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Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene

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Preferential crystallization of (±)-pinenyllithium·TMEDA

Alexander N Erickson¹, Curtis Haltiwanger², Masoumeh Rahim¹

¹Department of Chemistry, University of Memphis, Memphis, TN 38152, USA.

Acta Crystallographica. Section C, Structural Chemistry

|June 20, 2024

Abstract:

(±)-Pinenyllithium·TMEDA or (tetramethylethylenediamine-κ²N,N')(η³-6,6-dimethyl-2-methylenebicyclo[3.1.1]heptyl)lithium, [Li(C₁₀H₁₅)(C₆H₁₆N₂)], is readily prepared from β-pinene, butyllithium and TMEDA, and the racemic material preferentially crystallizes even from 96:4 (92% ee) mixtures of (-)- and (+)-β-pinene, respectively. The structure is monomeric, with the geminal-dimethyl bridge of the bicyclic structure shielding one face of the allyl system, restricting the lithium to the opposite face and preventing the Li-allyl-Li aggregation observed with some other allyllithium systems. The symmetry of the allyl system, bond lengths, bond angles and out-of-plane deviations are compared to existing structures. In addition, a much older structure of this complex is compared to this very recent one.

Keywords:

TMEDA allylic metalation allyllithium crystal structure pinene

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