Organopalladium functionalised dendrimers: insertion of Pd(O) into peripheral carbon-iodine bonds of carbosilane dendrimers derived from polyols. Crystal structure of Si{(CH2)3OC(O)C6H4I-4)}4

A carbosilane dendrimer with 12 peripheral iodoarene groups, Si{(CH2)3{Si(CH2)3O2C(C6H4I-4)}3}4 (G1-ArI, 5), and the corresponding G0 model compound, Si{(CH2)3O2CC6H4I-4}4 (G0-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)3O2C(C6H4-4)PdI(tmeda)}4 (G0-ArPdI(tmeda), 6) and Si{(CH2)3{Si(CH2)3O2C(C6H4-4)PdI(tmeda)}3}4 (G1-ArPdI(tmeda), 7). Dendrimer 7 represents the first example of an exclusively -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~N)Me3 [C~N = 8-(dimethylamino)-1-naphthyl]. The molecular structure of G0-ArI (5) has been determined by X-ray crystallography and has C2v symmetry in the solid state