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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 (R2N)3P=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)3P=N–P=NEt(NMe2)2 (Et-P2) and Verkade’s proazaphosphatrane superbases. Within the central [PIII–N=PV] scaffold, the phosphine PIII and not the phosphazene NIII 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·mol–1 [NR2 = N(CH2)4] and pKBH+ 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 P2- 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.

Basicity ; Phosphines ; Phosphazenes ; Density functional calculations ; Tolman electronic parameter

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