Determination of the molecular structures of tri(t-butyl)phosphine oxide and tri(t-butyl)phosphine imide in the gas phase by electron diffraction

Abstract

The molecular structures of the oxide and imide of tri(t-butyl)phosphine in the gas phase have been determined by electron diffraction. For PBu^t₃O important parameters (r_a) are: r(PO) 159.0(12), r(P–C) 188.8(6), r(C–C) 151.9(3) pm, OPC 106.1(5), and CCC 109.1(4)°. The butyl groups are tilted 3.1(8)° away from each other, and twisted 15.8(7)° away from the positions in a structure with C_3v symmetry, thus minimising steric interactions between the groups. For PBu^t₃NH important parameters are: r(PN) 165.2(11), r(P–C) 191.3(6), r(C–C) 153.2(2) pm, NPC 109.6(7), and CCC 107.8(5)°, the tilt and twist angles of the butyl groups are –2.3(11) and 18.5(14)° respectively. The structures are such that the oxygen and imide group are sterically well protected from attack, thus accounting for the remarkable chemical and thermal stability of the compounds.