4 research outputs found
Formation of Novel T‑Shaped NNN Ligands via Rare-Earth Metal-Mediated Si–H Activation
Reactions of silylamides
[LnÂ{NÂ(SiHMe<sub>2</sub>)<sub>2</sub>}<sub>3</sub>(thf)<sub>2</sub>] with sterically crowded terphenylamine DmpNH<sub>2</sub> (Dmp =
2,6-Mes<sub>2</sub>C<sub>6</sub>H<sub>3</sub> with Mes = 2,4,6-Me<sub>3</sub>C<sub>6</sub>H<sub>2</sub>) afforded via a template reaction
the formation of a new tridentate ligand, and derived complexes of
composition [LnNÂ{SiMe<sub>2</sub>NÂ(Dmp)}<sub>2</sub>] (Ln = Ce, Pr)
were obtained. Usage of the even more bulky amine Ar*NH<sub>2</sub> (Ar* = 2,6-Trip<sub>2</sub>C<sub>6</sub>H<sub>3</sub> with Trip
= 2,4,6-<i>i</i>Pr<sub>3</sub>C<sub>6</sub>H<sub>2</sub>) yielded the free protonated ligand NHÂ{SiMe<sub>2</sub>NHÂ(Ar*)}<sub>2</sub>
From Nitrobenzenes to Substituted Tetrahydroquinolines in a Single Step by a Domino Reduction/Imine Formation/Aza-Diels–Alder Reaction
The
three-component reaction between a nitrobenzene, an aldehyde,
and a dienophile in the presence of iron powder as a reductant and
montmorillonite K10 as a catalyst in aqueous citric acid delivers
the products of an aza-Diels–Alder (Povarov) reaction with
high <i>endo</i>-selectivity and yields up to 99%
Tuning Spin–Spin Coupling in Quinonoid-Bridged Dicopper(II) Complexes through Rational Bridge Variation
Bridged
metal complexes [{CuÂ(tmpa)}<sub>2</sub>Â(μ-L<sup>1</sup><sub>–2H</sub>)]Â(ClO<sub>4</sub>)<sub>2</sub> (<b>1</b>), [{CuÂ(tmpa)}<sub>2</sub>Â(μ-L<sup>2</sup><sub>–2H</sub>)]Â(ClO<sub>4</sub>)<sub>2</sub> (<b>2</b>), [{CuÂ(tmpa)}<sub>2</sub>Â(μ-L<sup>3</sup><sub>–2H</sub>)]Â(BPh<sub>4</sub>)<sub>2</sub> (<b>3</b>), and [{CuÂ(tmpa)}<sub>2</sub>Â(μ-L<sup>4</sup><sub>–2H</sub>)]Â(ClO<sub>4</sub>)<sub>2</sub> (<b>4</b>) (tmpa = trisÂ(2-pyridylÂmethyl)Âamine,
L<sup>1</sup> = chloranilic acid, L<sup>2</sup> = 2,5-dihydroxy-1,4-benzoquinone,
L<sup>3</sup> = (2,5-di-[2-(methoxy)-anilino]-1,4-benzoquinone, L<sup>4</sup> = azophenine) were synthesized from copperÂ(II) salts, tmpa,
and the bridging quinonoid ligands in the presence of a base. X-ray
structural characterization of the complexes showed a distorted octahedral
environment around the copperÂ(II) centers for the complexes <b>1</b>–<b>3</b>, the donors being the nitrogen atoms
of tmpa, and the nitrogen or oxygen donors of the bridging quinones.
