Polymerization of Allenes by Using an Iron(II) β‐Diketiminate Pre‐Catalyst to Generate High M (n) Polymers

Herein, we report an iron(II)‐catalyzed polymerization of arylallenes. This reaction proceeds rapidly at room temperature in the presence of a hydride co‐catalyst to generate polymers of weight up to M (n)=189 000 Da. We have determined the polymer structure and chain length for a range of monomers through a combination of NMR, differential scanning calorimetry (DSC) and gel permeation chromatography (GPC) analysis. Mechanistically, we postulate that the co‐catalyst does not react to form an iron(II) hydride in situ, but instead the chain growth is proceeding via a reactive Fe(III) species. We have also performed kinetic and isotopic experiments to further our understanding. The formation of a highly unusual 1,3‐substituted cyclobutane side‐product is also investigated.