Are sp lithiated carbons more nucleophilic than sp2 or sp3 ones? A comparative DFT study of the condensation of propynyllithium aggregates on formaldehyde.
The interaction between 1-propynyllithium, taken as a model of sp organolithium compound, and formaldehyde has been investigated with DFT theoretical methods. The unsolvated monomer, homogeneous dimer, trimer, tetramer, and hexamer have been considered, as well as the mixed aggregates with lithium dimethylamide in various oligomeric forms. In most cases, the separate entities, their docking complexes, the transition states, and the condensation products have been characterized. Overall, the general reaction scheme remains the same whatever the hybridization and the aggregation. However, the dimeric sp nucleophiles are expected to be more reactive (at least in kinetic conditions), while monomeric sp(3) entities would be the best nucleophiles in kinetic and thermodynamic conditions, even if its docking is the least exothermic. This work also suggests that the aggregation plays a relatively limited role on the model reaction.
Fressigné
Catherine
C
Laboratoire de Chimie Théorique, CNRS UMR 7616, Université Pierre et Marie Curie, Case Courrier 137, 4, place Jussieu, 75252 Paris Cedex 05, France.
Maddaluno
Jacques
J