In contrast, the copperÂ(II) centers in <b>4</b> display a distorted
square-pyramidal coordination, where one of the pyridine arms of each
tmpa remains uncoordinated. Bond-length analyses within the bridging
ligand exhibit localization of the double bonds inside the bridge
for <b>1</b>–<b>3</b>. In contrast, complete delocalization
of double bonds within the bridging ligand is observed for <b>4</b>. Temperature-dependent magnetic susceptibility measurements on the
complexes reveal an antiferromagnetic coupling between the copperÂ(II)
ions. The strength of antiferromagnetic coupling was observed to depend
on the energy of the HOMO of the bridging quinone ligands, with exchange
coupling constants <i>J</i> in the range between −23.2
and −0.6 cm<sup>–1</sup> and the strength of antiferromagnetic
coupling of <b>4</b> > <b>3</b> > <b>2</b> > <b>1</b>. Broken-symmetry density functional theory calculations
(DFT) revealed that the orientation of magnetic orbitals in <b>1</b> and <b>2</b> is different than that in <b>3</b> and <b>4</b>, and this results in two different exchange pathways.
These results demonstrate how bridge-mediated spin–spin coupling
in quinone-bridged metal complexes can be strongly tuned by a rational
design of the bridging ligand employing the [O] for [NR] isoelectronic
analogy
Tuning Spin–Spin Coupling in Quinonoid-Bridged Dicopper(II) Complexes through Rational Bridge Variation
Bridged
metal complexes [{CuÂ(tmpa)}<sub>2</sub>Â(μ-L<sup>1</sup><sub>–2H</sub>)]Â(ClO<sub>4</sub>)<sub>2</sub> (<b>1</b>), [{CuÂ(tmpa)}<sub>2</sub>Â(μ-L<sup>2</sup><sub>–2H</sub>)]Â(ClO<sub>4</sub>)<sub>2</sub> (<b>2</b>), [{CuÂ(tmpa)}<sub>2</sub>Â(μ-L<sup>3</sup><sub>–2H</sub>)]Â(BPh<sub>4</sub>)<sub>2</sub> (<b>3</b>), and [{CuÂ(tmpa)}<sub>2</sub>Â(μ-L<sup>4</sup><sub>–2H</sub>)]Â(ClO<sub>4</sub>)<sub>2</sub> (<b>4</b>) (tmpa = trisÂ(2-pyridylÂmethyl)Âamine,
L<sup>1</sup> = chloranilic acid, L<sup>2</sup> = 2,5-dihydroxy-1,4-benzoquinone,
L<sup>3</sup> = (2,5-di-[2-(methoxy)-anilino]-1,4-benzoquinone, L<sup>4</sup> = azophenine) were synthesized from copperÂ(II) salts, tmpa,
and the bridging quinonoid ligands in the presence of a base. X-ray
structural characterization of the complexes showed a distorted octahedral
environment around the copperÂ(II) centers for the complexes <b>1</b>–<b>3</b>, the donors being the nitrogen atoms
of tmpa, and the nitrogen or oxygen donors of the bridging quinones.
In contrast, the copperÂ(II) centers in <b>4</b> display a distorted
square-pyramidal coordination, where one of the pyridine arms of each
tmpa remains uncoordinated. Bond-length analyses within the bridging
ligand exhibit localization of the double bonds inside the bridge
for <b>1</b>–<b>3</b>. In contrast, complete delocalization
of double bonds within the bridging ligand is observed for <b>4</b>. Temperature-dependent magnetic susceptibility measurements on the
complexes reveal an antiferromagnetic coupling between the copperÂ(II)
ions. The strength of antiferromagnetic coupling was observed to depend
on the energy of the HOMO of the bridging quinone ligands, with exchange
coupling constants <i>J</i> in the range between −23.2
and −0.6 cm<sup>–1</sup> and the strength of antiferromagnetic
coupling of <b>4</b> > <b>3</b> > <b>2</b> > <b>1</b>. Broken-symmetry density functional theory calculations
(DFT) revealed that the orientation of magnetic orbitals in <b>1</b> and <b>2</b> is different than that in <b>3</b> and <b>4</b>, and this results in two different exchange pathways.
These results demonstrate how bridge-mediated spin–spin coupling
in quinone-bridged metal complexes can be strongly tuned by a rational
design of the bridging ligand employing the [O] for [NR] isoelectronic
analogy