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

• Published in: Journal of organometallic chemistry Vol. 896; pp. 70 - 76
• Main Authors: Sardo, Carla, Janczak, Sławomir, Leśnikowski, Zbigniew J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15-09-2019
• Subjects: Bridged metallacarborane; Cobalt bis dicarbollide; Hydrolysis; Phosphate; Phosphorothioate; Hydrolysis; Bridged metallacarborane; Phosphorothioate; Cobalt bis dicarbollide; Phosphate
• ISSN: 0022-328X; 1872-8561
• DOI: 10.1016/j.jorganchem.2019.06.001

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.
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•Phosphate and phosphorothioate triesters of [Co(1,2-C2B9H11)2]- are resistant to hydrolysis.•High resistance is explained by “metallacarborane effect”, a multifaceted phenomenon.•Metallacarborane produce a charge shielding effect towards approaching nucleophile.•Metallacarborane interact electronically with outer phosphorus bridge.•Steric hindrance and limited flexibility also contribute to the amazing stability.