Gold, reaction scheme with

A related dinuclear species 77, recently described, constitutes the first dinuclear gold(I) complex with heterobridged phosphor-1,1 -dithiolato moieties and bis(ylide) bridging ligands [ 102]. It is obtained by reaction between [ AuS2PPh2] and the diylide gold complex 74 (R=Me). No intermolecular Au-Au interaction is observed in 77 but the oxidative addition of chlorine to the product leads to a new complex 78 in which a single bond is formed between the two Au(II) centers (Scheme 26). 

It should be noted that the preparation of complexes (RNC)AuCN can be carried out via very special routes. Thus AuCN reacts with Mel to give (MeNC)AuCN. This reaction involves an interesting A-alkylation of an Au(i)-bound cyanide group.219 Other (RNG)AuGN complexes were obtained from the reaction of K[AuC14] with the isocyanide in methanol. Examples are the compounds (L)Au2(CN)2 with L = l,8-diisocyano-/>-menthane or 2,5-diisocyano-2,5-dimethyl-hexane. The reactions proceed with a dealkylation of an isocyanide in the coordination sphere of a gold(m) center to produce free cyanide (Scheme 53).201... 

A whole series of (imidazol-2-ylidene)gold(i) complexes with the 1 1 stoichiometry has been prepared from the readily available silver chloride adducts, which upon reaction with (Me2S)AuCl, followed by chloride metathesis, give the complexes shown in Scheme 60. 

The reaction worked with both internal and terminal alkynes (except silylated alkynes) and in many solvents, even in the neat alcohol added [105]. The mechanism proposed involved two catalytic cycles first, gold catalysis would lead to dihydro-furan by a fast intramolecular reaction then, the subsequent slower intermolecular reaction would be produced by the addition of alcohol to the enol ether to deliver a ketal (Scheme 8.18). 

The authors used silver salts since gold salts catalyzed the reaction with R=H (giving oxazole 34, Scheme 5.16) but not with R=Me. Moreover, only traces of the desired furopyrrolidinone were formed with the use of a cationic gold species activated with silver additives. Therefore, silver traces were thought to be the active reagent. Indeed, on activation of compound 33 mediated by AgN03 in the presence of sodium acetate (Scheme 5.16), the enol moiety V can then accomplish a nucleophilic attack to produce the pyrrolidinone W and after protonolysis give compound X. Pyrrolidinone Y (the enol version of X) can, in turn, be subject to an oxidative cyclization to yield the furopyrrolidinone 35. Two equivalents of silver salts are needed for the activation step and the oxidative cyclization. 

A mild conversion of a simple class of substrates, the /V-propargy I carbox am ides, is possible with gold catalysts. With gold , the alkylidene oxazoles are formed with gold(III), the aromatic oxazoles are formed.31 The reactions readily proceed at room temperature, and there are numerous examples of this reaction (Scheme 12.15). 

One group of NADH oxidants, which does not fit the proposed reaction scheme in Fig. 2.4 are the metal complexes. Examples of this type include nickel hexacyanoferrate deposited on porous nickel electrodes [29], gold electrodes modified with cobalt hexacyanoferrate films [30] and adsorbed l,10-phenanthroline-5,6-dione complexes of ruthenium and osmium [31]. It is unclear how these systems work and no mechanism has been proposed to date. It may be worth noting that dihydronicotinamide groups have been shown to reduce aldehydes in a non-enzymatic reaction when the reaction is catalysed by zinc, a metal ion [15]. In a reaction between 1,10-phenanthroline-2-carboxaldehyde and N-propyl-l,4-dihydronicotinamide, no reaction was seen in the absence of zinc but when added to the system, the aldehyde was reduced and the nicotinamide was oxidised. This implies that either coordination to, or close proximity of, the metal ion activates... 

The gold(II) compounds without Au-Au bonds are in general prepared by reduction of Au . There are several dinuclear gold(II) complexes with Au-Au bonds. They are obtained from the corresponding gold(I) complexes by oxidative addition reactions as shown in Scheme (2). In a special case, both the Au -Au and Au products were isolated. ... 

The ferrocenylphosphine-silver complex catalyzes the aldol-type reaction of tosylmethyl isocyanide 71 with aldehydes with higher stereoselectivity than the gold complex (Scheme 2-59) [84]. The reaction with several aldehydes produces trans-4-tosyloxazolines 72 in up to 86% ee, which can be converted into optically active l-alkyl-2-aminoethanols by reduction with LiAlH4. 

This reaction scheme was investigated by contact angle measurements and XPS. Images of water and diiodomethane droplets of the original gold substrate, of the SAM before and after UV-illumination, as well as after the post-treatment with perfluorobutyryl chloride are presented in Fig. 1. The contact angles and the calculated surface tension are summarized in Table 1. 

Methionine 149 is a very important amino acid, and several stereospecifically labeled samples have been prepared. Golding and others (140,141) prepared samples of ( )- and (Z)-[l, 2- H2]ethylene ISO, H = He = H, and 150, Ha = Hb = H, respectively, from [ HjJacetylene and converted these to the corresponding chlorides 151 by anti addition of methane sulfenyl chloride. Substitution by sodium acetylaminomalonate gave the products 152, the reaction occurring with retention of configuration via a thiiranium ion intermediate (Scheme 47). 

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