Versatile Methods for Preparation of New Cyclometalated Gold(III) Complexes

Versatile methods for the high-yield syntheses of new cyclometalated gold­(III) complexes are described. Mono- or dialkylated or arylated gold­(III) complexes are selectively obtained from reaction of Au­(OCOCF₃)₂(tpy) (tpy = 2-(<i>p</i>-tolyl)­pyridine) with either RMgX or RLi, respectively. Specifically, AuMe₂(tpy) and AuPh₂(tpy) were prepared with the respective lithium reagents, and AuBrMe­(tpy), AuBrEt­(tpy), and AuBrPh­(tpy) were prepared with Grignard reagents. The molecular structures of compounds Au­(OCOCF₃)₂(tpy) and AuMe₂(tpy) were determined by single crystal X-ray diffraction

Versatile Methods for Preparation of New Cyclometalated Gold(III) Complexes

Versatile methods for the high-yield syntheses of new cyclometalated gold­(III) complexes are described. Mono- or dialkylated or arylated gold­(III) complexes are selectively obtained from reaction of Au­(OCOCF₃)₂(tpy) (tpy = 2-(<i>p</i>-tolyl)­pyridine) with either RMgX or RLi, respectively. Specifically, AuMe₂(tpy) and AuPh₂(tpy) were prepared with the respective lithium reagents, and AuBrMe­(tpy), AuBrEt­(tpy), and AuBrPh­(tpy) were prepared with Grignard reagents. The molecular structures of compounds Au­(OCOCF₃)₂(tpy) and AuMe₂(tpy) were determined by single crystal X-ray diffraction

Versatile Methods for Preparation of New Cyclometalated Gold(III) Complexes

Versatile methods for the high-yield syntheses of new cyclometalated gold­(III) complexes are described. Mono- or dialkylated or arylated gold­(III) complexes are selectively obtained from reaction of Au­(OCOCF₃)₂(tpy) (tpy = 2-(<i>p</i>-tolyl)­pyridine) with either RMgX or RLi, respectively. Specifically, AuMe₂(tpy) and AuPh₂(tpy) were prepared with the respective lithium reagents, and AuBrMe­(tpy), AuBrEt­(tpy), and AuBrPh­(tpy) were prepared with Grignard reagents. The molecular structures of compounds Au­(OCOCF₃)₂(tpy) and AuMe₂(tpy) were determined by single crystal X-ray diffraction

A Gold Exchange: A Mechanistic Study of a Reversible, Formal Ethylene Insertion into a Gold(III)–Oxygen Bond

The Au­(III) complex Au­(OAc^F)₂(tpy) (<b>1</b>, OAc^F = OCOCF₃; tpy = 2-<i>p</i>-tolylpyridine) undergoes reversible dissociation of the OAc^F ligand <i>trans</i> to C, as seen by ¹⁹F NMR. In dichloromethane or trifluoroacetic acid (TFA), the reaction between <b>1</b> and ethylene produces Au­(OAc^F)­(CH₂CH₂OAc^F)­(tpy) (<b>2</b>). The reaction is a formal insertion of the olefin into the Au–O bond <i>trans</i> 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) (<b>3</b>) is formed as the major product. Both <b>2</b> and <b>3</b> have been characterized by X-ray crystallography. In TFA/TFE mixtures, <b>2</b> and <b>3</b> are in equilibrium with a slight thermodynamic preference for <b>2</b> over <b>3</b>. Exposure of <b>2</b> to ethylene-<i>d</i>₄ in TFA caused exchange of ethylene-<i>d</i>₄ for ethylene at room temperature. The reaction of <b>1</b> with <i>cis</i>-1,2-dideuterioethylene furnished Au­(OAc^F)­(<i>threo</i>-CHDCHDOAc^F)­(tpy), consistent with an overall <i>anti</i> addition to ethylene. DFT­(PBE0-D3) calculations indicate that the first step of the formal insertion is an associative substitution of the OAc^F <i>trans</i> to N by ethylene. Addition of free ^–OAc^F to coordinated ethylene furnishes <b>2</b>. While substitution of OAc^F by ethylene <i>trans</i> to C has a lower barrier, the kinetic and thermodynamic preference of <b>2</b> over the isomer with CH₂CH₂OAc^F <i>trans</i> to C accounts for the selective formation of <b>2</b>. 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

Markovnikov at Gold: Nucleophilic Addition to Alkenes at Au(III)

The reactivity of Au­(OAc^F)₂(tpy) (<b>1</b>, OAc^F = OCOCF₃; tpy = 2-(<i>p</i>-tolyl)­pyridine) toward a wide variety of different alkenes with various substitution patterns and different oxygen-based nucleophiles has been investigated. These reactions are two-step processes where a ligand substitution is followed by a nucleophilic addition furnishing Au­(III) complexes with C­(<i>sp</i>³) ligands. In this work we have found that the reactions always occur <i>trans</i> to tpy-<i>N</i> while the OAc^F ligand remains in place <i>trans</i> to tpy-<i>C</i>. The nucleophilic addition takes place exclusively at the most substituted side of the double bond, in a Markovnikov manner, and the nucleophilic addition occurs in an <i>anti</i> fashion as can be seen from the reaction with the 2,3-disubstituted alkene <i>trans</i>-2-hexene. This study has provided valuable insight into the scope and regiochemistry of Au­(III) mediated nucleophilic additions, which is of great importance for further development of Au­(III) catalysis and alkene functionalization