Organometallics
Article
General Procedure for the Reduction of Imine Using NaBH4.
For reactions in which the imine is unstable, the crude imine product
obtained from the hydroamination reaction was dissolved in dry
methanol. To this was added sodium borohydride (1.2 equiv), and the
mixture stirred at room temperature for 2 h. The solvent was then
evaporated, and the residue was quenched with water and then
extracted with ethyl acetate (3 × 15 mL). The combined extracts were
dried over magnesium sulfate, and then the solvent was evaporated
under reduced pressure. The crude amine product 5 was purified by
column chromatography using ethylacetate/hexane (15:85, v/v) as
eluent. Characterization data are given in the Supporting Information.
Deuterium Labeling Experiments. A sample of 4-methoxyani-
line (20 mg, 0.16 mmol) and a slight excess of phenylacetylene-d (19 μL,
0.18 mmol) were added using syringe to a suspension of 1 (1 mg, 1 mol %)
and NH4PF6 (1 mg, 3 mol %) in toluene (2 mL). The mixture was
degassed (three cycles of freeze−pump−thaw) and then stirred at 80 °C for
12 h, after which the solvent was removed under vacuum and the crude
REFERENCES
■
(1) (a) Hodgson, D. M.; Kaka, N. S. Angew. Chem., Int. Ed. 2008, 47,
9958−9960. (b) Mukherjee, S.; Yang, J. W.; Hoffman, S.; List, B.
Chem. Rev. 2007, 107, 5471−5569. (c) Spino, C. Angew. Chem., Int. Ed.
2004, 43, 1764−1766. (d) Shibata, I.; Kawakami, T. M.; Tanizawa, D.;
Suwa, T.; Sugiyama, E.; Matsuda, H.; Baba, A. J. Org. Chem. 1998, 63,
383−385. (e) Tsukinoki, T.; Mitoma, Y.; Nagashima, S.; Kawaji, T.;
Hashimoto, I.; Tashiro, M. Tetrahedron Lett. 1998, 39, 8873−8876.
(f) Kobayashi, S.; Ishitani, H. Chem. Rev. 1999, 99, 1069−1094.
(g) Sandhu, J. S.; Sain, B. Heterocycles 1987, 26, 777−818. (h) Cobas,
A.; Guitian, E.; Castedo, L. J. Org. Chem. 1993, 58, 3113−3117.
(i) Heaney, H.; Simcox, M. T; Slawin, A. M. Z.; Giles, R. G. Synlett
1998, 640−642. (j) Guijar
7768. (k) Okamoto, H.; Kato, S. Bull. Chem. Soc. Jpn. 1991, 64, 2128−
2130. (l) Fustero, S.; Torre, M. G.; Jofre, V.; Carlon, R. P.; Navarro,
A.; Fuentes, A. S. J. Org. Chem. 1998, 63, 8825−8836.
(2) Layer, R. W. Chem. Rev. 1963, 63, 489−510.
(3) (a) Raddelien, G. Chem. Ber. 1910, 43, 2476−2480. (b) Eisch, J. J.;
Sanchez, R. J. Org. Chem. 1986, 51, 1848−1852. (c) Nongkunsaran, P.;
Ramsden, C. A. Tetrahedron 1997, 53, 3805−3830.
(4) (a) Larock, R. C. Angew. Chem., Int. Ed. Engl. 1978, 17, 27−37.
(b) Barluenga, J.; Aznar, F. Synthesis 1975, 704−705.
(5) (a) Trost, B. M.; Fandrick, D. R. Org. Lett. 2005, 7, 823−826.
(b) Mujahidin, D.; Doye, S. Eur. J. Org. Chem. 2005, 2689−2693.
(c) Patil, N. T.; Pahadi, N. K.; Yamamoto, Y. Tetrahedron Lett. 2005,
46, 2101−2103.
(6) (a) Tillack, A.; Jiao, H.; Castro, I. G.; Hartung, C. G.; Beller, M.
