Latent, Yet Highly Active Photoswitchable Olefin Metathesis Precatalysts Bearing Cyclic Alkyl Amino Carbene (CAAC)/Phosphite Ligands

The
ligand shell that surrounds an active metal center has a paramount
effect on its reactivity and properties. In this work, the photoswitchable
nature of phosphite olefin metathesis precatalysts and the robustness
of cyclic alkyl amino carbene (CAAC) ligands are combined. Also, the
synthesis, characterization, and photoactivity of two ruthenium indenylidene
complexes bearing a CAAC/phosphite ligand system are reported. Exposure
to 405 nm light efficiently activates the precatalysts and promotes
a wide range of olefin metathesis reactions. Moreover, the catalysts
display formidable latency at ambient temperatures, even with the
highly reactive dicyclopentadiene and its derivatives, allowing the
preparation of stable monomer–catalyst formulations with a
long pot life. In addition, the chemoselectivity of CAAC catalysts
is preserved, preventing olefin migration reactions at elevated temperatures
and allowing efficient recycling for multiple reaction cycles under
air.