Selectivity in reductive elimination and organohalide transfer from methyl(aryl) benzylpalladium(IV) complexes of bidentate nitrogen donor ligands, PdBrMe(Ar) (CH2Ph) (L2)

Article abstract of DOI:10.1016/S0022-328X(96)06795-2

Oxidative addition of iodoarenes to bis(dibenzylideneacetone)palladium(0) in the presence of N, N, N′, N′-tetramethylethylenediamine (tmeda) affords PdIAr(tmeda) (Ar = 4-MeC₆H₄, 4-MeOC₆H₄, 4-Me(O)CC₆H₄, 4-O₂NC₆H₄, 3-MeOC₆H₄) in high yield. Some of these complexes (Ar = 4-MeC₆H₄, 4-MeOC₆H₄, 3-MeOC₆H₄) react with LiMe to form PdMeAr(tmeda), and the methyl(aryl)palladium(II) complexes react with 2,2′-bipyridyl (bpy) or 1,10-phenanthroline (phen) to afford PdMeAr(L₂); PdMePh(phen) may be obtained similarly. All of the diorganopalladium(II) complexes of bpy and phen react with benzyl bromide to form PdBrMeAr(CH₂Ph)(L₂) but a complex could not be isolated for Ar = 3-MeOC₆H₄, L₂ = bpy. The isolated palladium(IV) complexes react with PdMe₂(bpy) at -20°C in (CD₃)₂CO to selectively transfer benzyl bromide to give PdMeAr(L₂) and PdBrMe₂(CH2PhXbpy) respectively. The complexes PdBrMeAr(CH₂Ph)(bpy) (Ar = Ph, 4-MeC₆H₄, 4-MeOC₆H₄) undergo selective reductive elimination of Ar-Me in CDCl₃ to form PdBr(CH₂Ph)(L₂), but PdBrMeAr(CH₂Ph)(phen) (Ar = Ph, 4-MeC₆H₄, 4-MeOC₆H₄, 3-MeOC₆H₄) give mixtures of PdBr(CH₂Ph)(phen) and Me-Ar together with lesser amounts of PdBrMe(phen) and Ar-CH₂Ph (ca. 10-20%).