Oxidative Addition of CH₃I to Au^– in the Gas Phase

Reaction of the atomic gold anion (Au^–) with CH₃I under high-pressure helium gas affords the adduct AuCH₃I^–. Photoelectron spectroscopy and density functional theory calculations reveal that in the AuCH₃I^– structure the I and CH₃ fragments of CH₃I are bonded to Au in a linear configuration, which can be viewed as an oxidative addition product. Theoretical studies indicate that oxidative addition proceeds in two steps: nucleophilic attack of Au^– on CH₃I, followed by migration of the leaving I^– to Au. This mechanism is supported by the formation of an ion-neutral complex, [Au^–···<i>t</i>-C₄H₉I], in the reaction of Au^– with <i>t</i>-C₄H₉I because of the activation barrier along the S_N2 pathway resulting from steric effects. Theoretical studies are conducted for the formation mechanism of AuI₂^–, which is observed as a major product. From the thermodynamic and kinetic viewpoints, we propose that AuI₂^– is formed via sequential oxidative addition of two CH₃I molecules to Au^–, followed by reductive elimination of C₂H₆. The results suggest that Au^– acts as a nucleophile to activate C­(sp³)–I bond of CH₃I and induces the C–C coupling reaction of CH₃I

Hydride-Doped Gold Superatom (Au₉H)²⁺: Synthesis, Structure, and Transformation

Doping of a hydride (H^–) into an oblate-shaped gold cluster [Au₉(PPh₃)₈]³⁺ was observed for the first time by mass spectrometry and NMR spectroscopy. Density functional theory calculations for the product [Au₉H­(PPh₃)₈]²⁺ demonstrated that the (Au₉H)²⁺ core can be viewed as a nearly spherical superatom with a closed electronic shell. The hydride-doped superatom (Au₉H)²⁺ was successfully converted to the well-known superatom Au₁₁³⁺, providing a new atomically precise synthesis of Au clusters via a bottom-up approach

Photoassisted Homocoupling of Methyl Iodide Mediated by Atomic Gold in Low-Temperature Neon Matrix

Infrared spectroscopy and density functional theory calculations showed that the gold complexes [CH₃–Au–I] and [(CH₃)₂–Au–I₂], in which one and two CH₃I molecule(s), respectively, are oxidatively adsorbed on the Au atoms, are formed in a solid neon matrix via reactions between laser-ablated gold atoms and CH₃I. Global reaction route mapping calculations revealed that the heights of the activation barriers for the sequential oxidative additions to produce [CH₃–Au–I] and [(CH₃)₂–Au–I₂] are 0.53 and 1.00 eV, respectively, suggesting that the reactions proceed via electronically excited states. The reductive elimination of ethane (C₂H₆) from [(CH₃)₂–Au–I₂] leaving AuI₂ was hindered by an activation barrier as high as 1.22 eV but was induced by visible-light irradiation on [(CH₃)₂–Au–I₂]. These results demonstrate that photoassisted homocoupling of CH₃I is mediated by Au atoms via [(CH₃)₂–Au–I₂] as an intermediate

Collision-Induced Fission of Oblate Gold Superatom in [Au₉(PPh₃)₈]³⁺: Deformation-Mediated Mechanism

Collision-induced dissociation (CID) patterns of the phosphine-protected Au-based clusters [PdAu8(PPh3)8]2+ (PdAu8) and [Au9(PPh3)8]3+ (Au9), featuring crown-shaped M@Au8 (M = Pd, Au) cores, were investigated. For PdAu8, ordinary sequential PPh3 losses (PdAu8 → [PdAu8(PPh3)m]2+ + (8 – m)PPh3 (m = 7, 6, 5)) were observed. In contrast, Au9 underwent cluster-core fission (Au9 → [Au6(PPh3)6]2+ (Au6) + [Au3(PPh3)2]+ (Au3)) upon sufficiently high energy collision, associated with splitting the number of valence electrons in the superatomic orbitals from 6e (Au9) into 4e (Au6) and 2e (Au3). Density functional theory calculations revealed oblate and prolate cores of Au9 and Au6 with semiclosed superatomic electron configurations of (1S)2(1Px)2(1Py)2 and (1S)2(1Pz)2, respectively. This result indicated a significant deformation of the cluster-core motif during the CID process. We attribute the clear difference between PdAu8 and Au9 to the softer Au–Au bond in Au9 and propose that the collision-induced structural deformation plays a critical role in the fission

