Experimental and Theoretical Evidence for an Agostic Interaction in a Gold(III) Complex

Recent Trends in Group 11 Hydrogen Bonding

Conventional hydrogen bonding (H-bonding) has been extensively studied in organic and biological systems. However, its role in transition metal chemistry, particularly with Group 11 metals (i. e. Cu, Ag, Au) as hydrogen bond acceptors, remains relatively unexplored. Through a combination of experimental techniques, such as Nuclear Magnetic Resonance (NMR), Infrared spectroscopy (IR), X-Ray Diffraction (XRD), and computational calculations, several aspects of H-bonding interactions with Group 11 metals are examined, shedding light on its impact on structural motifs and reactivity. These include bond strengths, geometries, and effects on electronic structures. Understanding the intricacies of hydrogen bonding within transition metal chemistry holds promise for various applications, including catalytic transformations, the construction of molecular assemblies, synthesis of complexes displaying anticancer activities, or luminescence applications (e. g. Thermally Activated Delayed Fluorescence, TADF). This review encompasses the most significant recent advances, challenges, and future prospects in this emerging field.

Catechol/o-benzoquinone exchange at gold(iii)

Although gold(iii) chemistry has tremendously progressed in the past 2 decades, gold(iii) catecholate complexes remain extremely scarce and underdeveloped. Upon preparation and full characterization of P^C-cyclometalated gold(iii) complexes, we serendipitously uncovered an intriguing catechol exchange process at gold(iii). Electron-rich catecholates turned out to be readily displaced by electron-poor o-benzoquinones. DFT calculations revealed an original path for this transformation involving two consecutive Single Electron Transfer events between the catecholate and o-benzoquinone moieties while gold maintains its +III oxidation state. This catechol/o-benzoquinone exchange at gold(iii) represents a new path for the exchange of X-type ligands at transition metals.

Stimulus-Responsive Copper Complex Nanoparticles Induce Cuproptosis for Augmented Cancer Immunotherapy

Cuproptosis, an emerging form of programmed cell death, has received tremendous attention in cancer therapy. However, the efficacy of cuproptosis remains limited by the poor delivery efficiency of copper ion carriers. Herein, copper complex nanoparticles (denoted as Cu(I) NP) are developed that can efficiently deliver copper complex into cancer cells to induce cuproptosis. Cu(I) NP demonstrate stimulus-responsive release of copper complexes, which results in mitochondrial dysfunction and promotes the aggregation of lipoylated dihydrolipoamide S-acetyltransferase (DLAT), leading to cuproptosis. Notably, Cu(I) NP not only induce cuproptosis, but also elicit robust immune responses to suppress tumor growth. Overall, this study provides a promising strategy for cuproptosis-based cancer therapy.

On the performance of the M-C (M = Fe, Ru, Os) unit toward methane activation

Gas-phase reactions of [MC]+ (M = Os and Ru) with methane at ambient temperature have been studied by using quadrupole-ion trap (Q-IT) mass spectrometry combined with quantum chemical calculations. Theoretical calculations reveal the influence of electronic signatures and that it is the energy gap of the associated frontier molecular orbitals that dominates the ability of the cluster in the initial H3C-H bond breaking. By extension, a theoretical consideration upon changing the ligand from carbide to carbyne and eventually to carbene reveals that the reactivities of the M-complex (M = Os, Ru and Fe) are determined by the energy gap of the involved orbitals. In addition, a few factors like the dipole moment, spin density and charge distributions influence the orbital energy gap to different extents. Thus, altering the local structure of the active center to modulate the orbital distribution may be a possible means of regulation of the activity.

