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

A series of beta-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 (S-25 degrees = 4.8 (1), 4.9 (2), 2.7 (3) g/L). Upon coordination to Ru(II) arene centers both monodentate (kappa(1)-P) [RuCl2(eta(6)-toluene)(1-3)] and bidentate (kappa(2)-P,N) [RuCl(eta(6)-toluene)(1-3)]Cl coordination modes were observed. Ru(II) arene complexes 4-6 exhibited hemilabile behavior transitioning between kappa(1)-P and kappa(2)-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.