Co(iii) complexes of the pentadentate NHC ligand PY4Im: carbene-induced trans influences and the non-disappearing 13C NMR peak

Abstract

Co(III) complexes of the N-heterocyclic carbene ligand PY4Im (PY4Im = (1,3-bis(bis(2-pyridyl)methyl)imidazol-2-ylidene)) having the general formula [(PY4Im)Co(X)](ClO₄)_n (X = NCMe; n = 3: OH⁻, N₃⁻, NCS⁻, ONO⁻, F⁻; n = 2: O₂CO²⁻, n = 1; (N₃⁻)₃, n = 0) were prepared and structurally characterised. X-ray structural data are consistent with the presence of a trans influence due to the coordinated carbene carbon, and this is also supported by computational results. ¹³C NMR spectra of the complexes did not display peaks corresponding to the carbene carbon, except in the case of the [(PY4Im)Co(O₂CO)]⁺ cation, where a peak at δ = 170.21 ppm was observed. However, HMBC spectra allowed indirect determination of the chemical shifts of the carbene carbon in the remaining complexes, owing to the geometry of the PY4Im ligand. Calculated ¹³C chemical shifts for the complexes showed very good agreement with the experimental values for all but the carbene carbon atoms in all cases.