Chem. Eur. J. 2004, 10, 2409−2420. (b) Heutling, A.; Pohlki, F.; Doye,
S. Chem. Eur. J. 2004, 10, 3059−3071. (c) Anderson, L. L.; Arnold, J.;
Bergman, R. G. Org. Lett. 2004, 6, 2519−2522. (d) Mizushima, E.;
Chatani, N.; Kakiuchi, F. J. Organomet. Chem. 2006, 691, 5739−5745.
(e) Tokunaga, M.; Eckert, M.; Wakatsuki, Y. Angew. Chem., Int. Ed.
1999, 38, 3222−3225. (f) Lai, R. Y.; Surekha, K.; Hayashi, A.; Ozawa,
F.; Liu, Y. H.; Peng, S. M.; Liu, S. T. Organometallics 2007, 26, 1062−
1068. (g) Shimada, T.; Yamamoto, Y. J. Am. Chem. Soc. 2002, 124,
12670−12671. (h) Chessa, S.; Clayden, N. J.; Bochmann, M.; Wright,
J. A. Chem. Commun. 2009, 797−799. (i) Dash, C.; Shaikh, M. M.;
Butcher, R. J.; Ghosh, P. Inorg. Chem. 2010, 49, 4972−4983. (j) Luo,
Y.; Li, Z.; Li, C. J. Org. Lett. 2005, 7, 2675−2678.
(7) (a) Beller, M.; Eichberger, M.; Trauthwein, H. Angew. Chem., Int.
Ed. Engl. 1997, 36, 2225−2227. (b) Shen, X.; Buchwald, S. L. Angew.
Chem., Int. Ed. 2010, 49, 564−567. (c) Julian, L. D.; Hartwig, J. F.
J. Am. Chem. Soc. 2010, 132, 13813−13822. (d) Liu, Z.; Yamamichi,
H.; Madrahimov, S. T.; Hartwig, J. F. J. Am. Chem. Soc. 2011, 133,
2772−2782. (e) Lin, Y. S.; Ali, B. E.; Alper, H. J. Am. Chem. Soc. 2001,
123, 7719−7720. (f) Utsunomiya, M.; Kuwano, R.; Kawatsura, M.;
Hartwig, J. F. J. Am. Chem. Soc. 2003, 125, 5608−5609. (g) Takemiya,
A.; Hartwig, J. F. J. Am. Chem. Soc. 2006, 128, 6042−6043. (h) Liu, Z.;
Hartwig, J. F. J. Am. Chem. Soc. 2008, 130, 1570−1571.
̀
ro, D.; Yus, M. Tetrahedron 1993, 49, 7761−
́
́
1
product was characterized by H NMR and HRMS.
Similarly, aniline-d7 (20 μL, 0.2 mmol) was reacted with 4-
methoxypheneylacetylene (29 μL, 0.22 mmol) in the presence of 1
(1.2 mg, 1 mol %) and NH4PF6 (1 mg, 3 mol %) in toluene at 80 °C
for 12 h, after which the solvent was removed under vacuum and the
1
crude product was characterized by H NMR and HRMS.
Preparation of Cp*RhCl2(NH2Ph) (6). Aniline (10 μL, 0.105
mmol) and 1 (30 mg, 0.048 mmol) were dissolved in dichloromethane
(2 mL) and stirred for a few minutes. Then the solvent was removed
under vacuum, and the residue obtained was washed with hexane
1
(1 mL). H NMR (CDCl3): 1.41 (s, 15H, 5 × CH3, Cp*), 4.98 (bs,
3
2H, NH2), 7.09 (t, JHH = 6.64 Hz, 1H, para), 7.27−7.32 (m, 4H,
ortho and meta). 13C{1H} NMR (CDCl3): 9.05 (CH3, Cp*), 94.06 (d,
1JRhC = 34.5 Hz, ring C, Cp*), 120.41, 124.62, 129.44, and 142.17
(Ph). FAB-MS: 402. Anal. Calcd for C16H22Cl2NRh: C 47.78, H 5.51,
N 3.48. Found: C 47.36, H 5.15, N 3.69. A single-crystal X-ray
crystallographic study of 6 has also been carried out; details are given
in the SI.
