Cyclic Ruthenium-Alkylidene Catalysts for Ring-Expansion Metathesis Polymerization

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 imidazolylidine 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.

Cyclic polymers: Methods and strategies

“…The number of n carbons within the ring structure significantly influences the rate of polymerization, the amount of intramolecular cross-metathesis (or chain transfer), and reaction between free catalyst and cyclic polymer. 86 In general, the larger the n, the faster the rate of polymerization and the less likely that the Ru-catalyst will be released from the cyclic polymer. The general mechanism (given in Scheme 6) shows that monomer inserts into the cyclic Ru complex (or initiator) to form a macrocycle.…”

Metathesis of carbonyl containing olefins by 2nd generation Ru alkylidene catalysts: A computational study

“…Test calculations were carried out to establish the most appropriate theoretical model. Four different functionals B3LYP, MPW1K, M05 and PBE0 were tested to compare the optimized and experimental structures of recently synthesized rutheniumalkylidene complex [8] using double and triple f basis sets (LACVP* and LACV3P*, respectively) as defined in JAGUAR 7.0 suite of programs. Test calculations demonstrated that MPW1K and PBE0 reproduced best the experimental geometry (the largest deviation from experiment was found to be of 0.04 Å for Ru-Cl and Ru-P Scheme 1.…”

Ion pairing effects in the zwitterionic ring opening polymerization of δ-valerolactone

“…[5][6][7][8][9][10][11][12][13] We have reported a zwitterionic 14 ring-opening polymerization strategy 15 for the synthesis of cyclic polymers from lactones, [16][17][18][19][20][21][22][23] cyclic phosphates, 24 and carbosiloxanes; 25 Zhang has shown this strategy is also effective for generating cyclic poly( peptoid)s. 26 N-heterocyclic carbenes (NHC) have proven useful as intiators for ZROP due to the ability to tune the reactivity of the carbene to that of the monomer. NHC-mediated ZROP has recently been reported in the synthesis of ultra-high molecular weight cyclic polymers up to >900 kDa.…”