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

The formation of isolable monatomic BiI complexes and BiII radical species is challenging due to the pronounced reducing nature of metallic bismuth. Here, we report a convenient strategy to tame BiI and BiII atoms by taking advantage of the redox noninnocent character of a new chelating bis(germylene) ligand. The remarkably stable novel BiI cation complex 4 , supported by the new bis(iminophosphonamido-germylene)xanthene ligand [(P)GeII (Xant)GeII (P)] 1 , [(P)GeII (Xant)GeII (P) = Ph2 P(N t Bu)2 GeII (Xant)GeII (N t Bu)2 PPh2 , Xant = 9,9-dimethyl-xanthene-4,5-diyl], was synthesized by a two-electron reduction of the cationic BiIII I2 precursor complex 3 with cobaltocene (Cp2 Co) in a molar ratio of 1:2. Notably, owing to the redox noninnocent character of the germylene moieties, the positive charge of BiI cation 4 migrates to one of the Ge atoms in the bis(germylene) ligand, giving rise to a germylium(germylene) BiI complex as suggested by DFT calculations and X-ray photoelectron spectroscopy (XPS). Likewise, migration of the positive charge of the BiIII I2 cation of 3 results in a bis(germylium)BiIII I2 complex. The delocalization of the positive charge in the ligand engenders a much higher stability of the BiI cation 4 in comparison to an isoelectronic two-coordinate Pb0 analogue (plumbylone; decomposition below -30 °C). Interestingly, 4 [BArF ] undergoes a reversible single-electron transfer (SET) reaction (oxidation) to afford the isolable BiII radical complex 5 in 5 [BArF ]2 . According to electron paramagnetic resonance (EPR) spectroscopy, the unpaired electron predominantly resides at the BiII atom. Extending the redox reactivity of 4 [OTf] employing AgOTf and MeOTf affords BiIII (OTf)2 complex 7 and BiIII Me complex 8 , respectively, demonstrating the high nucleophilic character of BiI cation 4 .