Pnictogen\nBonding at the Core of a Carbene-Stiborane-Gold\nComplex: Impact on Structure and Reactivity

Our interest in the design of ambiphilic ligands and\ntheir coordination\nto gold has led us to synthesize an indazol-3-ylidene gold\nchloride complex functionalized at the 4-position of the indazole\nbackbone by a stibine functionality. The antimony center of this new\ncomplex cleanly reacts with <i>o</i>-chloranil to afford\nthe corresponding stiborane derivative. Structural analysis indicates\nthat the stiborane coordination environment is best described as a\ndistorted square pyramid whose open face is oriented toward the gold\ncenter, allowing for the formation of a long donor–acceptor,\nor pnictogen, Au → Sb bonding interaction. The presence of\nthis interaction, which has been probed computationally, is also manifested\nin the enhanced catalytic activity of this complex in the cyclization\nof <i>N</i>-propargyl-4-fluorobenzamide.