Iron(II) Complexes with Tetradentate Bis(aminophenolate) Ligands: Synthesis and Characterization, Solution Behavior, and Reactivity with O₂

Abstract

Tetradentate bis(aminophenolate) ligands H(2)salan(X) and H(2)bapen(X) (where X refers to the para-phenolate substituent = H, Me, F, Cl) react with [Fe{N(SiMe(3))(2)}(2)] to form iron(II) complexes, which in the presence of suitable donor ligands L (L = pyridine or THF) can be isolated as the complexes [Fe(salan(X))(L)(2)] and [Fe(bapen(X))(L)(2)]. In the absence of donor ligands, either mononuclear complexes, for example, [Fe(salan(tBu,tBu))], or dinuclear complexes of the type [Fe(salan(X))](2) are obtained. The dynamic coordination behavior in solution of the complexes [Fe(salan(F))(L)(2)] and [Fe(bapen(F))(L)(2)] has been investigated by VT (1)H and (19)F NMR spectroscopy, which has revealed equilibria between isomers with different ligand coordination topologies cis-α, cis-β and trans. Exposure of the iron(II) salan(X) complexes to O(2) results in the formation of oxo-bridged iron(III) complexes of the type [{Fe(salan(X))}(2)(μ-O)] or [{Fe(salan(X))(L)}(2)(μ-O)]. The lack of catalytic activity of the iron(II) salan and bapen complexes in the oxidation of cyclohexane with H(2)O(2) as the oxidant is attributed to the rapid formation of stable and catalytically inactive oxo-bridged iron(III) complexes.

A Preorganized Metalloreceptor for Alkaline Earth Ions Showing Calcium Versus Magnesium Selectivity in Water: Biological Activity of Selected Metal Complexes

“…In all cases, the ligand adopts a trans conformation around the copper ion according to ref. 19, and given that the nitrogen atoms of the H −2 L 2− anion have the same configuration ( R , R or S , S ), the expected trans ( R , R ) ( trans ( S , S )) topology of the isomers is observed 20…”

A Synthetic and Multispectroscopic Speciation Analysis of Controlled Radical Polymerization Mediated by Amine–Bis(phenolate)iron Complexes

“…Iron-Mediated Radical Polymerization with a Simultaneous ATRP and RT-OMRP Equilibrium a a Both reaction pathways involve the Fe II /L activator complex and growing radicals, R n • , of chain length n. Potential subsequent reactions such as degenerative transfer (DT) and catalytic radical termination (CRT) are also included. 39 UV/Vis Spectroscopy. Initial polymerization studies were performed with the stable (with respect to oxidation) Fe III species, i.e., Cl,Cl,NMe2 [O 2 NN′]Fe III Cl (Cl−Fe III /L, Figure 2).…”

A Straightforward Electrochemical Approach to Imine- and Amine-bisphenolate Metal Complexes with Facile Control Over Metal Oxidation State

“…Another reported synthetic method involves reaction of ligand precursors with Fe(OAc) 2 , though in our hands this route furnishes an Fe III complex when ligand precursor 1 b is used (see Supporting Information), as do other literature examples . Fe II –salens have been rendered inactive in catalysis in some cases, which may be explained by the presence of Fe III …”

“…A common method to prepare metal–salens involves reaction of the ligand with metal acetate, with high temperatures often being necessary (e.g., Fe and Mn) and column chromatography being required for purification (e.g., Cu), often resulting in low yields . Other general methods include reaction of the ligand with metal alkoxide 10 or amide precursors, or reaction with metal halide in the presence of a base . The use of sensitive precursors can lead to complicated product mixtures, particularly where metal–alkoxides are used due to the process being an equilibrium reaction .…”