Photoluminescence control by atomically precise surface metallization of C-centered hexagold(i) clusters using N-heterocyclic carbenes

The properties of metal clusters are highly dependent on their molecular surface structure. The aim of this study is to precisely metallize and rationally control the photoluminescence properties of a carbon(C)-centered hexagold(i) cluster (CAu^I₆) using N-heterocyclic carbene (NHC) ligands with one pyridyl, or one or two picolyl pendants and a specific number of silver(i) ions at the cluster surface. The results suggest that the photoluminescence of the clusters depends highly on both the rigidity and coverage of the surface structure. In other words, the loss of structural rigidity significantly reduces the quantum yield (QY). The QY in CH₂Cl₂ is 0.04 for [(C)(Au^I-BIPc)₆Ag^I₃(CH₃CN)₃](BF₄)₅ (BIPc = N-isopropyl-N'-2-picolylbenzimidazolylidene), a significant decrease from 0.86 for [(C)(Au^I-BIPy)₆Ag^I₂](BF₄)₄ (BIPy = N-isopropyl-N'-2-pyridylbenzimidazolylidene). This is due to the lower structural rigidity of the ligand BIPc because it contains a methylene linker. Increasing the number of capping Ag^I ions, i.e., the coverage of the surface structure, increases the phosphorescence efficiency. The QY for [(C)(Au^I-BIPc²)₆Ag^I₄(CH₃CN)₂](BF₄)₆ (BIPc² = N,N'-di(2-pyridyl)benzimidazolylidene) recovers to 0.40, 10-times that of the cluster with BIPc. Further theoretical calculations confirm the roles of Ag^I and NHC in the electronic structures. This study reveals the atomic-level surface structure-property relationships of heterometallic clusters.

(P,C)-cyclometalated complexes derived from naphthyl phosphines: versatile and powerful tools in organometallic chemistry

The chemistry of (P,C)-cyclometalated complexes derived from naphthyl phosphines [^Np(P,C)M] is presented and analysed in this review. The three main synthetic approaches, namely P-chelation assisted C-H activation, oxidative addition and transmetalation, are described and compared. If a naphthyl framework inherently predisposes a phosphorus atom and transition metal to interact, a rigid metallacycle may induce some strain and distortion, as apparent from the survey of the single-crystal X-ray diffraction structures deposited in the Cambridge Structural Database (77 entries with metals from groups 7 to 11). Generally, the ^Np(P,C)-cyclometalation imparts high thermal and chemical robustness to the complexes, and a variety of stoichiometric reactions have been reported. In most cases, the metalacyclic structure is retained, but protodecyclometalation and ring-expansion have been sparingly observed. [^Np(P,C)M] complexes have also proved to be competent and actually competitive catalysts in several transformations, and they act as key intermediates in some others. In addition, interesting phosphorescence properties have been occasionally pointed out.

Heart of gold: enabling ligands for oxidative addition of haloorganics in Au(I)/Au(III) catalysed cross-coupling reactions

The field of Au-catalysis has been an area rich with new discoveries due to the unique properties of the lustrous element. In the past decade, developments in Au(I)/Au(III) cross-coupling methodology have been made possible with the use of external oxidants that facilitate the challenging oxidation of Au(I) to Au(III) in a stable and catalytically competent fashion. Until recently, Au-chemistry was not known to undergo catalytic transformations that feature oxidative addition of haloarenes like those that were made famous by transition metals such as Pd and Ni. The discovery that ligand modification could facilitate the oxidative addition of Au(I) with haloorganics to provide Au(III) intermediates that are competent in other areas of catalysis (i.e. Lewis acid catalysis) has revolutionized this field and has led to the invention of new cross-coupling methodology. The recent advances at the leading edge in the emerging field of Au(I)/Au(III) catalysis under redox-neutral conditions are highlighted.

Three-centre electron sharing indices (3c-ESIs) as a tool to differentiate among (an)agostic interactions and hydrogen bonds in transition metal complexes

The agostic bond plays an important role in chemistry, not only in transition metal chemistry but also in main group chemistry. In some complexes with M⋯H-X (X = C, N) interactions, differentiation among agostic, anagostic, and hydrogen bonds is challenging. Here we propose the use of three-centre electron sharing indices to classify M⋯H-X (X = C, N) interactions.

