Two‐Electron Redox Chemistry and Reversible Umpolung of a Gold–Antimony Bond

Abstract

Two-electron redox processes occurring at the core of dinuclear metal complexes are important because of their implication in a number of chemical transformations ranging from the photocatalytic production of dihydrogen [1] to the oxidative functionalization of CÀH bonds.[2] Two-electron redox processes are also well documented for binuclear gold complexes [3] as well as for gold/rhodium, [4] gold/iridium [5] and gold/platinum [6] heterobimetallic complexes. One of the common features displayed by all of these complexes relates to their ability to sustain two-electron redox chemistry without decomposition of the bimetallic core. As part of our interest in fundamental aspects of main-group chemistry, we have recently questioned whether similar processes could also be observed at the bimetallic core of main-group/transitionmetal complexes.Triarylstibines are soft s-donor ligands which have been incorporated in a variety of late transition-metal complexes. [7] They are also well known to undergo facile two-electron oxidation when exposed to oxidizing agents such as halogens.[8] While there is precedent for dialkylstibido transitionmetal compounds (type A) to undergo oxidative addition at the antimony center, [9] no analogous reactivity has been reported for stibine metal complexes of type B. With the discovery of main-group-based, two-electron redox platforms in mind, we have now decided to study the synthesis and oxidation of complexes of type B. Herein, we report the first incarnation of this idea in the case of a gold-antimony compound.To prevent dissociation of the gold-antimony bimetallic core upon oxidation, we chose to work with a stibine ligand whose interaction with the gold center would be supported by pendant donor ligands. These considerations led us to focus on the triphosphanylstibine ligand [(o-(Ph 2 P)C 6 H 4 ) 3 Sb] (referred to as L) [10] which was allowed to react with [AuCl(tht)] in CH 2 Cl 2 /acetone to produce 1-Cl as a pale yellow precipitate (Scheme 1). At À55 8C in CDCl 3 , the 31 P{ 1 H} NMR spectrum of 1-Cl displays two signals at d = + 39.5 and À7.4 ppm in a 2:1 intensity ratio thus suggesting that only two of the three phosphine arms of the ligand are coordinated to the gold atom. Upon elevation of the temperature, these two peaks coalesce into one signal at d = + 24.4 ppm indicating the onset of a rapid exchange. Line shape analysis of the 31 P{ 1 H} NMR spectra of 1-Cl over the À55 8C-+ 22 8C temperature range followed by an Eyring analysis afforded DH°= + 16.7 (AE 0.9) kcal mol À1 and DS°= + 16.6(AE3.8) cal mol À11 K À11 , suggesting a dissociative exchange of the phosphine arms. The ESI mass spectrum of this complex shows a peak at m/z 1101.1180 amu corresponding to the [LAu] + ion. A final clarification of the structure of this compound was derived from a single-crystal diffraction study which confirmed the coordination of two of the phosphorus atoms to the gold chloride fragment (Figure 1).[11] Inspection of the P-Au-P and P-Au-Cl angles (AE = 359.468) shows that these prim...

Chemistry of Stannylene‐Based Lewis Pairs: Dynamic Tin Coordination Switching Between Donor and Acceptor Character

“…Furthermore, we are of the opinion that the NMR spectroscopic findings, especially in the 119 Sn NMR spectra of the nickel complexes, support this interpretation of the switching nickel–tin interaction: Whereas the chemical shifts of 9 ( δ =660 ppm) and 10 ( δ =671 ppm) are in the same shift range of 2 ( δ =554 ppm) and therefore consistent with tin as acceptor, changing to a donating tin goes along with a lowfield shift of almost δ =500 ppm for 7 ( δ =1041 ppm) and 8 ( δ =1053 ppm; Table 2). A comparable but redox‐driven switch of an AuSb interaction was published by Wade and Gabbai 29…”

An Antimony(V) Dication as a Z‐Type Ligand: Turning on Styrene Activation at Gold

“…As an entry point for the synthesis of ac omplex of type VI,w ec onsidered 1,aknown gold complex which features aphosphino arm free of metal coordination. [11] To test if this unit could be converted into the corresponding phosphine oxide,c omplex 1 was combined with one equivalent of hydrogen peroxide (Scheme 1). This reaction afforded complex [2a] [Cl] as an air-stable solid, the crystal structure of which (vide infra) confirmed the successful conversion of one of the three phosphino arms of the ligand into ap hosphine oxide.This complex has also been characterized by elemental analysis and 31 PM AS NMR spectroscopy.T he latter shows two signals at 60.2 ppm and 41.6 ppm.…”

Expansion of the (BB)Ru metallacycle with coinage metal cations: formation of B–M–Ru–B (M = Cu, Ag, Au) dimetalacyclodiboryls

“…Similarly to the copper coordination environment in 2-Cu , the Au(Cl) 2 (B)(Ru) moiety in 2-Au exhibits four-coordinate planar configuration that is unusual for Au( i ) 104 – 106 with slight distortion ( τ 4 = 0.11) as indicated by nearly linear Ru1–Au1–Cl1A and B2–Au1–Cl1 angles (167.5(1)° and 177.5(1)°, respectively).…”