Arenes catalysts

Typically, heterogeneous transfer hydrogenations are carried out at higher temperatures. The Noyori-Ikariya ruthenium arene catalysts are stable up to temperatures around 80 °C, whilst the rhodium and iridium CATHy catalysts are... 

The Cr(CO)6 and Cr(CO)3(arene) catalysts hydrogenate conjugated dienes by 1,4-addition of hydrogen. The diene coordinates in a cisoid configuration (equation 7)23. This... 

The a-phenyl substituted six-membered sulfur-containing material 399 was reduc-tively cleaved using DTBB (5%) as the arene catalyst in THF at —78°C. The resulting intermediate 400 was then reacted with an electrophile followed by hydrolysis, yielding functionalized thiols 401 (Scheme 112) . 

Finally, polymer 594 has been used as an arene-catalyst to activate nickel from nickel(II) chloride and lithium, in order to perform hydrogenation of different organic substrates such as afkenes, afkynes, carbonyl compounds and their imines, alkyl and aryl halides (chlorides, bromides and iodides), aromatic and heteroaromatic compounds as well as nitrogen-containing systems such as hydrazines, azoxy compounds or Af-amino oxides, giving comparable results to those obtained in the corresponding reaction in solution . 

The allenylidene-ruthenium(arene) catalyst precursors I have been used for the synthesis of macrocycles by the RCM reaction and were revealed as active as the first generation Grubbs catalyst RuCl2(=CHPh)(PCy3)2 [35], depending on the nature of the diene functional groups and macrocyde size [32] (Scheme 8.3).These macrocyde syntheses show that the allenylidene mthenium catalysts I offer functional group tolerance. 

S.2.3.4 lndenylidene-Ruthenium(arene) Catalyst in Diene and Enyne RCM... 

Aluminum-alkynyl covalent bonds, characteristics, 9, 249-250 Aluminum-aluminum bonds in A1(I) compounds, 9, 261 in Al(II) compounds, 9, 260 Aluminum aryloxides, reactivity, 9, 254—255 Aluminum(III)ates, in organic group-selective transfers, 9, 279 Aluminum(I)-boron bonds, characteristics, 9, 263 Aluminum(III)-boron exchange, process, 9, 266 Aluminum-calix[4]arene catalyst, for alternating epoxide-CC>2 co-polymerization, 11, 617... 

An alternative solution to the problem of purification is to use 1-dimethylaminonaphthalene 7 (DMAN),17 which can be removed from the product mixture by an acid wash. Reactions in the presence of this reagent must take place below -45 °C above this temperature the DMAN radical anion decomposes to give 1-lithionaphthalene.18 Polymer-supported arene catalysts can also be used.19 20... 

An important development followed in 1991,28 when Yus and Ramon showed that naphthalene, biphenyl and DBB could be used catalytically in the reduction of functionalised alkyl chlorides.29 9 Only 1% of the arene catalyst is required, and organolithiums are... 

Both sides of acetone have been alkylated with different alkyl groups, in one operation, by treatment of the A, A -dimethylhydrazone of acetone with n-BuLi, followed by a primary alkyl, benzylic, or allylic bromide or iodide then another mole of n-BuLi, a second halide, and finally hydrolysis of the hydrazone. " Alkylation of an unsymmetrical ketone at the more substituted position was reported using an alkyl bromide, NaOH, and a calix[n]arene catalyst (see p. 122 for calixarenes). ... 

The Friedel-Crafts alkylation of arenes with lactones provides a convenient method for the synthesis of arylalkanoic acids. However, depending on the nature of the arene, catalyst, temperature and reaction time, the resulting arylalkanoic acids can undergo partial or complete cyclization to the corresponding cyclic ketones (Scheme 10). Equations (65) to (68) show examples of Friedel-Crafts alkylations using lactones as the alkylating agents." "" ... 

In view of the enhancements bronght by the replacement of phosphines by NHCs in monometallic ratheninm-arene catalyst precursors of type 1-3, we decided to investigate the effect of similar modifications on the catalytic activity of complexes of type 4-5. The preparation of complexes 6 and 7 was rather straightforward and could be achieved in a single step by heating the commercially available [RuCl2(/i-cymene)]2 dimer with 1 equivalent of 1,3-dimesitylimidazolin-2-ylidene and 4,5-dichloro-l,3-dimesityl-imidazolin-2 ylidene, respectively (11). 

