Organogold chemistry is the study of compounds containing carbon-gold bonds. They are studied in academic research, but have not received widespread use otherwise. The dominant oxidation states for organogold compounds are I with coordination number 2 and a linear molecular geometry and III with CN = 2 and a planar molecular geometry. The gold carbide Au2C2 was discovered in 1900.
Gold(I) complexes are 2-coordinate, linear, diamagnetic, 14 electron species. They exist as adducts LAuR with as ligand L for instance a triphenylphosphine or an isocyanide. The ligand prevents reduction of Au(I) to metallic Au(0) with dimerization of the organic residue. Gold(I) can also exist as the aurate MAuR2 (the ate complex) whereby the cation is usually fitted with a complexing agent to improve stability. The AuR2- anion is also linear just as other M(d10) species such as Hg(Me)2 and Pd(Me)22+. Gold is known to form acetylides (capable of forming polymeric structures), carbenes and carbynes. The classic method for the preparation of LAuR compounds is by reaction of a Grignard reagent with a gold(I) halide. A subsequent reaction with an organolithium R-Li forms the ate complex.
In a special group of compounds, an aryl carbon atom acts as a bridge between two gold atoms. One such compound, (MesAu)5,is formed in a reaction between Au(CO)Cl and the mesityl Grignard. Carbon can be coordinated with gold up to a value to 6. Compounds of the type C(AuL)4 are isolobal with methane and those of type C(AuL)5+ isolobal with the methanium ion.
Gold cyanide compounds (MAu(CN)2) are of some importance to gold cyanidation, a process for the extraction of gold from low-grade ore. The carbon to metal bond in metal cyanides is usually ionic but evidence exists that the C-Au bonding in the gold cyanide ion is covalent.
Gold(III) complexes are 4 coordinate, square planar, diamagnetic, toxic, 16 electron species. When the formal coordination number is less than 4, ligands such as chlorine can make up for it by forming a bridging ligand. Intramolecular chelation is another strategy. In general gold(III) compounds are toxic and therefore less studied than gold(I). For all practical purposes the chemistry is confined to monoarylgold(III) complexes.
Gold-catalyzed reactions fall into two major categories: heterogeneous catalysis including catalysts by gold nanoparticles and thiol-monolayer gold surfaces, and homogeneous catalysis that occurs with gold(I) or gold(III) compounds and is used for organic synthesis. Common commercially available gold catalysts are gold(I) chloride, gold(III) chloride, chloroauric acid and a range of gold phosphines such as chloro(triphenylphosphine)gold(I) . To increase the electrophilicity at the gold center, a more dissociated complex can be created through halide abstraction with an additive like silver triflate (AgOTf).
Gold coordinates preferentially to alkene or alkyne bonds, and bonds following the Dewar-Chatt-Duncanson model. Gold is certainly not the only metal showing this type of bonding and reactivity, several metal ions isolobal with the simple hydrogen proton (cationic: emptied s-orbital) do as well: mercury(II) and platinum(II). In 2007 Fürstner & Davies  proposed the term pi-acid as a cognomen for this type of ion (See also: cation-pi interaction).
The resulting metal-multiple bond complex is electrophilic in nature and activated for nucleophilic attack. In oxymercuration the resultant organomercurial species is generated stoichiometrically, and requires an additional step to liberate the product. Facile protonolysis of the Au-C bond enables true catalysis. Other advantages of gold(I) catalysis include: air stability (high oxidation potential of Au(I) to Au(III) is a barrier to oxidation), lowered oxophilicity and thus tolerance towards water and alcohols, C-Au bonds that prefer protodeauration over beta-hydride elimination, and relative non-toxicity.
An early example of catalysis by gold was described by Ito in 1986  who reacted benzaldehyde and methyl isocyanoacetate with a chiral ferrocenylphosphine ligand and cationic gold(I) compound (Au(cHexCN)2)BF4 to form a chiral oxazoline. This reaction was a first in more than one way: asymmetric Aldol reactions already existed but this was also the first catalytic one.
In a simple mechanistic picture, gold(I) simultaneously coordinates to two phosphine ligands and the carbon isocyanate group  which is then attacked by the carbonyl group. Further studies on the bonding mode of Au(I) indicate that this simple picture may have to be revised.
In 1976, Thomas and coworkers reported conversion of phenylacetylene to acetophenone using tetrachloroauric acid in a 37% yield. In this reaction gold(III) was used as a homogeneous catalyst replacing mercury in oxymercuration. Interestingly, this same study lists a published yield >150%, indicating catalysis that perhaps was not acknowledged by the chemists.
In 1991 Utimoto reacted gold(III)(NaAuCl4) with alkynes and water. Teles identified a major drawback of this method as Au(III) was rapidly reduced to catalytically dead metallic gold and in 1998 returned to the theme of ligand supported Au(I) for the same transformation:
This particular reaction would trigger a lot of academic interest in gold catalysis in the years to come 
Further mechanistic studies conclude that this is not a concerted transformation, but rather an initial alkyne hydroarylation followed by a series of non-obvious intramolecular rearrangements, concluded with a 6-pi electrocyclization and rearomatization.
Heterogeneous gold catalysis is an older science. Gold is an attractive metal to use because of its stability against oxidation and its variety in morphology for instance gold cluster materials. Gold has been shown to be effective in low-temperature CO oxidation and acetylene hydrochlorination to vinyl chlorides. The exact nature of the catalytic site in this type of process is debated. The notion that gold can catalyse a reaction does not imply it is the only way. However, other metals can do the same job inexpensively, notably in recent years iron (see organoiron chemistry).
Gold catalyzed reactions
Gold catalyzes many organic transformations, usually carbon-carbon bond formation from Au(I), and C-X (X = O, N) bond formation from the Au(III) state, due to that ion's harder Lewis acidity. Hong C. Shen summarized homogeneous reactions forming cyclic compounds into 4 main categories:
- heteroatom nucleophilic addition to unsaturated C-C bonds, especially to form small heterocycles (furans, pyrroles, thiophenes)
- Hydroarylation: basically a Friedel-Crafts reaction using metal-alkyne complexes. Example, the reaction of mesitylene with phenylacetylene:
- Enyne cyclization, in particular cycloisomerization, one early example being an 5-exo-dig 1,6 enyne cycloisomerization:
- The soft gold(I) ion coordinates exclusively to the more pi-basic alkyne, leaving the alkene free to attack as the nucleophile.
- cycloaddition reactions with early example the cycloaddition of an nitrile oxide with an alkyne.
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- Catalytic asymmetric aldol reaction: reaction of aldehydes with isocyanoacetate catalyzed by a chiral ferrocenylphosphine-gold(I) complex Yoshihiko. Ito, Masaya. Sawamura, Tamio. Hayashi J. Am. Chem. Soc., 1986, 108 (20), pp 6405–6406 doi:10.1021/ja00280a056
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- Gold(III)-catalyzed one-pot synthesis of isoxazoles from terminal alkynes and nitric acid Francesco Gasparrini, Mario Giovannoli, Domenico Misiti, Giovanni Natile, Gianni Palmieri, Luciana Maresca J. Am. Chem. Soc., 1993, 115 (10), pp 4401–4402 doi:10.1021/ja00063a084
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- Other chemistries of carbon with other elements in the periodic table.
|Core organic chemistry||Many uses in chemistry|
|Academic research, but no widespread use||Bond unknown|