Anion-Controlled Positional Switching of a Phenyl Group about the Dinuclear Core of a AuSb Complex

As
part of our continuing interest in redox-active, anion-responsive
main-group transition-metal platforms, we have investigated the effect
of chloride by fluoride anion substitution on the core structure of
a dinuclear AuSb platform. Starting from [(o-(iPr2P)­C6H4)2Cl2SbPh]­AuCl (2) in which the antimony-bound
phenyl group is positioned trans to the gold atom, we found that the
introduction of fluoride anions, as in [(o-(iPr2P)­C6H4)2F2SbPh]­AuCl (3) and [(o-(iPr2P)­C6H4)2ClFSbPh]­AuCl (4), produces structures in which the phenyl
group switches to a perpendicular direction with respect to the gold
atom. Replacement of the gold-bound chloride anion in 3 by a fluoride anion can be achieved by successive treatment with
TlPF6 and [nBu4N]­[Ph3SiF2]. These reactions, which proceed via the intermediate
zwitterionc gold antimonate complex [o-(iPr2P)­C6H4)2F3SbPh]Au (6), trigger migration of the phenyl group to
gold and afford [(o-(iPr2P)­C6H4)2F3Sb]­AuPh (7). Because the phenyl group in 7 is orthogonal
to that in 3 and opposite to that in 2,
the title AuSb platform can be regarded as a molecular analogue of
a mechanical three-way switch in which the switching element is a
phenyl group. Finally, while all complexes involved retain a Au →
Sb interaction, this interaction is no longer present in the zwitterionic
derivative 6 because of the neutralization of the Lewis
acidity of the antimony center.