A Strategy for Preparing Star Polymers Containing Metal-Metal Bonds Along the Polymeric Arms Using Click Chemistry

The [(eta(5)-C5H4(CH2)(3)N-3)Mo(CO)(3)](2) dimer (3) was prepared and used to determine if the Huisgen cycloaddition reaction could be used to synthesize high molecular weight star polymers with metal-metal bonds in the arms. Several different click catalysts were examined. Cp*Ru(PPh3)(2)Cl (Cp* = eta(5)-C-5(CH3)(5)) was previously shown to catalyze the formation of metal-metal bond-containing polymers using click chemistry; however, this catalyst underwent a Staudinger reaction with dimer 3 when a model coupling reaction was attempted with phenylacetylene. In order to avoid the Staudinger reaction, Cp*Ru(COD)Cl was used as the catalyst in the reaction of 3 with phenylacetylene, and coupling was observed after 14 h. Synthesis of a star polymer was attempted with 3 and 1,3,5-triethynylbenzene. Instead of coupling, Cp*Ru(COD)Cl reacted with the 1,3,5-triethynylbenzene. A third catalyst, Cu(IMes)Cl (IMes = 1,3-dimesityl-imidazol-2-ylidene) was used to couple 3 with 1,3,5-triethynylbenzene in 48 h. Both a high molecular weight polymer (M (n) = 77,000 g mol(-1)) and a tripodal star core (M (n) = 1,800 g mol(-1)) were successfully prepared with this catalyst.