Amine- and Ether-Chelated Aryllithium ReagentsStructure and Dynamics

Abstract

Chelation and aggregation in phenyllithium reagents with potential 6- and 7-ring chelating amine (2, 3) and 5-, 6-, and 7-ring chelating ether (4, 5, 6) ortho substituents have been examined utilizing variable temperature (6)Li and (13)C NMR spectroscopy, (6)Li and (15)N isotope labeling, and the effects of solvent additives. The 5- and 6-ring ether chelates (4, 5) compete well with THF, but the 6-ring amine chelate (2) barely does, and 7-ring amine chelate (3) does not. Compared to model compounds (e.g., 2-ethylphenyllithium 7), which are largely monomeric in THF, the chelated compounds all show enhanced dimerization (as measured by K = [D]/[M](2)) by factors ranging from 40 (for 6) to more than 200 000 (for 4 and 5). Chelation isomers are seen for the dimers of 5 and 6, but a chelate structure could be assigned only for 2-(2-dimethylaminoethyl)phenyllithium (2), which has an A-type structure (both amino groups chelated to the same lithium in the dimer) based on NMR coupling in the (15)N, (6)Li labeled compound. Unlike the dimer, the monomer of 2 is not detectably chelated. With the exception of 2-(methoxymethyl)phenyllithium (4), which forms an open dimer (12) and a pentacoordinate monomer (13), the lithium reagents all form monomeric nonchelated adducts with PMDTA.

Structural Studies on (–)‐Sparteine‐Coordinated Lithiosilanes

“…: A: R = Ph, RЈ = NEt 2 ; [20] B: R = RЈ = Ph; [21] C: R = Ph, RЈ = NEt 2 . [22] conformational equilibria [14] and chelate isomerisations, [15] are often only observable on NMR spectroscopic timescales at low temperatures during the measurements. Moreover, due to the quadrupole moment of both 6 Li and 7 Li (spin quantum number Ͼ 1/2, 6 Li = 1, 7 Li = 3/2), NMR signals are often broadened and not fully resolved.…”

Toward Truly Water‐Soluble Rodlike Polyelectrolytes: Synthesis of Poly(para‐phenylenes) Wrapped in Ethylene Oxideand Amino Side Groups

“…On the other hand, the dilithiated product 23 proved to be rather stable: stirring at room temperature for several hours did not lead to any decomposition. Both, high rate of twofold halogen‐metal exchange and stability of intermediate 23 seemed to be due to the OEO substituents: there is efficient intramolecular complex formation possible involving the lithium ions (Scheme ) . With respect to the synthesis of monomer 22 , we concluded that dilithiated intermediate 23 is formed nicely but is of insufficient reactivity toward trimethyl borate—at least under the initially chosen conditions.…”

“…Both, high rate of twofold halogen-metal exchange and stability of intermediate 23 seemed to be due to the OEO substituents: there is effi cient intramolecular complex formation possible involving the lithium ions (Scheme 5 ). [ 47,48 ] With respect to the synthesis of monomer 22 , we concluded that dilithiated intermediate 23 is formed nicely but is of insuffi cient reactivity toward trimethyl borate-at least under the initially chosen conditions. The stability of intramolecular lithium complexes in general can be modulated by appropriate choice of solvent.…”

Carbanion generation through tin-lithium exchange of vinyl-, aryl-, and hetarylstannanes

“…This was illustrated in chelation studies of the aryllithiums in Figure 1, which were synthesized by tin-lithium exchange from the corresponding trimethylstannyl compounds. 62,63 The bromide byproducts from lithium-halogen exchange of the aryl bromides would have interfered with the intended spectroscopic studies. Halide-free aryllithium reagents were also obtained for the selenium and sulfur derivatives shown in Equation 36 and Equation 37.…”