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Knorr, Rudolf; Schmidt, Barbara; Mehlstaeubl, Johann; Roman, Therese von (2018): Structures and stereoinversions of beta-shielded alpha-Li (or K or Cs)-acrylonitriles: A mechanism with neighborly assistance. In: Journal of Organometallic Chemistry, Vol. 871: pp. 185-196
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Abstract

Neighborly intermolecular assistance is common within the clusters of aggregating organolithium compounds but rarely as continual and kinetically helpful as for the beta-shielded alpha-lithioacrylonitrile 2Li of the type N equivalent to C-C(Li) = C(tert-alkyl)(2) . Intermolecular NLi coordination with the alpha-cyano substituent of 2Li was discovered not only in single crystals of a cyclohexamer or of a (Li-C-CH)(2) eight-membered ring;it provided also in several solvents for a single kind of a THF-solvated cluster (presumably a cyclodimer or cyclooligomer). These NLi connections are thought to be the "glue" in this cluster and are proposed to substantially accelerate the molecular cis/trans stereoinversion. Due to such a neighborly assistance, the rate constants of this stereoinversion are surprisingly insensitive to usually very effective factors (cations, solvents, and electron-pair donor ligands at Li) if the NLi connections are not weakened or suppressed. The corresponding alpha-potassio and alpha-cesio congeners resemble 2Li with regard to both the ground states in solution and the fast stereoinversion processes with extrapolated rate constants roughly on the microsecond time scale at 25 degrees C.