Isolable monoatomic monovalent bismuth complexes with a redox non-innocent bis-silylenyl carborane ligand

Abstract

Utilizing the chelating bis(silylenyl)carborane [Si^II(closo-CB)Si^II] (A, Si^II = PhC(NtBu)₂Si, CB = o-C₂B₁₀H₁₀) ligand, a series of unprecedented bis(silylene)-stabilized monovalent bismuth complexes {[Si^II(closo-CB)Si^II]Bi}X (X = I, 1a; X = OTf, 1b), {[Si^II(nido-CB)Si^II]Bi} (2) and ({[Si^II(nido-CB)Si^II]Bi}K(thf)₂)₂ ([3K(thf)₂]₂) were synthesized, isolated and characterized. The electronic structures of the bismuth complexes are significantly influenced by the redox-active nature of the CB scaffold. Remarkably, a one-electron injection to 1b with KC₈ does not furnish a Bi⁰ complex but reduction of the CB backbone giving rise to the neutral Bi^I radical complex 2. Notably, compound 1b can also undergo a two-electron reduction with two molar equiv. of potassium naphthalenide, resulting in the formation of the diamagnetic Bi^I anion complex 3 as a dimer bridged via two K(thf)₂ cations. Density functional theory calculations reveal that upon reduction from 1a to 2, and 2 to 3, the added electron predominantly localizes within the carborane cage, with a marked preference for the carbon atoms, ruling out that these species exhibit characteristics of a molecular bismuth(0) electride.