A shift to the hydrogen economy requires the development of an effective hydrogen fuel carrier with high volumetric and gravimetric storage capacity. Ammonia borane (AB) has emerged as a leading ...candidate due to its light weight and multiple protic (NH) and hydridic (BH) hydrogens. As a consequence, much work has been directed towards fine tuning the release of H
2
from AB, in addition to its regeneration from the dehydrogenated spent fuel materials. This review summarizes the development of these regeneration methodologies.
A shift to the hydrogen economy requires the development of an effective hydrogen fuel carrier with high volumetric and gravimetric storage capacity.
The selectivity of the mixed-sandwich U(III) complexes of the type U(η-C8H6{Si i R3-1,4}2)(η-CpR′) (R = Me, iPr; R′ = Me4H, Me5, Me4 iPr, Me4SiMe3, Me4Et) toward the reductive coupling of CO to form ...uranium-bound oxocarbons has been explored. In this context, the new U(III) mixed-sandwich complexes U(η-C8H6{Si i Pr3-1,4}2)(η-CpMe4TMS), U(η-C8H6{Si i Pr3-1,4}2)(η-CpMe4iPr), U(η-C8H6{Si i Pr3-1,4}2)(η-CpMe4Et), U(η-C8H6{SiMe3-1,4}2)(η-Cp*), and U(η-C8H6{SiMe3-1,4}2)(η-CpMe4TMS) have been prepared and structurally characterized. The reactivity toward CO is dominated by the “global” sterics around the uranium center, while selectivity for oxocarbon formation is largely regulated by the steric bulk of the CpR′ ligand. Accordingly, with excess CO U(η-C8H6{Si i Pr3-1,4}2)(η-CpMe4TMS) and U(η-C8H6{Si i Pr3-1,4}2)(η-CpMe4iPr) show no reactivity, U(η-C8H6{SiMe3-1,4}2)(η-CpMe4TMS) is completely selective for the formation of the ynediolate complex U(η-C8H6{SiMe3-1,4}2)(η-CpMe4TMS)2(μ-η1:η1-13C2O2), U(η-C8H6{SiiPr3-1,4}2)(η-Cp*) affords only the deltate complex U(η-C8H6{SiiPr3-1,4}2)(η-Cp*)2(μ-η2:η2-C3O3), and U(η-C8H6{SiiPr3-1,4}2)(η-CpMe4H) gives solely the squarate complex U(η-C8H6{SiiPr3-1,4}2)(η-CpMe4H)2(μ-η2:η2-C4O4). Additionally, the squarate moiety has been removed from the uranium center in the last complex by reaction with Me3SiCl to afford the TMS ester of squaric acid, C4O2(OTMS)2.
Despite the long history of the Fischer-Tropsch reaction, carbon monoxide has proven remarkably resistant to selective homologation under mild conditions. Here, we find that an organouranium(III) ...complex induces efficient reductive trimerization of carbon monoxide at room temperature and pressure. The result is a triangular, cyclic$C_{3}O_{3}^{2-}$, or deltate, dianion held between two uranium(IV) units. The bonding within the$C_{3}O_{3}^{2-}$unit and its coordination to the two U centers have been analyzed by x-ray diffraction and density functional theory computational studies, which show a stabilizing C-C agostic interaction between the C3core and one U center. Solution nuclear magnetic resonance studies reveal a rapid equilibration of the deltate unit between the U centers.
The gravitational wave signal arising from the collapsing iron core of a Type II supernova progenitor star carries with it the imprint of the progenitor's mass, rotation rate, degree of differential ...rotation, and the bounce depth. Here, we show how to infer the gravitational radiation waveform of a core-collapse event from noisy observations in a network of two or more LIGO-like gravitational wave detectors and, from the recovered signal, constrain these source properties. Using these techniques, predictions from recent core-collapse modeling efforts, and the LIGO performance during its S4 science run, we also show that gravitational wave observations by LIGO might have been sufficient to provide reasonable estimates of the progenitor mass, angular momentum and differential angular momentum, and depth of the core at bounce, for a rotating core-collapse event at a distance of a few kpc.
Treatment of the dimetallynes Ar′EEAr′ E = Ge, Sn; Ar′ = C6H3-2,6-(C6H3-2,6-iPr2)2 with a cyclic olefincyclopentadiene (CpH), cyclopentene, 1,4-cyclohexadiene (CHD), or cyclohexeneshowed that, with ...the exception of cyclohexene, they react readily, affording C–H activation at room temperature. Reaction of the digermyne and distannyne with CpH gave the cyclopentadienyl anion, which is bound in a π-fashion to a mononuclear group 14 element center, along with evolution of hydrogen gas. Unusually, the digermyne also reacted with cyclopentene to give the same dehydroaromatization product, formed from triple C–H activation/dehydrogenation. It also was found to react with CHD to give a mixture of (Ar′GeH)2, benzene, and a new 7-germanorbornadiene species bound to a cyclohex-2-enyl fragment.
The adventures of tin‐tin: The activation of cyclooctatetraene by a distannyne results in complete SnSn bond cleavage and formation of a π‐bound planar aromatic C8H8 ring in an inverse sandwich ...complex (see scheme; Ar′=C6H3‐2,6‐(C6H3‐2,6‐iPr2)2)
It's hip to be square: A perfectly planar square of phosphorus atoms is prepared by the reduction of ZrCl2{PhP(CH2SiMe2NSiMe2CH2)2PPh} in the presence of P4 (see structure). On the basis of the PP ...single bond lengths and oxidation state of the Zr centers, this unit is formulated as a P44− fragment.
Use of SiCl4 as an organometallic reagent can be complicated by access to Si3+, Si2+, and unwanted sigmatropic rearrangements. Herein we report a mild reduction route, using (IP–)2Mg(THF) (1) and Mg ...metal, to cleanly access (IP2–)2Si (2). Electrochemical measurements show that IP2– is stabilized by Si4+ > Al3+ > Mg2+.
The reaction of the pentalene salt C8H4{SiiPr3-1,4}2K2 with SmCp*(μ-I)(THF)22 yields not the expected Sm(II) pentalene-bridged dimer but the Sm(III) sandwich complexes ...Sm(η8-C8H4{SiiPr3-1,4}2)(η5-Cp*) (1) and Sm(η8-C8H4{SiiPr3-1,4}2)(η5-C8H5{SiiPr3-1,4}2) (2) and the mixed-valence cluster Cp*6Sm6(OMe)8OK(THF)6 (3) via solvent activation of THF. The samarium(III) sandwich compound 2 incorporates an η8-pentalene ligand and an η5-hydropentalenyl ligand. X-ray crystallography shows the Sm(II)/Sm(III) mixed-valence cluster compound 3 to contain a centrosymmetric hexanuclear array of Cp*Sm units, bridged by face-centered μ3-methoxy groups, with a central oxo unit.
The reaction between {CeCp*2H}2 with CO2 in thf resulted in a new cerium(III) carbonate species, {Ce(Cp*)2(thf)}2(μ-η2:η1-CO3). Investigations into the mechanism suggest the intermediacy of a ...bridging oxo-complex, {CeCp*2(thf) x }2(μ-O), which could either be formed from the ring opening and oxygen abstraction from an oxygenated solvent such as thf or via insertion of CO2 and elimination of formaldehyde from the resulting methylenediolate intermediate.
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