Mechanism of Alkyne Hydroarylation Catalyzed by (P,C)-Cyclometalated Au(III) Complexes

Over the last 5-10 years, gold(III) catalysis has developed rapidly. It often shows complementary if not unique features compared to gold(I) catalysis. While recent work has enabled major synthetic progress in terms of scope and efficiency, very little is yet known about the mechanism of Au(III)-catalyzed transformations and the relevant key intermediates have rarely been authenticated. Here, we report a detailed experimental/computational mechanistic study of the recently reported intermolecular hydroarylation of alkynes catalyzed by (P,C)-cyclometalated Au(III) complexes. The cationic (P,C)Au(OAc^F)⁺ complex (OAc^F = OCOCF₃) was authenticated by mass spectrometry (MS) in the gas phase and multi-nuclear NMR spectroscopy in solution at low temperatures. According to density functional theory (DFT) calculations, the OAc^F moiety is κ²-coordinated to gold in the ground state, but the corresponding κ¹-forms featuring a vacant coordination site sit only slightly higher in energy. Side-on coordination of the alkyne to Au(III) then promotes nucleophilic addition of the arene. The energy profiles for the reaction between trimethoxybenzene (TMB) and diphenylacetylene (DPA) were computed by DFT. The activation barrier is significantly lower for the outer-sphere pathway than for the alternative inner-sphere mechanism involving C-H activation of the arene followed by migratory insertion. The π-complex of DPA was characterized by MS. An unprecedented σ-arene Au(III) complex with TMB was also authenticated both in the gas phase and in solution. The cationic complexes [(P,C)Au(OAc^F)]⁺ and [(P,C)Au(OAc^F)(σ-TMB)]⁺ stand as active species and off-cycle resting state during catalysis, respectively. This study provides a rational basis for the further development of Au(III) catalysis based on π-activation.

Enantioselective C-H Functionalization Reactions under Gold Catalysis

Transition metal-catalyzed enantioselective functionalization of ubiquitous C-H bonds has proven to be promising field as it offers the construction of chiral molecular complexity in a step- and atom-economical manner. In recent years, gold has emerged as an attractive contender for catalyzing such reactions. The unique reactivities and selectivities offered by gold catalysts have been exploited to access numerous asymmetric transformations based on gold-catalyzed C-H functionalization processes. Herein, this review critically highlights the major advances and discoveries made in the enantioselective C-H functionalization under gold catalysis which is accompanied by mechanistic insights at appropriate places.

Group 11 metal complexes of the dinucleating triazole appended bisphosphine 1,4-bis(5-(diisopropylphosphaneyl)-1-phenyl-1H-1,2,3-triazol-4-yl)benzene

The synthesis of a triazole appended dinucleating bisphosphine 1,4-bis(5-(diisopropylphosphaneyl)-1-phenyl-1H-1,2,3-triazol-4-yl)benzene (2) and its coinage metal complexes are described. The dinucleating bisphosphine 2 was obtained by the temperature-controlled lithiation of 1,4-bis(1-phenyl-1H-1,2,3-triazol-4-yl)benzene (1a) and 1,4-bis(1-(2-bromophenyl)-1H-1,2,3-triazol-4-yl)benzene (1b) followed by the reaction with ⁱPr₂PCl. The reactions of 2 with copper(I) halides in 1 : 2 molar ratios yielded the [Cu(μ₂-X)]₂ dimeric complexes [{Cu(μ₂-X)}₂(PⁱPr₂N₃PhC₂)₂C₆H₄] (3, X = Cl; 4, X = Br; and 5, X = I), whereas the reaction of 2 with AgBr resulted in the formation of hetero-cubane complex [{Ag₄(μ₃-Br)₄}{(PⁱPr₂N₃PhC₂)₂C₆H₄}₂] (7). Similar reactions of 2 with AgX in 1 : 2 molar ratios yielded disilver complexes [{Ag(μ₂-X)}₂{(PⁱPr₂N₃PhC₂)₂C₆H₄}] (6, X = Cl and 8, X = I). Treatment of 2 with AgOAc in a 1 : 2 molar ratio afforded a dinuclear complex [Ag₂(μ₂-OAc)₂{(PⁱPr₂N₃PhC₂)₂(C₆H₄)}] (9) with one of the acetate ligands bridging the two metal centres in the side-on mode, whereas the other one adopting the end-on mode keeping the >CO group uncoordinated. The reaction of 2 with two equivalents of [AuCl(SMe₂)] afforded the digold complex [(AuClPⁱPr₂N₃PhC₂)₂C₆H₄] (10). The molecular structures of 2-5 and 7-10 were confirmed by single crystal X-ray analysis. Non-covalent interactions between Cu and C_arene were observed in the molecular structures of 3, 4 and 5. These weak interactions were also assessed by DFT calculations in terms of their non-covalent interaction plots (NCI) and QTAIM analyses.

