Silver Adducts Research Articles

Synthesis and Lewis Acid Properties of Neutral Silver(III) Adducts Containing the AgIII(CF3)3 Moiety.

The acetonitrile AgIII complex [AgIII(CF3)3(NCCH3)] (2) has been reported independently by Eujen and Naumann in the last century, albeit with intriguing NMR discrepancy. In their reports, 2 was claimed to be obtained starting from either [AgIII(CF3)3Cl]- (3⋅Cl) or [AgIII(CF3)4]- (1) via halide abstraction using AgNO3 or acidic treatment, resp. These two synthetic routes are herein reinvestigated. The feasibility of Naumann's method is demonstrated, thus providing 2 yet accompanied by its s-triazinyl derivative [AgIII(CF3)3(C6H9N3)] (2'). The formation of 2' is unprecedented and was thereby investigated. Both 2 and 2' were isolated in pure fashion and fully characterized. In turn, halide extraction from 3⋅Cl leads to the AgIII-ONO2 anion 5 instead of 2, as evidenced by NMR spectroscopy, EA and Sc-XRD.

Breaching the Fortress: Photochemistry of DNA-Caged Ag106.

A DNA strand can encapsulate a silver molecule to create a nanoscale, aqueous stable chromophore. A protected cluster that strongly fluoresces can also be weakly photolabile, and we describe the laser-driven photochemistry of the green fluorophore C4AC4TC3GT4/Ag106+. The embedded cluster is selectively photoexcited at 490 nm and then bleached, and we describe how the efficiency, products, and route of this photochemical reaction are controlled by the DNA cage. With irradiation at 496.5 nm, the cluster absorption progressively drops to give a photodestruction quantum yield of 1.5 (±0.2) × 10-4, ∼103× less efficient than fluorescence. A new λabs = 335 nm chromophore develops because the precursor with 4 Ag0 is converted into a group of clusters with 2 Ag0 - Ag64+, Ag75+, Ag86+, and Ag97+. The 4-7 Ag+ in this series are chemically distinct from the 2 Ag0 because they are selectively etched by iodide. This halide precipitates silver to favor only the smallest Ag64+ cluster, but the larger clusters re-develop when the precipitated Ag+ ions are replenished. DNA-bound Ag106+ decomposes because it is electronically excited and then reacts with oxygen. This two-step process may be state-specific because O2 quenches the red luminescence from Ag106+. However, the rate constant of 2.3 (±0.2) × 106 M-1 s-1 is relatively small, which suggests that the surrounding DNA matrix hinders O2 diffusion. On the basis of analogous photoproducts with methylene blue, we propose that a reactive oxygen species is produced and then oxidizes Ag106+ to leave behind a loose Ag+-DNA skeleton. These findings underscore the ability of DNA scaffolds to not only tune the spectra but also guide the reactions of their molecular silver adducts.

Cryogenic infrared spectroscopy provides mechanistic insight into the fragmentation of phospholipid silver adducts

Tandem mass spectrometry is arguably the most important analytical tool for structure elucidation of lipids and other metabolites. By fragmenting intact lipid ions, valuable structural information such as the lipid class and fatty acyl composition are readily obtainable. The information content of a fragment spectrum can often be increased by the addition of metal cations. In particular, the use of silver ions is deeply rooted in the history of lipidomics due to their propensity to coordinate both electron-rich heteroatoms and C = C bonds in aliphatic chains. Not surprisingly, coordination of silver ions was found to enable the distinction of sn-isomers in glycerolipids by inducing reproducible intensity differences in the fragment spectra, which could, however, not be rationalized. Here, we investigate the fragmentation behaviors of silver-adducted sn- and double bond glycerophospholipid isomers by probing fragment structures using cryogenic gas-phase infrared (IR) spectroscopy. Our results confirm that neutral headgroup loss from silver-adducted glycerophospholipids leads to dioxolane-type fragments generated by intramolecular cyclization. By combining high-resolution IR spectroscopy and computational modelling of silver-adducted fragments, we offer qualitative explanations for different fragmentation behaviors of glycerophospholipid isomers. Overall, the results demonstrate that gas-phase IR spectroscopy of fragment ions can significantly contribute to our understanding of lipid dissociation mechanisms and the influence of coordinating cations.Graphical abstract

