Gold Complexes with Difunctional Perfluoroalkyl Chains: Quantifying the Energy of Aurophilic Interactions in Flexible Open-Chain Complexes

The first binuclear Au^I compounds containing bridging (CF₂)_n chains (n=4, 6, 8) and Au^III metallaperfluorocyclopentanes have been obtained by photoinitiated reactions of LAuMe (L=PPh₃, PMe₃, PCy₃, or IPr) with α,ω-diiodoperfluorocarbons. Complexes LAu(CF₂)₄AuL present an unusual looped structure stabilized by an aurophilic interaction for L=PMe₃, PPh₃, and PCy₃. The study of their dynamic behaviour has provided new insights about the strength of aurophilic interactions in solution, allowing quantification of the energy of a single Au⋅⋅⋅Au interaction.     

Gold Complexes with Difunctional Perfluoroalkyl Chains: Quantifying the Energy of Aurophilic Interactions in Flexible Open‐Chain Complexes

The first binuclear Au^I compounds containing bridging (CF₂)_n chains (n=4, 6, 8) and Au^III metallaperfluorocyclopentanes have been obtained by photoinitiated reactions of LAuMe (L=PPh₃, PMe₃, PCy₃, or IPr) with α,ω‐diiodoperfluorocarbons. Complexes LAu(CF₂)₄AuL present an unusual looped structure stabilized by an aurophilic interaction for L=PMe₃, PPh₃, and PCy₃. The study of their dynamic behaviour has provided new insights about the strength of aurophilic interactions in solution, allowing quantification of the energy of a single Au???Au interaction.     

Dinuclear Au(I), Au(II) and Au(III) Complexes with (CF2)n Chains: Insights into The Role of Aurophilic Interactions in the Au(I) Oxidation

New dinuclear Au(I), Au(II) and Au(III) complexes containing (CF₂)_n bridging chains were obtained. Metallomacrocycles [Au₂{μ-(CF₂)₄}{μ-diphosphine}] show an uncommon figure-eight structure, the helicity inversion barrier of which is influenced by aurophilic interactions and steric constraints imposed by the diphosphine. Halogenation of LAu(CF₂)₄AuL (L=PPh₃, PMe₃, (dppf)_1/2, (binap)_1/2) gave [Au(II)]₂ species, some of which display unprecedented folded structures with Au−Au bonds. Aurophilic interactions facilitate this oxidation process by preorganizing the starting [Au(I)]₂ complexes and lowering its redox potential. The obtained [Au(II)]₂ complexes undergo thermal or photochemical elimination of R₃PAuX to give Au(III) perfluorinated auracycles. Evidence of a radical mechanism for these decomposition reactions was obtained.     

Evolutionary Algorithm-based Crystal Structure Prediction for Gold(I) Fluoride

Solid gold(I) fluoride remains as an unsynthesized and uncharacterized compound. We have performed a search for potential gold(I) fluoride crystal structures using USPEX evolutionary algorithm and dispersion-corrected hybrid density functional methods. Over 4000 AuF crystal structures have been investigated. Behavior of the AuF crystal structures under pressure was studied up to 25 GPa, and we also evaluated the thermodynamic stability of the hypothetical AuF crystal structures with respect to AuF₃, AuF₅, and Au₃F₈. Mixed-valence compound Au₃[AuF₄] with Au atoms in various formal oxidation states emerged as the thermodynamically most stable AuF species.     

Bimetallic Gold(I) Complexes with Ethynyl‐Helicene and Bis‐Phosphole Ligands: Understanding the Role of Aurophilic Interactions in their Chiroptical Properties

Monometallic gold(I)‐alkynyl‐helicene complexes ( 1 a , b ) and bimetallic gold(I)‐alkynyl‐helicene architectures featuring the presence ( 2 a , b ) or absence ( 3 a , b ) of aurophilic intramolecular interactions were prepared by using different types of phosphole ligands (mono‐phosphole L1 or bis‐phospholes L2 , 3 ). The influence of the Au^I d¹⁰ metal center(s) on the electronic, photophysical, and chiroptical properties of these unprecedented phosphole‐gold(I)‐alkynyl‐helicene complexes was examined. Experimental and theoretical results highlight the importance of ligand‐to‐ligand‐type charge transfers and the strong effect of the presence or absence of Au^I–Au^I interactions in 2 a , b .     

