C O M M U N I C A T I O N S
Table 2. Reaction Substrate Scopea
intramolecular hydroamination.12 The substituted pyrroles 8 were
prepared in excellent yields, as shown in Scheme 2.
In conclusion, the investigation of triazole-Au coordination by
variable-temperature NMR spectroscopy revealed a dynamic co-
ordination between the triazole and the Au(I) cation, leading to
the discovery of a new class of thermally stable cationic Au(I)
catalysts. The superior stability and cationic Au reactivity of these
catalysts were evidenced in challenging transformations, such as
intermolecular internal alkyne hydroamination and reactions with
unprotected aliphatic amines. It is our belief that this catalytic
system may open a new temperature range for homogeneous Au(I)
catalysis, and therefore, the discovery of new reactivities is expected
in the near future.
Acknowledgment. We thank West Virginia University, the WV
Nano Initiative at the West Virginia University, and the ACS PRF
for financial support.
Supporting Information Available: Detailed experimental proce-
dures, spectral data for all new compounds, and CIF files for compounds
2a, 2b, and 3a. This material is available free of charge via the Internet
References
(1) For recent reviews, see: (a) Gorin, D. J.; Sherry, B. D.; Toste, F. D. Chem.
ReV. 2008, 108, 3351. (b) Li, Z. G.; Brouwer, C.; He, C. Chem. ReV. 2008,
108, 3239. (c) Jime´nez-Nu´n˜ez, E.; Echavarren, A. M. Chem. ReV. 2008,
108, 3326. (d) Hashmi, A. S. K. Chem. ReV. 2007, 107, 3180. (e) Marion,
N.; Nolan, S. P. Angew. Chem., Int. Ed. 2007, 46, 2750. (f) Hashmi,
A. S. K.; Hutchings, G. J. Angew. Chem., Int. Ed. 2006, 45, 7896. (g)
Zhang, L.; Sun, J.; Kozmin, S. A. AdV. Synth. Catal. 2006, 348, 2271.
(2) For reviews, see refs 1a and 1c and references therein. For some related
methodologies, see: (a) Hashmi, A. S. K.; Loos, A.; Littmann, A.; Braun,
I.; Knight, J.; Doherty, S.; Rominger, F. AdV. Synth. Catal. 2009, 351,
576. (b) Lee, J. H.; Toste, F. D. Angew. Chem., Int. Ed. 2007, 46, 912. (c)
Zhang, L.; Wang, S. J. Am. Chem. Soc. 2006, 128, 1442. (d) Zhang, Z.;
Liu, C.; Kinder, R. E.; Han, X.; Qian, H.; Widenhoefer, R. A. J. Am. Chem.
Soc. 2006, 128, 9066. (e) Buzas, A. K.; Istrate, F. M.; Gagosz, F. Angew.
Chem., Int. Ed. 2007, 46, 1141. (f) Nieto-Oberhuber, C.; Mun˜oz, M. P.;
Bun˜uel, E.; Nevado, C.; Ca´rdenas, D. J.; Echavarren, A. M. Angew. Chem.,
Int. Ed. 2004, 43, 2402. (g) Luzung, M. R.; Markham, J. P.; Toste, F. D.
J. Am. Chem. Soc. 2004, 126, 10858. (h) Mamane, V.; Gress, T.; Krause,
H.; Fu¨rstner, A. J. Am. Chem. Soc. 2004, 126, 8654.
a General reaction conditions: 4a (1.0 equiv), 5a (1.2 equiv), and
catalysts were mixed in dry toluene ([4a] ) 0.3 M). The reactions were
monitored by TLC. b NMR yield using 1,3,5-trimethoxybenzene as an
internal standard. c Isolated yield of reduced amine after treating 6a/6b
with BH3 in THF. d Determined by NMR analysis.11
amines were then performed. The reaction substrate scope is shown
in Table 2.
As expected, the triazole-Au catalyst gave a wide reaction
substrate scope. For more reactive terminal alkynes, excellent yields
(generally >90%) were achieved with only 0.1% catalyst loading.
With less reactive internal alkynes, higher catalytic loading was
needed; 1% loading generally produced the desired hydroamination
products in >85% yield. Moreover, with increased catalyst loading
(10%), the extremely challenging intermolecular, unprotected
aliphatic amine hydroaminations to afford 6y and 6z were achieved,
though with modest yields. Since the key side reaction for aliphatic
amine hydroamination is the decomposition of the imine, the diyne
7 was applied to trap the active imine intermediate through a second
(3) Zhang, G.; Huang, X.; Li, G.; Zhang, L. J. Am. Chem. Soc. 2008, 130,
1814.
(4) For a review, see: Widenhoefer, R. A.; Han, X. Eur. J. Org. Chem. 2006,
4555, and references therein.
(5) For recent reviews, see: (a) Marion, N.; Nolan, S. P. Chem. Soc. ReV. 2008,
37, 1776. (b) Lin, I. J. B.; Vasam, C. S. Can. J. Chem. 2005, 83, 812.
(6) (a) Mezailles, N.; Ricard, L.; Gagosz, F. Org. Lett. 2005, 7, 4133. (b) Ricard,
L.; Gagosz, F. Organometallics 2007, 26, 4704.
(7) (a) Sengupta, S.; Duan, H.; Lu, W.; Petersen, J. L.; Shi, X. Org. Lett. 2008,
10, 1493. (b) Liu, Y.; Yan, W.; Chen, Y.; Petersen, J. L.; Shi, X. Org.
Lett. 2008, 10, 5389. (c) Chen, Y.; Liu, Y.; Petersen, J. L.; Shi, X. Chem.
Commun. 2008, 3254.
(8) Duan, H.; Sengupta, S.; Petersen, J. L.; Shi, X. Organometallics 2009, 28,
2352.
Scheme 2
(9) For literature examples of N-heterocycle-bound Au complexes, see: (a)
Kieft, R. L.; Peterson, W. M.; Blundell, G. L.; Horton, S.; Henry, R. A.;
Jonassen, H. B. Inorg. Chem. 1976, 15, 1721. (b) Nomiya, K.; Noguchi,
R.; Oda, M. Inorg. Chim. Acta 2000, 298, 24. (c) Partyka, D. V.; Updegraff,
J. B.; Zeller, M.; Hunter, A. D.; Gray, T. G. Organometallics 2007, 26,
183. (d) Partyka, D. V.; Robilotto, T. J.; Zeller, M.; Hunter, A. D.; Gray,
T. G. Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 14293.
(10) Mizushima, E.; Hayashi, M.; Tanaka, M. Org. Lett. 2003, 5, 3349.
(11) Comparison of the catalytic reactivity of triazole-Au complexes and other
Au catalysts were also done and are provided in the Supporting Information.
(12) Ramanathan, B.; Keith, A. J.; Armstrong, D.; Odom, A. L. Org. Lett. 2004,
6, 2957.
JA9041093
9
12102 J. AM. CHEM. SOC. VOL. 131, NO. 34, 2009