C3-symmetry Mo3S4 aminophosphino clusters combining three sources of stereogenicity: stereocontrol directed by hydrogen bond interactions and ligand configuration

A diastereoselective synthesis of proline containing aminophosphino cubane-type Mo3S4 clusters, (P)-[Mo3S4Cl3((1S,2R)-PPro)3]Cl ((P)-[Mo-(SN,RC)]Cl) and (P)-[Mo3S4Cl3((1S,2S)-PPro)3]Cl ((P)-[Mo-(SN,SC)] Cl), has been achieved in high yields by reacting the corresponding enantiomerically pure PPro ((R)- and (S)-2-[(diphenylphosphino)methyl]pyrrolidine) ligands with the Mo3S4Cl4(PPh3)3(H2O)2 complex. Circular dichroism, nuclear magnetic resonance and X-ray techniques confirm that the (P)-[Mo-(SN,RC)]Cl and (P)-[Mo-(SN,SC)]Cl cluster cations are diastereoisomers which combine three sources of stereogenicity provided by the cluster framework, one carbon atom of the aminophosphine ligand and the nitrogen stereogenic center. The higher stability of the (P)-[Mo-(SN,SC)]+ cation is due to stabilizing vicinal Cl⋯HN interactions as well as due to the cis-fused conformation of the bicyclic system formed upon coordination of the aminophosphine ligand.The financial support of the Spanish Ministerio de Economía y Competitividad (Grant CTQ2011-23157 and CTQ2015-65207-P), Universitat Jaume I (Research Project P1·1B2013-19) and Generalitat Valenciana (PROMETEOII/2014/022) is gratefully acknowledged. The authors also thank the Servei Central d’Instrumentació Científica (SCIC) of the University Jaume I for providing us with the mass spectrometry, NMR and X-ray facilities. C. A. thanks the Spanish Ministerio de Economía y Competitividad for a predoctoral fellowship (FPI)

Influence of the Diphosphine Coordinated to Molybdenum and Tungsten Triangular M3S4 Cluster Hydrides in the Catalytic Hydrodefluorination of Pentafluoropyridine

Hydrido molybdenum and tungsten(IV) cluster cations of formula [M3S4H3(dppe)3]+ (dppe = 1,2-(bis)dimethylphosphinoethane), [Mo-1]+ (M = Mo) and [W-1]+ (M = W), have been isolated by reacting their halide precursors with borohydride. Synthetic procedures have been optimized by appropriate choice of the solvent. Furthermore, [M3S4F3(dppe)3]+ fluorido cluster complexes, [Mo-2]+ (M = Mo) and [W-2]+ (M = W) have been prepared through halogen substitution reactions using an excess of cesium fluoride. The structures of [Mo-1]+ and [Mo-2]+ have been determined by single crystal X-ray diffraction experiments. These [M-1]+ hydrido and [M-2]+ fluorido clusters have been used as catalysts and precatalysts, respectively, in the catalytic hydrodefluorination (HDF) of pentafluoropyridine using HSiMe2Ph as hydrogen source. The reaction proceeds under microwave and reflux conditions to selectively afford 2,3,5,6-tetrafluoropyridine. The [W-1]+ hydrido cluster is the most efficient catalyst with turnover numbers of 124, while the [Mo-1]+ hydrido cluster reacts faster. Fluorido [Mo-2]+ and [W-2]+ complexes provide lower yields and turnover numbers. In general, the molybdenum and tungsten [M-1]+ and [M-2]+ diphosphino complexes are more efficient than their dmpe (1,2-(bis)dimethylphosphinoethano) analogues and activate pentafluoropyridine under softer conditionsThe financial support of the Spanish Ministerio de Economía y Competitividad (Grant CTQ2011-23157), Universitat Jaume I (Research Project P1·1B2013-19) and Generalitat Valenciana (ACOMP/2013/215 and Prometeo/2009/053) is gratefully acknowledged. The authors also thank the Servei Central d’Instrumentació Científica (SCIC) of the University Jaume I for providing us with the mass spectrometry, NMR and X-ray facilities. C.A. thanks the Spanish Ministerio de Economía y Competitividad for a predoctoral fellowship (FPI)

Synthesis, conformational analysis, and cytotoxicity of conformationally constrained aplidine and tamandarin A analogues incorporating a spirolactam β-turn mimetic

