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. (c) 2019 Elsevier B.V. All rights reserved.