Reaction of 6 with Phenylacetylene. In a Carius tube were
placed 6 (25 mg, 0.062 mmol), NH4PF6 (15 mg, 0.093 mmol), and
toluene (3 mL). Phenylacetylene (13 μL, 0.12 mmol) was added, and
the mixture was stirred at 80 °C for 8 h. Analysis by 1H NMR
spectroscopy showed no formation of the ketimine product. A similar
reaction containing aniline (100 μL, 1.07 mmol), phenylacetylene
(110 μL, 1.07 mmol), 6 (5 mg, 0.012 mmol), and NH4PF6 (3 mg,
0.018 mmol) afforded the ketimine product in 85% yield.
Computational Studies. The reaction energetics were studied
using DFT theory utilizing Becke’s three-parameter hybrid function17
and Lee−Yang−Parr’s gradient-corrected correlation function
(B3LYP),18 together with the LanL2DZ (Los Alamos Effective Core
Potential Double-ζ) basis set. Spin-restricted calculations were used
for geometry optimization, and harmonic frequencies were then
calculated to characterize the stationary points as equilibrium
structures with all real frequencies and to evaluate zero-point energy
corrections. All calculations were performed using the Gaussian 03
suite of program.19
(8) (a) Field, L. D.; Messerle, B. A.; Vuong, K. Q.; Turner, P. Dalton
Trans. 2009, 3599−3614. (b) Burling, S.; Field, L. D.; Li, H. L.;
Messerle, B. A.; Turner, P. Eur. J. Inorg. Chem. 2003, 3179−3184.
(c) Field, L. D.; Messerle, B. A.; Vuong, K. Q.; Turner, P.
Organometallics 2005, 24, 4241−4250. (d) Burling, S.; Field, L. D.;
Messerle, B. A.; Turner, P. Organometallics 2004, 23, 1714−1721.
(e) Burling, S.; Field, L. D.; Messerle, B. A.; Rumble, S. L.
Organometallics 2007, 26, 4335−4343. (f) Dabb, S. L.; Ho, J. H. H.;
Hodgson, R.; Messerle, B. A.; Wagler, J. Dalton Trans. 2009, 634−642.
(g) Burling, S.; Field, L. D.; Messerle, B. A. Organometallics 2000, 19,
87−90. (h) Clentsmith, G. K. B.; Field, L. D.; Messerle, B. A.; Shasha,
A.; Turner, P. Tetrahedron Lett. 2009, 50, 1469−1471.
ASSOCIATED CONTENT
■
S
* Supporting Information
Further experimental details and characterization for 4 and 5,
crystallographic data for 6, and optimized geometry of A−D.
This material is available free of charge via the Internet at
(9) Hartung, C. G.; Tillack, A.; Trauthwein, H.; Beller, M. J. Org.
Chem. 2001, 66, 6339−6343.
(10) Dabb, S. L.; Messerle, B. A. Dalton Trans. 2008, 6368−6371.
(11) (a) Fukumoto, Y.; Asai, H.; Shimizu, M.; Chatani, N. J. Am.
Chem. Soc. 2007, 129, 13792−13792. (b) Moreno, C. A.; Hermosilla,
ACKNOWLEDGMENTS
■
This work was supported by Nanyang Technological University
and the Ministry of Education (Research Grant No.
T208B1111), and one of us (E.K.) thanks the University for
a Research Scholarship.
́ ́
F. C.; Fernandez, J. R.; Rodríguez, A. M.; Otero, A.; Antinolo, A. Adv.
Synth. Catal. 2009, 351, 881−890. (c) Sakai, K.; Kochi, T.; Kakiuchi, F.
Org. Lett. 2011, 13, 3928−3931.
1071
dx.doi.org/10.1021/om201134j | Organometallics 2012, 31, 1068−1072