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Issue 38, 2014
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Strong intramolecular calcium–π interactions with aryl substituents – requirements and limitations

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Abstract

The amidines Dipp–N[double bond, length as m-dash]C(tBu)–N(H)–Qu (1a) (Dipp = 2,6-diisopropylphenyl, Qu = 8-quinolyl) and Dipp–N[double bond, length as m-dash]C(tBu)–N(H)–Py (1b) (Py = 2-pyridyl) are deprotonated with KN(SiMe3)2, yielding potassium N-(2,6-diisopropylphenyl)-N′-(8-quinolyl)pivalamidinate (2a) and potassium N-(2,6-diisopropylphenyl)-N′-(2-pyridyl)pivalamidinate (2b). Metalation of 1a with [(thf)2Ca{N(SiMe3)2}2] in tetrahydrofuran (thf) leads to the formation of ether-free calcium bis[N-(2,6-diisopropylphenyl)-N′-(8-quinolyl)pivalamidinate] (3a) with a strong intramolecular calcium–π interaction with one Dipp group. Furthermore, agostic bonds to one tert-butyl substituent complete the coordination sphere of the metal center and stabilize this bonding situation. The metathesis reaction of 2b with [(thf)4CaI2] yields the thf adduct of calcium bis[N-(2,6-diisopropylphenyl)-N′-(2-pyridyl)pivalamidinate] (3b). In addition to the bonds between calcium and the hard Lewis bases (oxygen of thf, nitrogen atoms of the pyridylamido moieties), anagostic Ca–H bonds to the tert-butyl substituents complete the coordination sphere. The intramolecular calcium–π interaction with an aryl group as observed in 3a requires steric shielding of the alkaline earth metal center, safely excluding the formation of a complex with more than one thf ligand.

Graphical abstract: Strong intramolecular calcium–π interactions with aryl substituents – requirements and limitations

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Publication details

The article was received on 31 Mar 2014, accepted on 16 Jun 2014 and first published on 16 Jun 2014


Article type: Paper
DOI: 10.1039/C4DT00949E
Citation: Dalton Trans., 2014,43, 14440-14449
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    Strong intramolecular calcium–π interactions with aryl substituents – requirements and limitations

    C. Loh, S. Seupel, A. Koch, H. Görls, S. Krieck and M. Westerhausen, Dalton Trans., 2014, 43, 14440
    DOI: 10.1039/C4DT00949E

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