Search

Complexation of the glutamic-tyrosine-glutamic tripeptide (EYE) with a series of pseudopeptidic cages has been thoroughly investigated using different analytical techniques. The stoichiometry and affinities of the supramolecular host : guest complexes both in aqueous solution and in the gas-phase were obtained from a suitable combination of fluorescence spectroscopy, NMR, and mass spectrometry (MS) methods. The cages bearing basic groups (lysine, ornitine and histidine) display the tightest EYE binding in aqueous media following the order CyHis > CyLys > CyOrn, thus suggesting that Tyr side chain encapsulation is additionally modulated by the identity of the cage side chains and their ability to be engaged in polar interactions with the EYE peptide. Similarly, binding affinities estimated by MS methods clearly point towards a reduced affinity for the Cy cages with acidic pendant groups and a higher affinity of the CyHis cage over CyLys and CyOrn. Ion mobility spectrometry (IMS)-MS, assisted by molecular modelling, has been used to uncover the structural and conformational characteristics of the pseudopeptidic hosts and their supramolecular adducts with the EYE peptide. The cages display a collisional cross-section increase upon EYE inclusion that is associated with the expansion of the binding pocket of the cage cavity, thus constituting a unique example of conformational pseudopeptidic host adaptation to accommodate the inclusion of the guest., Financial support from the Spanish Ministry of Science and Innovation and the Spanish Research Agency (RTI2018-096182-B-I00, RED2018-102331-T, PID2021-128411NB-I00, MCI/AEI/10.13039/501100011033, and FEDER/EU) and AGAUR (2017 SGR 208) and personal support for L. Tapia (BES-2016-076863) are gratefully acknowledged. We also thank Naiara Solozabal for technical assistance in performing the NMR experiments. We are grateful to the Serveis Centrals d'Instrumentació Científica (SCIC-UJI) for providing the spectroscopy facilities. We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).

This is the peer reviewed version of the following article: Clippane: A Mechanically Interlocked Molecule (MIM) Based on Molecular Tweezers, which has been published in final form at https://doi.org/10.1002/anie.202112513. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited. In this study we report the preparation of a new mechanically interlocked molecule formed by the self-aggregation of two metallotweezers composed by two pyrene-imidazolylidene gold(I) arms and a pyridine-centered pentacyclic bis-alkynyl linker. The mechanically interlocked nature of this molecule arises from the presence of the bulky tert-butyl groups attached to the sides of the pyrene moieties of the arms of the tweezer, which act as stoppers avoiding the dissociation of the self-aggregated metallotweezer dimer once it is formed. By combining experimental techniques, we were able to confirm the mechanically interlocked nature of this molecule in solution, in the gas phase and in the solid state. The behavior of the tert-butyl substituted tweezer differs greatly form that shown by the tweezer lacking of these bulky groups, whose dimeric structure is in equilibrium with the monomeric structure, therefore not showing any mechanical coercion that avoids the disassembly of the self-aggregated structure. We gratefully acknowledge financial support from the Ministerio de Ciencia y Universidades (PGC2018-093382-B-I00) and the Universitat Jaume I (UJI-B2020-01). We are grateful to the Serveis Centrals d'Instrumentació Científica (SCIC-UJI) for providing with spectroscopic facilities.

The anion-induced folding of tripodal imidazolium receptors has been investigated by NMR spectroscopy, electrospray ionization ion mobility mass spectrometry and DFT calculations. Such folding can be switched by anion release upon collision induced dissociation.

This is the pre-peer reviewed version of the following article: Selective conversion of various monosaccharaides into sugar acids by additive‐free dehydrogenation in water, which has been published in final form at https://doi.org/10.1002/cctc.202000544. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. Abundant sugars of five and six carbon atoms are promising candidates for the production of valuable platform chemicals. Here, we describe the catalytic dehydrogenation of several pentoses and hexoses into their corresponding sugar acids with the concomitant formation of molecular hydrogen. This biomass transformation is promoted by highly active and selective catalysts based on iridium‐(III) complexes containing a triazolylidene as mesoionic carbene ligand (MIC). Monosaccharides are converted into sugar acids in an easy and sustainable manner using only catalyst and water, and in contrast to previously reported procedures, in the absence of any additive. The reaction is therefore very clean, and moreover highly selective, which avoids the tedious purification and product separation. Mechanistic investigations using 1 H NMR and UV‐vis spectroscopies and ESI mass spectrometry (ESI‐MS) indicates the formation of an unprecedented diiridium‐hydride as dormant species that correspond to the catalyst resting state.

A family of ruthenium(II) half-sandwich complexes was tested for the hydrolytic decomposition of amine-boranes. The analysis of the catalytic results, together with a multilateral approach based on 1H, 11B NMR, and ESI-MS were used to propose a plausible and conceptually unified mechanism for both the hydrolysis and competitive dehydrogenation of amine-boranes. We propose the intermediacy of solvent-stabilized borenium cations during the catalytic cycle, evolving toward dehydrogenation products in distilled THF or releasing amine-hydroxyboranes in aqueous media. Both reaction pathways would liberate up to 1 equivalent of hydrogen through a metal-catalyzed process, but an out-of-cycle low-barrier hydrolysis of amine-hydroxyboranes would produce the 2 additional equivalents of hydrogen in aqueous solutions. Metal-catalyzed deuteration of (non hydrogen-productive) trisubstituted amine-boranes by using D2O as deuterium source was observed, and included as part of the mechanism proposal.

Acceptorless dehydrogenative coupling (ADC) reactions catalyzed by a series of Ru and Os complexes were studied by ESI-MS. Important ethoxo, 1-ethoxyethanolate, and hydride intermediates were intercepted in the ADC of ethanol to ethyl acetate. Collision-induced dissociation (CID) experiments were applied as a structure elucidation tool and as a probe of the propensity of the reaction intermediates to evolve acetaldehyde, ethyl acetate, and H2, relevant to the catalytic cycle. The key mechanistic step producing ethyl acetate from the 1-ethoxyethanolate intermediates was documented. Energy-dependent CID experiments demonstrated the importance of a vacant coordination site for efficient production of ethyl acetate. The versatility and potential broad applicability of ESI-MS and its tandem version with CID was further illustrated for the ADC reaction of alcohols with amines, affording amides. A mechanism related to that found for the ester synthesis is plausible, with the key step involving formation of a hem...

Sodium salts of hybrid organometallic POM complexes consisting of [M6O19]8− (M = Nb, Ta) and half-sandwich fragments {Cp*M}2+ (Cp* = η5-C5(CH3)5; M = Rh, Ir) and {(C6H6)Ru}2+ dissolve only in one organic solvent, that is, in methanol. From methanolic solutions, crystals of Na4[trans-{(C6H6)Ru}2Nb6O19]·14.125MeOH·2H2O (1), K4[trans-{Cp*Rh}2Nb6O19]·4MeOH·10H2O (2) and K4[trans-{Cp*Ir}2Nb6O19]·10MeOH·4H2O (3) were isolated and characterized by X-ray analysis. Methoxo species [{LM′}2M6O19−n(OCH3)n] (n = 1–3) were detected in solution by ESI-MS and NMR, and they account only for about half of the total speciation in the solution. DFT calculations were used to calculate 13C NMR chemical shifts in the methoxo complexes and to assess their relative stability. Reasons for the preferred solubility in methanol are discussed.

