The synthesis and structure of new tin(II) complexes based on ferrocenyl-containing o -iminophenols

The Synthesis and Biological Activity of Organotin Complexes with Thio-Schiff Bases Bearing Phenol Fragments

A number of novel di- and triorganotin(IV) complexes 1-5 (Ph₂SnL¹, Ph₂SnL², Et₂SnL², Ph₃SnL³, Ph₃SnL⁴) with mono- or dianionic forms of thio-Schiff bases containing antioxidant sterically hindered phenol or catechol fragments were synthesized. Compounds 1-5 were characterized by ¹H, ¹³C NMR, IR spectroscopy, and elemental analysis. The molecular structures of complexes 1 and 2 in the crystal state were established by single-crystal X-ray analysis. The antioxidant activity of new complexes as radical scavengers was estimated in DPPH and ABTS assays. It was found that compounds 4 and 5 with free phenol or catechol fragments are more active in these tests than complexes 1-3 with tridentate O,N,S-coordinated ligands. The effect of compounds 1-5 on the promoted oxidative damage of the DNA by 2,2'-azobis(2-amidinopropane) dihydrochloride and in the process of rat liver (Wistar) homogenate lipid peroxidation in vitro was determined. Complexes 4 and 5 were characterized by more pronounced antioxidant activity in the reaction of lipid peroxidation in vitro than compounds 1-3. The antiproliferative activity of compounds 1-5 was investigated against MCF-7, HTC-116, and A-549 cell lines by an MTT test. The values of IC₅₀ are significantly affected by the presence of free antioxidant fragments and the coordination site for binding.

Heteroligand α-Diimine-Zn(II) Complexes with O,N,O'- and O,N,S-Donor Redox-Active Schiff Bases: Synthesis, Structure and Electrochemical Properties

A number of novel heteroligand Zn(II) complexes (1-8) of the general type (Lⁿ)Zn(NN) containing O,N,O'-, O,N,S-donor redox-active Schiff bases and neutral N,N'-chelating ligands (NN) were synthesized. The target Schiff bases LⁿH₂ were obtained as a result of the condensation of 3,5-di-tert-butyl-2-hydroxybenzaldehyde with substituted o-aminophenols or o-aminothiophenol. These ligands with combination with 2,2'-bipyridine, 1,10-phenanthroline, and neocuproine are able to form stable complexes upon coordination with zinc(II) ion. The molecular structures of complexes 4∙H₂O, 6, and 8 in crystal state were determined by means of single-crystal X-ray analysis. In the prepared complexes, the redox-active Schiff bases are in the form of doubly deprotonated dianions and act as chelating tridentate ligands. Complexes 6 and 8 possess a strongly distorted pentacoordinate geometry while 4∙H₂O is hexacoordinate and contains water molecule coordinated to the central zinc atom. The electrochemical properties of zinc(II) complexes were studied by the cyclic voltammetry. For the studied complexes, O,N,O'- or O,N,S-donor Schiff base ligands are predominantly involved in electrochemical transformations in the anodic region, while the N,N'-coordinated neutral nitrogen donor ligands demonstrate the electrochemical activity in the cathode potential range. A feature of complexes 5 and 8 with sterically hindered tert-butyl groups is the possibility of the formation of relatively stable monocation and monoanion forms under electrochemical conditions. The values of the energy gap between the boundary redox orbitals were determined by electrochemical and spectral methods. The parameters obtained in the first case vary from 1.97 to 2.42 eV, while the optical bang gap reaches 2.87 eV.

Heteroligand Metal Complexes with Extended Redox Properties Based on Redox-Active Chelating Ligands of o-Quinone Type and Ferrocene

A combination of different types of redox-active systems in one molecule makes it possible to create coordination compounds with extended redox abilities, combining molecular and electronic structures determined by the features of intra- and intermolecular interactions between such redox-active centres. This review summarizes and analyses information from the literature, published mainly from 2000 to the present, on the methods of preparation, the molecular and electronic structure of mixed-ligand coordination compounds based on redox-active ligands of the o-benzoquinone type and ferrocenes, ferrocene-containing ligands, the features of their redox properties, and some chemical behaviour.

