67 research outputs found

    Impedance Bridge Network Problem as Solved by Relaxation Method

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    Here it is shown how the relaxation method con be advantageously used to solve the problems of A. C. networks containing complex circuit constant. This has been done in the solution of impedance bridge network problem in which many useful information are obtained at a time. The results so obtained ate compared with those calculated by the conventional method

    Si–H Bond Activation and Dehydrogenative Coupling of Silanes across the Iron–Amide Bond of a Bis(amido)bis(phosphine) Iron(II) Complex

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    Despite the utility of Si–Si bonds, there are relatively few examples of Si–Si bond formation by base metals. In this work, a four-coordinate iron complex, (PNNP)FeII, is shown to strongly activate the Si–H bonds in primary silanes across the Fe–amide bonds in a metal–ligand cooperative fashion. Upon treatment with excess silane, Si–Si dehydrogenative homocoupling is shown to occur across the Fe–Namide bond without concomitant oxidation and spin state changes at the Fe center

    Coordinative Alignment To Achieve Ordered Guest Molecules in a Versatile Molecular Crystalline Sponge

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    A Mn<sup>2+</sup>-based metal–organic framework (coordination porous framework-5, CPF-5) can serve as a crystalline sponge for single crystal X-ray structural characterization of a variety of compounds using a combination of coordinative alignment and second coordination sphere interactions (e.g., hydrogen bonding). This technique requires only a conventional X-ray source to obtain high quality crystallographic data

    One Bridge, Three Bonds: A Frontier in Multiple Bonding in Heterobimetallic Complexes

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    A single bridging phosphinoamide ligand was shown to support a metal–metal triple bond in a Zr/Co heterobimetallic complex. The similarity of the bonding in this compound to previously synthesized Zr/Co species, and therefore the assignment of the Zr/Co triple bond, is supported by the structural parameters of the complex, the electronic structure predicted by density functional theory, and complete-active-space self-consistent-field (CASSCF) calculations. This demonstrates that metal–metal multiple bonds can be realized in heterobimetallic complexes without multiple bridging ligands to enforce the proximity of the two metals

    A Highly-Reduced Cobalt Terminal Carbyne: Divergent Metal- and α‑Carbon-Centered Reactivity

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    Reported here is the isolation of a dianionic cobalt terminal carbyne derived from chemical reduction of an encumbering isocyanide ligand. Crystallographic, spectroscopic and computational data reveal that this carbyne possesses a low-valent cobalt center with an extensively filled d-orbital manifold. This electronic character renders the cobalt center the primary site of nucleophilicity upon reaction with protic substrates and silyl electrophiles. However, reactions with internal alkynes result in [2+2] cycloaddition with the carbyne carbon to form a new C–C bond

    A Highly-Reduced Cobalt Terminal Carbyne: Divergent Metal- and α‑Carbon-Centered Reactivity

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    Reported here is the isolation of a dianionic cobalt terminal carbyne derived from chemical reduction of an encumbering isocyanide ligand. Crystallographic, spectroscopic and computational data reveal that this carbyne possesses a low-valent cobalt center with an extensively filled d-orbital manifold. This electronic character renders the cobalt center the primary site of nucleophilicity upon reaction with protic substrates and silyl electrophiles. However, reactions with internal alkynes result in [2+2] cycloaddition with the carbyne carbon to form a new C–C bond

    Cooperative Transition Metal/Lewis Acid Bond-Activation Reactions by a Bidentate (Boryl)­imino­methane Complex: A Significant Metal–Borane Interaction Promoted by a Small Bite-Angle LZ Chelate

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    The synthesis of a three-coordinate Pt–borane complex featuring a bidentate “LZ” (boryl)­imino­methane (BIM) ligand is reported. Unlike other LZ-type borane ligands featuring a single-donor buttress, the small bite angle enforced by the BIM ligand is shown to promote a significant metal–borane reverse-dative σ-interaction akin to multiply strapped metalloboratranes. The steric accessibility of the reactive Pt → B bond fostered by the BIM ligand allows for a rich reactivity profile toward small molecules that exploit metal–borane cooperative effects. The unligated (boryl)­imino­methane BIM is also synthetically accessible and functions as a Frustrated Lewis Pair (FLP). The ability of the free BIM to effect bond activation reactions is contrasted with the behavior seen in the corresponding platinum-bound complexes

    Controlled <i>cis</i> Labilization of CO from Manganese(I) Mixed Carbonyl/Isocyanide Complexes: An Entry Point to Coordinatively Unsaturated Metallo-Lewis Acids

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    Presented herein is a general design strategy for the formation of coordinatively unsaturated Mn­(I) fragments via the <i>cis</i> labilization of CO using metal carboxylates and subsequent deprotection by a range of abstraction agents. A consistent trend is observed in the ability of carboxylate ligands to facilitate CO dissociation as a function of the electron-releasing properties of the carboxylate R group. This is in agreement with previous theoretical work on <i>cis</i>-labilizing ligands. A variety of κ<sup>2</sup>-coordinated carboxylates function as site-protection ligands for the [Mn­(CO)<sub>2</sub>(CNAr<sup>Dipp2</sup>)<sub>2</sub>]<sup>+</sup> scaffold and can be liberated using a range of synthetic techniques. The coordinatively unsaturated species thus formed are shown to be strong metal-based Lewis acids and can engage in agostic-type interactions; in addition, they can be trapped as the corresponding solvento complexes by ethereal solvents

    Nitrite Formation at a Diiron Dinitrosyl Complex

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    Pathogenic bacteria employ iron-containing enzymes to detoxify nitric oxide (NO•) produced by mammals as part of their immune response. Two classes of diiron proteins, flavodiiron nitric oxide reductases (FNORs) and the hemerythrin-like proteins from mycobacteria (HLPs), are upregulated in bacteria in response to an increased local NO• concentration. While FNORs reduce NO• to nitrous oxide (N2O), the HLPs have been found to either reduce nitrite to NO• (YtfE), or oxidize NO• to nitrite (Mka-HLP). Various structural and functional models of the diiron site in FNORs have been developed over the years. However, the NO• oxidation reactivity of Mka-HLP has yet to be replicated with a synthetic complex. Compared to the FNORs, the coordination environment of the diiron site in Mka-HLP contains one less carboxylate ligand and, therefore, is expected to be more electron-poor. Herein, we synthesized a new diiron complex that models the electron-poor coordination environment of the Mka-HLP diiron site. The diferrous precursor FeIIFeII reacts with NO• to form a diiron dinitrosyl species ({FeNO}72), which is in equilibrium with a mononitrosyl diiron species (FeII{FeNO}7) in solution. Both complexes can be isolated and fully characterized. However, only oxidation of {FeNO}72 produced nitrite in high yield (71%). Our study provides the first model that reproduces the NO• oxidase reactivity of Mka-HLP and suggests intermediacy of an {FeNO}6/{FeNO}7 species

    Bottleable (Amino)(Carboxy) Radicals Derived from Cyclic (Alkyl)(Amino) Carbenes

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    Monomeric (amino)­(carboxy) radicals were synthesized in two steps: the addition of a stable cyclic (alkyl)­(amino) carbene to an acyl chloride, followed by a one-electron reduction. Their stability toward dimerization also allows for the synthesis of related bi- and triradicals
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