Pyridine(diimine) Iron Diene Complexes Relevant to Catalytic [2+2]-Cycloaddition Reactions.

ABSTRACT: 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 ?-olefins and (ii) the 1,4-hydrovinylation of isoprene with ethylene. In the former case, kinetic analysis implicates the diamagnetic ?⁴-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 occurs rapidly in solution at ambient temperature through a dissociative mechanism. The solid-state structure of (^Me(Et)PDI)Fe(?⁴-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.

SUBMITTER: Kennedy CR 

PROVIDER: S-EPMC7236768 | biostudies-literature | 2020 Jan

REPOSITORIES: biostudies-literature