Mono‐Phosphazenyl Phosphines (R 2 N) 3 P=N–P(NR 2 ) 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 (R 2 N) 3 P=N–P(NR 2 ) 2 [NR 2 = N(CH 2 ) 4 , N(CH 2 ) 5 , N(CH 2 ) 6 ]. These easily accessible mixed valent compounds display a surprisingly high proton affinity and basicity in the same range as the corresponding Schwesinger diphosphazene (Me 2 N) 3 P=N–P=NEt(NMe 2 ) 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 (NR 2 = NMe 2 ) and 274.7 kcal · mol –1 [NR 2 = N(CH 2 ) 4 ] and p K BH + values between 26.4 (NR 2 = NMe 2 ) and 31.5 [NR 2 = N(CH 2 ) 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.