Hydrogen Cyanide Exchange on [Al(HCN)6]3+ – A DFT Study

Abstract

AbstractThe hydrogen cyanide exchange mechanism of [Al(HCN)6]3+ has been investigated by DFT calculations (B3LYP/6‐311+G**). The calculations provide theoretical evidence that the hydrogen cyanide exchange proceeds via a limiting dissociative (D) mechanism involving a stable five‐coordinate intermediate [Al(HCN)5·(HCN)2]3+. The activation energy for the D‐mechanism is 23.4 kcal·mol–1, which is 2.8 kcal·mol–1 lower than for the seven‐coordinate transition state [Al(HCN)7]3+‡ for the alternative associative (A) pathway. The difference in stability between the two intermediates [Al(HCN)5·(HCN)2]3+ (12.1 kcal·mol–1) and [Al(HCN)7]3+ (25.7 kcal·mol–1) in comparison to [Al(HCN)6·(HCN)]3+ is much more pronounced and further supports a limiting dissociative mechanism.