Organopalladium-Functionalized Dendrimers:  Insertion of Palladium(0) into Peripheral Carbon−Iodine Bonds of Carbosilane Dendrimers Derived from Polyols. Crystal Structure of Si{(CH₂)₃O₂CC₆H₄I-4}₄

Abstract

A carbosilane dendrimer with 12 peripheral iodoarene groups, Si{(CH 2 ) 3 {Si(CH 2 ) 3 O 2 C(C 6 H 4 I-4)} 3 } 4 (G 1 -ArI, 5 ), and the corresponding G 0 model compound, Si{(CH 2 ) 3 O 2 CC 6 H 4 I-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{(CH 2 ) 3 O 2 C(C 6 H 4 -4)PdI(tmeda)} 4 (G 0 -ArPdI(tmeda), 6 ) and Si{(CH 2 ) 3 {Si(CH 2 ) 3 O 2 C(C 6 H 4 -4)PdI(tmeda)} 3 } 4 (G 1 -ArPdI(tmeda), 7 ). Dendrimer 7 represents the first example of an exclusively σ-bonded completely periphery-palladated dendrimer. Reactions of the model palladium(II) complexes PdI(EtO 2 C(C 6 H 4 )-4)(tmeda) ( 2 ) and PdI(EtO 2 C(C 6 H 4 )-4)(bpy) ( 3 ) (bpy = 2,2‘-bipyridyl) with the transmetalation reagents LiMe and SnMe 4 were not successful, while no reaction occurred with the related reagent Sn(C∼N)Me 3 [C∼N = 8-(dimethylamino)-1-naphthyl]. The molecular structure of G 0 -ArI ( 5 ) has been determined by X-ray crystallography and has C 2 v symmetry in the solid state.