Synthesis and Isolation of Bismuth Scorpionate Complexes: Toward Bond Activation via Bismuth-Ligand Cooperation

Over the past twenty years, main group chemistry has significantly expanded its scope to include reactivities once considered the exclusive domain of transition metals. Among the emerging concepts, element-ligand cooperation has proven to be a powerful strategy for enabling bond activation reactions but remains relatively unexplored for heavier group 15 elements. In this study, we present a novel class of ylide ligands incorporating additional amino donor sites, specifically designed to promote bismuth-ligand cooperativity. We successfully isolated a series of well-defined bismuth scorpionate complexes supported by these dianionic N,C_ylide,N ligands, each bearing different substituents at the ylide moiety. These variations modulate the degree of negative charge stabilization, thereby tuning the extent of electron donation to the bismuth center. Halide abstraction generated cationic bismuth complexes, which exhibited enhanced ligand-to-bismuth electron donation, resulting in low Lewis acidities and reduced reactivity. In contrast, deprotonation of the ylide ligand bearing an electron-withdrawing Ar^F substituent enabled the synthesis and NMR characterization of a rare bismuth yldiide complex. This yldiide underwent a [2 + 2] addition with a carbodiimide across the formal Bi = C double bond, demonstrating that bismuth yldiides can engage in bond activation through bismuth-ligand cooperativity.