The elusive zirconium(III)

Wielstra, Ytsen; Gambarotta, Sandro; Chiang, Michael Y.

doi:10.1002/recl.19891080102

“…[116][117] On the other hand, the Zr 4+/3+ and Hf 4+/3+ redox couples occur at very similar potentials to the TIP 0/-1 (typically observed between -1.70 V and -2.12 V) and consequently, they are extremely rare. [118][119][120][121][122][123] This suggests that titanium is more energetically mismatched with the ligand, and upon reduction it may be more favorable for the electron to sit at the metal rather than travel across the higher energy bridge. The energetic similarity of the respective 4d and 5d , where ΔE is the pulse amplitude.…”

Section: Resultsmentioning

confidence: 99%

Unusually Strong Long-range Electronic Coupling Across Redox-Active Bridges in M3+/M4+ Mixed-Valence Complexes of Group 4 Congeners

Bell

¹

,

DeYonker

²

,

Moore

³

et al. 2021

Preprint

0

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Homobimetallic complexes of Group 4 metals, supported by the redox-active tetrakis(imino)pyracene (TIP) ligand were synthesized and isolated. The formation of these complexes resulted in LUMOs having significantly lower energies than the free ligand and the respective metal salts, MCl4 (M = Ti, Zr, Hf), whereby all three complexes were readily reduced by one electron using the mild reductant, Cp*2Fe (E0 = -0.59 V). Spectroscopic characterization and quantum chemical analyses of the reduced species revealed that the resulting complexes are delocalized, borderline Class II-III (Ti) and Class III (Zr, Hf) mixed valence complexes. All three complexes display surprisingly strong long-range electronic coupling between the metal centers, as M to M distances, rAB, are nearly 12 Å. The coupling strengths of Zr and Hf were significantly stronger than those observed for the Ti complex, suggesting that better orbital overlap between the ligand and 4d or 5d metal centers helps to relieve the instability of the 3+ oxidation state via delocalization.

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“…[116][117] On the other hand, the Zr 4+/3+ and Hf 4+/3+ redox couples occur at very similar potentials to the TIP 0/-1 (typically observed between -1.70 V and -2.12 V) and consequently, they are extremely rare. [118][119][120][121][122][123] This suggests that titanium is more energetically mismatched with the ligand, and upon reduction it may be more favorable for the electron to sit at the metal rather than travel across the higher energy bridge. The energetic similarity of the respective 4d and 5d ions with TIP Me results in better orbital overlap and consequently, increased delocalization is observed.…”

Section: Figurementioning

confidence: 99%