From Boron to Bismuth: The Pre-transmetalation Complex in the Aryl Transfer

B-to-Bi transmetalation is increasingly encountered as a key organometallic step in Bi-based protocols. Yet, akin to transition metal complexes, obtaining structural evidence of pre-transmetalation intermediates that lead to the aryl transfer from B to a metal is challenging and rare. Herein, we provide structural characterization of two unprecedented pre-transmetalation complexes linking B and Bi through a F- or an OH- bridge. Inspired by earlier studies on d-block elements, we establish two general pathways by which transmetalation can occur: the <i>neutral</i> and the <i>ionic pathway</i>. These studies delineate the requirements for successful transmetalation of a wide range of unprecedented arylboron species.