A Zwitterionic Heterobimetallic Gold-Iron Complex Supported by Bis(N-Heterocyclic Imine)Silyliumylidene

The facile synthesis of the first bis-N-heterocyclic imine-stabilized chlorosilyliumylidene 1 is reported. Remarkably, consecutive reaction of 1 with PPh3 AuCl and K2 Fe(CO)4 gives rise to the unique heterobimetallic complex 1,2-(Mes NHI)2 -C2 H4 -ClSiAuFe(CO)4 (4). The overall neutral complex 4 bears an unusual linear Si-Au-Fe structure and a rare anagostic interaction between the d10 -configured gold atom and a CH bond of the mesityl ligand. According to the computational analysis and 57 Fe Mössbauer spectroscopy, the formal Fe-oxidation state remains at -II. Thus, the electronic structure of 4 is best described as an overall neutral-yet zwitterionic-heterobimetallic "Si(II)+ -Au(I)+ -Fe(-II)2- "-silyliumylidene complex, derived from double anion exchange. The computational analysis indicates strong hyperconjugative back donation from the gold(I) atom to the silyliumylidene ligand.

Au⋅⋅⋅H-C Hydrogen Bonds as Design Principle in Gold(I) Catalysis

Secondary ligand-metal interactions are decisive in many catalytic transformations. While arene-gold interactions have repeatedly been reported as critical structural feature in many high-performance gold catalysts, we herein report that these interactions can also be replaced by Au⋅⋅⋅H-C hydrogen bonds without suffering any reduction in catalytic performance. Systematic experimental and computational studies on a series of ylide-substituted phosphines featuring either a PPh3 (Ph YPhos) or PCy3 (Cy YPhos) moiety showed that the arene-gold interaction in the aryl-substituted compounds is efficiently compensated by the formation of Au⋅⋅⋅H-C hydrogen bonds. The strongest interaction is found with the C-H moiety next to the onium center, which due to the polarization results in remarkably strong interactions with the shortest Au⋅⋅⋅H-C hydrogen bonds reported to date. Calorimetric studies on the formation of the gold complexes further confirmed that the Ph YPhos and Cy YPhos ligands form similarly stable complexes. Consequently, both ligands showed the same catalytic performance in the hydroamination, hydrophenoxylation and hydrocarboxylation of alkynes, thus demonstrating that Au⋅⋅⋅H-C hydrogen bonds are equally suited for the generation of highly effective gold catalysts than gold-arene interactions. The generality of this observation was confirmed by a comparative study between a biaryl phosphine ligand and its cyclohexyl-substituted derivative, which again showed identical catalytic performance. These observations clearly support Au⋅⋅⋅H-C hydrogen bonds as fundamental secondary interactions in gold catalysts, thus further increasing the number of design elements that can be used for future catalyst construction.

