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out using reagent grade dichloromethane solvent that has not
undergone any prior degassing or distillation. The alkene
reagents, while stored in the glove box, can be brought out into
the air, and simply passed over alumina just before commence-
ment of the reaction to eliminate residual peroxides. Another
advantage of this NHC–phosphine series is that the reaction
progress can be followed visually. The initial color of the
catalytic solution upon addition of hydrogen is red–orange; the
color fades somewhat during the course of the reaction, but at
~
98% conversion, abruptly becomes almost colorless for ~ 30
s, and then neon yellow, as shown in the ESI.† The colorless
solution is still active, and additional olefin may be added at this
step and successfully hydrogenated. The yellow solution,
however, is inactive. In the case of 4, the solvent was removed
at the end of the reaction (yellow solution) and the residue
Fig. 2 PHIP 1H NMR spectra of the hydrogenation of [D
4.
8
] styrene with
1
dissolved in CD
2
Cl
2
. The final H NMR revealed at least 12
different carbene resonances and a complex hydride region,
with peaks ranging from d 212 to 233 ppm.
occurred before placement of the sample in the NMR tube.9a
This observation suggests that a dihydride mechanism is in
operation, but of course, one cannot rule out a parallel
monohydride mechanism since it would not appear in the PHIP
experiment.9
In summary, complexes having a combination of phosphine
and NHC ligands prove to be very reactive toward the
homogeneous catalytic hydrogenation of simple olefins, includ-
ing hindered substrates. This promising structural motif is
presently being expanded upon, and a more detailed analysis of
the mechanism of reaction under investigation.
In order to provide insight into the mechanism of the
1
hydrogenation reaction, PHIP H NMR studies were carried out
8
using 4 and [D ] styrene, following the procedure of Bargon et
9b
al. Enhancements in the hydrogenated product are only
observed if the two hydrogen atoms from the para-hydrogen
molecule are passed in pair-wise fashion to the olefin. The
spectrum obtained from the experiment with 4 is shown in Fig.
2
and shows a positive enhancement at d 2.68, and a
corresponding negative enhancement at d 1.25. The positive and
negative pattern indicates that the hydrogenation reaction
Support from NSF is gratefully acknowledged. J. M. B. is
holder of a Camille and Henry Dreyfus New Faculty Award
(1997–2002), a Camille and Henry Dreyfus Teacher Scholar
Table 1 Selected results for the catalytic homogeneous hydrogenation of
olefins using complexes 1 to 6
Award (2002–2004),
a
Sloan Foundation Fellowship
Catalyst
(mol%)
Time
(min)
Conversiond
(%)
(2000–2002), and is a Cottrell Teacher–Scholar of Research
Corporation (2000–2002). L. D. V. S. thanks the Sloan
Foundation for support, and NIH for a training grant. Dr Phil
Fanwick is thanked for solving the crystal structure of 4.
Substrate
-Octene
Catalyst
1
1
1
2
3
4
4
4
5
6
1a
9
41
14
25
13
62
18
11
280
100
> 99
100
100
100
100
100
100
> 99
b
0.1
a
1
a
1
Notes and references
a
1
b
0.1
1 (a) A. Herrmann, Angew. Chem., Int. Ed., 2002, 41, 1291; (b) W. A.
Herrmann and C. Köcher, Angew. Chem., Int. Ed. Engl, 1997, 36, 2163;
(c) J. Huang, H.-J. Schanz, E. D. Stevens and S. P. Nolan,
Organometallics, 1999, 18, 2370; (d) A. J. Arduengo, H. V. Rasika
Dias, R. L. Harlow and M. Kline, J. Am. Chem. Soc., 1992, 114,
5530.
2 A. J. Arduengo and T. Bannenberg, Strem Chem., 2002, 19, 2.
3 (a) J. Huang, E. D. Stevens, S. P. Nolan and J. L. Petersen, J. Am. Chem.