Synthesis and structural characterisation of some mononuclear 1:1:1 complexes of coinage metal(I) compounds with tertiary phosphines (arsines) and 1,2-diamines, [MX(EPh3)(N,N'-1,2-diamine)

Crystallization of adducts of simple copper(I) and silver(I) salts (MX) with triphenylphosphine from 'N,N,N′,N'-tetramethylethylenediamine', 'tmeda', has yielded adducts of 1:1:1 MX:PPh3:tmeda stoichiometry, all of which have been characterized by room temperature single crystal X-ray structure determinations. In all adducts, the complex is mononuclear [M(PPh3)(N,N′-tmeda)X] with four-coordinate N2PMX metal atom environments (M = Cu, X = Cl, Br, I; M = Ag, X = Cl or NO3). The tricyclohexylphosphine species [Ag(Pcy3)(N,N′-tmeda)(ONO2)], also in a N2PAgX metal environment, has been defined. A number of similar silver(I) adducts are obtained by using 1,2-diaminopropane, 'pn' as solvent. The chloride, bromide and iodide complexes are isomorphous, the complexes being mononuclear, [Ag(PPh3)(pn)X], with four-coordinate N2PAgX environments, the pn ligand chelating. An isomorphous arsenic analogue of the bromide has also been isolated. All complexes have been characterized by IR and NMR (1H and 31P) spectroscopy.

Determination of Monounsaturated Fatty Acid Isomers in Biological Systems by Modeling MS3 Product Ion Patterns.

Unsaturated free fatty acids are natively present in biological samples as isomers, where double bonds can be situated on different carbons in the acyl chain. While these isomers can have different actions and impacts on biological systems, they are inherently difficult to identify and differentiate by mass spectrometry alone. To address this challenge, several techniques for derivatization of the double bond or metal cationization at the carboxylic group have yielded diagnostic product ions for the respective isomer in tandem mass spectrometry. However, diagnostic product ions do not necessarily reflect quantitative isomeric ratios since fatty acid isomers have different ionization and fragmentation efficiencies. Here, we introduce a simple and rapid approach to predict the quantitative ratio of isomeric monounsaturated fatty acids. Specifically, empirically derived MS3 product ion patterns from fatty acid silver adducts are modeled using a stepwise linear model. This model is then applied to predict the proportion oleic and vaccenic acid in chemically complex samples at individual concentrations between 0.45 and 5.25 μM, with an average accuracy and precision below 2 and 5 mol %, respectively. We show that by simply including silver ions in the electrospray solvent, isomeric ratios are rapidly predicted in neat standards, rodent plasma, and tissue extract. Furthermore, we use the method to directly map isomeric ratios in tissue sections using nanospray desorption electrospray ionization MS3 imaging without any sample preparation or modification to the instrumental setup. Ultimately, this approach provides a simple and rapid solution to differentiate monounsaturated fatty acids using commonly available commercial mass spectrometers without any instrumental modifications.

Direct Identification of α-Bisabolol Enantiomers in an Essential Oil Using a Combined Ion Mobility-Mass Spectrometry/Quantum Chemistry Approach.

Enantiomer-specific identification of chiral molecules in natural extracts is a challenging task, as many routine analytical techniques fail to provide selectivity in multicomponent mixtures. Here we describe an alternative approach, based on the combination of ion mobility-mass spectrometry (IM-MS) and quantum chemistry (QM), for the direct enantiomers differentiation in crude essential oils. The identification of α-bisabolol enantiomers contained in the raw essential oil (EO) from the Corsican Xanthium italicum fruits is reported as a proof-of-concept. Accordingly, IM-MS experiments performed in Ag+-doped methanol revealed the presence of both (+)- and (-)-α-bisabolol in the EO, while molecular simulations provided the structures of the two α-bisabolol enantiomer silver(I) adducts.

