Synthesis, X‐ray Crystallographic and 1H NMR Spectroscopic Structural Studies on Cobalt( II ) Complexes of Homoscorpionate, Heteroscorpionates and Chiral Tris(pyrazolyl)borates Obtained from 5(3)‐Isopropyl‐3(5)‐phenylpyrazole and 3,5‐Dimethylpyrazole

Condensation of 5(3)‐isopropyl‐3(5)‐phenylpyrazole with sodium borohydride led to a mixture of tris(pyrazolyl)borate ligands (Tpx) − the homoscorpionate hydrotris(5‐isopropyl‐3‐phenylpyrazolyl)borate and the heteroscorpionates hydro(3‐isopropyl‐5‐phenylpyrazolyl)bis(5‐isopropyl‐3‐phenylpyrazolyl)borate and hydrobis(3‐isopropyl‐5‐phenylpyrazolyl)(5‐isopropyl‐3‐phenylpyrazolyl)borate − that were converted into TpxCo(NCS) complexes. The molecular structures of pentacoordinate[hydrotris(5‐isopropyl‐3‐phenylpyrazolyl)borato](tetrahydrofuran)(thiocyanato)cobalt(II) (1‐THF) and [hydrobis(3‐isopropyl‐5‐phenylpyrazolyl)(5‐isopropyl‐3‐cobalt(II) (3‐THF) were elucidated crystallographically. Hydro(3,5‐dimethylpyrazolyl)bis(5‐isopropyl‐3‐phenylpyrazolyl)borate was also obtained by condensation of 2.1 equiv. of 5(3)‐isopropyl‐3(5)‐phenylpyrazole and 0.9 equiv. of 3,5‐dimethylpyrazole with sodium borohydride, and it was converted into [hydro(3,5‐dimethylpyrazolyl)bis(5‐isopropyl‐3‐phenylpyrazolyl)borato](thiocyanato)cobalt(II) (4), which was characterized by X‐ray crystallography. The latter was converted thermally under mild conditions (358 K in toluene) into [hydro(3,5‐dimethylpyrazolyl)(3‐isopropyl‐5‐phenylpyrazolyl)(5‐isopropyl‐3‐phenylpyrazolyl)borato](thiocyanato)cobalt(II) (9) in 45% yield, as was concluded from the 1H NMR spectrum of the post‐reaction mixture. The dimer of 9 was obtained as single crystals from toluene/hexane and its structure was determined crystallographically. Two chiral Tpx ligands of opposite boron‐centered configurations are coordinated to cobalt(II) ions in a κ3 fashion. The pentacoordinate metal ions are bridged head‐to‐tail by the thiocyanate anions. This chiral Tpx ligand is the first example of a borate with fixed boron‐centered chirality. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)