Strongly basic proazaphosphatranes: P(EtNCH2CH2)(3)N and P(iso-PrNCH2CH2)(3)N

The two new azaphosphatranes HP(RNCH2CH2)(3)N+Cl- (R = Et, 2c and R = i-Pr, 2d) were prepared from the corresponding (RNHCH2CH2)(3)N 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)(3)N followed by deprotonation with tert-BuOK. Azaphosphatrane cation salts of 3d, [Z-P(iso-PrNCH2CH2)(3)N](+) (Z = H, 2d; X = D, 2d-D) were obtained from the reaction of 3d with ZCl. Competitive deprotonations of azaphosphatrane cation pairs with a stoichiometric deficit of tert-BuOK in DMSO showed the order of basicity: 3c > 3d > P(MeNCH2CH2)(3)N (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)(3)N](+) is observed. The molecular structure of 3d shows a P-N-ax distance of 3.29 Angstrom, which is 1.8% shorter than the sum of the corresponding van der Waals radii. Crystal data for 3d: a = 9.380 (2) Angstrom, b = 11.979(2) Angstrom, c = 16.063(3) Angstrom, beta = 95.62(1)degrees, V = 1796.2(6) Angstrom(3), Z = 4, space group P2(1)/n, R(F-o(2)) = 3.62%. The molecular structure of 2d exhibits a transannular R-N-ax bond of 1.95 Angstrom in a nearly undistorted trigonal bipyramidal phosphorus. Crystal data for 2d: a = 9.143(4) Angstrom, b = 9.319(4) Angstrom, c = 11.616(3) Angstrom, alpha = 87.07(3)degrees, beta = 88.64(3)degrees, gamma = 80.62(3)degrees, V = 972.8(6) Angstrom(3), Z = 2, space group P (1) over bar, R = 3.42%.