The effects of anions on the reactivity of d6 transition metal complexes.

This thesis is concerned with the effects of anions on the reactivity of d6 transition metal complexes. These complexes include trans-Iren2C12+, trans-Rhen2C12+, cis-Coen2C12+, tris-(1,10-phenanthroline) iron (II), tris-(ferrozine)iron(II) and a new low spin iron(II) complex, in which the ligand is the hexadentate Schiff base derived from phenyl 2-pyridyl ketone and triethylenetetramine. Rates of substitution at trans-Iren2C12+ and at trans-Rhen2C12+ show a marked dependence on the concentration, and a small dependence on the nature, of the incoming ligand. These results have been interpreted in terms of ion pair formation. Rates of aquation of cis-Coen2C12+, in 60%, 40%, and 20% dioxan-water, as in aqueous solution, show very little dependence on the nature and concentration of added anions. However rates of aquation of Fe(phen)32+, and its 5-nitro and 4,7- dimethyl derivatives, in 60%, 40%, and 20% dioxan-water are markedly sensitive both to the nature and concentration of added (non-substituting) anions, indicating an important role for ion pairs in these systems. Low spin iron(II) complexes react directly with hydroxide, cyanide, and peroxodisulphate; kinetic parameters for these substitution and redox reactions are reported and discussed for the complexes of ferrozine and of the hexadentate Schiff base mentioned above. The dependence of reactivity on solvent composition has been investigated for bromide substitution at trans-Iren2C12+ (ethanol- and dioxan-water) and trans- Rhen2C12+ (dioxan-water), for aquation of cis-Coen2C12+ (dioxan-water), for aquation of Fe(phen)32+, Fe( 5-NO2-phen)32+, and Fe(4,7-diMe-phen)32+ (dioxan-water), and for the reaction of the iron(II) complexes of ferrozine and of the hexadentate Schiff base with cyanide (ethanol-water).