Synthesis and Carbon-13 NMR Spectroscopy of Poly(pyrazol-1-yl)alkane Ligands

The use of polypyrazolylmethanes as ligands in coordination chemistry is increasing in an ever quicker pace. We here present a 13C NMR study of twelve bis- and tris-pyrazolylmethanes, eight of them never previously described. Those already known, bis(pyrazolyl)phenylmethane, tris(pyrazolyl)methane, tris(pyrazolyl)ethane, and tris(3,5-dimethylpyrazolyl)methane, have been extensively used in coordination chemistry. The carbon-13 chemical shifts show high internal consistency: for instance, a previously reported additive model predicts, with great accuracy, the chemical shift of the central sp3 carbon. Coupling constants proved to be useful tools for the assignment of pyrazole carbons. The 1J(IH-13C) coupling of the central carbon is linearly related to the basicity of the pyrazole substitutent in tris(pyrazol-1-yl)methanes.