Consequences of Correlated Solvation on the Structures and Reactivities of RLi-Diamine Complexes:  1,2-Addition and α-Lithiation Reactions of Imines by TMEDA-Solvated n-Butyllithium and Phenyllithium

Abstract

6Li and (13)C NMR spectroscopic studies were carried out on [(6)Li]n-BuLi and [(6)Li]PhLi (RLi) in toluene-d(8) containing the following diamines: N,N,N',N'-tetramethylethylenediamine (TMEDA), N,N,N',N'-tetraethylethylenediamine, 1,2-dipyrrolidinoethane, 1,2-dipiperidinoethane, N,N,N',N'-tetramethylpropanediamine, trans-(R,R)-N,N,N',N'-tetramethylcyclohexanediamine, and (-)-sparteine. Dimers of general structure (RLi)(2)S(2) (S = chelating diamine) are formed in each case. Treatment of RLi with two different diamines (S and S') affords homosolvates (RLi)(2)S(2) and (RLi)(2)S'(2) along with a heterosolvate (RLi)(2)SS'. Relative binding constants and associated free energies for the sequential solvent substitutions are obtained by competing pairs of diamines. The high relative stabilities of certain heterosolvates indicate that solvent binding to the RLi dimer can be highly correlated. Rate studies of both the 1,2-addition of RLi/TMEDA to the N-isopropylimine of cyclohexane carboxaldehyde and the RLi/TMEDA-mediated alpha-lithiation of the N-isopropylimine of cyclohexanone reveal monomer-based transition structures, [(RLi)(TMEDA)(imine)], in all cases. The complex relationships of solvent binding constants and relative reactivities toward 1,2-additions and alpha-lithiations are discussed.

End-group stannylation of regioregular poly(3-hexylthiophene)s

“…TMEDA has been reported to enhance the polarity of alkyllithium species or to break them into smaller clusters, leading to higher reactivity and faster metalation. 18,19 Thus, we have conducted the lithiation of P3HT in the presence of TMEDA. The 1 H NMR spectrum recorded after stannylation shows that the addition of TMEDA to the lithiation process resulted in the formation of stannylated P3HT (see Figure 2 for a typical 1 H NMR spectrum), as indicated by the presence of a characteristic -CH 3 peak at d ¼ 0.40 in the Me 3 Sn-group.…”

Reactivity series for s-BuLi/diamine-mediated lithiation of N-Boc pyrrolidine: applications in catalysis and lithiation of N-Boc piperidine

“…Indeed, to the best of our knowledge, only one quantitative rate comparison of RLi/diamine complexes has been described: Collum et al investigated nucleophilic addition to an imine and imine a-deprotonation for a range of n-BuLi/diamine and PhLi/diamine complexes. 17 Thus, we set out to determine an empirical order of reactivity of different s-BuLi/diamine complexes for the lithiation of N-Boc pyrrolidine 1. For this, an operationally simple approach was devised in which competition experiments between two different ligands would be used to assay relative reactivity.…”

The Use of (−)‐Sparteine/Organolithium Reagents for the Enantioselective Lithiation of 7,8‐Dipropyltetrathia[7]helicene: Single and Double Kinetic Resolution Procedures

“…At this stage, we extended our investigations to n BuLi and t BuLi which are also known to form aggregates with (−)‐sparteine; [(−)‐sparteine] 2 ⋅( n BuLi) 2 48 (−)‐sparteine⋅ t BuLi49 (Figure 2, structures 5 and 6 )]…”