Ferrocenyl-Substituted Tris(pyrazolyl)boratesA New Ligand Type Combining Redox Activity with Resistance to Hydrogen Atom Abstraction

The low-temperature syntheses of ferrocenyl-substituted tris­(pyrazolyl)­borate ligands Tp^Fc* (hydrobis­(3-ferrocenylpyrazolyl)­mono­(5-ferrocenylpyrazolyl)­borate), Tp^Fc,Me* (hydrobis­(3-ferrocenyl-5-methylpyrazolyl)­mono­(5-ferrocenyl-3-methylpyrazolyl)­borate), and Tp^Fc,iPr (hydrotris­(3-ferrocenyl-5-isopropylpyrazolyl)­borate) are reported. The Tl salts of Tp^Fc* and Tp^Fc,Me* can be thermally isomerized to the symmetric Tp^Fc (hydrotris­(3-ferrocenylpyrazolyl)­borate) and Tp^Fc,Me (hydrotris­(3-ferrocenyl-5-methylpyrazolyl)­borate) species, respectively. Conversely, upon heating, the thermal isomerization of Tp^Fc,iPr results in the generation of a mixture of regioisomers. These ligands display a reversible three-electron oxidation. The preparations of Tp^CF3,FcTl (hydrotris­(3-trifluoromethyl-5-ferrocenylpyrazolyl)­borate) and PhTp^Fc (phenyltris­(3-ferrocenylpyrazolyl)­borate) are also reported