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Synthesis of Selected Cationic Pnictanes [LnPnX3–n]n+ (L = Imidazolium-2-yl; Pn = P, As; n = 1–3) and Replacement Reactions with Pseudohalogens

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posted on 20.07.2015, 00:00 by F. D. Henne, A. T. Dickschat, F. Hennersdorf, K.-O. Feldmann, J. J. Weigand
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]+ (1P(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]+ (1P(Me/Me)+), the dication [L(Me/Me)2PCl]2+ (2P(Me/Me)2+), and the trication [L(Me/Me)3P]3+ (5P(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] (6Pn(R/R′)[OTf]) and diazido-substituted pnictanes [L(R/R′)Pn­(N3)2]­[OTf] (7Pn(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.