Co-ordination chemistry of bis(ferrocenylcarbaldimine) Schiff bases

The complex chemistries of 1,2-bis(ferrocen-1-ylmethyleneamino)ethane (L-1), 1,2-bis(ferrocen-1-ylmethyleneamino)benzene (L-2) and its 4-methyl (L-3), 4-chloro (L-4) and 4-nitro (L-5) derivatives have been reexamined. Complexation of L-1 by ZnCl2 afforded [ZnCl2(L-1)], whose single crystal structure reveals a distorted tetrahedral zinc(II) centre with Zn ... Fe 4.730(2) and 4.803(2) Angstrom. The complexes [ZnCl2(L)] (L = L-2-L-5), [ZnBr2(L)] (L = L-2-L-5) and [CoBr2(L-3)] are accessible by MX2-templated condensation of 2 equivalents of ferrocenecarbaldehyde (fcCHO) with the appropriate 1,2-diaminobenzene. Treatment of [Cu(NCMe)(4)]X (X- = BF4- or PF6-) with L-1, or fcCHO and the corresponding 1,2-diaminobenzene, yielded [Cu(L)(2)]X (L = L-1-L-3). The single crystal structure of [Cu(L-3)(2)]-PF6 .1.7CH(2)Cl(2) shows a tetrahedral copper(I) centre, the chelate ligands being substantially distorted from planarity. Compounds [ZnCl2(L)], [ZnBr2(L)] (L = L-2-L-5) and [CoBr2(L-3)] exhibit weak electronic communication between the two ferrocenyl centres, showing by cyclic voltammetry two chemically reversible Fe-II-Fe-III oxidations separated by 50-60 mV in CH2Cl2-0.5 M (NBu4PF6)-P-n at 293 K; [ZnCl2(L-1)] and [Cu(L)(2)]X (L = L-1-L-3) exhibit a single Fe-II-Fe-III couple under these conditions. Attempted template syntheses of L-2-L-5 employing other MX2 (M = Mn, Co, Ni or Cu; X- = Cl-, Br-, NO3-, BF4- or ClO4-) salts yielded primarily 2-ferrocenylbenzimidazole intramolecular cyclisation derivatives; the crystal structure of one such product was determined.