2010/12/02 by Sven Krieck, Helmar Görls, Matthias Westerhausen · 1 citation
Chemistry · #Coordination Chemistry and Organometallics #Organometallic Complex Synthesis and Catalysis #Synthesis and Reactivity of Heterocycles
paper · doi:10.1021/om1009632
openalex publication_date 2010/12/02 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/18
Alkali metal stabilized monoanions of 1,3,5-triphenylbenzene can be obtained by various reactions starting from the alkali metal. Reduction of the Grignard compound [(2,4,6-Ph 3 -C 6 H 2 )Mg(dme)Br 2 (μ -O,O′- dme)] ( 3 ) in DME (1,2-dimethoxyethane) with alkali metals yields solvent-separated ions [(dme) 3 A] + [C 6 H 2 -2,4,6-Ph 3 ] − (A = Li, Na ( 4 )) with a localized 2,4,6-triphenylphenyl carbanion via metal−metal exchange. Contrarily to this observation, radical monoanions of 1,3,5-triphenylbenzene are generated via transmetalation of the Grignard reagent [2,4,6-Ph 3 -C 6 H 2 Mg(thf) 2 Br] ( 2 ) with alkali metals in THF (including ether cleavage as the dominant reaction step). Reduction of 2 with lithium yields the solvent-separated ion pair [(tmta) 4 Li 7 Br 4 O] + [C 6 H 3 -2,4,6-Ph 3 ] − ( 6 ) (tmta = 1,3,5-trimethyl-1,3,5-triazinane) with an oxygen-centered lithium cage as complex cation. However, reactions of 2 with sodium as well as potassium lead to formation of halogen-free contact ion pairs [(thf) 3 Na( μ- η 6 -C 6 H 3 -2,4,6-Ph 3 )] ( 7 ) and [(thf) 4 K(μ - η 6 -C 6 H 3 -Ph 3 )] ( 8 ), respectively. Treatment of 1,3,5-triphenylbenzene in THF with lithium leads to fragmentation of the inner arene core, whereas usage of the corresponding heavier alkali metals sodium and potassium, respectively, also generates 7 or 8 . Depending on the metal counterion, reduction of the propeller-shaped 1,3,5-triphenylbenzene system leads to partial planarization in combination with bond elongations of the inner arene. Derivatives 7 and 8 consist of a 3,3′-di(phenyl)biphenyl moiety with phenyl substituents twisted by 11° in the same direction ( 7 ) or contrary to each other ( 8 ). The same high symmetry was found in the solid state as well as in solution, which was verified by X-ray structure determinations and EPR measurements including simulation studies. In the solid state, the alkali metal stabilized 1,3,5-triphenylbenzene radical-monoanions ( 6, 7, and 8 ) are pyrophoric and strong black-opalescent, whereas solutions show solvato- and thermochromic behavior.