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

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.