Hemilabile β‑Aminophosphine
Ligands Derived from 1,3,5-Triaza-7-phosphaadamantane: Application
in Aqueous Ruthenium Catalyzed Nitrile Hydration
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Abstract
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>-C<sub>6</sub>H<sub>4</sub>OCH<sub>3</sub>)NHPh (<b>2</b>), and PTA-CPh<sub>2</sub>NHPh (<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><sub>25</sub><sup>o</sup> = 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 (κ<sup>1</sup>-P) [RuCl<sub>2</sub>(η<sup>6</sup>-toluene)(<b>1</b>–<b>3</b>)] and bidentate (κ<sup>2</sup>-P,N) [RuCl(η<sup>6</sup>-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 κ<sup>1</sup>-P and κ<sup>2</sup>-P,N coordination upon change in
solvent or addition of a coordinating ligand such as Cl<sup>–</sup> or CH<sub>3</sub>CN. 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<sup>–1</sup> and TON of up to 97 000 observed