Unusual resistance of cobalt bis dicarbollide phosphate and phosphorothioate bridged esters towards alkaline hydrolysis: The “metallacarborane effect”

The extraordinary stability of bridged O,O-[cobalt bis(dicarbollide)ion] O-(4-nitrophenyl)phosphorothioate [2]- and phosphate [3]- esters under alkali conditions was discovered. The hydrolysis of metallacarborane esters [2]- and [3]- was studied, and the kinetic and thermodynamic parameters were measured and compared with those of their organic counterparts, parathion and paraoxon. The extreme differences between the hydrolytic properties of alkyl- and metallacarborane phosphate and phosphorothioate esters are attributed to the electronic and steric effects of the metallacarborane non leaving group (“metallacarborane effect”). The known “thio effect” contributes to a lesser extent to the resistance of [2]- to the basic conditions.