ON THE STABILIZATION OF 5-COORDINATE TRIGONAL-BIPYRAMIDAL PALLADIUM(II) SPECIES - CRYSTAL-STRUCTURE OF (2,9-DIMETHYL-1,10-PHENANTHROLINE)METHYLCHLOROPALLADIUM(II)

The role of the steric requirements of the N-N' chelate ligand in the stabilization of trigonal-bipyramidal [Pd(N-N')(olefin)RX] complexes is discussed. The crystal structure of the precursor (2,9-dimethyl-1,10-phenanthroline)methylchloropalladium(II) (1a) has been determined. The molecule adopts a significantly distorted square-planar coordination geometry in order to accomodate the crowding in the coordination plane. The most significant distortions involve the coordinated methyl group and the dimethylphenanthroline molecule, whose mean plane lies out of the coordination plane by 39.3-degrees. There is ready CO insertion into the Pd-Me bond of 1a to give an acyl derivative. The formation of a five-coordinate acyl derivative by subsequent uptake of an olefin also illustrates the importance of the steric effects of N-N' ligands.