The reaction of acidified aqueous solutions of Na2WO4, NaVO3 and SeO2 in a 16 : 4 : 3 molar ratio gives a complex mixture of polyoxometalates (POMs) with both WVI and VV addenda, formulated as [(SeIVWVIxVV9−xO33)2(WVIO(H2O))(VO)m]n− with x = 4, 5, 6; m = 2 or 3. In solution, the sandwich-type complexes [(SeIVWVIxVV9−xO33)2(WVIO(H2O))(VO)m]n− slowly lose Se and convert into [WVI4VV2O19]4− and further to [WVI5VVO19]3− with a Lindqvist-type structure. These transformations were monitored with 51V and 77Se NMR, electrospray mass-spectrometry and capillary electrophoresis. Crystals of (NMe4)2Na2[(W4V2)O19]·8H2O (1) and (NMe4)4.83[(SeW4.57V4.43O33)2(W(O)(H2O))(VO)2.6]·10.57H2O (2) were isolated and structurally characterized.

The reactions of [Cp*IrCl2]2 (Cp* = pentamethylcyclopentadienyl) with [M6O19]8– (M = Nb, Ta) anions lead to the formation of new hybrid organometallic–polyoxometalate (organometallic–POM) complexes, namely, single-capped Na8[H2{Cp*IrNb6O18}2(O)]·47H2O (Na8-IrNb12) and Na6[{Cp*Ir}Ta6O19]·27H2O (Na6-IrTa6) as well as double-capped trans-[{Cp*Ir}2M6O19]4– complexes. Their solution behavior was studied by NMR spectroscopy and ESI-MS techniques. Cyclic voltammetry (CV) experiments demonstrated efficient electrocatalytic water oxidation in the presence of trans-[{Cp*Ir}2Nb6O19]4–.

We describe an unprecedented catalytic dehydrogenation of glucose by homogeneous catalysts. Iridium(III) complexes containing the fragment [Cp*Ir(NHC)]2+ (NHC = N-heterocyclic carbene ligand) are shown to be very active and highly selective catalysts for the dehydrogenation of glucose to gluconic acid and molecular hydrogen. Glucose is converted to gluconic acid at a catalyst loading of 2 mol%, at reflux in water, without additives and with a selectivity of over 95%. Experimental evidence obtained by 1H NMR spectroscopy and mass spectrometry (ESI/MS) reveals the formation of iridium coordinated to glucose and gluconic acid species. A plausible mechanism is proposed, based on the experimental evidence and supported by DFT calculations., The authors thank the MINECO (Severo Ochoa, CTQ2015-69153-C2-1-R, CTQ2015-69153-C2-2-R and CTQ2015-67461-P), Diputación General de Aragón (Grupo Consolidado E21) and Universitat Jaume I (P1.1B2015-09) for financial support. P. Borja thanks the Universitat Jaume I for a postdoctoral grant.

Self-assembly reactions of Na2WO4, SeO2/SeO32–, and [Mo2O2(μ-S)2(H2O)6]2+ give, depending on the pH value, two new large polyoxometalate complexes: i.e., [(γ-Se2W14O52)3(Mo2O2(μ-S)2(H2O)2)6]24– (1) isolated at pH 3.5 and [(γ-Se2W14O52)4(WO3(H2O))8(W2O5)2(W4O12)2(Mo2O2(μ-S)2(H2O)2)4(Mo2O2(μ-S)2(SeO3))4]36– (2) isolated at pH 2. Both compounds were characterized in the solid state by single-crystal X-ray diffraction, EDX, elemental analysis, TGA, and FT-IR and in solution by ESI-MS and NMR.

International audience; Self-organizing processes are elegant ways to generate and control the nanostructuration of hybrid materials. We describe in this work the synthesis, self-organizing abilities and photo-physical properties of (nBu(4)N)(2)[Mo6Br8i(L)(a)(6)] clustomesogens containing 18 cyanobiphenyl (CB) mesogenic moieties spread equally around the metallic scaffold via aliphatic spacers. By controlling the spacer length and thus the mesogenic density around the rigid inorganic bulky scaffold, we tailored the morphology of hybrid supermolecular building blocks from rod-like to disk-like which strongly influenced their self-organizing abilities. The photophysical properties of hybrids were investigated in their glassy state and in solution. Temperature studies reveal different behaviours depending on the hybrid nanostructuration. Despite their isotropic nature, octahedral clusters offer numerous possibilities in the design of self-assembled hybrid materials showing strong luminescence properties, which is of particular interest in the fields of optics or optoelectronics.

Self-assembly reactions of Na

Reaction of early lanthanides, GeO2 , and Na2 WO4 in a NaOAc buffer results in large crown-shaped polyoxometalates based on [Ln2 GeW10 O38 ](6-) subunits. By using Ni(2+) as a crystallizing agent, [Na⊂Ln12 Ge6 W60 O228 (H2 O)24 ](35-) (Na⊂Ln12 ) hexamers formed by alternating β(1,5)/β(1,8) subunits were obtained for Ln=Pr, Nd. The addition of K(+) led to a similar anion for Ln=Sm, namely, [K⊂Sm12 Ge6 W60 O228 (H2 O)22 ](35-) (K⊂Sm12 ) and [K⊂K7 Ln24 Ge12 W120 O444 (OH)12 (H2 O)64 ](52-) (K⊂Ln24 ) dodecamers that consist of a central core identical to K⊂Sm12 decorated with six external γ(3,4) subunits for Ln=Pr, Nd. These anions dissociate in water into hexameric cores and monomeric entities, as shown by ESI mass spectrometry. The former self-assemble into spherical, hollow, and single-layered blackberry-type structures with radii of approximately 75 nm, as monitored by laser light scattering (LLS) and TEM techniques. Analogous studies performed for K⊂Nd24 in water/acetone mixtures show that the dodecamers remain stable and form in turn their own type of blackberries with sizes that increase from approximately 20 to 50 nm with increasing acetone content. This control over both the composition and size of the vesicle-like assemblies is achieved for the first time by modifying the architecture of the species that undergoes supramolecular association through the solvent polarity.

OsHCl(CO)[κ(3)-PyCH2NHC2H4NHPtBu2] is the first efficient catalyst for chemoselective reduction of challenging unsaturated esters to enols and for acceptorless coupling of amines with MeOH and EtOH affording formamides and acetamides. The NMR, ESI-MS, and DFT data indicate a mechanism proceeding in the metal coordination sphere and producing no free organic intermediates.

