[4 + 4] and [2 + 2] cycloadditions are unique reactions
since they
form and deform cycloadducts under irradiation due to their inherent
reversible nature. Whereas promising for the field of recycling, these
reactions usually suffer from two major shortcomings: long reaction
durations (hours) and the requirement of high-intensity light (∼100
W/cm2), typically at a short wavelength (<330 nm). We
demonstrate several tetra-dentate catalysts that can overcome these
fundamental limitations. Among them is a tin complex that enables
76% conversion within only 2 min of irradiation at 395 nm, much faster
than the known ruthenium-based catalyst, under irradiation with light
intensity two orders of magnitude lower than that reported in the
literature. Due to the short photopolymerization time, low intensity
(27 mW/cm2), and long UV light (395 nm), this unique complex
opens new avenues for recycling three-dimensional printing products
based on photopolymerization of cycloaddition reactions.