Gold Carbonyl Research Articles

Gold carbonyl cations and beyond: homoleptic gold(I) complexes with P4 and P4S3 and the half-sandwich cation [Au(C6H6)(CO)

Oxidation of Au0 with the synergistic Ag+/0.5 I2 system in the commercial organic solvent 1,2,3,4-tetrafluorobenzene led to the perfluoroalkoxyaluminate salt of the [Au(CO)2]+ cation known from superacid chemistry. This [Au(CO)2]+ salt proved to be an excellent 'naked' Au+-synthon yielding complex salts with [Au(η2-P4)2]+, [Au(η1-P4S3)2]+ and half-sandwich [Au(η2-C6H6)(CO)]+ cation.

Classical Gold Carbonyl Complexes in Tetrahedral and Trigonal-Planar Settings.

A unique four-coordinate, classical gold(I)-carbonyl complex with substantial backdonation from gold has been isolated by using a B-methylated and fluorinated tris(pyridyl)borate chelator. Its lighter silver(I) and copper(I) analogs enabled a study of trends in the coinage-metal family. The B-arylated ligand version also afforded a gold-carbon monoxide complex that displays a notably low C-O stretch value, but with trigonal planar geometry at the gold. A computational analysis shows that the AuI -CO bonds of these tris(pyridyl)borate ligand-supported molecules consist of electrostatic attraction, OC→Au σ-donation, and very significant Au→CO π-back-bonding components. The latter is responsible for the observed C-O stretching frequencies, which are lower than in free CO.

Experimental and theoretical studies on gold(III) carbonyl complexes: reductive C,H- and C,C bond formation.

The reactivity of cationic (C^C)gold(iii) carbonyl complexes was investigated. While the in situ-formed IPrAu(bph)CO+ complex (bph = biphenyl-2,2'-diyl) does not undergo a migratory insertion of CO into the neighboring gold-carbon bond, nucleophiles can attack the coordinated CO moiety intermolecularly. Water as a nucleophile initiates a CO2 extrusion combined with a reductive C,H bond formation. The rapid formation of a gold(i) species from an intermediary gold(iii) carbonyl has not been observed before and shows a significant difference in reactivity between (C^C) and (C^N^C)gold(iii) carbonyls. The latter have been reported to form stable gold(iii) hydrides via the WGS reaction. In the case of methanol acting as a nucleophile attacking the gold(iii) carbonyl, no extrusion of CO2 is observed. Instead an intermediary gold(iii) carboxyl complex forms an aryl carboxylate via reductive C-C bond elimination. Experimental and theoretical studies on the mechanism explain the observed selectivities and give new insights into the reactivity of elusive gold(iii) carbonyls.

Ligand Effect on Bonding in Gold(III) Carbonyl Complexes.

We quantitatively assess the Dewar-Chatt-Duncanson (DCD) components of the Au(III)-CO bond and the charge density polarization at the CO, in a series of neutral, cationic, and dicationic bis- and monocyclometalated gold(III) complexes via charge-displacement (CD) analysis. A striking feature concerns the very small net electron charge flux from CO to the metal fragment which is unexpectedly stable toward both the charge of the complex and the oxidation state of gold (I, III). All systems exhibit a similar trend for the σ charge rearrangement in the region of the carbonyl bond, where, by contrast, the π back-donation trend variation is large, which is strictly correlated to the change in CO bond distance and the shift in CO stretching frequencies, in close analogy with the gold(I) carbonyl complexes. In the whole series of gold(III) compounds, a large Au(III) ← CO σ donation is measured (from 0.19 to 0.31 electrons), as well as a significant Au(III) → CO π back-donation (from -0.09 to -0.22 electrons), which however is not generally able to completely balance the polarization of the CO π electrons in the direction from oxygen to carbon (C ← O) induced by the presence of the metal fragment [LAu(III)]0/+1/+2. Surprisingly, all the gold(III) complexes in the series are characterized by a very small anisotropy in the Au(III) → CO in-plane and out-of-plane π back-donation components, in sharp contrast with the marked anisotropy found before for the experimentally characterized [(C^N^C)Au(III)CO]+ complex. A first attempt to figure out a rationale on the bonding/reactivity relationship for Au(III)-CO is made by performing a comparative study with an isostructural [(N^N^C)Pt(II)CO]+ complex in a model water-gas shift (WGS) reaction.

The gold(iii)-CO bond: a missing piece in the gold carbonyl complex landscape.