A study, involving kinetic measurements on the stopped-flow and conventional UV/Vis timescales, ESI-MS, NMR spectroscopy and DFT calculations, has been carried out to understand the mechanism of the reaction of [Mo3S4(acac)(3)(py)(3)][PF6] ([1]PF6; acac = acetylacetonate, py = pyridine) with two RC equivalent to CR alkynes (R = CH2OH (btd), COOH (adc)) in CH3CN. Both reactions show polyphasic kinetics, but experimental and computational data indicate that alkyne activation occurs in a single kinetic step through a concerted mechanism similar to that of organic [3+2] cycloaddition reactions, in this case through the interaction with one Mo(mu-S)(2) moiety of [1](+). The rate of this step is three orders of magnitude faster for adc than that for btd, and the products initially formed evolve in subsequent steps into compounds that result from substitution of py ligands or from reorganization to give species with different structures. Activation strain analysis of the [3+2] cycloaddition step reveals that the deformation of the two reactants has a small contribution to the difference in the computed activation barriers, which is mainly associated with the change in the extent of their interaction at the transition-state structures. Subsequent frontier molecular orbital analysis shows that the carboxylic acid substituents on adc stabilize its HOMO and LUMO orbitals with respect to those on btd due to better electron-withdrawing properties. As a result, the frontier molecular orbitals of the cluster and alkyne become closer in energy; this allows a stronger interaction.

Reaction of [(C6H6)RuCl2]2 and Na8[Ta6O19] gives two new hybrid organometallic POM complexes, Na10[{(C6H6)RuTa6O18}2(μ-O)]·39.4H2O (Na10-1) and Na4(trans-[{(C6H6)Ru}2Ta6O19]·20H2O (Na4-2). In both cases the half-sandwich fragments {(C6H6)Ru}2+ are coordinated as additional vertices to the {Ta3(μ2-O)3} triangles of the hexatantalate. According to NMR and ESI-MS data, the dimeric complex [{(C6H6)RuTa6O18}2(μ-O)]10- dissociates in water with the formation of monomeric [(C6H6)RuTa6O19]6– species (1a). X-ray structural characterization and aqueous speciation of the complexes by 13C, 1H, and DOSY NMR; ESI-MS; and capillary electrophoresis (CE) have been carried out.

The reaction between in situ generated H2Se and [Cp*MoO2Cl] (1) produces a mixture of binuclear and trinuclear selenium clusters. New selenide complex [Cp*2Mo2Se6] (2) was isolated from CH2Cl2 extracts of the products mixture and characterized by X-ray analysis. This binuclear cluster contains two unprecedented Se34− ligands isoelectronic to I3−. Column chromatography of extracts in air produced two bands, from which [Cp*2Mo2O2Se2] (3) and a new triangular cluster [Cp*3Mo3Se4][ZnCl3(H2O)] (4) were isolated and structurally characterized. The products were characterized by 1H and 77Se NMR, ESI–MS, IR and elemental analysis. Quantum-chemical calculations were used to analyze the Mo–Mo bonding and to help identify lines in 77Se NMR spectra. Crystal and molecular structure of starting [Cp*MoO2Cl] was also determined.

The gas-phase fragmentation reactions of Keggin-type [PW11O39MCl]5– (M = Rh, Ir) polyoxometalates (POMs) featuring chloride terminal ligands have been investigated. Different adducts of the general formulas [PW11O39MCl + 2cat]3– and [PW11O39MCl + 3cat]2– [cat = alkylammonium cations (Me4N+, Bu4N+), alkali cations (Na+, K+) or protons] were subjected to collision-induced dissociation (CID) conditions. The (cat)Cl (cat = H+, Na+ or K+) fragments were released as a common fragmentation pathway and were taken as a fingerprint of the ligands attached at the noble metal site. Other {PW11O39ML} POMs (M = Rh, Ir) with L = thiocyanate, nitrite, methyl, phenylacetate or phenyl were identified on the basis of CID experiments. Coordination studies of thiocyanate anions and CO to {PW11O39Ru} POMs to yield the new compounds [PW11O39RuSCN]5– and [PW11O39RuCO]4– are also reported. CID experiments were also used to validate that thiocyanate and CO ligation at the Ru metal site had occurred.

Two geometrical isomers of the composition [Mo3S4Se3(dtp)3]Cl (dtp is O,O′-diethyldithiophosphate) have been prepared and characterized by multinuclear NMR, electrospray ionization mass spectrometry (ESI–MS) and quantum chemical calculations. The first isomer was prepared by reaction of the aqua cluster ([Mo3(μ3-S)(μ2-Se)3(H2O)9]4+) with a large excess of P4S10/EtOH in 2 M HCl. Its structure corresponds to [Mo3(μ3-S)(μ2-Seax-Seq)3(dtp)3]Cl (1). The second isomer, [Mo3(μ3-S)(μ2-Sax-Seeq)3(dtp)3]Cl (2) was prepared by the reaction of [Mo3S7Cl6]2− with SePPh3 followed by treatment with a stoichiometric amount of P4S10/EtOH. The reason for the isomerism is that the μ2-SSe ligand is coordinated asymmetrically, so that one chalcogen atom is almost coplanar with the Mo3 plane (called equatorial) and the other one is strongly out of the plane (axial). Alternative occupancy of these positions by S or Se leads to a rare kind of linkage isomerism. Each isomer has distinctive spectroscopic signature and fragmentation pattern in ESI–MS. Isomer 2 with μ2-SaxSeeq coordination mode was found to be slightly more stable than isomer 1 with μ2-SeaxSeq coordination. Two new geometrical isomers (1) and (2) of the composition [Mo3(µ3–S)(µ2–Seax–Seq)3(dtp)3]Cl and [Mo3(µ3–S)(µ2-Seq–Seax)3(dtp)3]Cl have been prepared and characterized by multinuclear NMR, electrospray ionization, mass spectrometry (ESI-MS) and quantum chemical calculations.

The reaction of [Mo6I14]2– with methyl propiolate HC≡CC(O)OMe in the presence of Ag+ and Et3N yielded the new luminescent complex [Mo6I8(C≡CC(O)OMe)6]2–, the first fully organometallic complex in the family of octahedral {M6X8} clusters. The cluster was crystallized as tetraphenylphosphonium salt and characterized by X-ray single-crystal diffraction and elemental analyses, mass spectrometry, 13C NMR, UV–vis, and luminescence spectroscopies.

A new synthetic entry to iridium Keggin-type polyoxometalate complexes from [PW11O39](7-) and K-3[IrCl6] under harsh conditions is reported. The complex [PW11O39IrCl](5-) (1(5-)) featuring an IrCl functionality was obtained in high yield and characterized by NMR spectroscopic and ESI-MS techniques. The presence of Li+ (3-4 M) is essential for a quantitative yield of 1(5-). The reactivities of 1(5-) and its rhodium analogue [PW11O39RhCl](5-) in ligand substitution at the noble metal site were studied. Thiocyanate coordination successfully yielded (Bu4N)(5)[PW11O39M(SCN)] [M = Rh (2a), Ir, (3a)]. In both cases, the SCN ligands are coordinated by sulfur atoms, according to C-13 NMR and IR spectroscopic data. Gas-phase fragmentation reactions of compounds 2a and 3a were also investigated by collision-induced dissociation (CID) experiments. Reaction of [PW11O39RhCl](5-) with NaN3 resulted in Cl- to OH- replacement accompanied by the liberation of the RhCl fragment, whereas 1(5-) proved unreactive with NaN3. Attempts to coordinate NO2- are adversely affected by competing noble metal excision with formation of free [PW11O39](7-).

