Aqueous-Phase Nitrile Hydration Catalyzed by an In Situ Generated Air-Stable Ruthenium Catalyst

RuCl₂ (PTA)₄ (PTA=1,3,5-triaza-7-phosphaadamantane) is an active, recyclable, air-stable, aqueous-phase nitrile hydration catalyst. The development of an in situ generated aqueous-phase nitrile hydration catalyst (RuCl₃ ⋅3 H₂ O+6 equivalents PTA) is reported. The activity of the in situ catalyst is comparable to RuCl₂ (PTA)₄ . The effects of [PTA] on the activity of the reaction were investigated: the catalytic activity, in general, increases as the pH goes up, which shows a positive correlation with [PTA]. The pH effects were further explored for both the in situ and RuCl₂ (PTA)₄ catalyzed reaction in phosphate buffer solutions with particular attention given to pH 6.8 buffer. Increased catalytic activity was observed at pH 6.8 versus water for both systems with turnover frequency (TOF) up to 135 h^-1 observed for RuCl₂ (PTA)₄ and 64 h^-1 for the in situ catalyst. Catalyst loading down to 0.001 mol % was examined with turnover numbers as high as 22 000 reported. Similar to the preformed catalyst, RuCl₂ (PTA)₄ , the in situ catalyst could be recycled more than five times without significant loss of activity from either water or pH 6.8 buffer.