NMR and kinetic studies of the interactions of [Au(<i>cis</i>-DACH)Cl₂]Cl and [Au(<i>cis</i>-DACH)₂]Cl₃ with potassium cyanide in aqueous solution

<div><p>The interactions of [Au(<i>cis</i>-DACH)Cl₂]Cl and [Au(<i>cis</i>-DACH)₂]Cl₃ [where <i>cis</i>-DACH is <i>cis</i>-1,2-diaminocyclohexane] with enriched KCN were carried out in CD₃OD and D₂O, respectively. The reaction pathways of these complexes were studied by ¹H, ¹³C, ¹⁵N NMR, UV spectrophotometry, and electrochemistry. The kinetic data for the reaction of cyanide with [Au(<i>cis</i>-DACH)₂]Cl₃ are <i>k</i> = 18 M⁻¹s⁻¹, ∆<i>H</i>^≠ = 11 kJ M⁻¹, ∆<i>S</i>^≠ = −185 JK⁻¹ M⁻¹, and <i>E</i>_a = 13 kJ M⁻¹ with square wave voltammetric (SWV) peak +1.35 V, whereas the kinetic data for the reaction of cyanide ion with [Au(<i>cis</i>-DACH)Cl₂]Cl are <i>k</i> = 148 M⁻¹s⁻¹, ∆<i>H</i>^≠ = 39 kJM⁻¹, ∆<i>S</i>^≠ = −80 JK^-1 M⁻¹, and <i>E</i>_a = 42 kJM⁻¹ along with SWV peak +0.82 V, indicating much higher reactivity of [Au(<i>cis</i>-DACH)Cl₂]Cl toward cyanide than [Au(<i>cis</i>-DACH)₂]Cl₃. The interaction of these complexes with potassium cyanide resulted in an unstable [Au(¹³CN)₄]⁻ species which readily underwent reductive elimination reaction to generate [Au(¹³CN)₂]⁻ and cyanogen.</p></div