creators_name: Boydston, Andrew J.
creators_name: Xia, Yan
creators_name: Kornfield, Julia A.
creators_name: Gorodetskaya, Irina A.
creators_name: Grubbs, Robert H.
creators_id: Boydston-A-J
creators_id: Xia-Y
creators_id: Kornfield-J-A
creators_id: Gorodetskaya-I-A
creators_id: Grubbs-R-H
type: article
datestamp: 2008-10-06 03:38:31
lastmod: 2008-10-06 03:38:31
metadata_visibility: show
title: Cyclic Ruthenium-Alkylidene Catalysts for Ring-Expansion Metathesis Polymerization
ispublished: pub
subjects: cls
full_text_status: restricted
note: Copyright © 2008 American Chemical Society. 

Received May 27, 2008. 

Web Release Date: August 27, 2008. 

We gratefully acknowledge Materia, Inc. for the generous gift of catalyst 1. We thank the DOE (DE-FG02-05ER46218), NIH (5RO1GM-31332), and the California Institute of Technology for generous financial support. A.J.B. thanks the NIH/NCI for a postdoctoral fellowship. We thank Professor Gregory B. McKenna for helpful discussions, as well as Matthew T. Whited, Larry M. Henling, and Dr. Michael W. Day for help in obtaining X-ray data. 

Supporting Information Available: Additional representations of Figure 4, NMR spectra for all new compounds, CIF files containing X-ray structural data, atomic coordinates, thermal parameters, bond distances, and bond angles for complexes 5cyc·H2, 6cyc, and 6cyc·H2. This material is available free of charge via the Internet at http://pubs.acs.org.
abstract: A series of cyclic Ru-alkylidene catalysts have been prepared and evaluated for their efficiency in ring-expansion metathesis polymerization (REMP). The catalyst structures feature chelating tethers extending from one N-atom of an N-heterocyclic carbene (NHC) ligand to the Ru metal center. The catalyst design is modular in nature, which provided access to Ru complexes having varying tether lengths, as well as electronically different NHC ligands. Structural impacts of the tether length were unveiled through 1H NMR spectroscopy as well as single-crystal X-ray analyses. Catalyst activities were evaluated via polymerization of cyclooctene, and key data are provided regarding propagation rates, intramolecular chain transfer, and catalyst stabilities, three areas necessary for the efficient synthesis of cyclic poly(olefin)s via REMP. From these studies, it was determined that while increasing the tether length of the catalyst leads to enhanced rates of polymerization, shorter tethers were found to facilitate intramolecular chain transfer and release of catalyst from the polymer. Electronic modification of the NHC via backbone saturation was found to enhance polymerization rates to a greater extent than did homologation of the tether. Overall, cyclic Ru complexes bearing 5- or 6-carbon tethers and saturated NHC ligands were found to be readily synthesized, bench-stable, and highly active catalysts for REMP.
date: 2008-09-24
date_type: published
publication: Journal of the American Chemical Society
volume: 130
number: 38
publisher: American Chemical Society
pagerange: 12775-12782
id_number: CaltechAUTHORS:BOYjacs08
refereed: TRUE
issn: 0002-7863
official_url: http://resolver.caltech.edu/CaltechAUTHORS:BOYjacs08
related_url_url: http://dx.doi.org/10.1021/ja8037849
related_url_type: doi
referencetext: 1. For general reviews on Ru-catalyzed olefin metathesis, see: (a) Bielawski, C. W.; Grubbs, R. H. Prog. Polym. Sci. 2007, 32, 1–29.   (b) Grubbs, R. H. Tetrahedron 2004, 60, 7117.   (c) Grubbs, R. H. Handbook of Metathesis; Wiley-VHC: Weinheim, Germany, 2003. (d) Trkna, T. M.; Grubbs, R. H. Acc. Chem. Res. 2001, 34, 18.    (e) Grubbs, R. H.; Chang, S. Tetrahedron 1998, 54, 4413.   (f) Ivin, K. J.; Mol, J. C. Olefin Metathesis and Metathesis Polymerization; Academic Press: San Diego, CA; 1997. 
2. (a) Xia, Y.; Verduzco, R.; Grubbs, R. H.; Kornfield, J. A. J. Am. Chem. Soc. 2008, 130, 1735.     (b) Gorodetskaya, I. A.; Choi, T.-L.; Grubbs, R. H. J. Am. Chem. Soc. 2007, 129, 12672.     (c) Choi, T.-L.; Rutenberg, I. M.; Grubbs, R. H. Angew. Chem., Int. Ed. 2002, 41, 3839.   
