Mechanistic Aspects of Nucleophilic Substitution at Half-Sandwich Metal Complexes

Abstract

The hydrolysis reactions of organometallic ruthenium(II) piano-stool complexes of the type [RuII(η6-cymene)(L)Cl]0/+ (1−5, where L = κ1- or κ2-1,1-bis(diphenylphosphino)methane, 1,1-bis(diphenylphosphino)methane oxide, κ1-mercaptobenzothiazole) have been studied using density functional theory at the B3LYP level. In addition to considering a syn attack in an associative fashion, where the nucleophile approaches from the same side as the leaving group, we have explored alternative paths such as an anti attack in an associative manner, where the nucleophile attacks from the opposite side of the leaving group. During the anti attack, an intermediate is formed and there is a coordination mode change of the arene ring from η6 to η2 along with its rotation. When the intermediate goes to the product, the arene ring slips back from η2 to η6 coordination. This coordinated movement of the arene ring makes the associative anti attack an accessible pathway for the substitution process. Our calculations predict very s...