NMR study of substituent effects in platinum(II) intercalating agents

Abstract

AbstractA series of (4‐X‐thiophenolato) (2,2′:6′,2″‐terpyridine)platinum(H) complexes [X = H, F, Cl, Br, CH3, OCH3, NH2, N(CH3)2, NO2, COOCH3, CN, NH], which have potential as DNA intercalators, have been synthesized. 13C and 195Pt NMR spectra of these complexes have been obtained in both D2O and DMSO‐d6. The 195Pt shifts are highly sensitive to both solvent and distant substituent effects and span a chemical shift range of 72 ppm. The propagation and transmission of substituent effects within the complexes have been studied, and the 195Pt and thiophenolato C‐1 13C chemical shifts correlated with Hammett substituent constants, using the dual substituent approach. The results show that the (terpy)Pt—S— group is an effective π‐donor to the aromatic ring. Further, a normal substituent chemical shift effect is seen with the thiophenol C‐1, whereby electron‐withdrawing groups cause a decrease in electron density, whereas the platinum centre shows the reverse effect, i.e. electron‐withdrawing groups cause an increase in electron density. The latter effect has been explained in terms of a π‐polarization effect, with electron density from the terpyridine ligand being supplied to the platinum centre in response to demand by the thiophenol substituent.