Structure of the non-stabilized phosphonium ylid methylenetriphenylphosphorane

Abstract

The structure of methylenetriphenylphosphorane, Ph₃P:CH₂, has been elucidated by three-dimensional X-ray diffraction methods. The crystals are monoclinic, spacegroup P2₁/c with a= 18·455, b= 9·614, c= 18·103 Å, and β= 106° 56′. The positions for the two independent molecules in the asymmetric unit were derived from the Patterson and Fourier maps and refined by a block-diagonal least-squares method using 2586 observed intensities collected with a linear diffractometer. The methylene hydrogen atoms were located from a difference synthesis and their co-ordinates were refined together with the hydrogen atoms of the aromatic rings. The final R factor was 0·064. Ph₃PCH₂ has a pyramidal configuration. The non-equivalent molecules are nearly identical and lack symmetry because of the asymmetric orientations of the benzene rings. The mean P–C(Ph) length is 1·823 Å. The length of the bond, formally written as PC is 1·661 Å, which is amongst the shortest values observed so far in phosphoranylidenes. The methylene carbon atoms are sp² hybridized. The benzene rings are planar with some significant in- and out-of-plane bendings of the P–C bonds. The triphenylphosphorus group has a propeller shape. No evidence is available for dimerization or any strong molecular interaction in the solid. The structure is of pseudo P2₁/a type.