Grubbs third generation

Fig. 3 Olefin metathesis catalysts Schrock tungsten (Cl) and molybdenum (C2) alkylidene complexes, Grubbs first- (C3) and second-generation (C4) catalysts, Hoveyda-Grubbs second-generation catalyst (C5), and Grubbs third-generation catalyst (C6)...

Frechet et al. described the first synthesis of such a linear dendronized block copolymer 10 (Figure 37.6) [23]. For this purpose, a setof G2 and G3 aryl ether-based dendrons equipped with a norbornene unit was synthesized. Unfortunately, only the G3-exo-isomer could be polymerized, using a Grubbs third-generation catalyst the endo-isomer failed to polymerize, possibly due to a shielding effect of the G3 dendron. The obtained polydispersity index (PDI) of 1.03 indicated a good control over the polymerization process. However, when this G3 polymer was used as a macroinitiator for polymerization of the G2 monomer, the system failed to produce any diblock copolymer. Gonsequently, the order of monomer addition was reversed, such that the G2 macromonomer was polymerized first to complete conversion. 

The reaction of the Grubbs third-generation complex (l,3-bis(2,6-diisopropylimidazolin)-2-ylidene complex) with 2-ethenyl-N-methylaniline results in the formation of complexes 8.66. As compared to the respective eonventional, O-Hoveyda-Grubbs eomplex (such as 8.56-8.64, 8.67 in Fig. 8.3), the new... 

Grubbs third-generation catalyst HC=CH (black solid) [66]... 

Fig. 3.28 ROMP initiators, first, second and third generation Grubbs catalysts (complexes 71, 72, and 73, respectively) 74a-c 3-phenyl-indenylidene replaces the benzylidene carbene...

Similarly to the third generation Grubbs catalyst preparation, the related catalyst XXVI was obtained on addition of pyridine to precursor DC (Equation 8.6) [59]. 

FIGURE 3.23 Selection of Grubbs-type initiators of first to third generation. 

Other complex symmetrical architectures were obtained using bis-dendritic CTAs [130]. A symmetrical olefin was functionalized, with third-generation Fr chet-type polyfbenzyl ether) dendrons serving as the CTA. Polymerization of COE with the Grubbs second-generation ruthenium catalyst in the presence of this CTA and subsequent hydrogenation with /j-toluenesulfonylhydrazide in o-xylene resulted in bis-dendritic PE (Figure 3.14). 

Scheme 9.7 (a) Grafting from cobalt/carbon [82], (b) Water-soluble third-generation nanoparticles, attachment of monomer by ruthenium catalysts 49a-c, PEG oligomers diazonium precursor, copolymerization with attached in ortho, meta, and para positions, Grubbs second-generation ruthenium cat- phosphorylcholine in para position [84]. alyst, and reaction with palladium acetate... 

A -Heterocyclic carbenes (24.64) have become important ligands in organometallic chemistry, notable examples being Grubbs second and third generation catalysts. Synthetic routes to A -heterocyclic carbene complexes (which are stable to air) typically involve salt metathesis or elimination reactions. Reaction 24.103 shows the use of a 1,3-dialkylimidazolium salt as a precursor, and scheme 24.104 illustrates conversions relevant to Grubbs catalysts (see next page). 

The catalysts that have played a dominant role in the development of this area of chemistry are those designed by Schrock (e.g. catalysts 25.1 and 25.2) and Grubbs (catalysts 25.3 and 25.4). Catalyst 25.3 is the traditional Grubbs catalyst , and related complexes are also used. The second-generation catalyst 25.4 exhibits higher catalytic activities in alkene metathesis reactions. Catalysts 25.1-25.4 are commercially available. There are around 15 modifications of Grubbs catalysts which are optimized for different catalytic roles. This includes the recent third-generation catalyst (see structure 24.68). 

Figure 5.1 Alkene metathesis catalysts Grubbs-type first generation, second generation, and third generation. (From left side, top row to right side, second row) Grubbs-Blechert-Hoveyda catalyst, Grela s nitro derivative, and Schrock-type catalyst [7-11].

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