Structure evolution has become an effective way to assemble novel monolayer‐protected metal nanomolecules. However, evolution with alkynyl‐stabilized metal clusters still remains rarely explored. Herein, we present a carboranealkynyl‐protected gold nanocluster [Au28(C4B10H11)12(tht)8]3+ (Au28, tht=tetrahydrothiophene) possessing an open‐shell electronic structure with 13 free electrons, which was isolated by a facile self‐reduction method with 9‐HC≡C‐closo‐1,2‐C2B10H11 as the two‐in‐one reducing and protecting agent. Notably, Au28 undergoes a complete transformation in methanol into a stable and smaller‐sized nanocluster [Au23(C4B10H11)9(tht)6]2+ (Au23) bearing 12 valence electrons and crystal‐field‐like split superatomic 1D orbitals. The transformation process was systematically monitored with ESI‐MS and UV/Vis absorption spectra. Au28 and Au23 both display optical absorption covering the UV/Vis–NIR range and NIR emission, which facilitates their potential application in the biomedical and photocatalytic fields.
Diradical generation followed by
radical–radical cross-coupling
is a powerful synthetic tool, but its detailed mechanism has yet to
be established. Herein, we proposed and confirmed a new model named
relayed proton-coupled electron transfer (relayed-PCET) for diradical
generation, which could open a door for new radical–radical
cross-coupling reactions. Quantum mechanics calculations were performed
on a selected carbene-mediated diradical cross-coupling reaction model
and a designed model, and the exact electronic structural changes
during the radical processes have been observed for the first time.
We have rationally designed a new class of alkyne‐tethered oximes and applied them in an unprecedented iron‐catalyzed radical relay protocol for the rapid assembly of a wide array of structurally new and interesting fused pyridines. This method shows broad substrate scope and good functional‐group tolerance and enabled the synthesis of several biologically active molecules. Furthermore, the fused pyridines could be diversely functionalized through various simple transformations, such as cyclization, C−H alkylation, and a click reaction. DFT calculation studies indicate that the reactions involve cascade 1,5‐hydrogen atom transfer, 5‐exo‐dig radical addition, and cyclization processes. Moreover, preliminary biological investigations suggest that some of the fused pyridines exhibit good anti‐inflammatory activity by restoring the imbalance of inflammatory homeostasis of macrophages in a lipopolysaccharide‐induced model.
A new strategy for the direct cleavage
of the C(sp3)–OH
bond has been developed via activation of free alcohols with neutral
diphenyl boryl radical generated from sodium tetraphenylborate under
mild visible light photoredox conditions. This strategy has been verified
by cross-electrophile coupling of free alcohols and carbon dioxide
for the synthesis of carboxylic acids. Direct transformation of a
range of primary, secondary, and tertiary benzyl alcohols to acids
has been achieved. Control experiments and computational studies indicate
that activation of alcohols with neutral boryl radical undergoes homolysis
of the C(sp3)–OH bond, generating alkyl radicals.
After reducing the alkyl radical into carbon anion under photoredox
conditions, the following carboxylation with CO2 affords
the coupling product.
Stable
stimulus-responsive materials are highly desirable due to
their widespread potential applications and growing demand in recent
decades. Despite the fact that viologen derivatives have long been
known as excellent photochromic and electrochromic materials, the
development of stable viologen-based multifunctional smart materials
with short coloration times remains an exciting topic. To obtain photochromic
and electrochromic dual responsive materials, embedding the viologen
ligand into a robust metal oxide cluster to increase its stability
and sensitivity is an effective strategy. Herein, a viologen-based
metal–organic polyhedron (MOP) {[Zr6L3(μ3-O)2(μ2-OH)6Cp6]·8Cl·CH3OH·DMF} [Zr-MOP-1; H2L·2Cl = 1,1′-bis(4-carboxyphenyl)-4,4′-bipyridinium
dichloride, and Cp = η5-C5H5] was successfully prepared and characterized. It consists of trinuclear
Zr–oxygen secondary building units and exhibits reversible
photochromic and electrochromic dual responsive behaviors. As expected,
the designed robust viologen-based nanocage with a V2E3 (V = vertex, and E = edge) topology can maintain its stability
and rapid photo/electrochromic behaviors with an obvious reversible
change in color from purple (brown) to green, mainly due to the enclosed
cluster structure and the abundant free viologen radicals that originate
from the effective Cl → N and O → N electron transfers.
Spectroelectrochemistry and theoretical calculations of this Zr-MOP
were also performed to verify the chromic mechanism.
The origin of stereoselectivity for BINOL-catalyzed insertion into the C(sp2)-B bond of alkylboronic ester by in situ generated carbene has been investigated using density functional theory (DFT). The reaction to...
A series of density functional theory calculations have been carried out to investigate the detailed mechanisms of C-H activation and oxidation reactions, and further to disclose the distinct effects of mononuclear- and binuclear-palladium on these reaction pathways. The results of calculations demonstrated that the C-H activation of 2-phenylpyridine with mononuclear Pd(OAc)2 prefers the inner-shell proton-abstraction mechanism, while that with binuclear Pd2(μ-OAc)4 is biased to the outer-shell proton-abstraction mechanism. The rate-determining free-energy barriers of the two mechanisms were calculated to be 24.2 and 24.8 kcal mol-1, respectively. More importantly, we have simulated the oxidation pathways of PdII → PdIII and PdII → PdIV with strong oxidants including PhI(OAc)2, PhICl2 and NCS, and found that a binuclear PdII-precursor would be oxidized to the corresponding binuclear PdIII-complex while a mononuclear PdII-precursor was deemed to evolve to the corresponding mononuclear PdIV-complex. In addition, the oxidation of PdII with PhI(OAc)2 has been characterized as a radical mechanism, in sharp contrast to the ion-pair mechanism prevalent for the oxidation of PdII with PhICl2. The calculated kinetic and thermodynamic parameters could be qualitatively consistent with the related experimental observations. This molecular modelling can provide valuable insights into the understanding of the distinct effects of the resting state and oxidant on these important transformations.
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