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Published September 24, 2008 | Accepted Version + Cover Image + Supplemental Material
Journal Article Open

Cyclic Ruthenium-Alkylidene Catalysts for Ring-Expansion Metathesis Polymerization


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.

Additional Information

© 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.

Attached Files

Accepted Version - nihms86291.pdf

Supplemental Material - ja8037849-File004.pdf

Supplemental Material - ja8037849-File005.cif

Supplemental Material - ja8037849-File006.cif

Supplemental Material - ja8037849-File007.cif

Cover Image - ja-2008-037849_0012.gif


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August 22, 2023
October 17, 2023