Catalysts Grubbs-type

Green polymer, 31 Grignard reagents, 467, 484 Grubbs-type carbenes, 433 Grubbs-type catalysts, 438... 

CM reactions with terpenoids containing two double bonds such as citronellene are hampered by low yields because of RCM competition among other side reactions. Mauduit et al. performed the CM of several terpenoids with n-butyl acrylate and crotonaldehyde using Hoveyda-Grubbs type catalysts containing an aminocarbonyl function [89]. Yields below 43% were obtained in all cases with 1 mol% catalyst. In contrast to these results, the hydrated masked form of citronellene, i.e., dihydromyrcenol, gave 71% yield of the CM product. It was thus proposed that in order to avoid selectivity problems in the CM of terpenoids containing two double bonds, masked derivatives can be used followed by a simple elimination step to recover the olefin functionality. 

Fig. 28 OS supported Grubbs type catalysts and comparaison in recycling...

Grubbs-type catalysts containing bridged diphosphino ligands were reported by several groups. Hoffmann and co-workers reported on the use of dtbpm (= di-t-bu-tyldiphosphinomethane) based systems (Scheme 5.15) [200, 201]. 

Fig. 5.6 Tris(pyrazolyl)borate- [a], cydopentadienyl- (Cp-) (b), and penta-methyl-Cp- (c) based Grubbs-type catalysts.

Figure 4. Water-soluble Grubbs-type catalysts.

Scheme 18. Tris(pyrazolyl)borate-, Cyclopentadienyl- (Cp), and Pentamethyl-Cp-Based Grubbs-Type Catalysts...

While the basic Chauvin mechanism of olefin metathesis has been appreciated and acknowledged for some time, the studies on both Schrock and Grubbs type catalysts show that the knowledge of the mechanistic steps necessary to access Ghauvin-metathesis intermediates, and details concerning the structures and geometries of these intermediates, can lead to ever-improving and selective catalysts for this important polymerization reaction. 

The Attachment of Grubbs-Type Catalysts via the X-Type Ligand The substitution... 

Examples of using functionalized, fluorinated carboxylates as alternative X-type ligands for the generation of supported catalyst analogs were previously introduced in section The Attachment of Grubbs-Type Catalysts via the X-Type Ligand . However, the introduction of fluorous functionalities within the catalyst architecture can also be employed to aid in product isolation and to effectively recover/recycle a catalyst via fluorous extraction [141]. Although similar to the IL systems that were discussed in the previous section, this approach instead uses... 

Chart 9.6 Activation parameters for pairs of fluorinated Hoveyda-type and Grubbs-type catalysts. 

In line with earlier reports on the degradation of Grubbs type catalysts [89,90], the in situ formation of [Ru(SIMes)(PCy3)(CO)HCl] via the reaction of [Ru(SIMe)(PCy3)(=CHPh)Cl2] with either Me3SiOCH=CH2 or MeOH has been exploited for C=C bond isomerization. As shown in Table 12.6, a range of terminal alkenes can be transformed, in many cases with high selectivity [91-93]. The possibilities provided by such isomerization reactions have been utilized in the... 

As a practical example of application of this method, the Miyano reaction proved useful for the preparation of chiral binaphthyl Hoveyda-Grubbs-type catalyst 47, which finds utility in asymmetric metathesis (Scheme 8.10) [37]. This chiral complex possessing a stereogenic Ru center can be prepared in greater than 98% enantiomeric purity without resolution from optically pure binaphthalene 46 prepared by the Miyano method. Howevo", in contrast to the Meyers reaction, the Miyano reaction has so far not been employed for the total synthesis of natural products. 

SCHEME 8.10 Preparation of chiral binaphthyl Hoveyda-Grubbs-type catalyst 47. 

Nunez-Zarur F, Solans-Monfort X, Pleixats R, Rodnguez-Santiago L, Sodupe M. DPT Study on the Recovery of Hoveyda-Grubbs-Type Catalyst Precursors in Enyne and Diene Ring-Closing Metathesis. Chem Eur J. 2013 19(43) 14553-14565. 

Figure 12.2 2" generation Grubbs type catalyst with PMej ligand (2). 

A key step in the olefin metatiiesis mechanism using Grubbs-type catalysts is the formation of a 14-electron species by decoordination of an L ligand [16] (Scheme 2). 

The more favourable steric and electronic properties of imidazolidinylidene ligands reported for Grubbs type catalysts [58,59] led us to test the activity of catalyst B (Eq. 13) generated from the same Ru source and the same base but in the presence of bis(mesityl)imidazDlinium chloride as carbene precursor. 

---