[AU(DIEN)Cl]Cl2: Exchange Phenomena Observed by H1 and C13 NMR Spectroscopy

Abstract

The solution behaviour of the square-planar gold(III) complex [Au(dien)Cl]Cl2 (dien = 1,5- diamino-3-azapentane) was investigated by H1 and C13 NMR spectroscopy. We have found that H1 NMR spectra of [Au(dien)Cl]Cl2 are characterised by exchange behaviour over the whole pH range, and some exchange effects are also seen in C13 NMR spectra of the deprotonated hydroxo derivative of the complex in alkaline solution. An exchange rate of > 378 s-1 was determined from H1 NMR spectra at pH∗2 (coalescence temperature 40C° ). In slightly acidic solutions of the complex, H1 chemical shifts are in accordance with the known deprotonation of the central amine group of the complexed diethylenetriamine ligand. In C13 NMR spectra, two separate sets of resonances are observed for the chloro and the hydroxo complex of gold(III) diethylenetriamine. The hydroxo complex [Au(dien-H)OH]+ shows exchange effects in C13 NMR spectra. Variable temperature studies show the carbon atoms next to the central secondary amine to be inequivalent and each present in two different environments that are in intermediate to fast exchange on the NMR time-scale.