Unravelling the factors that drive separation in differential mobility spectrometry: A case study of regioisomeric phosphatidylcholine adducts

Differential mobility spectrometry (DMS) has shown promise as an analytical tool in the field of lipidomics. However, the underlying mechanism that drives DMS-based lipid separations is still somewhat unclear. Here, we investigate the finer details in the separability of the regioisomeric lipids 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) from 1-oleoyl-2-palmitoyl-sn-glycero-3-phosphocholine (OPPC), including the effect of cation choice, chemical modifier, and temperature. We conduct DMS-MS studies that are supported by a hybrid molecular dynamics and quantum mechanical approach to explore the conformations and energetics of the [OPPC···X]+ and [POPC···X]+ (X = Ag, K) constructs. Computational models evaluated using density functional theory reveal structural differences between low energy regioisomeric silver adducts, which translates to unique collision cross sections. Structural differences in regioisomers, as reflected through collision cross section evaluations, are not retained in potassiated adducts. Population weightings suggest coalescence of [OPPC···Ag]+ and [POPC···Ag]+ collision cross sections as higher energy species become populated at elevated temperatures. This effect presents itself experimentally, revealing diminished resolving power as the temperature of the DMS cell is increased. The results outlined here provides atomistic insight into how dynamic ion collision cross sections affect separations and guidance for future DMS-driven lipidomics applications.

Vinyltrifluoroborate Complexes of Silver Supported by N‐Heterocyclic Carbenes

Silver complexes involving vinyltrifluoroborate, (IPr)Ag(CH2=CHBF3) (4), [(IPr)2Ag][CH2=CHBF3] (5), (SIPr)Ag(CH2=CHBF3) (6) and (IPr*)Ag(CH2=CHBF3) (7) have been synthesized by using (NHC)AgNO3 [NHC = IPr (1), SIPr (2) and IPr* (3)] and K(CH2=CHBF3) in a metathesis process. NMR spectroscopic details of 1–7 and X‐ray crystal structures of compounds 5–7 as well as that of a precursor (IPr)AgNO3 are reported. Compounds 6 and 7 are more stable in solution compared to 4 (which forms 5) indicating a supporting ligand effect in the stability of monomeric (NHC)Ag(CH2=CHBF3). Calculated metal–ligand binding energies show that [CH2=CHBF3]− is a significantly better ligand for AgI than CH2=CH2 or isoelectronic CH2=CHCF3. IPr, SIPr and IPr* carbenes coordinate to Ag(CH2=CHBF3) moiety forming silver adducts 4, 6 and 7, with binding energies of about –72.1, –72.1 and –83.8 kcal/mol, respectively. The C=C bond length of [CH2=CHBF3]− (calculated value of 1.341 Å) increases upon coordination to the silver ion. Experimental data show a similar trend for structurally characterized 6 and 7. Electrostatic attraction dominates the bonding between the alkene ligand [C2H3BF3]− and the metal fragments [Ag(IPr)]+ and [Ag(SIPr)]+ in 4 and 6. The strongest orbital interaction involves σ‐donation from the occupied π‐orbital of the [C2H3BF3]− ligand to the vacant orbital of the metal fragment, while AgI→[C2H3BF3]− π‐backbonding is relatively weak but not insignificant.

