Stabilizing Monoatomic Two-Coordinate Bismuth(I) and Bismuth(II) Using a Redox Noninnocent Bis(germylene) Ligand.

The formation of isolable monatomic Bi complexes and Bi radical species is challenging due to the pronounced reducing nature of metallic bismuth. Here, we report a convenient strategy to tame Bi and Bi atoms by taking advantage of the redox noninnocent character of a new chelating bis(germylene) ligand. The remarkably stable novel Bi cation complex , supported by the new bis(iminophosphonamido-germylene)xanthene ligand [(P)Ge(Xant)Ge(P)] , [(P)Ge(Xant)Ge(P) = PhP(NBu)Ge(Xant)Ge(NBu)PPh, Xant = 9,9-dimethyl-xanthene-4,5-diyl], was synthesized by a two-electron reduction of the cationic BiI precursor complex with cobaltocene (CpCo) in a molar ratio of 1:2. Notably, owing to the redox noninnocent character of the germylene moieties, the positive charge of Bi cation migrates to one of the Ge atoms in the bis(germylene) ligand, giving rise to a germylium(germylene) Bi complex as suggested by DFT calculations and X-ray photoelectron spectroscopy (XPS). Likewise, migration of the positive charge of the BiI cation of results in a bis(germylium)BiI complex. The delocalization of the positive charge in the ligand engenders a much higher stability of the Bi cation in comparison to an isoelectronic two-coordinate Pb analogue (plumbylone; decomposition below -30 °C). Interestingly, [BAr] undergoes a reversible single-electron transfer (SET) reaction (oxidation) to afford the isolable Bi radical complex in [BAr]. According to electron paramagnetic resonance (EPR) spectroscopy, the unpaired electron predominantly resides at the Bi atom. Extending the redox reactivity of [OTf] employing AgOTf and MeOTf affords Bi(OTf) complex and BiMe complex , respectively, demonstrating the high nucleophilic character of Bi cation .