Treatment of the N-thiophosphorylated iminophosphorane ligands (PTA)═NP(═S)(OR)2 [PTA = 1,3,5-triaza-7-phosphaadamantane, 3a and 3b] and (DAPTA)═NP(═S)(OR)2 [DAPTA = 3,7-diacetyl-1,3,7-triaza-5-bicyclo[3.3.1]nonane, 4a and 4b] with an equimolecular amount of AgSbF6 leads to high-yield formation of the new one-dimensional coordination polymers [Ag{μ(2)-N,S-(PTA)═NP(═S)(OR)2}]x[SbF6]x (5a and 5b) and [Ag{μ(2)-O,S-(DAPTA)═NP(═S)(OR)2}]x[SbF6]x (6a and 6b), respectively. These new (iminophosphorane)silver(I) coordination polymers are efficient catalyst precursors for the Meyer-Schuster isomerization of both terminal and internal alkynols. Reactions proceeded in water, under aerobic conditions and using microwave irradiation as heating source, to afford the corresponding α,β-unsaturated carbonyl compounds in excellent yields, without the addition of any cocatalyst. Remarkably, it should be noted that this catalytic system can be recycled up to 10 consecutive runs (1st cycle 45 min, 99%; 10th cycle 6 h, 97%). ESI-MS analysis of 5a in water has been carried out providing valuable insight into the monomeric active species responsible for catalytic activity in water.

The coordination chemistry of dithiolene and diselenolene ligands towards the all-selenium [Mo3Se7Br6]2– dianion has been investigated. Complexes (nBu4N)2[Zn(dmit)2] (dmit = 1,3-dithia-2-thioxo-4,5-dithiolate) and (nBu4N)2[Zn(dsit)2] (dsit = 1,3-dithia-2-thioxo-4,5-diselenolate) were employed as ligand precursors. The (nBu4N)2[Zn(dmit)2] complex in acetonitrile at reflux showed unexpected reactivity with [Mo3Se7Br6]2– dianion in which the inner Se atoms were replaced by S (all but the μ3-Se atom) to afford a series of mixed chalcogen [Mo3Se7–xSx(dmit)3]2– (x = 0–6) dianions. Reaction of the [Mo3S4Se3Br6]2– dianion with (nBu4N)2[Zn(dmit)2] under similar conditions also produced a mixed dmit-containing cluster formulated as [Mo3S7–xSex(dmit)3]2– (x = 0–3). The reactions were conveniently monitored by electrospray ionization mass spectrometry. The reactions of (nBu4N)2[Zn(dmit)2] and (nBu4N)2[Zn(dsit)2] with the [Mo3Se7Br6]2– dianion in dichloromethane at room temperature prevented chalcogen scrambling and allowed us to isolate the cluster salts (nBu4N)2[Mo3Se7(dmit)3] {(nBu4N)2[1]} and (nBu4N)2[Mo3Se7(dsit)3] {(nBu4N)2[2]} in analytically pure form. The crystallization of (nBu4N)2[1] from dichloromethane/diethyl ether resulted in (nBu4N)2[Mo3Se6.1S0.9(dmit)3] with partial substitution of the Seeq atoms in the cluster core. The crystal structure of (nBu4N)2[Mo3Se6.1S0.9(dmit)3] was determined by single-crystal X-ray analysis. Dianionic complexes (nBu4N)2[1], (nBu4N)2[2], and (nBu4N)2[Mo3Se7–xSx(dmit)3] (x = 0–6) were partially oxidized by iodine to afford dark semiconducting powders. These solids exhibit moderate electrical conductivities (7 × 10–2 to 6 × 10–3 S cm–1) and present antiferromagnetic exchange interactions and therefore represent new examples of magnetic Mo3Q7-based single-component conductors.

A unique series of unsymmetrically substituted [Mo3S4(dmpe)3Cl3–x(dca)x]PF6 (x = 0–3) clusters that feature mixed Cl/dca terminal ligands, prepared by thermal reaction of [Mo3S4(dmpe)3Cl3]PF6 ([1]PF6) [dmpe = 1,2-bis(dimethylphosphanyl)ethane] with sodium dicyanamide [Na(dca); dca = dicyanamide] is reported. The cluster/Na(dca) ratio, reaction time as well as the nature of the solvent dictate the relative ratio of [Mo3S4(dmpe)3Cl2(dca)]PF6 ([2]PF6), [Mo3S4(dmpe)3Cl(dca)2]PF6 ([3]PF6) and [Mo3S4(dmpe)3(dca)3]PF6 ([4]PF6). An electrospray ionization mass spectrometry (ESI-MS) based protocol was employed for high-throughput optimization of reaction conditions directed to obtain [2–4]PF6 in optimal yield. The incorporation of dca confers significant polarity differences on the [2–4]PF6 series, so that compounds [2–4]PF6 can be efficiently isolated in analytically pure form after silica gel chromatography and represent the first examples of unsymmetrically substituted Mo3S44+ clusters that feature mixed terminal ligands. The structural, spectroscopic and electrochemical consequences of the stepwise Cl/dca replacement along the [1–4]PF6 series are also presented. The distinctive UV/Vis and electrochemical features along the [1–4]PF6 series illustrate the ability to fine-tune the physicochemical properties of Mo3S44+ clusters upon stepwise dca incorporation more efficiently than upon complete ligand substitution.

New complexes of triangular clusters M3S44+ (M = Mo, W) with incomplete cuboidal metal–chalcogenide framework bearing chiral α-hydroxy and amino acids have been prepared. l -lactic acid (H2lac), l -mandelic acid (H2man), and l -alanine (Hala) react with [W3S4Br4(PPh3)3] in 1:1 ratio to yield, respectively, monosubstituted complexes [W3S4(PPh3)3Br3(Hlac)(CH3CN)] (1), [W3S4(PPh3)3Br3(Hman)(CH3CN)] (2), and [W3S4(PPh3)3Br3(Hala)(CH3CN)]Br (3). In the presence of base [Mo3S4Cl4(PPh3)3] gives trisubstituted complexes [Mo3S4(PPh3)3(Hlac)2(lac)] (4) and [Mo3S4(PPh3)3(Hman)3]Cl (5). Circular dichroism studies of 4 indicate chirality transfer from the ligand to the Mo3S44+ cluster core. These complexes incorporate Cu+ with the formation of corresponding {M3CuS4}5+ cuboidal derivatives. NMR and ESI-MS studies of solution behavior are presented.

Methylation of amines is a fundamental and commonly used reaction in organic synthesis. Many methods are known including various reductive methylations using formaldehyde, formic acid, or carbon dioxide in the presence of reductants. However, several of these methods suffer from limited substrate scope and chemoselectivity because of the different nucleophilicities of substrates. In this respect, the combination of carbonates and hydrosilanes is a valuable methylation source in the presence of Pt-based catalysts. This highly tunable method allows for methylation of both aromatic and aliphatic amines, and chemoselective methylation of aminoalcohols and diamines. Notably, the in situ-formed catalyst can also be used for the reduction of carbonates to methanol at room temperature. Mechanistic insights on intermediates formed during the reaction pathway were obtained by using ESI mass spectrometry.

A convenient, practical and green N-alkylation of amines has been accomplished by applying readily available carboxylic acids in the presence of molecular hydrogen. Applying an in situ formed ruthenium/triphos complex and an organic acid as cocatalyst, a broad range of alkylated secondary and tertiary amines are obtained in good to excellent yields. This novel method is also successfully applied for the synthesis of unsymmetrically substituted N-methyl/alkyl anilines through a direct three-component coupling reaction of the corresponding amines, carboxylic acids, and CO2 as a C1 source.

