Mono-Phosphazenyl Phosphines (R2N)(3)P=N-P(NR2)(2) - Strong P-Bases, P-Donors, and P-Nucleophiles for the Construction of Chelates

We present a convenient three-step synthesis of amino substituted phosphazenyl phosphines of the general formula (R2N)(3)P=N-P(NR2)(2) [NR2 = N(CH2)(4), N(CH2)(5), N(CH2)(6)]. These easily accessible mixed valent compounds display a surprisingly high proton affinity and basicity in the same range as the corresponding Schwesinger diphosphazene (Me2N)(3)P=N-P=NEt(NMe2)(2) (Et-P-2) and Verkade's proazaphosphatrane superbases. Within the central [P-III-N=P-V] scaffold, the phosphine P-III and not the phosphazene N-III atom is the center of highest proton affinity, basicity and donor strength. As P-bases, the title compounds display calculated proton affinities between 265.8 (NR2 = NMe2) and 274.7 kcal center dot mol(-1) [NR2 = N(CH2)(4)] and pK(BH)(+) values between 26.4 (NR2 = NMe2) and 31.5 [NR2 = N(CH2)(4)] on the acetonitrile scale. As P-nucleophiles, they are key intermediates in the synthesis of hyperbasic bis(diphosphazene) proton sponges, chiral bis(diphosphazene) proton pincers, bisphosphazides, and superbasic P-2-bisylides. Their Staudinger reactions as nucleophile towards 1,8-diazidonaphthalene leading to 1,8-naphthalene-bisphosphazides is described in detail. The donor strength of the title compounds towards fragments [Se] and [Ni(CO)(3)] is in the same range as that of N-heterocyclic carbenes.