cis-Dichloro(dimethyl sulfoxide-S)(2-methoxypyridine-N)platinum(II)

Abstract

The title complex, [PtCl 2 (C 6 H 7 NO)(C 2 H 6 OS)], exhibits square-planar geometry. The plane of the pyridine ring makes a dihedral angle of 67.2 (3) with the square plane of the metal center. The SÐO bond is nearly aligned with the adjacent PtÐ N bond, leaving the methyl groups of the dimethyl sulfoxide ligand to stagger the PtÐCl bond. CommentCisplatin, cis-[Pt(NH 3 ) 2 Cl 2 ], is extensively used in the treatment of a variety of cancers (Kelland et al., 1992). Most of its second generation analogs are simple amines with a cis geometry about the metal, which is in either the +2 or +4 oxidation state. These compounds share a common rationale in their design (Cleare & Hoeschle, 1973). Reports of the biological effects of unusual Pt derivatives (Hambley, 1997), such as triamine complexes (Hollis et al., 1989;Baird et al., 1997) or those with a trans geometry (Van Beusichem & Farrell, 1992), have appeared in the literature. The antitumor activity of sulfoxide derivatives has also been noted (Farrell et al., 1990). This has prompted us to investigate the antitumor activity of both cis and trans isomers of the general formula (N-Het)Pt(dmso)Cl 2 , where N-Het is a nitrogen heterocycle. The title compound, (I), is a member of a series of complexes prepared as part of our study.Compound (I) is a square-planar Pt derivative with bond distances and angles at the Pt atom in the normal range (Sundquist et al., 1987;Melanson & Rochon, 1977b). The Pt atom deviates by 0.012 (1) A Ê from the mean plane of the ligand atoms (NÐSÐCl1ÐCl2). The structure validates 195 Pt NMR chemical shift data, which suggested a cis geometry for the product. The PtÐCl bond cis to the dimethyl sulfoxide (dmso) ligand is slightly shorter than the trans-PtÐCl bond, in line with the trend generally observed for ligands with a trans in¯uence. While the PtÐS distance is within the range reported for other Pt II ±sulfoxide derivatives (Pasini et al., 1994;Sundquist et al., 1987), it is noteworthy that this bond length of 2.220 (3) A Ê is greater than the value expected when considering the cis in¯uence of related ligands (Belsky et al., 1991). This is likely to be due to the electron-donating ability of the methoxy group in the 2-position of the ring.The S atom of the coordinated dmso ligand is tetrahedral. The SÐO distance in Pt±dmso complexes is typically shorter than in the free ligand, and (I) also possesses a shortened bond. A near eclipsing of the PtÐN bond by the SÐO group has been observed in other cis-Pt±dmso complexes (Melanson & Rochon, 1977b;Dyksterhouse et al., 2000) and compound (I) is no exception. The resulting coplanarity of the SÐO bond with the square plane of the metal atom in (I) [torsion angle O2ÐSÐPtÐN 7.3 (4) ] and other cis complexes contrasts with trans derivatives, in which the SÐO bond is perpendicular to the Pt square plane.Another feature of (I) is a weak association of O1 to Pt, with a contact of 2.972 (8) A Ê . Furthermore, the dihedral angle between the pyridine plane and the metal coordination plane is 67.2 (3) . T...