Chloro(triphenylphosphine)gold(I)

Template:Chembox Chloro(triphenylphosphine)gold(I) or triphenylphosphinegold(I) chloride is a coordination complex with the formula (Ph₃P)AuCl. This colorless solid is a common reagent for research on gold compounds.

Preparation and structure

The complex is prepared by reducing chloroauric acid with triphenylphosphine in 95% ethanol:

HAuCl₄ + H₂O + 2 PPh₃ → (Ph₃P)AuCl + Ph₃PO + 3 HCl

Ph₃PAuCl can also be prepared by treating a thioether complex of gold like (dimethyl sulfide)gold(I) chloride, [(Me₂S)AuCl], with triphenylphosphine.

The complex adopts a linear coordination geometry, which is typical of most gold(I) compounds. It crystallizes in the orthorhombic space group P2₁2₁2₁ with a = 12.300(4) Å, b = 13.084(4) Å, c = 10.170(3) Å with Z = 4 formula units per unit cell.

Reactivity

Triphenylphosphinegold(I) chloride is a popular stable precursor for a cationic gold(I) catalyst used in organic synthesis. Typically, it is treated with silver(I) salts of weakly coordinating anions (e.g., X^– = SbF₆^–, BF₄^–, TfO^–, or Tf₂N^–) to generate a weakly bound Ph₃PAu–X complex, in equilibrium with the catalytically-active species [Ph₃PAu]⁺X^– in solution. Among these, only the bistriflimide complex Ph₃PAuNTf₂ can be isolated as the pure compound. The nitrate complex Ph₃PAuONO₂ and the oxonium species [(Ph₃PAu)₃O]⁺[BF₄]^– are also prepared from the chloride.

As shown in the scheme below, the methyl complex Ph₃PAuMe is prepared from triphenylphosphinegold(I) chloride by transmetalation with a Grignard reagent. Further treatment of Ph₃PAuMe with methyllithium displaces the phosphine ligand and generates lithium di- and tetramethylaurate, Li⁺[AuMe₂]^– and Li⁺[AuMe₄]^–, respectively.

File:Reaction scheme of gold(I) and gold(III) organometallic compounds.png

Reaction scheme of Au(I) and Au(III) organometallic compounds, with (Ph₃P)AuCl as the precursor.