Ole Mønsted

Mechanism of lactic acid formation catalyzed by tetraamine rhodium(III) complexes

The transformation of methylglyoxal and of 1,3–dihydroxyacetone and glyceraldehyde into lactic acid can be catalyzed by cis- tetraaminediaquarhodium(III) complexes of ethane-1,2–diamine and of the macrocyclic racemic 5,5,7,12,12,14–hexamethyl-1,4,8,11– tetraazacyclotetradecane ligand. The detailed stoichiometry of this process has been investigated by isotopic labelling studies and 1H and 13C-n.m.r. spectroscopy.The suggested mechanism of the methylglyoxal transformation process involves bidentate substrate coordination, followed by an intramolecular 1,2–hydride shift in a resonance stabilized carbocation. The transformations of 1,3–dihydroxyacetone and glyceraldehyde are stoichiometrically more complicated, and rhodium(III) catalyzed conversion of 1,3–dihydroxyacetone into glyceraldehyde is observed. Ultimately both substrates are converted into coordinated lactate in which one hydrogen atom in the methyl group originates from the solvent water.

Reaction kinetic and equilibrium studies of the oxidation of oxalic acid by thallium(III) in aqueous perchlorate solutions

The oxidation of oxalic acid by thallium(III) in 3 M (Na++ H+) perchlorate solutions can be described by the following scheme : Tl3++ H2C2O4⇌ TlC2O+4+ 2H+(K25°= 8.6 × 102 mol l.–1, ΔHo=–3.4 kcal mol–1) followed by TlC2O+4→ Tl++2 CO2(k= 1016.2 exp (–28.400/RT) s–1).

[CrIII8MII6]12+ Coordination Cubes (MII=Cu, Co)

[CrIII8MII6]12+ (MII=Cu, Co) coordination cubes were constructed from a simple [CrIIIL3] metalloligand and a “naked” MII salt. The flexibility in the design proffers the potential to tune the physical properties, as all the constituent parts of the cage can be changed without structural alteration. Computational techniques (known in theoretical nuclear physics as statistical spectroscopy) in tandem with EPR spectroscopy are used to interpret the magnetic behavior.

Computationally inexpensive interpretation of magnetic data for finite spin clusters

We show that high-temperature expansion of the partition function is a computationally convenient tool to interpretation of magnetic properties of spin clusters wherein the spin centers are interacting via an isotropic Heisenberg exchange operator. High-temperature expansions up to order 12 are used to reproduce temperature dependent magnetic susceptibilities of a Cr(III) tetramer, a decanuclear Fe(III) wheel, a 3x3 grid arrangement of nine Mn(II) ions, and a dodecanuclear Ni(II) wheel. Excellent agreement with experiments as well as with results from computationally more elaborate methods is achieved.

Base hydrolysis of macrocyclic chromium(III) complexes. Importance of ion-pair formation for kinetics and mechanism

A series of cis and trans complexes of the general formula [Cr(cyc)(OH2)X]2+, where cyc is the macrocyclic tetraamines meso- or rac- 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane and X− = NCS−, N3− and Cl−, have been prepared in solution via anation of the diaqua complexes. The kinetics of the monodendate X ligand release in alkaline media have been studied at a range of temperatures and hydroxide concentrations at ionic strengths of 1.0 or 2.0 M using NaClO4, NaBr or NaCl as “inert” electrolytes. A higher order than linear dependence of the pseudo-first-order rate constant on the hydroxide concentration has been observed for all the systems investigated. These results have been rationalized in terms of specific ion-pair interactions between the macrocyclic chromium(III) reactants and counterions of the supporting electrolytes, followed by proton transfer in the hydroxide ion pair to give a reactive conjugate base.

First aminoacetone chelate: [Co(tren){NH2CH2C(O)CH3}]3+—a substrate binding and activation model for zinc(II)-dependent 5-aminolaevulinic acid dehydratase

The complex p-[Co(tren){NH(2)CH(2)C(O)CH(3)}](ClO(4))(3).H(2)O was produced stereoselectively from [Co(tren)(O(3)SCF(3))(2)]O(3)SCF(3) () and 2-(aminomethyl)-2-methyl-1,3-dioxolane. The structure of was determined by X-ray crystallography. The complex is the first aminoacetone chelate to be reported and the first structurally characterized example of a non-conjugated ketone moiety coordinated to cobalt(iii). The robust complex was stable to aquation in strong acid and behaved as an acid with pK(a) = 4.99(1) indicative of a strong activation of the aminoacetone ligand towards deprotonation. The complex constitutes a structural model for a proposed substrate binding mode relevant for substrate activation of the zinc(ii)-dependent enzyme 5-aminolaevulinic acid dehydratase.