Tricyanoborane-Functionalized Anionic N-Heterocyclic Carbenes: Adjustment of Charge and Stereo-Electronic Properties |
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Authors: | Ludwig Zapf Sven Peters Dr Rüdiger Bertermann Prof Dr Udo Radius Prof Dr Maik Finze |
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Institution: | Institute for Sustainable Chemistry & Catalysis with Boron (ICB) Institute of Inorganic Chemistry, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg, Germany |
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Abstract: | The 1-methyl-3-(tricyanoborane)imidazolin-2-ylidenate anion ( 2 ) was obtained in high yield by deprotonation of the B(CN)3-methylimidazole adduct 1 . Regarding charge and stereo-electronic properties, anion 2 closes the gap between well-known neutral NHCs and the ditopic dianionic NHC, the 1,3-bis(tricyanoborane)imidazolin-2-ylidenate dianion ( IIb ). The influence of the number of N-bonded tricyanoborane moieties on the σ-donating and π-accepting properties of NHCs was assessed by quantum chemical calculations and verified by experimental data on 2 , IIb , and 1,3-dimethylimidazolin-2-ylidene (IMe, IIa ). Therefore NHC 2 , which acts as a ditopic ligand via the carbene center and the cyano groups, was reacted with alkyl iodides, selenium, and Ni(CO)4] yielding alkylated imidazoles 3 and 4 , the anionic selenium adduct 5 , and the anionic nickel tricarbonyl complex 8 , respectively. The results of this study prove that charge, number of coordination sites, buried volume (%Vbur) and σ-donor and π-acceptor abilities of NHCs can be effectively fine-tuned via the number of tricyanoborane substituents. |
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Keywords: | N-heterocyclic carbene anionic carbene boron cyanoborate imidazolate |
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