The kinetics of methoxydechlorination of 5-chloro-1,10-phenanthroline when co-ordinated to NiII, RuII, and OsII have been studied in dimethyl sulphoxide–methanol (89.9 : 10.1 w/w). In all cases studied there is a considerable enhancement of reactivity which bears more relationship to the total charge on the complex than it does to the nature of the central metalion. The following complexes have been examined (relative rates at 25°C in parentheses: [Ru(5-Cl-phen)3]2+(5 420), [Ni(5-Cl-phen)3]2+(3160), [Os(5-Cl-phen)3]2+(2 680), [Os(5-Cl-phen)2(acac)]+(353); [Os(5-Cl-phen)2(ox)]°(95), and 5-Cl-phen (1). This is in contrast to the N-alkyl compounds which add methoxide in the 2-position and are deactivated towards methoxydechlorination.