The p-sulfonatocalix[n]arenes 4, originally synthesized by Shinkai et al." as water soluble calixarenes for catalytic studies in water solution, were more recently used by Ueoka et alP as catalysts in the specific acid catalyzed methanolysis of A -Ac-L-amino acids (Phe, lyr, Trp, His, Lys, Arg). Rates of methanolysis in the presence of the calix[n] arene catalysts, normalized per sulfonic group, were compared with rates obtained in the presence of the noncyclic analogue p-hydroxybenzenesulfonic add. Rate enhancements - ranging from 12- to 86-fold - relative to control were recorded only in the methanolysis of basic amino acid derivatives (His, Lys, Arg), but neutral amino add derivatives (Phe, Tyr, Trp) responded virtually in the same way to the presence of cyclic and non-cyclic catalyst. Michaelis-Menten kinetics and H NMR spectral evidence pointed to the intermediacy of inclusion complexes of 4 with the protonated form of basic amino acid derivatives, as shown in 5 for the His-4 (n = 4) combination. 

The best-studied precatalysts for this reaction are of the type L3Cr(CO)3, in which L3 is an arene," " (CH3CN)3, or (CO)3." -" The arene catalysts are thought to generate Cr(CO)3(S)3 (in which S = solvent) after thermal or photochemical activation" " of the coordinatively saturated precatalyst. The most active catalyst of this type is the naphthalene complex (Ti -naphthalene)Cr(CO)3." " "... 

OLEFIN METATHESIS WITH RUTHENIUM-ARENE CATALYSTS BEARING A-HETEROCYCLIC CARBENE... 

To further expand the scope of Ru-arene catalyst precursors in olefin metathesis, we have investigated the replacement of phosphine ligands by NHC species, either preformed or generated in situ, in monometallic dichlororuthenium complexes of the [RuCl2(p-cymene)(L)] type/ In this contribution, we summarize the main results that were obtained with both imidazole- or triazole-based ancillary ligands for the ROMP of cyclooctene. 

Ruthenium-arene catalysts bearing imidazolin-2-ylidene and unidazolidin-2-ylidene ligands... 

Olefin metathesis with ruthenium-arene catalysts... 

The Maruoka group developed asymmetric MPV allq nylations catalysed by the axially chiral biphenol ligands derived catalyst 46 (Scheme 19.55), and the corresponding alcohols were obtained in 64-96% enantiomeric excess. Very recently, Nandi, Katz and coworkers reported an Al-calix[4]arene-catalyst 47 for the asymmetric MPV reduction (Scheme 19.56). The most enantioselective catalyst consisted of a new axially chiral vaulted-hemispherical calyx[4]arene phosphite ligand, which delivered the chiral alcohols with enantiomeric excesses up to 99%. 

Scheme 19.56 Asymmetric MPV reductions catalysed by Al-calix[4]arene catalyst.

Heterobifunctional Guanidinium-Metal Ion Calix[4] arene Catalysts... 

Effective transesterification reactions of Passiflora seed oil with methanol or ethanol in the presence of solid p-sulfonic acid calix[4]arene catalyst (40, n = 4) was reported by Le Hyaric et al. [36] The calixarene catalyst is described as non-corrosive, easily recoverable from the reaction medium and reusable. High and fast conversions into desired products are reported. 

In our discussion, many calixarens have been mentioned in number of chemical reactions as catalyst, however out of these, quaternary ammonium-terminated calixarenes calix[4]arene 4 and calix[6]arene 2 catalysts were used in one-pot Mannich reaction of benzaldehyde, acetophenone and aniline in aqueous media to produce p-aminocarbonyl compounds (see Fig. 27.7) [19]. These calix[n]arene catalysts emphasized not only the high catalytic activity but also have an outstanding reusability with high yield, at low loading amoxmt. Advantages of that were, short reaction times, high yields, and easy work-up that make them great candidate for Mannich-type reactions (see Table 27.5). 

Fig. 27.7 Three component Mannich reaction in the presence of calix[n]arene catalysts Table 27.5 Mannich reaction in the presence of calix[4]arene 4 or calix[6]arene 2 catalyst [22]...

Fig. 27.8 Three component Mannich reaction in the presence of Bronsted-type calix[n]arene catalysts...

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