As-P vs. P-P Insertion in AsP3: Kinetic Control of the Formation of [AsP3NO]+

The synthesis of mixed arsenic phosphorus cations was investigated on theoretical and experimental grounds by replacing P-4 with AsP3 in the known syntheses of [P4NO](+) and [P-9](+). Calculations of [AsP3NO](+) and [AsP8](+) showed that 1-[AsP3NO](+) and 3-[AsP8](+) should be the most stable isomers. However, 2-[AsP3NO](+) was prepared by reacting [NO](+)[Al(ORF)(4)](-) (R-F = C(CF3)(3)) with AsP3 with a regioselectivity of 45:1. The kinetic control of this reaction was proven by calculation of the complete reaction mechanism. Examination of the formation energetics of the [AsxP4-xNO](+) (x = 0, 1, 4) and [AsxP9-x](+) (x = 0, 1, 9) cations at the CCSD(T)/complete basis set limit level showed that for [AsxP4-xNO](+) (x = 0, 1, 4), the replacement of phosphorus by arsenic leads to more exergonic formation energetics. For the [AsxP9-x](+) clusters (x = 0, 1, 9), the reaction to [AsP8](+) is slightly more exergonic compared to the synthesis of [P-9](+). The calculation of the reaction to the homopolyatomic arsenic cation [As-9](+) suggested that this reaction will at least be very difficult. Attempts to prepare [AsxP9-x](+) from AsP3 as well as [As-x](+) from gray arsenic led to the formation of [AsP3NO](+), [P4NO](+), [P-9](+) and P-4 in case of [AsxP9-x](+) and decomposition products (e.g. novel As(ORF)(3)) for [As-x](+).