3. (a) Copéret, C.; Basset, J. M. Adv. Synth. Catal. 2007, 349, 78.  (b) Colacino, E.; Martinez, J.; Lamaty, F. Coord. Chem. Rev. 2007, 251, 726.   
4. (a) Funk, T. W.; Berlin, J. M.; Grubbs, R. H. J. Am. Chem. Soc. 2006, 128, 1840.     (b) Berlin, J. M.; Goldberg, S. D.; Grubbs, R. H. Angew. Chem., Int. Ed. 2006, 45, 7591.   
5. (a) Louie, J.; Bielawski, C. W.; Grubbs, R. H. J. Am. Chem. Soc. 2001, 123, 11312.     (b) Bielawski, C. W.; Louie, J.; Grubbs, R. H. J. Am. Chem. Soc. 2000, 122, 12872.    
6. (a) Choi, T.-L.; Grubbs, R. H. Angew. Chem., Int. Ed. 2003, 42, 1743.   (b) Love, J. A.; Morgan, J. P.; Trnka, T. M.; Grubbs, R. H. Angew. Chem., Int. Ed. 2002, 41, 4035.   
7. (a) Matloka, P. P.; Wagener, K. B. J. Mol. Catal. A: Chem. 2006, 257, 89.   (b) Baughman, T. W.; Wagener, K. B. Adv. Polym. Sci. 2005, 176, 1.  (c) Schwendeman, J. E.; Church, A. C.; Wagener, K. B. Adv. Synth. Catal. 2002, 344, 597.   
8. (a) Vougioukalakis, G. C.; Grubbs, R. H. J. Am. Chem. Soc. 2008, 130, 2234.     (b) Plietker, B.; Neisius, N. M. J. Org. Chem. 2008, 73, 3218.    (c) Vougioukalakis, G. C.; Grubbs, R. H. Organometallics 2007, 26, 2469.    (d) Vehlow, K.; Maechling, S.; Blechert, S. Organometallics 2006, 25, 25.    (e) Hansen, E. C.; Lee, D. Org. Lett. 2004, 6, 2035.     (f) Chatterjee, A. K.; Choi, T.-L.; Sanders, D. P.; Grubbs, R. H. J. Am. Chem. Soc. 2003, 125, 11360.     
9. For the synthesis and structural characterization of 4cyc and 5cyc, see: Fürstner, A.; Ackermann, L.; Gabor, B.; Goddard, R.; Lehmann, C. W.; Mynott, R.; Stelzer, F.; Thiel, O. R. Chem.—Eur. J. 2001, 7, 3236.  
10. Here we use the subscript “cyc” to denote the “cyclic” catalysts and the subscript “acyc” to denote the precyclized, acyclic complexes. 
11. (a) Bielawski, C. W.; Benitez, D.; Grubbs, R. H. J. Am. Chem. Soc. 2003, 125, 8424.     (b) Bielawski, C. W.; Benitez, D.; Grubbs, R. H. Science 2002, 297, 2041.    
12. For additional cyclic polymer syntheses involving ring-expansion approaches, see: (a) Culkin, D. A.; Jeong, W.; Csihony, S.; Gomez, E. D.; Balsara, N. P.; Hedrick, J. L.; Waymouth, R. M. Angew. Chem., Int. Ed. 2007, 46, 2627.   (b) Li, H.; Debuigne, A.; Jérome, R.; Lecomte, P. Angew. Chem., Int. Ed. 2006, 45, 2264.   (c) He, T.; Zheng, G.-H.; Pan, C.-Y. Macromolecules 2003, 36, 5960.    (d) Kudo, H.; Makino, S.; Kameyama, A.; Nishikubo, T. Macromolecules 2005, 38, 5964.    (e) Shea, K. J.; Lee, S. Y.; Busch, B. B. J. Org. Chem. 1998, 63, 5746.     
13. For cyclic polymer syntheses involving ring-closing of telechelic polymers, see: (a) Schappacher, M.; Deffieux, A. Science 2008, 319, 1512.    (b) Laurent, B. A.; Grayson, S. M. J. Am. Chem. Soc. 2006, 128, 4238.     (c) Oike, H.; Mouri, T.; Tezuka, Y. Macromolecules 2001, 34, 6229.    (d) Alberty, K. A.; Tillman, E.; Carlotti, S.; Bradforth, S. E.; Hogen-Esch, T. E.; Parker, D.; Feast, W. J. Macromolecules 2002, 35, 3856.    (e) Roovers, J. J. Polym. Sci., Part B: Polym. Phys. 1988, 26, 1251.   (f) Roovers, J.; Toporowski, P. M. Macromolecules 1983, 16, 843.    (g) Geiser, D.; Hoeker, H. Macromolecules 1980, 13, 653.    
