Dibenzotropylidene Substituted Ligands for Early Main Group Metal-Alkene Bonding

Martin J, Langer J, Wiesinger M, Elsen H, Harder S (2020)

Publication Type: Journal article

Publication year: 2020

Journal

DOI: 10.1002/ejic.202000524

Abstract

New N-ligands with TROP-substituents are introduced (TROP = [5H]dibenzo[a,d]cyclohepten-5-yl): (TROP)(DIPP)N (DIPP = 2,6-diisopropylphenyl), ^TROPBDI (HC[C(Me)N-TROP]2) and the β-diketiminate ligand ^TROP–DIPPBDI with TROP and DIPP substituents at N. Several Li, Mg, Ca and Zn complexes with these ligands have been isolated and were characterized by X-ray diffraction. While TROP-substituents in the protonated ligands show endo-exo exchange, TROP-substituents in the metal complexes are in endo-conformation due to metal···alkene bonding. Short contacts between the metal and the TROP alkene unit are observed and some of these are the shortest reported; (^TROPBDI)Li: Li···C 2.416(3) Å, [(TROP)(DIPP)N]2Ca: Ca···C 2.742(2) Å. ^TROPBDI shows superior metal shielding properties to the Li complex with a buried volume of VB = 78.7 %. DFT calculations on [(TROP)(DIPP)N]2Mg show a minimum with asymmetric Mg···alkene bonding. Symmetric Mg···alkene bonding is a transition state 1.9 kcal/mol higher in energy. Asymmetry in alkene-Mg bonding is explained by an ion-induced polarization of the C=C bond and electrostatic Mg²⁺···(δ-)C=C(δ+) attraction. The TROP-substituent stabilizes low valent radical species but attempts to isolate (^TROPBDI)Mg^· or (^TROPBDI)Zn^· by reduction of the iodide precursors failed. Intensely black coloured raw products hint towards formation of radical species. Several radical decomposition products have been structurally characterized.

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How to cite

APA:

Martin, J., Langer, J., Wiesinger, M., Elsen, H., & Harder, S. (2020). Dibenzotropylidene Substituted Ligands for Early Main Group Metal-Alkene Bonding. European Journal of Inorganic Chemistry. https://dx.doi.org/10.1002/ejic.202000524

MLA:

Martin, Johannes, et al. "Dibenzotropylidene Substituted Ligands for Early Main Group Metal-Alkene Bonding." European Journal of Inorganic Chemistry (2020).

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