We investigate the Au(iii)-CO bond in the [(C∧N∧C)Au(iii)CO]+ complex via charge-displacement (CD) analysis, revealing surprising peculiarities with respect to the Au(i)-CO bond. It shows a large Au(iii) ← CO σ donation and, unexpectedly, an even larger Au(iii) → CO π back-donation. The overall bonding picture, including a marked anisotropy in the Au(iii) → CO in-plane and out-of-plane π back-donation components, is consistent with a CO carbon atom highly susceptible to nucleophilic attack.

Methanol carbonylation catalyzed by TiO2–supported gold: An in-situ infrared spectroscopic investigation

TiO2–supported gold samples prepared by deposition-precipitation were tested as catalysts for methanol carbonylation to give methyl acetate at atmospheric pressure in the presence of methyl iodide as cocatalyst. Infrared (IR) spectroscopy was used to investigate the reactions of methanol, CO and CH3I on the surface of the samples. The results show the formation of methoxy species bonded to Ti4+ sites upon adsorption of methanol on the supported gold samples. Admission of CO to the flow reactor/IR cell led to the formation of gold carbonyls, which reacted with the surface methoxy species only when CH3I was present to give methyl acetate. The data indicate that CH3I is necessary to form gold–acetyl species, which are attacked by neighboring methoxy species to give the carbonylation product. Our results show that the methanol carbonylation catalyzed by TiO2–supported gold in the presence of CH3I occurs by a reaction mechanism that is similar to that occurring on supported Rh catalysts.

ChemInform Abstract: Organic and Organometallic Derivatives of Propargylallene: Syntheses, Structures, Reactivity and Rearrangements

AbstractReview: < 80 refs.

End-On and Side-On π-Acid Ligand Adducts of Gold(I): Carbonyl, Cyanide, Isocyanide, and Cyclooctyne Gold(I) Complexes Supported by N-Heterocyclic Carbenes and Phosphines

N-heterocyclic carbene ligand SIDipp (SIDipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) and trimesitylphosphine ligand have been used in the synthesis of gold(I) cyanide, t-butylisocyanide, and cyclooctyne complexes (SIDipp)Au(CN) (3), (Mes(3)P)Au(CN) (4), [(Mes(3)P)(2)Au][Au(CN)(2)] (5), [(SIDipp)Au(CN(t)Bu)][SbF(6)] ([6][SbF(6)]), [(SIDipp)Au(cyclooctyne)][SbF(6)] ([8][SbF(6)]), and [(Mes(3)P)Au(cyclooctyne)][SbF(6)] ([9][SbF(6)]). A detailed computational study has been carried out on these and the related gold(I) carbonyl adducts [(SIDipp)Au(CO)][SbF(6)] ([1][SbF(6)]), [(Mes(3)P)Au(CO)][SbF(6)] ([2][SbF(6)]), and [(Mes(3)P)Au(CN(t)Bu)](+) ([7](+)). X-ray crystal structures of 3, 5, [6][SbF(6)], [8][SbF(6)], and [9][SbF(6)] revealed that they feature linear gold sites. Experimental and computational data show that the changes in π-acid ligand on (SIDipp)Au(+) from CO, CN(-), CN(t)Bu, cyclooctyne as in [1](+), 3, [6](+), and [8](+) did not lead to large changes in the Au-C(carbene) bond distances. A similar phenomenon was also observed in Au-P distance in complexes [2](+), 4, [7](+), and [9](+) bearing trimesitylphosphine. Computational data show that the Au-L bonds of "naked" [Au-L](+) or SIDipp and Mes(3)P supported [Au-L](+) (L = CO, CN(-), CN(t)Bu to cyclooctyne) have higher electrostatic character than covalent character. The Au←L σ-donation and Au→L π-back-donation contribute to the orbital term with the former being the dominant component, but the latter is not negligible. In the Au-CO adducts [1](+)and [2](+), the cationic gold center causes the polarization of the C-O σ and π orbitals toward the carbon end making the coefficients at the two atoms more equal which is mainly responsible for the large blue shift in the CO stretching frequency. The SIDipp and Mes(3)P supported gold(I) complexes of cyanide and isocyanide also exhibit a significant blue shift in υ(CN) compared to that of the free ligands. Calculated results for Au(CO)Cl and Au(CF(3))CO suggest that the experimentally observed blue shift in ν(CO) of these compounds may at least partly be caused by intermolecular forces.

