Diphosphonio-1,2-diphospholes: Structural P-III/P-V hybrids

P-Methylation of the 3,5-bis(triphenylphosphonio)-1,2-diphosholide 1 leads to the dicationic diphosphole 3a. A crystal its bis(triflate) was used for a structure analysis. It indicates that in contrast to the known phospholes the cyclic pi(6) system is preserved in 3a. The coordination geometry of the methylated phosphorus atom shows a flat pyramid with a sum of angles of 339 degrees. Therefore, 3a represents a state that is intermediate between a phosphane and a bis(methylene)phosphorane, i.e. between P-III and P-V.