Hemilabile β‑Aminophosphine Ligands Derived from 1,3,5-Triaza-7-phosphaadamantane: Application in Aqueous Ruthenium Catalyzed Nitrile Hydration

A series of β-aminophosphines derived from 1,3,5-triaza-7-phosphaadamantane (PTA) are described. PTA-CHPhNHPh (1), PTA-CH­(p-C6H4OCH3)­NHPh (2), and PTA-CPh2NHPh (3) were prepared in good yield (62–77%) by reaction of lithiated PTA with the corresponding imine followed by hydrolysis. Compounds 1 and 2 were synthesized as pairs of diastereomers which were separated by successive recrystallization from THF/hexane. Compounds 1–3 are somewhat soluble in water (S25o = 4.8 (1), 4.9 (2), 2.7 (3) g/L). Upon coordination to Ru­(II) arene centers both monodentate (κ1-P) [RuCl2(η6-toluene)­(1–3)] and bidentate (κ2-P,N) [RuCl­(η6-toluene)­(1–3)]Cl coordination modes were observed. Ru­(II) arene complexes 4–6 exhibited hemilabile behavior transitioning between κ1-P and κ2-P,N coordination upon change in solvent or addition of a coordinating ligand such as Cl– or CH3CN. Complexes (4–6) were found to be active air stable catalysts for the aqueous phase hydration of various nitriles with TOF up to 285 h–1 and TON of up to 97 000 observed.