Unusual Water-Soluble Imino Phosphine Ligand: Enamine And Imine Derivatives Of 1,3,5-Triaza-7-Phosphaadamantane (Pta)

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 similar to 55/45 mixtures of E and Z isomerization is reported. Upon coordination of 1-4 to W(CO)(4)(pip)(2,) a k(1) -P enamine is formed, [W(CO)(4)(pip)(k(1)-P-PTA = CRNH2)]. Enamineimine tautomerization of the metal bound phosphine was observed resulting in k(2)-P,N imine complexes, [W(CO)(4) (k(2)-P,N-PTA-CR = NH)], 9-12. The crystal structures of the k(1)-P enamine 11a, k(2)-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.