The Ambivalent Bonding of the 3(5)‐Isopropylpyrazolyl Moiety in Homo‐ and Heteroscorpionate Hydrobis(3‐R 1 ‐5‐R 2 ‐pyrazolyl)( y ‐isopropylpyrazolyl)boratocobalt( II ) Complexes ( y = 3 or 5)

The synthesis of hydrotris(pyrazol‐1‐yl)borate ligands (Tp x ) by condensation of sodium borohydride with 3(5)‐isopropylpyrazole and either 5(3)‐methyl‐3(5)‐phenylpyrazole or 3,5‐diphenylpyrazole gave the novel heteroscorpionate ligands hydrobis(5‐methyl‐3‐phenylpyrazolyl)(5‐isopropylpyrazolyl)borate and hydrobis(3,5‐diphenylpyrazolyl)(5‐isopropylpyrazolyl)borate, respectively. These were converted into CoTp x (NCS) complexes as well as CoTp x 2 in the case of the former ligand. In an attempted synthesis of heteroscorpionates bearing two y ‐isopropylpyrazolyl moieties ( y = 3 or 5) formation of the homoscorpionate hydrotris(3‐isopropylpyrazolyl)borate along with the above‐mentioned heteroscorpionates was noticed; no formation of the desired heteroscorpionates could be detected. The bis[hydrobis(5‐methyl‐3‐phenylpyrazolyl)(5‐isopropylpyrazolyl)borato]cobalt( II ) and tetrahydrofuranothiocyanatobis[hydrobis(5‐methyl‐3phenylpyrazolyl)(5‐isopropylpyrazolyl)borato]cobalt( II ) tetrahydrofuran solvate complexes were studied by X‐ray crystallography. Two Tp x ligands provide six nitrogen donors from pyrazol‐1‐yl residues to form a Tp x 2 Co complex in which two 5‐isopropylpyrazolyl rings are placed in a plane of symmetry, whereas the same Tp x ligand is bound in an η 3 fashion in the pentacoordinate [CoTp x (NCS)(THF)]·THF complex, in which a nitrogen atom from thiocyanate and an oxygen atom from THF complete the coordination sphere of the central metal ion. These compounds as well as the complexes thiocyanatohydrobis(3,5‐diphenylpyrazolyl)(5‐isopropylpyrazolyl)boratocobalt( II ) and thiocyanatohydrotris(3‐isopropylpyrazolyl)boratocobalt( II ) were characterized by 1 H NMR and IR spectroscopy. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2003)