Structural and Electronic Effects of Stepwise Reduction of a Tetraaryl[3]Cumulene

Abstract

The chemical reduction of a [3]cumulene ([3]TrTol) has been explored using alkali metals. Mono‐ and doubly reduced forms of [3]TrTol were isolated as solvent‐separated ion pairs with {Na(18‐crown‐6)THF2}+ and {K(18‐crown‐6)THF2}+ counterions and crystallographically characterized. This allowed analysis of structural parameters of the “naked” anions of [3]TrTol without interference from metal binding. The dianion of [3]TrTol was also isolated as a contact‐ion complex with {Cs(18‐crown‐6)}+ cations, thereby adding the effect of metal coordination to the core. Structural comparisons of anions to the neutral molecule, [3]TrTol, outline monotonic increases in bond‐length alternation (BLA) upon stepwise reduction. The greatest BLA value is found for the contact‐ion complex, which shows an alternating sequence of short and long carbon–carbon bonds, consistent with the structure of an alkyne. In contrast to studies on tetraphenyl[3]cumulene, the cumulenic framework of [3]TrTol remains planar in all the derivatives.

Compressing Double [7]Helicene by Successive Charging with Electrons

“…Charging non‐planar PAHs with electrons as well as investigation of their electronic and structural responses are of great fundamental importance in PAH chemistry [9] . Comprehensive studies of electron transfer for carbon bowls, [10] belts, [11] and wires [12] revealed a pronounced dependence on π topology and charge, opening a broad exploration of redox chemistry of curved and twisted molecular nanocarbons [13–15] …”

Compressing Double [7]Helicene by Successive Charging with Electrons

“…Charging non‐planar PAHs with electrons as well as investigation of their electronic and structural responses are of great fundamental importance in PAH chemistry [9] . Comprehensive studies of electron transfer for carbon bowls, [10] belts, [11] and wires [12] revealed a pronounced dependence on π topology and charge, opening a broad exploration of redox chemistry of curved and twisted molecular nanocarbons [13–15] …”

Bending a Cumulene with Electrons: Stepwise Chemical Reduction and Structural Study of a Tetraaryl[4]Cumulene

“…To better appreciate the potential of [ n ]cumulenes as materials, characterization of redox characteristics is a vital step, particularly in terms how their intricate π ‐systems can accommodate charge. The redox properties of [3]cumulenes have been studied, including structure‐property relationships using stepwise alkali metal reduction of the [3]cumulene framework to provide crystallographic analysis of the mono‐ and dianions [9–12] . Theoretical studies suggest that the π ‐systems of cumulenes accommodate additional charge by twisting the endgroups.…”