[(ClImDipp)PP(Dipp)][GaCl4]: a polarized, cationic diphosphene

Abstract

The reaction of the neutral diphosphanide [(^ClIm^Dipp)P–P(Cl)(Dipp)] (6) (^ClIm^Dipp = 4,5-dichloro-1,3-bis(Dipp)-imidazol-2-yl; Dipp = 2,6-di-iso-propylphenyl) with methyl triflate (MeOTf) leads to the formation of cationic diphosphane [(^ClIm^Dipp)(Me)P–P(Cl)(Dipp)]⁺ (8⁺) in a stereoselective methylation. In contrast, reacting 6 with the Lewis acid GaCl₃ yields cationic diphosphene [(^ClIm^Dipp)PP(Dipp)]⁺ (7⁺), which is explained by a low P–Cl bond dissociation energy. The significantly polarized PP double bond in 7⁺ allows for its utilization as an acceptor for nucleophiles – the reaction with Cl⁻ regenerates diphosphanide 6 and the reaction with PMe₃ gives cation [(^ClIm^Dipp)P–P(PMe₃)(Dipp)] (9⁺). In depth DFT investigation provides detailed insights into the bonding situation of the reported compounds.