For a series of Fe(IV) =O complexes with tetra- and pentadentate bispidine ligands, the correlation of their redox potentials with reactivity, involving a variety of substrates for alkane hydroxylation (HAT), alkene epoxidation, and phosphine and thioether oxidation (OAT) are reported. The redox potentials span approximately 350 mV and the reaction rates over 8 orders of magnitude. From the experimental data and in comparison with published studies it emerges that electron transfer and the driving force are of major importance, and this is also supported by the DFT-based computational analysis. The striking difference of reactivity of two isomeric systems with pentadentate bispidines is found to be due to a destabilization of the S=1 ground state of one of the ferryl isomers, and this is supported by the experimentally determined redox potentials and published stability constants with a series of first-row transition metal ions with these two isomeric ligands.

It is better to light a candle than to curse the dark. AbstractThe copper-catalyzed azide-alkyne cycloaddition for the synthesis of 1,4-disubstituted 1,2,3-triazoles (CuAAC) is a variant of Huisgen's 1,3-dipolar cycloaddition which disburdens the thermal reaction from its major drawbacks such as poor regioselectivity, long reaction times and harsh conditions. In contrast to the widely used "black box" reagent mixtures, a molecularly defined, highly active catalyst system for homogeneous CuAAC reactions has been developed in this PhD project. In dependence on the postulated stepwise mechanism, its most important structural feature is the presence of two copper(I) ions irreversibly bound in the same catalyst molecule.A highly modular and profitable synthesis for bistriazolium hexafluorophosphate salts as precursors for the ancillary ligand system was devised. In analogy to the CuAAC catalyst systems of general formula [(NHC) 2 Cu]PF 6 described in literature, novel dinuclear copper(I) complexes with a bistriazolylidene ligand backbone and 1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene (IPr) as sacrificial ligand were prepared.However, these complexes did not show the expected high catalytic activity, most probably due to the strong coordination of the IPr ligands. In consequence, another family of dinuclear copper(I) complexes with m-coordinated acetate as labile ligand was synthesized by reaction of the bistriazolium hexafluorophosphate ligand precursors with copper(I) acetate in the presence of a base.The broad applicability and high catalytic activity of one of these bistriazolylidene dicopper acetate complexes was confirmed by a series of gaschromatographically mo-

The synthesis of a new tetradentate bispidine ligand (LH2 = 2,2′-(1,5-dimethyl-3,7-diazabicyclo[3.3.1]nonan-3,7-diyl)diacetic acid), containing two tertiary amine and two carboxylic groups, is reported along with the preparation and characterization of the corresponding Cu(ii) and Fe(iii) complexes. The mononuclear [LCu(OH2)]·4H2O (1) complex contains a five-coordinate Cu(ii) centre, which adopt a square pyramidal geometry with the four donor atoms of the ligand (N2O2) occupying the equatorial plane and a water molecule occupying the axial position. An axial electron paramagnetic resonance (EPR) signature is observed for 1 (gx = 2.054, gy = 2.050, gz = 2.234; Ax = 18 × 10–4 cm–1, Ay = 20 × 10–4 cm–1, Az = 188 × 10–4 cm–1) in frozen methanolic solution (0.1 mM). Dimerization of 1 in concentrated solution (10 mM) was observed by EPR spectroscopy (g∥ = 2.24, g⊥ = 2.07, A∥ = 195 × 10–4 cm–1, and A⊥ = 12 × 10–4 cm–1 for each Cu centre). The structure of the dimeric species [LCu(OH2)]2 (1b) was determined by a combination of molecular mechanics with the simulation of the EPR spectrum (MM-EPR). The dimer has each Cu(ii) centre coordinated by the two amines and one carboxylate of one ligand (L), while the other carboxylate bridges to the second Cu(ii) centre; each coordination sphere is completed by an axial water ligand, with the Cu···Cu distance 5.5 Å (relative orientation from EPR simulation: α = 60°, β = 0°, γ = 25°). The aqueous reaction between the tetradentate ligand (L) and Fe(ii) leads to the formation of an oxo-bridged diiron(iii) complex, [LFe-(μ-O)-FeL] (2), with a Fe–O–Fe angle of 180° (dFe···Fe = 3.516 Å), as revealed by X-ray crystallography. The Mössbauer spectrum of 2 consists of one quadrupole doublet with an isomer shift (δ) of 0.37 mm s–1 and a quadrupole splitting (ΔEQ) of 0.73 mm s–1, which is consistent with S = 5/2 Fe(iii) centres. Variable-temperature magnetic susceptibility measurements show the presence of intramolecular antiferromagnetic interactions between the two Fe(iii) centres, with an exchange coupling constant J of –91(3) cm–1 (H = –2JS1·S2).

Oxygen activation by copper(I) complexes with tetra- or pentadentate mono- or dinucleating bispidine ligands is known to lead to unusually stable end-on-[{(bispidine)Cu}(2)(O(2))](2+) complexes (bispidines are methyl-2,4-bis(2-pyridin-yl)-3,7-diazabicyclo-[3.3.1]-nonane-9-diol-1,5-dicarboxylates); catecholase activity of these dinuclear Cu(II/I) systems has been demonstrated experimentally, and the mechanism has been thoroughly analyzed. The present density functional theory (DFT) based study provides an analysis of the electronic structure and catalytic activity of [{(bispidine)Cu}(2)(O(2))](2+). As a result of the unique square pyramidal coordination geometry, the d(x(2)-y(2)) ground state leads to an unusual σ/π bonding pattern, responsible for the stability of the peroxo complex and the observed catecholase activity with a unique mechanistic pathway. The oxidation of catechol to ortho-quinone (one molecule per catalytic cycle and concomitant formation of one equivalent of H(2)O(2)) is shown to occur via an associative, stepwise pathway. The unusual stability of the end-on-peroxo-dicopper(II) complex and isomerization to copper(II) complexes with chelating catecholate ligands, which inhibit the catalytic cycle, are shown to be responsible for an only moderate catalytic activity.

No abstract