Zwitterionic Relatives of Cationic Platinum Group Metal Complexes: Applications in Stoichiometric and Catalytic σ‐Bond Activation

Abstract

Zwitterionic platinum group metal complexes that feature formal charge separation between a cationic metal fragment and a negatively charged ancillary ligand combine the desirable reactivity profile of related cationic complexes with the broad solubility and solvent tolerance of neutral species. As such, zwitterionic complexes of this type have emerged as attractive candidates for a diversity of applications, most notably involving the breaking and/or forming of E-H and E-C sigma bonds involving a main group element E. Important advances in ancillary ligand design are documented that have enabled the construction of platinum group metal zwitterions. Also summarized are the results of stoichiometric and catalytic investigations in which the reactivity of such zwitterions and their more traditionally employed cationic relatives in sigma bond activation chemistry are compared and contrasted.

Zwitterionic Rhodium and Iridium Complexes Based on a Carboxylate Bridge-Functionalized Bis-N-heterocyclic Carbene Ligand: Synthesis, Structure, Dynamic Behavior, and Reactivity

“…In addition, the cod ligand exhibits two well separate resonances for the =CH olefin protons at δ 6.03 and 5.22 ppm, also largely downfield shifted compared to that of 13, as a consequence of the oxidation of the iridium centre. Similarly to compound 18, the equivalent C NCN carbon atoms were observed at δ 147.3 ppm in the 13 (20) was isolated as a yellow solid in 87% yield (Scheme 7). The ionic character of the compound was established by conductivity measurement, that lies in the expected range for a 1:1 electrolyte (84.7 Ω -1 ·cm 2 ·mol -1 , methanol), and the ESI+ mass spectra that showed a peak at m/z 647.0 with the expected isotopic distribution for the cation [IrI(cod){(MeIm) 2 CHCOO}] + .…”

“…Calc. for C 20 (7). CF 3 SO 3 Me (16.0 µL,  = 1.45 g·mL -1 , 0.141 mmol) was added to a solution of [Cp*RhCl{(MeIm) 2 CHCOO}] (3) (63.1 mg, 0.128 mmol) in CH 2 Cl 2 (5 mL).…”

“…Notably, the rigid structure of the latter prevents unwanted ion-pairing between the metal and the remote anionic moiety, and provides an easy access to the corresponding zwitterionic metal complexes that are generally water soluble and therefore particularly attractive in catalysis. 20,21 Chart 1. Selected functionalized bis-NHC ligands based on imidazole units and other ditopic NHCs.…”

An Unusual Organoyttrium Alkyl Complex Containing a [C5HMe3(η3‐CH2)‐C5H4N‐κ]− Ligand and an Elusive Cyclopentadienide‐Based Scandium Tuck‐Over Zwitterion Obtained by CH Bond Activation

“…On the other hand, zwitterionic metal complexes featuring formal charge separation between cationic metal fragments and anionic ancillary ligands, which possess the desirable reactivities of the cationic complexes and comparably high solubilities and solvent tolerances of the neutral species, have been exploited widely. [8] Numerous efforts have been made to obtain carbanion-based (such as indenide and tris(pyrazolyl)methanide) zwitterionic complexes, which have exhibited new reactivity patterns and have emerged as attractive candidates for a variety of applications. [9] However, the synthesis of carbanion-based zwitterionic metal com-…”

A New Approach to Non-Coordinating Anions: Lewis Acid Enhancement of Porphyrin Metal Centers in a Zwitterionic Metal–Organic Framework

“…Another attractive approach involves the use of zwitterionic metal complexes, in which a cationic metal fragment and a negatively charged ancillary ligand are covalently bonded together to achieve a formal charge separation . The internal charge neutralization and tunable electrophilicity of zwitterionic metal complexes have been particularly appealing for a variety of catalytic reactivity studies …”