Four related diethyl [(arylamino)(4-ethynylphenyl)methyl]phosphonates.

Crystal structures are reported for four related diethyl [(aryl­amino)­(4-ethynyl­phenyl)lmethyl]phosphon­ate derivatives, namely diethyl [(4-bromo­anilino)(4-ethynyl­phenyl)methyl]phosphon­ate, C19H21BrNO3P, (I), diethyl ((4-chloro-2-methylanilino){4-[2-(tri­methyl­silyl)ethynyl]phenyl}methyl)phosphon­ate, C23H31ClNO3PSi, (II), diethyl ((4-fluoroanilino){4-[2-(tri­methyl­silyl)ethynyl]phenyl}methyl)phosphonate, C22H29FNO3PSi, (III), and diethyl [(4-ethynyl­phenyl)(naphthalen-2-yl­amino)­methyl]phosphon­ate, C23H24NO3P, (IV). The conformation of the anilino­benzyl group is very similar in all four compounds. The P—C bond has an approximately staggered conformation, with the aniline and ethynylphenyl groups in gauche positions with respect to the P=O double bond. The two six-membered rings are almost perpendicular. The sums of the valence angles about the N atoms vary from 344 (2) to 351 (2)°. In the crystal structures, mol­ecules of (I), (III) and (IV) are arranged as centro­symmetric or pseudo­centro­symmetric dimers connected by two N—H⋯O=P hydrogen bonds. The mol­ecules of (II) are arranged as centro­symmetric dimers connected by Cmeth­yl—H⋯O=P hydrogen bonds. The N—H bond of (II) is not involved in hydrogen bonding.