2-(α-[6Li]lithiobenzylidene)-1,1,3,3-tetramethylindane | 1448719-76-3

• 分子结构分类: 有机化合物 - 苯类化合物 - 苯和取代衍生物
• 英文名称: 2-(α-[6Li]lithiobenzylidene)-1,1,3,3-tetramethylindane
• 英文别名: 2-(α-[⁶Li]lithiobenzylidene)-1,1,3,3-tetramethylindane
• CAS: 1448719-76-3
• 化学式: C₂₀H₂₁Li
• 分子量: 267.387
• InChiKey: IXTWPLTYMVEVCT-HCMAANCNSA-N

计算性质

• 辛醇/水分配系数(LogP)：
  4.84
• 重原子数：
  21.0
• 可旋转键数：
  1.0
• 环数：
  3.0
• sp3杂化的碳原子比例：
  0.3
• 拓扑面积：
  0.0
• 氢给体数：
  0.0
• 氢受体数：
  0.0

反应信息

• 作为反应物：
  描述：

  二苯甲酮 、 2-(α-[6Li]lithiobenzylidene)-1,1,3,3-tetramethylindane 以 甲苯 为溶剂， 反应 0.5h， 生成 1,1,α-triphenyl-α-(1,1,3,3-tetramethyl-2-indanylidene)ethanol
  参考文献：
  名称：

  Pseudomonomolecular, Ionic sp²-Stereoinversion Mechanism of 1-Aryl-1-alkenyllithiums

  摘要：

  The trans/cis stereoinversion of the trigonal carbanion centers C-alpha in a series of monomeric 2-(alpha-aryl-alpha-lithiomethylidene)-1,1,3,3-tetramethylindanes (known to be trisolvated at Li) is rapid on the NMR time scales (400 and 100.6 MHz) in THF solution. The far-reaching redistribution of electric charge in the ground-state molecules caused by lithiation (formal replacement of alpha-H by alpha-Li) is illustrated through NMR shifts, Delta delta. The transition states for stereoinversion are significantly more polar and charge-delocalized than the ground states (Hammett rho = +5.2), pointing to a mechanism that involves heterolysis of the C-Li bond via a solvent-separated ion pair (SSIP). This requires immobilization of only one additional (the fourth) THF molecule at Li+, which accounts for part of the apparent activation entropies of ca. -23 cal mol(-1) K-1 and constitutes a kinetic privilege of THF depending on microsolvation at Li. Thus, the sp(2)-stereoinversion process is "catalyzed" by the solvent THF; its mechanism is monomolecular with respect to the ground-state species because the pseudo-first-order rate constants, measured through NMR line shape analyses, are independent of the concentrations (inclusive of decomposition) of the dissolved species (hence no associations and no dissociation to give free carbanion intermediates). In the deduced pseudomonomolecular mechanism (bimolecular through solvent participation), the angular C-alpha of the SSIP undergoes rehybridization (approximately in-plane inversion) through a close-to-linear transition state; this motion occurs with a concomitant "conducted tour" migration of Li(THF)(4) and is unimpaired by additional ortho-methylations at alpha-aryl. The synthetic route started with preparations of three alpha-chloro congeners through the carbenoid chain reaction, followed by vinylic substitution of alpha-Cl by alpha-SnMe3 (most efficient in THF despite steric congestion). The final Sn/Li interchange reaction afforded the new 1-aryl-1-alkenyllithium samples, initially uncontaminated by free Li+.

  DOI：

  10.1021/om4000852
• 作为产物：
  描述：

  在 甲基叔丁基醚 作用下， 以 氘代甲苯 为溶剂， 以34%的产率得到2-(α-[6Li]lithiobenzylidene)-1,1,3,3-tetramethylindane
  参考文献：
  名称：

  Microsolvation and ¹³C−Li NMR Coupling

  摘要：

  The empirical expression (1)J(CLi) = L[n(a + d)](-1) is proposed; it claims a reciprocal dependence of the NMR coupling constant (1)J(C-13, Li) in a C-Li compound on two factors: (i) the number n of lithium nuclei in bonding contact with the observed carbanion center and (ii) the sum (a + d) of the numbers a of anions and d of donor ligands coordinated at the Li nucleus that generates the observed (1)J(CLi) value. The expression was derived from integrations of separate NMR resonances of coordinated and free monodentate donor ligands (t-BuOMe, Et2O or THF) in toluene solutions of dimeric and monomeric 2-(alpha-aryl-alpha-lithiomethylidene)-1,1,3,3-tetramethylindan at moderately low temperatures. This unusually slow ligand interchange is ascribed to steric congestion in these compounds, which is further characterized by measurements of nuclear Overhauser correlations and by solid-state structures of the dimers bearing only one donor per lithium atom (d = 1). Increasing microsolvation numbers dare also accompanied by typical changes of the NMR chemical shifts delta (positive for the carbanionic C-13(alpha), negative for C-para and p-H). The aforementioned empirical expression for (1)J(CLi) appears to be applicable to other cases of solvated monomeric, dimeric, or tetrameric C-Li compounds (alkyl, alkenyl, alkynyl, and aryl) and even to unsolvated (d approximate to trimeric, tetrameric, or hexameric organolithium aggregates, indicating that (1)J(CLi) might serve as a tool for assessing unknown microsolvation numbers. The importance of obtaining evidence about the C-13 NMR C-Li multiplet splitting of both the nonfluxional and fluxional aggregates is emphasized.

  DOI：

  10.1021/ja8026828