5 research outputs found
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(OCOCF<sub>3</sub>)<sub>2</sub>(tpy) (tpy = 2-(<i>p</i>-tolyl)pyridine) with either RMgX or RLi, respectively. Specifically,
AuMe<sub>2</sub>(tpy) and AuPh<sub>2</sub>(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(OCOCF<sub>3</sub>)<sub>2</sub>(tpy) and AuMe<sub>2</sub>(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(OCOCF<sub>3</sub>)<sub>2</sub>(tpy) (tpy = 2-(<i>p</i>-tolyl)pyridine) with either RMgX or RLi, respectively. Specifically,
AuMe<sub>2</sub>(tpy) and AuPh<sub>2</sub>(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(OCOCF<sub>3</sub>)<sub>2</sub>(tpy) and AuMe<sub>2</sub>(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(OCOCF<sub>3</sub>)<sub>2</sub>(tpy) (tpy = 2-(<i>p</i>-tolyl)pyridine) with either RMgX or RLi, respectively. Specifically,
AuMe<sub>2</sub>(tpy) and AuPh<sub>2</sub>(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(OCOCF<sub>3</sub>)<sub>2</sub>(tpy) and AuMe<sub>2</sub>(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<sup>F</sup>)<sub>2</sub>(tpy) (<b>1</b>, OAc<sup>F</sup> = OCOCF<sub>3</sub>; tpy = 2-<i>p</i>-tolylpyridine) undergoes reversible
dissociation of the OAc<sup>F</sup> ligand <i>trans</i> to
C, as seen by <sup>19</sup>F NMR. In dichloromethane or trifluoroacetic
acid (TFA), the reaction
between <b>1</b> and ethylene produces Au(OAc<sup>F</sup>)(CH<sub>2</sub>CH<sub>2</sub>OAc<sup>F</sup>)(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<sup>F</sup>)(CH<sub>2</sub>CH<sub>2</sub>OCH<sub>2</sub>CF<sub>3</sub>)(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><sub>4</sub> in TFA caused
exchange of ethylene-<i>d</i><sub>4</sub> for ethylene at
room temperature. The reaction of <b>1</b> with <i>cis</i>-1,2-dideuterioethylene furnished Au(OAc<sup>F</sup>)(<i>threo</i>-CHDCHDOAc<sup>F</sup>)(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<sup>F</sup> <i>trans</i> to N by ethylene. Addition
of free <sup>–</sup>OAc<sup>F</sup> to coordinated ethylene
furnishes <b>2</b>. While substitution of OAc<sup>F</sup> by
ethylene <i>trans</i> to C has a lower barrier, the kinetic
and thermodynamic preference of <b>2</b> over the isomer with
CH<sub>2</sub>CH<sub>2</sub>OAc<sup>F</sup> <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 CH<sub>2</sub>Cl<sub>2</sub> arise from
stabilization of the <sup>–</sup>OAc<sup>F</sup> anion lost
during the first reaction step
Markovnikov at Gold: Nucleophilic Addition to Alkenes at Au(III)
The reactivity of
Au(OAc<sup>F</sup>)<sub>2</sub>(tpy) (<b>1</b>, OAc<sup>F</sup> = OCOCF<sub>3</sub>; 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><sup>3</sup>) ligands. In this work we have found that
the reactions always occur <i>trans</i> to tpy-<i>N</i> while the OAc<sup>F</sup> 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