On the Ability of Bismuth to Couple Weakly Coordinating Anions

ABSTRACT Similar to aryldiazonium salts, hypervalent bismuth species have been shown to promote coupling of weakly coordinating anions (WCAs) such as triflate and tetrafluoroborate. In this study, we identify the origin of the driving force for these transformations by quantifying scalar relativistic effects in high‑valent bismuth chemistry. All‑electron DFT comparisons between relativistic and non‑relativistic limits reveal pronounced stabilization of the Bi 6s orbital in the former framework. As a result, the structure and frontier‑orbital energetics of the Bi(V)/Bi(III) processes are heavily affected, thus having a pronounced effect on the reductive elimination. Specifically, relativistic contributions to Bi could be observed on different scales ranging from a simple monoatomic model to complex reaction profiles. These results rationalize the facile WCA coupling from catalytically relevant Bi(V) complexes and establish the basis of why Bi(III) is an exceptionally potent nucleofuge in bismuth‑mediated bond formation.