SYNTHESIS AND STRUCTURAL STUDIES OF PHENYL(IODO)PALLADIUM(II) AND METHYL(PHENYL)PALLADIUM(II) COMPLEXES OF BIDENTATE NITROGEN DONOR LIGANDS

Phenylpalladium(II) complexes of the type PdLPh(N-N), with N-N = N,N,N ',N'-tetramethylethylenediamine (tmeda) or 2,2'-bipyridyl (bpy), can b e conveniently prepared in 70-95% yield by oxidative addition of iodob enzene to bis(dibenzylideneacetone)palladium(0) in the presence of the appropriate nitrogen donor ligand. The bromo analogues were obtained in only 5-12% yield in this way. The complex PdIPh(tmeda) (1a) reacts readily with MeLi to give PdMePh(tmeda) (3) in 88% yield, whereas PdIP h(bpy) (2a) gives PdMePh(bpy) (4) and PdMe(2)(bpy) in varying ratios. The formation of PdMe,(bpy) was found to result from the synergistic a ction of lithium iodide and methyllithium. Pure PdMePh(bpy) (4) was ob tained in 82% yield via ligand-exchange from PdMePh(tmeda) (3). The cr ystal structures of PdIPh(N-N) (1a, 2a) and PdMePh(N-N) (3, 4) complex es were determined by X-ray diffraction studies. The results show that the phenyl group is always oriented perpendicular to the coordination plane around palladium, with the largest deviation found for 3 (14.3( 2)degrees). The Pd-N bond distances in the tmeda complexes (2.127(6)-2 .210(3) Angstrom) are larger than those in the bpy-coordinated complex es (2.070(8)-2.144(8) Angstrom. Similarly, the Pd-C(Me) bond distances (2.5703(8) and 2.575(1) Angstrom) are larger than the Pd-C(Ph) bond d istances (1.985(3)-1.996(10) Angstrom).