Synthesis, structure, and properties of a T-shaped 14-electron stiboranyl-gold complex

A cyclic stiboranyl-gold complex (1) supported by two 1,8-naphthalenediyl linkers has been synthesized and structurally characterized. The gold atom of this complex adopts a T-shaped geometry and is separated from the antimony center by only 2.76 Å. Surprisingly, the trivalent gold atom of this complex is involved in an aurophilic interaction, a phenomenon typically only observed for monovalent gold complexes. This phenomenon indicates that the stiboranyl ligand possesses strong σ-donating properties making the trivalent gold atom of 1 electron rich. This view is supported by DFT calculations as well as Au L(3)- and Sb K-edge XANES spectra which reveal that 1 may also be described as an aurate-stibonium derivative. In agreement with this view, complex 1 shows no reactivity toward the halides Cl(-), Br(-), and I(-). It does, however, rapidly react with F(-) to form an unprecedented anionic aurate fluorostiborane complex ([2](-)) which has been isolated as the tetra-n-butylammonium salt. The increased coordination number of the antimony center in this anionic complex ([2](-)) does not notably affect the Au-Sb separation (2.77 Å) or the geometry at the gold atom which remains T-shaped.