Studies on 24-membered macrocyclic mononuclear and dinuclear iron complexes: Stability and catalytic hydroxylation of adamantane by divalent iron complexes

The dinucleating 24-membered hexaazadiphenol macrocyclic ligand 3,6,9,17,20 ,23-hexaaza-29,30-dihydroxy-13,27-dimethyltricyclo[23.3.1.1(11,15)]triacont a-1(28),11,13,15(30),25,26-hexaene (L or [24]BDBPH) is prepared by the NaBH 4 reduction of the Schiff base obtained from [2 + 2] template condensation of 2,6-diformyl-p-cresol with diethyltriamine. The ligand maintains dinucle ar integrity for both iron(II,II) and iron(III,III) complexes, while facili tating the formation of bridging phenolate diiron cores. Potentiometric equ ilibrium studies indicate that a variety of protonated, mononuclear and din uclear iron(II) and iron(III) complexes form from p[H] 2-11 in an aqueous s olution. The protonation constants and stability constants of the 1:1, 1:2 [ligand/iron(II) or ligand/iron(III)], and 1:1:1 [ligand/iron(III)/iron(II) ] complexes were determined in a KCl supporting electrolyte (mu = 0.100 M) at 25 degrees C. The mechanisms for the formation of dinuclear iron(II), ir on(III), sind mixed-valence iron(II,III) complexes are described. Prelimina ry results showed that the dinuclear iron(II) complexes catalyze hydroxylat ion of adamantane in the presence of H2S as a two-electron reductant.