Reaction of [Nb6O19](8-) with H6TeO6 in water gives telluropentaniobate [(OH)TeNb5O18](6-) (1) as single product, which was isolated as Na(+) and mixed Na(+)/K(+) salts. Crystal structures were determined for Na6[(OH)TeNb5O18]·15H2O (Na6-1) and K6Na[Nb(5.5){Te(OH)}(0.5)O(18.5)]·26H2O (K6Na-1). Formation of 1 was monitored with electrospray ionization mass spectrometry (ESI-MS) and (125)Te NMR techniques. Capillary electrophoresis was used to calculate electrophoretic mobilities and radii of the anionic species in solutions of [(OH)TeNb5O18](6-) and [Nb6O19](8-) in borate buffer. No condensation or degradation products were detected. Reactions of 1 with {Cp*Rh}(2+) sources gives 1:1 and 2:1 hybrid polyoxometalate, which are present in solution as a mixture of isomers, as detected by (125)Te NMR. The isomerism is related to various possibilities of coordination of {Cp*Rh}(2+) to different {M3O3} faces, relative to the unique Te atom. According to ESI-MS experiments in water and methanol, rapid redistribution of the organometallic fragments between the 1:1 and 2:1 complexes takes place. The 1:1 complexes are more stable in water, while 2:1 complexes dominate in methanol. X-ray structural analysis of the crystals isolated from 2:1 reaction mixture allowed identification of Na3[{Cp*Rh}2TeNb5O19]·24H2O (Cp*2Rh2-1) with two {Cp*Rh}(2+) fragments capping the opposing faces of the Lindqvist anion.

Ruthenium complexes containing N-heterocyclic carbene ligands functionalized with different polyaromatic groups (pentafluorophenyl, anthracene, and pyrene) are immobilized onto the surface of reduced graphene oxide. The hybrid materials composed of organometallic complexes and graphene are obtained in a single-step process. The hybrid materials are efficient catalysts for the synthesis of carboxylic acids from the dehydrogenation of alcohols in aqueous media. The catalytic materials can be recycled up to ten times without significant loss of activity. The catalytic activity of the pyrene derivative, Pyr–Ru (3) is enhanced when the ruthenium complex is anchored onto the surface of graphene. The carbonaceous material limits the degradation of the ruthenium complex resulting in increased activity and requiring lower catalyst loading. The catalytic process of the pyrene hybrid material is heterogeneous in nature due to the strong interaction between the pyrene and graphene. The catalytic process of the anthracene and pentafluorophenyl hybrid materials is governed by the so-called ‘boomerang effect’. The ruthenium molecular complex is released from and returned to the graphene surface during the catalytic reaction. Mechanistic insight has been obtained experimentally and theoretically. The energy profile suggests that the rate-determining step is the nucleophilic attack of water on a coordinated aldehyde complex to form a gem-diolate complex., The authors acknowledge the financial support from MINECO (CTQ2015-69153-C2-2-R and CTQ2015-67461-P), Generalitat Valenciana (AICO/2015/039), Universitat Jaume I (P1.1B2015-09) and Universidad de Zaragoza (UZ2014-CIE-01).

A general protocol to access Mo(3)FeS(4)(4+) clusters selectively modified at the Fe coordination site is presented starting from the all-chlorine Mo(3)(FeCl)S(4)(dmpe)(3)Cl(3) (1) [dmpe = 1,2-bis(dimethylphosphane-ethane)] cluster and tetrabutylammonium salts (n-Bu(4)NX) (X = CN(-), N(3)(-), and PhS(-)). Clusters Mo(3)(FeX)S(4)(dmpe)(3)Cl(3) [X = CN(-) (2), N(3)(-) (3), and PhS(-) (4)] are prepared in high yield, and comparison of geometric and redox features upon modification of the coordination environment at the Fe site at parity of ligands at the Mo sites is also presented. The existence of the cubane-type Mo(3)FeS(4)(4+,5+) redox couple is demonstrated by cyclic voltammetry and for compound 1 by cluster synthesis and X-ray structure determinations. Ground states for the 1/1(+) redox couple are evaluated on the basis of magnetic susceptibility measurements, electron paramagnetic resonance, and (57)Fe Mössbauer spectroscopy aimed at providing an input of experimental data for electronic structure determination based on density functional theory calculations.

Bis-allyl ruthenium(IV) complexes containing 1,3 azole β-N-H protic ligands [Ru(η3:η3-C10H16)Cl2L] (C10H16 = 2,7-dimethylocta-2,6-diene-1,8-diyl) (L = imidazole (1a), benzimidazole (1b)), and N-methylimidazole (1c) are highly active precatalysts in the redox isomerization of allylic alcohols into carbonyl compounds in aqueous medium and in the absence of base. A wide series of primary and secondary allylic alcohols can be isomerized into the corresponding carbonyl compounds. Remarkably, complex 1b has been found to be the most efficient catalyst reported to date for the isomerization of 1-octen-3-ol in water leading to a turnover frequency (TOF) value of 60 000 h–1. Moreover, catalyst 1b can be recycled remaining active up to seven cycles. Density functional theory (DFT) calculations give evidence that the hydroxo complexes derived from 1a–c species can be formed in aqueous solution and that they can act as the catalytic active species in a bifunctional catalyzed process. This study demonstrate that in wa...

Chemoselective cubes: Cubane-type [Mo(3)S(4)X(3)(dmpe)(3)](+) clusters (dmpe = 1,2-(bis)dimethylphosphinoethane), in combination with an azeotropic 5:2 mixture of HCOOH and NEt(3) as the reducing agent, act as selective cluster catalysts (X = H) or precatalysts (X = Cl) for the transfer hydrogenation of functionalized nitroarenes, without the formation of hazardous hydroxylamines.

The [Mo(3)S(4)Cl(3)(dhprpe)(3)](+) (1(+)) cluster cation has been prepared by reaction between Mo(3)S(4)Cl(4)(PPh(3))(3) (solvent)(2) and the water-soluble 1,2-bis(bis(hydroxypropyl)phosphino)ethane (dhprpe, L) ligand. The crystal structure of [1](2)[Mo(6)Cl(14)] has been determined by X-ray diffraction methods and shows the typical incomplete cuboidal structure with a capping and three bridging sulfides. The octahedral coordination around each metal center is completed with a chlorine and two phosphorus atoms of the diphosphine ligand. Depending on the pH, the hydroxo group of the functionalized diphosphine can substitute the chloride ligands and coordinate to the cluster core to give new clusters with tridentate deprotonated dhprpe ligands of formula [Mo(3)S(4)(dhprpe-H)(3)](+) (2(+)). A detailed study based on stopped-flow, (31)P{(1)H} NMR, and electrospray ionization mass spectrometry techniques has been carried out to understand the behavior of acid-base equilibria and the kinetics of interconversion between the 1(+) and the 2(+) forms. Both conversion of 1(+) to 2(+) and its reverse process occur in a single kinetic step, so that reactions proceed at the three metal centers with statistically controlled kinetics. The values of the rate constants under different conditions are used to discuss on the mechanisms of opening and closing of the chelate rings with coordination or dissociation of chloride.

