Structure and reactivity of low-spin iron(II)-diimine complexes: Effect ofligand nature and of solvent composition (DMSO-water) on base hydrolysis rate constants

Rate constants are reported for base hydrolysis of a number of iron(II)-dii mine complexes, in water and in dimethyl sulphoxide - water mixtures. These new results are combined with rate constants determined previously, in wat er and in selected binary aqueous solvent mixtures, to give an overall pict ure of reactivity in such systems. We document and compare the effects of l igand variation and of solvent composition. Variation of reactivity of this class of complex with ligand structure depends on ligand type and denticit y; reactivities are very much lower for semi-encapsulating and, especially, for encapsulating ligands. There is in almost all cases a marked accelerat ing effect of increasing the dimethyl sulphoxide content of these solvent m ixtures. Reactivities range over several powers of ten for ligand variation over the range of complexes studied, around four powers of ten for solvent variation (water --> DMSO) for a given complex.