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-(iPr(2)P)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 iPr(2)P ancillary ligands blocking access to the reactive gold center.