Synthesis of organoplatinum poly(dendrimer)s: pronounced effect of size and geometry of small organoplatinum linkers on the copolymerization efficiency with bifunctional dendritic macromonomers.

The copolymerizations of two series of surface functionalized bis(acetylene) G1-G3 dendrimers, one (S-Gn) having a structural rigid skeleton and the other (L-Gn) a relatively more flexible architecture, with two platinum linkers, cis-[(Et(2)PCH(2)CH(2)PEt(2))PtCl(2)] (2) and Cl(Et(3)P)(2)Pt-C[triple bond]C-p-C(6)H(4)- (3) were investigated. For both series of dendrimers, only linear and/or cyclic oligomers were formed when the cis-platinum linker 2 was used. However, high molecular weight (100-200 kD) organoplatinum poly(dendrimer)s were obtained from both series when the elongated linear rod-liked platinum linker 3 was employed and the formation of cyclic oligomers was greatly suppressed for both the structural rigid S-Gn and the structural flexible L-Gn series. These results are in sharp contrast to our earlier findings (S.-Y. Cheung, H.-F. Chow, T. Ngai, X. Wei, Chem. Eur. J. 2009, 15, 2278-2288) obtained by using a shorter linear platinum linker trans-[Pt(PEt(3))(2)Cl(2)] (1), where a larger amount of cyclic oligomers was formed from the structural flexible L-Gn dendrimers. A model was proposed to rationalize how the geometry and size of the platinum linker could control the copolymerization behaviours of these dendritic macromonomers.