Abstract
Two new bis(aryl‐imino)‐acenaphthene, Ar‐BIAN (Ar = 2,4,6‐trimethylphenyl = mes) ligands, bearing the NO2 group in the naphthalene moiety of the iminoacenaphthene at para‐ (5‐NO2) and meta‐ (4‐NO2) position, of formulations 1,2‐bis(mes‐imino)‐5‐nitroacenaphthene, 1, and 1,2‐bis(mes‐imino)‐4‐nitroacenaphthene, 2, were synthesized. Their respective dinuclear iodide bridged copper(I) complexes [Cu2(µ‐I)2(mes‐BIAN‐5‐NO2)2], 3 and [Cu2(µ‐I)2(mes‐BIAN‐4‐NO2)2], 4, were obtained in good yields by treatment with an equimolar amount of CuI. All compounds were characterized by elemental analysis, single‐crystal X‐ray diffraction, 1H‐NMR, 13C‐NMR, FTIR, UV/Vis spectroscopy. DFT calculations helped to understand the different molecular structure observed in the crystals of 3 and 4 and the determining role of packing forces. TDDFT revealed that the absorption bands in the visible were essentially MLCT (Metal to Ligand Charge Transfer), with some n→π* character (intra ligand). The shift to the red compared to the spectrum of the Cu(I) complex analogue without the NO2 group, [Cu2(µ‐I)2](mes‐BIAN)2], 6, could be explained by the stabilization of the ligand unoccupied π* orbitals in the presence of NO2.
Highlights
The design and synthesis of copper complexes is a subject of current interest since they can be applied in a large variety of metal-mediated transformations.[1]
The first step in the synthesis of the ligands is the functionalization of acenaphthenequinone by the NO2 group, which has been described in the literature under different experimental conditions, at room temperature, 0 °C and 80 °C, using NaNO3 or HNO3 as nitration agents.[38,39]
The authors claimed that the nitro-acenaphthenequinone held the NO2 group at the para-position, our attempts to repeat the synthesis following the three described methods afforded in all cases a mixture of products functionalized at para- and meta-position in roughly 1:2 meta-:para-proportion, on we will indistinctly name para-position to 5-NO2 and meta-position to 4-NO2 (Scheme 1)
Summary
The design and synthesis of copper complexes is a subject of current interest since they can be applied in a large variety of metal-mediated transformations.[1]. We have been engaged during the last decade in the synthesis of α-diimine transition metal compounds, either for structural studies[17,18,19,20,21] or catalytic applications.[22,23,24,25,26,27] copper(I) complexes bearing Ar-BIAN ligands have been reported by us[18,22,23,24,26] and other authors.[28]
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