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Phosphinopnictonium Cations: High Yield and General Preparative Procedures for New Interpnictogen Frameworks Exploiting As→P and Sb→P Coordinate Bonds

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posted on 25.11.2009, 00:00 by Eamonn Conrad, Neil Burford, Robert McDonald, Michael J. Ferguson
Reactions of R3Pn (Pn = As or Sb; R = Me, Et or Ph) with R′2PCl or R′PCl2 (R′ = Me, Et, Ph, Cy, iPr), in the presence of a halide abstracting agent (Me3SiOSO2CF3, GaCl3, or AlCl3), give salts with cations containing Pn−P bonds. The bond formation is envisaged to proceed by activation of the P−Cl bond and coordination of the pnictine to the resulting phosphorus cation (R′2P+ or R′P2+, respectively). Salts of the first phosphinoarsonium cations, [R3As-PR′2]+, and the first 2-phosphino-1,3-diarsonium dications, [R3AsP(R′)AsR3]2+, have been isolated and comprehensively characterized. In contrast, reactions involving Ph3Sb give 2,3-diphosphino-1,4-distibonium dications, [R3SbP(R′)P(R′)SbR3]2+, resulting from a single P−Cl activation (abstraction) at each of two phosphorus centers and reductive P−P coupling effected by Ph3Sb. The analogous 2,3-diphosphino-1,4-diarsonium dication [R3AsP(R′)P(R′)AsR3]2+ can be accessed from the 2,3-diphosphino-1,4-distibonium cation by a ligand exchange reaction, which also provides the phosphorus derivative 2,3-diphosphino-1,4-diphosphonium [R3PP(R′)P(R′)PR3]2+. The versatile synthetic methodologies toward the new P−As and P−Sb frameworks demonstrate the potential for diversification and systematic expansion of interpnictogen compounds.