Soc., 1999, 121, 2674; (b) T. Weskamp, V. P. W. Böhm and W. A.
Herrmann, J. Organomet. Chem, 1999, 585, 348; (c) W. A. Herrmann,
J. Schwarz, M. G. Gardiner and M. Spiegler, J. Organomet. Chem.,
1999, 575, 80; W. A. Herrmann, M. Elison, J. Fischer, C. Köcher and G.
R. J. Artus, Chem. Eur. J., 1996, 2, 772.
4 J. Huang, L. Jafarpour, A. C. Hillier, E. D. Stevens and S. P. Nolan,
Organometallics, 2001, 20, 2878.
5 T. Weskamp, W. C. Schattenmann, M. Spiegler and W. A. Herrmann,
Angew. Chem., Int. Ed., 1998, 37, 2490; M. Scholl, S. Ding, C. W. Lee
and R. H. Grubbs, Org. Lett., 1999, 1, 953; D. S. Clyne, J. Jin, J. C.
Gallucci and T. V. RajanBabu, Org. Lett., 2000, 2, 1125.
6 S. Bhadur and D. Mukesh, Homogeneous Catalysis: Mechanisms and
Industrial Applications, John Wiley & Sons, New York, USA, 1994.
7 (a) H. M. Lee, T. Jiang, E. D. Stevens and S. P. Nolan, Organometallics,
2001, 20, 1255; (b) M. T. Powell, D.-R. Hou, M. C. Perry, X. Cui and
K. Burgess, J. Am. Chem. Soc., 2001, 123, 8878.
8 R. H. Crabtree, H. Felkin and G. E. Morris, J. Organomet. Chem., 1977,
141, 205; R. H. Crabtree, Acc. Chem. Res., 1979, 12, 331.
9 (a) R. Eisenberg, Acc. Chem. Res., 1991, 24, 110; (b) J. Bargon, J.
Kandels and K. Woelk, Z. Phys. Chem., 1993, 180, 65.
a,c
1
a
1
a
1
Cyclohexene
1
1
2
3
4
4
4
5
6
1a
9
36
15
22
15
100
16
14
100
99
b
0.1
a
1
100
100
100
> 99
100
100
> 99
a
1
a
1
b
0.1
a,c
1
a
1
a
1
240
1-Methyl-1-cyclohexene
1
1
2
3
4
4
4
5
1a
16
60
30
60
21
130
55
180
99
70
100
100
100
71
b
0.1
a
1
a
1
a
1
b
0.1
a,c
1
94
100
a
1
2,3-Dimethyl-2-butene
1
1
2
3
4
4
4
5
1a
40
50
12
50
39
30
45
220
95
49
46
14
> 99
5
b
0.1
a
1
a
1
a
1
10 T. M. Trnka and R. H. Grubbs, Acc. Chem. Res., 2001, 34, 18.
b
0.1
11 Crystal data: C25
P2 /c (no. 14), a = 13.9526 (2), b = 9.8549(2), c = 21.4354(4) Å, b
= 99.1310(10)°, V = 2910.05(16) Å , T = 150 K, Z = 4, m = 4.733
47 6 2 2
H F IrN P , M = 743.81, monoclinic, space group
a,c
1
13
19
1
a
3
1
21
a
mm , 20628 reflections measured, 6834 unique (Rint = 0.031) which
Conditions: cat, 0.01 mol; olefin, 1.0 mmol; CH
2
Cl
Cl
2
, 5 ml; H , 1 atm;
2
, 10 ml; H , 1 atm;
2
2
b
were used in all calculations. The final wR(F ) was 0.069 (all data).
CCDC 192727. See http://www.rsc.org/suppdata/cc/b2/b208403a/ for
crystallographic files in CIF or other electronic format.
temp 25 °C. cat, 0.005 mol; olefin, 5.0 mmol; CH
2
2
c
d
temp 25 °C. Reaction carried out in air. By GC.
CHEM. COMMUN., 2002, 2518–2519
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