T‑Shaped Gold→Stiborane Complexes as Carbophilic Catalysts: Influence of the Peripheral Substituents

As part of our efforts
toward the discovery of new late transition
metal catalysts, we synthesized [(o-(Ph2P)­C6H4)2(o-C6Cl4O2)­SbPh)­Au]+ (3+) and [(o-(iPr2P)­C6H4)2(o-C6Cl4O2)­SbPh)­Au]+ (4+), two cationic bis­(phosphino)gold stiborane
complexes, which were isolated as their hexafluorophosphate salts
and fully characterized. Structural and computational studies indicate
that the cores of these two complexes are almost structurally and
electronically identical. Despite these similarities, these two complexes
exhibit different catalytic activities in the hydroamination of phenylacetylene
using anilines or in the cyclization of N-(prop-2-yn-1-yl)­benzamide.
Indeed, whereas 3+ catalyzes both reactions,
we found that 4+ is inactive. The data collected
on these two complexes suggest that the origin of this contrasting
behavior is steric, rather than electronic, with the relatively bulky iPr2P ancillary ligands blocking access to the
reactive gold center.