenation;3 reagent for hydride abstraction4 and alkoxy abstraction5)

Alternate Names: trityl hexafluorophosphate; triphenylcarbenium hexafluorophosphate.

Physical Data: mp 145 °C (dec.)6

Form Supplied in: brown powder; widely available.

Handling, Storage, and Precautions: trityl hexafluorophosphate should be stored in the dark as exposure to light darkens the compound. It is rapidly hydrolyzed by exposure to moist air.7,8

Michael Reactions.

Silyl enol ethers and a,b-unsaturated ketones react in the presence of trityl hexafluorophosphate (2-3 mol %) to give predominantly the anti Michael addition products (eq 1).1 Steroeselectivity is similar to that found when Triphenylmethyl Perchlorate is used as the catalyst.1

Aldol Reactions.

Trityl hexafluorophosphate catalyzes the reaction of silyl enol ethers with aldehydes to give aldol products (eq 2).2 Yields are similar to those obtained with trityl perchlorate as catalyst, being slightly higher or lower depending on the substrate.2


Ergosteryl acetate can be converted photochemically to the corresponding peroxide by oxygen in the presence of trityl hexafluorophosphate (eq 3).3 Other trityl salts can also be used.3

Hydride Abstraction.

Trityl hexafluorophosphate has been used with great success to abstract hydride ions from transition metal-complexed alkenic systems. For instance, with iron as the transition metal, the complex (1) gives the cyclobutatropylium iron complex (2) (eq 4).9

The regiochemistry of hydride abstraction by trityl hexafluorophosphate from a cycloheptadienyl iron complex can be controlled. The complex (3) undergoes hydride abstraction to give the iron cycloheptadienyl cation complex (4) (eq 5).10,11

The ability of trityl hexafluorophosphate to abstract hydride from variously substituted cyclohexadiene iron complexes has been reported. The two complexes (5) and (6) undergo smooth hydride abstraction, whereas the complexes (7) and (8) are resistant to hydride abstraction with trityl hexafluorophosphate (Scheme 1).4

Other transition metal alkene complexes are known to undergo hydride abstraction with trityl hexafluorophosphate. The p-allyl molybdenum complex (9) gives the cycloheptadiene complex (10) upon treatment with trityl hexafluorophosphate (eq 6).12,13

Hydride abstraction also occurs from the benzyl rhenium complex (11) when it is treated with trityl hexafluorophosphate; the rhenium carbene complex (12) results (eq 7).14

Alkoxy Abstraction.

Upon treatment with trityl hexafluorophosphate the alkoxy substituted p-allyl molybdenum complex (13) is ionized by ethoxy abstraction to give the complex (14). Fluoroboric acid failed to achieve the same ionization cleanly (eq 8).5

Alkoxy abstraction has also been observed with the two cyclopentadienyliron dicarbonyl complexes (15) and (16), which both give vinyl ether cyclopentadienyliron dicarbonyl complexes (17) and (18) upon treatment with trityl hexafluorophosphate (eqs 9 and 10).15

1. Mukaiyama, T.; Tamura, M.; Kobayashi, S. CL 1986, 1017.
2. Kobayashi, S.; Murakami, M.; Mukaiyama, T. CL 1985, 1535.
3. Barton, D. H. R.; Haynes, R. K.; Leclerc, G.; Magnus, P. D.; Menzies, I. D. JCS(P1) 1975, 2055.
4. Pearson, A. J.; Zettler, M. W. JACS 1989, 111, 3908.
5. Rubio, A.; Liebskind, L. S. JACS 1993, 115, 891.
6. Olah, G. A.; Svoboda, J. J.; Olah, J. A. S 1972, 544.
7. Sharp, D. W. A.; Sheppard, N. JCS 1957, 674.
8. For further information, see: The Sigma-Aldrich Library of Chemical Safety Data, 2nd ed.; Lenga, R. E., Ed.; Sigma-Aldrich: Milwaukee, 1987; Vol. 2, p 3516.
9. Stringer, M. B.; Wege, D. TL 1977, 18, 65.
10. Pearson, A. J.; Kole, S. L.; Chen, B. JACS 1983, 105, 4483.
11. Pearson, A. J.; Kole, S. L.; Ray, T. JACS 1984, 106, 6060.
12. Pearson, A. J.; Khan, M. N. I. TL 1985, 26, 1407.
13. Pearson, A. J.; Khan, M. N. I. JOC 1985, 50, 5276.
14. O'Connor, E. J.; Kobayashi, M.; Floss, H. G.; Gladysz, J. A. JACS 1987, 109, 4837.
15. Crawford, E. J.; Bodnar, T. W.; Cutler, A. R. JACS 1986, 108, 6202.

Christopher J. Urch

Zeneca Agrochemicals, Bracknell, UK

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