Complexity of imine and amine Schiff-base tin(II) complexes: drastic differences of amino and pyridyl side arms

A series of homoleptic and heteroleptic imine and amine Schiff-base tin(II) complexes containing dimethylamino and pyridyl side arms were synthesized and structurally characterized. While the tin complexes containing the dimethylamino side arm could be prepared in good yield, unusual cyclodimerization and ligand dimerization were observed for the first time for Schiff-base tin complexes having a pyridyl side arm due to the added stabilization offered by the pyridyl ring. The amine Schiff-base tin(II) complexes were active for the ring-opening copolymerization of succinic anhydride (SA) and cyclohexene oxide (CHO) at 110 °C giving highly alternating poly(SA-alt-CHO).

Ferrocene-Containing Tin(IV) Complexes Based on o-Benzoquinone and o-Iminobenzoquinone Ligands. Synthesis, Molecular Structure, and Electrochemical Properties

The addition of different substituted o-benzoquinones and o-iminobenzoquinones to tin(II) bis(o-iminophenolates) of the types (Fc-IP)₂Sn^II and (Fc-4,6-IP)₂Sn^II (where Fc-IP is anion 2-(ferrocenylmethyleneamino)phenolate [Fc-C(H)═N(C₆H₄)O^-] and Fc-4,6-IP is anion 2-(ferrocenylmethyleneamino)-4,6-di-tert-butylphenolate [Fc-C(H)═N(4,6-tBu-C₆H₂)O^-]) in tetrahydrofuran leads to the oxidation of Sn(II) to Sn(IV) with formation of the corresponding tin(IV) catecholates (Fc-4,6-IP)₂Sn^IV(3,6-Cat) (1), (Fc-IP)₂Sn^IV(3,6-Cat) (2), (Fc-4,6-IP)₂Sn^IV(4-Cl-3,6-Cat) (3), (Fc-IP)₂Sn^IV(4-Cl-3,6-Cat) (4), (Fc-4,6-IP)₂Sn^IV(4,5-Cl₂-3,6-Cat) (5), and (Fc-IP)₂Sn^IV(4,5-Cl₂-3,6-Cat) (6) or the o-amidophenolates (Fc-4,6-IP)₂Sn^IV(AP-Me) (7), (Fc-IP)₂Sn^IV(AP-iPr) (8), and (Fc-4,6-IP)₂Sn^IV(AP-iPr) (9). Here ligands 3,6-Cat, 4-Cl-3,6-Cat, and 4,5-Cl₂-3,6-Cat are dianions 3,6-di-tert-butyl-, 4-chloro-3,6-di-tert-butyl-, and 4,5-dichloro-3,6-di-tert-butylcatecholates, respectively, and AP-Me and AP-iPr are dianions 4,6-di-tert-butyl-N-(2,6-dimethylphenyl)-o-amidophenolate and 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-amidophenolate, respectively. Complexes 1-9 have been characterized in detail by IR spectroscopy, cyclic voltammetry, and ¹H, ¹³C, and ¹¹⁹Sn NMR spectroscopy. The molecular structures of tin(IV) complexes 5, 7, and 9 in the crystalline state were determined by single-crystal X-ray diffraction analysis. Complexes demonstrate a series of successive oxidations involving alternately catecholato/o-amidophenolato centers and ferrocenyl moieties. The relative oxidation potentials of these redox centers depend on the acceptor properties of the redox-active chelating O,O' or O,N ligand. An increase in the acceptor properties of redox-active o-quinonato-type ligands leads to an increase in the oxidation potentials of redox ligands as well as the following oxidation of ferrocenyl group(s). In two series of complexes, (Fc-4,6-L)₂SnL' and (Fc-L)₂SnL', where L' is AP-iPr, AP-Me, 3,6-Cat, 4-Cl-3,6-Cat, and 4,5-Cl₂-3,6-Cat, a more pronounced convergence of the oxidation potentials of the redox-active o-quinonato ligand and ferrocenyl group occurs in the series (Fc-L)₂SnL'.