The catalytic activity of ruthenium(IV) ([Ru(η(3):η(3)-C(10)H(16))Cl(2)L]; C(10)H(16) = 2,7-dimethylocta-2,6-diene-1,8-diyl, L = pyrazole, 3-methylpyrazole, 3,5-dimethylpyrazole, 3-methyl-5-phenylpyrazole, 2-(1H-pyrazol-3-yl)phenol or indazole) and ruthenium(II) complexes ([Ru(η(6)-arene)Cl(2)(3,5-dimethylpyrazole)]; arene = C(6)H(6), p-cymene or C(6)Me(6)) in the redox isomerisation of allylic alcohols into carbonyl compounds in water is reported. The former show much higher catalytic activity than ruthenium(II) complexes. In particular, a variety of allylic alcohols have been quantitatively isomerised by using [Ru(η(3):η(3)-C(10)H(16))Cl(2)(pyrazole)] as a catalyst; the reactions proceeded faster in water than in THF, and in the absence of base. The isomerisations of monosubstituted alcohols take place rapidly (10-60 min, turn-over frequency = 750-3000 h(-1)) and, in some cases, at 35 °C in 60 min. The nature of the aqueous species formed in water by this complex has been analysed by ESI-MS. To analyse how an aqueous medium can influence the mechanism of the bifunctional catalytic process, DFT calculations (B3LYP) including one or two explicit water molecules and using the polarisable continuum model have been carried out and provide a valuable insight into the role of water on the activity of the bifunctional catalyst. Several mechanisms have been considered and imply the formation of aqua complexes and their deprotonated species generated from [Ru(η(3):η(3)-C(10)H(16))Cl(2)(pyrazole)]. Different competitive pathways based on outer-sphere mechanisms, which imply hydrogen-transfer processes, have been analysed. The overall isomerisation implies two hydrogen-transfer steps from the substrate to the catalyst and subsequent transfer back to the substrate. In addition to the conventional Noyori outer-sphere mechanism, which involves the pyrazolide ligand, a new mechanism with a hydroxopyrazole complex as the active species can be at work in water. The possibility of formation of an enol, which isomerises easily to the keto form in water, also contributes to the efficiency in water.

[EN] A new molybdenum siloxo cluster of formula [Mo3S4(dmpe)(3)(MPTES)(3)]PF6 (dmpe = 1,2-(bis)dimethylphosphinoethane; MPTES = (3-mercaptopropyl)triethoxysilane) has been synthesized with the ultimate goal of incorporating it into ordered mesoporous silica via covalent attachment. For this purpose, two different approaches, in situ and grafting, are employed. The first one is based in the co-condensation of the Mo3S4 siloxo cluster and tetraethylorthosilicate (TEOS) as mixed silicon sources in the presence of a surfactant (CTAB). The use of this approach allows for the incorporation of the Mo3S4 siloxo cluster into the structure of the mesoporous silica. For comparison purposes, the same Mo3S4 siloxo cluster has been immobilized on the surface of conventional mesoporous silica MCM-41, using more traditional grafting techniques. The physical and structural properties of both series of materials, containing different Mo3S4 cluster loadings, have been thoroughly investigated by means of powder X-ray diffraction (XRD), N-2 adsorption/desorption isotherms, transmission electron microscopy (TEM), magic-angle spinning (MAS) P-31 and CP/MAS Si-29 NMR, Fourier transform infrared (FT-IR) and UV-Vis diffuse reflectance (DRUV-Vis) spectroscopies. The chemical and structural integrity of the diphosphino Mo3S4 siloxo cluster is preserved in both the in situ and grafted mesoporous silica based materials. Depending on the incorporation approach, immobilization of the trinuclear sulfido cluster occurs into the silica matrix structure for the in situ materials or on the surface for the grafted ones. With these results, we show that it is possible to extend the incorporation of chemical functionalities into the structure of mesoporous materials to Mo3S4 siloxo clusters. (C) 2011 Elsevier Inc. All rights reserved., The financial support of the Spanish Ministerio de Ciencia e Innovacion (CTQ2005-09385-C03-02 and CTQ2008-02670), Fundacio Bancaixa-UJI (P1.1B2010-46), and Generalitat Valenciana (ACOMP/2011/037 and Prometeo/2009/053) is gratefully acknowledged. I.S. thanks the Spanish Ministerio de Ciencia e Innovacion (MICINN) for a doctoral fellowship (FPU). E.S. acknowledges financial support from Spanish MICINN through the Juan de la Cierva Program (ref. JCI-2008-2165) and from Generalitat Valenciana (ref. BEST2011/223). The authors thank Dr. Cristina Almansa Carrascosa, for assistance with the Transmission Electron Microscopy. Special thanks go to Dr. Wieslaw Roth for his advice and helpful comments on the work presented in this manuscript. The authors also thank the Servei Central d'Instrumentacio Cientifica (SCIC) of the University Jaume I and the Technical Services of the University of Alicante.

A new cluster of formula {[Mo3(μ3-S)(μ-S)(μ-S2)2(dtp)3(μ-OAc)][Mo3NiS4(dtp)3(μ-OAc)(CH3CN)]} (1; dtp = diethyl dithiophosphate; OAc = acetate) comprising the novel Cs-symmetrized Mo3(μ3-S)(μ-S)(μ-S2)2 structural type covalently attached to a cubane-type Mo3NiS4 core has been isolated and fully characterized. The reaction of a 2 M HCl solution of [Mo3S4(H2O)9]4+ with an excess of potassium diethyl dithiophosphate and acetic acid in the presence of the [Mo3(NiCl)S4(H2O)9]3+ cluster afforded a mixture of products encompassing different Mo3Sx (x = 4–7) cluster cores from which the Mo3(μ3-S)(μ-S)(μ-S2)2 structural type has been isolated in analytically pure form as a Mo3NiS4 adduct. The robustness of the aggregate 1 was also retained in solution as judged by ESI-MS and 31P NMR techniques. Single-crystal X-ray analysis revealed in detail the complementary association of the newly formed Mo3(μ3-S)(μ-S)(μ-S2)2 entity and the Mo3NiS4 cluster in which μ-S sulfide ligands and μ-S2 disulfide ligands act as nucleophilic and electrophilic functional groups, respectively, towards the Mo3NiS4 cube through directional Ni–S covalent bonds and short S···S contacts (below 3.3 A).

A series of nine [Sb7W36O133Ln3M2(OAc)(H2O)8](17-) heterometallic anions (Ln3M2; Ln=La-Gd, M=Co; Ln=Ce, M=Ni and Zn) have been obtained by reacting 3 d metal disubstituted Krebs-type tungstoantimonates(III) with early lanthanides. Their unique tetrameric structure contains a novel {MW9O33} capping unit formed by a planar {MW6O24} fragment to which three {WO2} groups are condensed to form a tungstate skeleton identical to that of a hypothetical trilacunary derivative of the ɛ-Keggin cluster. It is shown, for the first time, that classical Anderson-Evans {MW6O24} anions can act as building blocks to construct purely inorganic large frameworks. Unprecedented reactivity in the outer ring of these disk-shaped species is also revealed. The Ln3M2 anions possess chirality owing to a {Sb4O4} cluster being encapsulated in left- or right-handed orientations. Their ability to self-associate in blackberry-type vesicles in solution has been assessed for the Ce3Co2 derivative.

