ChemInform Abstract: Novel Polypyrazolylborate Ligands: Coordination Control Through 3-Substituents of the Pyrazole Ring.

ChemInform Abstract

The new polypyrazolylborate ligands (Ia)-(Id) are prepared by reaction of the tetrahydridoborate ion with the appropriate pyrazole depending on the molar ratio. The ligands (Ie) and (If) are obtained by mixing (Ia), (Ib) with additional pyrazole in refluxing anisole. A series of transition-metal complexes, shown in the scheme, is prepared by mixing the ligand with the metal salt. The bulky substituents in the 3-position of the pyrazolyl rings have a strong effect on the coordination chemistry of these ligands. Contrary to known derivatives the formation of bis-chelate complexes with (Ic)-(If) is impossible. Two complexes, (VIII) and (IX) are characterized by an X-ray analysis (both crystallize in the space group P2₁/n with Z=4). The results indicate that appropriate selection of the 3-Rgroup in the ligand will permit the construction of custom-sized pockets around metal ions, allowing access only to molecules of predetermined size and/or shape.