Structure and bonding in (dimethyl acetylenedicarboxylate)bis(triphenylphosphine)palladium

Abstract

The crystal and molecular structure of a disubstituted acetylene complex of palladium, [Pd{C₂(CO₂Me)₂}(PPh₃)₂], has been determined from three-dimensional X-ray diffraction data. The complex crystallises in space group P2₁/c,C_2h⁵, of the monoclinic system, with four molecules in a unit cell of dimensions a= 11·816(3), b= 15·331(4), c= 21·891(6)Å, β= 113·22(1)°. No crystallographic symmetry is imposed upon the molecules and there is one molecule in the asymmetric unit. The structural parameters were refined by least squares techniques, the R-factor on F converging to 5·2% for the 3365 reflections, collected using a four-circle diffractometer, for which F > 0. Co-ordination around palladium is approximately planar: the dihedral angle between the plane defined by the palladium and two phosphorus atoms and that defined by the palladium and the two acetylenic carbon atoms is 9·7(4)°. The acetylenic carbon–carbon separation in the complex is 1·28(1)Å, longer than expected for the free acetylene. Each substituent upon acetylene is planar to a reasonable approximation and is bent away from the metal by about 35° from the CC bond axis. The acetylenic carbon atoms are separated from the metal by 2·074(6) and 2·051(6)Å and the metal–phosphorus bond lengths are 2·321(2) and 2·330(2)Å. This slight asymmetry in the bond lengths to palladium is tentatively ascribed to the electronic effects of the differing orientations of the substituents upon acetylene.