Applications ofthese complexes in olefin metathesis are described.

Since N-aryl,N-alkyl NHC ruthenium catalysts display good stability, complexes 1 and 2 bearing a sterically hindered N-tert-butyl substituent on the NHC were synthesized and screened for latent behavior during cross-metathesis (CM) and ring-opening metathesis polymerization (ROMP) reactions (). At ambient temperature, solutions of complexes 1 and 2 in CDCl3 showed no decomposition by NMR spectroscopy over 14 days and were stable in air for over four months. Additionally, complexes 1 and 2 could be heated in chloroform at 60 °C for 5 days without any signs of decomposition, thus indicating good thermal stability. At 90 °C in toluene, catalysts 1 and 2 began showing slight decomposition after 30 hours. This observed catalyst stability was promising for applications in latent metathesis chemistry, where the catalyst must remain active at high temperature for the duration of the reaction.

CM – Cross MetathesisROMP – Ring Opening Metathesis Polymerization

Cazin 16 Hoveyda-Type Olefin Metathesis Complexes 437 Yakov Ginzburg and N.

Latent Ruthenium Olefin Metathesis Catalysts That …

This work was inspired by the report of complex cis-Caz-1 in 2010, a 2nd generation-type pre-catalyst displaying latent character and acknowledged as state-of-the-art for challenging transformation in olefin metathesis.

9 Multifold Ring-Closing Olefin Metatheses in ..

The stability and the reactivity of such species led us to investigate the possibility to perform the catalysis in air with reagent-grade solvents, so that olefin metathesis reaction can be easily carried out in synthetic laboratories avoiding restricting inert conditions (Chapter 2).

The first examples of Ru-F species for olefin metathesis reaction are reported in Chapter 3.

Ruthenium Olefin Metathesis Catalysts Featuring a Labile ..

Catalysts 1 and 2 were initially screened and compared for latency for the homodimerization of 1-hexene to 5-decene (). Both catalysts showed less than 5% conversion of 1-hexene after 24 hours at 25 °C while maintaining catalyst structural integrity as confirmed by 1H NMR spectroscopy (, entries 1 and 2). The reactions were subsequently heated at 85 °C for 24 hours, and the conversions were determined by 1H NMR spectroscopy (, entries 3 and 4). Both catalysts gave clean conversion of 1-hexene to 5-decene, without detectable side products by 1H NMR spectroscopy. Since catalyst 1 achieved 90% conversion of 1-hexene to 5-decene compared to 41% afforded by catalyst 2, it was considered optimal for further latent cross-metathesis studies. Catalyst 2 was still active with no signs of decomposition after 24 hours at 85 °C. Presumably the better activity of catalyst 1 in relation to catalyst 2 is due to less steric hindrance of the former on the N-aryl ring (mono-tert-butyl versus di-isopropyl). Since both catalysts are latent for cross-metathesis of 1-hexene, the better activity of catalyst 1 is preferential for these reactions. The crystal structures of complexes 1 and 2 show expected geometry ().

the same olefin metathesis catalysts can efficiently promote ..

Olefin metathesis is widely used as a method of constructing carbon-carbon double bonds. Toward this end, highly efficient metathesis catalysts have been designed through improvement of activity, stability, and selectivity of the catalysts. Recently, efforts have been directed toward the development of latent metathesis catalysts., Latent catalysts are defined as complexes that show little or no activity at a particular (usually ambient) temperature and initiate only upon activation. This activation can be caused by a variety of different stimuli, including heat,, acid, light,- and chemical activation. Latent metathesis catalysts primarily have applications in polymer chemistry. One such application is the advantage of preparing monomer solutions in a mold with a catalyst that is unreactive at ambient temperature, thus allowing for good mixing and even distribution of monomeric solution before initiating polymerization. Previous literature reports describe latent ruthenium catalysts whereby the initiators and organic ligand structure were altered to induce latency.- The structure of initiators, such as variations of the Hoveyda-type chelating ligand, has been particularly well-explored and documented.- Another approach toward tuning the latency of a catalyst involves manipulation of the N-heterocyclic carbene (NHC) ligand. This method of inducing latent behavior is attractive in that it enables a straightforward catalyst design and synthesis while maintaining the functional group tolerance and stability of second generation ruthenium catalysts. Reported herein is the investigation of four new ruthenium-based latent catalysts for cross-metathesis and ROMP that were prepared adopting this strategy.

chelated latent olefin‐metathesis ..

Further studies were conducted with catalyst 1 to determine the optimal temperature for carrying out cross-metathesis reactions. In addition to 1-hexene, 1-octene, 5-hexenyl acetate, and 4-penten-1-ol were used as cross-metathesis substrates for homodimerization to assure that the observed results were general to simple alkyl olefins (). Catalyst 1 proved to be latent for these substrates even at 40 °C, showing no appreciable reactivity until 50 °C. Moderate conversion to product was obtained for all substrates at 60 °C; however, 85 °C was considered optimal for attaining good conversion of the starting material. The reactions gave the desired homocoupled product of these substrates as a mixture of cis and trans isomers.

13 Well-Defined Olefin Metathesis Catalysts Based on ..

The advantage of the latent catalysts is demonstrated in the ring-opening metathesis polymerization of dicyclopentadiene, where the latency of 6 assures adequate mixing of catalyst and monomer before initiation.

Olefin Metathesis - Institute of Chemistry and …

The complexes are inactive in ring-closing metathesis and ring-opening metathesis polymerization reactions even at elevated temperatures in the absence of stimuli.