Stabilizing Monoatomic Two-Coordinate Bismuth(I) and Bismuth(II) Using a Redox Noninnocent Bis(germylene) Ligand
Jian Xu, Sudip Pan, Shenglai Yao, Christian Lorent, Christian Teutloff, Zhaoyin Zhang, Jun Fan, Andrew Molino, Konstantin B. Krause, Johannes Schmidt, Robert Bittl, Christian Limberg, Lili Zhao, Gernot Frenking, Matthias Drieß
Abstract
High Resolution Image Download MS PowerPoint Slide The formation of isolable monatomic Bi I complexes and Bi II radical species is challenging due to the pronounced reducing nature of metallic bismuth. Here, we report a convenient strategy to tame Bi I and Bi II atoms by taking advantage of the redox noninnocent character of a new chelating bis(germylene) ligand. The remarkably stable novel Bi I cation complex 4, supported by the new bis(iminophosphonamido-germylene)xanthene ligand [(P)Ge II (Xant)Ge II (P)] 1, [(P)Ge II (Xant)Ge II (P) = Ph 2 P(N t Bu) 2 Ge II (Xant)Ge II (N t Bu) 2 PPh 2, Xant = 9,9-dimethyl-xanthene-4,5-diyl], was synthesized by a two-electron reduction of the cationic Bi III I 2 precursor complex 3 with cobaltocene (Cp 2 Co) in a molar ratio of 1:2. Notably, owing to the redox noninnocent character of the germylene moieties, the positive charge of Bi I cation 4 migrates to one of the Ge atoms in the bis(germylene) ligand, giving rise to a germylium(germylene) Bi I complex as suggested by DFT calculations and X-ray photoelectron spectroscopy (XPS). Likewise, migration of the positive charge of the Bi III I 2 cation of 3 results in a bis(germylium)Bi III I 2 complex. The delocalization of the positive charge in the ligand engenders a much higher stability of the Bi I cation 4 in comparison to an isoelectronic two-coordinate Pb 0 analogue (plumbylone; decomposition below −30 °C). Interestingly, 4 [BAr F ] undergoes a reversible single-electron transfer (SET) reaction (oxidation) to afford the isolable Bi II radical complex 5 in 5 [BAr F ] 2 . According to electron paramagnetic resonance (EPR) spectroscopy, the unpaired electron predominantly resides at the Bi II atom. Extending the redox reactivity of 4 [OTf] employing AgOTf and MeOTf affords Bi III (OTf) 2 complex 7 and Bi III Me complex 8, respectively, demonstrating the high nucleophilic character of Bi I cation 4 .