Preparation and characterization of d6 tungsten compounds with amino acid derivatized diimine ligands and preparation of dipeptide derivatives using peptide coupling agents

Dioxime and pyridine-2-aldoxime complexes of

“…Examples of complexes of diimines can be found across the transition metals [1], and d 6 complexes, such as those of group 7, have been much studied [2]. The types of diimines that have been investigated can be broken down into ligands with two, one, or no basic heterocycles as part of the a-diimine (Scheme 1), as shown for the 2,2'-bipyridine ligand [1a], pyridinecarbaldehyde imine (pyca) ligand [2d] and diazabutadiene (dab) [3], respectively. The pyca and dab ligands have been prepared with a variety of aliphatic and aromatic amines [4] including amino acids, amino esters and amino alcohols [5].…”

Carbonyl complexes of manganese, rhenium and molybdenum with 2-pyridylimino acid ligands

“…GABA is an important inhibitor which acts in a wide variety of biological processes, whereas b-alanine, the simplest b-amino acid (and the only one occurring naturally) is believed to be involved in the visual system [17] and, together with GABA, to act as a neurotransmitter in the central nervous system [18]. A series of complexes of the W(CO) 4 fragment containing iminopyridines derived from 3-aminobenzoic acid [19] and a series of amino acids and dipeptides [20] have been recently reported, as well as the bromo tricarbonyl rhenium iminopyridine derivative of x-amino undecanoic acid [21].…”

Synthesis of tungsten compounds with Schiff base ligands prepared from ferrocenecarboxaldehyde: Observation of the migration of an imine double bond

“…While some Schiff base compounds containing pyridine are isolable, in many cases they are not [2][3][4][5][6]. Attempts to extend this work preparing Schiff base ligands using ethylenediamine and ferrocenecarboxaldehyde in the presence of W(CO) 4 (pip) 2 led to insoluble products that could not be analyzed.…”

“…The stability stems from the favorable backbonding works better between the metal dp orbitals and the p * orbitals of the rigidly planar pyca ligand created by conjugation of the pyridine ring with the exocyclic imine. Complexes created using aromatic amines, aliphatic amines and amino esters and acids have been the focus of several studies [1][2][3][4][5][6][7][8].…”

“…Two non-conjugated diimine ligands with one or two methylene groups separating the pyridine from the imine were targeted. Reflux of either 2-(aminomethyl)pyridine or 2-(2-aminoethyl)pyridine with ferrocenecarboxaldehyde in the presence of W(CO) 4 (pip) 2 led to two new compounds, W(CO) 4 (g 2 -NC 5 H 4 CH@NCH 2 -C 5 H 4 FeCp) (1) and W(CO) 4 (g 2 -NC 5 H 4 C 2 H 4 N@CHC 5 H 4 FeCp) (2), respectively (see Scheme 1). While the desired compound (2), with the ethylene group separating the pyridine from the imine nitrogen was prepared, the corresponding compound with the methylene group separating the pyridine from the imine nitrogen was not obtained.…”