[1H,15N] NMR studies of the aquation of cis-diamine platinum(II) complexes

Abstract

Two 15N-labelled cis-Pt(II) diamine complexes with dimethylamine (15N-dma) and isopropylamine (15N-ipa) ligands have been prepared and characterised. [1H,15N] HSQC NMR spectroscopy is used to obtain the rate and equilibrium constants for the aquation of cis-[PtCl2(15N-dma)2] at 298 K in 0.1 M NaClO4 and to determine the pKa values of cis-[PtCl(H2O)(15N-dma)2]+ (6.37) and cis-[Pt(H2O)2(15N-dma)2]2+ (pKa1 = 5.17, pKa2 = 6.47). The rate constants for the first and second aquation steps (k1 = (2.12 ± 0.01) × 10−5 s−1, k2 = (8.7 ± 0.7) × 10−6 s−1) and anation steps (k−1 = (6.7 ± 0.8) × 10−3 M−1 s−1, k−2 = 0.043 ± 0.004 M−1 s−1) are very similar to those reported for cisplatin under similar conditions, and a minor difference is that slow formation of the hydroxo-bridged dimer is observed. Aquation studies of cis-[PtCl2(15N-ipa)2] were precluded by the close proximity of the NH proton signal to the 1H2O resonance.