FcTp(R) (R = ⁱPr or ^tBu): third-generation ferrocenyl scorpionates

Scorpionate (or trispyrazolylborate) ligands have seen much structural variation due to the relative ease of modifying their electronic and steric effects. Second-generation scorpionates were created by increasing the bulk in the 3-position of the pyrazole (pz) ring. A new class of third-generation scorpionates was obtained by modifying the remaining boron substituent. A series of thallium(I) and cobalt(II) complexes of the ferrocenyltris(3-R-pyrazolyl)borate ligand [FcTp^R; R = isopropyl (ⁱPr) or tert-butyl (^tBu)] have been synthesized in order to expand the range of redox-active third-generation scorpionates. These are [ferrocenyltris(3-tert-butylpyrazol-1-yl-κN²)borato]thallium(I), [FeTl(C₅H₅)(C₂₆H₃₇BN₆)], [ferrocenyltris(3-isopropylpyrazol-1-yl-κN²)borato]thallium(I), [FeTl(C₅H₅)(C₂₃H₃₁BN₆)], chlorido[ferrocenyltris(3-tert-butylpyrazol-1-yl-κN²)borato]cobalt(II), [CoFe(C₅H₅)(C₂₆H₃₇BN₆)Cl], [ferrocenyltris(3-tert-butylpyrazol-1-yl-κN²)borato]iodidocobalt(II) benzene disolvate, [CoFe(C₅H₅)(C₂₆H₃₇BN₆)I]·2C₆H₆, and [ferrocenyltris(3-isopropylpyrazol-1-yl-κN²)borato]iodidocobalt(II), [CoFe(C₅H₅)(C₂₃H₃₁BN₆)I]. The structures demonstrate that the metal coordination site can easily be modified by using bulkier substituents at the pz 3-position.