Repeated and Folded DNA Sequences and Their Modular Ag106+ Cluster

Molecular silver clusters are optical chromophores, and species with distinct spectra form with DNA strands. One such hybrid chromophore is a violet cluster bound to repeated C2X sequences where X ≠ C. We varied the number of C2X repeats and the X nucleobase and consider three observations. First, different lengths of (C2A)y and (C2T)y strands with y = 3–12 identify a minimal (C2X)6 scaffold that forms a specific Ag10 adduct. This cluster has a +6 oxidation state, absorbs between 400–450 nm, and folds its DNA host. Second, different X nucleobases alter the (C2X)6 binding site. The natural nucleobases preferentially form the Ag106+ cluster and yield strong circular dichroism. These ligands coordinate via their heteroatoms, and the N3 of thymine was identified via cluster fluorescence that varies with pH. In contrast, abasic sites and imidazole substitutions suppress circular dichroism and diminish the number of silver adducts. These observations suggest that a (C2X)6 coordinates Ag106+ via multiple nucleobases. Third, beyond the minimal (C2X)6 binding site, longer strands still form Ag106+ but can also coordinate additional Ag+ adducts. The added Ag+ do not perturb the Ag0 and their spectra and thus may partition to open C2X subunits outside the core (C2X)6–Ag106+ complex. Thus, these modular complexes distinguish oxidized and reduced silvers. Collectively, these three observations suggest that the DNA and silver cluster play complementary roles: a repeated C2X sequence stabilizes the Ag106+ cluster, while the cluster folds its host. We specifically suggest that the Ag+ within Ag106+ cross-links remote C2X subunits and the Ag0 coordinate with mismatch sites in a hairpin-like secondary structure. Distinct roles for Ag+ and Ag0 within a cluster are considered in light of the X-ray spectra of related complexes.

Impedimetric detection of bacteria by using a microfluidic chip and silver nanoparticle based signal enhancement.

The authors describe a method that can significantly improve the performance of impedimetric detection of bacteria. A multifunctional microfluidic chip was designed consisting of interdigitated microelectrodes and a micro-mixing zone with a Tesla structure. This maximizes the coating of bacterial surfaces with nanoparticles and results in improved impedimetric detection. The method was applied to the detection of Escherichia coli O157:H7 (E. coli). Silver enhancement was accomplished by coating E.coli with the cationic polymer diallyldimethylammonium chloride (PDDA) to form positively charged E. coli/PDDA complexes. Then, gold nanoparticles (AuNPs) were added, and the resulting E. coli/PDDA/AuNPs complexes were collected at interdigitated electrodes via positive dielectrophoresis (pDEP). A silver adduct was then formed on the E. coli/PDDA/AuNP complexes by using silver enhancement solutions and by using the AuNPs as catalysts. The combination of pDEP based capture and of using silver adducts reduces impedance by increasing the conductivity of the solution and the double layer capacitance around the microelectrodes. Impedance decreases linearly in the 2 × 103-2 × 105cfu·mL-1 E. coli concentration range, with a 500cfu·mL-1 detection limit. Egg shell wash samples and tap water spiked with E. coli were successfully used for validation, and this demonstrates the practical application of this method. Graphical abstract Schematic representation of the AuNP@Ag enhancement method integrated with multifunctional microfluidic chip platform for impedimetric quantitation of bacteria. The method significantly improves the performance of impedimetric detection of bacteria.

A Phosphorescent Trinuclear Gold(I) Pyrazolate Chemosensor for Silver Ion Detection and Remediation in Aqueous Media.

