Metal ion promoted reactions in organic synthesis. Intramolecular condensations between ligands containing amine and carbonyl groups

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

“…While monodentate, N-bound aminoacetone cobalt(III) complexes have been reported, the pendant carbonyl functionality always condensed in basic conditions with a coordinated amine group of another ligand to produce extended chelate structures linked by carbinolamine or imine units. 7,29,30 This study has emphasized the greatly enhanced reactivity that a chelated 2-amino ketone moiety may experience at a metal centre. In this way the study lends credibility to proposals 2,3 that imply similar chelation of the A-site ALA substrate in the action of Zn 2+ -dependent ALAD.…”

“…An earlier study by Engelhardt et al 7 reported the chloro complex p-[Co(tren)Cl{NH 2 CH 2 C(OCH 2 CH 2 O)CH 3 }](ClO 4 ) 2 which is structurally related to 3, differing only by a chloride ligand at the position occupied by hydroxide ion in 3. Hydrolysis of the acetal of the chloro complex was effected in 1 M HCl at 45 • C, and the derivative, monodentate aminoacetone complex, p-[Co(tren)Cl{NH 2 CH 2 C(O)CH 3 }](ClO 4 ) 2 (chloride ligand retained), was subsequently crystallized from strong perchloric acid in 84% yield.…”

A simple method for identifying and distinguishing between the diastereoisomers that result from wrapping polydentate ligands around octahedral metal ions

“…In most cases, this kind of isomerism is well described by the easily interpreted notation in which the isomers with the substituent of highest priority trans to imine, primary, secondary or tertiary nitrogen donors of the polydentate ligand are known as the i, p, s or t isomers respectively. 14 However, there are, for example, possible cases of isomeric complexes of linear polyamines (e.g. Fig.…”

“…A similar kind of approach has been used to describe complexes of pentadentate ligands as combinations of tetradentate structural descriptions, for example as αα or αβ. 14 The Saito system is an attractive starting point for an octahedral nomenclature system because it is directly related to octahedral topology, leads to easy visualisation of isomers, and can be readily extended to longer chain linear pentadentate and hexadentate ligands, and (with some minor modifications) to tripodal and macrocyclic systems, without reference to model systems. This extension of the Saito system forms the basis of the general system we propose for the description of the diastereoisomers that result from wrapping polydentate ligands around an octahedral metal ion.…”

Assembly of polyamines via amino acids from three components using cobalt(iii) template methodology

“…Addition of acetylacetone monoanion to the Si face of 5 may be impeded by the adjacent propane-1,3-diamine ligand. Hydroxide-induced intramolecular condensation 11 of one of the acetyl functions of 6 with the nearest apical amino group gives an intermediate imine that loses the other acetyl group (NB alternatively, initial loss of one acetyl followed by intramolecular condensation may occur). One-pot reduction of the imine function and the metal centre, 12 leading from complex 3 to amino acid 2, was achieved by treatment of the imino complex 3 with sodium borohydride at pH 9 followed by acidification to pH 5.…”