A Dinucleating Ligand System with Varying Terminal Donors to Mimic Diiron Active Sites

To mimic dinuclear active sites of metalloproteins, we have developed a dinucleating ligand system consisting of two tetradentate tripodal ligand compartments with varying terminal donors (carboxylates, phenolates, and pyridines). These ligands provide access to a series of μ-oxo-bridged diferric complexes. The spectroscopic study allows to investigate the molecular structures even in solution, e. g. depending on protonation/deprotonation of coordinated OH⁻ and H₂O ligands or to observe a reversible pH-dependent carboxylate-shift between terminal and bridging binding mode. The electrochemical behavior is strongly influenced by the exogenous ligands, e. g. OH⁻ facilitates oxidation to Fe^IV by 690 mV relative to Cl⁻. Using the terminal carboxylates and a {Fe^III(μ-O)₂Fe^III} core even allows oxidation with O₂ to a high-valent species with Fe^IV (S=2). The implications of this study for further generation of high-valent or peroxo species and their utilization in catalysis is discussed.     

Synthesis of Semicyclic/Exocyclic Amino-1,3-dienes by organocuprate addition to semicyclic propyniminium salts

Conjugate addition of organocuprates to the 2-ethynyl-substituted cyclic iminium triflates 3 generates aminoallenes which tautomerize immediately to semicyclic 2-amino-1,3-dienes ( 6 , 8 ) or exocyclic 1-amino-1,3-dienes ( 9 , 10 ) with the enamine function incorporated into or attached to a 5-, 6-, or 7-membered ring. In those cases where tautomeric equilibria between the two aminodiene species are possible, the five-membered ring exists virtually exclusively with an exocyclic enamine double bond, but the six-membered ring prefers the exocyclic form. The seven-membered ring can accomodate both forms quite well.