Ruthenium-Catalyzed Metathesis of Conjugated Polyenes

In the past decade, numerous examples of chemical technologies based on olefin metathesis have been developed to make olefin metathesis increasingly dominant in several sustainable and green chemical processes. In spite of the wide application profile, conjugated olefin metathesis, especially conjugated polyene metathesis, is an area of great interest with little exploration. The metathesis of conjugated polyenes is often cumbersome and requires a high catalyst loading, most probably because of the formation of poorly active or inactive ruthenium h 3-vinylcarbene intermediates. A mechanistic understanding and the development of a new highly active catalytic system for olefin metathesis will open new areas for exploration, such as the utilisation of cyclopentadiene and other petrochemical by-products or a new way to use butadiene, isoprene and conjugated electron systems that contain natural products such as terpenes and polyunsaturated fatty acids. An understanding of the mechanism of ruthenium h 1-h 3-vinylcarbene interconversion may open the way to the development of a new generation of Ru-based latent metathesis catalyst systems. This review summarises the most relevant pioneering work focused on the metathesis of conjugated polyenes to open new ideas for the development of forthcoming latent metathesis catalysts and to explore different applications.