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.     

Fast Oxygen Reduction Catalyzed by a Copper(II) Tris(2‐pyridylmethyl)amine Complex through a Stepwise Mechanism

Catalytic pathways for the reduction of dioxygen can either lead to the formation of water or peroxide as the reaction product. We demonstrate that the electrocatalytic reduction of O₂ by the pyridylalkylamine copper complex [Cu(tmpa)(L)]²⁺ in a neutral aqueous solution follows a stepwise 4 e^?/4 H⁺ pathway, in which H₂O₂ is formed as a detectable intermediate and subsequently reduced to H₂O in two separate catalytic reactions. These homogeneous catalytic reactions are shown to be first order in catalyst. Coordination of O₂ to Cu^I was found to be the rate‐determining step in the formation of the peroxide intermediate. Furthermore, electrochemical studies of the reaction kinetics revealed a high turnover frequency of 1.5×10⁵ s^?1, the highest reported for any molecular copper catalyst.     

Spectroscopic Evidence for a Monomeric Copper(I) Hydride and Crystallographic Characterization of a Monomeric Silver(I) Hydride

(1,3‐bis[2,6‐bis[di(4‐tert‐butylphenyl)methyl]‐4‐methylphenyl]imidazol‐2‐ylidene)CuOPh [(IPr**)CuOPh] reacts with poly(methylhydrosiloxane) as the hydride donor to afford the monomeric (IPr**)CuH complex, which was spectroscopically characterized. The latter is in equilibrium in solution with [(IPr**)CuH]₂, the dimer being exclusively present in the solid state. These results support the hypothesis that copper hydride aggregates dissociate in solution. In contrast, addition of pinacolborane to [(IPr**)AgOPh] at −40 °C allows the isolation of the monomeric (IPr**)AgH complex, which was crystallographically characterized.     

Temperature‐Mediated Template Release: Facile Growth of Copper(I) Mixed Ethynediide/Isopropylethynide Nanoclusters

In the comproportionation reaction of Cu^IIX₂ and Cu⁰ with isopropylacetylene (iPr−C≡C−H), the ethynediide species C₂²⁻ is generated via concomitant C−H/C−C bond cleavage of the iPr−C≡C−H precursor under moderate temperature to direct the formation of Cu^I mixed ethynediide/isopropylethynide nanoclusters (potentially explosive). The active ethynediide dianion C₂²⁻ exhibits chameleon‐like templating behavior to form C₂@Cu_m (m =6 ( 3 , 4 ), 7 ( 2 , 4 ), 8 ( 1 )) central structural units for successive formation of {C₂²⁻⊂Cu₂₄} ( 1 , 2 ), {6 C₂²⁻⊂Cu₄₈} ( 3 ), and {18 C₂²⁻⊂Cu₉₂} ( 4 ) complexes. Bearing the highest C₂²⁻ content, complex 4 features an unprecedented nanoscale Cu₂C₂ kernel. Furthermore, 1 – 3 exhibit structure‐controlled photoluminescence in the solid state.     

From Cluster to Polymer: Ligand Cone Angle Controlled Syntheses and Structures of Copper(I) Alkynyl Complexes

Copper(I) alkynyl complexes have attracted tremendous attention in structural studies, as luminescent materials, and in catalysis, and homoleptic complexes have been reported to form polymers or large clusters. Herein, six unprecedented structures of Cu^I alkynyl complexes and a procedure to measure the cone angles of alkynyl ligands based on the crystal structures of these complexes are reported. An increase of the alkynyl cone angle in the complexes leads to a modulation of the structures from polymeric [((PhC≡CC≡C)Cu)₂(NH₃)]_∞, to a large cluster [(TripC≡CC≡C)Cu]₂₀(MeCN)₄, to a relatively small cluster [(TripC≡C)Cu]₈ (Trip=2,4,6‐iPr₃‐C₆H₂). The complexes exhibit yellow‐to‐red phosphorescence at ambient temperature in the solid state and the luminescence behavior of the Cu₂₀ cluster is sensitive to acetonitrile.     

Resolution of Stepwise Cooperativities of Copper Binding by the Homotetrameric Copper‐Sensitive Operon Repressor (CsoR): Impact on Structure and Stability

The cooperativity of ligand binding is central to biological regulation and new approaches are needed to quantify these allosteric relationships. Herein, we exploit a suite of mass spectrometry (MS) experiments to provide novel insights into homotropic Cu‐binding cooperativity, gas‐phase stabilities and conformational ensembles of the D₂‐symmetric, homotetrameric copper‐sensitive operon repressor (CsoR) as a function of Cu^I ligation state. Cu^I binding is overall positively cooperative, but is characterized by distinct ligation state‐specific cooperativities. Structural transitions occur upon binding the first and fourth Cu^I, with the latter occurring with significantly higher cooperativity than previous steps; this results in the formation of a holo‐tetramer that is markedly more resistant than apo‐, and partially ligated CsoR tetramers toward surface‐induced dissociation (SID).     

An All‐Alkynyl Protected 74‐Nuclei Silver(I)–Copper(I)‐Oxo Nanocluster: Oxo‐Induced Hierarchical Bimetal Aggregation and Anisotropic Surface Ligand Orientation

The hardness of oxo ions (O^2?) means that coinage‐metal (Cu, Ag, Au) clusters supported by oxo ions (O^2?) are rare. Herein, a novel μ₄‐oxo supported all‐alkynyl‐protected silver(I)–copper(I) nanocluster [Ag_74?xCu_xO₁₂(PhC≡C)₅₀] ( NC‐1 , avg. x=37.9) is characterized. NC‐1 is the highest nuclearity silver–copper heterometallic cluster and contains an unprecedented twelve interstitial μ₄‐oxo ions. The oxo ions originate from the reduction of nitrate ions by NaBH₄. The oxo ions induce the hierarchical aggregation of Cu^I and Ag^I ions in the cluster, forming the unique regioselective distribution of two different metal ions. The anisotropic ligand coverage on the surface is caused by the jigsaw‐puzzle‐like cluster packing incorporating rare intermolecular C?H???metal agostic interactions and solvent molecules. This work not only reveals a new category of high‐nuclearity coinage‐metal clusters but shows the special clustering effect of oxo ions in the assembly of coinage‐metal clusters.     

Construction of Chiral 2,3-Allenols through a Copper(I)-Catalyzed Asymmetric Direct Alkynylogous Aldol Reaction

Chiral 2,3-allenols were constructed through copper(I)-catalyzed asymmetric direct alkynylogous aldol reaction. With aromatic and heteroaromatic aldehydes, the alkynylogous aldol reaction with (R)-DTBM-SEGPHOS as the ligand proceeded smoothly to furnish the products in excellent regioselectivity with good to high diastereoselectivity and excellent enantioselectivity. In the cases of aliphatic aldehydes, esters of but-2-yn-1-ol as the substrates and (R,R)-Ph-BPE as the ligand were found to be crucial to get good to high regio- and diastereoselectivity. The produced chiral 2,3-allenols are easily transformed into synthetically useful 2-furanones through cyclization. Finally, the developed method was successfully applied in the rapid synthesis of two chiral intermediates toward the synthesis of two pharmaceutically active compounds that have been proposed for the treatment of neurological disorders.