The square pyramidal tungstacyclopentane complex, W(NAr)(OSiPh3)2(C4H8) (Ar = 2,6-i-Pr2C6H3), reacts with ethylene at 22 °C in ambient (fluorescent) light over several days to give propylene and the square pyramidal tungstacy-clobutane complex, W(NAr)(OSiPh3)2(C3H6). No reaction takes place in the dark,but the reaction is &gt;90% complete in ~15 minutes in blue LED light (~450 nm). W(NAr)(OSiPh3)2(C4H8) deposited on silica also ring-contracts to give tungstacyclobutane complexes, partially upon deposition, and completely upon irradiating the grafted complex.These results constitute the first documented examples of contraction of a metallacyclopentane ring to a metallacyclobutane ring, establish how metathesis-active methylene and metallacyclobutane complexes can be formed, and reformed, in the presence of ethylene, homogeneously or on silica, and raise the possibility that ambient light could play a role in metathesis reactions that involve ethylene and tungsten-based metathesis catalysts

Formation of metathesis-relevant tungstacyclobutane complexes and propylene from tungstacyclopentane complexes and ethylene

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ACS Fall 2022

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