We report the preparation and characterization of zinc(II) hydrotris(3-cumenyl-5-methylpyrazolyl)borate (LZn) complexes, (LZn)(2)1'-H and (LZn)(2)1, of a bis(catechol) ligand. The formation of (LZn)(2)1'-H, an S = 1/2 complex, rather than (LZn)(2)1, an S = 1 complex, is observed due to tautomerization of a reaction intermediate. The biradical complex, (LZn)(2)1, can be prepared from (LZn)(2)1'-H by oxidation, a conversion that is accompanied by a blue-green to red-purple color change and an increase in spin from 1/2 to 1. The frozen solution EPR spectrum of the biradical complex (LZn)(2)1 exhibits zero-field splitting and a Delta m(s) = 2 transition characteristic of a triplet state. The temperature dependence of the EPR signal intensity is consistent with high-spin coupling of the unpaired electrons of the ligand.