Synthesis, structure and reactivity of dimolybdenum complexes with multiple metal-metal bonds

Falta palabras clavesAt the beginning of this millennium our research group became involved in the study of metal-metal bonds following the unexpected discovery of decamethyldizincocene, [fórmula], the first complex with a direct Zn-Zn bond unsupported by bridging ligands. In the following years other complexes of this type were prepared and characterized. One year after our initial observation of the Zn-Zn bond, the group of Power made a landmark discovery with the characterization of the first complex with a quintuple bond between metal atoms. Considering the previous experience of our group on the coordination and organometallic chemistry of the Group 6 elements molybdenum and tungsten, a systematic study of new binuclear molybdenum compounds featuring a quadruple Mo-Mo bonds was undertaken. The work carried out initially provided the grounds for the PhD Theses of Dr. Mario Carrasco and Dr. Irene Mendoza. The present Thesis completes and extends the research carried out in the chemistry of dimolybdenum complexes. In these regards, two chapters are included. Chapter I contains synthetic, structural and reactivity studies on dimolybdenum complexes that exhibit quadruple or quintuple Mo-Mo bonds. Firstly, Section 1.2 concentrates on dimolybdenum complexes derived from these molecules, with formula trans- [fórmula], where N^N represents a monoanionic aminopyridinate or amidinate bearing bulky ligands. The above complexes are suitable precursors for low-coordinate polymethyl and polyhydride complexes of the Mo-Mo quadruple bond. Alkylation with an excess of LiMe of the [fórmula] aminopyridinate complex that contains two Xyl groups as substituents of both the Namido donor atom and the pyridinic ring, allowed the synthesis and structural characterization of the new lithium trimethyl dimolybdenum ate complex [fórmula]. Likewise, some important features of the unsaturated Lewis base free dimethyl species were studied (with 13Clabelled experiments), as well as the synthesis of a new complex with the 4-dimethylaminopyridine ligand. The hydrogenation of the dimethyl complex afforded the synthesis of the bis(hydride) analogue compound, as described in a previous Thesis. We have found that this process proceeds through an intermediacy, and also kinetic studies on this reaction were carried out. To complete previous, related work from our laboratory, the unsaturated bis(hydride) complex [fórmula] was prepared for the first time and characterized by NMR spectroscopy and X-ray crystallography. Related adducts of this complex were also synthesized. Moreover, it is also described in this Section that the reaction of the paddlewheel bis(formate) complex [fórmula] with LiAlH4 proceeds in a step-wise manner forming the lithium dimolybdenum polyhydride ate complexes [fórmula] and [fórmula], that feature unprecedented cores. Last section comprises the study of the coordination of different substituted arenes to the Mo-Mo quintuple bond, and the reaction with hydrogen, to afford the bis(hydride) complex. On the other hand, studies related to the topological properties of the Mo−Mo bond are described in Chapter II of this Thesis. It contains experimental and theoretical charge density studies performed on the [fórmula] complexes: [fórmula] and [fórmula]. As far as we know, these are the first experimental charge density studies performed on multiple Mo-Mo bond complexes in the post-QTAIM age. This analysis is complementary to studies already mentioned in Chapter I and gives a fully coherent and more complete view of the bonding in complexes with quadruple Mo-Mo bond

Influence of strain rate on the ashby-gibson parameters of sheet diamond lattice structures

Triply periodic minimal surface structures (TPMSs) can be used as a substitute for polymeric foams in applications where is necessary to absorb a large amount of energy with high structural deformation. Diamond TPMS offers higher energy absorption per unit weight. This structure is based on the Ashby-Gibson material model that establishes the main mechanical material properties as functions of the relative density and material properties. However, since TPMSs are used in dynamic applications, it is essential to analyse them under dynamic loads. In this study, we investigate the influence of the strain rate on the Ashby-Gibson parameters of sheet diamond

Boryl-assisted hydrogenolysis of a nickel–methyl bond

A stable Nickel(II) methyl complex containing a diphosphinoboryl (PBP) pincer ligand is described. Mechanistic studies on the hydrogenolysis of the Ni-Me bond suggest a metal ligand cooperation mechanism that involves the intermediacy of a - B‒H Ni(0) species that further undergoes B‒H oxidative addition to form a Ni(II) hydride complex

Metal-Dependent DNA Recognition and Cell Internalization of Designed, Basic Peptides

