Complexes of heteroscorpionate trispyrazolylbo rate anionic ligands. Part III. X-ray crystallographic and NMR studies on cobalt(II) complexes with tris(pyrazolyl)borate anionic ligands obtained from 3,5-di-methylpyrazole and3(5)-methyl,5(3)-phenylpyrazole

Condensation of 2 equiv. of 5(3)-methyl,3(5)-phenylpyrazole and 1 equiv. of 3,5-di-methylpyrazole with NaBH4 resulted in the formation of sodium [hydr obis(3-phenyl,5-methylpyrazolyl)(3,5-di-methylpyrazolyl)borate]. The ligand was converted into the pentacoordinate [HB(3,5-di-Mepz)(3-Ph,5-Mepz)(2)]Co (NCS)(THF).THF complex for which the molecular structure was determined by the X-ray crystallographic method. The geometry of the ligand in the cobalt (II) complex was compared with that of the homoscorpionate ligand in [HB(3- Ph,5-Mepz)(3)]Co(NCS)(THF).0.5THF on the basis of X-ray structural data. Th e condition for the thermal conversion of the ligands in the studied Tp'Co( NCS) was established. The heating of the mentioned complexes at 428 K in pr opylbenzene resulted in a borotropic shift of 3-phenyl,5-methylpyrazolyl mo ieties resulting in the formation of new heteroscorpionates: the chiral [HB (3.5-di-Mepz)(3-Ph,5-Mepz)(3-Me,5-Phpz)]Co(NCS) and [HB(3-Me,5-Phpz)(2)(3-P h,5-Mepz)]Co(NCS), which were characterized in solution by H-1 NMR spectros copy. (C) 2001 Elsevier Science Ltd. All rights reserved.