Journal of the American Chemical Society
COMMUNICATION
after 2 days.13 To probe the turnovernumberof the Me3PAuþ ⊂ 1
catalyst, we added 250 equiv of 2 to a solution of the catalyst in 2:3
MeOD/D2O. After 6 days of vigorous stirring of the biphasic
mixture, 3 was isolated in 27% yield, corresponding to 67 turn-
overs. Although more sterically demanding substrates can also be
employed in the reaction, the rate enhancement observed for these
substrates is smaller than that with 2.14
Reek and coworkers reported the encapsulation of an NHCꢀAu catalyst
in a self-assembled host in organic solvent. However, the catalytic activity
of the gold catalyst was reduced upon encapsulation. See: Cavarzan, A.;
Scarso, A.; Sgarbossa, P.; Strukul, G.; Reek, J. N. H. J. Am. Chem. Soc. 2010,
133, 2848. (c) Kuil, M.; Soltner, T.; van Leeuwen, P. W. N. M.; Reek,
J. N. H. J. Am. Chem. Soc. 2006, 128, 11344.
(7) Slagt, V. F.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.; Reek,
J. N. H. J. Am. Chem. Soc. 2004, 126, 1526.
In conclusion, we have shown that goldꢀphosphine complexes
are readily encapsulated in 1 in both methanol and water. Notably,
the encapsulation of Me3PAuþ (generated from Me3PAuBr in
water) led to an enhancement in the catalytic activity in the
hydroalkoxylation of allenes. This reaction constitutes the first
example of acceleration of a gold-catalyzed process in which the
reactivity and lifetime of the catalyst were enhanced by supramo-
lecular encapsulation. Moreover, encapsulation of the gold catalyst
allowed us to perform reactions that previously required organic
solvents in water.9 Studies directed toward taking further advan-
tage of this strategy are ongoing.
(8) (a) Leung, D. H.; Bergman, R. G.; Raymond, K. N. J. Am. Chem.
Soc. 2007, 129, 2746. (b) Leung, D. H.; Bergman, R. G.; Raymond, K. N.
J. Am. Chem. Soc. 2006, 128, 9781. (c) Fiedler, D.; Leung, D. H.;
Bergman, R. G.; Raymond, K. N. Acc. Chem. Res. 2005, 38, 351. Also see
refs 2a,2d, 3a, 4 and 5.
(9) For reviews of gold-catalyzed cyclization reactions of allenes, see:
(a) Krause, N.; Winter, N. Chem. Rev. 2011, 111, 1994. (b) Shen, H. C.
Tetrahedron 2008, 64, 3885. For a review of gold-catalyzed reactions of
alcohols, see: (c) Muzart, J. M. Tetrahedron 2008, 64, 5815. For recent
general reviews of gold catalysis, see: (d) Shapiro, N. D.; Toste, F. D.
Synlett 2010, 675. (e) Hashmi, A. S. K. Angew. Chem., Int. Ed. 2010,
49, 5232. (f) F€urstner, A. Chem. Soc. Rev. 2009, 38, 3208.
(10) (a) Hamilton, G. L.; Kang, E. J.; Mba, M.; Toste, F. D. Science
2007, 317, 496. (b) Zhang, Z.; Widenhoefer, R. A. Angew. Chem., Int. Ed.
2007, 46, 283. (c) Zhang, Z.; Liu, C.; Kinder, R. E.; Han, X.; Qian, H.;
Widenhoefer, R. A. J. Am. Chem. Soc. 2006, 128, 9066. (d) Nishina, N.;
Yamamoto, Y. Tetrahedron Lett. 2008, 49, 4908. (e) Hadfield, M.; Lee, A.
Org. Lett. 2010, 12, 484. (f) LaLonde, R. L.; Wang, Z. J.; Mba, M.;
Lackner, A. D.; Toste, F. D. Angew. Chem., Int. Ed. 2010, 49, 598. For a
study of the mechanism of gold-catalyzed additions to allenes, see:
(g) Wang, Z. J.; Benitez, D.; Tkatchouk, E.; Goddard, W. A., III; Toste,
F. D. J. Am. Chem. Soc. 2010, 132, 13064.
’ ASSOCIATED CONTENT
S
Supporting Information. Experimental procedures and
b
additional spectroscopic and kinetic data. This material is avail-
’ AUTHOR INFORMATION
Corresponding Author
rbergman@berkeley.edu; raymond@socrates.berkeley.edu; fdtoste@
berkeley.edu
(11) In comparison, the same reaction catalyzed by Et3PAuþ ⊂ 1
proceeded to only 2% conversion after 18 h. We believe this to result
from the increased steric demand of the cation, which leaves less space
available inside the cluster for the substrate.
