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In page Ferrocene:

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Unsubstituted ferrocene undergoes aromatic substitution more easily than benzene, because electrophiles can attack the metal ion before rearranging to the Wheland intermediate.[5] Thus ferrocene reacts with the weak electrophile Phosphorus pentasulfide (P4S10) to form a diferrocenyl-dithiadiphosphetane disulfide.[6] Mannich conditions suffice to iminylate ferrocene to N,N-Dimethylaminomethylferrocene.[citation needed]