With the aim of studying the contribution of the β II turn conformation at the side chain of didemnins to the bioactive conformation responsible for their antitumoral activity, conformationally restricted analogues of aplidine and tamandarin A, where the side chain dipeptide Pro8-N-Me-d-Leu7 is replaced with the spirolactam β II turn mimetic (5R)-7-[(1R)-1-carbonyl-3-methylbutyl]-6-oxo-1,7-diazaspiro[4.4]nonane, were prepared. Additionally, restricted analogues, where the aplidine (pyruvyl9) or tamandarin A [(S)-Lac9] acyl groups are replaced with the isobutyryl, Boc, and 2-methylacryloyl groups, were also prepared. These structural modifications were detrimental to cytotoxic activity, leading to a decrease of 1−2 orders of magnitude with respect to that exhibited by aplidine and tamandarin A. The conformational analysis of one of these spirolactam aplidine analogues, by NMR and molecular modeling methods, showed that the conformational restriction caused by the spirolactam does not produce significant changes in the overall conformation of aplidine, apart from preferentially stabilizing the trans rotamer at the pyruvyl9−spirolactam amide bond, whereas in aplidine both cis and trans rotamers at the pyruvyl9−Pro8 amide bond are more or less equally stabilized. These results seem to indicate a preference for the cis form at that amide bond in the bioactive conformation of aplidine. The significant influence of this cis/trans isomerism upon the cytotoxicity suggests a possible participation of a peptidylprolyl cis/trans isomerase in the mechanism of action of aplidine.This work was supported by CICYT (Grant SAF2000-0147), MCYT-FEDER (Grant BIO2002-2301), Generalitat de Catalunya (Group Consolidat 1999SGR0042 and Centre de Referència en Biotecnologia), and Pharma Mar, S.A

Tioclústeres de molibdeno o wolframio homo- y heterometálicos con estructura de cubano

En esta tesis doctoral se han desarrollado nuevas vías de síntesis de clústeres trinucleares cuboidales de molibdeno y wolframio con unidad central [M3S4] coordinados a difosfinas. La reactividad del metal M se ha investigado con vistas a sus aplicaciones potenciales en medicina y se ha realizado un estudio del mecanismo de protonación de los clústeres hidruro de wolframio. La obtención de complejos clúster heterobimetálicos tetranucleares derivados de la unidad [M3M'S4], donde M' puede ser cobre, níquel o paladio, en altos rendimientos ha permitido caracterizar estructuralmente estos compuestos, estudiar su reactividad y evaluar sus propiedades como limitadores ópticos y catalizadores. El estudio de la relación entre la estructura electrónica y molecular, a través de metodologías mecanocuánticas ab initio, combinadas con teorías topológicas del enlace, ha contribuido a determinar la naturaleza del enlace en estos compuestos clúster

Tioclústeres de molibdeno o wolframio homo- y heterometálicos con estructura de cubano

En esta tesis doctoral se han desarrollado nuevas vías de síntesis de clústeres trinucleares cuboidales de molibdeno y wolframio con unidad central [M3S4] coordinados a difosfinas. La reactividad del metal M se ha investigado con vistas a sus aplicaciones potenciales en medicina y se ha realizado un estudio del mecanismo de protonación de los clústeres hidruro de wolframio. La obtención de complejos clúster heterobimetálicos tetranucleares derivados de la unidad [M3M'S4], donde M' puede ser cobre, níquel o paladio, en altos rendimientos ha permitido caracterizar estructuralmente estos compuestos, estudiar su reactividad y evaluar sus propiedades como limitadores ópticos y catalizadores. El estudio de la relación entre la estructura electrónica y molecular, a través de metodologías mecanocuánticas ab initio, combinadas con teorías topológicas del enlace, ha contribuido a determinar la naturaleza del enlace en estos compuestos clúster

Intrinsic gas-phase reactivity toward methanol of trinuclear tungsten W3S4 complexes bearing W-X (X=Br, OH) groups

Electrospray ionization (ESI) tandem mass spectrometry is used to investigate the gas-phase dissociation of trinuclear sulfide W3S4 complexes containing three diphosphane ligands and three terminal bromine atoms, namely, [W3S4(dmpe)3(Br)3]+ (1+) or hydroxo groups, [W3S4(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 W—Br, W—OH, and W═O 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

Enhanced Photocatalytic Activity and Stability in Hydrogen Evolution of Mo6 Iodide Clusters Supported on Graphene Oxide

Catalytic properties of the cluster compound (TBA)2[Mo6Ii8(O2CCH3)a6] (TBA = tetrabutylammonium) and a new hybrid material (TBA)2Mo6Ii8@GO (GO = graphene oxide) in water photoreduction into molecular hydrogen were investigated. New hybrid material (TBA)2Mo6Ii8@GO was prepared by coordinative immobilization of the (TBA)2[Mo6Ii8(O2CCH3)a6] onto GO sheets and characterized by spectroscopic, analytical, and morphological techniques. Liquid and, for the first time, gas phase conditions were chosen for catalytic experiments under UV¿Vis irradiation. In liquid water, optimal H2 production yields were obtained after using (TBA)2[Mo6Ii8(O2CCH3)a6] and (TBA)2Mo6Ii8@GO) catalysts after 5 h of irradiation of liquid water. Despite these remarkable catalytic performances, ¿liquid-phase¿ catalytic systems have serious drawbacks: the cluster anion evolves to less active cluster species with partial hydrolytic decomposition, and the nanocomposite completely decays in the process. Vapor water photoreduction showed lower catalytic performance but offers more advantages in terms of cluster stability, even after longer radiation exposure times and recyclability of both catalysts. The turnover frequency (TOF) of (TBA)2Mo6Ii8@GO is three times higher than that of the microcrystalline (TBA)2[Mo6Ii8(O2CCH3)a6], in agreement with the better accessibility of catalytic cluster sites for water molecules in the gas phase. This bodes well for the possibility of creating {Mo6I8}4+-based materials as catalysts in hydrogen production technology from water vaporThis research was funded by the Severo Ochoa Program, grant number SEV-2016-0683, Ministerio de Ciencia e Innovación, grant number PGC2018-099744, Consejo Superior de Investigaciones Científicas, grant number I-Link1063, and Russian Foundation for Basic Research, grant number 18-33-20056

