Chloro(triphenylphosphine)gold(I) explained

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:^{[1] [2]}

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.^[3] 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. ^[4]

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.^[5] The nitrate complex Ph₃PAuONO₂ and the oxonium species [(Ph₃PAu)₃O]⁺[BF₄]^– are also prepared from the chloride.^[6]

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.^{[7] [8]}

Notes and References

1. Book: Pierre Braunstein . Hans Lehner . Dominique Matt . A Platinum-Gold Cluster: Chloro-¹κ^Cl-Bis(Triethylphosphine-¹κ^P)Bis(Triphenylphosphine)-2κP, 3κP-Triangulo- Digold-Platinum(1 +) Trifluoromethanesulfonate . Inorganic Syntheses . 1990 . 27 . 218–221 . 10.1002/9780470132586.ch42.
2. Book: M. I. Bruce . B. K. Nicholson . O. Bin Shawkataly . Inorganic Syntheses . Synthesis of Gold-Containing Mixed-Metal Cluster Complexes . 1989 . 26 . 324–328 . 10.1002/9780470132579.ch59 . 9780470132579.
3. 10.1107/S0567740876004330 . Chloro(triphenylphosphine)gold(I) . 1976 . Baenziger . N. C. . Bennett . W. E. . Soborofe . D. M. . Acta Crystallographica Section B . 32 . 3 . 962.
4. 10.1021/jp807258d . Estimation of Dissociation Energy in Donor−Acceptor Complex AuCl·PPh3via Topological Analysis of the Experimental Electron Density Distribution Function . 2008 . Borissova . Alexandra O. . Korlyukov . Alexander A. . Antipin . Mikhail Yu. . Lyssenko . Konstantin A. . The Journal of Physical Chemistry A . 112 . 46 . 11519–22 . 18959385.
5. Mézailles . Nicolas . Ricard . Louis . Gagosz . Fabien . 2005-09-01 . Phosphine Gold(I) Bis-(trifluoromethanesulfonyl)imidate Complexes as New Highly Efficient and Air-Stable Catalysts for the Cycloisomerization of Enynes . Organic Letters. 7. 19. 4133–4136. 10.1021/ol0515917. 16146370. 1523-7060.
6. A. M. Mueting, B. D. Alexander, P. D. Boyle, A. L. Casalnuovo, L. N. Ito, B. J. Johnson, L. H. Pignolet "Mixed-Metal-Gold Phosphine Cluster Compounds" Inorganic Syntheses, 1992, Volume 29, Pages 279–298, 2007.
7. Rice . Gary W. . Tobias . R. Stuart . Isolation of thermally stable compounds containing the dimethylaurate(I) and tetramethylaurate(III) anions . Inorganic Chemistry . 1976 . en . 15 . 2 . 489–490 . 10.1021/ic50156a058 . 0020-1669.
8. Zhu . Dunming . Lindeman . Sergey V. . Kochi . Jay K. . X-ray Crystal Structures and the Facile Oxidative (Au−C) Cleavage of the Dimethylaurate(I) and Tetramethylaurate(III) Homologues . Organometallics . 1999 . en . 18 . 11 . 2241–2248 . 10.1021/om990043s . 0276-7333.