New cluster complex [Mo3SeO3(acac)3(py)3]+ was obtained by ligand substitution in the aqua complex [Mo3SeO3(H2O)9]4+. Crystal structure was determined for [Mo3SeO3(acac)3(py)3]PF6·C6H5CH3. The complex was characterized by 77Se NMR, electrospray mass-spectrometry, and cyclic voltammetry. DFT calculations were used to confirm the assignment of chemical shift and to study Mo–Mo bonding in the cluster core.

Summary: This paper describes the electrochemical reduction of nitrite ion in 0.1MNaClO 4 , on glassy carbon or ITO electrodes modified with mixtures PVC- tetraruthe-nated metalloporphyrins. This electrode is able to keep the extraordinary electro-catalytic properties of the macrocycle allowing multielectronic transfers and a greatstability as a consequence of the inclusion of the macrocycles into a polymericsupport such as PVC. On the other hand, the electrochemical reduction of nitrite ionon these modified electrodes studied by cyclic voltammetry shows an enhancementin the current values and lower overpotential compared with the activity of the bareglassy carbon electrode. Controlled potential electrolysis experiments verify theproduction of ammonia, hydrazine and hydroxylamine, showing the electrocatalyticcharacter and the stability of this modified electrode. Keywords: electrocatalysis; modified electrodes; nitrite; PVC; tetraruthenated porphyrins Introduction Nitrite ions are produced by photolysis ofnitrate ions and by photodegradation ofaquatic humic substances present in theaquatic environment. Nitrite is a keyspecies in global nitrogen cycle. Nitritesshow environmental and biological impor-tance. Moreover, they have an importantrole as additive in the alimentary industryas preservative, antimicrobial and colorfixative agent.

New triangular Mo and W cluster complexes incorporating (S)-lactic acid (HLac), [Mo3S4(μ-Lac)(dtp)3(py)] (1) and [W3S4(μ-Lac)(dtp)3(py)] (2), were prepared [dtp = (EtO)2PS2]. Analogous synthetic procedures were adapted for the synthesis of cuboidal Mo3NiS4 to yield [Mo3(Nipy)S4(py)(μ-OAc)(dtp)3(py)] (3). The crystal structures of 1 and 3 were determined. A detailed variable-temperature 31P{1H} and 1H NMR study of compounds 1 and 3 indicated fluxional behaviour in non-coordinating solvents (CDCl3, CD2Cl2 and CDCl2CDCl2). A number of dynamic processes were identified involving the Mo–py site that include configuration inversion [(P) to (M)], hindered Mo–N rotation and pyridine exchange. Experiments with deuterated pyridine revealed a faster substitutional lability of Mo–py compared with Ni–py.

The present article reviews synthetic approaches to efficiently prepare Mo3S7 clusters coordinated to 1,2-bis-dithiolene ligands of general formula [Mo3S7(dithiolene)3]2− where dithiolene stands for tfd (bis(trifluoromethyl)-1,2-dithiolene), bdt (1,2-benzenedithiolene), mnt (maleonitriledithiolene), tdas (1,2,5-thiadiazole-3,4-dithiolene), dmid (1,3-dithia-2-one-4,5-dithiolene), dmit (1,3-dithia-2-thione-4,5-dithiolene) and the diselenolene dsit (1,3-dithia-2-thione-4,5-diselenolene). These [Mo3S7(dithiolene)3]2− dianions serve as starting materials to access new dithiolene clusters featuring Mo3S4 and Mo2O2S2 cluster cores. The electrochemical and spectroscopic properties as well as solid state structures of Mo3S7/dithiolene compounds are also described. These C3-symmetry [Mo3S7(dithiolene)3]2− molecules inherently possess degenerate frontier orbitals and display a rich structural diversity due to the electrophilic character of the three sulfur atoms in axial positions. These characteristics make the [Mo3S7(dithiolene)3]2− dianions, versatile targets for the development of new molecular conductors. Several examples of hybrid charge-transfer salts based on TTF-donors and [Mo3S7(dithiolene)3]2−/[Mo3S7X6]2− dianions (X = Cl, Br) are discussed as well as the preparation of the first family of cluster-based single-component magnetic conductors of formula Mo3S7(dithiolene)3.

The synthesis, X-ray structure and variable-temperature magnetic study of new compounds of formula PPh4[Cr(dmbipy)(ox)2]·5H2O (1), AsPh4[Cr(dmbipy)(ox)2]·5H2O (2), {Ba(H2O)2[Cr(dmbipy)(ox)2]2}n·17/2nH2O (3) and {Ag(H2O)[Cr(dmbipy)(ox)2]}n·3nH2O (4) (PPh4+ = tetraphenylphosphonium cation; AsPh4+ = tetraphenylarsonium cation; dmbipy = 4,4′-dimethyl-2,2′-bipyridine; ox2− = oxalate dianion) are reported herein. The isomorphous compounds 1 and 2 are made up of discrete [Cr(dmbipy)(ox)2]− anions, XPh4+ cations [X = P (1) and As (2)] and uncoordinated water molecules. The chromium environment in 1 and 2 is distorted octahedral with Cr–O and Cr–N bond distances varying in the ranges 1.950(2)–1.9782(12) and 2.047(3)–2.0567(14) A, respectively. The angles subtended at the chromium atom by the two bidentate oxalate ligands cover the range 82.58(10)–83.11(5)°, and they are somewhat greater than those concerning the chelating dmbipy [79.04(10) (1) and 79.24(5)° (2)]. The [Cr(dmbipy)(ox)2]− unit of 1 and 2 also occurs in 3 and 4 but it adopts different coordination modes. It acts as a chelating ligand through its two oxalate groups towards the divalent barium cations in 3 affording neutral chains with diamond-shaped units sharing the barium atoms, while the two other corners are occupied by two crystallographically independent chromium atoms. The barium atom in 3 is coordinated by eight oxygen atoms from four oxalate groups and two aqua ligands. The structure of 4 consists of neutral bimetallic layers where the [Cr(dmbipy)(ox)2]− unit acts as a ligand towards the univalent silver(I) cation through its two oxalate groups, one of them being bidentate and the other bidentate/monodentate (outer). Each silver atom is six-coordinated with a water molecule and five oxygen atoms from three oxalate groups building a highly distorted octahedral environment. Magnetic susceptibility measurements for 1–4 in the temperature range 1.9–300 K show the occurrence of weak ferro- (1 and 2) and antiferromagnetic (3 and 4) interactions which are mediated by π–π stacking between dmbipy ligands through the spin polarization mechanism. A comparative study of the potentiality of the [Cr(AA)(ox)2]− unit (AA = bidentate nitrogen donor) as a building block for designing heterometallic species is carried out in the light of the available structural information.