14. (a) Sanford, M. S.; Love, J. A.; Grubbs, R. H. J. Am. Chem. Soc. 2001, 123, 6543.     (b) Bielawski, C. W.; Grubbs, R. H. Angew. Chem., Int. Ed. 2000, 39, 2903.   
15. Supporting Information. 
16. In solution, complexes 4acyc−7acyc appeared to exist as a mixture of two rotamers as shown by two benzylidene signals (ratio ca. 10:1). The major isomer appeared as a singlet, analogous to complex 2, whereas a second signal was observed further downfield as a doublet (e.g., 3JH,P = 12.9 Hz for 6cyc)15. 
17. Purchased from TSI Scientific, 230−400 mesh, neutral pH. 
18. Notably, “open” complexes 4acyc−7acyc were routinely used in subsequent cyclization steps following only filtration through a short silica gel plug and concentration under vacuum. Residual tricyclohexylphosphine was efficiently removed from the cyclized catalysts (4cyc−7cyc) during purification. 
19. Additional considerations should be noted: (1) Intramolecular cyclization may proceed to directly give an acyclic methylidene complex that is identical to the product that would be obtained between CM of styrene and the cyclic catalyst, and (2) in rare cases, olefin isomerization and cyclization to give small amounts of cyclic catalysts bearing a one-carbon shorter tether were observed (e.g., 7acyc → 6cyc). 
20. Perillo, I.; Caterina, M. C.; López, J.; Salerno, A. Synthesis 2004, 851. 
21. For an alternative, two-step procedure for the synthesis of imidazolinium salts bearing one N-aryl and one N′-alkyl group, see ref 8d. 
22. Attempts at ligand exchange via deprotonation of imidazolinium salts 10 in hexanes were also unsuccessful. 
23. (a) Courchey, F. C.; Sworen, J. C.; Ghiviriga, I.; Abboud, K. A.; Wagener, K. B. Organometallics 2006, 25, 6074.   (b) Trnka, T. M.; Morgan, J. P.; Sanford, M. S.; Wilhem, T. E.; Scholl, M.; Choi, T.-L.; Ding, S.; Day, M. D.; Grubbs, R. H. J. Am. Chem. Soc. 2003, 125, 2546.     
24. This reaction was found to be solvent-dependent, and PhCH3, PhH, pentane, and PhH/pentane mixture gave inferior results. 
25. Unfortunately, attempts to isolate pure samples of 7cyc·H2 were unsuccessful. 
26. Attempts to obtain X-ray quality crystals of 7cyc were met with limited success. 
27. Since single-crystal X-ray data were not obtained for 7cyc, it was not possible to determine the direction of the rotation about the Ru1−C2 bond with respect to complexes 4cyc−6cyc. We speculate that the long tether of 7cyc may allow for conformations that collectively frustrate crystallization. 
28. Additional representations of the data in Figure 4 are provided.15 
29. Ritter, T.; Hejl, A.; Wenzel, A. G.; Funk, T. W.; Grubbs, R. H. Organometallics 2006, 25, 5740.    
30. Other terminating agents have also been employed; see: (a) Matson, J. B.; Grubbs, R. H. Macromolecules 2008, 41, 5626.    (b) Hilf, S.; Berger-Nicoletti, E.; Grubbs, R. H.; Kilbinger, A. F. M. Angew. Chem., Int. Ed. 2006, 45, 8045.   (c) Owen, R. M.; Gestwicki, J. E.; Young, T.; Kiessling, L. L. Org. Lett. 2002, 4, 2293.     
31. In light of the relatively low activity of 4cyc, 4acyc was not evaluated in these experiments. 
32. Under identical conditions, 5acyc−7acyc gave faster conversions of COE to PCOE than the corresponding “closed” systems (5cyc−7cyc). The higher polymerization activities of 5acyc−7acyc versus 5cyc−7cyc may reflect restricted conformations of the latter. Further investigations are underway. 
33. Molecular-weight data were obtained from triple-angle laser light-scattering and refractive index measurements. 
34. Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.; Timmers, F. J. Organometallics 1996, 15, 1518–1520.    
35. The compound appeared to be hygroscopic, producing a thick, viscous material when collected under air.
citation: Boydston, Andrew J. and Xia, Yan and Kornfield, Julia A. and Gorodetskaya, Irina A. and Grubbs, Robert H. (2008) Cyclic Ruthenium-Alkylidene Catalysts for Ring-Expansion Metathesis Polymerization. Journal of the American Chemical Society, 130 (38). pp. 12775-12782. ISSN 0002-7863 http://resolver.caltech.edu/CaltechAUTHORS:BOYjacs08 <http://resolver.caltech.edu/CaltechAUTHORS:BOYjacs08>
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