Ruthenium polymers, structures

Fig. 3. (A) Unfiltered ex-situ STM image of an HOPG electrode modified with an electropolymerized film of [[(v-tpy)Ru]2(tppz)](PF6)4- Tip bias = 100 mV, tunneling current = 500 pA, scan rate = 60.3 Hz. (B) Structure of the symmetric ruthenium polymer.

Grubbs-type initiators are well-defined ruthenium aUcylidenes. Compared to molybdenum- or tungsten-based Schrock catalysts, the reactivity of ruthenium-based Grubbs catalysts is somewhat different. In terms of polymer structure, ROMP of norbom-2-enes and norbomadienes using ruthenium-based systems generally results in the formation of polymers that, in most cases, predominantly contain frany-vinylene units. Polymerizations initiated by Grubbs-type initiators are best terminated by the use of ethyl vinyl ether, yielding methylidene-terminated polymers. 

Olefin isomerization is a well-known side reaction of many Grubbs ruthenium catalysts [27]. Double bonds may migrate both along the polymer backbone and also in the monomer itself, resulting in a loss of control over the precise placement of both double bonds and branch points in the polymer structure. To create a well-defined polymer, it is critical that isomerization be controlled [27c,d,e, 28]. 

Fig.4A,B. Ring-opening metathesis polymerization (ROMP) A Structures of organometal-lic initiators that have been used in ROMP to generate neobiopolymers. B General pathway for polymer synthesis using ROMP. Molybdenum-initiated reactions are typically capped with aldehydes and ruthenium-initiated with end ethers.

The results presented here seem to indicate that 1) the local order about ruthenium centers in the polymers is essentially unchanged from that in the monomer complex and 2) that the interaction with the electrode surface occurs without appreciable electronic and structural change. This spectroscopic information corroborates previous electrochemical results which showed that redox properties (e.g. as measured by formal potentials) of dissolved species could be transferred from solution to the electrode surface by electrodepositions as polymer films on the electrode. Furthermore, it is apparent that the initiation of polymerization at these surfaces (i.e. growth of up to one monolayer of polymer) involves no gross structural change. 

Having established that there were no significant structural perturbations in the coordination spheres of the ruthenium centers in the polymer films we investigated the effect of oxidation of the ruthenium to the 3+ state. This was performed in acetonitrile/0.1M TBAP by holding the potential at +1.6 V for 5 minutes to ensure oxidation of the film. A change in the color of... 

A complete description of the synthetic methodology and the characterization of the obtained metallosupramolecular block copolymers was reported in a recent paper [324]. These compounds have been referred to as metallosupramolecular block copolymers and designated by the acronym Ax-[Ru]-By, where A and B are the two different polymer blocks, -[Ru]- denotes the fczs-2,2/ 6/,2/terpyridine-ruthenium(II) linkage between the A and B blocks, and x and y represent the average degree of polymerization of the A and B blocks, respectively. The chemical structure of a PEB-[Ru]-PEO metallosupramolecular copolymer is depicted in Fig. 23. 

The chemical structure of the polymers was confirmed by NMR and elemental analysis, and spectroscopically characterized in comparison with monodisperse low molecular weight model compounds. Scheme 5 outlines the approach to the model compounds. Model compounds 31-34 were synthesized by complexation of the ruthenium-free model ligands 29/30 with 3/4. The model ligands were synthesized in toluene/diisopropylamine, in a similar fashion as the polycondensation using Pd(PPh3)4 and Cul as catalyst (Sonogashira reaction) [34,47-49]. 

The polymers are synthesized by utilizing the Heck coupling reaction. Their structures are shown as polymers V to VII (Scheme 6). The metal-to-ligand charge transfer of the ruthenium complexes of polymer VI results in... 

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