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