[(Im)PQP(Dipp)][GaCl4]: a polarized, cationic diphosphene†

The reaction of the neutral diphosphanide [(Im)P–P(Cl)(Dipp)] (6) (Im = 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 [(Im)(Me)P–P(Cl)(Dipp)] (8) in a stereoselective methylation. In contrast, reacting 6 with the Lewis acid GaCl3 yields cationic diphosphene [( Im)PQP(Dipp)] (7), which is explained by a low P–Cl bond dissociation energy. The significantly polarized PQP 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 [(Im)P–P(PMe3)(Dipp)] (9 ). In depth DFT investigation provides detailed insights into the bonding situation of the reported compounds.