ROMP with Schrock Initiators

These two rotamers, the reactivity and relative ratio of which is governed by the electronic nature of the alkoxide ligand, were found to be responsible for the structure of the final polymer if used in ROMP. In-depth investigations on the reactivity of these rotamers were carried out in order to shed some light onto 

As very little of the anti-form is present under equilibrium conditions (without irradiation) in Mo(NAr )(OCMe(CF3)2)2(CHR), and the syn- to anti onversion is slow (ca. 10 s ), the dx-polymers were proposed to be formed from the syn-species of a catalyst via olefin attack on the CNO-face of the initiator [87]. In a f-butoxide system, where interconversion is relatively fast (ca. Is ), it was proposed that the anti-form was the only propagating alkylidene species. This proposal was further supported by studies carried out by Feast and coworkers [94]. Using highly unreactive monomers such as 1,7,7-trimethylnorbornene, only the reaction of the anti-rotamer at a very slow monomer concentration-independent rate was observed. Additionally, the calculated rate constant was essentially identical with that for the xyn-anti onversion. The high dependency of the dx-tranx ontents of a polymer on the temperature, as was found for the polymerization of 2,3- 

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One of the newest developments in ROMP-based monohths for bioseparations is boronate affinity columns synthesized via Schrock-initiated ROMP of NBE and DMN-H6 with the porogenic solvents w-hexane and 1,2-dichloroethane. Functionalization was achieved via post-grafting of a boronate-containing monomer. These columns were used to separate cis-diol-based biomolecules, such as adenosine [116]. 

The capability of ROMP of polymerizing even more complex functional monomers was demonstrated by the fact that the cationic NHC precursor l,3-di(l-mesityl)-4- [(bicydo[2.2.1 ]hept-5-en-2-ylcarbonyl)oxy]methyl -4,5-dihydro-lH-imidazol-3-ium tetrafluoroborate can be polymerized with the Schrock initiator Mo(N-2,6-f-Pr2-C6H3) (CHCMe2Ph)(OCMe(CF3)2)2 at ambient temperature in CH2CI2. The observed theoretical DP of 7 was in excellent accordance with a DP of 7 1 found via end-group analysis using H-NMR. The polymerization system fulfilled at least the requirements of a class-V living polymerization system. 

Keeping the above-mentioned prerequisites in mind, a ROMP-based precipitation copolymerization setup was created. In this setup, living homopolymers prepared from a functional monomer were finally cross-linked to form polymeric beads approximately 30-60 pm in size. For the s)mthesis of carboxylic acid-derivatized particles, DMN-H6 was used as a CTOss-linker and its copolymerization with NDCA using the well-defined Schrock initiator Mo(N-2,6-i-Pr2-(C6H3) (CHCMe2Ph)(OCMe(CF3)2)2 was established for the synthesis of high-capacity, wc-dicarboxylic acid-derivatized resins (Scheme 18). 

Note that there is a preferred direction of reaction with the original complex. The reaction is prevented from developing into a chain reaction by the propensity of the [Ta]=CH2 complex to undergo the homologation reaction (McLain 1977 Schrock 1980 Rocklage 1981) see Abbenhuis (1994) for another example of a tantalum carbene complex which will undergo only stoichiometric metathesis. However, the complexes 2 and 3 (Table 2.2) are good initiators of ROMP as also is the tantalacyclobutane complex derived from 2 by the addition of norbomene. The complexes 1 and 2 are both effective for the metathesis of ds-pent-2-ene. 

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