Grubbs-Herrmann catalyst

Fig.1 Well-defined metathesis initiators. Schrock catalyst (A, R = Me, Ph, R = CMes, CMe(CF3)2), Grubbs-catalyst (B), Grubbs-Herrmann catalyst (C), Grubbs-Hoveyda catalyst (D, R " = H, NO2)...

Scheme 11 Synthesis of a silica-immobUized Grubbs-Herrmann catalyst...

Grubbs, Grubbs-Herrmann, Grubbs-Hoveyda Catalysts). 141... 

Almost at the same time, Grubbs, Herrmann, and Nolan reported on the design and synthesis of novel Ru alkylidene pre-catalysts containing nucleophilic NHCs as ancillary ligands. 

This short analysis supports (a) the statement by Herrmann that from the work in numerous academic laboratories and in industry, a revolutionary turning point in organometahc catalysis is emerging thanks to NHC (b) the conclusion by Grubbs that the exact mechanism of these powerful new catalysts remains... 

Scheme 8.23 Preparation of Herrmann s bis(NHC) ruthenium(II) complexes 84 and the mono(NHC) complexes 85 and 86 from the first generation Grubbs catalyst 83b (X = H) as the precursor...

Several catalysts for ring-closing metathesis are now known. Prominent examples are shown in Scheme 1 the molybdenum carbene complex 8, introduced by Schrock et al. [4], methyltri-oxorhenium 9, discovered by Herrmann et al. [5] and the ruthenium carbene complex 10, developed by Grubbs et al. [6]... 

Note The second generation Grubbs catalyst [Ru(PCyJ(IMes)(=CHPh)ClJ [117] employs a phosphane and a NHC and is activated by loss of the PCy ligand. The Herrmann variant [Ru(IMes)J=CHPh)ClJ [116] is inferior simply because it would have to lose one of the two NHC ligands, a process that takes longer because NHC bind stronger than phosphanes. 

In 1998, Herrmann reported that first-generation Grubbs catalyst [RuCl2(PCy3)2(CHPh)] (72) (Scheme 12) underwent substitution of the two phosphines by two equivalents of alkyl carbene affording complex (74). On the other hand, when only a slight excess of the free carbene was added monosubstitution of phosphine was achieved, and complex (73) was obtained. ... 

With the work by Grubbs et al. [27] and Herrmann et al. [28], the use of ruthenium carbene complexes as homogeneous catalysts for the ROMP (Ring-Opening Metathesis Polymerization) of olefins was estabhshed (see Section 2.4.4.3). The development of catalysts that can catalyze hving polymerization in water was an important goal to achieve, especially for applications in biomedicine. In this context, two water-soluble ruthenium carbene complexes (3 and 4) have been reported that act as initiators for the living polymerization of water-soluble monomers in a quick and quantitative manner [29]. 

RuCl(=C=C=CPh2XPCy3)]. However, subsequent work from the groups of Nolan " and Furstner showed that the end products formed in these reactions were actually VMr-indenylidene compounds. Thus, the correct molecular representation for the synthesis of homobimetallic adduct 8 from monometallic precursor 7 is depicted in Scheme 3. In sharp contrast with the trends observed previously by Grubbs and Herrmann, bimetallic species 8 was repeatedly found to be a less efficient catalyst than its monometallic parent 7 in the RCM of several dienes. 

Over the last decade, our group has shown in multiple instances that monometallic Ru catalysts active in olefin metathesis could also be turned into efficient promoters for atom transfer radical reactions with only minor ligand tuning. Such a dual activity was evidenced, among others, for Grubbs catalyst Ru-arene complex 3, Herrmann bis-NHC or mixed-... 

After the initial activity in the 1960s and 1970s, Arduengo drew attention back to the area in 1991 with the isolation of the first NHC in the free state, where bulky R groups stabilize the carbene center. From 1994, Herrmann developed the use of NHCs as spectator ligands in homogeneous catalysis. Perhaps the most dramatic success in area came from the modification of the Grubbs catalyst... 

Grubbs, 1 generation, 1995 - (2) Grubbs, Nolan, Herrmann, 2"< generation, 1999 -(3) Hoveyda, 2001. Hoveyda s first catalyst with PCya instead of the diaminocarbene (1999). 

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