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

Reaction of [(η5-C5H4Me)4Fe4(HCCH)­(HCCBr)]­(PF6) ([2]­(PF6)) with AgPF6 in acetonitrile gave [(η5-C5H4Me)4Fe4(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 [(η5-C5H4Me)4Fe4(HCCH)­(HCC)]2+, [(η5-C5H4Me)4Fe4(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 [(η5-C5H4Me)4Fe4(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.