Gold cations

Isocyanides RNC have been employed extensively as ligands for gold cations, and gold(i) complexes of the types (RNC)AuX and [(RNC)2Au]+X in particular are legion. As for alkynylgold compounds (Section 4), research activities in this area have several quite obvious reasons, as follows. 

One Au-C bond in bis(thiazol-2-ylidene)gold cations is cleaved in the reaction with elemental iodine to give the corresponding (carbene)AuI complex and a 2-iodo-thiazolium salt, while chlorine and bromine oxidize the gold center to the gold(m) state.267... 

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. 

Xenon fluorides, 77 323-325 binary, 77 335-336 Xenon-gold cations, 77 332 Xenon halides, 77 323-325 Xenon hexafluoride, 7 7 325, 329 uses for, 7 7 336 Xenon ion lasers, 74 685 Xenon isotopes, in fission reactors, 77 375 Xenon oxide difiuoride, 77 326 Xenon oxide fluorides, 7 7 326 Xenon oxides, 77 325-326 Xenon oxide tetrafluoride, 77 326 Xenon testing, in plastics weathering, 79 584-585... 

Nevertheless, in some cases, cation- -anion contacts give rise to extended structures, as in both the colorless and the yellow polymorph of [Au(C = NC6H11)2][PF6] [13], where the gold cations aggregate via aurophilic contacts into infinite linear chains, which are further connected through Au- F contacts to afford two-dimensional... 

Figure 5.1 Chains of gold cations and PF6 anions in the colorless (a) and yellow (b) polymorphs of [Au(C= NC6Hn)2][PF6] showing the Au- -F contacts.

In a joint study by Schmidbaur and Raubenheimer, several phosphine carboxylates and sulfonates of gold and silver were tested as catalysts for the hydration of nonactive alkynes [99]. While the gold complexes showed high activity for these reactions, analogous silver (I) complexes were not active in them. This different behavior was due to the fact that gold cations are weaker acceptors for their ligands and counterions than silver (I) cations (Figure 8.3). 

From the Au-Au bond lengths shown and related theoretical calculations, the valence states of the Au atoms are in the sequence of Au(III)-Au(I)-Au(I)-Au(I)-Au(III). The molecular cation is composed of the central unit [AuCCeFshl and two outer dinuclear gold cations... 

The easiest reactions are those in which the nucleophile is the gold-activated species. Examples of this are Au(I)-catalyzed carbene and nitrene transfers (equations 142 and 143) that convert olefins into cyclopropanes or aziridines, respectively. In the carbene transfer, ethyl diazoacetate is the source of carbene and the active NHC-gold cationic catalyst is generated by chloride abstraction with sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate NaBAT4. The cyclopropanation is competitive with other carbene insertions with active C H or N H bonds present in the substrate. For the aziridinations of olefins, nitrene formation is accomplished by the oxidation of sulfonamides with PhI(OAc)2 and the catalyst of choice is a gold-(I) triflate with a terpyridine ligand. 

With the bidentate gold cations [Au2(dppx)]-+ (x = m, e, b), the reaction with... 

Gold Cationic gold(I) catalysts are also active (Scheme 26b, c) [156-158] factors controlling the selectivity in substrates that can cyclize either to 5- or... 

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