Synthesis of Selected Cationic Pnictanes [L_nPnX_3–n]ⁿ⁺ (L = Imidazolium-2-yl; Pn = P, As; n = 1–3) and Replacement Reactions with Pseudohalogens

Herein we report on reactions of “imidazoliumyl-transfer” reagents [L^(R/R′)SiMe₃]­[OTf] (4^(R/R′)[OTf]); L = imidazolium-2-yl, R/R′: Me/Me, ⁱPr/Me, Dipp/H, Dipp/Cl) with pnictogen trichlorides PnCl₃ (Pn = P, As, Sb) in various stoichiometries. In the case of the 1:1 reaction of [L^(R/R′)SiMe₃]­[OTf] with PCl₃ the corresponding cationic imidazoliumyl-substituted dichlorophosphanes [L^(R/R′)PCl₂]⁺ (1_P^(R/R′))⁺ are obtained as triflate salts on a multigram scale. We found that the reactions using various stoichiometries of [L^(R/R′)SiMe₃]­[OTf] and PnCl₃ are less selective in the case of the heavier congeners or by decreasing steric demand of the R-group attached to the N atoms of the heterocycle. An equilibrium between the monocation [L^(Me/Me)PCl₂]⁺ (1_P^(Me/Me)+), the dication [L^(Me/Me)₂PCl]²⁺ (2_P^(Me/Me)2+), and the trication [L^(Me/Me)₃P]³⁺ (5_P^(Me/Me)3+) is observed in solution. Reactions of the monocationic derivatives [L^(R/R′)PnCl₂]­[OTf] (Pn = P, As) with Me₃SiX (X = CN, N₃) resulted in the exchange of the chloro groups for the respective pseudohalogen and yielded the dicyano [L^(R/R′)Pn­(CN)₂]­[OTf] (6_Pn^(R/R′)[OTf]) and diazido-substituted pnictanes [L^(R/R′)Pn­(N₃)₂]­[OTf] (7_Pn^(R/R′)[OTf]), respectively. All new compounds are thoroughly characterized by multinuclear NMR, IR, and Raman spectroscopy. For most cases the molecular structure was confirmed by X-ray crystal structure analysis.