(12) The reported rate enhancement is in comparison to Me3PAuBr
and applies only to this catalyst. For instance, as Me3PAuCl is already a
relatively active catalyst, catalysis with the encapsulated species led to
52% conversion after 18 h, which is comparable to the rate of reaction for
the unencapsulated catalyst.
(13) At low conversion (0ꢀ12%), [2]0 ≈ [2]t, and thus, there
should be a pseudolinear correlation between conversion and time.
(14) For example, cyclization of 5 proceeded to 28% conversion in
the presence of Me3PAuþ ⊂ 1 but to only 14% conversion with
Me3PAuBr alone.
’ ACKNOWLEDGMENT
Research leading to this project was partially supported by the
Director, Office of Science, Office of Basic Energy Sciences, and the
Division of Chemical Sciences, Geosciences, and Biosciences of the
U.S. Department of Energy at LBNL (DE-AC02-05CH11231).
We thank Dr. Anthony Iavarone at QB3/Chemistry Mass Spectro-
metry at UC Berkeley for help with mass spectrometry. Z.J.W.
thanks the Hertz Foundation for a graduate fellowship.
’ REFERENCES
(1) (a) Pluth, M. D.; Bergman, R. G.; Raymond, K. N. Acc. Chem. Res.
2009, 42, 1650. (b) Yoshizawa, M.; Tamura, M.; Fujita, M. Science 2007,
312, 251. (c) Kang, J.; Rebek, J., Jr. Nature 1997, 385, 50. (d) Marty,
Z. C.; Watson, L. J.; Twyman, M.; Nakash, J. K. M.; Sanders Chem.
Commun 1998, 2265. (e) Chen, J.; Rebek, J., Jr. Org. Lett. 2002, 4, 327.
(2) (a) Fiedler, D.; Bergman, R. G.; Raymond, K. N. Angew. Chem.,
Int. Ed. 2004, 43, 6748. (b) Hastings, C. J.; Fiedler, D.; Bergman, R. G.;
Raymond, K. N. J. Am. Chem. Soc. 2008, 130, 10977. (c) Hastings, C. J.;
Pluth, M. D.; Bergman, R. G.; Raymond, K. N. J. Am. Chem. Soc. 2010,
132, 6938. (d) Fiedler, D.; van Halbeek, H.; Bergman, R. G.; Raymond,
K. N. J. Am. Chem. Soc. 2006, 128, 10240. (e) Nishioka, Y.; Yamaguchi,
T.; Yoshizawa, M.; Fujita, M. J. Am. Chem. Soc. 2007, 129, 7000.
(3) (a) Leung, D. H.; Fiedler, D.; Bergman, R. G.; Raymond, K. N.
Angew. Chem., Int. Ed. 2004, 43, 963. (b) Pluth, M. D.; Bergman, R. G.;
Raymond, K. N. Science 2007, 316, 85.
(4) (a) Fiedler, D.; Bergman, R. G.; Raymond, K. N. Angew. Chem.,
Int. Ed. 2006, 45, 745. (b) Fielder, D.; Pagliero, D.; Brumaghim, J. L.;
Bergman, R. G.; Raymond, K. N. Inorg. Chem. 2004, 43, 846.
(5) Fiedler, D.; Leung, D. H.; Bergman, R. G.; Raymond, K. N. J. Am.
Chem. Soc. 2004, 126, 3674.
(6) (a) Brown, C. J.; Bergman, R. G.; Raymond, K. N. J. Am. Chem.
Soc. 2009, 131, 17530. (b) During the preparation of this manuscript,
7360
dx.doi.org/10.1021/ja202055v |J. Am. Chem. Soc. 2011, 133, 7358–7360