Preparation of Polymers Containing Metal–Metal Bonds along the Backbone Using Click Chemistry Sarah E. Brady • Ginger V. Shultz • David R. Tyler Received: 12 April 2010 / Accepted: 26 April 2010 / Published online: 11 May 2010 Ó Springer Science+Business Media, LLC 2010 Abstract The [(g 5 -C 5 H 4 (CH 2 ) 3 OC(O)(CH 2 ) 2 C: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 (PPh 3 ) 2 Cl 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, dis- proportionation of the Mo–Mo bonded unit occurred before complete coupling was observed. The reaction was also slow when the Cp*Ru(PPh 3 ) 2 Cl catalyst was used; however, no disproportionation products were observed and a high molecular weight polymer (M n = 120,000 g/mol) was pro- duced. The Cp*Ru(PPh 3 ) 2 Cl catalyst was also used to couple 1 with azide-terminated poly(ethylene glycol). After 15 h, this reaction produced a polymer with M n = 73,000 g mol -1 . It is concluded that, although somewhat slow, click chemistry using the Cp*Ru(PPh 3 ) 2 Cl catalyst is an excellent method for synthesizing high molecular weight polymers with metal– metal bonds along the backbone. Keywords Click coupling  Metal–metal bond  Photochemically degradable polymer  Huisgen cycloaddition reaction  Metal–polymer complexes 1 Introduction The photochemical degradation reactions of polymers are conveniently studied using polymers that have organome- tallic molecules containing metal–metal bonds along their backbone [1, 2]. The two primary reasons these materials are so useful are that metal–metal bonds are cleavable by visible light (Scheme 1) and the metal–metal bond chro- mophore provides a convenient spectroscopic handle for monitoring degradation of the polymer backbone [1, 2]. The utility of the metal–metal bond-containing polymers in photodegradation studies was demonstrated in previous investigations into the effects of mechanical stress [3], polymer morphology [4], and temperature [5] on polymer photodegradation rates. Synthetic methods for the preparation of metal-con- taining polymers are relatively underdeveloped [6–9] and the incorporation of metal–metal bonds into the backbone of a polymer, in particular, presents a unique synthetic challenge. The metal–metal bond in organometallic dimers is relatively weak (e.g., D Mo–Mo & 32 kcal mol -1 ) and will not stand up to many of the reaction conditions typi- cally used for the synthesis, isolation, and purification of organic polymers [1]. For example, the metal–metal bond is subject to disproportionation by the nucleophiles and coordinating solvents that are commonly used in poly- merization reactions [1, 10]. Polymerization strategies must therefore be carefully designed to avoid cleavage of the metal–metal bond during polymerization. The Huisgen cycloaddition reaction (Eq. 1), commonly referred to as the ‘‘click reaction,’’ may be an effective method for incorporating metal–metal bonded organome- tallic units into polymer backbones [11–13]. Several groups have reported the addition of pendant metal com- plexes to polymers using click chemistry [11, 14, 15]; This paper is dedicated to the wonderful Charles Pittman on the occasion of his retirement. S. E. Brady  G. V. Shultz  D. R. Tyler (&) 1253 Department of Chemistry, University of Oregon, Eugene, OR 97403, USA e-mail: dtyler@uoregon.edu 123 J Inorg Organomet Polym (2010) 20:511–518 DOI 10.1007/s10904-010-9364-7