Reactions of ferrocenylboranes with 2,5-bis(pyridyl)pyrazine and quaterpyridine:: charge-transfer complexes and redox-active macrocycles

Reactions of FcB(Me) Br[1; Fc=(C5H5)Fe(C5H4)] and 1,1'-fc[B(Me)Br](2) [2; fc=(C5H4)2 Fe] with 2,5-bis(pyridyl) pyrazine (bppz) and 2,2': 4', 4": 2", 2'''-quaterpyridine (qpy) are reported. The pyrazine derivative bppz forms stable boronium cations with 1 and 2 to give the complexes [FcB(Me)bppz]Br, [1C] Br, and {1,1'-fc[B(Me)bppz](2)}Br-2, [2C(2)]Br-2. The 4,4'-bipyridine derivative qpy can be used to link two ferrocenylborane moieties together, which gives access to the open-chain dinuclear aggregate [FcB(Me)qpyB(Me)Fc]Br-2, [1D1]Br-2, and to the macrocyclic molecule [2D](2)Br-4. The bppz adducts possess an intense green colour, and the qpy complexes are deeply blue coloured, which is indicative of charge-transfer interactions between the electron-rich ferrocene moieties and their electron-poor aromatic substituents. The hexafluorophosphate salts of all compounds undergo a reversible ferrocene oxidation and several consecutive reduction processes, which are centred at the cationic sidechains.