Cu-Catalyzed P-C bond formation/cleavage: straightforward synthesis/ring-expansion of strained cyclic phosphoniums

Upon reaction with copper(i), peri-halo naphthyl phosphines readily form peri-bridged naphthyl phosphonium salts. The reaction works with alkyl, aryl and amino substituents at phosphorus, with iodine, bromine and chlorine as a halogen. It proceeds under mild conditions and is quantitative, despite the strain associated with the resulting 4-membered ring structure and the naphthalene framework. The transformation is amenable to catalysis. Under optimized conditions, the peri-iodo naphthyl phosphine 1-I is converted into the corresponding peri-bridged naphthyl phosphonium salt 2b in only 5 minutes at room temperature using 1 mol% of CuI. Based on DFT calculations, the reaction is proposed to involve a Cu(i)/Cu(iii) cycle made of P-coordination, C-X oxidative addition and P-C reductive elimination. This copper-catalyzed route gives a general and efficient access to peri-bridged naphthyl phosphonium salts for the first time. Reactivity studies could thus be initiated and the possibility to insert gold into the strained P-C bond was demonstrated. It leads to (P,C)-cyclometallated gold(iii) complexes. According to experimental observations and DFT calculations, two mechanistic pathways are operating: (i) direct oxidative addition of the strained P-C bond to gold,(ii) backward-formation of the peri-halo naphthyl phosphine (by C-P oxidative addition to copper followed by C-X reductive elimination), copper to gold exchange and oxidative addition of the C-X bond to gold. Detailed analysis of the reaction profiles computed theoretically gives more insight into the influence of the nature of the solvent and halogen atom, and provides rationale for the very different behaviour of copper and gold in this chemistry.

C-HAu interactions and optical properties of [(P,P)4Au6]2+ molecular gold nanoclusters

Two hexagold diphosphine-stabilized [(P,P)4Au6]2+ molecular nanoclusters with the same [core + exo] arrangement differing in the linker (phenylene or trimethylene) connecting the two P-donor sites have been subjected to theoretical studies with the aim of shedding light on two main questions. On one hand, from a previous study [J. Vícha, C. Foroutan-Nejadand M. Straka,Nat. Commun., 2019, 10, 1643], it is still unclear whether short C-H2Au contacts revealed in the corresponding crystal structures are just forced by bulky P(Ph)2 groups and, on the other hand, to what extent the linker affects the visible band position [M. A. Bakar, M. Sugiuchi, M. Iwasaki, Y. Shichibuand K. Konishi, Nat. Commun., 2017, 8, 576]. Here, it is demonstrated that even in simpler model systems in which bulky groups were replaced by PH2 groups, C-H2Au hydrogen bonding interactions are retained and show comparable values, as measured by NBO and QTAIM analyses, to those of 1 and 2. These analyses further confirmed a stronger HB in 1 than in 2. Also, the comparison of model systems without and with a linker connecting the phosphine groups showed a bathochromic shift of 47 and 60 nm, revealing the key role of the linker. The Δρ(r)EE-GS plots of 1 and 2 revealed electron density depletion in the inter-nuclear C-H2 region upon electronic transition unveiling its contribution to their optical properties.

Proximity Enforced Agostic Interactions Involving Closed-Shell Coinage Metal Ions

A proximity enforcing diarylsilane ligand is reported, which gives rise to unusual Si-H···M interactions with the d¹⁰ metal ions Cu⁺ and Ag⁺ upon complexation. These interactions are studied in detail both experimentally and computationally and can be classified to be weakly agostic in nature for the Si-H···Cu interaction. The Si-H···Ag interaction has more signatures of an electrostatic contact.

Agostic Interactions in Early Transition-Metal Complexes: Roles of Hyperconjugation, Dispersion, and Steric Effect

The agostic interaction is a ubiquitous phenomenon in catalytic processes and transition-metal complexes, and hyperconjugation has been well recognized as its origin. Yet, recent studies showed that either short-range London dispersion or structural constraints could be the driving force, although proper evaluation of the role of hyperconjugation therein is needed. Herein, a simple variant of valence bond theory was employed to study a few exemplary Ti complexes with α- or β-agostic interactions and interpret the agostic effect in terms of the steric effect, hyperconjugation, and dispersion. For the complexes [MeTiCl₃ (dmpe)] and [MeTiCl₃ (dhpe)] with α-agostic interactions, hyperconjugation plays the dominant role with comparable magnitudes in both systems, but dispersion is solely responsible for the stronger agostic interaction in the former compared with the latter. For the complexes [EtTiCl₃ (dmpe)] and [EtTiCl₃ (dhpe)] with β-agostic interactions, however, hyperconjugation and dispersion play comparable roles, and the weaker steric repulsion leads to a stronger agostic effect in the former than in the latter. Thus, the present study clarifies the variable and sensitive roles of steric, hyperconjugative, and dispersion interactions in the agostic interaction.

