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

Abstract

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-(NtBu) 2 Ge II (Xant)Ge II (NtBu) 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.

The Chlorido-Bismuth Dication: A Potent Lewis Acid Captured in a Hepta-Coordinate Species with a Stereochemically Active Lone Pair

“…A fascinating field of study in the chemistry of Group 15 elements, focusing on bonding and reactivity, revolves around cationic compounds with unusual coordination numbers . It allows exploring the boundaries of coordination chemistry of this class of compounds and has uncovered unexpected properties and reactivity patterns.…”

“…A fascinating field of study in the chemistry of Group 15 elements, focusing on bonding and reactivity, revolves around cationic compounds with unusual coordination numbers. 1 It allows exploring the boundaries of coordination chemistry of this class of compounds and has uncovered unexpected properties and reactivity patterns. Examples include the isolation of species in unusual oxidation states, 2 the exploration of strongly Lewis acidic complexes, 1f , 3 new structural motifs, 4 small molecule activation, 5 polymer functionalization, 6 and catalytic applications.…”

A trimetallic bismuth-based allyl cation

“…21 Recently, the group of Driess and Frenking developed a similar structure with germylenes as supporting ligands. 22 For many years, overlapping of large and diffused orbitals leading to chemical bonding between 5p and 6p orbitals was regarded as a challenge in organometallic chemistry. 23,24 However, this canonical notion has recently been challenged with several examples of heavy main group elements (HMGE) that form double and triple bonds akin the lightest main group elements.…”