Exploring the potential energy surface for interaction of a trichloro(diethylenetriamine)gold(III) complex with strong nucleophiles

Substitution reactions for the complex [Au(dien)Cl]2+ (dien = 3-azapentane-1,5-diamine) have been explored. Second-order rate constants, k 2 , were predicted for chloride exchange and ring-opening processes using water and the stronger nucleophiles N3− and SCN−. Under neutral and basic conditions, the deprotonated form of the complex [Au(dien-H)Cl]+ dominates and reacts promptly with all nucleophiles. The predicted reactivity order is SCN− (k2 = 5.5 × 103 M−1 s−1) > N3− (k2 = 10.1 × 101 M−1 s−1) > H2O (k2 = 0.4 M−1 s−1), in line with the experiment SCN− (k2 = 1.3 × 103 M−1 s−1) > N3− (k2 = 8.0 × 101 M−1 s−1) > H2O (k2 = 0.6 M−1 s−1). Ring-opening is thermodynamically unfavourable but presents fast kinetics for stronger nucleophiles.