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

Abstract

Oxidative addition of iodoarenes to bis(dibenzylideneacetone)palladium(0) in the presence of N, N,N',N'-tetramethylethylenediamine (tmeda) affords PdIAr(tmeda) (Ar = 4-MeC{6}H{4}, 4-MeOC{6}H{4}, 4-Me(O)CC{6}H{4}, 4-O{2}NC{6}H{4}, 3-MeOC{6}H{4}) in high yield. Some of these complexes (Ar = 4-MeC{6}H{4}, 4-MeOC{6}H{4}, 3-MeOC{6}H{4}) 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(L{2}); PdMePh(phen) may be obtained similarly. All of the diorganopalladium(II) complexes of bpy and phen react with benzyl bromide to form PdBrMeAr(CH{2}Ph)(L{2}) but a complex could not be isolated for Ar = 3-MeOC{6}H{4}, L{2} = bpy. The isolated palladium(IV) complexes react with PdMe{2}(bpy) at -20}o{C in (CD{3}){2}CO to selectively transfer benzyl bromide to give PdMeAr(L{2}) and PdBrMe{2}(CH{2}Ph)(bpy) respectively. The complexes PdBrMeAr(CH{2}Ph)(bpy) (Ar = Ph, 4-MeC{6}H{4}, 4-MeOC{6}H{4}) undergo selective reductive elimination of Ar-Me in CDCl{3} to form PdBr(CH{2}Ph)(L{2}), but PdBrMeAr(CH{2}Ph)(phen) (Ar = Ph, 4-MeC{6}H{4}, 4-MeOC{6}H{4}, 3-MeOC{6}H{4}) give mixtures of PdBr(CH{2}Ph)(phen) and Me-Ar together with lesser amounts of PdBrMe(phen) and Ar-CH{2}Ph (ca. 10-20%).