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 TpFc* (hydrobis­(3-ferrocenylpyrazolyl)­mono­(5-ferrocenylpyrazolyl)­borate), TpFc,Me* (hydrobis­(3-ferrocenyl-5-methylpyrazolyl)­mono­(5-ferrocenyl-3-methylpyrazolyl)­borate), and TpFc,iPr (hydrotris­(3-ferrocenyl-5-isopropylpyrazolyl)­borate) are reported. The Tl salts of TpFc* and TpFc,Me* can be thermally isomerized to the symmetric TpFc (hydrotris­(3-ferrocenylpyrazolyl)­borate) and TpFc,Me (hydrotris­(3-ferrocenyl-5-methylpyrazolyl)­borate) species, respectively. Conversely, upon heating, the thermal isomerization of TpFc,iPr results in the generation of a mixture of regioisomers. These ligands display a reversible three-electron oxidation. The preparations of TpCF3,FcTl (hydrotris­(3-trifluoromethyl-5-ferrocenylpyrazolyl)­borate) and PhTpFc (phenyltris­(3-ferrocenylpyrazolyl)­borate) are also reported.