Reactivity of a diphosphorus complex towards phosphenium ions

Abstract

The reaction of white phosphorus (P₄) with phosphenium ions [R₂P]⁺ yields [P₅R₂]⁺ cages via insertion of [R₂P]⁺ into a P–P bond of P₄. Herein, a systematic study on the reactivity of the P₄ isolobal diphosphorus complex [{CpMo(CO)₂}₂(μ,η^2:2-P₂)] (A) towards differently substituted phosphenium ions was conducted. The phosphenium ions [R¹R²P]⁺ (R¹ = R² = Cl, Br and R¹ = Ph, R² = Cl) were found to insert into a Mo–P bond of A followed by an unprecedented halide shift to yield [{CpMo(CO)₂}₂(μ,η^1:1:1:1-P(R¹)P(R²)P)][WCA] (1a: R¹ = R² = Cl, [WCA]⁻ = [BArF₂₄]⁻; 1b: R¹ = R² = Br, [WCA]⁻ = [BArF₂₄]⁻; 2: R¹ = Ph, R² = Cl, [WCA]⁻ = [TEF]⁻ with [BArF₂₄]⁻ = [B(3,5-C₆H₃(CF₃)₂)₄]⁻ and [TEF]⁻ = [Al{OC(CF₃)₃}₄]⁻). In contrast, [Ph₂P]⁺ reacts with A in a complex reaction involving Mo–P and Mo–Mo bond insertion of the phosphenium ion leading to a mixture of [{CpMo(CO)}₂(μ₄,η^2:2:2:1:1–2-(Ph₂P)P₄)(μ-PPh₂){CpMo(CO)₂}₂][TEF]₂ (3) and [{CpMo(CO)}₂(μ,η^2:1:1-PP(Cl)PPh₂)(μ-PPh₂)][TEF] (4) depending on the used stoichiometry. Furthermore, the reaction of A with [Cy₂P]⁺ leads to CO elimination and formation of [{CpMo(CO)}₂(μ,η^2:2-P₂)(μ-PCy₂)][TEF] (5) in which the phosphenium ion bridges the Mo–Mo bond. Reaction monitoring and additional DFT computations shed light on the ongoing reaction pathways and reveal crucial intermediates of the respective reactions.