A fragment of the DNA basic region (br) of the GCN4 bZIP transcription factor has been modified to include two His residues at designed i and i+4 positions of its N-terminus. The resulting monomeric peptide (brHis2) does not bind to its consensus target DNA site (5′-GTCAT-3′). However, addition of Pd(en)Cl2 (en, ethylenediamine) promotes a high-affinity interaction with exquisite selectivity for this sequence. The peptide–DNA complex is disassembled by addition of a slight excess of a palladium chelator, and the interaction can be reversibly switched multiple times by playing with controlled amounts of either the metal complex or the chelator. Importantly, while the peptide brHis2 fails to translocate across cell membranes on its own, addition of the palladium reagent induces an efficient cell internalization of this peptide. In short, we report (1) a designed, short peptide that displays highly selective, major groove DNA binding, (2) a reversible, metal-dependent DNA interaction, and (3) a metal-promoted cell internalization of this basic peptideThis work has received financial support from the MINECO (SAF2013-41943-R, SAF2016-76689-R, and CTQ2015-70698-R), the Xunta de Galicia (2015-CP082, ED431C 2017/19, and Centro Singular de Investigación de Galicia Accreditation 2016–2019, ED431G/09), the European Union (European Regional Development Fund, ERDF), and the European Research Council (Advanced Grant No. 340055). Support of COST CM1306 and the orfeo-cinqa network are also acknowledged. J.R. thanks the Xunta de Galicia for a Ph.D. fellowship. We also wish to acknowledge the generous support by the Fundación AECC (IDEAS197VAZQ grant)S

An Unsaturated Four-Coordinate Dimethyl Dimolybdenum Complex with a Molybdenum–Molybdenum Quadruple Bond

We describe the synthesis and the molecular and electronic structures of the complex [Mo2Me2{μ‐HC(NDipp)2}2] (2; Dipp=2,6‐iPr2C6H3), which contains a dimetallic core with an Mo–Mo quadruple bond and features uncommon four‐coordinate geometry and has a fourteen‐electron count for each molybdenum atom. The coordination polyhedron approaches a square pyramid, with one of the molybdenum atoms nearly co‐planar with the basal square plane, in which the trans coordination position with respect to the Mo−Me bond is vacant. The other three sites are occupied by two trans nitrogen atoms of different amidinate ligands and the methyl group. The second Mo atom occupies the apex of the pyramid and forms an Mo–Mo bond of length 2.080(1) Å, consistent with a quadruple bond. Compound 2 reacts with tetrahydrofuran (THF) and trimethylphosphine to yield the mono‐adducts [Mo2Me(μ‐Me){μ‐HC(NDipp)2}2(L)] (3⋅THF and 3⋅PMe3, respectively) with one terminal and one bridging methyl group. In contrast, 4‐dimethylaminopyridine (dmap) forms the bis‐adduct [Mo2Me2{μ‐HC(NDipp)2}2(dmap)2] (4), with terminally coordinated methyl groups. Hydrogenolysis of complex 2 leads to the bis(hydride) [Mo2H2{μ‐HC(NDipp)2}2(thf)2] (5⋅THF) with elimination of CH4. Computational, kinetic, and mechanistic studies, which included the use of D2 and of complex 2 labelled with 13C (99 %) at the Mo–CH3 sites, supported the intermediacy of a methyl‐hydride reactive species. A computational DFT analysis of the terminal and bridging coordination of the methyl groups to the Mo≣Mo core is also reported.Ministerio de Ciencia e Innovación CTQ2010-15833, CTQ2013-42501-P, CTQ2014-52769-C3-3-R, CTQ2015-64579-C3-1-P, Consolider-Ingenio 2010 CSD2007-00006Junta de Andalucía FQM-119, P09-FQM-5117Ministerio de Educación AP-4193Ministerio de Ciencia e Innovación BES-2011-04764

Coordination of LiH Molecules to Mo Mo Bonds: Experimental and Computational Studies on Mo2LiH2, Mo2Li2H4, and Mo6Li9H18 Clusters

The reactions of LiAlH4 as the source of LiH with complexes that contain (H)Mo≣Mo and (H)Mo≣Mo(H) cores stabilized by the coordination of bulky AdDipp2 ligands result in the respective coordination of one and two molecules of (thf)LiH, with the generation of complexes exhibiting one and two HLi(thf)H ligands extending across the Mo≣Mo bond (AdDipp2 = HC(NDipp)2; Dipp = 2,6-iPr2C6H3; thf = tetrahydrofuran, C4H8O). A theoretical study reveals the formation of Mo-H-Li three-center-two-electron bonds, supplemented by the coordination of the Mo≣Mo bond to the Li ion. Attempts to construct a [Mo2{HLi(thf)H}3(AdDipp2)] molecular architecture led to spontaneous trimerization and the formation of a chiral, hydride-rich Mo6Li9H18 supramolecular organization that is robust enough to withstand the substitution of lithium-solvating molecules of tetrahydrofuran by pyridine or 4-dimethylaminopyridine

