Hydrogenation of the dearomatized
PNN ligand of the Milstein bipyridyl
complex RuH(CO)[PNN] (2) gives a square-pyramidal Ru(II)
product RuH(CO)[pPNN] (5). The central ring of the pPNN
ligand is a piperidine. A minor byproduct of the hydrogenation reaction
is complex 6 which has a dimeric structure made of two
Ru(II) fragments each possessing a partly hydrogenated PNN ligand.
The structures of 5 and 6 have been elucidated
by NMR spectroscopy and X-ray crystallography. The PNN ligand of 2 is also hydrogenated under the conditions of the catalytic
dehydrogenative coupling of ethanol to ethyl acetate. No direct evidence
of the aromatized dihydride RuH2(CO)[PNN] (4) was found in this study. However, treating RuHCl(CO)[PNN] with
Li[HBEt3] or reacting 2 with H2 at low temperature resulted in a structurally characterized hydride-bridged
dimer (7) bearing intact aromatized bipyridyl ligands.
M06-L/def2-QZVP DFT calculations provided insights into the thermodynamics
of the stoichiometric reactions of this work and into the nature of
the intermediates of the catalytic ester hydrogenation facilitated
by RuH2(CO)[pPN(H)N] (8) formed from 5 under H2.
A convenient, inexpensive and effective route for the preparation of a Cu 2 O-CuO-Cu-C nanocomposite is described here by applying Cu(II) as a source of copper. Characterization of the nanocomposite was performed with X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDX). Analysis of the data showed that the particles of the nanocomposite are uniformly distributed and show high catalytic activity in the cross-coupling of sodium azide with various aryl iodides and bromides. This nanocomposite has a high level of performance, and even led to the synthesis of the products at room temperature. In addition, this is the first report of the synthesis of aryl azides under both base-and ligand-free conditions. For the first time, both ligand-and base-free conditions were applied for the synthesis of aryl azides, which implies exceptional performance of the Cu 2 O-CuO-Cu-C nanocomposite. Simultaneous removal of the base and ligand in a green solvent is the main advantage of this reaction. Unfortunately, aryl bromides and aryl iodides with electron-withdrawing functional groups in their scaffold did not give the desired aryl azides.
An efficient and selective azidation of aryl halides by reacting sodium azide with aryl halides is described. The heterogeneous nature of the copper(Ι) catalyst, which catalyzes the crosscoupling reactions, and the antiviral and antibacterial properties of the products are features of this methodology. It is also worth noting that no aryl amines are produced as byproducts under these conditions.
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