NHC‐Coordinated Diphosphene‐Stabilized Gold(I) Hydride and Its Reversible Conversion to Gold(I) Formate with CO2

An NHC‐coordinated diphosphene is employed as ligand for the synthesis of a hydrocarbon‐soluble monomeric Au^I hydride, which readily adds CO₂ at room temperature yielding the corresponding Au^I formate. The reversible reaction can be expedited by the addition of NHC, which induces β‐hydride shift and the removal of CO₂ from equilibrium through the formation of an NHC‐CO₂ adduct. The Au^I formate is alternatively formed by dehydrogenative coupling of the Au^I hydride with formic acid (HCO₂H), thus in total establishing a reaction sequence for the Au^I hydride mediated dehydrogenation of HCO₂H as chemical hydrogen storage material.     

Air‐Stable Cationic Gold(I) Catalyst Featuring a Z‐Type Ligand: Promoting Enyne Cyclizations

An air‐stable cationic Au^I complex featuring a Z‐type ligand (boron atom) as a σ‐acceptor was developed for elucidating the effect of B on catalytic reactions. An enyne cyclization in the presence of either [Au→B]⁺ or [Au]⁺ showed that [Au→B]⁺ promotes the reactivity, which enabled the effective construction of not only five‐ and six‐membered rings, but also seven‐membered rings.     

Isolation and Structural Determination of a Hexacoordinated Antimony(V) Dication

The hexacoordinated antimony(V) dication [(ppy)₃Sb]²⁺ ([ 1 ]²⁺; ppy=2-(2-pyridyl)phenyl), stabilized by three intramolecular donor–acceptor interactions, has been isolated as its hexachloroantimonate salt [ 1 ][SbCl₆]₂, prepared by the oxidative addition of chlorine to the neutral stibine [(ppy)₃Sb] ( 1 ), followed by the abstraction of chloride. Air-stable [ 1 ][SbCl₆]₂ exhibits remarkable thermal stability and the three ppy ligands on the antimony atom are shown to be magnetically inequivalent in the ¹H and ¹³C NMR spectra. A hexacoordinated, meridional octahedral bonding geometry has been determined for [ 1 ][SbCl₆]₂ by X-ray crystallographic analysis. Theoretical calculations were performed to investigate why the meridional form was generated preferentially over the facial form. In addition, the dynamics of the ppy ligands were investigated by variable-temperature ¹H NMR spectroscopy. The potential to generate dications by using a single-electron-transfer reagent has also been investigated. The dication [ 1 ]²⁺ is the first [12–Sb–6]²⁺ chemical species to have been structurally determined.     

Copper(I) and Gold(I) Complexes with N,N′‐Bis(diphenylphosphino)‐2,6‐diaminopyridine as Ligand: Synthesis and Molecular Structures

Reaction of CuI with 1 or 2 equivalent(s) N,N′‐Bis(diphenylphosphino)‐2,6‐diaminopyridine (BDDP) gives two different complexes, [Cu(I)μ‐(BDDP‐κP,N_py)]₂ ( 1 ) and [Cu(BDDP‐κP,N_py)₂]I ( 2 ), in high yields. The determination of the molecular structure show that both Cu^I atoms are tetrahedrally coordinated, rather than a square‐planar geometry reported for Cr⁰, Ni^II‐BDDP complexes before, which contains a planar tridentate chelate ring system. The introduction of AuCl(tht) (tht = tetrahydrothiophene) into [Cu(BDDP‐κP,N_py)₂]I leads unexpectedly to the formation of a digold complex 2,6‐[(ClAuPh₂P)HN]₂C₅H₃N and dimeric [Cu(I)μ‐(BDDP‐κP,N_py)]₂.     

Redox and Anion Exchange Chemistry of a Stibine–Nickel Complex: Writing the L,X, Z Ligand Alphabet with a Single Element

According to the covalent bond classification (CBC) method, two‐electron donors are defined as L‐type ligands, one‐electron donors as X‐type ligands, and two‐electron acceptors as Z‐type ligands. These three ligand functions are usually associated to the nature of the ligating atom, with phosphine, alkyl, and borane groups being prototypical examples of L‐, X‐ and Z‐ligands, respectively. A new SbNi platform is reported in which the ligating Sb atom can assume all three CBC ligand functions. Using both experimental and computational data, it is shown that PhICl₂ oxidation of (o‐(Ph₂P)C₆H₄)₃SbNi(PPh₃) ( 1 ) into [(o‐(Ph₂P)C₆H₄)₃ClSb]NiCl ( 2 ) is accompanied by a conversion of the stibine L‐type ligand of 1 into a stiboranyl X‐type ligand in 2 . Furthermore, the reaction of 2 with the catecholate dianion in the presence of cyclohexyl isocyanide results in the formation of [(o‐(Ph₂P)C₆H₄)₃(o‐O₂C₆H₄Sb)]Ni(CNCy) ( 4 ), a complex featuring a nickel atom coordinated by a Lewis acidic, Z‐type, stiborane ligand.     

Antimony Complexes for Electrocatalysis: Activity of a Main‐Group Element in Proton Reduction

Main‐group complexes are shown to be viable electrocatalysts for the H₂‐evolution reaction (HER) from acid. A series of antimony porphyrins with varying axial ligands were synthesized for electrocatalysis applications. The proton‐reduction catalytic properties of TPSb(OH)₂ (TP=5,10,15,20‐tetra(p ‐tolyl)porphyrin) with two axial hydroxy ligands were studied in detail, demonstrating catalytic H₂ production. Experiments, in conjunction with quantum chemistry calculations, show that the catalytic cycle is driven via the redox activity of both the porphyrin ligand and the Sb center. This study brings insight into main group catalysis and the role of redox‐active ligands during catalysis.