The trans influence in platinum chemistry. A platinum-195 nuclear magnetic resonance study of [15N]nitrito-, chloro-, and bromo-platinum-(II) and -(IV) complexes

Abstract

Reactions of chloro–bromo- Pt^II and -Pt^IV complexes with sodium nitrite in aqueous solution have been studied by ^l95Pt n.m.r. spectroscopy. Chemical shifts and ¹J(¹⁹⁵Pt^–15N) coupling constants of all 21 possible Pt^II complexes, and 47 of the possible 56 Pt^IV complexes are reported. Regular incremental shift patterns were observed for Cl^–/Br^– substitutions in each set of complexes, but only partially for NO₂^– substitutions for Pt^IV, and not for Pt^II NO₂^–/Cl^– substitution shifts were in opposite directions for Pt^II(to low frequency) and Pt^IV(to high frequency), but in the same direction for NO₂^–/Br^–substitutions. ¹J(¹⁹⁵Pt–¹⁵N) coupling constants were linearly dependent on the number of nitrite ligands for both Pt^II and Pt^IV. Both chemical shift and coupling constant changes upon ligand substitution are dominated by the nature of the trans ligand. trans Pairs of nitrite ligands destabilize complexes and account for the nine undetected Pt^IV complexes.