Imidazolium 1,3-Benzazaphospholide Ion Pairs with Strong C-H•••N Hydrogen Bonds - Synthesis, Structures, and Reactivity

The treatment of 2-phenyl-1H-1,3-benzazaphosphole (H[2-ph-bp], 1) with free 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes, 2) and 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene (SIMes, 3) afforded two imidazolium 1,3-benzazaphospholides, [1,3-bis(2,4,6-trimethylphenyl)imidazolium 2-phenyl-1,3-benzazaphospholide [(IMesH)(+)(2-ph-bp)(-), 4] and 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazolium 2-phenyl-1,3-benzazaphospholide [(SIMesH)(+)(2-ph-bp)(-), 5], which further reacted with carbodiimide to give 2-(N,N-diisopropylcarbamimidoyl)-1,3-bis(2,4,6-trimethylphenyl)imidazolium 2-phenyl-1,3-benzazaphospholide (6) and 2-(N,N-diisopropylcarbamimidoyl)-1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazolium 2-phenyl-1,3-benzazaphospholide (7), respectively. These compounds were characterized by multinuclear (H-1, C-13{H-1}, and P-31{H-1}) NMR and IR spectroscopy, and X-ray diffraction analysis. The structures feature ion pair conformation in the solid state with strong charge-assisted C-HN or N-HN interaction.