Photoinitiated Reactions of Haloperfluorocarbons with Gold(I) Organometallic Complexes: Perfluoroalkyl Gold(I) and Gold(III) Complexes

The study of perfluoroalkyl metal complexes is key to understand and improve metal-promoted perfluoroalkylation reactions. Herein, we report the synthesis of the first gold complexes with primary or secondary perfluoroalkyl ligands by photoinitiated reactions between Au^I organometallic complexes and iodoperfluoroalkanes. Complexes of the types LAuR_F (L=PPh₃ or N,N-bis(2,6-diisopropylphenyl)imidazol-2-ylidene; R_F=n-C₄F₉, n-C₆F₁₃, i-C₃F₇, c-C₆F₁₁) and [Au(R_F)(Ar)I(PPh₃)] (Ar=2,4,6-trimethylphenyl) have been isolated and characterized. Alkynes R_FC≡CR were formed by reaction of Ph₃PAuC≡CR (R=Ph, nHex) with IR_F (R_F=n-C₄F₉, i-C₃F₇). According to the evidences obtained, this transformation undergoes through a photoinitiated radical mechanism. Au^III complexes [Au(n-C₄F₉)(X)(Y)L] (X=Y=Cl, Br, I, Me; X=Me, Y=I) have been prepared or in situ generated, and their thermal or photochemical decomposition reactions have been studied.     

Heterometallic Complexes with Gold(I) Metalloligands: Self‐Assembly of Helical Dimers Stabilized by Weak Intermolecular Interactions and Solvophobic Effects

New gold(I) alkynyl metalloligands bpylC?CAuL, bpyl′C?CAuPPh₃, and PPN[Au(C?Cbpyl′)₂] (bpyl or bpyl′=2,2′‐bipyridin‐5‐yl or ?4‐yl, respectively; L=PMe_xPh_3?x (x=1–3), P(C₆H₃Me₂‐3,5)₃, PCy₃, XyNC) have been synthesized. Ligands bpylC?CH and metalloligands bpylC?CAuL (L=PPh₃, PMePh₂, PCy₃, CNXy) react with MX₂ (M=Fe, Zn, X=ClO₄; M=Co, X=BF₄) to give complexes [M(bpylC?CZ)₃]X₂ (Z=H or AuL). In most cases, these complexes are mixtures of fac and mer isomers in a statistical distribution, in both CH₂Cl₂ and MeCN. However, for L=PPh₃, the fac isomer is dominant in MeCN. NMR and ESI‐MS studies, together with the crystal structure of [Co(bpylC?CAuPPh₃)₃](BF₄)₂, suggest that this solvent dependence is originated by the formation of helical dimers between two fac complexes in MeCN. These dimers are stabilized by solvophobic effects and multiple intermolecular interactions. Complex [Fe(Ph₃PAuC?CbpdiylC?CAuPPh₃)₃](ClO₄)₂ (bpdiyl=2,2′‐bipyridin‐5,5′‐diyl) was obtained by reaction of three diauro diethynylbipyridines and Fe(ClO₄)₂.     

Enantioselective Cyclopropanation Catalyzed by Gold(I)-Carbene Complexes

The formation of polysubstituted cyclopropane derivatives in the gold(I)-catalyzed reaction of olefins and propargylic esters is a potentially useful transformation to generate diversity, therefore any method in which its stereoselectivity could be controlled is of significant interest. We prepared and tested a series of chiral gold(I)-carbene complexes as a catalyst in this transformation. With a systematic optimization of the reaction conditions, we were able to achieve high enantioselectivity in the test reaction while the cis:trans selectivity of the transformation was independent of the catalyst. Using the optimized conditions, we reacted a series of various olefins and acetylene derivatives to find that, although the reactions proceeded smoothly and the products were usually isolated in good yield and with good to exclusive cis selectivity, the observed enantioselectivity varied greatly and was sometimes moderate at best. We were unable to establish any structure-property relationship, which suggests that for any given reagent combination, one has to identify individually the best catalyst.     