Proof of Concept for Hydrogen Bonding to Gold, Au⋅⋅⋅H-X

Convincing and consistent evidence for the existence of hydrogen bonding to gold has been obtained. An ammonium or pyridinium group has been shown to be an efficient hydrogen bond donor unit for gold(I) coordination centers, and the assembly leads to the structural pattern typical for standard hydrogen bonds. This constitutes the first rigorous, scrutinizing, and comprehensive study of hydrogen bonds to a metal atom, with gold being an ideal model element because of relativistic effects.

Spectroscopic and Computational Evidence of Intramolecular AuI ⋅⋅⋅H+ -N Hydrogen Bonding

Despite substantial evidence of short Au⋅⋅⋅H−X contacts derived from a number of X‐ray structures of Au^I compounds, the nature of Au^I⋅⋅⋅H bonding in these systems has not been clearly understood. Herein, we present the first spectroscopic evidence for an intramolecular Au^I⋅⋅⋅H⁺−N hydrogen bond in a [Cl−Au−L]⁺ complex, where L is a protonated N‐heterocyclic carbene. The complex was isolated in the gas phase and characterized with helium‐tagging infrared photodissociation (IRPD) spectra, in which H⁺−N‐mode‐derived bands evidence the intramolecular Au^I⋅⋅⋅H⁺−N bond. Quantum chemical calculations reproduce the experimental IRPD spectra and allow to characterize the intramolecular Au⋅⋅⋅H⁺−N bonding with a short r_Au⋅⋅⋅H distance of 2.17 Å and an interaction energy of approximately −10 kcal mol⁻¹. Various theoretical descriptors of chemical bonding calculated for the Au⋅⋅⋅H⁺−N interaction provide strong evidence for a hydrogen bond of moderate strength.

Evidence for genuine hydrogen bonding in gold(I) complexes

The ability of gold to act as proton acceptor and participate in hydrogen bonding remains an open question. Here, we report the synthesis and characterization of cationic gold(I) complexes featuring ditopic phosphine-ammonium (P,NH+) ligands. In addition to the presence of short Au∙∙∙H contacts in the solid state, the presence of Au∙∙∙H-N hydrogen bonds was inferred by NMR and IR spectroscopies. The bonding situation was extensively analyzed computationally. All features were consistent with the presence of three-center four-electron attractive interactions combining electrostatic and orbital components. The role of relativistic effects was examined, and the analysis is extended to other recently described gold(I) complexes.

A noncovalent interaction insight onto the concerted metallation deprotonation mechanism

The CMD/AMLA mechanisms of cyclopalladation and the parent fictitious cyclonickelation of N,N-dimethylbenzylamine have been investigated by joint DFT-D and DLPNO-CCSD(T) methods assisted by QTAIM.

A d10 Ag(i) amine-borane σ-complex and comparison with a d8 Rh(i) analogue: structures on the η1 to η2:η2 continuum

H3B·NMe3 σ-complexes of d8 [(L1)Rh][BArF4] and d10 [(L1)Ag][BArF4] (where L1 = 2,6-bis-[1-(2,6-diisopropylphenylimino)ethyl]pyridine) have been prepared and structurally characterised. Analysis of the molecular and electronic structures reveal important but subtle differences in the nature of the bonding in these σ-complexes, which differ only by the identity of the metal centre and the d-electron count. With Rh the amine-borane binds in an η2:η2 fashion, whereas at Ag the unsymmetrical {AgH3B·NMe3} unit suggests a structure lying between the η2:η2 and η1 extremes.

