Chemistry Letters Vol.35, No.2 (2006)
Table 1. Heck coupling reactions of iodobenzene with styrenea
155
Entry
Catalyst
Amount/mol %
Base
T/ꢁC
Time/h
Yield/%b
TON
495
495
370
485
4500
48000
135000
Ratio of A:Bd
1
2
3
4
5
6
7
1
1
2
2
1
1
1
2:0 ꢂ 10ꢃ1
2:0 ꢂ 10ꢃ1
2:0 ꢂ 10ꢃ1
2:0 ꢂ 10ꢃ1
2:0 ꢂ 10ꢃ2
2:0 ꢂ 10ꢃ3
2:0 ꢂ 10ꢃ4
Cs2CO3
NEt3
Cs2CO3
NEt3
NEt3
150
110
150
110
110
110
110
6
6
2
8
8
99
99
74c
97
90
96
27
89:11
89:11
88:12
90:10
88:12
88:12
88:12
NEt3
NEt3
20
48
aReactions were carried out with 2.0 mmol of iodobenzene, 2.8 mmol of styrene, and 2.2 mmol of base in 5 mL of DMA. bTotal yield
for A and B determined by GC. Yield for 6 h was also 74%. dDetermined by GC.
c
complex 1 or 2
base
I
Organometallics 2004, 23, 323.
+
+
(3)
5
a) J. J. Van Veldhuizen, S. B. Garber, J. S. Kingsbury, A. H.
Hoveyda, J. Am. Chem. Soc. 2002, 124, 4954. b) H. Aihara,
T. Matsuo, H. Kawaguchi, Chem. Commun. 2003, 2204. c)
A. W. Waltman, R. H. Grubbs, Organometallics 2004, 23,
3105. d) B. E. Ketz, A. P. Cole, R. M. Waymouth, Organo-
metallics 2004, 23, 2835.
C. Yang, H. M. Lee, S. P. Nolan, Org. Lett. 2001, 3, 1511; N.
Tsoureas, A. A. Danopoulos, A. A. D. Tulloch, M. E. Light,
Organometallics 2003, 22, 4750.
DMA
A
B
The catalytic activities for complexes 1 and 2 were investi-
gated in the Heck reactions of iodobenzene with styrene in DMA
as illustrated in eq 3. The reactions were carried out at 110 ꢁC,
while Entries 1 and 3 were investigated at higher temperature be-
cause of incomplete dissolution of Cs2CO3 in DMA. As summa-
rized in Table 1, reaction products were trans-stilbene (A) and
1,1-diphenylethylene (B), of which ratio was about 9:1.14 The
reactions catalyzed by complex 1 proceeded quantitatively at
both 150 and 110 ꢁC (Entries 1 and 2). In the case of complex
2 (Entry 4), slightly longer reaction time was necessary for the
reaction completed at 110 ꢁC. On the other hand, the lower yield
of the reaction products in Entry 3 is interpreted by the decom-
position of the complex at 150 ꢁC. These findings might indicate
that complex 1 having five- and six-membered chelate rings
showed higher thermal stability and catalytic activity than 2.
In addition, 1 also showed good catalytic performance; the turn-
over number (TON) of 135,000 is comparable to those for other
pincer carbene complexes (Entries 5–7).2a,2c This high TON
signifies that new tridentate carbene ligand containing aryloxy
group plays an important role for stabilization and activation
of palladium complex.
6
7
S. Kimura, E. Bill, E. Bothe, T. Weyhermuller, K. Wieghardt,
¨
J. Am. Chem. Soc. 2001, 123, 6025; L. Benisvy, E. Bill, A. J.
Blake, D. Collison, E. S. Davies, C. D. Garner, C. I. Guindy,
E. J. L. McInnes, G. McArdle, J. McMaster, C. Wilson, J.
Wolowska, Dalton Trans. 2004, 3647.
L. Jafarpour, E. D. Stevens, S. P. Nolan, J. Organomet. Chem.
2000, 606, 49.
8
9
Anal. for C18H18ClN3OPd: Found C 49.39, H 4.22, N 9.34,
Calcd. C 49.79, H 4.18, N 9.68.
10 Anal. for C15H12N2O3Pd: Found C 47.75, H 3.19, N 7.18,
Calcd C 48.08, H 3.22, N 7.48.
11 Crystal data for 1: single crystals contain a MeOH molecule
in an asymmetric unit; C19H22ClN3O2Pd, MW 466.25, mono-
ꢀ
ꢀ
clinic, C2=c (No. 15), a ¼ 28:766ð2Þ A, b ¼ 9:4846ð4Þ A, c ¼
ꢁ
ꢀ
ꢀ 3
14:8720ð7Þ A, ꢀ ¼ 104:450ð2Þ , V ¼ 3929:2ð3Þ A , Z ¼ 8,
T ¼ 173 K, Dcalcd ¼ 1:576 g/cm3, total reflections = 15901,
unique reflections = 4484, R1 ¼ 0:053, Rw ¼ 0:155. Crystal
data for 2: C15H12N2O3Pd, MW 374.67, orthorhombic,
In summary, we prepared and characterized two new palla-
dium(II) complexes with the pincer-type tridentate carbene
ligands. The high catalytic activity for Heck reaction might be
caused by the thermal stability of the palladium complex with
rigid pincer-type ligand, in which the short Pd–C bond distance
is important.
ꢀ
ꢀ
P212121 (No. 19), a ¼ 6:828ð3Þ A, b ¼ 12:274ð5Þ A, c ¼
ꢀ
ꢀ 3
15:206ð7Þ A, V ¼ 1274:4ð10Þ A , Z ¼ 4, T ¼ 173 K, Dcalcd
¼
1:953 g/cm3, total reflections = 10260, unique reflections =
1690, R1 ¼ 0:029, Rw ¼ 0:072. Crystallographic data reported
in this manuscript have been deposited with Cambridge Crys-
tallographic Data Centre. Copies of the data can be obtained
12 W. A. Herrmann, J. Schwarz, M. G. Gardiner, Organometallics
1999, 18, 4082; H. M. Lee, C. Y. Lu, C. Y. Chen, W. L. Chen,
H. C. Lin, P. L. Chiu, P. Y. Cheng, Tetrahedron 2004, 60,
5807.
References and Notes
1
W. A. Herrmann, Angew. Chem., Int. Ed. 2002, 41, 1290;
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2
¨
Loch, J. W. Faller, R. H. Crabtree, Organometallics 2001,
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X. Hu, I. Castro-Rodriguez, K. Meyer, J. Am. Chem. Soc. 2003,
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¨
Kovacevic, J. W. Faller, R. H. Crabtree, J. Chem. Soc., Dalton
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¨
C. W. Lehmann, Organometallics 2003, 22, 907; A. A.
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3
4
14 Preliminary study for Heck reaction of bromobenzene with
styrene gave a yield of 36% for 24 h at 110 ꢁC.
´
125, 12237; E. Mas-Marza, M. Poyatos, M. Sanau, E. Peris,
´