Cyano-stabilized triphenyl­phospho­nium ylids

Crystalline cyano-stabilized triphenyl­phospho­nium ylids with keto or ester groups give rise to an extended electronic delocalization. In methyl 2-cyano-2-(trimethyl­phospho­nio)­ethenoate, Ph₃P=C(CN)CO₂CH₃ or C₂₂H₁₈NO₂P, (I), and 1-cyano-1-(trimethyl­phospho­nio)prop-1-en-2-olate, Ph₃P=C(CN)CO-CH₃ or C₂₂H₁₈NOP, (II), the carbonyl groups are oriented toward the cationoid P atom. Bond lengths and angles, torsion angles and P...O contact distances are consistent with a dominant coplanar conformation where the mol­ecular structures are the result of a balance between intra- and inter­molecular inter­actions. The main inter­actions presented by cyano-ester (I) and cyano-keto (II) are intra­molecular inter­actions between the carbonyl O and the P atoms. In addition, both compounds show other less important intra­molecular inter­actions between the carbonyl O and phenyl H atoms, which could contribute to form a preferred conformation in the crystal structure.

Differences in the crystal structures of two dialkyl diester triphenyl­phospho­nium ylids

Hydrogen bonding and crystal packing play major roles in determining the conformations of ethyl methyl 2-(triphenyl­phospho­ranyl­idene)malonate, Ph₃P=C(CO₂CH₃)CO₂CH₂CH₃ or C₂₄H₂₃O₄P, (I), and dimethyl 2-(triphenyl­phosphor­anyl­idene)malonate, Ph₃P=C(CO₂CH₃)₂ or C₂₃H₂₁O₄P, (II). In (I), the acyl O atom of the ethyl ester group is anti to the P atom, while the O atom of the methyl ester group is syn. In (II), the dimethyl diester is a 1:1 mixture of anti-anti and syn-anti conformers.