Carbon‐Based Weakly Coordinating Anions: Molecular Design, Synthesis and Applications

Although carbanions, which are usually regarded as reactive species and powerful metalation reagents, can be stabilized through choice of the substitution pattern, they have rarely been considered for the design of weakly coordinating anions (WCA). Here, we report on an evaluation of the potential of a series of differently substituted carbanions to serve as WCA by computational methods. This led us to the synthesis of the water‐ and air‐stable allyl anion 1 with triflyl and 3,5‐bis(trifluoromethyl)phenyl (ArF) moieties, which can be isolated in high yields even on a gram‐scale. Single crystal X‐ray crystallography and NMR studies confirmed the weak coordination ability of the anion by showing negligible or only weak interactions with different cations. This property enabled the application of 1 in the stabilization of reactive group 14 and 15 cations. In addition to the crystallization of a phosphenium cation, the first all‐carbon salt with a non‐aromatic carbanion is reported, which revealed to be a convenient reagent for hydride ion such as from silanes. Overall, this work demonstrates the so far untapped potential of carbanions as WCA, that are accessible with a variety of different cations for various applications. Based on a systematic, computational evaluation of the potential of differently substituted methanide and propenide anions to serve as as weakly coordinating anion, the mixed 3,5‐bistrifluoromethylphenyl (ArF) and triflyl (Tf) substituted propenide was prepared in gram‐scale and shown to balance proton affinity and coordination ability. The applicability of this weakly coordinating carbanion was demonstrated by the stabilization of p‐block cations.