Superbasic Anionic Calcium Alkyl Complexes: Templated Twofold Deprotonation of Benzene

Anionic calcium alkyl complexes have been synthesised through the reduction of ethylene by an anionic calcium hydride. The alkyl complexes are demonstrated to be superbasic, rapidly deprotonating ethers below room temperature, leading to C─O bond cleavage. In reactions with benzene, selective 1,4-metalation of benzene is observed, forming an inverse-crown areneide complex. This transformation, previously inaccessible to calcium, proceeds via a stepwise mechanism, which can also be facilitated by co-complexation with organometallic reagents such as tert-butyllithium and phenylpotassium.