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

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)](ClO 4 ) n (X = NCMe; n = 3: OH − , N 3 − , NCS − , ONO − , F − ; n = 2: O 2 CO 2− , n = 1; (N 3 − ) 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. 13 C NMR spectra of the complexes did not display peaks corresponding to the carbene carbon, except in the case of the [(PY4Im)Co(O 2 CO)] + 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 13 C chemical shifts for the complexes showed very good agreement with the experimental values for all but the carbene carbon atoms in all cases. The carbene carbon of the multidentate ligand PY4Im induces a consistent trans influence in a number of Co( iii ) complexes.