Among the pnictogen elements (N, P, As, Sb, Bi) a clear trend has emerged, as group 15 is descended, low-valent and cationic compounds become substantially more reactive. This is particularly true for compounds that feature reactive antimony or bismuth centers stabilized by carbon donor ligands (e.g., carbenes, carbones). This can be attributed to the increase in covalent and van der Waals radii, a change in the radial extension between the s and p orbitals, and the resulting decrease in effectiveness of the 2pπ-npπ (n = 2-6) orbital overlap. Thus, those trends, and the thermodynamically weaker bonds easily result in Sb, and especially Bi, being irreversibly reduced or oxidized to insoluble heterogeneous materials. As a result, there is a substantial gap in the literature concerning the structural characterization of redox-active or Lewis acidic bismuth compounds compared to those of the lighter pnictogen elements. However, harnessing this unusual behavior can result bonding and reactivity patterns that are important for the activation of chemical bonds. Bismuth has come to the forefront due to its non-toxic nature, advances in bonding models, and newfound ability to participate in catalysis. Recently, our laboratory prepared the first example of a two-coordinate carbene-bismuthinidene (CAAC-BiPh, CAAC = cyclic(alkyl)(amino) carbene). However, this required an unusual beryllium(0) reduction strategy and CAAC-BiPh was still extremely reactive. This led us to explore the use of carbones as a ligand in heavy pnictenium ion chemistry, which resulted in the structural characterization of a series of carbone-stibenium and bismuthenium ions. This presentation will highlight our most results in this area, including an assessment of their Lewis acidity using the Guttmann-Beckett method.

Taming reactive heavy pnictogen species: Carbones as a molecular platform for the stabilization of stibenium and bismuthenium ions

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ACS Fall 2022

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