Octahedral Molybdenum Iodide Clusters Supported on Graphene for Resistive and Optical Gas Sensing

This paper reports for the first time a gas-sensitive nanohybrid based on octahedral molybdenum iodide clusters supported on graphene flakes (Mo6@Graphene). The possibility of integrating this material into two different transducing schemes for gas sensing is proposed since the nanomaterial changes both its electrical resistivity and optical properties when exposed to gases and at room temperature. Particularly, when implemented in a chemoresistive device, the Mo6@Graphene hybrid showed an outstanding sensing performance toward NO2, revealing a limit of quantification of about 10 ppb and excellent response repeatability (0.9% of relative error). While the Mo6@Graphene chemoresistor was almost insensitive to NH3, the use of an optical transduction scheme (changes in photoluminescence) provided an outstanding detection of NH3 even for a low loading of Mo6. Nevertheless, the photoluminescence was not affected by the presence of NO2. In addition, the hybrid material revealed high stability of its gas sensing properties over time and under ambient moisture. Computational chemistry calculations were performed to better understand these results, and plausible sensing mechanisms were presented accordingly. These results pave the way to develop a new generation of multi-parameter sensors in which electronic and optical interrogation techniques can be implemented simultaneously, advancing toward the realization of highly selective and orthogonal gas sensing.J.C.-C. gratefully thanks ICREA Academia (project: 2018 ICREA Academia-01-AJUT). This research was funded from project PID2021-123163OB-I00 funded by MCIN/AEI/10.13039/501100011033/ and FEDER A way of making Europe, and Generalitat Valenciana (grant number AICO/2020/149). This work was partially funded by MICINN and FEDER via grant no. RTI2018-101580-B-I00. E. L. was supported by the Catalan Institution for Research and Advanced Studies via the 2018 Edition of the ICREA Academia Award

Octahedral Molybdenum Cluster-Based Single Crystals as Fabry–Pérot Microresonators

Single crystals built up from octahedral Mo6 cluster units, with appropriate geometry and size, constitute Fabry–Pérot-type optical microcavities with well-defined resonances. Such resonances appear in the VIS-NIR range when performing optical transmittance (OT) or photoluminescence (PL) measurements. They strongly depend on the crystal thickness and on the optical constants of the material, specifically the real and imaginary parts of the refractive index. In this work, the accurate measurement of the crystal thickness is used for the determination of the optical constants by means of a fitting process, and the preferred orientation of the crystals was determined by X-ray diffraction.This research was funded by the Severo Ochoa Program (grant number SEV-2016-0683), Ministerio de Ciencia e Innovación (grant number PGC2018-099744), and Generalitat Valenciana (grant number AICO/2020/149). The authors also thank the Electron Microscopy Service of the Universitat Politècnica de Valencia for their support in FESEM image acquisition.Peer reviewe

Optoelectronic properties of octahedral molybdenum cluster-based materials at a single crystal level

Octahedral molybdenum (Mo) clusters constitute suitable building blocks for the design of promising single crystal materials in the field of optoelectronics. Here, we prepared single crystals composed of hydroxo MoX (X = Br, Cl) cluster complexes interconnected by H-bonding interactions with water molecules and protons. The optoelectronic responses and the absorption and emission spectra of these cluster-based single crystals were acquired upon light irradiation, and they show dependency on the nature of the halogens, with the brominated cluster being the most conductive. A fast photoelectrical response was recorded and it showed remarkable stability after multiple illumination on/off cycles. The results obtained provide relevant information for the development of photonic and optoelectronic devices, sensors and photocatalysts.We would like to thank the technical team at the Instituto de Tecnología Química for providing us all the facilities for all the characterization processes. This research was supported by the project PID2021-123163OB-I00 funded by MCIN/AEI/10.13039/501100011033/and FEDER A way of making Europe and Severo Ochoa Centre of Excellence Program (CEX2021-001230-S). F. R. M. acknowledges CSIC under the program: Ayudas para la incorporación de nuevos Científicos Titulares (Grant No. 202280I200)