Aromaticity versus Stability of Chelate Complexes. Study on Metalcomplexes of Hydroxypyrones and Related Ligands

The thesis about the influence of induced by metal ion aromaticity on properties of some chelate type metalcomplexes is presented. Such idea was decribed firstly long time ago by Calvin and Wilson [1] but has received sporadic interest until recently. In this decade, the concept has been renewed as it appeared to be useful in explaining of many properties of chelates that may have appeared unlinked. For example, the electronic, vibrational, and NMR spectra, as well as the electrochemistry, and X-ray structure can be interpreted in the frame of this theory [2]. Importance of chelatoaromaticity is presented on the example of metalomplexes of hydroxypyrones and their derivatives. For many years maltol (3-hydroxy-2-methyl-4-pyrone) and others hydroxypyrones have been widely known as useful ligand in coordination chemistry. In addition its metalcomplexes with various metal ions (like vanadium, iron, aluminium and others) have strong biological activity [3]. On the other hand, structurally similar hydroxypiridinones are widely used as iron ions scavengers in the thallassemia treatment. Recently, thiomaltol (3-hydroxy-2-methyl-4-thiopyrone), compound in which the keto oxygen atom is replaced by sulphur [4] was synthetized and used as ligand for metalcomplexes with potential environmental applications [5-6]. Aromaticity data for various forms of studied ligands and their metalcomplexes are presented and discussed. It is shown that during complexation ligands change their properties from antiaromatic/nonaromatic to aromatic. Authors are grateful for access to the computational facilities of the Warsaw University Interdisciplinary Centre for Mathematical and Computational Modelling ICM (Project Number G178) and the Academic Computer Center “Cyfronet” Krakow (Grant Number KBN/S2000/UJ/025/1998)