Ring Size-Selective Ring-Closing Olefin Metathesis: Taking Advantage of the Deleterious Effect of Ethylene Gas

Engineering a Metathesis-Catalyzing Artificial Metalloenzyme Based on HaloTag

Artificial metalloenzymes (ArMs) are created by embedding a synthetic metal catalyst into a protein scaffold. ArMs have the potential to merge the catalytic advantages of natural enzymes with the reaction scope of synthetic catalysts. The choice of the protein scaffold is of utmost importance to tune the activity of the ArM. Herein, we show the repurposing of HaloTag, a self-labeling protein widely used in chemical biology, to create an ArM scaffold for metathesis. This monomeric protein scaffold allows for covalent attachment of metathesis cofactors, and the resulting ArMs are capable of catalyzing ring-closing metathesis. Both chemical and genetic engineering were explored to determine the evolvability of the resulting ArM. Additionally, exploration of the substrate scope revealed a reaction with promising turnover numbers (>48) and conversion rates (>96%).

Light guided chemoselective olefin metathesis reactions

An appealing concept in synthetic chemistry is photo-induced catalysis; where dormant complexes become catalytically active upon activation with light. The ruthenium-based olefin metathesis complexes founded on the original Grubbs catalyst have probably been one of the most widely studied families of catalysts for the past 25 years. Greater stability and versatility of these olefin-metathesis catalysts has been achieved by careful design of the ligand sphere, including latent catalysts which are activated by external stimuli. This article describes our recent developments towards light-induced olefin metathesis reactions based on photoactive sulfur-chelated ruthenium benzylidene catalysts. Alternative chemical reactions, be it photo-induced olefin metathesis or other direct photochemical processes, by using light of different frequencies were studied in chemoselective chromatic orthogonal pathways. The lessons learned during the development of these reactions have given birth to selective photo-deprotection sequences and novel pathways for stereolithographic applications.

Ethenolysis: A Green Catalytic Tool to Cleave Carbon-Carbon Double Bonds

Remarkable innovations have been made in the field of olefin metathesis due to the design and preparation of new catalysts. Ethenolysis, which is cross-metathesis with ethylene, represents one catalytic transformation that has been used with the purpose of cleaving internal carbon-carbon double bonds. The objectives were either the ring opening of cyclic olefins to produce dienes or the shortening of unsaturated hydrocarbon chains to degrade polymers or generate valuable shorter terminal olefins in a controlled manner. This Review summarizes several aspects of this reaction: the catalysts, their degradation in the presence of ethylene, some parameters driving their productivity, the side reactions, and the applications of ethenolysis in organic synthesis and in potential industrial applications.

Regioselective chromatic orthogonality with light-activated metathesis catalysts

The ability to selectively guide consecutive chemical processes towards a preferred pathway by using light of different frequencies is an appealing concept. Herein we describe the coupling of two photochemical reactions, one the photoisomerization and consequent activation of a sulfur-chelated latent olefin-metathesis catalyst at 350 nm, and the other the photocleavage of a silyl protecting group at 254 nm. Depending on the steric stress exerted by a photoremovable neighboring chemical substituent, we demonstrate the selective formation of either five- or six-membered-ring frameworks by light-triggered ring-closing metathesis. The orthogonality of these light-induced reactions allows the initiation of these processes independently and in interchangeable order, according to the wavelength of light used to promote them.