Synthesis and structural studies of phenyl(iodo)- and methyl(phenyl)palladium(II) complexes of bidentate nitrogen donor ligands

Abstract

Phenylpalladium(II) complexes of the type PdIPh(N@?N), with N@?N = N, N,N',N'-tetramethylethylenediamine (tmeda) or 2,2'-bipyridyl (bpy), can be conveniently prepared in 70-95% yield by oxidative addition of iodobenzene to bis(dibenzylideneacetone)palladium(O) 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 PdIPh(bpy) (2a) gives PdMePh(bpy) (4) and PdMe{2}(bpy) in varying ratios. The formation of PdMe{2}(bpy) was found to result from the synergistic action of lithium iodide and methyllithium. Pure PdMePh(bpy) (4) was obtained in 82% yield via ligand-exchange from PdMePh (tmeda) (3). The crystal structures of PdIPh(N@?N) (1a, 2a) and PdMePh(N@?N) (3, 4) complexes were determined by X-ray diffraction studies. The results show that the phenyl group is alw ays oriented perpendicular to the coordi 3 (14.3(2)}o{). The Pd@?N bond distances in the tmeda complexes (2.127(6)-2.210(3) @9) are larger than those in the bpy-coordinated complexes (2.070(8)-2.144(8) @9). Similarly, the Pd@?C(Me) bond distances (2.5703(8) and 2.575(1) @9) are larger than the Pd@?C(Pb) bond distances (1.985(3)-1.996(10)@9).