Abstract
The synthesis and characterisation of two cobalt(II) complexes, [Co
II
L
Br-acr
Cl
2
] (1a) and [Co
II
L
H-acr
Cl
2
] (1b), with acridine head-units resulting from an unexpected ligand rearrangement from a diphenylamine head-unit, and the intended cobalt(II) complex, Co
II
L
Br-dpa
(Cl)(H
2
O) (2), are reported. Single crystals of the two dark green acridine-based cobalt(II) complexes, 1a and 1b, form in a one-pot reaction of cobalt(II) chloride, the chosen diphenylamine-2,2′-dicarboxaldehyde (Ia 4,4-′dibromo- or Ib unsubstituted), triethylamine and two equivalents of 2,4-dimethylaniline in acetonitrile, in 23% yield. In contrast, the intended diphenylamine-based complex was isolated in two steps: first isolation of the Schiff base ligand, then complexation with cobalt(II) chloride and deprotonation with potassium tert-butoxide, in methanol/dichloromethane, giving 2 as a bright yellow solid in 67% yield. All three complexes feature cobalt(II) centres, with N
2
Cl
2
approximately tetrahedral coordination for 1a and 1b confirmed by single crystal structure determinations. It is proposed that after one imine 'arm' forms, cobalt(II) coordination facilitates the other aldehyde undergoing an intramolecular cyclisation to form the new heterocyclic acridine head-unit. The structures of both of the resulting acridine-based complexes, 1a and 1b, and that of the originally intended Schiff base ligand, HL
Br-dpa
, were confirmed by single-crystal X-ray diffraction. These are the first examples of complexes of an acridine ligand of this type.