Latency for All: Enabling Latency of Hoveyda-Grubbs Second-Generation Catalysts by Adding Phosphite Ligands.

The Hoveyda-Grubbs catalyst (HG2, M720 Umicore) is among the most widely used catalysts in olefin metathesis reactions. Given the usefulness of HG2 and the great interest in developing latent olefin metathesis catalysts for numerous applications, we developed a method to introduce phosphite molecules as ancillary ligands into the precatalyst framework. This modification alters the geometry of the complex from an active trans-dichloro form to a latent cis-dichloro species. Most unusually, the ligands coordinate to HG2 only in solidified solutions (most likely due to entropic factors), providing latent catalysts that can be activated on demand by heat or light by regenerating the original HG2 catalyst. Of particular interest is the use of these latent catalysts in ring-opening metathesis polymerization (ROMP) reactions and 3D printing methods. Indeed, the novel complexes displayed the required latency toward ROMP monomers, even the most reactive dicyclopentadiene. Irradiation with 405 nm light readily results in the expedited formation of the desired polymers. This novel approach provides a general and straightforward way to access efficient and well-defined latent olefin metathesis catalysts.

Plasmonic visible-near infrared photothermal activation of olefin metathesis enabling photoresponsive materials.

Light-induced catalysis and thermoplasmonics are promising fields creating many opportunities for innovative research. Recent advances in light-induced olefin metathesis have led to new applications in polymer and material science, but further improvements to reaction scope and efficiency are desired. Herein, we present the activation of latent ruthenium-based olefin metathesis catalysts via the photothermal response of plasmonic gold nanobipyramids. Simple synthetic control over gold nanobipyramid size results in tunable localized surface plasmon resonance bands enabling catalyst initiation with low-energy visible and infrared light. This approach was applied to the ROMP of dicyclopentadiene, affording plasmonic polymer composites with exceptional photoresponsive and mechanical properties. Moreover, this method of catalyst activation was proven to be remarkably more efficient than activation through conventional heating in all the metathesis processes tested. This study paves the way for providing a wide range of photoinduced olefin metathesis processes in particular and photoinduced latent organic reactions in general by direct photothermal activation of thermally latent catalysts.