Coordination chemistry of a weakly coordinating carbanion

Abstract

Carbanions are typically highly reactive species but can be efficiently stabilized to even function as stable weakly coordinating anions (WCA). We now report on the coordination chemistry of the recently introduced allyl anion 1, stabilized by Ar^F (Ar^F = 3,5-bis(trifluoromethyl)phenyl), triflyl substituents, with various s-block metals. A systematic crystallographic study on the s-block metal salts (Li-Cs, Ca) showed that the alkali metals have minimal impact on the anion, as indicated by the similar structural properties compared to the phosphonium salt of 1. In contrast, the calcium complex showed a slightly more pronounced distortion of the allyl symmetry due to stronger Ca–O interactions with the triflyl group. Additionally, the significance of the allyl moiety in stabilizing the carbanionic charge in 1 was demonstrated by comparing the structural parameters and charge distribution with those of an analogous C1-anion. Overall, these studies confirm the enhanced stability of 1 and its weak coordination tendency.