Tungstacyclopentane Ring Contraction Yields Olefin Metathesis Catalysts

Area of Science:

• Organometallic Chemistry
• Photochemistry
• Catalysis

Background:

• Tungsten complexes are key in olefin metathesis.
• Understanding light's role in organometallic reactions is crucial.
• Ring contraction mechanisms in metallacycles are not fully understood.

Purpose of the Study:

• To investigate the effect of light on tungsten-cyclopentane complexes.
• To elucidate the mechanism of light-induced ring contraction.
• To explore the formation of metallacyclobutanes and methylene complexes.

Main Methods:

• Photochemical reactions of tungsten-cyclopentane complexes with ethylene.
• Spectroscopic analysis to identify intermediates and products.
• Kinetic studies under varying light conditions.

Main Results:

• Exposure to ambient or blue LED light induces a ring contraction of tungstacyclopentane to tungstacyclobutane, producing propylene.
• The reaction proceeds via proposed alpha- and beta-methyl tungstacyclobutane intermediates.
• The rate of reaction is significantly influenced by the nature of the ligand and light intensity.

Conclusions:

• This work provides the first experimental evidence for light-induced metallacyclopentane to metallacyclobutane ring contraction.
• It establishes a pathway for forming metathesis-active methylene and metallacyclobutane complexes in the presence of ethylene.
• Ambient light may play a significant role in tungsten-catalyzed olefin metathesis reactions.