Unusual Water-Soluble Imino Phosphine Ligand: Enamine and Imine Derivatives of 1,3,5-Triaza-7-phosphaadamantane (PTA).

Abstract

A series of water-soluble and air-stable E-enamine derivatives of 1,3,5-triaza-7-phosphaadamantane (PTA), PTA═C(R)NH2, 1-4, are reported along with data on E-Z isomerization and tautomerization to the imine form (PTA-CR═NH). Reaction of 1,3,5-triaza-7-phosphaamantane-6-yl lithium, PTA-Li, with aromatic nitriles afforded E-enamine derivatives of PTA in good yield (49-91%). Phosphines 1-4 are stable toward water and air, and do not appear to isomerize or tautomerize, unless coordinated to a metal or oxidized. The corresponding oxides, O═PTA═C(R)NH2 (5-8), were observed as ∼55/45 mixtures of E and Z isomers. Kinetic data on the E-Z isomerization is reported. Upon coordination of 1-4 to W(CO)4(pip)2, a κ1- P enamine is formed, [W(CO)4(pip)(κ1- P-PTA═CRNH2)]. Enamine-imine tautomerization of the metal bound phosphine was observed resulting in κ2- P, N imine complexes, [W(CO)4(κ2- P, N-PTA-CR═NH)], 9-12. The crystal structures of the κ1- P enamine 11a, κ2- P, N imine 9 and 12, phosphines 1 and 3, as well as phosphine oxide 8a were obtained. DFT calculations on the various isomers of the phosphines and phosphine oxides are also reported.