Reactions of Terminal Olefins With Iron Carbenes

The application of sustainable, earth-abundant iron complexes to the olefin metathesis of terminal olefins remains a formidable challenge due to competitive, metathesis-divergent deactivation pathways. Herein, we investigate the reactivity of pincer-supported iron carbenes toward various terminal olefins. Reactions with styrene, ethylene, or 2-vinylanisole under ambient conditions proceed through 2π + 2π cycloadditions to generate transient metallacyclobutane intermediates that rapidly undergo metathesis-divergent β-hydride elimination to yield stable iron allyl hydride complexes. The addition of benzonitrile to the iron allyl hydride complexes demonstrates a unique hydride transfer from the iron center to the nitrile carbon, yielding a paramagnetic terminal imide complex. Conversely, reactions with the sterically demanding 1,1-disubstituted olefin α-methylstyrene successfully suppress β-hydride elimination. Heating this mixture induces a 2π + 2π cycloaddition followed by cycloreversion and a subsequent 1,2-hydride shift, resulting in productive, albeit low-yield, metathesis to generate a paramagnetic side-bound iron olefin complex.