Alkenes are the basic building blocks of the chemical industry. The development of vast domestic shale gas reserves has created an over abundance of small alkenes such as ethylene and propylene. New methods to valorize these hydrocarbons, aside from alkene polymerization, are highly valuable. Bis(imino)pyridine iron- and cobalt catalysts have been discovered that promote the unprecedented [2π+2π] cycloaddition of terminal alkenes to cyclobutanes. High degree of stereo- and regioselectivity has been observed and been attributed to formation of metallocyclic intermediates (Science 2015, 349, 960.; J. Am. Chem. Soc. 2015, 137, 7903.). Diene-alkene [2π+2π] cycloadditions have also been discovered and yield vinyl cyclobutane products that are useful precursors for exploring the four-membered ring hydrocarbon core in fine chemicals (J. Am. Chem. Soc. 2011, 133, 8858.; Science 2015, 349, 960.). Mechanistic studies highlight the involvement of the redox-active bis(imino)pyridine ligand in promoting the C(sp3)-C(sp3) reductive elimination (J. Am. Chem. Soc. 2013, 135, 4862.). Future efforts are using this information to expand the scope of the reaction to build more valuable structures from shale gas byproducts.
Iron-catalyzed intermolecular [2+2] cycloadditions of unactivated alkenes
Jordan M. Hoyt, Valerie A. Schmidt, Aaron M. Tondreau, and Paul J. Chirik
Science 2015, 349, 960-963.
Cobalt-Catalyzed [2π + 2π] Cycloadditions of Alkenes: Scope, Mechanism, and Elucidation of Electronic Structure of Catalytic Intermediates
Valerie A. Schmidt, Jordan M. Hoyt, Grant M. Margulieux, and Paul J. Chirik
J. Am. Chem. Soc. 2015, 137, 7903-7914.
Synthesis and Electronic Structure of Bis(imino)pyridine Iron Metallacyclic Intermediates in Iron-Catalyzed Cyclization Reactions
Jordan M. Hoyt, Kevin T. Sylvester, Scott P. Semproni, and Paul J. Chirik
J. Am. Chem. Soc. 2013, 135, 4862-4877.
Iron-Catalyzed Intermolecular [2π + 2π] Cycloaddition
Sarah K. Russel, Emil Lobkovsky, and Paul J. Chirik
J. Am. Chem. Soc. 2011, 133, 8858-8861.