Gold -complexes, cationic

Figure 8.26 Schematic formula (a) molecular single crystal X-ray diffraction structure (b), and solid state packing (c) ofthe cationic gold complex [Au bimy(Ci6H33) 2]Br H20. (Reproduced from Ref [52] by permission.)...

As already mentioned, CAAC ligands can stabilize electron-deficient metal centers such as in cationic gold complexes. Complex 29 catalyzes a very unique reaction of enamines with acetylene, which produces a cumulene and an imine... 

The cationic gold complex with CAAC ligand 29 can also catalyze the unprecedented hydroamination reaction of alkynes and allenes using ammonia [59, 60]. It was also demonstrated that it can catalyze the simple hydroamination reaction. It... 

Since the metal center in gold complexes usually displays acid character, Au- -NM contacts will be more easily formed as the basicity of the non-metal increases. Thus, there are many gold- -halogen weak interactions between cationic gold complexes and halides or anions of which the halogen forms part, but most are individual contacts between ions that do not generate supramolecular structures. For example, about 50% of Au- -Cl contacts are isolated cation- -anion interactions. 

In 1986 Ito, Sawamura, and Hayashi [4] reported that gold(I) complexes prepared from cationic gold complex 1 and chiral ferrocenylphosphine ligands (2) bearing a tertiary amino group at the terminal position of a pendant chain are effective catalysts for asymmetric aldol reaction of... 

Activation of the triple bond of enynes with electrophilic metal derivatives, especially cationic gold complexes, platinum salts such as PtCl2, and ruthenium derivatives, has been reviewed.117 These catalysts make possible nucleophilic addition of the double... 

TABLE 12.8. Cationic Gold Complexes are Crucial for the Rearrangement... 

In this reaction, silver is successful (Table 12.11, entry 1) gold(III) leads to an unselective conversion (entry 2), but gold is more active and selective. As usual, coordinatively saturated gold complexes fail (entry 3), but cationic gold complexes deliver very good yields in short reaction times (entries 4 and 5). 

With gold(III), no conversion was observed (Table 12.16, entry 1) the coordina-tively saturated gold complex gave a low yield of the 6-endo-dig cyclization product (entry 2). The cationic gold complex with a free coordination site gives an excellent yield with the same selectivity (entry 3) the same is true for AgSbF6 alone (entry 4). But this is not true for all silver catalysts with a systematic increase in the pK.A value of the conjugate acid of the silver counterion, increased portions of the 5-exo-dig product were produced (entries 5 and 6). 

The cationic gold complex with CAAC ligand 29 can also catalyze the unprece-... 

Hydroarylation can also be mediated by Au(I) and Au(III) (Scheme 33) (384). In the case of aryl substituted alkynes, the Au(III) Ji complex undergoes electrophilic aromatic substitution with the electron-rich arene to give aLkenyl-Au(III) complex, which is immediately protonated by the H generated upon C C bond formation. For the Au(I)-catalyzed hydroarylation, the cationic gold complex k coordinates the alkyne, with subsequent nucleophilic attack by the arene from the opposite face leading to an alkenyl-gold complex, which is protonated to the desired products. The nature of the reaction causes the regioselectivity of this reaction to be sensitive to electronic rather than steric factors. 

The nucleophilic addition of alcohols to alkynes was reported by Utimoto with NaAuCU and later by Teles with cationic gold complexes.The enol ethers formed can be hydrolyzed to form carbonyl compounds or trapped as ketals (equations 4 and 5). An intramolecular version of this reaction was reported by the group of Genet to give bicyclic ketals (equation On the basis of this concept, a glycosidation... 

Abstract Progress in the field of metal-catalyzed redox-neutral additions of oxygen nucleophiles (water, alcohols, carboxylic acids, and others) to alkenes, alkynes, and allenes between 2001 and 2009 is critically reviewed. Major advances in reaction chemistry include development of chiral Lewis acid catalyzed asymmetric oxa-Michael additions and Lewis-acid catalyzed hydro-alkoxylations of nonacti-vated olefins, as well as further development of Markovnikov-selective cationic gold complex-catalyzed additions of alcohols or water to alkynes and allenes. 

In the case of other systems prepared by adsorption of gold acetyl acetonate, it seems that only cationic gold complexes could be active in CO oxidation. In the case of Au/NaY zeolite the Au precursor is reduced to Au under reaction conditions at 298 K with no evidence of formation of Au [164]. The catalyst shows activity although the Au complex (initial catalyst) is an order of magnitude more active than Au. The authors, however, report that the catalyst is less active than... 

A recent example by Pale and co-workers used the cationic gold complex PPhsAuSbFg as a catalyst and methanol as a nucleophile to generate the desired 2,3-substituted furan in 92% yield. 2,3,5-Trisubstituted furans, such as 2-(methoxy(2-nitrophenyl)methyl)-4,5,6,7-tetrahydrobenzofuran (shown below) were also prepared in modest yields using this methodology. 

Nolan and coworkers reported the cytotoxicity of different neutral and cationic complexes. The first series of systems studied were Au-IPr derivatives bearing biocompatible moieties such as amino acids (L-proline or L-cysteine, Figure 7.16) [17]. In parallel, a second series of systems was selected, as it is well-known in the literature that cationic gold complexes can induce apoptosis of cancer cell lines. The IC50 were measured with LNCaP (prostate carcinoma) and MDA MB231 (breast carcinoma). 

Apart from these findings, Echavarren and coworkers found a different strategy to isolate catalytically active gold(l) phosphine and NHC complexes [25]. They were able to isolate an array of different cationic gold complexes with noncoordinating anions, typically SbFs , which bear a nitrile ligand (see Scheme 9.9). 

The popularity of the biphenyl moiety in many ligands is not a mere result of adding bulk. The second aryl ring, twisted at an angle to its partner, may affect the metal directly by coordination, as in the cationic gold complex (Figure 1.10). ° The X-ray structure (anionic counter ion not shown) clearly shows the proximity of the second ring to the metal atom. 

Figure 5.5 Chemical plating of gold onto the surface of the ion exchange polymer using a cationic gold complex such as dichlorophenanthrolinegold (III) (Reprinted with permission from Fujiwara, N., Asaka, K., Nishimura, Y. et al. Preparation of Gold-Solid Polymer Electrolyte Composites As Electric Stimuli-Responsive Materials, Chem. of Mat., 12 (6), 1750—4. Copyright (1999) American Chemical Society).

Encapsulation Studies of Cationic Gold Complexes within a Self-Assembled Hexameric Resorcin[4]arene Capsule... 

Gold-Catalyzed Formal [4+2] Cyclization of Ene-Arenynes In 2008, Echavarren and coworkers described the formal [4+2] cyclization of ene-arenynes, leading to stereoselective multiple bond formation. Thus, treatment of a trisubstituted ene-arenyne with a cationic gold complex led to the corresponding tricyclic product bearing an unsaturated side chain in high yield and selectivity (Scheme 7.19) [30]. 

Treatment of the 1,5-enyne 66 with a cationic gold complex caused cycliza-tion to generate the spirocyclic carbene complex 67 (Scheme 7.26) [35]. 1,2-Alkyl migration followed to furnish the tricyclic compound 68. 

Aurophilic interactions in cationic gold complexes with two lisocyanide ligands. Polymorphic yellow and colorless forms of [(cyclohexyl isocyanide)2Au ](PF6) with distinct luminescence, R. L. White-Morris,... 

Cationic gold complexes are useful catalysts for anft -Markovnikov-t5q)e hydrothiolation with excellent regio- and stereoselectivities (Scheme 19) [56]. 

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