SYNTHESIS OF NEW EXCEEDINGLY STRONG NONIONIC BASES - RN=P(MENCH2CH2)3N

The syntheses of MeN=P(MeNCH2CH2)3N (4), [HRNP(MeNCH2CH2)3N](CF3CO2) (R = Ph, 5(CF3-CO2); R = Me, 6(CF3CO2)), [MePhNP(MeNCH2CH2)3N]I (7(I)), the stable azide adduct MeN3P(MeNCH2CH2)3N (8), and [HRNP(NMe2)3](CF3CO2)(R = Ph, 9(CF3CO2) are reported. Equilibria measured by P-31 NMR spectroscopy reveal the relative ordering of basicity: t-BuN=P[N=P(NMe2)3]3 > P(MeNCH2CH2)3N (1) > MeN=P(MeNCH2-CH2)3N (4) > MeN=P(NMe2)3 > DBU > PhN=P(MeNCH2CH2)3N (3) > PhN=P(NMe2)3 in CD3CN. The unusually strong basicities of the polycyclic cage bases (e.g., those of 1 and 4 are ca. 17 and more than 3 pK(b) units stronger than DBU, respectively) and the stability of adduct 8 is rationalized on the basis of partial transannulation from the bridgehead nitrogen to phosphorus which effectively delocalizes positive charge. The structure of 5(CF3CO2) determined by X-ray means is also reported, revealing a transannular distance of 2.559(4) angstrom which is facilitated by a widened average MeN-P-NMe bond angle of 114.9(2)degrees.