Inhibition of the Decomposition Pathways of Ruthenium Olefin Metathesis Catalysts: Development of Highly Efficient Catalysts for Ethenolysis.

Ruthenium-based Hoveyda-type olefin metathesis catalysts bearing novel rigid spirocyclic alkyl amino carbenes (CAACs) have been developed. They are characterized by exceptional stability toward decomposition through ß-elimination and bimolecular pathways, thus enabling unprecedented efficiency in the cross-metathesis of seed oil-derived fatty acid esters with ethylene (ethenolysis). Catalyst loading as low as 100 ppb was applied to the ethenolysis of the model substrate methyl oleate, leading to a remarkable turnover number (TON) of 2.6 million, significantly higher than previously reported (TON 340 000 at 1 ppm and 744 000 at 0.5 ppm catalyst loading). Ethenolysis of methyl esters derived from high oleic sunflower oil and rapeseed oil, readily available on an industrial scale, inexpensive, and renewable feedstocks, was for the first time effectively carried out with 0.5 ppm catalyst loading with TON as high as 964 000.

A versatile catalyst system for enantioselective synthesis of 2-substituted 1,4-benzodioxanes.

We report the synthesis of enantiomerically enriched 1,4-benzodioxanes containing alkyl, aryl, heteroaryl, and/or carbonyl substituents at the 2-position. The starting 1,4-benzodioxines were readily synthesized via ring closing metathesis using an efficient nitro-Grela catalyst at ppm levels. Excellent enantioselectivities of up to 99:1 er were obtained by using the versatile catalyst system [Ir(cod)Cl]2/BIDIME-dimer in the asymmetric hydrogenation of 2-substituted 1,4-benzodioxines. Furthermore, DFT calculations reveal that the selectivity of the process is controlled by the protonation step; and coordinating groups on the substrate may alter the interaction with the catalyst, resulting in a change in the facial selectivity.

Ammonium-tagged ruthenium-based catalysts for olefin metathesis in aqueous media under ultrasound and microwave irradiation.

The influence of microwave and ultrasonic irradiation on the performance of ammonium-tagged Ru-based catalysts in olefin metathesis transformations in aqueous media was studied. Differences in the catalytic activity in correlation with the nature of the present counter ion and the size of the N-heterocyclic carbene (NHC) ligand were revealed. The presented methodology allows for preparation of a variety of polar and non-polar metathesis products under environmentally friendly conditions.

Nitro-Grela-type complexes containing iodides - robust and selective catalysts for olefin metathesis under challenging conditions.

Iodide-containing nitro-Grela-type catalysts have been synthesized and applied to ring closing metathesis (RCM) and cross metathesis (CM) reactions. These new catalysts have exhibited improved efficiency in the transformation of sterically, non-demanding alkenes. Additional steric hindrance in the vicinity of ruthenium related to the presence of iodides ensures enhanced catalyst stability. The benefits are most apparent under challenging conditions, such as very low reaction concentrations, protic solvents or with the occurrence of impurities.