C O M M U N I C A T I O N S
catalytic activity of the metal bound to the carbene center and may
offer some advantages for aqueous-based systems.
In conclusion, we have synthesized and characterized the first
bimetallic ruthenium-palladium complex containing a cyclopen-
tadienyl-annulated imidazol-2-ylidene ligand and demonstrated its
capability to function as catalyst in the Suzuki reaction in aqueous
media. We are currently investigating this novel ligand class and
its application to a variety of catalytic processes.
Acknowledgment. We gratefully acknowledge support for this
dissertation research from Atotech U.S.A. (Fellowship to D.T.), E.
I. du Pont de Nemours and Co., and grants from the National
Science Foundation (CHE-0413521 and CHE-0115760). A.J.A.
gratefully acknowledges the Saxon Endowment of the University
of Alabama.
Supporting Information Available: Description of the preparation,
NMR spectra, and elemental analyses of 2, 3, and 4, cross-coupling
procedures; cyclic voltammograms and a complete description of the
X-ray crystallographic determination on 3 and 4, including tables of
fractional coordinates, isotropic and anisotropic thermal parameters,
bond distances and angles. This material is available free of charge
Figure 2. KANVAS drawing of the complex 4. Selected bond lengths
(pm) and angles (deg): C2-N1(3) ) 134.3(4), 134.9(5); N1(3)-C6a(3a)
) 140.9(5), 141.1(4); Pd-P1(2) ) 227.48(10), 238.24(10); C3a-C6a )
139.4(5); C3a(6a)-C4(6) ) 142.5(5), 142.5(5); C4(6)-C5 ) 146.0(6),
144.7(6); av(Ru-C3a-6a) ) 216.5; C2-Pd ) 202.9(3); av(Ru-CCp*) )
219.34; C2-N1(3)-C6a(3a) ) 109.1(3), 109.4(3); C4-C5-C6 ) 110.7(3);
N1-C2-N3 ) 108.7(3); C2-Pd1-P2 ) 173.76(10); C2-Pd1-P1 )
88.95(10); N1(3)-C6a(3a)-C3a(6a) ) 106.8(3), 105.9(3); C3a(6a)-
C6a(3a)-C6(4) ) 110.2(3), 110.8(3); C3a(6a)-C4(6)-C5 ) 103.8(3),
104.5(3).
References
(1) (a) Arduengo, A. J., III; Harlow, R. L.; Kline, M. J. Am. Chem. Soc.
1991, 113, 361-363. (b) Lee, S.; Hartwig, J. F. J. Org. Chem. 2001, 66,
3402-3415. (c) Herrmann, W. A.; Reisinger, C. P.; Spiegler, M. J.
Organomet. Chem. 1998, 557, 93-96. (d) Herrmann, W. A.; Kocher, C.;
Goosen, L. J.; Artus, G. R. J. Chem.sEur. J. 1996, 2, 1627-1636. (e)
Arnold, P. L.; Scarisbrick, A. C.; Blake, A. J.; Wilson, C. Chem. Commun.
2001, 22, 2340-2341. (f) Van Veldhuizen, J. J.; Garber, S. B.; Kingsbury,
J. S.; Hoveyda, A. H. J. Am. Chem. Soc. 2002, 124, 4954-4955. (g)
Bildstein, B.; Malaun, M.; Kopacka, H.; Ongania, K. H.; Wurst, K. J.
Organomet. Chem. 1998, 552, 54-61. (h) Bildstein, B.; Malaun, M.;
Kopacka, H.; Wurst, K.; Mitterbo¨ck, M.; Ongania, K. H.; Opromolla, G.;
Zanello, P. Organometallics 1999, 18, 4325-4336. (i) Seo, H.; Park, H.
J.; Kim, B. Y.; Lee, J. H.; Son, S. U.; Chung, Y. K. Organometallics
2003, 22, 618-620. (j) Albrecht, M.; Crabtree, R. H.; Mata, J.; Peris, E.
