Gold complexes with alkynes

In general, gold cations Au+ and their adducts with auxiliary ligands [LAu]+, as well as gold(i) halides AuX, form only weak 7r-complexes with alkynes. Stable compounds have been isolated only with special combinations of components, but unstable species may nevertheless play an important role in gold chemistry as short-lived intermediates or transient species. 

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... 

It has been noted that metal-carbon triple bonds behave in a similar way as alkynes with respect to jr-complex formation13,15. Various heterometallic gold complexes with bridging carbyne ligands reflect this analogy. Alkylidyne complexes like [W(=CR)(CO)2( 5-C5H5)], [W(=CR)(CO)2( 75-C2B9H9R )] (R = alkyl, aryl, amino R = H, Me) readily... 

Cyclic(alkyl)(amino)carbene (CAAC) ligands are unique donor Hgands with an easily tailored steric environment and have yielded a variety of robust gold complexes with unusual catalytic activity with alkyne substrates [179-181]. Here a CAAC-gold complex (23) could mediate the hydroamination of 3-hexyne in a sealed tube at 160° C to give imine product as observed by H NMR spectroscopy (Scheme 15.23) [179]. 

Fig. 2.12 Silver, gold and platinum complexes with monodentate NHC ligands as catalysts for the diboration of alkenes and alkynes...

Another particularly convenient preparative method is the reaction of the corresponding gold(l) acetylacetonate complex with the alkyne, which requires no auxiliary base.42 68-71 This reaction is also useful for the simple acetylides (L)AuC=CH.72 The acetylacetonates can be isolated and introduced as the true reagents, or prepared in situ using the corresponding gold(l) halide complex and Tl(acac) (Equations (16) and (17)).73... 

Hydroarylations of alkynes are catalyzed by gold complexes and these bear some resemblance to the Fujiwara Pd-catalyzed reaction. In general, when using gold chemistry, better Z/E selectivities are observed compared with palladium, lower catalyst loadings and milder conditions (neutral not TFA) are used. The mechanism involves the attack of ArH on the Au-coordinated alkyne. Flowever, electron-poor acetylenes only appear to work with palladium chemistry (Equations (75) and (76)).72... 

Alkynyl complexes with copper, 2, 160 with Cp Re(CO) (alkyne), 5, 916 with dicarbonyl(cyclopentadienyl)hydridoirons, 6, 175 with diiron carbonyls, 6, 232-233 donor-free, with gold(I), 2, 255 with gold(I)... 

Bis(adamantylimido) compounds, with monomeric chromium(VI) complexes, 5, 348 Bis(alkene) complexes conjugated, Rh complexes, 7, 214 mononuclear Ru and Os compounds, 6, 401 -02 in Ru and Os half-sandwich rj6-arenes, 6, 538 with tungsten carbonyls and isocyanides, 5, 685 Bis(u-alkenylcyclopentadienyl) complexes, with Ti(II), 4, 254 Bis(alkoxide) nitrogen-donor complexes, with Zr(IV), 4, 805 Bis(alkoxide) titanium alkynes, in cross-coupling, 4, 276 Bis(alkoxo) complexes, with bis-Cp Ti(IV), 4, 588 Bis[alkoxy(alkylamino)carbene]gold complexes, preparation, 2, 288... 

Cyclohexyldienyl complexes, with Ti(IV), 4, 327 Cyclohexylisocyanides, with gold(I) halides, 2, 281 Cyclohexylphosphine, for semiconductor growth, 12, 9 Cyclohexyl selenides, preparation, 9, 480 Cyclohydrocarbonylation alkenes, 11, 515 alkynes, 11, 522 dienes, 11, 522 overview, 11, 511-555 for ring expansion, 11, 527 Cycloisomerizations, via silver catalysts, 9, 558 Cyclomanganation, product types, 5, 777-778 Cyclometallated azobenzenes, liquid crystals, 12, 251 Cyclometallated complexes for OLEDs... 

Similar to the abovementioned silver nhc coordination compounds, carbene chemistry has also been dominant in the field of gold organometallic chemistry. Noteworthy examples include a Au(PPh3)-compound derived from tetraaminoallene, that can be rationalised in terms of a dicarbene with ylide character and which, owing to the electron-rich character of the central carbon atom, offers the potential for dimetallation products.108 Non-activated allenes and alkynes have been found by Lavallo to be readily aminated by cationic carbene gold complexes.109 For this purpose, a 2,6-diisopropylphenyl functionalized cyclic alkylaminocarbene gold(I) complex... 

Athene complexes of platinnm have been well established since the middle of the nineteenth centnry (see Zeise s Salt), bnt TT-complexes of gold were only discovered by Htittel in 1965, with alkyne complexes following in 1972. All of these complexes have very limited stability, and therefore their chemistry is still poorly developed, even today. 

Alkenes act as nucleophiles with alkynes in the presence of gold catalysts. In the most simple version of the reaction, enynes are converted with gold complexes or salts, and in the absence of nucleophiles, into rearranged dienes, cyclopropanated carbocycles, and/or bicyclic cyclobutenes. Depending on the length of the tether and the nature of the substituents, the olefin attack to the alkyne occurs in an endo or an exo fashion (equation 33). Besides, substitution at the alkene plays an important role on the regioselectivity of the nucleophilic attack. ... 

As outlined in previous volumes, the chemistry of ylides coordinated to noble metals, particularly palladium, platinum and gold continues to attract most attention. Refluxing (dppm)palladium(II) dichloride [dppm = bis(diphenylphosphino)methane] with alkynes in mixtures of 1,2-dichloro-ethane/l,4-dioxane provides a novel route to palladium-bound alkenyl phosphorus ylide complexes (53) (Scheme 1)P The reaction represents the... 

Vicente and co-workers have recently synthesized platinum(n) 7 and mixed platinum(II)/ gold(I) a-alkynyl polymers 8.53 The monomers were prepared via dehydrohalogenation between c -[PtCI2( PR jb I and various alkynes. Polymerization occurred via the reaction of the platinum complex with PPN[Au(acac)2], giving polymers with mixed metal backbones. 

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. 

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