We report a phosphorescent chemosensor based on a trinuclear Au(I) pyrazolate complex or [Au(3-CH3,5-COOH)Pz]3 (aka Au3Pz3) stabilized in aqueous chitosan (CS) polymer media. Au3Pz3 is synthesized in situ within aqueous CS media at pH ∼ 6.5 and room temperature (RT). Au3Pz3 exhibits strong red emission (λmax ∼ 690 nm) in such solutions. On addition of silver salt to Au3Pz3/CS aqueous media, a bright-green emissive adduct (Au3Pz3/Ag+) with a peak maximum within 475-515 nm is developed. The silver adduct exhibits a 4-fold increase in quantum yield (0.19 ± 0.02) compared to Au3Pz3 alone (0.05 ± 0.01), along with a corresponding increase in phosphorescence lifetime. With almost zero interference from 15 other metal ions tested, Au3Pz3 exhibits extreme selectivity for Ag+ with nM/ppb detection limits (6.4-72 ppb, depending on %CS and on the sensitivity basis being a signal-to-noise ratio (S/N) = 3 or a baseline-corrected signal change = 10%). Au3Pz3 exhibits sensitivity to higher concentrations (>1 mM) of other metal ions (Tl+/Pb2+/Gd3+). The sensing methodology is simple, fast, convenient, and can even be detected by the naked eye. On addition of ethylenediaminetetraacetic acid (EDTA), the red Au3Pz3 emission can be restored. Au3Pz3 and its silver adduct retain their characteristic photophysical properties in thin film forms. Remarkable photostability with <7% photobleaching after 4 h of UV irradiation is attained for Au3Pz3 solutions or thin films.

Stabilization of the cyclodecadiene derivative isofuranodiene by silver (I) coordination. Mechanistic and biological aspects

The industrial extraction and further applications of isofuranodiene are limited because at room temperature it spontaneously converts to curzerene, a structurally less active isomer. This work definitively identified the structure of isofuranodiene in the solid state, showing the two methyl groups in syn position. In addition, two bioactive metal cations, namely, silver(I) and copper(II) ions, were used in the attempt to obtain the chemical stability of isofuranodiene: in the case of silver(I), a labile adduct was formed, while in the case of copper(II), a more stable 1:1 adduct was achieved. In the former, the presence of silver did not significantly affect the biological activities of isofuranodiene, while in the latter, the copper(II) coordination suppressed them. The biological activities of the isofuranodiene adducts were then evaluated as antiproliferative agents against human tumor cell lines (HCT116, MDA-MB 231, and T98G). In addition, for the first time, isofuranodiene was tested as an inhibitor of DHFR (DiHydroFolateReductase) from Escherichia coli. Anticancer activity was observed in the isofuranodiene with the AgCF3SO3 adduct, in the tested cell lines, with IC50 values ranging from 4.89μM to 13.06μM, while inhibition assays highlighted a Ki of 6.22μM for isofuranodiene and of 0.17μM for the related silver adduct. Docking studies indicated a binding mode score of −6.83Kcal/mol for isofuranodiene, and an energy value of −11.82Kcal/mol for methotrexate (a classic DHFR inhibitor).

The silver(I) complex [HB{3-(CF3),5-(CH3)Pz}3]AgNCCH3 supported by a partially fluorinated scorpionate ligand.

Tris(pyrazolyl)borates are used extensively in metal coordination chemistry and belong to a class of ligands generally referred to as scorpionates. The steric and electronic properties of these ligands can be modified quite easily by varying the substituents on the 3-, 4-, and 5-positions of the pyrazolyl moieties on the B atom. Fluorinated tris(pyrazolyl)borates are useful in the stabilization of rare silver(I) complexes. The silver(I) adduct (acetonitrile-κN){tris[5-methyl-3-(trifluoromethyl)pyrazol-1-yl-κN2]hydroborato}silver(I), [Ag(C15H13BF9N6)(CH3CN)] or [HB{3-(CF3),5-(CH3)Pz}3]AgNCCH3, was obtained by treating [HB{3-(CF3),5-(CH3)Pz}3]Na with CF3SO3Ag in the presence of acetonitrile, and was isolated in 85% yield. Single-crystal X-ray diffraction analysis reveals that the AgI center has a pseudo-tetrahedral all-nitrogen coordination sphere, and is supported by a tris(pyrazolyl)borate ligand that binds to the AgI center in a κ3-fashion.

