Formation of Novel T‑Shaped NNN Ligands via Rare-Earth Metal-Mediated Si–H Activation

Reactions of silylamides [Ln­{N­(SiHMe₂)₂}₃(thf)₂] with sterically crowded terphenylamine DmpNH₂ (Dmp = 2,6-Mes₂C₆H₃ with Mes = 2,4,6-Me₃C₆H₂) afforded via a template reaction the formation of a new tridentate ligand, and derived complexes of composition [LnN­{SiMe₂N­(Dmp)}₂] (Ln = Ce, Pr) were obtained. Usage of the even more bulky amine Ar*NH₂ (Ar* = 2,6-Trip₂C₆H₃ with Trip = 2,4,6-<i>i</i>Pr₃C₆H₂) yielded the free protonated ligand NH­{SiMe₂NH­(Ar*)}₂

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 [{Cu­(tmpa)}₂­(μ-L¹_–2H)]­(ClO₄)₂ (<b>1</b>), [{Cu­(tmpa)}₂­(μ-L²_–2H)]­(ClO₄)₂ (<b>2</b>), [{Cu­(tmpa)}₂­(μ-L³_–2H)]­(BPh₄)₂ (<b>3</b>), and [{Cu­(tmpa)}₂­(μ-L⁴_–2H)]­(ClO₄)₂ (<b>4</b>) (tmpa = tris­(2-pyridyl­methyl)­amine, L¹ = chloranilic acid, L² = 2,5-dihydroxy-1,4-benzoquinone, L³ = (2,5-di-[2-(methoxy)-anilino]-1,4-benzoquinone, L⁴ = azophenine) were synthesized from copper­(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 copper­(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 copper­(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 copper­(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^–1 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 [{Cu­(tmpa)}₂­(μ-L¹_–2H)]­(ClO₄)₂ (<b>1</b>), [{Cu­(tmpa)}₂­(μ-L²_–2H)]­(ClO₄)₂ (<b>2</b>), [{Cu­(tmpa)}₂­(μ-L³_–2H)]­(BPh₄)₂ (<b>3</b>), and [{Cu­(tmpa)}₂­(μ-L⁴_–2H)]­(ClO₄)₂ (<b>4</b>) (tmpa = tris­(2-pyridyl­methyl)­amine, L¹ = chloranilic acid, L² = 2,5-dihydroxy-1,4-benzoquinone, L³ = (2,5-di-[2-(methoxy)-anilino]-1,4-benzoquinone, L⁴ = azophenine) were synthesized from copper­(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 copper­(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 copper­(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 copper­(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^–1 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