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 [FcTpR; 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.
Keywords: cobalt; coordination compounds; crystal structure; ferrocene; redox-active; thallium; third-generation scorpionates; trispyrazolylborate.