The work in this thesis is mainly concerned with the discussion of the effects of pressure and medium on the kinetics of iron(II) complexes. The kinetics of dissociation of several iron(II) diimine complexes by aqueous hydroxide and cyanide ions have been studied spectrophotometrically at atmospheric pressure and elevated pressures. Pressure and solvent modification of the rate of base hydrolysis of the complex ion, [Fe(Me2bsb)3]2+, are reported and discussed, in different binary aqueous solvent mixtures. The dependence of rate constants for base hydrolysis on solvent composition for [Fe(phen)3]2+ and solvolysis of cis-[Co(en)2CI2]+ has been reported in diols-water mixtures. The observed reactivity trends are discussed in terms of hydrophilic and hydrophobic properties of the respective diols. These dependences are compared with analogous reactivity trends for binary aqueous solvent mixtures containing monohydroxylic alcohols. A series of limiting dissociative substitution reactions of pentacyanoferrate(II) complexes were studied as a function of pressure in order to investigate the dependence of the associated volume of activation on the size of leaving group. The effects of solvent and salt on reactivity and the activation volume of [Fe(CN)5L]n-are discussed. Dependence of wavenumbers of maximum absorption for the lowest metal to ligand charge-transfer (MLCT) bands of pentacyanoferrate(II) complexes has been reported in a series of solvent mixtures. Pressure effects on the MLCT bands of these complexes have been established. The relation of these piezochromic effects to the solvatochromic effects has been reported.