Grubbs-type

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

Given the success of the Grubbs-type NHC-Ru catalysts in metathesis polymerisation (Chapter 3), it is somewhat surprising that more research has not been done on mid-transition metal carbene complexes for coordination-insertion polymerisation. At this stage however, there are only a few reported attempts with the metals Co, Fe and Ir. 

By contrast, much of the work performed using ruthenium-based catalysts has employed well-defined complexes. These have mostly been studied in the ATRP of MMA, and include complexes (158)-(165).400-405 Recent studies with (158) have shown the importance of amine additives which afford faster, more controlled polymerization.406 A fast polymerization has also been reported with a dimethylaminoindenyl analog of (161).407 The Grubbs-type metathesis initiator (165) polymerizes MMA without the need for an organic initiator, and may therefore be used to prepare block copolymers of MMA and 1,5-cyclooctadiene.405 Hydrogenation of this product yields PE-b-PMMA. N-heterocyclic carbene analogs of (164) have also been used to catalyze the free radical polymerization of both MMA and styrene.408... 

In 2003, Efskind and Undheim reported dienyne and triyne domino RCMs of appropriately functionalized substrates with Grubbs type II or I catalysts (Scheme 6.71, reactions a and b, respectively) [151]. While the thermal processes (toluene, 85 °C) required multiple addition of fresh catalyst (3 x 10 mol%) over a period of 9 h to furnish a 92% yield of product, microwave irradiation for 10 min at 160 °C (5 mol% catalyst, toluene) led to full conversion. The authors ascribe the dramatic rate enhancement to rapid and uniform heating of the reaction mixture and increased catalyst lifetime through the elimination of wall effects. In some instances, use of the Grubbs I catalyst was more efficient than use of the more common Grubbs II equivalent. 

A Grubbs-type ruthenium complex and a Hoveyda ruthenium complex were compared under similar conditions for recycled activity. Both the reference catalysts showed a large drop in metathesis activity in the subsequent tests. For example, a Grubbs-type ruthenium alkylidene catalyst showed a drop of nearly 50% conversion in the second run. 

NBE/DMN-H6 Chemical, Grubbs type initiator 2-Propanol/toluene 5 mm, 3 mm, and 200 pm I.D., biopolymer chromatography and SEC of synthetic polymers [39-42]... 

Routes to the important class of well-defined ruthenium initiators of the Grubbs type (20b-22b) are summarized in Eigure 4 for details, see Table 2. COMC (1995) described the first example of this family, vinylalkylidene 20a, prepared by reaction of RuCl2(PPh3)3 with 2,2-diphenylcyclopropene. Subsequent treatment with PCys yields 20b (path (a)). (The corresponding complex 21a was later prepared by reaction of RuHCl(PPh3)3 with propargyl chloride see below). Initiator 20a effected controlled ROMP of and bicyclo[3.2.0]heptene M6, but ROMP of less... 

A dominant feature of the type c ring-construction approach to azepine systems has been ruthenium-catalyzed ringclosing metathesis reactions. Examples include the synthesis of the azepine derivative 157 from 156 using either the Grubbs type I catalyst 159 or type II 160. The diene precursor 156 was prepared in turn from 154 via 155, as shown in Scheme 21. Hydrogenation of the C-C double bond in 157 afforded the azepane 158 <2005SL631>. 

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. 

First generation Grubbs type ruthenium catalysts... 

A common procedure used to forge carbocyclic systems is represented by the ring-closing metathesis reactions exploiting various Grubbs-type carbene catalysts. Based on this cyclization technology, Skaanderup and Madsen [71], on the way to polyhydroxy-nortropane calystegines, reported the asymmetric synthesis of aminated 6a-carbahexoseptanose derivatives 311. 

It should be noted that while enyne metathesis is considered incompatible with molybdenum catalyst 1, ruthenium catalysts other than the Grubbs type also promote the reaction. Semeril et al. [103] reported efficient enyne RCM with a catalyst conveniently generated in situ from [RuCl2(p-cymene)]2,1,3-bis(mesityl)imidazolium chloride and caesium carbonate. Interestingly the authors found that the in situ derived system gave better results than the isolated catalyst. One of the most impressive examples of the use of enyne RCM is the total synthesis of (-)-longithorone by Layton et al. [104]. Inspired by a pro-... 

Neutral or cationic Grubbs-type complexes bearing an alkylidene fragment and either phosphine, N-heterocyclic carbene (NHC), or Schiff base ligands. 

Beyond the use of the Fischer-type chromium carbenes as stoichiometric reagents and the Grubbs-type ruthenium carbenes as versatile catalysts for the preparation of organic compounds, Schrock s molybdenum and tungsten complexes of the general composition M(CHR)(NAr)(OR )2 (and derivatives thereof) and... 

S. M. Hansen, F. Rominger, M. Metz, and P. Hofmann, The First Grubbs-Type Metathesis Catalyst with cis Stereochemistry Synthesis of [(rf-dtbpm)Cl2Ru=CH—CH=CMe2] from a Novel, Coordinatively Unsaturated Dinuc-lear Ruthenium Dihydride, Chem. Eur. J. 5, 557-566 (1999). 

Ferroelectric liquid crystalline monomers (Fig. 21, XXXVII) bearing two terminal vinyl groups were polymerized directly from their smectic A" liquid crystal phase using a Grubbs-type initiator. 

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

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