The synthesis, characterization, and catalytic activity of pyridine(diimine) iron piperylene and isoprene complexes are described. These diene complexes are competent precatalysts for (i) the selective cross-[2+2]-cycloaddition of butadiene or (E)-piperylene with ethylene and α-olefins and (ii) the 1,4-hydrovinylation of isoprene with ethylene. In the former case, kinetic analysis implicated the diamagnetic η4-piperylene complex as the resting state prior to rate-determining oxidative cyclization. Variable temperature 1H NMR and EXSY experiments established that diene exchange from the diamagnetic, 18e– complexes occurred rapidly in solution at ambient temperature through a dissociative mechanism. The solid-state structure of (Me(Et)PDI) Fe(η4-piperylene) (Me(Et)PDI=2,6-(2,6-Me2-C6H3N=CEt)2C5H3N) was determined by single-crystal X-ray diffraction and confirmed the s-trans coordination of the monosubstituted 1,3-diene. Possible relationships between ligand-controlled diene coordination geometry, metallacycle denticity, and chemoselectivity of iron-mediated cycloaddition reactions are discussed. (Figure presented.).
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- diene ligands