The Au(III) complex Au(OAc(F))2(tpy) (1, OAc(F) = OCOCF3; tpy = 2-p-tolylpyridine) undergoes reversible dissociation of the OAc(F) ligand trans to C, as seen by (19)F NMR. In dichloromethane or trifluoroacetic acid (TFA), the reaction between 1 and ethylene produces Au(OAc(F))(CH2CH2OAc(F))(tpy) (2). The reaction is a formal insertion of the olefin into the Au-O bond trans to N. In TFA this reaction occurs in less than 5 min at ambient temperature, while 1 day is required in dichloromethane. In trifluoroethanol (TFE), Au(OAc(F))(CH2CH2OCH2CF3)(tpy) (3) is formed as the major product. Both 2 and 3 have been characterized by X-ray crystallography. In TFA/TFE mixtures, 2 and 3 are in equilibrium with a slight thermodynamic preference for 2 over 3. Exposure of 2 to ethylene-d4 in TFA caused exchange of ethylene-d4 for ethylene at room temperature. The reaction of 1 with cis-1,2-dideuterioethylene furnished Au(OAc(F))(threo-CHDCHDOAc(F))(tpy), consistent with an overall anti addition to ethylene. DFT(PBE0-D3) calculations indicate that the first step of the formal insertion is an associative substitution of the OAc(F) trans to N by ethylene. Addition of free (-)OAc(F) to coordinated ethylene furnishes 2. While substitution of OAc(F) by ethylene trans to C has a lower barrier, the kinetic and thermodynamic preference of 2 over the isomer with CH2CH2OAc(F) trans to C accounts for the selective formation of 2. The DFT calculations suggest that the higher reaction rates observed in TFA and TFE compared with CH2Cl2 arise from stabilization of the (-)OAc(F) anion lost during the first reaction step.

International audienceA Missing Gold Link: An Au(III) alkene complex has been prepared and characterized by NMR spectroscopy and X-ray crystallography. Its bonding features have been analyzed by DFT calculations and natural bond orbital (NBO) analysis. In [(cod)AuMe(2) ](+) , the unequal AuC bond lengths result from the domination of the preference of 1,5-cyclooctadiene (cod) for nonparallel double bonds over back donation from the metal which favors parallel double bonds

The interest in organogold compounds continues to grow. Gold(III) complexes are being investigated as catalysts for organic transformations as well as tested as potential anti-cancer drugs. Despite this wide-ranging interest in the properties of such complexes, the synthetic methods for preparing them are underdeveloped. Thus, Chapter 2 discusses the synthesis of cyclometalated gold(III) complexes bearing the C-N chelating ligand 2-(p-tolyl)pyridine (tpy). Monoalkylation andarylation were possible by use of Grignard reagents, whereas alkyl and aryl lithium reagents gave the dialkylated and diarylated gold(III) complexes. By a combination of the two alkylation procedures, mixed alkyl/aryl complexes of the type AuMePh(tpy) were obtained and both isomers were available. Chapter 3 discusses the reactivity of the cyclometalated gold(III) complexes towards different gases such as carbon monoxide and oxygen. Most of the cyclometalated gold(III) complexes prepared react with acids. The monoalkylated and-arylated complexes of the type AuBrR(tpy) (R = Me, Et, CHCH 2 , CCH, Ph) react with silver(I) salts to give a potential open coordination site at gold(III). Ethylene formally inserts into the Au-O bond trans to nitrogen in the chelating C-N ligand of the complex Au(OCOCF 3) 2 (tpy) (62) in trifluoroacetic acid or dichloromethane, to yield Au(CH 2 CH 2 OCOCF 3)(OCOCF 3)(tpy) (94). In trifluoroethanol, a slightly different complex resulted due to nucleophilic attack by trifluoroethanol rather than trifluoroacetate, Au(CH 2 CH 2 OCH 2 CF 3)(OCOCF 3)(tpy) (95). The mechanism of the insertion was investigated experimentally as well as computationally and the results are discussed in Chapter 4. The formal insertion takes place with alkenes other than ethylene, and alkynes react too. A key step in the catalytic reactions involving gold(III) is assumed to be the coordination of a CC multiple bond to the gold centre. Various catalytic cycles involving a gold(III) π-complex have been proposed. However, gold(III) alkene, alkyne, allene, or arene complexes have until recently not been conclusively detected and characterised. Chapter 5 discusses the first, and thus far only, crystallographically characterised gold(III) alkene complex, Au(cod)Me 2 BArF (133-BArF, BArF = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, cod = 1,5-cyclooctadiene).

The Au(III) complex Au(OAc F) 2 (tpy) (OAc F = OCOCF 3 ; tpy = 2-(p-tolyl)pyridine) catalyzes the anti addition of trifluoroacetic acid (HOAc F) to acetylene to furnish vinyl trifluoroacetate. The Au(III) vinyl complex Au(tpy)(OAc F)(CH=CHOAc F) (vinyl group bonded trans to tpy-N) is formed during the early stage of the reaction. The vinyl complex, which has been isolated and structurally characterized, resists protolytic cleavage of the vinyl group and therefore catalysis does not proceed by a simple formal insertion (i.e. coordinationnucleophilic attack-protolysis at the site trans to tpy-N) mechanism. Experimental evidence, including isotopic labeling, rather suggests that a double-insertion process is operative. The unobserved Au(III) divinyl complex Au(tpy)(CH=CHOAc F) 2 is a crucial intermediate for which the true catalytic activity, comprising a coordination-nucleophilic attack-protolysis sequence, occurs at the site trans to tpy-C. The overall mechanism is in full agreement with DFT calculations and is a result of the considerable differences in the kinetic and thermodynamic trans effects of tpy-N vs. tpy-C on each reaction step. The computational data provide a rationale for the catalytic functionalization of acetylene trans to tpy-C, whereas

Incorporation of the simple, readily available, building blocks ethylene, water and acetonitrile into Au(tpy)(OCOCF3)2 (tpy = 2-(p-tolyl)pyridine) in a one-step reaction leads to high yields of a new 6-membered ring gold(iii) metallacycle complex. The metallacycle has been characterized spectroscopically and crystallographically, and the mechanism of its formation has been investigated with the aid of DFT calculations.