Design of Coordinatively Unsaturated Iron Species for Homogeneous Catalysis

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Three types of coordinatively unsaturated iron species were designed by appropriate choice of auxialiry ligands, and their reactivity towards alkenes and related unsaturated compounds was investigated. Triazacyclononane(TACN) derivatives were a good ligand for Fe(II) complexes. Coordinatively unsaturated 16e-(TACN) FeX2 species behaved as a catalyst for atom transfer radical polymerization. Two concepts for generation of 16e-Fe(II) species were proposed ; one was based on favorable equiliblim between a halogen-bridged dimer and a catalytically active monomer controlled by steric bulkiness of nitrogen substituents of TACN, whereas another was stabilization of active monomeric species by weakly coordinating ligands. Treatment of a 14e-organoiron complex bearing two mesityl groups and a tetraethylenediamine ligand with electron deficient alkenes resulted in coupling reaction of the mesityl ligands as well as conjugate addition of a mesityl group toα,β-unsaturated ketones. Disilametallacylic 16e-Fe(II) species was generated from a nitrogen-bridged dimer precursor reacted with alkenes to form cyclic organosilicon compounds.