Tunable Trimers: Using Temperature and Pressure to Control Luminescent Emission in Gold(I) Pyrazolate‐Based Trimers

A systematic investigation into the relationship between the solid‐state luminescence and the intermolecular Au???Au interactions in a series of pyrazolate‐based gold(I) trimers; tris(μ₂‐pyrazolato‐N,N′)‐tri‐gold(I) ( 1 ), tris(μ₂‐3,4,5‐ trimethylpyrazolato‐N,N′)‐tri‐gold(I) ( 2 ), tris(μ₂‐3‐methyl‐5‐phenylpyrazolato‐N,N′)‐tri‐gold(I) ( 3 ) and tris(μ₂‐3,5‐diphenylpyrazolato‐N,N′)‐tri‐gold(I) ( 4 ) has been carried out using variable temperature and high pressure X‐ray crystallography, solid‐state emission spectroscopy, Raman spectroscopy and computational techniques. Single‐crystal X‐ray studies show that there is a significant reduction in the intertrimer Au???Au distances both with decreasing temperature and increasing pressure. In the four complexes, the reduction in temperature from 293 to 100 K is accompanied by a reduction in the shortest intermolecular Au???Au contacts of between 0.04 and 0.08 Å. The solid‐state luminescent emission spectra of 1 and 2 display a red shift with decreasing temperature or increasing pressure. Compound 3 does not emit under ambient conditions but displays increasingly red‐shifted luminescence upon cooling or compression. Compound 4 remains emissionless, consistent with the absence of intermolecular Au???Au interactions. The largest pressure induced shift in emission is observed in 2 with a red shift of approximately 630 cm^?1 per GPa between ambient and 3.80 GPa. The shifts in all the complexes can be correlated with changes in Au???Au distance observed by diffraction.     

Gold(I) and Gold(III) Trifluoromethyl Derivatives

Trifluoromethylation of AuCl₃ by using the Me₃SiCF₃/CsF system in THF and in the presence of [PPh₄]Br proceeds with partial reduction, yielding a mixture of [PPh₄][Au^I(CF₃)₂] ( 1′ ) and [PPh₄][Au^III(CF₃)₄] ( 2′ ) that can be adequately separated. An efficient method for the high‐yield synthesis of 1′ is also described. The molecular geometries of the homoleptic anions [Au^I(CF₃)₂]^? and [Au^III(CF₃)₄]^? in their salts 1′ and [NBu₄][Au^III(CF₃)₄] ( 2 ) have been established by X‐ray diffraction methods. Compound 1′ oxidatively adds halogens, X₂, furnishing [PPh₄][Au^III(CF₃)₂X₂] (X=Cl ( 3 ), Br ( 4 ), I ( 5 )), which are assigned a trans stereochemistry. Attempts to activate C? F bonds in the gold(III) derivative 2′ by reaction with Lewis acids under different conditions either failed or only gave complex mixtures. On the other hand, treatment of the gold(I) derivative 1′ with BF₃?OEt₂ under mild conditions cleanly afforded the carbonyl derivative [Au^I(CF₃)(CO)] ( 6 ), which can be isolated as an extremely moisture‐sensitive light yellow crystalline solid. In the solid state, each linear F₃C‐Au‐CO molecule weakly interacts with three symmetry‐related neighbors yielding an extended 3D network of aurophilic interactions (Au???Au=345.9(1) pm). The high $\tilde \nu $ _CO value (2194 cm^?1 in the solid state and 2180 cm^?1 in CH₂Cl₂ solution) denotes that CO is acting as a mainly σ‐donor ligand and confirms the role of the CF₃ group as an electron‐withdrawing ligand in organometallic chemistry. Compound 6 can be considered as a convenient synthon of the “Au^I(CF₃)” fragment, as it reacts with a number of neutral ligands L, giving rise to the corresponding [Au^I(CF₃)(L)] compounds (L=CNtBu ( 7 ), NCMe ( 8 ), py ( 9 ), tht ( 10 )).     

Tetranuclear Dicationic Aurophilic Gold(I) Catalysts in Enyne Cycloisomerization: Cooperativity for a Dramatic Shift in Selectivity

In comparison to mononuclear gold Lewis acid catalysts, digold complexes and dual-gold catalysis have illustrated a distinct and powerful potential for the activation of carbon-carbon multiple bonds. Herein, this concept is pushed further by designing novel tetranuclear gold(I) dicationic complexes structurally supported by strongly stabilizing constraint diphosphinoferrocenyl ligands and attractive closed-shell Au⋅⋅⋅Au aurophilic interactions. The use of a molecularly-defined tetranuclear dicationic aurophilic gold(I) precatalyst for the selectivity-challenging cycloisomerization of low-substituted 1,6-enynes favors the formation with high selectivity of strained azabicyclo[4.1.0]hept-4-enes – even in the complete absence of activating/orienting substituents on alkyne and olefin reactive functions. This selectivity is not achieved by the reported phosphine- and carbene-stabilized mono- and dinuclear cationic gold(I) complexes, including the ones formed from the same ligands. More importantly this selectivity differs also from nanoparticles and heterogeneous gold catalysts reported to date. DFT studies correlated to experimental mechanistic investigations support an unprecedented “cluster-like” reactivity from polynuclear cooperation at the origin of this peculiar selectivity where the aurophilic interactions preexist, and pre-organize, gold cluster reactive intermediates.     

