Organometallics 2010, 29, 403–408 403
DOI: 10.1021/om900864r
Ruthenium Olefin Metathesis Catalysts Bearing Carbohydrate-Based
N-Heterocyclic Carbenes
Benjamin K. Keitz and Robert H. Grubbs*
Arnold and Mabel Beckman Laboratory of Chemical Synthesis, Division of Chemistry and Chemical
Engineering, California Institute of Technology, Pasadena, California 91125
Received October 5, 2009
Ru-based olefin metathesis catalysts containing carbohydrate-derived NHCs from glucose and
galactose were synthesized and characterized by NMR spectroscopy. 2D-NMR spectroscopy
revealed the presence of Ru-C (benzylidene) rotamers at room temperature, and the rate of rotation
was measured using magnetization transfer and VT-NMR spectroscopy. The catalysts were found to
be effective at ring-opening metathesis polymerization (ROMP), ring-closing metathesis (RCM),
cross-metathesis (CM), and asymmetric ring-opening cross-metathesis (AROCM) and showed
surprising selectivity in both CM and AROCM.
Introduction
A common strategy for improving catalyst activity and
selectivity involves modification of the NHC ligand. The
majority of efforts thus far have focused on modification of
the NHC backbone or aryl substituents.5 In general, N-aryl
bulk was found to increase activity, while increased back-
bone substitution decreased activity but increased catalyst
lifetime.6 However, these structural studies were limited to
catalysts with NHCs containing N-aryl substituents. NHC-
based metathesis catalysts with N-alkyl groups, on the other
hand, have received relatively little attention due to their
lower stability in solution.7,8 Recently, certain N-alkyl
NHCs have demonstrated remarkable activity, including
the traditionally difficult RCM of tetrasubstituted olefins.9
One class of N-alkyl substituents for NHCs which have
not yet been explored for metathesis applications are carbo-
hydrates. Carbohydrates are extremely abundant molecules
and comprise some of the most important biological ma-
chinery in living organisms, including glycolipids, glycopro-
teins, and nucleic acids. Thus, it is no surprise that their
synthesis10 and their biological function continue to be
studied extensively.11 As ligands, carbohydrates are advan-
tageous because of their innate chirality and steric bulk in
addition to their long history of synthetic manipulation and
solubility in water. Indeed, carbohydrates have already
The development of powerful air-stable catalysts has
made olefin metathesis an indispensable tool in a variety
of fields, including organic synthesis, materials science, and
biochemistry.1 Among the most versatile and robust cata-
lysts are those based on ruthenium, the first of which was
synthesized in 1992.2 The continued evolution of this
catalyst via replacement of one phosphine by an N-hetero-
cyclic carbene (NHC)3 and the other by a chelating ether
moiety4 (Chart 1) has propelled advancements in a multi-
tude of reactions, including cross-metathesis (CM), ring-
closing metathesis (RCM), ring-opening cross-metathesis
(ROCM), and ring-opening metathesis polymerization
(ROMP). Nevertheless, more stable and E/Z selective cata-
lysts are still required for both laboratory and industrial
applications.
*To whom correspondence should be addressed. E-mail: rhg@
caltech.edu.
(1) Furstner, A. Angew. Chem., Int. Ed. 2000, 39, 3013. (b) Trnka,
€
T. M.; Grubbs, R. H. Acc. Chem. Res. 2001, 34, 18.
(2) (a) Nguyen, S. T.; Johnson, L. K.; Grubbs, R. H.; Ziller, J. W.
J. Am. Chem. Soc. 1992, 114, 3974. (b) Schwab, P.; France, M. B.; Ziller,
J. W.; Grubbs, R. H. Angew. Chem., Int. Ed. 1995, 34, 2039. (c) Schwab, P.;
Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc. 1996, 118, 100.
(3) Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Org. Lett. 1999, 1,
953.
(4) (a) Kingsbury, J. S.; Harrity, J. P. A.; Bonitatebus, P. J.; Hoveyda,
A. H. J. Am. Chem. Soc. 1999, 121, 791. (b) Garber, S. B.; Kingsbury, J. S.;
Gray, B. L.; Hoveyda, A. H. J. Am. Chem. Soc. 2000, 122, 8168.
(5) (a) Van Veldhuizen, J. J.; Garber, S. B.; Kingsbury, J. S.;
Hoveyda, A. H. J. Am. Chem. Soc. 2002, 124, 4954. (b) Despagnet-Ayoub,
E.; Grubbs, R. H. Organometallics 2005, 24, 338. (c) Weigl, K.; Kohler, K.;
Dechert, S.; Meyer, F. Organometallics 2005, 24, 4049. (d) Funk, T. W.;
Berlin, J. M.; Grubbs, R. H. J. Am. Chem. Soc. 2006, 128, 1840. (e) Vehlow,
K.; Maechling, S.; Blechert, S. Organometallics 2006, 25, 25. (f) Anderson,
D. R.; Lavallo, V.; O'Leary, D. J.; Bertrand, G.; Grubbs, R. H. Angew. Chem.,
Int. Ed. 2007, 46, 7262. (g) Berlin, J. M.; Campbell, K.; Ritter, T.; Funk,
T. W.; Chlenov, A.; Grubbs, R. H. Org. Lett. 2007, 9, 1339. (h) Stewart, I. C.;
Ung, T.; Pletnev, A. A.; Berlin, J. M.; Grubbs, R. H.; Schrodi, Y. Org. Lett.
2007, 9, 1589. (i) Chung, C. K.; Grubbs, R. H. Org. Lett. 2008, 10, 2693.
(j) Vougioukalakis, G. C.; Grubbs, R. H. J. Am. Chem. Soc. 2008, 130, 2234.
(6) Kuhn, K. M.; Bourg, J. B.; Chung, C. K.; Virgil, S. C.; Grubbs,
R. H. J. Am. Chem. Soc. 2009, 131, 5313.
(7) Schuster, O.; Yang, L.; Raubenheimer, H. G.; Albrecht, M.
Chem. Rev. 2009, 109, 3445.
(8) (a) Weskamp, T.; Kohl, F. J.; Hieringer, W.; Gleich, D.; Herrmann,
W. A. Angew. Chem., Int. Ed. 1999, 38, 2416. (b) Ledoux, N.; Allaert, B.;
Linden, A.; Van Der Voort, P.; Verpoort, F. Organometallics 2007, 26, 1052.
(c) Boydston, A. J.; Xia, Y.; Kornfield, J. A.; Gorodetskaya, I. A.; Grubbs, R. H.
J. Am. Chem. Soc. 2008, 130, 12775.
(9) Savoie, J.; Stenne, B.; Collins, S. K. Adv. Synth. Catal. 2009, 351,
1826.
(10) Hudlicky, T.; Entwistle, D. A.; Pitzer, K. K.; Thorpe, A. J. Chem.
Rev. 1996, 96, 1195.
(11) (a) Gamblin, D. P.; Scanlan, E. M.; Davis, B. G. Chem. Rev.
2008, 109, 131. (b) Murrey, H. E.; Hsieh-Wilson, L. C. Chem. Rev. 2008,
108, 1708.
r
2009 American Chemical Society
Published on Web 12/18/2009
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