Activation of a Hydroamination Gold Catalyst by Oxidation of a Redox-Noninnocent Chlorostibine Z-Ligand

Abstract

In search of new platforms that support redox-controlled catalysis, we have investigated the noninnocent behavior of chlorostibine ligands coordinated to gold. The gold chlorostibine complex ((o-(Ph2P)C6H4)2SbCl)AuCl (1-Cl) undergoes a clean oxidation reaction on treatment with PhICl2. This oxidation reaction affords the corresponding trichlorostiborane complex ((o-(Ph2P)C6H4)2SbCl3)AuCl (2-Cl), which can be converted into the more tractable trifluoride analogue ((o-(Ph2P)C6H4)2SbF3)AuCl (3-Cl) by treatment with a fluoride source. As supported by experimental and computational results, these complexes possess a Au→Sb donor-acceptor interaction which is distinctly stronger in the oxidized complexes 2-Cl and 3-Cl. Both 1-Cl and 3-Cl undergo a clean chloride abstraction reaction to afford the corresponding cationic gold species [((o-(Ph2P)C6H4)2SbCl)Au](+) ([1](+)) and [((o-(Ph2P)C6H4)2SbF3)Au](+) ([3](+)), which have been isolated as SbF6(-) salts. As a result of a stronger Au→Sb interaction, cation [3](+) features a more Lewis acidic gold center. It forms an isolable water adduct and also activates terminal alkynes toward hydroamination with arylamines. These results demonstrate that the redox state of noninnocent Z-ligands can be used to control the catalytic activity of the adjoining metal center.

Digging the Sigma‐Hole of Organoantimony Lewis Acids by Oxidation

“…[1] Antimony derivatives,b ecause of their intrinsically higher Lewis acidity, [2] are also drawing considerable attention both in the areas of small-molecule activation and catalysis, [3] as well as in anion complexation. [7] Based on the same principle,w ea lso found that antimony(III) halides could serve to promote the activation of transition metals either by direct interaction with the metal (III) [8] or anion abstraction (IV) [9] (Figure 1). [7] Based on the same principle,w ea lso found that antimony(III) halides could serve to promote the activation of transition metals either by direct interaction with the metal (III) [8] or anion abstraction (IV) [9] (Figure 1).…”

Oxidative‐Insertion Reactivity Across a Geometrically Constrained Metal→Borane Interaction

“…[1] In particular,cooperation between an electronrich metal and s-acceptor ligand ("Z-type ligand") has recently become of increasing interest. [14,15] Whereas the chemistry of complexes containing group-15-based Lewis acids has recently received increased attention, [16][17][18] most examples of such cooperative reactivity and coordinative flexiblity have exploited boranes (BR 3 )a st he Z-type ligand. [14,15] Whereas the chemistry of complexes containing group-15-based Lewis acids has recently received increased attention, [16][17][18] most examples of such cooperative reactivity and coordinative flexiblity have exploited boranes (BR 3 )a st he Z-type ligand.…”

Activation of an Au−Cl Bond by a Pendent SbIII Lewis Acid: Impact on Structure and Catalytic Activity

“…Taking this interaction into account, the antimony center adopts a disphenoid geometry, as indicated by the Au(1)‐Sb(1)‐C(7) and Au(2)‐Sb(2)‐C(37) angles of 171.4(2)° and 169.9(2)°, and C(1)‐Sb‐C(13) and C(31)‐Sb(2)‐C(43) angles of 95.5(3)° and 96.4(3)°. Similar geometries have been observed at the antimony centers in the related tris‐ and bis‐phosphinylstibine gold complexes . As in 1 , these metrical parameters show that the antimony atom does not interact strongly with the gold center as a Lewis base .…”

“…A related strategy involves the design of ligands containing pendent Lewis acid functionalities, which are able to effect intramolecular halide abstraction from the gold center as in the case of C . In addition to facilitating halide abstraction, pendent Lewis acids have also been shown to improve the activity of electrophilic catalysts, even in cases when the structurally observed M→LA appears to be weak . Finally, we note that the zwitterionic products of Lewis acid‐mediated intramolecular halide abstraction bear comparison to a number of zwitterionic gold complexes featuring an anionic N ‐heterocyclic carbene (NHC) coordinated to a cationic gold center, a number of which have been shown to be active electrophilic catalysts…”

“…Although triarylstibines have been shown to be mildly acidic, to our knowledge no halide adducts of such species have been reported. Instead of facilitating chloride abstraction from the proximal gold center, the weakly Lewis acidic pendent stibine may serve instead to activate the gold center via inductive effects . Compound 2 proved to be considerably more competent than 1 in the cyclization of the substrate, converting 87 % over 33 hours.…”