Osmium–Germanium and Osmium–Germanium–Gold Carbonyl Cluster Complexes: Syntheses, Structures, Bonding, and Reactivity

Reactions of Os3(CO)10(NCMe)2 with HGePh3 have yielded the compounds Os3(CO)10(NCMe)(GePh3)(μ-H) (1) and Os3(CO)10(GePh3)2(μ-H)2 (2) by the sequential replacement of the NCMe ligands and the oxidative addition of the GeH bonds of one and two HGePh3 molecules, respectively, to the osmium atoms of the cluster. Compound 2 exists as two isomers in solution at low temperatures which interconvert rapidly on the 1H NMR time scale at room temperature. When it was heated, 1 was transformed into the pentaosmium complex Os5(CO)17(μ-GePh2) (3), which exhibits a planar raft structure with one bridging GePh2 ligand. Compound 1 reacts with the compound PhAu(PPh3) to yield the compound Os3(CO)8(μ-CO)(μ-O═CPh)(μ-GePh2)(μ-AuPPh3) (4), which contains a bridging O═CPh ligand and a Au(PPh3) group that bridges an Os–Ge bond. A minor product, Os(CO)4(GePh3)(AuPPh3) (5), was also obtained in this reaction. Compound 4 was also obtained from the reaction of 1 with CH3Au(PPh3). Compound 4 reacted with PhC2Ph to yield the complex Os...

Synthesis and Structures of Iridium–Gold Carbonyl Cluster Compounds Containing Methyl and σ-Aryl Ligands

The compounds Ir4(CO)11(R)(μ-AuPPh3) (3, R = C6H5; 4, R = CH3; 5, R = 2-C16H10) were obtained from the reactions of [NEt4][Ir4(CO)11Br] with (R)Au(PPh3) (R = C6H5, CH3, 1-C16H10) at 25 °C by the loss of Br– and the oxidative addition of the Au–C bond of the (R)Au(PPh3) to the Ir4 cluster. Each compound contains a tetrahedral Ir4 cluster with an Au(PPh3) group bridging one of the six Ir–Ir bonds and a R group coordinated to one of the Au-bridged Ir atoms. The reaction of (CH3)Au(PPh3) with [PPN][HIr4(CO)11] yielded compound 4 and the higher nuclearity compound Ir4(CO)9(CH3)2(AuPPh3)4 (6). The reaction of PhAu(PPh3) with [PPN][HIr4(CO)11] yielded compound 3 and the higher nuclearity compounds Ir4(CO)9(PPh3)(Ph)(AuPPh3)3 (7) and Ir4(CO)9(Ph)2(AuPPh3)4 (8). Compounds 6 and 8 both contain butterfly Au4(PPh3)4 clusters bridging a triangular face of a tetrahedral Ir4 cluster and a CH3 group or Ph group, respectively, on two neighboring Ir atoms. Compound 7 contains a triangular (AuPPh3)3 group bridging a triangular face of a tetrahedral Ir4 cluster. Compounds 6 and 8 were obtained in better yields from the reactions of Ir4(CO)11(AuPPh3)2 with (CH3)Au(PPh3) and PhAu(PPh3), respectively. Compound 7 was obtained independently in high yield by the reaction of Ir4(CO)10(PPh3)(AuPPh3)2 with PhAu(PPh3). All of the new products were characterized by single-crystal X-ray diffraction analyses.

Au(CF3)(CO)]: A Gold Carbonyl Compound Stabilized by a Trifluoromethyl Group

Au(CF₃)(CO)]: A Gold Carbonyl Compound Stabilized by a Trifluoromethyl Group

Au(CF3)(CO)]: A Gold Carbonyl Compound Stabilized by a Trifluoromethyl Group

This work was supported by the Spanish MICINN (DGPTC)/FEDER (Project CTQ2008-06669-C02-01/BQU) and the Gobierno de Aragon (Grupo Consolidado 21: Quimica Inorganica y de los Compuestos Organometalicos).

Cationic Gold Carbonyl Complex on a Phosphine Support

A cationic gold carbonyl complex has been synthesized and characterized using several techniques including X-ray crystallography. [(Mes(3)P)Au(CO)][SbF(6)] (Mes = 2,4,6-Me(3)C(6)H(2)) has a linear, two-coordinate gold atom. This compound displays the CO stretching frequency at 2185 cm(-1). The (13)C NMR signal of the gold-bound (13)CO appears as a doublet centered at δ 182.6 ((2)J(C,P) = 115 Hz). A computational study shows that the Au-CO bond consists of electrostatic attraction, Au ← CO donation, and significant Au → CO π-back-bonding components. Polarization of the CO bond caused by the electrostatic effect of the cationic gold center is mainly responsible for the large blue shift in the CO stretching frequency.

