Surprisingly Different Reaction Behavior of Alkali and Alkaline Earth Metal Bis(trimethylsilyl)amides toward Bulky N‐(2‐Pyridylethyl)‐N′‐(2, 6‐diisopropylphenyl)pivalamidine. Issue 31 (29th June 2016)

• Record Type: Journal Article
• Authors: Kalden, Diana; Oberheide, Ansgar; Loh, Claas; Görls, Helmar; Krieck, Sven; Westerhausen, Matthias
• Is Part Of: Chemistry. Volume 22:Issue 31(2016)
• Page Start: 10944
• Page End: 10959
• Publication Date: 2016-06-29
• Subjects: 1, 3-diazaallyl anions -- alkali metals -- alkaline earth metals -- formamidinates -- pivalamidinates; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201602074
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: N ‐(2, 6‐Diisopropylphenyl)‐ N′ ‐(2‐pyridylethyl)pivalamidine (Dipp‐N=C( t Bu)‐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( t Bu)‐N‐C2 H4 ‐Py}] (6 ), [Mg{Dipp‐N=C( t Bu)‐N‐C2 H4 ‐Py}2 ] (3 ), and heteroleptic [{(Me3 Si)2 N}Ae{Dipp‐N=C( t Bu)‐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 of1 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( t Bu)‐N(H)}] (4 a ) or [(thf)2 K{Dipp‐N=C( t Bu)‐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 of4 a or the metathesis reaction of4 b with CaI2 in tetrahydrofuran yields N ‐(2, 6‐diisopropylphenyl)pivalamidine (Dipp‐N=C( t Bu)‐NH2 ) (5 ), or [(thf)4 Ca{Dipp‐N=C( t Bu)‐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. Abstract : Amides, amidines, and amidinates : N ‐(2, 6‐Diisopropylphenyl)‐ N′ ‐(2‐pyridylethyl)pivalamidine reacts with metalation reagents of lithium, magnesium, calcium, and strontium to give the corresponding pivalamidinates. These bulky ligands show diverse coordination to s‐block metals and even surprising reactivity with metalation reagents depending on the softness of the metal and bulkiness of the ligand.