ROMP catalysts

Rolling ball viscometers, 21 738 Roll mills, 16 722 Rolls, high pressure, 16 612-613 Romanechite, 15 540 Romascone, 24 571 Romet-30/Romet-B. See Ormetoprim ROMP catalysts, 17 707, 708 ROM polymers. See also Ring-opening metathesis (ROM) polymers, 26 947-948 Roof coatings... 

The reaction is thought to proceed with the dissociation of CT followed by release of the extra charge of the mthenium complex by dissociating a proton from the alkyhdene hgand. Such an exchange in itself does not lead to the decomposition of the alkyhdene complex. Nevertheless, both the formation of the charged species, both the intermediate existence of the carbyne complex (Scheme 9.5) may open new ways to the deterioration of the ROMP catalysts. 

Compound 22 is a surprisingly stable ROMP catalyst (in both protic and aprotic media). It was made available via the courtesy of Dr. G.L. Gould (U.I.C. — Chemistry). 

Compound 23 is the most active of the only two commercially available (Strem Chemicals, Inc.) ROMP catalysts (the other one being the corresponding nonfluorinated product). Its availability prompted the author to test it before similar catalysts that contain tungsten as a core metal and that have been shown to be more stable and more active than the molybdenum ones molybdenum catalysts seem, nevertheless, to tolerate more functionalities than the tungsten ones. 

There is a very large number of ROMP catalysts described in literature that might work with basketene or diazanorbormene type of monomers. Of a special... 

Thus, the catalyst must have certain special properties, to be regarded as a living ROMP catalyst. 

This finding is a significant improvement over aqueous ROMP systems using aqueous ROMP catalysts. The propagating species in these reactions is stable. The synthesis of water-soluble block copolymers can be achieved via sequential monomer addition. The polymerization is not of living type in the absence of acid. In addition to eliminating hydroxide ions, which would cause catalyst decomposition, the catalyst activity is also enhanced by the protonation of the phosphine ligands. Remarkably, the acids do not react with the ruthenium alkylidene bond. 

Norbornene polymers or polymers from dicyclopentadiene, respectively, may be formed by the interaction of a cyclic olefin with a ROMP catalyst. Increased reinforcement density provides for extremely high stiffness and strength in poly(norbornene) composites. As catalyst, Phenylmethylene-bis-(tricyclohexylphosphine) ruthenium dichloride is used (30). 

Figure 3.16 Structural variants for the screening of [ R2P(CH2) PR2-k2P XRu=CHR]+ cationic ROMP catalysts [48].

W(CHtBu)(OCH2tBu)2 [53e] (39) is a mildly active ROMP catalyst [54] that can be further activated by the addition of Lewis acids such as GaBr3 to form... 

These highly activated aqueous ROMP catalysts can be applied to the polymerization of monomers hitherto reluctant to polymerize in aqueous solution. This can be illustrated with the following example. When either 7-oxanorbomene-2,3-dicarboxylic acid, 46, or its dipotassium salt, which posses both the 1,4-bridging epoxide and the dicarboxylate moieties, is allowed to react with a wide range of metathesis catalysts, only catalyst deactivation is observed, Eq. (48) [79]. 

The ROMP catalyst of the current invention, (I), is illustrated below. 

Using the ROMP catalyst bis(tricyclopentylphosphine)dichloro-(3-methyl-2-butenylidene)-ruthenium, (IV), Piccinelli [3] prepared low molecular weight polynorbomene derivatives functionalized with hydrophilic polyethers, (V), which were subsequently hydrogenated, (VI), as illustrated in the second equation. 

Ring-Opening Metathesis Polymerization (ROMP) Catalyst... 

More recent developments in the mechanistic aspects of the alkene metathesis reaction include the observation that the alkene coordinates to the metal carbene complex prior to the formation of the metallacyclobutane complex. Thns a 2 - - 2 addition reaction of the alkene to the carbene is very unlikely, and a vacant coordination site appears to be necessary for catalytic activity. It has also been shown that the metal carbene complex can exist in different rotameric forms (equation 11) and that the two rotamers can have different reactivities toward alkenes. " The latter observation may explain why similar ROMP catalysts can produce polymers that have very different stereochemistries. Finally, the synthesis of a well-defined Ru carbene complex (equation 12) that is a good initiator for ROMP reactions suggests that carbenes are probably the active species in catalysts derived from the later transition elements. ... 

These compounds are of particular interest as they have been shown to be active Ring Opening Metathesis Polymerization (ROMP) catalysts (see Metathesis Polymerization Processes by Homogeneous Catalysis). They are not, however, as effective as imido-based alkylidene systems (see next section). 

W(NAr)(=CHBuO(OR)2 (R = CMe(CF3)2, 50) are highly active catalysts for the metathesis of internal alkenes (equation 16), and also effect the stereoselective olefmation of hydroxy ketones (equation 17). The reactivity of these catalysts can be tuned by varying the aUcoxide ligands for example, when R = Bn, the complex acts only upon strained cyclic alkenes and is a highly effective ring-opening metathesis polymerization (ROMP) catalyst (see Metathesis Polymerization Processes by Homogeneous Catalysis). 

Ru(H20)5(alkene) . In the absence of water these metal halides act as ROMP catalysts only after long induction periods. 

It was also found that the recycled aqueous catalyst solutions were actually more active than the original solutions. This increase in activity was attributed to the in situ formation of ruthenium(II) olefin complexes that were shown, after isolation, to be highly active ROMP catalysts. The mechanism involved in converting these olefin complexes to either metallacyclobutane or metal carbene species remains unknown. 

Grubbs, R. H. The development of functional group tolerant ROMP catalysts. J. Macromol. ScL, Pure Appl. Chem. 1994, A31,1829-1833. 

Recent years have seen rapid advancements in development of W, Mo, and Ru carbene complexes that serve not only as catalysts for metathesis of small molecules (Section 11-1-3) but also as ROMP catalysts. Grubbs use of a Ru(III) catalyst for ROMP in aqueous medium helped pave the way for development of his first- and second-generation Ru alkylidenes, which also catalyze ROMP. The Schrock catalysts that we have encountered already (compounds 15... 

The last two catalysts, 76a,b, have been recently developed by Grubbs. The difference between them is that 76b is much more soluble in water than is 76a. Moreover, the decomposition half-life of 76b in water is over a week at ambient temperature under inert conditions. Both catalysts 76a and 76b are highly competent ROMP catalysts, rapidly transforming e t /o-norbornene monomer into a polymeric product (Scheme 1.43). 

A description of the evolution of ROMP catalysts involving these metal hydrates can be found in the literature [70]. 

The synthesis of alkylidenes incorporating late transition metals has resulted in alkene metathesis catalysts having unprecedented functional group tolerance. In particular, the discovery that complexes of Group VIII transition metals were efficient ROMP catalysts introduced several advantages. Relative to their early transition metal counterparts, these classical catalysts functioned well in the presence of a variety of polar and protic functional groups (Table 2), and they functioned homogeneously in water. 

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