67 research outputs found
Impedance Bridge Network Problem as Solved by Relaxation Method
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
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
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
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
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
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
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
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
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
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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