ISSN:
0009-2940
Keywords:
4-Alkylpyridines, lithiated
;
Lithium coordination in solution
;
Calculations, MNDO
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The First X-ray Structures of N-Lithiated 4-Alkylidene-1,4-dihydropyridines [{4-(CH3CR)C5H4N}Li(TMEDA)]2: Comparison of the X-ray and MNDO Geometries and Investigation of Lithium Coordination in SolutionThe 4-ethyl- and -isopropylpyridines 5a and b were transformed into the lithiated compounds [{4-(CH3CH)C5H4N}-Li(TMEDA)]2 (6a) and [{4-(CH3CCH3)C5H4N}Li(TMEDA)]2 (6b) by reaction with LDA and in the presence of TMEDA. These compounds were recrystallized from a toluene/hexane solution to obtain suitable crystals for X-ray investigations. Both structures are dimeric containing nonstoichiometric amounts of toluene in the crystals. The structural parameters of the heterocyclic moieties of 6a or b are typical of N-lithiated 4-alkylidene-1,4-dihydropyridines. MNDO geometries compare quite well with the X-ray structure of 6a. The lithium atom of 6a in solution prefers the same type of coordination as in the crystal: Two-dimensional 6Li,1H-HOESY showed Li contacts only to ortho-hydrogen atoms (Figure 3). 6a and b react differently with chlorotrimethylsilane (8). The variations of the alkylidene moieties of 6a and b, although seemingly small, are decisive: While the α,α-dimethyl compound 6b reacts exclusively as an N nucleophile, the α-methyl compound 6a functions also exclusively as a Cα nucleophile.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19921250537
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