Experimental and theory studies of the oxidation reaction of neutral gold carbonyl clusters in the gas phase

Neutral gold carbonyl clusters, Au m (CO) n ( m = 3–9, n = 2–7, m ≥ n), are generated by laser ablation of Au into a mixture of CO/He, cooled in a supersonic expansion, and reacted with O 2 and N 2O in a fast flow reactor. The neutral reactants and products are detected in a time of flight mass spectrometer through single photon ionization by a 193 nm laser. Signal intensities of Au 3(CO) 2,3, Au 5(CO) 4, and Au 7(CO) 4,5 decrease significantly following reaction of these clusters with O 2 in the fast flow reactor; only Au 3(CO) 2 and Au 3(CO) 3 signals decrease moderately following reaction with N 2O. The reaction cross section for Au m (CO) n with N 2O is significantly smaller than that with O 2. Density functional theory calculations with and without explicit consideration of relativistic effects are performed to investigate the reaction mechanisms for the oxidation of Au 3(CO) 2 and Au 3(CO) 3 clusters with O 2 and N 2O. Both calculational algorithms predict a considerable barrier for the reactions of Au 3(CO) 2,3 with N 2O. Non relativistic density functional theory calculations predict a positive overall barrier for the reactions of Au 3(CO) 2,3 with O 2, in disagreement with experimental observations. Relativistic density functional theory calculations for the reactions Au 3(CO) 2,3 with O 2 predict that they are thermodynamically allowed, although the barrier heights are not in the appropriate order to support the apparent relative reactivities of Au 3(CO) 2 and Au 3(CO) 3 with O 2.

Isolable, gold carbonyl complexes supported by N-heterocyclic carbenes

Cationic gold carbonyl complexes supported by N-heterocyclic carbene ligands, SIDipp and IDipp, have been synthesized. [(SIDipp)Au(CO)][SbF(6)] has a linear, two-coordinate gold center. [(SIDipp)Au(CO)][SbF(6)] and [(IDipp)Au(CO)][SbF(6)] display ̃ν(CO) values at 2197 and 2193 cm(-1), respectively. Computational studies on [(SIMe)Au(CO)](+) indicate the presence of a strong Au(I)-CO bond.

Characterization of alumina- and niobia-supported gold catalysts used for oxidation of glycerol

Gold catalysts supported on niobia and alumina are active in glycerol oxidation performed in liquid basic solution in the presence of oxygen. Niobia-supported gold is only slightly less active than commercial Au/TiO 2 catalyst. XPS data allow to characterize gold nanoparticles on both supports. IR studies show that CO adsorbs on gold particles loaded on niobia producing well characterized terminal carbonyls whose C–O stretching frequency shifts up by decreasing CO coverage, an usual behaviour for gold carbonyls. Two families of gold nanoparticles on niobia are characterized by CO stretching frequencies of adsorbed CO at 2098–2112 cm −1 after reduction at 573 K and at 2108–2120 and 2125–2135 cm −1 after reduction at 773 K. However, after both reduction pretreatments such gold metal particles coexist with strongly oxidizing gold species which are able to convert CO into CO 2 at 153–193 K. Based on IR and XPS experiments, the lower activity of alumina-supported gold may be due to a lower density of corner and edge sites on Au nanoparticles, associated to the minor dispersing ability of alumina for gold.

Adsorption of CO on gas phase and zeolite supported gold monomers: A computational study

We report for the first time the interaction of carbon monoxide with gold monomer in three oxidation states 0, +1 and +3 on FAU zeolite support using density functional theory. The gas phase structures of the gold carbonyls are retained on the zeolite support with only a slight change in the O–C–Au bond angle. For the supported cluster the CO vibrational frequency shows a blue shift on going to higher oxidation states. The CO binding energies on the supported gold monomers are 1.01, 1.15 and 1.12 eV in the oxidation states 0, +1 and +3, respectively.

