Iron-Catalyzed Intermolecular [2π+2π] Cycloaddition

The bis(imino)pyridine iron dinitrogen compounds, ((PDI)-P-iPr)Fe(N-2)(2) and [((PDI)-P-Me)Fe(N-2)](2)(mu(2)-N-2) ((PDI)-P-R = 2,6-(2,6-R-2-C6H3N=CMe)(2)C6H3N; R = Pr-i, Me), promote the catalytic intermolecular [2 pi + 2 pi] cycloaddition of ethylene and butadiene to form vinylcyclobutane. Stoichiometric experiments resulted in isolation of a catalytically competent iron metallocycle intermediate, which was shown to undergo diene-induced C-C reductive elimination. Deuterium labeling experiments establish competitive cyclometalation of the bis(imino)pyridine aryl substituents during catalytic turnover.