Strongly Basic Proazaphosphatranes: P (EtNCH 2 CH 2 ) 3 N and P (iso-PrNCH 2 CH 2 ) 3 N

Abstract

The two new azaphosphatranes HP(RNCH₂CH₂)₃N⁺Cl⁻ (R = Et, 2c and R = i-Pr, 2d) were prepared from the corresponding (RNHCH₂CH₂)₃N and CIP(NEt₂)₂. They were transformed into the title proazaphosphatranes 3c and 3d, respectively, with tert-BuOK. Alternatively, 3d was prepared by the transamination reaction of PCl(NMe₂)₂ with (iso-PrNCH₂CH₂)₃N followed by deprotonation with tert-BuOK. Azaphosphatrane cation salts of 3d, [Z-P (iso-PrNCH₂CH₂)₃N]⁺ (Z = H, 2d; X = D, 2d-D) were obtained from the reaction of 3d with ZC1. Competitive deprotonations of azaphosphatrane cation pairs with a stoichiometric deficit of tert-BuOK in DMSO showed the order of basicity: 3c > 3d > P (MeNCH₂CH₂)₃N (3b). Compound 3d is also a more efficient catalyst for the trimerization of phenyl isocyanate to phenylisocyanurate than is 3b. A strong correlation (r = 0.996) of the transannular distance with the distance of the P from the plane of its amido nitrogens in nine compounds of the type [ZP(RNCH₂CH₂)₃N]⁺ is observed. The molecular structure of 3d shows a P—N_ax distance of 3.29 Å, which is 1.8% shorter than the sum of the corresponding van der Waals radii. Crystal data for 3d: a = 9.380 (2) Å, b = 11.979(2) Å, c = 16.063(3) Å, β = 95.62(1)°, V = 1796.2(6) ų, Z = 4, space group P2₁/n₁ R(F₀²)= 3.62%. The molecular structure of 2d exhibits a transannular R—N_ax bond of 1.95 Å in a nearly undistorted trigonal bipyramidal phosphorus. Crystal data for 2d: a = 9.143(4) Å, b = 9.319(4) Å, c = 11.616(3) Å, α = 87.07(3) °, β = 88.64(3)°, γ = 80.62(3)°, V = 972.8(6) ų, Z = 2, space group P1, R = 3.42%.