Partially fluorinated Scorpionate [HB(3-(CF3),5-(Ph)Pz)3]− as a supporting ligand for silver(I)-benzene, -carbonyl, and -PPh3 complexes

The benzene, CO, and PPh3 adducts [HB(3-(CF3),5-(Ph)Pz)3]AgL (L=C6H6, CO, or PPh3) have been synthesized by a metathesis process using [HB(3-(CF3),5-(Ph)Pz)3]Na(THF), CF3SO3Ag, and the corresponding co-ligands. These silver(I) adducts have been characterized by NMR spectroscopy, and by X-ray crystallography. In all cases the Scorpionate is bound to silver in typical κ3-fashion. The X-ray crystallographic data of [HB(3-(CF3),5-(Ph)Pz)3]Ag(η2-C6H6) show that it has a η2-bound benzene molecule. NMR data point to fluxional behavior in solution. The 13C NMR resonance corresponding to the CO moiety of [HB(3-(CF3),5-(Ph)Pz)3]Ag(CO) appears as a single peak at δ 177.4ppm and the ν¯co is observed at 2148cm−1. These values indicate the presence of a fairly Lewis acidic silver atom in [HB(3-(CF3),5-(Ph)Pz)3]Ag(CO) and significantly diminished Ag→CO π-backbonding. Interesting coupling is observed in the solution 19F and 31P NMR spectra of the Ag(I) adduct [HB(3-(CF3),5-(Ph)Pz)3]Ag(PPh3). A detailed analysis of the spectral and structural features of these complexes has been described herein.

Silver adducts of four-branched histidine rich peptides exhibit synergistic antifungal activity

Previously, a four branched histidine-lysine rich peptide, H3K4b, was shown to demonstrate selective antifungal activity with minimal antibacterial activity. Due to the potential breakdown from proteases, H3K4b was further evaluated in the current study by varying the D- and l-amino acid content in its branches. Whereas analogues of H3K4b that selectively replaced l-amino acids (H3k4b, h3K4b) had improved antifungal activity, the all d-amino acid analogue, h3k4b, had reduced activity, suggesting that partial breakdown of the peptide may be necessary. Moreover, because histidines form coordination bonds with the silver ion, we examined whether silver adducts can be formed with these branched histidine-lysine peptides, which may improve antifungal activity. For Candida albicans, the silver adduct of h3K4b or H3k4b reduced the MIC compared to peptide and silver ions alone by 4- and 5-fold, respectively. For Aspergillus fumigatus, the silver adducts showed even greater enhancement of activity. Although the silver adducts of H3k4b or h3K4b showed synergistic activity, the silver adduct with the all l-amino acid H3K4b surprisingly showed the greatest synergistic and growth inhibition of A. fumigatus: the silver adduct of H3K4b reduced the MIC compared to the peptide and silver ions alone by 30- and 26-fold, respectively. Consistent with these antifungal efficacy results, marked increases in free oxygen radicals were produced with the H3K4b and silver combination. These studies suggest that there is a balance between stability and breakdown for optimal antifungal activity of the peptide alone and for the peptide-silver adduct.

Solvent-free silver-nanoparticle surface-assisted laser desorption/ionization imaging mass spectrometry of the Irganox 1010 coated on polystyrene

Imaging mass spectrometry (IMS) of the antioxidant Irganox 1010 coated on a polystyrene (PS) was conducted using solvent-free silver-nanoparticle surface-assisted laser desorption/ionization (Ag-NP SALDI). The lateral resolution and probing depth of Ag-NP SALDI-IMS, which are important factors in determining the surface sensitivity, were investigated. Direct Ag vapor deposition produced a 10-nm-thick homogenous layer of Ag-NPs on the Irganox 1010/PS thin film. Ag adduct ions of Irganox 1010 and PS repeating structures, and Ag cluster ions appeared in the mass spectrum, which showed that Ag-NPs on the sample surface enhanced the ionization efficiency by functioning as cationization agents. At the lateral resolution of this method (20μm), complementary grid patterns (55 lines per inch) of Irganox 1010 on the PS were observed. The probing depth was investigated with Irganox 1010 layers of different thicknesses, the detection of silver adduct ions of PS indicated Ag-NP SALDI could ionize the PS layer beyond the Irganox 1010 layer. The probing depth was 50–100nm for 10-nm-thick Ag-NP SALDI.

