Water soluble diphosphine ligands based on 1,3,5-triaza-7-phosphaadamantane (PTA-PR2): Synthesis, coordination chemistry, and ruthenium catalyzed nitrile hydration

Two chiral chelating 1,3,5-triaza-7-phosphaadamantane (PTA) derivatives were synthesized, in racemic form, by addition of (ClPPr2)-Pr-i or ClP((NPr)-Pr-i)(2)(CH2)(2) to lithiated PTA. PTA-(PPr2)-Pr-i (1) and PTA-P((NPr)-Pr-i)(2)(CH2)(2) (2) were isolated in good yield, 73% and 56% respectively, and fully characterized by multinuclear NMR spectroscopy, mass spectrometry, and X-ray crystallography. PTA-(PPr2)-Pr-i is highly air sensitive, but stable and somewhat soluble in degassed water. PTA-P((NPr)-Pr-i)(2)(CH2)(2) (2) is air-stable, but decomposes in water over the course of hours. Two tungsten tetracarbonyl complexes were prepared by addition of the PTA-PR2 to [W(CO)(4)(pip)(2)] and characterized by NMR and IR spectroscopies and X-ray crystallography in the case of [W(CO)(4)(PTA-(PPr2)-Pr-i)]. Based on IR spectroscopy PTA-(PPr2)-Pr-i (1) is more electron donating than PTA-P((NPr)-Pr-i)(2)(CH2)(2) (2) or the previously published PTA-PPh2. Products isolated from the reaction of [(eta(6)-toluene)RuCl2](2) with two equivalents of 1 were found to contain monodentate (k(1)), bidentate (k(2)), and possibly bridging coordination modes of PTA-(PPr2)-Pr-i. These ruthenium complexes were explored as catalysts for aqueous phase nitrile hydration. Of the ruthenium complexes explored [(eta(6)-toluene) RuCl2(k(1)-PTA-(PPr2)-Pr-i)] (7) was the most active towards nitrile hydration. In the presence of air at 100 degrees C 7 converted various nitriles to the respective amides with 43-99% conversions in 7 h. (C) 2015 Elsevier B.V. All rights reserved.