Collision-Induced Fission of Oblate Gold Superatom in [Au₉(PPh₃)₈]³⁺: Deformation-Mediated Mechanism

Collision-induced dissociation (CID) patterns of the phosphine-protected Au-based clusters [PdAu8(PPh3)8]2+ (PdAu8) and [Au9(PPh3)8]3+ (Au9), featuring crown-shaped M@Au8 (M = Pd, Au) cores, were investigated. For PdAu8, ordinary sequential PPh3 losses (PdAu8 → [PdAu8(PPh3)m]2+ + (8 – m)PPh3 (m = 7, 6, 5)) were observed. In contrast, Au9 underwent cluster-core fission (Au9 → [Au6(PPh3)6]2+ (Au6) + [Au3(PPh3)2]+ (Au3)) upon sufficiently high energy collision, associated with splitting the number of valence electrons in the superatomic orbitals from 6e (Au9) into 4e (Au6) and 2e (Au3). Density functional theory calculations revealed oblate and prolate cores of Au9 and Au6 with semiclosed superatomic electron configurations of (1S)2(1Px)2(1Py)2 and (1S)2(1Pz)2, respectively. This result indicated a significant deformation of the cluster-core motif during the CID process. We attribute the clear difference between PdAu8 and Au9 to the softer Au–Au bond in Au9 and propose that the collision-induced structural deformation plays a critical role in the fission

Suppressing Isomerization of Phosphine-Protected Au₉ Cluster by Bond Stiffening Induced by a Single Pd Atom Substitution

The fluxional nature of small gold clusters has been exemplified by reversible isomerization between [Au₉(PPh₃)₈]³⁺ with a crown motif (<b>Au</b>_<b>9</b>(C)) and that with a butterfly motif (<b>Au</b>_<b>9</b>(B)) induced by association and dissociation with compact counteranions (NO₃^–, Cl^–). However, structural isomerization was suppressed by substitution of the central Au atom of the Au₉ core in [Au₉(PPh₃)₈]³⁺ with a Pd atom: [PdAu₈­(PPh₃)₈]²⁺ with a crown motif (<b>PdAu</b>_<b>8</b>(C)) did not isomerize to that with a butterfly motif (<b>PdAu</b>_<b>8</b>(B)) upon association with the counteranions. Density functional theory calculation showed that the energy difference between <b>PdAu</b>_<b>8</b>(C) and <b>PdAu</b>_<b>8</b>(B) is comparable to that between <b>Au</b>_<b>9</b>(C) and <b>Au</b>_<b>9</b>(B), indicating that the relative stabilities of the isomers are not a direct cause for the suppression of isomerization. Temperature dependence of Debye–Waller factors obtained by X-ray absorption fine-structure analysis revealed that the intracluster bonds of <b>PdAu</b>_<b>8</b>(C) were stiffer than the corresponding bonds in <b>Au</b>_<b>9</b>(C). Natural bond orbital analysis suggested that the radial Pd–Au and lateral Au–Au bonds in <b>PdAu</b>_<b>8</b>(C) are stiffened due to the increase in the ionic nature and decrease in electrostatic repulsion between the surface Au atoms, respectively. We conclude that the formation of stiffer metal–metal bonds by Pd atom doping inhibits the isomerization from <b>PdAu</b>_<b>8</b>(C) to <b>PdAu</b>_<b>8</b>(B)