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Arene complexes reactions

A variety of transition metals, for example, chromium, molybdenum, tungsten, iron, vanadium, manganese, and rhodium can be used to prepare relatively stable j -arene complexes (see Arene Complexes). Reactions of j -arene chromium tricarbonyl complexes have been extensively examined, and numerous reviews are available. Although chromium complexes are by far the most utilized in organic synthesis, complexes of iron and manganese are emerging as potentially useful alternatives. [Pg.3235]

Chloroarene compounds can be activated for nucleophilic substitution by complexation to transition metals. [CpRu] fragments have been particularly useful for this SjjAr reaction from a synthetic point of view because they can be used for the formation of arylethers as shown in Scheme 5.39 [175]. There is no catalytic variant of this reaction yet. The [CpRu(arene)] complexes are stable in air and water and can be isolated, purified and characterized. Indeed, metal decom-plexation is achieved by photolysis of the compounds in CHjCN. It is worth noting that this reaction is the exact reverse of the arene complexation reaction mentioned in Section 5.3.2.5. The Ru-assisted arylether formation is the key step in recent total syntheses of several natural products, for example the protease inhibitors K-13 (76) and OF-4949-III (77, Scheme 5.40). Model compounds for several antibiotics such as Vancomycin have also been synthesized via this route. [Pg.164]

Partial aspects of the chemistry discussed in this chapter have been reviewed earlier the Meyers reaction [12, 13], transition metal q -arene complex reactions [14], and atroposelective approaches to axially chiral biaryls [15]. The Sj Ar approach is only briefly presented in Franqois Terrier s monograph (3 pages over a 460-page book) [2]. [Pg.197]

The I9e electron-reservoir complexes Fe Cp(arene) can give an electron to a large number of substrates and several such cases have been used for activation. After ET, the [FenCp(arene)]+ cation left has 18 valence electrons and thus cannot react in a radical-type way in the cage as was the case for 20e Fe°(arene)2 species. Thus the 19e Fe Cp(arene) complexes react with the organic halide RX to give the coupled product and the [FeCp(arene)]+ cation. Only half of the starting complex is used e.g., the theoretical yield is limited to 50% [48] (Scheme VI) contrary to the reaction with Fe°(arene)2 above. [Pg.59]

Semmelhack ME, Chlenov A (2004) (Arene)Cr(Co)3 Complexes Arene Lithiation/Reaction with Electrophiles. 7 21-42... [Pg.294]

Further investigations revealed that this hydrogenation is accelerated in pentane solution. These results are shown in brackets in Table 3 [31]. Under optimized reaction conditions high catalyst TOF up to 5,300 were achieved when 10 was used. In the absence of both hydrogen and nitrogen, 10 was converted into the q -arene complexes such as the bis(imino)pyridine iron q -phenyl complex, 10-Phenyl, and the corresponding q -2,6-diisopropylphenyl complex, 10-Aryl, in the 85 15 ratio in... [Pg.34]

CeDs solution (Scheme 7). Both t -arene complexes were also determined by the X-ray diffraction and showed no reaction to hydrogen and olefins. Therefore, it was considered that the formation of the t -arene complexes was a deactivation pathway in the catalytic hydrogenation. [Pg.35]

Furthermore, ir-arene complexes of transition metals are seldom formed by the direct reaction of benzene with metal complexes. More usually, the syntheses require the formation of (often unstable) metal aryl complexes and these are then converted to ir-arene complexes. The analogous formation of w-adsorbed benzene at a metal surface via the initial formation of ff-adsorbcd phenyl, merits more consideration than it has yet been given. It is to be hoped that the recognition and study of structure-sensitive reactions will allow more exact definition of the sites responsible for catalytic activity at metal surfaces. The reactions of benzene, using suitably labeled materials, may prove to be useful probes for such studies. [Pg.154]

Loss of Coordinated Arene. We previously stated that the arene ligand in ruthenium(II)-arene complexes is relatively inert towards displacement under physiological conditions. While this is generally true, there are a few exceptions to this rule and this type of reactivity can be used to advantage. Weakly bound arenes, for instance, can be thermally displaced, a property convenient for the synthesis of ruthenium-arene complexes that are not readily available through more common synthetic routes. This way, the reaction of a precursor dimer, [RuCl2(etb)]2 (etb, ethylbenzoate) (68), with either 3-phenyl-1-propylamine or... [Pg.36]

Histidine residues are, however, generally regarded as major possible binding sites for ruthenium-arene complexes in proteins. To model this interaction, we also studied the reaction of [RuCl(en)(rj6-bip)]+ (10) with L-histidine at 310 K in aqueous solution (91). The reaction was quite sluggish and did not reach equilibrium until 24 h at 310 K, by which time only about 22% of the complex had reacted. Two isomeric imidazole-bound histidine adducts could be discerned, with more or less equal binding of Ne... [Pg.45]

Denmark pursued intramolecular alkyne hydrosilylation in the context of generating stereodefined vinylsilanes for cross-coupling chemistry (Scheme 21). Cyclic siloxanes from platinum-catalyzed hydrosilylation were used in a coupling reaction, affording good yields with a variety of aryl iodides.84 The three steps are mutually compatible and can be carried out as a one-pot hydro-arylation of propargylic alcohols. The isomeric trans-exo-dig addition was also achieved. Despite the fact that many catalysts for terminal alkyne hydrosilylation react poorly with internal alkynes, the group found that ruthenium(n) chloride arene complexes—which provide complete selectivity for trans-... [Pg.806]

Complex iron(III) salts are frequently used in oxidative arene coupling reactions and quinone formation and tetra-n-butylammonium hexacyanoferrate(III) has several advantages in it use over more conventional oxidative procedures. When used as the dihydrogen salt, Bu4N[H2Fe(CN)6], it oxidizes 2,6-di-z-buty 1-4-methylphenol (1) to the coupled diarylethane (2), or aryl ethers (3) and (4) (Scheme 10.4), depending on the solvent. It is noteworthy that no oxidation occurs even after two days with the tris-ammonium salt. [Pg.441]

Perhaps the most compelling evidence for the intermediacy of rf-vinylketene complexes in the Dotz annulation has been provided by the isolation of both free and complexed vinylketenes from the reaction mixture. Dotz himself has reported52,53 the isolation of both arene-complexed (38) and... [Pg.284]

In 1996, Noyori and co-workers discovered that Ru(II) ri-arene complexes containing either a chiral 1,2-amino alcohol such as in 41 or a chiral N-monotosylated 1,2-diamine ligand, see 42, serve as excellent catalysts. It was a breakthrough for catalytic ATH reactions to ketones in terms of enantioselectivities, catalyst loading and... [Pg.44]

The Dotz benzannulation reaction yields either arene chromium tricarbonyl complexes or the decomplexed phenols, depending on the work-up conditions. Because of the instability of hydroxy-substituted arene chromium tricarbonyl complexes, yields of the latter tend to be low. High yields of arene complexes can, however, be obtained by in situ silylation of the crude product of the benzannulation reaction [336]. Oxidative work-up yields either decomplexed phenols or the corresponding quinones. Treatment of the benzannulation products with phosphines also leads to decomplexed phenols [272]. [Pg.52]

Some Schrock-type carbene complexes, i.e. high-valent, electron-deficient, nucleophilic complexes of early transition metals, can undergo C-H insertion reactions with simple alkanes or arenes. This reaction corresponds to the reversal of the formation of these carbene complexes by elimination of an alkane (Figure 3.36). [Pg.119]


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See also in sourсe #XX -- [ Pg.594 , Pg.595 , Pg.596 , Pg.597 , Pg.598 ]




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