¹H, ¹³C and ¹⁵N NMR studies on adducts formation of rhodium(II) tetraacylates with some azoles in CDCl₃ solution

Abstract

Adduct formations of rhodium(II) tetraacetate and tetratrifluoroacetate with some 1H-imidazoles, oxazoles, thiazoles, 1H-pyrazoles and isoxazole have been investigated by the use of 1H, 13C, 15N NMR and electronic absorption spectroscopy (VIS) in the visible range. Azoles tend to form axial adducts containing rhodium(II) tetraacylates bonded via nitrogen atom. Bulky substituents close to the nitrogen atom prevent the Rh--N bond formation, and in several cases switch over the binding site to the oxygen or sulphur atoms. The (15)N adduct formation shift Deltadelta(15N) (Deltadelta = delta(adduct) - delta(ligand)) varied from ca - 40 to - 70 ppm for the nitrogen atom involved in complexation, and of a few parts per million only, from ca - 6 to 3 ppm, for the non-bonded nitrogen atom within the same molecule. The Deltadelta(1H) values do not exceed one ppm; Deltadelta(13C) ranges from - 1 to 6 ppm. Various complexation modes have been proved by electronic absorption spectroscopy in the visible region (VIS). For comparison purposes, some adducts of pyridine, thiophene and furan derivatives have been measured as well. The experimental findings were compared with calculated chemical shifts, obtained by means of DFT B3LYP method, using 6-311 + G(2d,p), 6-31(d)/LanL2DZ and 6-311G(d,p) basis set.

NMR studies on interaction of rhodium(II) tetratrifluoroacetate with the ligands containing nitrile, isonitrile, isothiocyanate or isocyanate functional groups

“…À55 ppm, is observed. This effect is comparable with the values found for pyridine and azoles [11,14] and much larger than for amines (typically a dozen ppm) [12].…”

“…The Vis absorption changes slightly (Fig. 3), but it is analogous to this observed for thiophene and furan [25]. These effects suggest the complexation via X atom (S or O).…”

“…The details concerning basis sets used are given as footnotes below Tables 2-4. Absolute shieldings have been calculated by GIAO method, then shielding scale has been recalculated to chemical shift scale assuming the shielding values of 182.47 ppm for 13 C signal of TMS (d = 0 ppm) and À165.31 ppm for 15 N signal of CH 3 NO 2 (d = 0 ppm); both values have been calculated at B3LYP//6-311G + (2d,p) theory level [14,16]. Theoretical Dd values have been obtained as a difference between two chemical shifts calculated at the same theory level, Dd calc.…”

“…In the past, our attention was focused on the ligands containing a nitrogen atom in the molecule, due to their importance in natural products chemistry. Our earlier NMR investigation comprised the interaction of rhodium salts with the following ligands: mesoionic heterocycles [10], pyridines-type compounds [11], amines [12,13] and azoles [14]. Nitrogen-15 nuclear magnetic resonance ( 15 N NMR) turned out to be useful tool in adduct investigation.…”

Polymeric adducts of rhodium(II) tetraacetate with aliphatic diamines: natural abundance 13C and 15N CPMAS NMR investigations

“…The complexation properties of dirhodium tetracarboxylates have been utilised in numerous areas, in organic chemistry, in spectroscopy of chiral organic compounds and in biology and medicine. In our previous works, we explored the complexation of rhodium tetracarboxylates with organic ligand such as amines, azoles and derivatives of pyridine, nitriles and isonitriles using NMR techniques . Our investigations were mainly focused on the formation of adducts in situ in CDCl 3 solution.…”