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Surprisingly Different Reaction Behavior of Alkali and Alkaline Earth Metal Bis(trimethylsilyl)amides toward Bulky N ‐(2‐Pyridylethyl)‐ N′ ‐(2,6‐diisopropylphenyl)pivalamidine
Author(s) -
Kalden Diana,
Oberheide Ansgar,
Loh Claas,
Görls Helmar,
Krieck Sven,
Westerhausen Matthias
Publication year - 2016
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201602074
Subject(s) - chemistry , trimethylsilyl , medicinal chemistry , deprotonation , protonation , metalation , tetrahydrofuran , alkali metal , lithium (medication) , alkaline earth metal , sodium , potassium , reagent , metathesis , stereochemistry , organic chemistry , polymerization , ion , medicine , solvent , endocrinology , polymer
Abstract N ‐(2,6‐Diisopropylphenyl)‐ N′ ‐(2‐pyridylethyl)pivalamidine (Dipp‐N=C( t Bu)‐N(H)‐C 2 H 4 ‐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‐C 2 H 4 ‐Py}] ( 6 ), [Mg{Dipp‐N=C( t Bu)‐N‐C 2 H 4 ‐Py} 2 ] ( 3 ), and heteroleptic [{(Me 3 Si) 2 N}Ae{Dipp‐N=C( t Bu)‐N‐C 2 H 4 ‐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( 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 of 4 a or the metathesis reaction of 4 b with CaI 2 in tetrahydrofuran yields N ‐(2,6‐diisopropylphenyl)pivalamidine (Dipp‐N=C( t Bu)‐NH 2 ) ( 5 ), or [(thf) 4 Ca{Dipp‐N=C( t Bu)‐N(H)} 2 ] ( 7 ), respectively. The reaction of AN(SiMe 3 ) 2 (A=Na, K) with less bulky formamidine Dipp‐N=C(H)‐N(H)‐C 2 H 4 ‐Py ( 8 ) leads to deprotonation of the amidine functionality, and [(thf)Na{Dipp‐N=C(H)‐N‐C 2 H 4 ‐Py}] 2 ( 9 a ) or [(thf)K{Dipp‐N=C(H)‐N‐C 2 H 4 ‐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.