Pyramidal five-co-ordination with flattened tetrahedral basal bonds. Crystal and molecular structures of dibromotris-(5-ethyl-5H-dibenzophosphole)palladium(II)–chlorobenzene, dibromotris-(5-ethyl-5H-dibenzophosphole)platinum(II)–bromobenzene, and dibromotris-(5-methyl-5H-dibenzophosphole)platinum(II)–bromobenzene

Abstract

In the molecules of the title compounds one bromine atom is at the apex of a distorted tetragonal pyramid which has the five-co-ordinate metal atom in the centre of the base. The other bromine atom and the three phosphorus atoms lie in basal positions. The angle between apical and basal bonds is greater than 90° for the bromine atom (mean 100°) and for the phosphorus atom trans to it (mean 108°). The similar angles for the other two phosphorus atoms are less than 90°(both mean 86°). The basal bonds are directed to the corners of a flattened and distorted tetrahedron.

The apical bond is always longer by at least 0·4 Å than the metal–bromine basal bond. Differences in apical bond length between the closely related Pd and Pt compounds (1) and (2) with identical ligands, and between the two platinum compounds (2) and (3) which differ only in alkyl substituent (Me or Et) are discussed. The former is a chemical effect, the latter may, in part, arise from intermolecular effects. The bond from M to the phosphorus atom trans to the basal bromine is ca. 0·06 Å shorter than the other M–P bonds.

The plane of one phosphole ligand L(I) is steeply inclined to those of the others L(II), L(III). An interaction is found between L(II), trans to the basal bromine, and L(III) which brings them parallel plane-to-plane and makes the angle P(II)–M–P(III) < P(II)–M–P(I) by ca. 5·4°.

The detailed stereochemistry of the metals is explained in terms of steric effects and ligand interaction.