From the Alkyllithium Aggregate [{(nBuLi)₂⋅PMDTA}₂] to Lithiated PMDTA

200 Years of Lithium and 100 Years of Organolithium Chemistry

“…The TMEDA ligands of the latter two compounds are found in bridging position between tetrameric units. If n ‐butyllithium is coordinated by TMCDA or PMDTA in a ratio 2:1 an open tetramer is formed, where the four Li n Bu units form a ladder instead of a cube (TMCDA‐Li n Bu‐[Li n Bu] 2 ‐Li n Bu‐TMCDA, or PMDTA‐Li n Bu‐[Li n Bu] 2 ‐Li n Bu‐PMDTA). When the concentration of the ligand TMEDA or TMCDA is high enough, n ‐butyllithium can also form dimers instead of tetramers ([Li n Bu‐TMEDA] 2 , or [Li n Bu‐TMCDA] 2 ).…”

Single-shot titrations and reaction monitoring by slice-selective NMR spectroscopy

“…This signal was assigned to the complex [(nBuLi) 2 PMDTA] 2 (see Figure 2 top), which seems to be remarkably stable and has been characterised by x-ray crystallography, 1 H NMR and quantum chemical calculations as an intermediate in the lithiation of PMDTA before. 21 Further 1 H signals reported for [(nBuLi) 2 PMDTA] 2 were found in the crowded regions of the corresponding slices (see Supplementary Information). The connection between the reaction progress and the appearance of the peak at -0.59 ppm can nicely be illustrated by integrating this peak and the remaining nBuLi α-CH 2 signal over the course of three days ( Figure 3).…”

“…Increasingly broad signals in slices 17-13 with chemical shifts between 2.3 and 1.6 ppm mark the reaction front between PMDTA and nBuLi, at which multiple dynamic processes take place. 21 Although the corresponding 1 H spectra are relatively crowded with signals of different reaction components as well as residual signals from the polymer, the isolated region of the nBuLi α-CH 2 protons (-0.5 to -1 ppm) is quite informative (Figure 2 bottom right): The signal for the nBuLi hexamer 22,23 at -0.92 ppm moves downfield and broadens from slice 19 to 13, presumably due to unspecific deaggregation and/or complexation of nBuLi by PMDTA. These processes are fast to intermediate on the NMR timescale such that only averaged chemical shifts are observed by 1 H and 7 Li NMR.…”

Structure–Reactivity Relationship in Organolithium Compounds

“…(Figure 1.15). The lithiation of PMDETA is also reported as NMR studies indicate the presence of lithiated PMDETA in solution [35]. The preferred fourfold coordination of lithium is reached by the two nitrogen atoms of the chelating TMEDA coordinating to the same lithium atom.…”

“…In 21 and 22, a (LiC) 2 fourmembered ring is assembled as each C α binds both lithium atoms. Even more interestingly, a potential intermediate [(pmdeta(n-BuLi) 2 ) 2 ] in the deprotonation process could be isolated [35]. While the Li-C bonds are almost of the same length in 21 (around 223 pm), they vary from 218 to 232 pm in 22 (Table 1.6).…”