Isolable Ethylene Complexes of Copper(I), Silver(I), and Gold(I) Supported by Fluorinated Scorpionates [HB{3‐(CF3),5‐(CH3)Pz}3]– and [HB{3‐(CF3),5‐(Ph)Pz}3

The group 11 metal adducts [HB{3‐(CF3),5‐(CH3)Pz}3]M(C2H4) (M = Au, Ag, and Cu; Pz = pyrazolyl) have been synthesized via a metathesis process using [HB{3‐(CF3),5‐(CH3)Pz}3]Na and CF3SO3Cu, CF3SO3Ag, AuCl and ethylene. The related [HB{3‐(CF3),5‐(Ph)Pz}3]Ag(C2H4) has also been synthesized using [HB{3‐(CF3),5‐(Ph)Pz}3]Na(THF), CF3SO3Ag and ethylene. These group 11 metal ethylene complexes are white solids and form colorless crystals. They have been characterized by NMR spectroscopy and X‐ray crystallography. The gold‐ethylene adduct [HB{3‐(CF3),5‐(CH3)Pz}3]Au(C2H4) shows large upfield NMR shifts of the ethylene proton and carbon signals relative to the corresponding peaks of the free ethylene, indicating relatively high Au→ethylene backbonding. NMR chemical shift data suggest that the silver complexes of both the tris(pyrazolyl)borate ligands [HB{3‐(CF3),5‐(CH3)Pz}3]– and [HB{3‐(CF3),5‐(Ph)Pz}3]– exhibit the weakest interaction with ethylene as compared to the respective copper and gold complexes. X‐ray crystal structures reveal that the gold atom in [HB{3‐(CF3),5‐(CH3)Pz}3]Au(C2H4) binds to scorpionate in κ2‐fashion while the related silver adduct features a κ3‐bonded scorpionate. [HB{3‐(CF3),5‐(CH3)Pz}3]Cu(C2H4) has a scorpionate that binds to copper with two short Cu–N bonds and one long Cu–N distance.

Well-defined coinage metal transfer agents for the synthesis of NHC-based nickel, rhodium and palladium macrocycles.

With a view to use as carbene transfer agents, well-defined silver(i) and copper(i) complexes of a macrocyclic NHC-based pincer ligand, bearing a central lutidine donor and a dodecamethylene spacer [CNC-(CH2)12, 1], have been prepared. Although the silver adduct is characterised by X-ray diffraction as a dinuclear species anti-[Ag(μ-1)]2(2+), variable temperature measurements indicate dynamic structural interchange in solution involving fragmentation into mononuclear [Ag(1)](+) on the NMR time scale. In contrast, a mononuclear structure is evident in both solution and the solid-state for the analogous copper adduct partnered with the weakly coordinating [BAr(F)4](-) counter anion. A related copper derivative, bearing instead the more coordinating cuprous bromide dianion [Cu2Br4](2-), is notable for the adoption of an interesting tetranuclear assembly in the solid-state, featuring two cuprophilic interactions and two bridging NHC donors, but is not retained on dissolution. Coinage metal precursors [M(1)]n[BAr(F)4]n (M = Ag, n = 2; M = Cu, n = 1) both act as carbene transfer agents to afford palladium, rhodium and nickel complexes of 1 and the effectiveness of these precursors has been evaluated under equivalent reaction conditions.

