Preparation of Polymers Containing Metal–Metal Bonds along the Backbone Using Click Chemistry

Abstract

The [(η5-C5H4(CH2)3OC(O)(CH2)2C≡CH)Mo(CO)3]2 complex (1) was synthesized and used to explore the feasibility of using the Huisgen cycloaddition reaction (a click reaction) to incorporate molecules with metal–metal bonds into polymer backbones. In a model reaction, coupling of 1 with benzyl azide was observed in 24 h using Cp*Ru(PPh3)2Cl as a catalyst. In contrast, the reaction of 1 with benzyl azide using a CuBr/ligand catalyst (where the ligand is either PMDETA or bipyridine), resulted in disproportionation of the Mo–Mo unit in 1. Complex 1 was also coupled with telechelic azide-terminated polystyrene oligomers. With either the CuBr/PMDETA or CuBr/bipyridine catalyst, disproportionation of the Mo–Mo bonded unit occurred before complete coupling was observed. The reaction was also slow when the Cp*Ru(PPh3)2Cl catalyst was used; however, no disproportionation products were observed and a high molecular weight polymer (Mn = 120,000 g/mol) was produced. The Cp*Ru(PPh3)2Cl catalyst was also used to couple 1 with azide-terminated poly(ethylene glycol). After 15 h, this reaction produced a polymer with Mn = 73,000 g mol−1. It is concluded that, although somewhat slow, click chemistry using the Cp*Ru(PPh3)2Cl catalyst is an excellent method for synthesizing high molecular weight polymers with metal–metal bonds along the backbone.