Metallkomplexe unsymmetrisch überbrückter [N₄]‐Makrocyclen: Synthese, Struktur und Redoxverhalten

Abstract

Metal Complexes of Unsymmetrically Bridged IN4] Macrocycles: Synthesis, Structure and Redox BehaviourMetal complexes M-5a (M = Cu, Ni, CO, Fe, and I-Fe") of 6,13-Di(ethoxycarbonyl)-7,12-dimethyl-benzo[ b]-l,4,8,11tetraaza-cyclotetradeca-2,5,7,11,13-pentaene and the free ligand H2-5a have been synthesized. The crystals of Cu-5a . H20 and Ni-5a . H 2 0 consist of planar complex molecules which are linked by H bridges between the water molecules and the peripheric ester groups to give 1D chains. The average M-N-distances are equal for both complexes (Cu 1.928, Ni 1.924 A), being unexpectedly large for the nickel complex. 'The redox properties of all the new compounds as well as some acetyl derivatives M-5b have been examined by cyclic voltammetry and compared with those of the previously re-ported symmetrically phenylene (M-4) and ethylene (M-6) bridged derivatives. All complexes give a reversible single electron reduction which clearly shows the increasing electron density around the central atom in the order M-4 < M-5 < M-6. Like the carbonyl substituted tetraazaannulenes M-4 the copper complexes Cu-5 give two, the cobalt complexes CO-5 three, and the iron complex Fe-5a probably four reversible single electron oxidations. They can be attributed to the species [M"'L-I']+, (M"L0J2+, [M"1Lo]3f, and [Fe1VLo]4+ with Lo being a "non innocent" neutral 1,2-quinodiimine ligand. Very surprisingly, since in contrast to Ni-4 and Ni-6, the nickel complexes Ni-5 gave no reversible oxidation. Makrocyclisch [Ni-1-koordinierte Chelatkomplexe der 3d-Elemente wirken als Aktivzentren vieler Biokatalysatoren. Beispiele sind das allen Hamenzymen zugrunde liegende Eisenporphyrin 1, das Corrin 2 der B12-Enzyme und das Dihydrocorphingeriist 3 des Cofaktors F 430[']. Obwohl sie fur unterschiedlichste Prozesse der biologischen Stoff-und Energiewandlung funktionsoptimiert sind, zeigen sie eine Reihe ubereinstimmender Strukturmotive, die offenbar gunstige Voraussetzungen fur eine Steuerung der katalytischen Eigenschaften biecen: Das Zentraiion bildet mit dem Bquatorial koordinierten, anionischen [N4]-Liganden mindestens zwei konjugiert-ungesattigte Chelatsechsringe aus. Hinsichtlich des x-Elektronensystems und der Ringgliederzahl m des inneren Makrocyclus sowie der Ladung z des Ligandanions bestehen charakteristische Unterschiede (1: 18 n; m = 16, z = -2; 2: 14 x; m = 15, z = -1; 3: 12 x; m = 16, z = -1). Die fur das Design biomimetischer Katalysatoren wichtige Frage, wie derartige Strukturmerkmale das katalytische Leistungsvermogen und die dafur entscheidenden Eigenschaften solcher Komplexe beeinflussen, 1al3t sich bisher kaum beantworten. Vor 30 Jahren erhielten wir uber eine Templatsynthese erstmals Komplexe des ,,Tetraaza[14]annulen6'-Typs 4, die sich von cyclischen 2:2-Kondensationsprodukten aus p-Dicarbonylverbindungen und 1,2-Phenylendiamin ableitenL'1. Sie unterscheiden sich vom inneren Makrocyclus des Por-1 4 4-8 I R' R2 R3 2 R2 5 X=C2H, p 3 R3&R1 / N \ A X M X ' 6 phyrinsystems nur durch das Fehlen zweier Methingruppen (16 n; m = 14...

Chemistry of Iron(III) in a Hemin-like Macrocyclic [N4]2-Environment: Relationship between CT Absorption and EPR Spectra

“…Magnetic Behavior. The iodides 1 -I are intermediate-spin complexes with magnetic moments of 3.56 ( 1a -I), 4.06 ( 1b -I), and 4.01 μ B ( 1c -I) at 295 K without any temperature dependence of the magnetic moment down to 77 K. , This is in agreement with a 4 A 2 ( S = 3 / 2 ) ground state stabilized by the strong tetragonal distortion effected by the pentacoordination with the halide as a relatively weak axial ligand . The same behavior was found in the case of the iodides of the parent complexes 5 and 3 without the free carbonyl substituents. , In contrast to this, the halides of iron(III) porphyrins show high-spin character.…”

“…Synthesis. The macrocyclic ligand of 1a , the Fe(III) complex 1b -I, and the Fe(II) complex 1c were prepared as previously described.…”

“…Some years ago we described the parent iron(II) complexes 1a and 2 . , Recently we reported on the corresponding iron(III) derivatives. − The iodo derivatives of these iron(III) complexes ( 1a -I, 2 -I) are distinguished from 5 mainly by the free carbonyl groups in the meso position, which lead to some advantageous properties: (1) In contrast to the unsubstituted macrocycles 3 and 5 , the iron(III) derivatives are stable in air because the meso substituents protect the ligand from the electophilic attack of dioxygen. (2) They are soluble without decomposition in water as well as in organic solvents.…”

Structural, Magnetic, and Electronic Properties of a Pentacoordinated Intermediate-Spin (S = 3/2) Iron(III) Complex with a Macrocyclic [N4]2- Ligand

“…As part of a program to investigate the electronic structure of 3d-metal complexes with varying macrocyclic ligands which are not porphin derivatives but have a similar equatorial [N 4 ] 2- donor set, we synthesized the iron(III) complex 3 and its ethylene/phenylene and phenylene/phenylene bridged analogs, which belong to the general class of the complexes 1 . Recently, we reported about the spectroscopic properties of the octahedral diadducts, the equilibria and kinetics of the stepwise substitution of axial ligands, the redox potentials, and the catalytic performance of these complexes .…”

An Unusual Metal-Mediated Formation of an Asymmetrical Carboxylate-Bridged Dinuclear Copper(II) Complex

“…Although copper(II) is generally known to be a good catalyst for hydrolysis reactions on its own ligands 8b and in phosphatase analogous systems, 1a, such a finding is nevertheless remarkable, because related complexes containing peripheral ester groups, e.g., open-chain Schiff base complexes and tetraazaannulene derivatives, are characterized by an extreme stability against bases as well as acids . Although the complexes 1 (Cu) and H- 2 (Cu) are sensitive to hydrolysis, they are hydrolyzed exclusively on the imine bond and not on the ester group.…”