Anion-Directed Solid-State Structures of Copper(I) and Silver(I) Adducts of Ruthenium Ethyne-1,2-diyl Compounds

A number of group 11 salts, [MX] (M = Ag, X– = –O3SCF3, –O2CCF3, BF4–; M = Cu; X = Cl, Br) and [Cu(MeCN)4][PF6], were found to react in varying stoichiometries with ethyne-1,2-diyl compounds, [{Ru(CO)2(η-C5H4R)}2(μ2-C≡C)] (R = H, Me), to give a number of complex cations. The trication salts [Ag3({Ru(CO)2(η-C5H4Me)}2(μ2-η1:η1-C≡C))3](O3SCF3)3, [Ag3({Ru(CO)2(η-C5H4R)}2(μ2-η1:η1-C≡C))({Ru(CO)2(η-C5H4R)}2(μ2-η1:η2-C≡C))2](BF4)3, and [Cu3({Ru(CO)2(η-C5H4R)}2(μ2-η1:η2-C≡C))({Ru(CO)2(η-C5H4R)}2(μ2-η2-C≡C))](PF6)3 result from the use of the respective anion salts in their syntheses. Coordination of Ag+ by the ethyne-1,2-diyl complexes in the presence of F3CCO2– yields the tetranuclear complexes [Ag4({Ru(CO)2(η-C5H4R)}2(μ2-η2-C≡C))2](μ2-O2CCF3)4 (R = H, Me). The reaction of CuCl does not afford the discrete dimeric complexes normally observed for internal alkynes and metal alkynyl complexes but, rather, the 1-D polymer [Cu2(μ-Cl)2({Ru(CO)2(η-C5H4R)}2(η2-C≡C))](∞|∞), while CuBr gives the discrete dimer motif known in the literature. The solution structures at 1/2, 1/1, and 2/1 stoichiometries of Ag+/[{Ru(CO)2(η-C5H5)}2(μ2-C≡C)] have been probed spectroscopically, and the {Ru(CO)2(η-C5H4R)} environments appear to be equivalent and, likewise, the resonances attributable to their C≡C units. In a subsequent reaction of [{Ru(CO)2(η-C5H4R)}2(μ2-C≡C)] and AgBF4 use of a strict Ag+/ethyne-1,2-diyl ratio gave [Ag({Ru(CO)2(η-C5H5)}2(η2-C≡C))2](BF4). The analogous Cu+ adduct [Cu({Ru(CO)2(η-C5H5)}2(η2-C≡C))2](PF6) is observed, along with the tricopper(I) adduct from the reaction of [{Ru(CO)2(η-C5H4R)}2(μ2-C≡C)] and [Cu(NCMe)4](PF6). A combination of factors appears to control the solid-state structures of these coinage metal adducts, with the anion found to be that which influences the packing to the greatest extent.

Iridium(I) Complexes of π-Acidic Carboxamides

The silver salts of the conjugate bases of the nitrogen acids N-nitroacetamide (Ag[CH3C(O)NNO2] (1)), N-nitrocarbamate (Ag[R′OC(O)NNO2], R′ = CH3 (2), C2H5 (3)), N-nitrosomethylcarbamate (Ag[CH3OC(O)NNO] (4)), and N-nitro-p-tolylsulfonamide, (Ag[p-tolylSO2NNO2] (5)) react with trans-Ir(Cl)(CO)(PPh3)2 (Vaska’s complex) to give trans-Ir(η1-nitrogen acid)(CO)(PPh3)2 complexes (6–10). The related silver amides dinitramide and bistriflimide also react with trans-Ir(Cl)(CO)(PPh3)2, to give trans-Ir[η1-N(NO2)2](CO)(PPh3)2 (11) and the unusual silver adduct [trans-Ir(Cl)(CO)(PPh3)2][Ag[N(SO2CF3)2]] (12), respectively. The reaction of trimethylsilyl bistriflimide, prepared in situ from trimethylsilyl bromide and Ag[N(SO2CF3)2] in acetonitrile, and Ir(F)(CO)(PPh3)2 gives [trans-Ir(CH3CN)(CO)-(PPh3)2][N(SO2CF3)3] (13). The molecular structures of these complexes are all square planar, with the exception of 12, which is square pyramidal with the AgX ligand in the apical position. Complexes 6–9, 12, and 13 are stable ...