title: Surprisingly Different Reaction Behavior of Alkali and Alkaline Earth Metal Bis(trimethylsilyl)amides toward Bulky N-(2-Pyridylethyl)-N'-(2,6-diisopropylphenyl)pivalamidine.
abstract: N-(2,6-Diisopropylphenyl)-N'-(2-pyridylethyl)pivalamidine (Dipp-N=C(tBu)-N(H)-C2 H4 -Py) (1), reacts with metalation reagents of lithium, magnesium, calcium, and strontium to give the corresponding pivalamidinates [(tmeda)Li{Dipp-N=C(tBu)-N-C2 H4 -Py}] (6), [Mg{Dipp-N=C(tBu)-N-C2 H4 -Py}2 ] (3), and heteroleptic [{(Me3 Si)2 N}Ae{Dipp-N=C(tBu)-N-C2 H4 -Py}], with Ae being Ca (2 a) and Sr (2 b). In contrast to this straightforward deprotonation of the amidine units, the reaction of 1 with the bis(trimethylsilyl)amides of sodium or potassium unexpectedly leads to a β-metalation and an immediate deamidation reaction yielding [(thf)2 Na{Dipp-N=C(tBu)-N(H)}] (4 a) or [(thf)2 K{Dipp-N=C(tBu)-N(H)}] (4 b), respectively, as well as 2-vinylpyridine in both cases. The lithium derivative shows a similar reaction behavior to the alkaline earth metal congeners, underlining the diagonal relationship in the periodic table. Protonation of 4 a or the metathesis reaction of 4 b with CaI2 in tetrahydrofuran yields N-(2,6-diisopropylphenyl)pivalamidine (Dipp-N=C(tBu)-NH2 ) (5), or [(thf)4 Ca{Dipp-N=C(tBu)-N(H)}2 ] (7), respectively. The reaction of AN(SiMe3 )2 (A=Na, K) with less bulky formamidine Dipp-N=C(H)-N(H)-C2 H4 -Py (8) leads to deprotonation of the amidine functionality, and [(thf)Na{Dipp-N=C(H)-N-C2 H4 -Py}]2 (9 a) or [(thf)K{Dipp-N=C(H)-N-C2 H4 -Py}]2 (9 b), respectively, are isolated as dinuclear complexes. From these experiments it is obvious, that β-metalation/deamidation of N-(2-pyridylethyl)amidines requires bases with soft metal ions and also steric pressure. The isomeric forms of all compounds are verified by single-crystal X-ray structure analysis and are maintained in solution.
authors.affiliation: Institute of Inorganic and Analytical Chemistry, Friedrich Schiller University, Humboldstrasse 8, 07743, Jena, Germany.
authors.forename: Diana
authors.initials: D
authors.lastname: Kalden
authors.affiliation: Institute of Inorganic and Analytical Chemistry, Friedrich Schiller University, Humboldstrasse 8, 07743, Jena, Germany.
authors.forename: Ansgar
authors.initials: A
authors.lastname: Oberheide
authors.affiliation: Institute of Inorganic and Analytical Chemistry, Friedrich Schiller University, Humboldstrasse 8, 07743, Jena, Germany.
authors.forename: Claas
authors.initials: C
authors.lastname: Loh
authors.affiliation: Institute of Inorganic and Analytical Chemistry, Friedrich Schiller University, Humboldstrasse 8, 07743, Jena, Germany.
authors.forename: Helmar
authors.initials: H
authors.lastname: Görls
authors.affiliation: Institute of Inorganic and Analytical Chemistry, Friedrich Schiller University, Humboldstrasse 8, 07743, Jena, Germany.
authors.forename: Sven
authors.initials: S
authors.lastname: Krieck
authors.affiliation: Institute of Inorganic and Analytical Chemistry, Friedrich Schiller University, Humboldstrasse 8, 07743, Jena, Germany. m.we@uni-jena.de.
authors.forename: Matthias
authors.initials: M
authors.lastname: Westerhausen
keywords: 1,3-diazaallyl anions; alkali metals; alkaline earth metals; formamidinates; pivalamidinates