4 research outputs found
Synthesis and Reactivity of a Cobalt-Supported Singlet Nitrene
The synthesis, characterization, and reactivity of a
series of
cobalt terminal imido complexes supported by an N-anchored tripodal tris(carbene) chelate is described, including
a Co-supported singlet nitrene. Reaction of the CoI precursor
[(TIMMNmes)CoI](PF6) (TIMMNmes = tris-[2-(3-mesityl-imidazolin-2-ylidene)-methyl]amine) with p-methoxyphenyl azide yields a CoIII imide [(TIMMNmes)CoIII(NAnisole)](PF6) (1). Treatment of 1 with 1 equiv of [FeCp2](PF6) at −35 °C affords a formal CoIV imido
complex [(TIMMNmes)Co(NAnisole)](PF6)2 (2), which features a bent Co–N(imido)–C(Anisole)
linkage. Subsequent one-electron oxidation of 2 with
1 equiv of AgPF6 provides access to the tricationic cobalt
imido complex [(TIMMNmes)Co(NAnisole)](PF6)3 (3). All complexes were fully characterized,
including single-crystal X-ray diffraction (SC-XRD) analyses, infrared
(IR) vibrational, ultraviolet/visible (UV/vis) electronic absorption,
multinuclear NMR, X-band electron paramagnetic resonance (EPR), electron
nuclear double resonance (ENDOR), and high-energy-resolution fluorescence-detected
X-ray absorption spectroscopy (HERFD XAS). Quantum chemical calculations
provide additional insight into the electronic structures of all compounds.
The dicationic CoIV imido complex 2 exhibits
a doublet ground state with considerable imidyl character as a result
of covalent Co–NAnisole bonding. At room temperature, 2 readily converts to a CoII amine complex involving
intramolecular C–H bond amination. Electronically, tricationic
complex 3 can be understood as a singlet nitrene bound
to CoIII with significant CoIV imidyl radical
character. Verifying the pronounced electrophilicity, nucleophiles
such as H2O and tBuNH2 add to 3analogous to the parent free nitrenein
the para position of the aromatic substituent, thus,
clearly corroborating singlet nitrene-type reactivity
Uranium-Mediated Peroxide Activation and a Precursor toward an Elusive Uranium <i>cis</i>-Dioxo Fleeting Intermediate
The activation of chalcogen–chalcogen bonds using
organometallic
uranium complexes has been well documented for S–S, Se–Se,
and Te–Te bonds. In stark contrast, reports concerning the
ability of a uranium complex to activate the O–O bond of an
organic peroxide are exceedingly rare. Herein, we describe the peroxide
O–O bond cleavage of 9,10-diphenylanthracene-9,10-endoperoxide
in nonaqueous media, mediated by a uranium(III) precursor [((Me,AdArO)3N)UIII(dme)] to generate a
stable uranium(V) bis-alkoxide complex, namely, [((Me,AdArO)3N)UV(DPAP)]. This reaction proceeds via
an isolable, alkoxide-bridged diuranium(IV/IV) species, implying that
the oxidative addition occurs in two sequential, single-electron oxidations
of the metal center, including rebound of a terminal oxygen radical.
This uranium(V) bis-alkoxide can then be reduced with KC8 to form a uranium(IV) complex, which upon exposure to UV light,
in solution, releases 9,10-diphenylanthracene to generate a cyclic
uranyl trimer through formal two-electron photooxidation. Analysis
of the mechanism of this photochemical oxidation via density functional
theory (DFT) calculations indicates that the formation of this uranyl
trimer occurs through a fleeting uranium cis-dioxo
intermediate. At room temperature, this cis-configured
dioxo species rapidly isomerizes to a more stable trans configuration through the release of one of the alkoxide ligands
from the complex, which then goes on to form the isolated uranyl trimer
complex
Uranium-Mediated Peroxide Activation and a Precursor toward an Elusive Uranium <i>cis</i>-Dioxo Fleeting Intermediate
The activation of chalcogen–chalcogen bonds using
organometallic
uranium complexes has been well documented for S–S, Se–Se,
and Te–Te bonds. In stark contrast, reports concerning the
ability of a uranium complex to activate the O–O bond of an
organic peroxide are exceedingly rare. Herein, we describe the peroxide
O–O bond cleavage of 9,10-diphenylanthracene-9,10-endoperoxide
in nonaqueous media, mediated by a uranium(III) precursor [((Me,AdArO)3N)UIII(dme)] to generate a
stable uranium(V) bis-alkoxide complex, namely, [((Me,AdArO)3N)UV(DPAP)]. This reaction proceeds via
an isolable, alkoxide-bridged diuranium(IV/IV) species, implying that
the oxidative addition occurs in two sequential, single-electron oxidations
of the metal center, including rebound of a terminal oxygen radical.
This uranium(V) bis-alkoxide can then be reduced with KC8 to form a uranium(IV) complex, which upon exposure to UV light,
in solution, releases 9,10-diphenylanthracene to generate a cyclic
uranyl trimer through formal two-electron photooxidation. Analysis
of the mechanism of this photochemical oxidation via density functional
theory (DFT) calculations indicates that the formation of this uranyl
trimer occurs through a fleeting uranium cis-dioxo
intermediate. At room temperature, this cis-configured
dioxo species rapidly isomerizes to a more stable trans configuration through the release of one of the alkoxide ligands
from the complex, which then goes on to form the isolated uranyl trimer
complex
Enhanced Photostability of Lead Halide Perovskite Nanocrystals with Mn<sup>3+</sup> Incorporation
Recently, lead halide perovskite nanocrystals (NCs) have shown
great potential and have been widely studied in lighting and optoelectronic
fields. However, the long-term stability of perovskite NCs under irradiation
is an important challenge for their application in practice. Mn2+ dopants are mostly proposed as substitutes for the Pb site
in perovskite NCs synthesized through the hot-injection method, with
the aim of improving both photo- and thermal stability. In this work,
we employed a facile ligand-assisted reprecipitate strategy to introduce
Mn ions into perovskite lattice, and the results showed that Mn3+ instead of Mn2+, even with a very low level of
incorporation of 0.18 mol % as interstitial dopant, can enhance the
photostability of perovskite binder film under the ambient conditions
without emission change, and the photoluminescent efficiency can retain
70% and be stable under intensive irradiation for 12 h. Besides, Mn3+ incorporation could prolong the photoluminescent decay time
by passivating trap defects and modifying the distortion of the lattice,
which underscores the significant potential for application as light
emitters