Hexadentate phenol ligand

A dinuclear iron(ll/Ill) complex bearing a hexadentate phenol ligand displayed moderate activity toward aziridination of alkenes with PhlNTs a large excess of alkene (2,000 equiv. vs PhlNTs) was required for good product yields (Scheme 22) [76]. It is noteworthy that complex 4 is active in the aziridination of aliphatic alkenes, affording higher product yields than copper (11) catalysts with tetradentate macrocyclic ligands [77]. 

Another non-heme system made use of hexadentate phenol ligands [98]. However, the catalytically active species was only formed upon ligand oxidation by excess of PhI=NTs. Furthermore, a large excess of the alkene was required (2000 equiv. vs. PhI=NTs). The reaction of cyclooctene and 1-hexene gave yields of about 50%, which represents a significant improvement over the earlier described copper systems [99]. 

An intermediate product was identified and characterized in the reaction outlined in Scheme 27. X-Ray analysis has shown that this intermediate product contains a hexadentate monoanionic ligand formed through the reaction of a phenol group with an aziridine group once coordinated to nickel(II). 4,2335... 

A typical example of the more complex reactions that may occur when aromatic compounds react with dioxygen in the presence of copper salts is seen in Fig. 9-30. When solutions of the hexadentate ligand 9.14 react with copper salts and dioxygen, a complex of a new ligand is obtained. The new phenolic compound that is formed acts as a dinucleating ligand and its dinuclear copper(n) complexes turn out to be effective oxygenation catalysts for other substrates. 

Linear hexadentate tetramine phenols such as (26) have been shown to form metal derivatives that are very stable in aqueous solutions.34 This class of ligands generally binds the metals in a dianionic N402-donor form, yielding an octahedral environment. The four nitrogen atoms of the tetra-amine backbone form the equatorial plane of the octahedron, whereas the two phenolates are coordinated trans to each other.34... 

---