VINYLLITHIUM - DYNAMIC BEHAVIOR IN TETRAHYDROFURAN SOLUTION AND COMPREHENSIVE ANALYSIS OF NMR SPIN-SPIN COUPLING-CONSTANTS
VINYLLITHIUM - DYNAMIC BEHAVIOR IN TETRAHYDROFURAN SOLUTION AND COMPREHENSIVE ANALYSIS OF NMR SPIN-SPIN COUPLING-CONSTANTS
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DOI：
10.1021/ja00076a051
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发表时间：
1993-11-17
影响因子：
15
通讯作者：
GRIESINGER, C
中科院分区：
文献类型：
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作者：
BAUER, W;GRIESINGER, C
乙烯基锂（ViLi；用Li-6同位素标记）在-90℃（1.6 M溶液）下，在四氢呋喃-d8 （THF-d8）中呈8:1的四聚体/二聚体平衡。在等摩尔量的TMEDA（四亚甲基乙二胺）存在下，四聚体：二聚体在-80℃（1.9 M溶液）的THF-d8中比例为1:13。在ViLi四聚体中观察到动态核磁共振现象：在-90°c的THF-d8中，发现了一个“静态”聚集体，而在-60°c的聚集体内四个锂位点的快速交换表明了一个“流动”四聚体。在“静态”四聚体中，单体单元的快速翻滚是从C、Li和H、Li核磁共振耦合模式推断出来的。从ViLi的H-1， C-13 hetkor光谱中交叉峰多重态的倾斜（由于与被动Li-6自旋耦合）可以得出1J（C-13, Li-6）的符号为正的结论。在完全耦合的异核Li-6， H-1位移相关实验（FUCOUP）中，四聚体ViLi的Li-6， H（gem）和Li-6， H（trans）之间分别观察到强烈和较弱的交叉峰。这表明Li-6， H-1耦合。在具有小（36度）H-1混合脉冲（“β -FUCOUP”）的Li-6， H-1 FUCOUP光谱中，Li-6， H（trans）交叉峰的倾斜表明2J（Li-6， H(gem)）的符号和大小为+0.4Hz。与四聚体类似，二聚体的Li-6， H-1 β - fucoup显示3J（Li-6， H（反式））为+0.4 Hz。乙烯基锂中的C-13、C-13偶联常数非常小（二聚体，35.0 Hz；四聚体，36.3 Hz）。同样，单键C-13， H-1偶联常数1J（C1， H(gem)）是迄今为止报道的单取代乙烯（二聚体，91.7 Hz；四聚体，93.2 Hz）中最低的。结合C-13门控解耦和C-13， H-1 β - fucoup数据，还发现了二聚体2J（C-13, H-1）耦合常数的极值值：二聚体，2J(C1， H(cis)) = +13.5 HZ；2J(C1， H(trans)) = -5.9 Hz；2J(C2， H(gem)) = -10.5 Hz；四聚体，2J(C1， H(cis)) = +13.5 HZ；2J(C1， H(trans)) = -6.1 HZ；2J(C2，H(gem)) = -12.1 Hz。
Vinyllithium (ViLi; isotopically labeled with Li-6) is an 8:1 tetramer/dimer equilibrium in tetrahydrofuran-d8 (THF-d8) at -90-degrees-C (1.6 M solution). In the presence of equilmolar amounts of TMEDA (tetramethylethylenediamine), the tetramer:dimer ratio is 1:13 in THF-d8 at -80-degrees-C (1.9 M solution). Dynamic NMR phenomena are observed in the ViLi tetramer: at -90-degrees-C in THF-d8, a ''static'' aggregate is found, whereas at -60 -degrees-C rapid intraaggregate exchange of the four lithium sites indicates a ''fluxional'' tetramer. Within a ''static'' tetramer, rapid tumbling of a monomer unit is deduced from C, Li and H, Li NMR coupling patterns. From tilts within cross peak multiplets in H-1, C-13 HETCOR spectra of ViLi (due to coupling with the passive Li-6 spin), it is concluded that the sign of 1J(C-13, Li-6) is positive. In a fully coupled heteronuclear Li-6, H-1 shift correlation experiment (FUCOUP), an intense and a weaker cross peak are observed between Li-6, H(gem) and Li-6, H(trans), respectively, of tetrameric ViLi. This is indicative of scalar Li-6, H-1 coupling. In a Li-6, H-1 FUCOUP spectrum with a small (36-degrees) H-1 mixing pulse (''beta-FUCOUP''), the tilt of the Li-6, H(trans) cross peak indicates the sign and magnitude of 2J(Li-6, H(gem)) to be +0.4Hz. Analogous to the tetramer, Li-6, H-1 beta-FUCOUP of the dimer reveals 3J(Li-6, H(trans)) to be +0.4 Hz. The C-13, C-13 coupling constant in vinyllithium is extraordinarily small (dimer, 35.0 Hz; tetramer, 36.3 Hz). Likewise,the one-bond C-13, H-1 coupling constant 1J(C1, H(gem)) is the lowest reported so far for monosubstituted ethylenes (dimer, 91.7 Hz; tetramer, 93.2 Hz). By combination of C-13 gated decoupled and C-13, H-1 beta-FUCOUP data, extreme numbers are also found for geminal 2J(C-13, H-1) coupling constants: dimer, 2J(C1, H(cis)) = +13.5 HZ; 2J(C1, H(trans) = -5.9 Hz; 2J(C2, H(gem)) = -10.5 Hz; tetramer, 2J(C1, H(cis)) = +13.5 HZ; 2J(C1, H(trans)) = -6.1 HZ; 2J(C2,H(gem)) = -12.1 Hz.