Selective
amination of σ and π entities such as C–H
and CC bonds of substrates remains a challenging endeavor
for current catalytic methodologies devoted to the synthesis of abundant
nitrogen-containing chemicals. The present work addresses an approach
toward discriminating aromatic over aliphatic alkenes in aziridination
reactions, relying on the use of anionic metal reagents (M = Mn, Fe,
Co, Ni) to attenuate reactivity in a metal-dependent manner. A family
of MnII reagents bearing a triphenylamido-amine scaffold
and various pendant arms has been synthesized and characterized by
various techniques, including cyclic voltammetry. Aziridination of
styrene by PhINTs in the presence of each MnII catalyst
establishes a trend of increasing yield with increasing MnII/III anodic potential. The FeII, CoII, and NiII congeners of the highest-yielding MnII catalyst
have been synthesized and explored in the aziridination of aromatic
and aliphatic alkenes, exhibiting good to high yields with para-substituted
styrenes, low to modest yields with sterically congested styrenes,
and invariably low yields with aliphatic olefins. CoII mediates
faster styrene aziridination in comparison to MnII but
is less selective than MnII in competitive aziridinations
of conjugated versus nonconjugated olefins. Indeed, MnII proved to be highly selective even versus well-established copper
and rhodium aziridination reagents. Mechanistic investigations and
computational studies indicate that all metals follow a two-step styrene
aziridination pathway (successive formation of two N–C bonds),
featuring a turnover-limiting metal–nitrene addition to an
olefinic carbon, followed by product-determining ring closure. Both
steps exhibit activation barriers in the order Fe > Mn > Co,
most
likely stemming from relevant metal–nitrene electrophilicities
and MII/III redox potentials. The aziridination of aliphatic
olefins follows the same stepwise path, albeit with a considerably
higher activation barrier and a weaker driving force for the formation
of the initial N–C bond, succeeded by ring closure with a miniscule
barrier.
A new
material, MOF-type [Ir]@NU-1000, was accessed from the incorporation
of the iridium organometallic fragment [Ir{κ3(P,Si,Si)PhP(o-C6H4CH2Si
i
Pr2)2}] into NU-1000. The new
material incorporates less than 1 wt % of Ir(III) (molar ratio Ir
to NU-1000, 1:11), but the heat of adsorption for SO2 is
significantly enhanced with respect to that of NU-1000. Being a highly
promising adsorbent for SO2 capture, [Ir]@NU-1000 combines
exceptional SO2 uptake at room temperature and outstanding
cyclability. Additionally, it is stable and can be regenerated after
SO2 desorption at low temperature.
Tetrahydroquinazoline (THQ) was designed as an all-nitrogen analogue of main-stream benzoxazine monomers. THQ solutions in DMF gelled at 100 °C via HCl-catalyzed ring-opening polymerization to polybenzodiazine (PBDAZ) wet gels, which were dried in an autoclave with supercritical fluid CO 2 to aerogels. These as-prepared PBDAZ-100 aerogels undergo ring-fusion aromatization at 240 °C under O 2 . This oxidized form is referred to as PBDAZ-240. Chemical identification of PBDAZ-100 and PBDAZ-240 relied on consideration of all nine possible polymerization pathways, in combination with elemental analysis, infrared and solid-state 13 C NMR spectroscopy, and 15 N NMR spectroscopy of aerogels from the selectively 15 N-enriched THQ monomer. Fully oxidized PBDAZ-240 aerogels were carbonized at 800 °C under Ar to carbon aerogels with 61% w/w yield and with retention of the nanomorphology of the parent PBDAZ-100 aerogels. Direct pyrolysis of PBDAZ-100 at 800 °C, i.e., without prior oxidation, resulted in only 40% w/w yield and complete loss of the fine nanostructure. The evolution of PBDAZ-240 aerogels along pyrolysis toward carbonization was monitored using progressively higher pyrolysis temperatures from 300 to 800 °C under Ar. Aerogels received at 600 and 800 °C (referred to as PBDAZ-600 and PBDAZ-800, respectively) had relatively high surface areas (432 and 346 m 2 g −1 , respectively), a significant portion of which (79% in both materials) was assigned to micropores. The new polymer aerogels, together with polybenzoxazine aerogels, comprise a suitable basis set for comparing N-rich versus O-rich porous carbons as adsorbers.
Herein we report an experimental and computational study of a family of four coordinated 14-electron complexes of Rh(III) devoid of agostic interactions. The complexes [X-Rh(κ3(P,Si,Si)PhP(o-C6H4CH2SiiPr2)2], where X = Cl (Rh-1),...
The new material [RuGa]@NU-1000 incorporates Ru and Ga in 1.2 and 1.8 wt.% respectively (molar ratio 1 : 2). It stems from the grafting of the heterobimetallic ruthenium gallate complex,...
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