Experimental and Theoretical Evidence for an Agostic Interaction in a Gold(III) Complex

π-Backbonding and non-covalent interactions in the JohnPhos and polyfluorothiolate complexes of gold(i)

We studied the influence of changing the degree of fluorination in eight new gold(i) derivatives containing both JohnPhos phosphine and polyfluorinated thiolates: [Au(SR_F)(JPhos)], JPhos = P(C₆H₄-C₆H₅)(t-But)₂ and R_F = C₆F₅ (1), C₆HF₄ (2), C₆H₃F₂-3,5 (3), C₆H₃F₂-2,4 (4), C₆H₄F-2 (5), C₆H₄F-3 (6), C₆H₄F-4 (7) and CF₃ (8). We determined the molecular and crystal structures of all new compounds by single crystal X-ray diffraction. Later, we characterised the chemical bonding scenario with quantum chemical topology tools, specifically the Quantum Theory of Atoms in Molecules (QTAIM) and the analysis of the NCI-index. Our QTAIM results indicate that while the linear S-Au-P moiety is unaffected by the variation of the fluorine content on the thiolates and that Au-S and Au-P bond strengths are mostly constant for all compounds in the series, the π character of gold bonds seems to be modified by the fluorination of the substituents at the thiolate ligand. Besides, the examination of the NCI-index reveals the presence of weak Au-π_Phenyl non-covalent interactions in all compounds. Overall, this study shows the relevance of (i) the π-backbonding properties of the metal centre and (ii) different non-covalent interactions in the stability of JohnPhos gold(i) compounds.

Hydrogen bonds to Au atoms in coordinated gold clusters

It is well known that various transition elements can form M···H hydrogen bonds. However, for gold, there has been limited decisive experimental evidence of such attractive interactions. Herein we demonstrate an example of spectroscopically identified hydrogen bonding interaction of C-H units to Au atoms in divalent hexagold clusters ([Au₆]²⁺) decorated by diphosphine ligands. X-ray crystallography reveals substantially short Au-H/Au-C distances to indicate the presence of attractive interactions involving unfunctionalized C-H moieties. Solution ¹H and ¹³C NMR signals of the C-H units appear at considerably downfield regions, indicating the hydrogen-bond character of the interactions. The Au···H interactions are critically involved in the ligand-cluster interactions to affect the stability of the cluster framework. This work demonstrates the uniqueness and potential of partially oxidised Au cluster moieties to participate in non-covalent interaction with various organic functionalities, which would expand the scope of gold clusters.Many transition metals can form hydrogen bonds to organic species, but experimental evidence for Au is still lacking. Here, the authors obtain crystallographic and NMR spectroscopic evidence of hydrogen bonding between C-H groups and Au atoms of gold clusters, suggesting that non-covalent interactions may play a role in gold cluster catalysis.

Gold(iii)-arene complexes by insertion of olefins into gold-aryl bonds

The synthesis and characterization of the first gold(iii)-arene complexes are described. Well-defined (P,C)-cyclometalated gold(iii)-aryl complexes were prepared and characterized by NMR spectroscopy. These complexes swiftly and cleanly reacted with norbornene and ethylene to provide cationic gold(iii)-alkyl complexes, in which the remote phenyl ring was η2-coordinated to gold. The interaction between the aromatic ring and the gold(iii) center was thoroughly analyzed by NMR spectroscopy, X-ray diffraction, and DFT calculations. The π-arene coordination was found to significantly influence the stability and reactivity of low coordinated gold(iii) alkyl species.

Gold-catalyzed bis(stannylation) of propiolates

Bis(stannylation) of propiolates with hexabutylditin is achieved under mild conditions using a cationic gold(i) catalyst.