Gold(I) Complexes Stabilized by Nine- and Ten-Membered N-Heterocyclic Carbene Ligands

Nine- and ten-membered N-heterocyclic carbene (NHC) ligands have been developed and for the first time their gold(I) complexes were synthesized. The protonated NHC pro-ligands 2 a – h were prepared by the reaction of readily available N,N′-diarylformamidines with bis-electrophilic building blocks, followed by anion exchange. In situ deprotonation of the tetrafluoroborates 2 a – h with tBuOK in the presence of AuCl(SMe₂) provided fast access to NHC-gold(I) complexes 3 – 10 . These new NHC-gold(I) complexes show very good catalytic activity in a cycloisomerization reaction (0.1 mol % catalyst loading, up to 100 % conversion) and their solid-state structures reveal high steric hindrance around the metal atom (%V_bur up to 53.0) which is caused by their expanded-ring architecture.     

Gold(I) and Silver(I) Complexes of Diphosphacyclobutadiene Cobaltate Sandwich Anions

The synthesis and structural characterization of the first coordination compounds of bis(diphosphacyclobutadiene) cobaltate anions [M(P₂C₂R₂)₂]^? is described. Reactions of the new potassium salts [K(thf)₃{Co(η⁴‐P₂C₂tPent₂)₂}] ( 1 ) and [K(thf)₄{Co(η⁴‐P₂C₂Ad₂)₂}] ( 2 ) with [AuCl(tht)] (tht=tetrahydrothiophene), [AuCl(PPh₃)] and Ag[SbF₆] afforded the complexes [Au{Co(P₂C₂tPent₂)₂}(PMe₃)₂] ( 3 ), [Au{Co(P₂C₂Ad₂)₂}]_x ( 4 ), [Ag{Co(P₂C₂Ad₂)₂}]_x ( 5 ), [Au(PMe₃)₄][Au{Co(P₂C₂Ad₂)₂}₂] ( 6 ), [K([18]crown‐6)(thf)₂][Au{Co(P₂C₂Ad₂)₂}₂] ( 7 ), and [K([18]crown‐6)(thf)₂][M{Co(P₂C₂Ad₂)₂}₂] ( 8 : M=Au 9 : M=Ag) in moderate yields. The molecular structures of 2 and 3 , and 6 – 9 were elucidated by X‐ray crystallography. Complexes 4 – 9 were thoroughly characterized by ³¹P and ¹³C solid state NMR spectroscopy. The complexes [Au{Co(P₂C₂Ad₂)₂}]_x ( 4 ) and [Ag{Co(P₂C₂Ad₂)₂}]_x ( 5 ) exist as coordination polymers in the solid state. The linking mode between the monomeric units in the polymers is deduced. The soluble complexes 1 – 3 , 6 , and 7 were studied by multinuclear ¹H‐, ³¹P{¹H}‐, and ¹³C{¹H} NMR spectroscopy in solution. Variable temperature NMR measurements of 3 and 6 in deuterated THF reveal the formation of equilibria between the ionic species [Au(PMe₃)₄]⁺, [Au(PMe₃)₂]⁺, [Co(P₂C₂R₂)₂]^?, and [Au{Co(P₂C₂R₂)₂}₂]^? (R=tPent and Ad).     

A Unique Au–Ag–Au Triangular Motif in a Trimetallic Halonium Dication: Silver Incorporation in a Gold(I) Catalyst

As a result of explorations into the solution chemistry of silver/gold mixtures, a unique diphosphine trimetallic chloronium dication was discovered that incorporates silver–arene chelation and a triangular mixed gold/silver core in the solid state. Notably, it was isolated from a Celite prefiltered solution initially thought to be silver‐free. The crystal structure also incorporates the coordination to silver of one fluorine atom of one SbF₆^? counterion. The structure was compared to two new, but well‐precedented, phosphine digold chloride cations. DFT calculations supported significant silver–halide and silver–arene interactions in the mixed gold/silver complex and metallophilic interactions in all three complexes. Comparison of computed data revealed that the ωB97X‐D functional, which has a long‐range corrected hybrid with atom–atom dispersion corrections, gave a better fit to the experimental data compared with the PBE0 functional, which has previously failed to capture aurophilic interactions. Preliminary studies support the presence of the mixed gold/silver structure in solution.