An unsaturated four-coordinate dimethyl dimolybdenum complex with a molybdenum-molybdenum quadruple bond

We describe the synthesis and the molecular and electronic structures of the complex [Mo2Me2{mu-HC(NDipp)(2)}(2)] (2; Dipp=2,6-iPr(2)C(6)H(3)), which contains a dimetallic core with an Mo-Mo quadruple bond and features uncommon four-coordinate geometry and has a fourteen-electron count for each molybdenum atom. The coordination polyhedron approaches a square pyramid, with one of the molybdenum atoms nearly co-planar with the basal square plane, in which the trans coordination position with respect to the Mo-Me bond is vacant. The other three sites are occupied by two trans nitrogen atoms of different amidinate ligands and the methyl group. The second Mo atom occupies the apex of the pyramid and forms an Mo-Mo bond of length 2.080(1) angstrom, consistent with a quadruple bond. Compound 2 reacts with tetrahydrofuran (THF) and trimethylphosphine to yield the mono-adducts [Mo2Me(mu-Me){mu-HC(NDipp)(2)}(2)(L)] (3 center dot THF and 3 center dot PMe3, respectively) with one terminal and one bridging methyl group. In contrast, 4-dimethylaminopyridine (dmap) forms the bis-adduct [Mo2Me2{mu-HC(NDipp)(2)}(2)(dmap)(2)] (4), with terminally coordinated methyl groups. Hydrogenolysis of complex 2 leads to the bis(hydride) [Mo2H2{mu-HC(NDipp)(2)}(2)(thf)(2)] (5 center dot THF) with elimination of CH4. Computational, kinetic, and mechanistic studies, which included the use of D-2 and of complex 2 labelled with C-13 (99%) at the Mo-CH3 sites, supported the intermediacy of a methyl-hydride reactive species. A computational DFT analysis of the terminal and bridging coordination of the methyl groups to the Mo Mo core is also reported

Coordination of LiH Molecules to Mo≣Mo Bonds: Experimental and Computational Studies on Mo2LiH2, Mo2Li2H4, and Mo6Li9H18 Clusters

The reactions of LiAlH4 as the source of LiH with complexes that contain (H)Mo≣Mo and (H)Mo≣Mo(H) cores stabilized by the coordination of bulky AdDipp2 ligands result in the respective coordination of one and two molecules of (thf)LiH, with the generation of complexes exhibiting one and two HLi(thf)H ligands extending across the Mo≣Mo bond (AdDipp2 = HC(NDipp)2; Dipp = 2,6-iPr2C6H3; thf = tetrahydrofuran, C4H8O). A theoretical study reveals the formation of Mo–H–Li three-center–two-electron bonds, supplemented by the coordination of the Mo≣Mo bond to the Li ion. Attempts to construct a [Mo2{HLi(thf)H}3(AdDipp2)] molecular architecture led to spontaneous trimerization and the formation of a chiral, hydride-rich Mo6Li9H18 supramolecular organization that is robust enough to withstand the substitution of lithium-solvating molecules of tetrahydrofuran by pyridine or 4-dimethylaminopyridine.España Ministry of Economy and Competitiveness (PID2019-110856GA-I00 and PGC2018-093863-B-C21)Generalitat de Catalunya - AGAUR (grant 2017-SGR1289

A focal plane detector design for a wide-band Laue-lens telescope

The energy range above 60 keV is important for the study of many open problems in high energy astrophysics such as the role of Inverse Compton with respect to synchrotron or thermal processes in GRBs, non thermal mechanisms in SNR, the study of the high energy cut-offs in AGN spectra, and the detection of nuclear and annihilation lines. Recently the development of high energy Laue lenses with broad energy bandpasses from 60 to 600 keV have been proposed for a Hard X ray focusing Telescope (HAXTEL) in order to study the X-ray continuum of celestial sources. The required focal plane detector should have high detection efficiency over the entire operative range, a spatial resolution of about 1 mm, an energy resolution of a few keV at 500 keV and a sensitivity to linear polarization. We describe a possible configuration of the focal plane detector based on several CdTe/CZT pixelated layers stacked together to achieve the required detection efficiency at high energy. Each layer can operate both as a separate position sensitive detector and polarimeter or work with other layers to increase the overall photopeak efficiency. Each layer has a hexagonal shape in order to minimize the detector surface required to cover the lens field of view. The pixels would have the same geometry so as to provide the best coupling with the lens point spread function and to increase the symmetry for polarimetric studies.Comment: 10 pages, 9 figure