PSb+P Ligand: Platform for a Stibenium to Transition-Metal Interaction

The coordination chemistry of cationic divalent pnictogen ligands, such as nitrenium and phosphenium, has been well-explored in recent years. However, corresponding studies of a heavier congener, stibenium ion, are rare. To better facilitate a Sb+–metal interaction, a tridentate P-Sb+-P ligand with two phosphine buttresses was designed and synthesized, and its coordination chemistry toward late transition metals was investigated. The stibenium ligand was delivered as an activated P­(SbCl)­P-AgOTf complex (2) that releases AgCl and the P-Sb+-P ligand upon the treatment with transition metals. Reacting 2 with Rh­(I) and Ir­(I) metals yielded the anticipated stibenium–transition-metal complexes [(Rh­(COD)­Cl)2(μ-PSb+P)] OTf ([3]­[OTf]) and [(Ir­(COD)­Cl)2(μ-PSb+P)] OTf ([4]­[OTf]). The M–Sb+–M bridging structure was confirmed by single-crystal X-ray crystallography, and the bonding situation was examined computationally. Theoretical studies revealed the presence of three-center delocalized M–Sb+–M bonding interactions in [3]­[OTf] and [4]­[OTf].