Opening the cluster core: Substitution of the chloride ligand in the novel cationic cluster [W(3)CuS(4)H(3)Cl(dmpe)(3)](+) (see figure; dmpe=1,2-bis(dimethylphosphino)ethane) by acetonitrile is promoted by water addition. Kinetic and density functional theory studies lead to a mechanistic proposal in which acetonitrile or water attack causes the opening of the cluster core with dissociation of one of the Cu--S bonds to accommodate the entering ligand.Reaction of the incomplete cuboidal cationic cluster [W(3)S(4)H(3)(dmpe)(3)](+) (dmpe=1,2-bis(dimethylphosphino)ethane) with Cu(I) compounds produces rare examples of cationic heterodimetallic hydrido clusters of formula [W(3)CuClS(4)H(3)(dmpe)(3)](+) ([1](+)) and [W(3)Cu(CH(3)CN)S(4)H(3)(dmpe)(3)](2+) ([2](2+)). An unexpected conversion of [1](+) into [2](2+), which involves substitution of chloride by CH(3)CN at the copper centre, has been observed in CH(3)CN/H(2)O mixtures. Surprisingly, formation of the acetonitrile complex does not occur in neat acetonitrile and requires the presence of water. The kinetics of this reaction has been studied and the results indicate that the process is accelerated when the water concentration increases and is retarded in the presence of added chloride. Computational studies have also been carried out and a mechanism for the substitution reaction is proposed in which attack at the copper centre by acetonitrile or water causes disruption of the cubane-type core. ESI-MS experiments support the formation of intermediates with an open-core cluster structure. This kind of process is unprecedented in the chemistry of M(3)M'Q(4) (M=Mo, W; Q=S, Se) clusters, and allows for the transient appearance of a new coordination site at the M' site which could explain some aspects of the reactivity and catalytic properties of this kind of clusters.

The substitutional lability of Mo-Cl and Cu-Cl bonds in cubane-type Mo(3)CuS(4) and incomplete cubane-type Mo(3)S(4) clusters is exploited in an attempt to prepare cyanide-terminated complexes, namely [Mo(3)S(4)(CuCN)(dmpe)(3)Cl(3)]PF(6) ([2]PF(6)) and [Mo(3)S(4)(dmpe)(3)(CN)(3)]PF(6) ([5]PF(6)), and to subsequently use them as precursors in low-dimensional linking reactions. Mixed-metal assemblies formulated as [Mo(3)S(4)(Cu-muCN...Mo(CO)(5))(dmpe)(3)Cl(3)](+) ([3](+)) and [Mo(3)S(4)(dmpe)(3)(muCN...Mo(CO)(5))(3)](+) ([6](+)) are obtained by reaction of tetrahydrofuran solutions of [2]BPh(4) and [5]BPh(4) with the complex (THF)Mo(CO)(5). The intrinsic stability of the (M'-muCN...Mo(CO)(5)) linkages (M' = Cu in 3(+) and Mo in 6(+)) in solution and in the gas phase is investigated through a combination of variable-temperature (31)P NMR, IR, UV-vis spectroscopies, and electrospray ionization tandem mass spectrometry. The spectroscopic and electrochemical consequences of CN coordination as well as Mo(CO)(5) ligation either at the Cu or the Mo site in Mo(3)CuS(4) and Mo(3)S(4) clusters are reported. Replacement of Cl by CN or CN...Mo(CO)(5) at the Cu site does not affect the redox potentials, whereas analogous substitution at Mo sites exerts a profound anodic shift of 220 and 500 mV upon Cl to CN and Cl to CN...Mo(CO)(5) replacement, respectively.

In our pursuit of mixed chalcogen-bridged cluster complexes, solids of the compositions Mo3SSe6Br4 and W3SSe6Br4 were prepared using high-temperature synthesis from the elements. Treatment of Mo3SSe6Br4 with Bu4NBr in a vibration mill yielded (Bu4N)3{[Mo3(μ3-S)(μ2-Se2)3Br6]Br} (I). Its all-selenide analogue (Bu4N)3{[Mo3(μ3-Se)(μ2-Se2)3Br6]Br} (II) was prepared from Mo3Se7Br4 in a similar way. Both compounds were characterized by IR, Raman, and 77Se NMR spectroscopy. The structure of II was determined by X-ray single-crystal analysis. Compound I is isostructural with II and contains the new Mo3(μ3-S)Se64+ cluster core. By treatment of a 4 M Hpts solution of I with PPh3 followed by cation-exchange chromatography, the new mixed chalcogenido-molybdenum aqua ion, [Mo3(μ3-S)(μ2-Se)3(H2O)9]4+, was isolated and characterized using UV−vis spectroscopy and, after derivatization into [Mo3(μ3-S)(μ2-Se)3(acac)3(py)3]+, electrospray ionization mass spectrometry. From HCl solutions of the aqua ion, a supramolecular addu...

Electrospray ionization (ESI) of the Lindqvist (n-Bu4N)2[M6O19] (M = Mo, W) polyoxometalates provides a straightforward entry for the generation of an assortment of oxo- and hydroxo anions in the gas-phase. In particular, the series of oxo dianions of general formula [(MO3) n O]2− (n = 2–6; M = Mo, W), monoanions, namely [(MO3) n O]− (n = 1, 2) and [(MO3) n ]− (n = 1, 2), and the hydroxo [(MO3) n (OH)]− (n = 1–6) species can be readily generated in the gas-phase upon varying the solvent composition as well as the ionisation conditions (typically the Uc cone voltage). Complementary tandem mass experiments (collision induced dissociation and ion–molecule reactions) are also used aimed to investigate the consecutive dissociation of these species and their intrinsic gas-phase reactivity towards methanol. Special emphasis is paid to some of the key factors of these group 6 anions related to the gas-phase activation of methanol, such as molecular composition, open vs closed shell electronic nature and cluster size.

Electrospray ionization (ESI) tandem mass spectrometry is used to investigate the gas-phase dissociation of trinuclear sulfide W(3)S(4) complexes containing three diphosphane ligands and three terminal bromine atoms, namely, [W(3)S(4)(dmpe)(3)(Br)(3)](+) (1(+)) or hydroxo groups, [W(3)S(4)(dmpe)(3)(OH)(3)](+) (2(+)) (dmpe = 1,2-bis(dimethylphosphanyl)ethane). Sequential evaporation of two diphosphane ligands is the sole fragmentation channel for the 1(+) cation that yields product ions with one or two unsaturated W-Br functional groups, respectively. Conversely, evaporation of one diphosphane ligand followed by two water molecules is observed for cation 2(+). Complementary deuterium-labeling experiments in conjunction with computational studies provide deep insight into the thermodynamically favored product ion structures found along the fragmentation pathways. From these results, the formation of a series of cluster cations with WBr, WOH, and WO functional groups either on saturated or unsaturated metal sites is proposed. The effect of the properties of these cluster cations, among them chemical composition and coordinative saturation, on their reactivity toward methanol is discussed.

Reaction of [Mo6(μ3-Cl)8Cl6]2− with H2Se, generated in situ from ZnSe and 4 M HCl under hydrothermal conditions lead to the substitution of one or two bridging chlorides, depending on the reagents ratio. With the Mo6/ZnSe 1:3 molar ratio [Mo6(μ3-SeCl7)Cl6]3− forms selectively in high yield. Further substitution is more hindered, and even at 1:20 cluster-to-selenide molar ratio a mixture of [Mo6(μ3-SeCl7)Cl6]3− and [Mo6(μ3-Se2Cl6)Cl6]4− is formed. The products were characterized by X-ray, Raman spectra and electrospray ionization mass spectrometry.