Lewis Acid Chemistry of a Cationic [CCH] Subunit in a Bisdisphenoidal Eight-Atom Tetrairon-Tetracarbon Cluster

Reaction of [(eta(5)-C6H4Me)(4)Fe-4(HCCH)(HCCBr)](PF6) ([2](PF6)) with AgPF6 in acetonitrile gave [(eta(5)-C5H4Me)(4)Fe-4(HCCH)(HCCNCMe)](PF6)(2) ([3]-(PF6)(2)). The X-ray diffraction study revealed that the cationic [CCH] subunit is stabilized through coordination of the acetonitrile molecule to the cationic carbon atom. As a synthon for a donor-free [(eta(5)-C5H4Me)(4)Fe-4(HCCH)(HCC)](2+), [(eta(5)-C5H4Me)(4)Fe-4(HCCH)(HCCL)](PF6)(2) ([6](PF6)(2), L = pyrazine) was synthesized by the reaction of [2](PF6) with AgPF6 in the presence of pyrazine. Treatment of [6](PF6)(2) with tertiary amines in acetonitrile led to deprotonation of acetonitrile to form [(eta(5)-C5H4Me)(4)Fe-4(HCCH)(HCCCH2CN)](PF6) ([11](PF6)). Treatment of [6](PF6)(2) with maleimide in the presence of tertiary amine in acetonitrile allowed the functionalization of the coordinated acetonitrile through the nucleophilic attack of maleimide at the nitrile carbon atom.