Abstract: | The Influence of Phosphoryl Substituents on the Properties of P‐Substituted 2‐Methylimidazolium Ions and 2‐Methyleneimidazolines 1] The imidazolines ImCHP(E)Ph2 6 , E = S ( a ), Se ( b )] are obtained from ImCHPPh2 ( 4 ) and sulfur or selenium. HBF4 reaction yields the corresponding imidazolium salts ImCH2P(E)Ph2]BF4] 5 , E = S ( a ), Se ( b )]. 1, 3, 4, 5‐Tetramethyl‐2‐methylenimidazoline ( 1 , ImCH2) reacts with Ph2P(O)Cl to give the corresponding phosphane salt ImCH2P(O)Ph2]Cl ( 7 ) from which the vinyl compound ImCHP(O)Ph2 ( 8 ) is formed through deprotonation. 8 reacts with excess HBF4 to give the phosphine oxide BF3 adduct ImCH2P(O)Ph2 · BF3]BF4] ( 9 ). The crystal structures of 5a , 5b , 6b , 7 · CH2Cl2 and 9 · H2O as well as preliminary data of 8 are reported and discussed on comparison with the phosphanes ImCH2PPh2]BF4] ( 3b ) and ImCHPPh2 ( 4 ). From structural data, π‐electron delocalisation is concluded for 6b and 8 . |