Synthesis and solution studies of ruthenium(II) complexes with thiazole and antileukaemic drug thiopurines. Crystal structure of trans-dichlorotris(1,3-thiazole)(triphenylphosphine)ruthenium(II) ‡

Abstract

The crystalline complexes [RuCl₂(PPh₃)₂(thz)₂] 1, [RuCl₂(PPh₃)(thz)₃] 2, [Ru(H₂tp)₂(PPh₃)(thz)]Cl₂·2H₂O 3·2H₂O, [Ru(H₂tg)₂(PPh₃)₂]Cl₂·2H₂O·EtOH 4·2H₂O·EtOH, [Ru(H₂tprta)₂(PPh₃)₂]Cl₂·3H₂O 5·3H₂O, [Ru(H₂tp)₂(PPh₃)₂][CF₃SO₃]₂·H₂O·EtOH 6·H₂O·EtOH, [Ru(H₂tg)₂(PPh₃)₂][CF₃SO₃]₂·3H₂O 7·3H₂O, [Ru(H₂tp)₂(AsPh₃)(MeOH)]Cl₂·MeOH 8·MeOH, [Ru(bzim)₂Cl₂(PPh₃)₂] 9, and [RuCl₂(PPh₃)₂(mpym)₂] 10 (H₂tg = purine-2-amino-6-thione, H₂tp = purine-6-thione, H₂tprta = purine-6-thione 2′,3′,5′-tri-O-acetylriboside, thz = 1,3-thiazole, bzim = benzimidazole, mpym = 4-methylpyrimidine) have been prepared from [RuCl₂(PPh₃)₃] or [RuCl₃(AsPh₃)₂(MeOH)] and the base in alcoholic solution under nitrogen. The structures of the complexes were investigated by X-ray diffraction (2), NMR, conventional spectroscopic techniques and electrochemical methods. All the complex molecules have a pseudo-octahedral co-ordination geometry. The donor set of 2 consists of a phosphorus atom, two chloride anions trans to each other and three thz ligands bound to the metal through nitrogen. The sulfur atom of thz does not show any donor ability. However, the thione function of purine is much more active and in complexes 3–8 the purine base is chelated through S and N(7) atoms. On refluxing a suspension of 2 and H₂tp in ethanol compound 3 was obtained, which has a slight solubility in water. Electrochemical studies carried out on 7 in acetonitrile revealed a monoelectronic oxidation process at E_½ 1.02 V. The [Ru^III(H₂tg)₂(PPh₃)₂]³⁺ species which forms at this potential is relatively stable under the experimental conditions [25 °C; N₂, 1 bar (10⁵ Pa)] can be reversibly reduced to the starting compound which was recovered from the mixture. A molecular mechanics analysis, carried out for 1 and 2, produced a force field for this class of compounds and showed that the trans,trans,trans-[RuCl₂(PPh₃)₂(thz)₂] isomer of 1 is the most stable.

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