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Abstract Herein, we report four new chiral 1,4,7‐triazacyclononane (TACN) derivatives and their corresponding nickel(II) chloride complexes. All TACN ligands are bearing one chiral N‐substituent and two alkyl (methyl ortert‐butyl) N‐substituents, and we have developed a new synthetic method for the dimethyl‐substituted TACN derivative, in order to prevent the rotational isomers that hinder the cyclization reaction. The nickel complexes change their coordination geometry significantly depending on the steric bulk of the N‐alkyl substituents, from a dinuclear tris(μ‐chloro)dinickel complex to mononuclear Ni‐dichloride and Ni‐chloride complexes. These complexes were then employed in the alkyl‐alkyl Kumada cross‐coupling reaction and revealed that the more sterically hindered ligands produced more homocoupled product rather than the cross‐coupled product, while the mononuclear Ni‐dichloride complex exhibited significantly lower catalytic activity. These chiral complexes were also employed in enantioconvergent cross‐coupling reactions as well, to afford significant enantioenrichment. Overall, the least sterically hindered Ni complex yields the best yields in the alkyl‐alkyl Kumada cross‐coupling reaction among the four complexes investigated, as well as the highest enantioselectivity.
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This content will become publicly available on April 9, 2026
Steric Tuning of Spin States and Redox Potentials in Tris(imidazole) Triazacyclononane Complexes of Fe 2+/3+ and Co 2+/3+
Abstract A series of Co2+/3+and Fe2+/3+complexes is prepared using three variants of a hexadentate tris(imidazole)triazacyclononane ligand bearing different 4‐alkyl substituents on the imidazole rings. The steric bulk of the alkyl substituent (R=H,iPr, ortBu) alters the preferred size of the ligand binding cavity by inhibiting close approach of the imidazole donors with bulky substituents. The resulting changes in geometry, redox potentials, spin states, and optical properties are catalogued across the series, demonstrating redox potential tuning over at least 670 mV as well as spin state switching based on the choice of substituent. The ligand field splitting of the complexes decreases with increasing bulk of the substituents. Tuning of the steric bulk of the substituents in these positions therefore allows for the electronic properties of the complexes to be fine‐tuned in a manner orthogonal to the donor properties of the substituents.
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- Award ID(s):
- 2304919
- PAR ID:
- 10582541
- Publisher / Repository:
- European Journal of Inoganic Chemistry
- Date Published:
- Journal Name:
- European Journal of Inorganic Chemistry
- Volume:
- 28
- Issue:
- 11
- ISSN:
- 1434-1948
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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