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

Over the past twenty years, main group chemistry has broadened its horizons to encompass reactivities once thought to be exclusive domains of transition metals. Element-ligand cooperation has emerged as a promising approach for enabling bond activation reactions, yet it remains relatively unexplored for heavier group 15 elements. In this study, we present a novel class of ylide ligands featuring additional amino donor sites, specifically designed to promote bismuth-ligand cooperativity. We successfully isolated a series of well-defined bismuth scorpionate complexes with a dianionic N,Cylide,N ligand, bearing different substituents at the ylide moiety. These variations result in differing degrees of negative charge stabilization, which in turn leads to variable donation of electron density to the central bismuth atom. Halide abstraction to form cationic bismuth complexes enhanced ligand-to-bismuth electron donation, resulting in low Lewis acidities and reduced reactivity. Conversely, deprotonation of the ylide ligand bearing an electron-withdrawing ArF substituent enabled the synthesis and NMR characterization of a rare bismuth yldiide, which underwent a [2+2] addition of carbodiimide across the formal Bi=C double bond, demonstrating the ability of bismuth yldiides to activate bonds through bismuth-ligand cooperativity.