Organopalladium-functionalized dendrimers: Insertion of palladium(0) into peripheral carbon-iodine bonds of carbosilane dendrimers derived from polyols. Crystal structure of Si{(CH2)(3)O2CC6H4I-4}(4)

A carbosilane dendrimer with 12 peripheral iodoarene groups, Si{(CH2)(3){Si(CH2)(3)O2C(C6H4I-4)}(3)}(4) (G(1)-ArI, 5), and the corresponding G(0) model compound, Si{(CH2)(3)O2CC6H4I-4}(4) (G(0)-ArI, 4) have been prepared from polyol precursors. These compounds react with Pd(dba)(2)/tmeda (dba = dibenzylideneacetone, tmeda = N,N,N',N'-tetramethylethylenediamine) to yield periphery-palladated complexes, Si{(CH2)(3)O2C(C6H4-4)PdI(tmeda)}(4) (G(0)-ArPdI(tmeda), 6) and Si{(CH2)(3){Si(CH2)(3)O2C(C6H4-4)PdI(tmeda)}(3)}(4) (G(1)-ArPdI(tmeda), 7). Dendrimer 7 represents the first example of an exclusively sigma-bonded completely periphery-palladated dendrimer. Reactions of the model palladium(II) complexes PdI(EtO2C(C6H4)-4)(tmeda) (2) and PdI(EtO2C(C6H4)-4)(bpy) (3) (bpy = 2,2'-bipyridyl) with the transmetalation reagents LiMe and SnMe4 were not successful, while no reaction occurred with the related reagent Sn(C similar to N)Me-3 [C similar to N = 8-(dimethylamino)-1-naphthyl]. The molecular structure of G(0)-ArI (5) has been determined by X-ray crystallography and has C-2 upsilon symmetry in the solid state.