BENZYLIC LITHIUM COMPOUNDS - THE MISSING LINK IN CARBON-LITHIUM COVALENCY - DYNAMICS OF ION REORIENTATION, ROTATION AROUND THE RING-BENZYL BOND, AND BIMOLECULAR C-LI EXCHANGE

被引:57
作者
FRAENKEL, G
MARTIN, KV
机构
[1] Department of Chemistry, The Ohio State University, Columbus, Ohio 43210
关键词
D O I
10.1021/ja00146a018
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
Benzyllithium compounds, hitherto assumed from NMR data to consist of ion pairs, have been found to exhibit spin coupling between C-13 and directly bound Li-6 under conditions wherein bimolecular carbon-lithium bond exchange is too slow to average the coupling constants. These conditions involved the use of species in which lithium is internally solvated or of dilute solutions (0.005 M) of benzyllithium-C-13-Li-6 (enriched at C-alpha) at low temperature. The low values of (1)J(C-13-Li-6), 3-4 Hz, imply a small detectable degree of C-Li covalence with the arrangement around C-alpha distorted from coplanarity. The C-Li bonds in benzyllithium are concluded to lie in a continuum of C-Li covalency between the many monomeric species in which (1)J(C-13-Li-6) is 16 +/- 1 Hz and separated ion pairs. NMR line shape analysis of data for internally solvated benzyllithium 2b provides quantitative insight into the dynamics of intramolecular reorientation of coordinated lithium with respect to the benzyl plane, rotation around the ring-C-alpha bond, and bimolecular carbon-lithium bond exchange, listed in order of widely different increasing rates, the activation parameters being Delta H-double dagger (kcal/mol) and Delta S-double dagger (eu) in the same order: 14 and 6.6; 6.4 and -14; 10.8 and -21.
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页码:10336 / 10344
页数:9
相关论文
共 57 条
[1]  
AHLBRECHT H, 1995, LIEBIGS ANN, P211
[2]  
ALBRECHT H, 1992, CHEM BER, V125, P1753
[3]  
[Anonymous], COMMUNICATION
[4]   VINYLLITHIUM - DYNAMIC BEHAVIOR IN TETRAHYDROFURAN SOLUTION AND COMPREHENSIVE ANALYSIS OF NMR SPIN-SPIN COUPLING-CONSTANTS [J].
BAUER, W ;
GRIESINGER, C .
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1993, 115 (23) :10871-10882
[5]  
Bauer W., 1992, ADV CARBANION CHEM, V1, P81
[6]  
BAUER W, 1987, ORGANOMETALLICS, V6, P2731
[7]   ISOLATION AND X-RAY CRYSTAL-STRUCTURES OF THE SOLVATE COMPLEXES [LI(ET2O)BENZYL]X AND [LI(THF)2MESITYL]2 [J].
BENO, MA ;
HOPE, H ;
OLMSTEAD, MM ;
POWER, PP .
ORGANOMETALLICS, 1985, 4 (12) :2117-2121
[8]   DYNAMIC BEHAVIOR AND REACTIVITY OF (1,1,3,3-TETRAMETHYLALLYL)LITHIUM [J].
CABRAL, J ;
FRAENKEL, G .
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1992, 114 (23) :9067-9075
[9]   SILICON-SUBSTITUTED MEDICINAL AGENTS - PHENYL-SUBSTITUTED SILACARBAMATES [J].
FESSENDEN, RJ ;
COON, MD .
JOURNAL OF MEDICINAL CHEMISTRY, 1966, 9 (02) :262-+
[10]   DYNAMICS INSIDE ION-PAIRS - NMR-STUDIES OF A [1-SILYLALLYL]LITHIUM WITH A PENDANT LIGAND - [1-[[[BIS(2-METHOXYETHYL)AMINO]METHYL]DIMETHYLSILYL]ALLYL]-LITHIUM [J].
FRAENKEL, G ;
CABRAL, JA .
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 1993, 115 (04) :1551-1557