The Crystal Structures of the Chiral Alkyllithium Bases [n-BuLi·(−)-Sparteine]₂ and [Et₂O·(i-PrLi)₂·(−)-Sparteine]

Abstract

The crystal structures of the two chiral alkyllithium bases [n-BuLi.(-)-sparteine]2 (1) and [Et2O.(i-PrLi)2.(-)-sparteine] (2) have been determined. For compound 1, a symmetric dimer is observed in the solid state, with two (-)-sparteine ligands coordinating to the lithium centers. Because of steric reasons, compound 2 crystallizes as an unsymmetric dimer with the four methyl groups pointing away from the sterically demanding (-)-sparteine ligand. Compound 2 contains one four-coordinate lithium center [coordinated to (-)-sparteine] and one three-coordinate lithium center (coordinated to Et2O). As a result of this arrangement, significantly different Li-C distances are found in the central four-membered ring of compound 2.

A Combined 1H/6Li NMR DOSY Strategy Finally Uncovers the Structure of Isopropyllithium in THF

“…To date, mostly complexes involving i PrLi have attracted attention and the corresponding structures, either in the solid state and/or in solution, are available in literature . They imply chelating additives such as N , N , N′ , N′ ‐tetramethylethylenediamine (TMEDA), N , N , N′ , N′ ‐tetraethylethylenediamine (TEEDA), ( R , R )‐ N , N , N′ , N′ ‐tetramethylcyclohexane‐1,2‐diamine (TMCDA), (−)‐sparteine and (+)‐sparteine surrogate . A [ i PrLi] 2 dimeric core has been put in evidence in the presence of TMEDA, ( R , R )‐TMCDA, (−)‐sparteine and O'Brien's sparteine (+)‐surrogate (Figure , A – D ).…”

“…They imply chelating additives such as N , N , N′ , N′ ‐tetramethylethylenediamine (TMEDA), N , N , N′ , N′ ‐tetraethylethylenediamine (TEEDA), ( R , R )‐ N , N , N′ , N′ ‐tetramethylcyclohexane‐1,2‐diamine (TMCDA), (−)‐sparteine and (+)‐sparteine surrogate . A [ i PrLi] 2 dimeric core has been put in evidence in the presence of TMEDA, ( R , R )‐TMCDA, (−)‐sparteine and O'Brien's sparteine (+)‐surrogate (Figure , A – D ). If the presence of diethylether seems not to prevent the dimerization ( C ), introducing THF to the above (−)‐ and (+)‐sparteine dimeric complexes ( C and D , respectively) provides monomeric i PrLi chelates incorporating one molecule of THF ( E and F ).…”

General Principles ofortho-Lithiation in Arylphosphinamides

“…Normalmente a N,N,N',N'-tetrametiletilenodiamina (TMEDA) é utilizada para esta finalidade, unindo-se ao lítio como um ligante bidentado, como se comprovou no estudo de cristalografia de raios-X de monocristal para a TMEDA e para a (-)-esparteína. [4][5][6] Durante a última década se utilizou também triaminas em litiações, cujos complexos com bases organolitiadas são bases mais fortes que as geradas com as diaminas comentadas anteriormente. 7 Em solução, a adição de TMEDA provoca a dissociação dos agregados devido à tendência do lítio a coordenar-se ao nitrogênio, formando um complexo no qual o átomo de Os autores sugerem a existência de um intermediário muito reativo proveniente da dissociação do dímero [TMEDA.n-BuLi] 2 e posterior complexação do substrato que atua, neste caso, como agente quelante (Esquema 4).…”

Synthesis and spectral characterization of sparteine and α -isosparteine complexes with copper(II) sulfate

“…(À)-Sparteine and its diastereoisomer -isosparteine are well-suited as chiral bidentate ligands for many applications, e.g., for metal complexation [1][2][3][4][5][6][7][8] and asymmetric synthesis [9][10][11][12][13][14]. They are composed of two quinolizidine systems; in sparteine, one forms a double-chair trans-quinolizidine system A/B, which is relatively resistant to configurational-conformational changes, the other, of rings C and D, is much more susceptible to inversion at the N16 atom.…”