Organometallic gold(iii) complexes with hybrid SNS-donating thiosemicarbazone ligands: cytotoxicity and anti-Trypanosoma cruzi activity

Stable organogold(iii) compounds of the composition [Au^III(Hdamp)(L1)]Cl are formed from reactions of [AuCl₂(damp)] with H₂L1 (damp^- = dimethylaminomethylphenyl; H₂L1 = N'-(diethylcarbamothioyl)benzimidothiosemicarbazides). The cationic complexes can be neutralized by reactions with weak bases under the formation of [Au^III(damp)(L1)] compounds. The structures of the products show interesting features like relatively short AuH contacts between the methylene protons of the Hdamp ligand and the gold(iii) ions. Preliminary biological studies on the uncoordinated compounds H₂L1 and their gold complexes indicate considerable cytotoxicity for the [Au^III(Hdamp)(L1)]Cl complexes against MCF-7 cells. The in vitro trypanocidal activity was evaluated against the intracellular form of Trypanosoma cruzi. The organometallic complexes display a remarkable activity, which is dependent on the alkyl substituents of the thiosemicarbazone building blocks of the ligands. One representative of the cationic [Au^III(Hdamp)(L1)]Cl complexes, where H₂L1 contains a dimethylthiosemicarbazide building block, shows a trypanocidal activity against the intracellular amastigote form in the same order of magnitude as that of the standard drug benznidazole. Furthermore, no appreciable toxicity to mice spleen cells is observed for this compound resulting in a therapeutic index of about 30, which strongly recommends it as a promising candidate for the development of a future antiparasitic drug.

Cyclometalated gold(iii) complexes: noticeable differences between (N,C) and (P,C) ligands in migratory insertion

Gold(iii) complexes are garnering increasing interest for opto-electronic, therapeutic and catalytic applications.

Gold(iii) complexes are garnering increasing interest for opto-electronic, therapeutic and catalytic applications. But so far, very little is known about the factors controlling their reactivity and the very influence of the ancillary ligand. This article reports the first comprehensive study on this topic. The reactivity of a cationic (N,C) gold(iii) complex, namely 1A, towards ethylene has been thoroughly studied and compared with that of the related (P,C) complex 1C. A cationic gold(iii) complex 5A resulting from double insertion of ethylene was selectively obtained. Complex 5A was found to be remarkably stable. It was trapped with chloride and fully characterized. In marked contrast to that observed with 1C, no β-H elimination or linear-to-branched rearrangement of the alkyl chain occurred with 1A. The energy profile for the reactions of 1A with ethylene has been comprehensively investigated computationally, and the influence of the ancillary ligand has been precisely delineated. Because nitrogen is a weaker donor than carbon (and phosphorus), the (N,C) ligand is very electronically dissymmetric, much more than the (P,C) ligand. This makes the two reactive sites at gold quite different, which noticeably influences the competition between migratory insertion and β-H elimination, and actually changes the outcome of the olefin insertion at gold. This study provides valuable insight into the influence of ancillary ligands on gold(iii) reactivity, something critical to further develop Au(iii) and Au(i)/Au(iii) catalysis.

Gold(iii) π complexes

Recent achievements in the preparation, characterization and reactivity of gold(iii) complexes of alkenes, alkynes and arenes are presented and discussed.

Aurophilicity vs. thiophilicity: directing the crystalline supramolecular arrangement in luminescent gold compounds

The fluorination of thiolate ligands is applied as a tool that allows control of the prevalence of thiophilic (Au–S) interactions over the expected aurophilic contacts in luminescent gold compounds.

Synthesis of a (N,C,C) Au(iii) pincer complex via Csp3–H bond activation: increasing catalyst robustness by rational catalyst design

The synthesis of a (N,C,C) Au(iii) catalyst via C_sp3–H bond activation has been achieved following a rational catalyst design approach.