Metal-free pincer ligand chemistry polycationic phosphonium Lewis acids.

Oxidation of 2,6-bis(diphenylphosphine)methyl pyridine with MeO3 SCF3 , yields the dication [2,6-(CH2 PMePh2 )2 C5 H3 N][CF3 SO3 ]2 2, while subsequent treatment with two equivalents of [K(THF)n ][B(C6 F5 )4 ] (n = 1.3-1.5) afforded [2,6-(CH2 PMePh2 )2 C5 H3 N][B(C6 F5 )4 ]2 3. Analogous treatment using XeF2 afforded 2,6-(CH2 PF2 Ph2 )2 C5 H3 N 4, while subsequent fluoride abstractions afford the corresponding [BF4 ], [CF3 SO3 ] and [B(C6 F5 )4 ] salts, 5-7, respectively. Compound 4 reacts with an excess of MeO3 SCF3 to give [2,6-(CH2 PF2 Ph2 )2 C5 H3 N(CH3 )][CF3 SO3 ] 8 while subsequent reaction with [Et3 Si·2C7 H8 ][B(C6 F5 )4 ] gave the related tricationic species, 9. The Lewis acidity of these di- and triphosphonium cations 3, 7 and 9 was examined and their utility as Lewis acid catalysts was assessed in the dimerization of 1,1-diphenylethylene, the hydrodefluorination of 1-fluoroadamantane, and the dehydrocoupling of phenol and silane.