Biomimetic Catalysis of Catechol Cleavage by O2 in Organic Solvents − Role of Accessibility of O2 to FeIII in 2,11-Diaza[3,3](2,6)pyridinophane-Type Catalysts

Abstract

Three new complexes, [Fe(LN 4 H 2 )Cl 2 ] + , [Fe(LN 4 H 2 )(Cat)] + , and [Fe(LN 4 H 2 )(DBC)] + , were synthesized by using the tetradentate macrocyclic ligand LN 4 H 2 (where LN 4 H 2 , Cat, and DBC stand for 2,11-diaza[3,3](2,6) pyridinophane, catecholate, and 3,5-di-tert-butylcatecholate, respectively). The structure of [Fe(LN 4 H 2 )Cl 2 ] + was determined by X-ray diffraction. It crystallizes in the monoclinic space group C2/c with a = 9.613(1), b = 11.589(1), c = 14.063(2) Å , β=110.20(2)°, V = 1541.9(3) Å 3 , and Z = 4. These complexes were found to catalyze the oxidation of catechol groups using O 2 . This was performed in various organic solvents at 20°C. The reaction

Functional models for catechol dioxygenases: Iron(III) complexes of cis-facially coordinating linear 3N ligands

“…Obviously, the lone pair orbital on the nitrogen atom of the sterically hindered-NMe 2 group is not oriented exactly towards the iron(III) orbital rendering the Fe-N3 bond longer. Similar lengthening of Fe-NMe 2 bond has been observed [27,39,45] previously. Further, the longer Fe-N3 bond distance is expected to shorten the trans Fe-Cl3 bond.…”

“…The observed values [21,23,45] of k O 2 for the oxidative reaction catalyzed by the complexes follow the trends: Fe(L2) 3+ > Fe(L1) 3+ ; Fe(L5) 3+ > Fe(L3) 3+ > Fe(L4) 3+ . As they correspond to mainly the intradiol-cleavage pathway, the observed trends may be illustrated in the light of the proposed substrate-activation mechanism [5,8].…”

A linear correlation between energy of LMCT band and oxygenation reaction rate of a series of catecholatoiron(III) complexes: initial oxygen binding during intradiol catechol oxygenation

“…For several model systems, the following reactivity tendencies have been reported: (1) electron-rich catecholate ligands enhance the reactivity [12,13,30] and (2) a high reactivity requires a ferric center having a high Lewis acidity [8,9,31]. To examine if our results are in agreement with these tendencies, we have tried to find a correlation between the electrochemical data and the oxygen reactivity.…”

Chemical characteristics of the products of the complexation reaction between copper(II) and a tetra-aza macrocycle in the presence of chloride ions

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Historically, transition metal tetra-aza complexes have been utilized extensively in biomimetic inorganic chemistry as functional models for superoxide dismutase, catalase, and copper oxidase active sites. [18][19][20][21][22][23][24][25] Metal complexes derived from tetra-aza macrocyclic ligands generally present large stability constants, on the order of log K ≥ 20.0 in the case of copper(II) complexes. 17,18,[26][27][28][29][30][31][32] In a 1969 paper by Margerum and Cabbiness, the copper(II) complex derived from a tetra-aza macrocycle was determined to be 10 4 times more stable than the non-cyclic tetraamine ligand.…”