Chem. Commun. 2002, 32-33.
(2) (a) Arduengo, A. J., III; Bannenberg, T. P.; Tapu, D.; Marshall, W. J.
Chem. Lett. 2005, 34, 1010-1011. (b) Arduengo, A. J., III; Bannenberg,
T. P.; Tapu, D.; Marshall, W. J. Tetrahedron Lett. 2005, 46, 6847-6850.
(3) McGuinness, D. S.; Cavell, K. J.; Yates, B. F.; Skelton, B. W.; White, A.
H. J. Am. Chem. Soc. 2001, 123, 8317-8328.
(4) Fagan, P. J.; Ward, M. D.; Calabrese, J. C. J. Am. Chem. Soc. 1989, 111,
1698-1719.
A comparative cyclic voltammetry study was conducted for 3
and 4.8 As expected, the ruthenocene 3 is more difficult to oxidize
(Epa ) 1.09 V vs SCE) than complex 4 (Epa ) 0.96 V), due to the
inductive effect of the chlorine in the 2-position. Interestingly, while
3 shows an irreversible oxidation wave, 4 shows a reduction wave
(Epc ) 0.83 V). In general, ruthenocene derivatives show irreversible
redox behavior, presumably due to the susceptibility of rutheno-
cenium ions toward nucleophilic attack9 or dimerization.10,11 Steric
hindrance may suppress these side reactions for 4.
(5) This drawing was made with the KANVAS computer graphics program.
This program is based on the program SCHAKAL of E. Keller (Kristal-
lographisches Institute der Universitat Freiburg, Germany), which was
modified by A. J. Arduengo, III (The University of Alabama), to produce
the back and shadowed planes. The planes bear a 50 pm grid, and the
lighting source is at infinity so that shadow size is meaningful.
(6) (a) Langer, V.; Huml, K.; Reck, G. Acta Crystallogr., Sect. B 1982, 38,
298-300. (b) Luger, P.; Ruban, G. Z. Kristallogr. 1975, 142, 177-185.
(c) Abdul-Sada, A. K.; Greenway, A. M.; Hitchcock, P. B.; Mohammed,
T. J.; Seddon, K. R.; Zora, J. A. J. Chem. Soc., Chem. Commun. 1986,
1753-1754.
Demonstration that the palladium-ruthenium complex 4 is an
active catalyst for aqueous Suzuki coupling reactions was provided
by preliminary experiments (Scheme 2). Cross-coupling of para-
Scheme 2. Suzuki Cross-Coupling Reactions Catalyzed by 4
(H2O:CH3CN ) 9:1, Na2CO3, 80 °C, 2 h)
(7) Fu¨rstner, A.; Seidel, G.; Kremzow, D.; Lehmann, C. W. Organometallics
2003, 22, 907-909.
(8) Cyclic voltammograms were measured in dichloromethane at 20 °C
containing 0.1 mol dm-3 n-Bu4NBF4 as a supporting electrolyte using a
Pt electrode; scan rate was 200 mV s-1
.
bromobenzoic acid with phenylboronic acid in the presence of 2.4
mol % of 4 in a water:acetonitrile (9:1) mixture afforded the
expected product in 94% yield. para-Bromophenol and para-
bromoanisole yielded the respective coupling products with phen-
ylboronic acid in 83.3 and 82.4%, respectively. Fusion of the
ruthenocene moiety to the imidazole ring does not impair the
(9) Hill, M. G.; Lamanna, W. M.; Mann, K. R. Inorg. Chem. 1991, 30, 4687-
4690.
(10) Droege, M. W.; Harman, W. D.; Taube, H. Inorg. Chem. 1987, 26, 1309-
1315.
(11) Mueller-Westerhoff, U. T.; Rheingold, A. L.; Swiegers, G. F. Angew.
Chem., Int. Ed. Engl. 1992, 31, 1352-1354.
JA055565F
9
J. AM. CHEM. SOC. VOL. 127, NO. 47, 2005 16401