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 (<b>1</b>), PTA-CH­(<i>p</i>-C₆H₄OCH₃)­NHPh (<b>2</b>), and PTA-CPh₂NHPh (<b>3</b>) were prepared in good yield (62–77%) by reaction of lithiated PTA with the corresponding imine followed by hydrolysis. Compounds <b>1</b> and <b>2</b> were synthesized as pairs of diastereomers which were separated by successive recrystallization from THF/hexane. Compounds <b>1</b>–<b>3</b> are somewhat soluble in water (<i>S</i>₂₅^o = 4.8 (<b>1</b>), 4.9 (<b>2</b>), 2.7 (<b>3</b>) g/L). Upon coordination to Ru­(II) arene centers both monodentate (κ¹-P) [RuCl₂(η⁶-toluene)­(<b>1</b>–<b>3</b>)] and bidentate (κ²-P,N) [RuCl­(η⁶-toluene)­(<b>1</b>–<b>3</b>)]Cl coordination modes were observed. Ru­(II) arene complexes <b>4</b>–<b>6</b> 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 (<b>4</b>–<b>6</b>) 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