A tert-butyl substituted trispyrazolylborate (Tptbu) was synthesized from sodium borohydride and 3-tert-butylpyrazole using a melt method with a 59% yield. This Tptbu ligand was reacted with copper nitrate hemihydrate and copper chloride dihydrate to form TptbuCuNO3 (1) and TptbuCuCl (2) complexes, respectively, in good yields. Addition of 5 eq. of NaX to complex 1 or 2 in methanol (X = Br- and NO2-) resulted in the formation of the respective TptBuCuX complex in yields ranging from 70 to 97% depending on the complex. The compounds were characterized using 1H-NMR, IR, and UV-vis spectroscopy. The NMR spectroscopy displayed paramagnetic behavior with resonances located in the range of -5 to 50 ppm with the pyrazole protons being the most shifted downfield. The IR spectra of the copper complexes exhibited B-H stretching frequencies at 2500 cm-1, which is higher energy than the corresponding stretch in the free ligand. The UV-vis spectra of the complexes contained a combination of d-d transitions and charge transfer bands depending on the complex. Attempts to grow X-ray diffraction quality crystals, by solvent evaporation, resulted in the decomposition of the complexes resulting from B-N bond cleavage in the ligand. The electrochemical properties of the complexes were determined using cyclic voltammetry. Each complex contained a Cu2+/Cu1+ reduction wave with varying reversibility. The reduction potential trend was consistent with the donor properties of the unique X- ligand in each complex. However, the differences in potential across the series are larger than a similar series of nickel complexes. This suggests that the redox properties of the copper center are more sensitive to changes in ligand coordination in Tp systems.

Synthesis, characterization, and electrochemical properties of tris(3-tert-butylpyrazolyl)borate copper complexes

249th National Meeting (2015)

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