Gold complexes with olefins

From the encouraging results obtained in the reactions of a series of gold(III) oxo complexes with olefins [56], Cinellu et al. tried to achieve the supposed oxametalla-cyclic intermediate, which had never been isolated before [25]. In the reaction of 8 and norbornene 56, if the - atoms were considered to be equivalents of coordinated water, and it was therefore possible to talk about the gold-catalyzed addition of water to an alkene. The metallaoxetane 58 was separated from the gold-alkene complex 57 and characterized by X-ray crystal structure analysis. The subsequent stoichiometric reaction yielded epoxide 59 (Scheme 8.5). 

Copper, silver, and gold form complexes with olefins of the following composition [CuX(olefin)] (X = C1, Br olefin = ethylene, propylene, butenes, COT, NBD, etc. dienes in these complexes are monodentate ligands), [Cu2X2(COD)2],... 

Olefin and acetylene complexes of Au(I) can be prepared by direct iateraction of the unsaturated compounds with a Au(I) hahde (190,191). The resulting products, however, are not very stable and decompose at low temperatures. Reaction with Au(III) hahdes leads to halogenation of the unsaturated compound and formation of Au(I) complexes or polynuclear complexes with gold ia mixed oxidatioa states. 

It has been known from the earliest observations in gold chemistry that olefins form very weak 7r-complexes with gold in any of its oxidation states.1-3 Therefore, only a very few stable complexes of this type have been isolated. However, unstable 7r-complexes of olefins with gold compounds are believed to be important intermediates or transient species in gold-catalyzed reactions of unsaturated organic compounds.122-125,131,286-288,307-312... 

The cationic dinuclear oxo-gold(m) complexes of substituted bipyridyls react with olefins to give the stable coordination compounds shown in Scheme 79. The reactions are often incomplete, produce many byproducts, and give low yields of the olefin complexes/... 

III) complexes were able to hydrogenate olefins with high turnover frequencies(TOFs) (71). Scheme 15 shows the structure of these gold complexes. The isoelectronic Pd(II) complexes were also synthesized, having a similar activity as its gold analogs. 

Molecular weight and conductivity measurements on the simple gold(I) complexes [AuCl(olefin)] showed (5/) them to be monomeric and undissociated in solution. The mixed complexes, on the other hand, were found to be 1 1 electrolytes in polarizing solvents with AuClJ as anion and, presumably, a bis- or tris(olefin)gold(I) species as cation. Of the mixed valence complexes only [Au2Cl4(nbd)] was undissociated, due to the necessity to retain a linear, two-coordinate gold(I) center. 

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. ... 

Olefin-metal complexes are frequently labile, especially those of copper, silver and gold, and treatment of most olefin-metal complexes with ligands such as tertiary phosphines results in the displacement of the olefin. In the square-planar acetylacetonate complex (acac)Rh(C2H4)2 the ethylenes readily exchange with free ethylene - as is also found in the square-planar platinum-olefin complexes [17]. In these planar molecules exchange of olefins may involve olefin attack on the exposed metal atom, via a five-co-ordinated intermediate [65, 66]. 

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