LITHIUM DIALKYLAMIDE MIXED AGGREGATION - MNDO COMPUTATIONAL STUDY OF SALT AND SOLVENT DEPENDENCIES

被引:68
作者
ROMESBERG, FE [1 ]
COLLUM, DB [1 ]
机构
[1] CORNELL UNIV,BAKER LAB,DEPT CHEM,ITHACA,NY 14853
关键词
D O I
10.1021/ja00099a038
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
Mixed aggregation of lithium diaikylamides with various LiX salts is studied by semiempirical (MNDO) computational methods. The relative stabilities of mixed aggregates of lithium diisopropylamide and lithium 2,2,6,6-tetramethylpiperidide with LiCl as well as the enolates derived from acetone, cyclohexanone, and 2,4-dimethylpentanone are described. The unsolvated forms are compared with the analogous structures solvated by tetrahydrofuran and hexamethylphosphoramide. The structural types studied include mixed cyclic dimers (R(2)NLi-LiX), trimers [(R(2)NLi)2(LiX)2], and tetramers [(R(2)NLi)(2)(LiX)(2)]; 3-rung ladders [(R(2)NLi)(2)(LiX)] and 4-rung ladders [(R(2)NLi)(2)(LiX)(2)]; two isomeric open dimer topologies corresponding to cyclic dimers fragmented at N-Li and X-Li bonds; triple ions (R(2)NLiX(-)//Li-+). A complex interplay of steric effects appears to be the dominant influence on the mixed aggregate structures and relative stabilities.
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页码:9187 / 9197
页数:11
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