Oxidation of gold metal particles supported on TiO2: an FTIR study by means of low-temperature CO adsorption

Two Au/TiO2 samples with different gold loadings (0.7 and 4.0 wt.% Au) were prepared by deposition-precipitation with urea and calcined at 673 K. TEM revealed gold particles of 3.2 and 3.9 nm for the 0.7 and 4.0 wt.% samples, respectively. The samples were subjected to different red-ox treatments and then the state of gold was determined by the FTIR spectra of CO adsorbed at low temperature. Several kinds of gold carbonyl species were detected during the experiments: (i) Au0–CO at around 2107 cm−1; (ii) Au+–CO at ca. 2175 cm−1; (iii) Auδ+–CO in the region of 2140–2137 cm−1 and (iv) Auδ′+–CO (δ′ > δ) at around 2155 cm−1. The 4.0 wt.% sample contained mainly metallic gold after evacuation at 673 K. Subsequent interaction with oxygen at 373 K leads to oxidation of a fraction of the surface metallic gold sites to Auδ+ sites. These sites were considered as cations located on the surface of the metal particles with a partially positive charge δ+ (0 < δ < 1) because of electron transfer from the gold bulk. Evacuation at 673 K leads to back reduction of the Auδ+ sites to metallic gold. The oxidation of gold particles was more efficient when performed with a NO + O2 mixture. It resulted in creation of Auδ′+ sites with a higher positive charge than that of the Auδ+ sites. In this case the oxidation involved a higher number of Au0 sites. A similar treatment of the 0.7 wt.% Au sample, however, resulted in formation of “isolated” Au+ species. The results indicate that small metal particles are more easily oxidized by a NO + O2 mixture. A model of the formation of the different sites, explaining well the experimental results, is proposed.

Comparative study of Au/Al2O3 and Au/CeO2-Al2O3 catalysts

Two gold-containing catalysts, Au/Al2O3 and Au/CeO2-Al2O3, have been prepared by deposition–precipitation and characterized by different techniques (XRD, transmission electron microscopy (TEM), FTIR spectroscopy of adsorbed CO and catalytic test). The Au/CeO2-Al2O3 sample demonstrates a much higher catalytic activity in the CO oxidation reaction than does the Au/Al2O3 sample. IR spectroscopy of adsorbed CO reveals that ceria generally keeps gold in a more oxidized state. Gold is in the form of Au3+ on the as-prepared samples. Low-temperature CO adsorption on the Au/Al2O3 sample evacuated at 473K leads to the formation of Au+–CO species evidencing reduction of Au3+ to Au+. No gold carbonyls are detected on the Au/CeO2-Al2O3 sample evacuated at the same temperature, this indicating that no auto-reduction has occurred. A carbonyl band at 2143cm−1, assigned to Au+–CO species formed with Au+ cations on metal gold particles, is registered after low-temperature CO adsorption on the Au/CeO2-Al2O3 sample evacuated at 673K, while CO adsorption on the Au/Al2O3 sample treated in the same way leads to the formation of Au0–CO species (carbonyl band at 2106cm−1). Only metal gold was detected on the hydrogen-reduced Au/Al2O3 sample (carbonyl band at 2101cm−1) while on the Au/CeO2-Al2O3 sample reduced with hydrogen, in addition to the metal gold (carbonyl band at 2108cm−1), Au+ sites were also detected (carbonyl band at 2131cm−1). The role of the cationic gold sites in the CO oxidation reaction is discussed.

Synthesis and Structural Analysis of the First Nanosized Platinum−Gold Carbonyl/Phosphine Cluster, Pt13[Au2(PPh3)2]2(CO)10(PPh3)4, Containing a Pt-Centered [Ph3PAu−AuPPh3]-Capped Icosahedral Pt12 Cage

The preparation and molecular structure of the initial nanosized platinum-gold carbonyl cluster, Pt(13)[Au(2)(PPh(3))(2)](2)(CO)(10)(PPh(3))(4) (1), are described. A comparative analysis reveals its pseudo-D(2)(h) geometry, consisting of a centered Pt(13) icosahedron encapsulated by two centrosymmetrically related bidentate [Ph(3)PAu-AuPPh(3)]-capped ligands along with 4 PR(3) and 10 CO ligands, to be remarkably similar to that of the previously reported Pt(17)(mu(2)-CO)(4)(CO)(8)(PEt(3))(8) (2). Reformulation of 2 as Pt(13)[(PtPEt(3))(2)(mu(2)-CO)](2)(CO)(10)(PEt(3))(4) emphasizes the steric/electronic resemblance of the bulky-sized bidentate [Ph(3)PAu-AuPPh(3)] and [(PtPEt(3))(2)(mu(2)-CO)] capping ligands in 1 and 2, respectively, as well as their identical electron counts of 162 cluster valence electrons for a centered Pt(13) icosahedron. We hypothesize that analogous steric effects of their ligand polyhedra in 1 and 2 play a crucial role along with electronic effects in the formation and stabilization of these two nanosized clusters that contain an otherwise unknown centered icosahedron of platinum atoms.