Strong intramolecular calcium-π interactions with aryl substituents--requirements and limitations
The amidines Dipp-N=C(tBu)-N(H)-Qu (1a) (Dipp = 2,6-diisopropylphenyl, Qu = 8-quinolyl) and Dipp-N=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...
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Published in | Dalton transactions : an international journal of inorganic chemistry Vol. 43; no. 38; pp. 14440 - 14449 |
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Main Authors | , , , , , |
Format | Journal Article |
Language | English |
Published |
England
14.10.2014
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Subjects | |
Online Access | Get full text |
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Summary: | The amidines Dipp-N=C(tBu)-N(H)-Qu (1a) (Dipp = 2,6-diisopropylphenyl, Qu = 8-quinolyl) and Dipp-N=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. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 1477-9226 1477-9234 |
DOI: | 10.1039/c4dt00949e |