Linear transition metal coordination polymers

Linear Werner-type coordination polymers are defined as linear polymers, the main chains of which contain coordinate covalent bonds of transition metals. In this article, we restrict the discussion to the linear coordination polymers which can exist as a stable form in solution and thus our purpose is somewhat complementary, for example, to review dimensional inorganic complexes such as those of Miller and Epsteinld). 

The first linear polymers containing [2]catenanes in their backbones (mechanically linked main chain polymers, architecture A) were based on the Sauvage transition metal-coordinated catenanes. Polycondensation reactions were carried out between a diacid and a catenane diol to give a poly[2]catenane with Mn (600000) and Mw (4200000) based on polystyrene standards (Figure 4). 

Historically, high-pressure free radical copolymerization has been used to produce highly branched, ill-defined copolymers of ethylene and various polar monomers. Although these materials are in production and extensively used throughout the world, the controlled incorporation of polar functionality coupled with linear polymer structure is still desired to improve material properties. Recent focus in this area has led to the development of new transition metal catalysts for ethylene copolymerization however, due to the electro-philicity of the metal centers in these catalysts, polar functional groups often coordinate with the metal center, effectively poisoning the catalyst. There has b een some success, but comonomer incorporation is hard to control, leading to end-functionalized, branched polyethylenes [44, 46]. These results are undesirable due to low incorporation of polar monomer into the polymer as well... 

The 4,4 -bipyridine ligand has been utilized in the synthesis of linear coordination polymers as well as grids and networks through reaction with transition metal ions. These inorganic-organic polymers and frameworks are potential candidates for use in catalysis, molecular recognition, and nonlinear optics.257-262... 

Other transition metal ions also work as glue . When Zn(N03)2 and Ni(N03)2 are reacted with PR44, the ID polyrotaxanes 15 and 16, respectively, are produced (Figure 16 and 17) [39]. In both structures, two pseudorotaxane units are linked by a metal ion which is coordinated by four water molecules and two pyridyl group of the two pseudorotaxanes in an octahedral coordination geometry. The two pyridyl groups occupy cis positions in 15 whereas they occupy trans positions in 16. Therefore, the former ID polyrotaxane has a zigzag shaped polymer chain whereas the latter has a linear structure. 

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