[AU(DIEN)Cl]Cl(2): Exchange Phenomena Observed by H and C NMR Spectroscopy

Area of Science:

• Inorganic Chemistry
• Coordination Chemistry
• Solution Chemistry

Background:

• Square-planar gold(III) complexes are of interest due to their diverse applications.
• Understanding the solution behavior of these complexes is crucial for predicting their reactivity and stability.
• The ligand 1,5-diamino-3-azapentane (dien) forms stable complexes with metal ions.

Purpose of the Study:

• To investigate the solution behavior of the square-planar gold(III) complex [Au(dien)Cl]Cl(2) using NMR spectroscopy.
• To characterize the ligand exchange dynamics and deprotonation effects on the complex.
• To elucidate the structural changes occurring in different pH conditions.

Main Methods:

• Proton ((1)H) and Carbon-13 ((13)C) Nuclear Magnetic Resonance (NMR) spectroscopy were employed.
• Variable temperature NMR studies were conducted to analyze exchange processes.
• The influence of pH on the complex's solution behavior was systematically investigated.

Main Results:

• Proton NMR spectra exhibited significant exchange behavior across the entire pH range.
• Exchange effects were also observed in the Carbon-13 NMR spectra of the deprotonated hydroxo derivative.
• An exchange rate exceeding 378 s(-1) was determined at pH 2 and 40°C.
• Deprotonation of the central amine group in acidic solutions was confirmed by (1)H chemical shifts.
• Two distinct sets of resonances in (13)C NMR spectra indicated the presence of both chloro and hydroxo gold(III) complexes.
• The hydroxo complex showed exchange effects in (13)C NMR, with inequivalent carbon atoms near the central amine undergoing intermediate to fast exchange.

Conclusions:

• The gold(III) complex [Au(dien)Cl]Cl(2) displays dynamic solution behavior influenced by pH and ligand deprotonation.
• Ligand exchange processes are rapid and significantly affect the observed NMR spectra.
• The study provides insights into the structural lability and reactivity of gold(III) complexes in aqueous solutions.