Activation of a Hydroamination Gold Catalyst by Oxidation of a Redox-Noninnocent Chlorostibine Z-Ligand.
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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 AuSb 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](+) ((+)) and [((o-(Ph2P)C6H4)2SbF3)Au](+) ((+)), which have been isolated as SbF6(-) salts. As a result of a stronger AuSb interaction, cation (+) 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.