Carbodicarbene Bismaalkene Cations: Unravelling the Complexities of Carbene versus Carbone in Heavy Pnictogen Chemistry

Abstract

We report a combined experimental and theoretical study on the first examples of carbodicarbene (CDC)‐stabilized bismuth complexes, which feature low‐coordinate cationic bismuth centers with C=Bi multiple‐bond character. Monocations [(CDC)Bi(Ph)Cl][SbF6] (8) and [(CDC)BiBr2(THF)2][SbF6] (11), dications [(CDC)Bi(Ph)][SbF6]2 (9) and [(CDC)BiBr(THF)3][NTf2]2 (12), and trication [(CDC)2Bi][NTf2]3 (13) have been synthesized via sequential halide abstractions from (CDC)Bi(Ph)Cl2 (7) and (CDC)BiBr3 (10). Notably, the dications and trication exhibit C⇉ Bi double dative bonds and thus represent unprecedented bismaalkene cations. The synthesis of these species highlights a unique non‐reductive route to C−Bi π‐bonding character. The CDC‐[Bi] complexes (7–13) were compared with related NHC‐[Bi] complexes (1, 3–6) and show substantially different structural properties. Indeed, the CDC ligand has a remarkable influence on the overall stability of the resulting low‐coordinate Bi complexes, suggesting that CDC is a superior ligand to NHC in heavy pnictogen chemistry.

Indirect Access to Carbene Adducts of Bismuth- and Antimony-Substituted Phosphaketene and Their Unusual Thermal Transformation to Dipnictines and [(NHC)2OCP][OCP]

“…The C1–Sb1 bond distance in compound 1 [2.356(3) Å] is outside the range of other NHC C–Sb bonds (2.144–2.268 Å); 16o , 16q , 16r , 17 likewise, the C1–Bi1 bond in compound 2 [2.489(6)] is slightly longer than the known range for NHC C–Bi bonds (2.339–2.428 Å). 17b , 18 The Pn–Cl bond lengths in 1 (2.8006(8) Å) and 2 (2.8696(16) Å) are also significantly longer than those in reported complexes containing Sb–Cl (2.332–2.402 Å) 17a − 17c and Bi–Cl (2.437–2.705 Å) 18a , 18b bonds. The longer NHC C–Pn bonds results from the weak Lewis acidity of Ph 2 PnCl compared to PhBiCl 2 and BiCl 3 .…”

Charge Makes a Difference: Molecular Ionic Bismuth Compounds

“…They are characterized by high coordination numbers. Typically, five primary metal‐ligand‐interactions are observed (Scheme 15a) [37, 38, 48, 49, 63] . This results in a (distorted) square pyramidal coordination geometry, which has previously been interpreted as a hint towards the presence of a stereochemically active lone pair [48] .…”

“…ligands that contain CH bonds) has originally been focused on cationic bismuth(III) (and to a lesser extent bismuth(V)) compounds bearing aryl ligands. Recent developments in synthetic chemistry have granted access to compounds with other classical ligands (alkyl, allyl, silyl, aminyl), [32–35] species with higher charges, [36–38] and with new ligand sets such as β‐diketiminato‐supported gallyl moieties [39] . In addition, first glances at well‐defined low‐valent bismuth compounds bearing charges have been reported [39, 40] …”

“…Early examples of dicationic bismuth(III) compounds that were accessed via salt elimination protocols faced the problem of ligand redistribution reactions (3 [BiR] 2+ ⇌ 2 [Bi] 3+ +BiR 3 and the like) [48] or led to compounds with significant Bi‐counteranion interactions (for anions such as carbonate, sulfate, and nitrate) [49] . These challenges have been met by the use of chelating ligands, bulky ligands with π‐donating abilities, and weakly coordinating anions [36–38, 51] . Very recently, the reversible protonation of a dianionic ligand at its carbodiphosphorane functional group has been reported as a new access to cationic bismuth compounds [64] …”

Bismuth Cations: Fluoride Ion Abstraction, Isocyanide Coordination, and Impact of Steric Bulk on Lewis Acidity

“…These findings initiated investigations towards a more detailed understanding of bismuth‐based Lewis acidity. As a result, the ability of bismuth(III) species to adopt formal charges ranging from +1 to +3, [1,9,13,14,16] to bear multiple Lewis acidic binding sites that can reversibly be occupied by Lewis bases, [13] and to act as exceptionally strong and soft Lewis acids has been uncovered [17] . Smart ligand design including the use of chelating ligands and the control of the ligand bite angle can be exploited to significantly increase the Lewis acidity of bismuth cations [18,19] .…”