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Aerobic reaction between the pyridine-2-carboxamide-2-aminophenol N3O ligand (H3L1) and Zn(ClO4)2·6H2O in CH3CN affords an N3 phenoxazinylate coordinated Zn(II) complex; its diradical electronic structure [ZnII{(L1*)˙−}2] has been elucidated from redox, spectroscopic (UV-VIS and EPR), and magnetic measurements and DFT calculations. Isolation and characterization of the metal-assisted redox-driven modified N3 ligand as a radical cation (H2L1*)˙+ and its Ni(II)-diradical complex [NiII{(L1*)˙−}2] have also been achieved. [ABSTRACT FROM AUTHOR]

Multiple spectroscopic techniques, along with single-crystal X-ray analysis, have been used to reveal the detailed structural and electronic information on reaction intermediates of a new copper(II)-DBU catalytic system for the N-arylation of 7-Azaindole. The reaction mixture of Chan-Lam cross-coupling yields two dimeric copper(II)-7-azaindole complexes, including one attached with DBU, prior to adding arylboronic acid and are confirmed structurally and spectroscopically. A suitable mechanism has been proposed using the dimeric copper(II) complex as a catalyst for the coupling reactions. The role of DBU as a base and also as an auxiliary ligand in the course of the reaction has been established. The transmetalated monomeric aryl-copper(II) species generated from the dimeric unit is oxidized by another equivalent of copper(II) to yield an aryl-copper(III) intermediate for facile Narylation, which has been authenticated with UV-vis spectroscopy. The regeneration of the copper(II)-catalyst by aerial oxidation of colorless copper(I) species (generated via reductive elimination and disproportionation step) is confirmed by mass and absorption spectroscopy. Detailed DFT and TD-DFT calculations help to rationalize the proposed reaction intermediates and their corresponding electronic transitions. Moreover, the confirmation of copper(I)-7-azaindole intermediate via HRMS reaffirmed the involvement of Cu(II)/Cu(III)/Cu(I) species in the Chan-Lam type of coupling. A medicinallyimportant 7-azaindole-based SHP2 inhibitor has been synthesized via sequential arylation. [ABSTRACT FROM AUTHOR]

Three square planar nickel(II) complexes of a new asymmetric tetradentate redox-active ligand H3L2 in its deprotonated form, at three redox levels, open-shell semiquinonate(1−) π radical, quinone(0) and closed-shell dianion of its 2-aminophenolate part, have been synthesized. The coordinated ligand provides N (pyridine) and N′ and N′′ (carboxamide and 1,2-phenylenediamide, respectively) and O (phenolate) donor sites. Cyclic voltammetry on the parent complex [Ni(L2)] 1 in CH2Cl2 established a three-membered electron-transfer series (oxidative response at E1/2 = 0.57 V and reductive response at −0.32 V vs. SCE) consisting of neutral, monocationic and monoanionic [Ni(L2)]z (z = 0, 1+ and 1−). Oxidation of 1 with AgSbF6 affords [Ni(L2)](SbF6) (2) and reduction of 1 with cobaltocene yields [Co(η5-C5H5)2][Ni(L2)] (3). The molecular structures of 1·CH3CN, 2·0.5CH2Cl2 and 3·C6H6 have been determined by X-ray crystallography at 100 K. Characterization by 1H NMR, X-band EPR (gav = 2.006 (solid); 2.008 (CH2Cl2–C6H5CH3 glass); 80 K) and UV-VIS-NIR spectral properties established that 1, 2 and 3 have [NiII{(L2)˙2−}], [NiII{(L2)−}]+/1+ and [NiII{(L2)3−}]−/1− electronic states, respectively. Thus, the redox processes are ligand-centred. While 1 possesses paramagnetic St (total spin) = 1/2, 2 and 3 possess diamagnetic ground-state St = 0. Interestingly, the variable-temperature (2–300 K) magnetic measurement reveals that 1 with the St = 1/2 ground state attains the antiferromagnetic St = 0 state at a very low temperature, due to weak noncovalent interactions via π–π stacking. Density functional theory (DFT) electronic structural calculations at the B3LYP level of theory rationalized the experimental results. In the UV-VIS-NIR spectra, broad absorptions are recorded for 1 and 2 in the range of 800–1600 nm; however, such an absorption is absent for 3. Time-dependent (TD)-DFT calculations provide a very good fit with the experimental spectra and allow us to identify the observed electronic transitions. [ABSTRACT FROM AUTHOR]

A controlled reaction in DMF/CH3CN between a facially disposed tricyanide-containing building block (nBu4N)[FeIII(Tp)(CN)3] (Tp(--) = tris(pyrazol-1-yl)borate anion) and tailor-made Mn(II) and Cu(II) complexes of two tripodal tetradentate ligands providing two 1-methylbenzimidazole, a pyridyl, and a tertiary amine as donor sites, differing only in the (2-pyridyl)alkylamine chain length, has been employed to assemble cyanide-bridged complexes. The heterobimetallic complexes [FeIII(Tp)(CN)2(μ-CN)MnIICl(L¹)]·3DMF·3H2O (1), [FeIII(Tp)(CN)2(μ-CN)MnIICl(L²)]·DMF (2), [FeIII(Tp)(CN)2(μ-CN)CuII(L¹)](ClO4)·2CH3OH (3), and [FeIII(Tp)(CN)2(μ-CN)CuII(L²)](ClO4)·2CH3CN (4) [L¹ = bis{(N-methyl-benzimidazol-2-yl)methyl}(2-pyridylmethyl)amine; L² = bis{(N-methyl-benzimidazol-2-yl)methyl}(2-pyridylethyl)amine (L²)] have been structurally authenticated, revealing single cyanide-bridged discrete dimers with Fe(III)(μ-CN)Mn(II) and Fe(III)(μ-CN)Cu(II) structural motifs. In 1 and 2, both the metal ions have a distorted octahedral geometry. In 3 and 4, the Fe(III) centres are six-coordinate, but the two five-coordinate Cu(II) centres assume two different geometries: distorted trigonal bipyramidal in 3 and almost ideal square pyramidal in 4. Investigation of the magnetic properties reveals an antiferromagnetic interaction through the cyanide bridge between the six-coordinate low-spin Fe(III) (S = 1/2) ions and high-spin six-coordinate Mn(II) (S = 5/2) ions in 1 and 2 with the total spin St = 2 ground state; while 3 exhibits a ferromagnetic interaction between the cyanide-bridged Fe(III) (S = 1/2) and Cu(II) (S = 1/2) ions with the St = 1 state, 4 displays an antiferromagnetic interaction leading to the St = 0 state. [ABSTRACT FROM AUTHOR]

Synergy between a pair of weak non-covalent interactions can predispose a molecular self-assembly towards a specific pathway. We report assisted π-stacking, a synergy between aromatic π-stacking and n →π* interactions that exhibits an unprecedented strength and thermal stability. Natural bond orbital analysis reveals the non-additive nature of the interaction. [ABSTRACT FROM AUTHOR]