Synthesis of Arylpalladium(II) Complexes Derived from Benzyl Alcohol, Reactivity toward Alkyl Halides, and Synthesis of Dinuclear Arylpalladium(II) Complexes

The
aryl palladium complexes [PdI­(C6H4CH2OH-2)­(N∧N)] (N∧N = bpy
= 2,2′-bipyridyl (1a), tbbpy = 4,4′-di-tert-butyl-2,2′-bipyridine (1b), tmeda
= N,N,N′,N′-tetramethylethylenediamine
(1c)) were synthesized by oxidative addition of 2-iodobenzyl
alcohol to one equivalent of “[Pd­(dba)2]”
(dba = dibenzylideneacetone) in the presence of the N∧N ligands. By reaction of 1a with three equivalents
of XyNC (Xy = 2,6-dimethylphenyl) the insertion complex trans-[PdI­{C­(NXy)­(C6H4CH2OH-2)}­(CNXy)2] (2) was formed. The reaction of 1a with KOtBu resulted in the formation of the chelate complex
[Pd­(κ2-C,O-C6H4CH2O-2)­(bpy)] (3), which
crystallizes as pairs of molecules bridged by hydrogen bonds to water
of crystallization. Complex 3 reacts with XyNC, forming
the cyclic imidate N-(2,6-dimethylphenyl)-2-benzofuran-1­(3H)-imine (4). By reaction of 3 with various primary alkyl halides RCH2X, the complexes
[PdX­(C6H4CH2OCH2R-2)­(bpy)]
(X = I, R = H (5a), X = Br, R = Ph (5b), p-C6H4CH2Br (5c), p-C6H4Br (5d), and p-C6H4I (5e)) were obtained. When the reaction of 3 with p-C6H4(CH2Br)2 was carried out in a 2:1 ratio, the dinuclear arylpalladium complex
[{(bpy)­BrPd­(C6H4CH2OCH2-2)}2­(C6H4-1,4)] (6) formed. An halide exchange reaction on 5e, using AgOTf
and an excess of NaI, afforded [PdI­{C6H4(CH2OCH2­(C6H4I-4))-2}­(bpy)]
(5f), which by oxidative addition to [Pd­(dba)2] in the presence of bpy formed another dinuclear arylpalladium complex,
[(bpy)­IPd­(C6H4CH2-2)­O­(CH2C6H4-4)­PdI­(bpy)] (7). All
the complexes have been extensively characterized by NMR spectroscopy.
The crystal structures of 1a, 3·H2O, and 5e were determined by X-ray diffraction
studies.