A DFT Theoretical Study of the Condensation of Aggregates of sp 2 Organolithium Compounds on Formaldehyde

Catherine Fressigné (1) , Anne Lautrette (1) , Jacques Maddaluno (1)

1 COBRA - Chimie Organique et Bioorganique : Réactivité et Analyse

The interaction between three different sp2 organolithium compounds (vinyllithium, 2-methoxyvinyllithium and phenyllithium) and formaldehyde has been investigated using DFT theoretical methods. The unsolvated monomers and dimers have been considered and compared to the 1:1 mixed aggregates formed with lithium dimethylamide. In all cases, the separate entities, their docking complexes, the transition states, and the condensation products have been characterized and compared to the corresponding situations involving methyllithium, taken as a prototypic sp3 nucleophile. Regarding the monomers, this study shows that, in the three cases considered, formaldehyde forms a pretransition state complex in which the oxygen of the carbonyl interacts with the lithium cation along one of its lone pair. A small energy barrier (≤2.1 kcal·mol-1) brings to the transition state, then to the lithium alcoholate resulting from the largely exothermic condensation (∼40 kcal·mol-1). The structure of the homogeneous dimers considered in a second step has been optimized and lead to arrangements in which a planar quadrilateral C−Li−C−Li is always obtained. In the presence of formaldehyde, these entities provide complexes exhibiting lithium−oxygen interaction similar to those occurring with the monomers. For the dimers, the geometry at the TS evokes a π-complex between the CO and the lithium cation, particularly pronounced in the case of phenyllithium. The resulting alcoholates are obtained following a larger exothermic reaction (∼55 kcal·mol-1). The heterogeneous dimers with lithium dimethylamide have been finally examined. In these cases, the aldehyde can orientate toward either the carbon or the nitrogen, leading to the expected lithium alcoholate or α-amino alcoholate, respectively. Whatever the orientation, the complexes present characteristics close to those calculated for the homogeneous dimer complexes. These similarities are conserved at the transition state.

Domaines: Chimie

Catherine Fressigné, Anne Lautrette, Jacques Maddaluno. A DFT Theoretical Study of the Condensation of Aggregates of sp 2 Organolithium Compounds on Formaldehyde. Journal of Organic Chemistry, 2005, 70 (20), pp.7816-7828. ⟨10.1021/jo050524n⟩. ⟨hal-02357630⟩