Gold‐Catalyzed Intermolecular Formal Insertion of Aryldiazo Esters into Cp−H Bonds of Iron and Ruthenium Metallocenes

Abstract

The reaction of ferrocene and ruthenocene with aryldiazo acetates in the presence of gold catalysts produced new functionalized metallocenes resulting from a C-H bond functionalization process. This process is believed to proceed through initial decomposition of the diazo component and formation of an electrophilic gold-carbene intermediate, which is subsequently involved in an electrophilic aromatic substitution. The gold-catalyzed functionalization of ruthenocene exhibited a broad scope and a notable functional-group tolerance. Interestingly, the functionalized ferrocene derivatives were found to react with molecular oxygen to yield α-aryl-α-ferrocenyl-α-hydroxyacetates. Adsorption on silica gel was found to be essential for this dioxygen activation/C(sp )-H bond functionalization sequence. The methodologies reported herein provide a simple and efficient approach to functionalized metallocene derivatives that are difficult to access through conventional organic functional group transformations.

Gold-catalyzed stereoselective dearomatization/metal-free aerobic oxidation: access to 3-substituted indolines/oxindoles

“…Just recently, López and co-workers reported the gold-catalyzed formal insertion of aryl diazoesters into ferrocene to generate functionalized metallocenes. 18 They also found that the silica gel promoted the aerobic oxidation leading to tertiary-substituted ferrocenyl alcohols. In that case, they believed the aerobic oxidation might proceed through initial electron-transfer from iron to molecular oxygen, which triggered the radical sequence to give the target product.…”

Rhodium(III)‐Catalyzed Direct C−H Alkylation of Ferrocenes with Diazo Compounds under Weakly Coordinating Approach

“…Schmalz and co‐workers reported the first catalytically functionalized ferrocenes using a Cu‐catalyzed intramolecular carbene insertion into a Cp−H bond . Lopez and co‐workers provided a method for Au‐catalyzed reaction of ferrocene and ruthenocene with aryldiazo acetates, producing a new series of functionalized metallocenes . Despite such elegant progress in the field, novelty of the reaction protocol is limited to the migratory insertion of diazo compounds with ferrocenes by Friedel‐Crafts type electrophilic substitution.…”

Ferrocene‐Decorated Phenol Derivatives by Trapping ortho‐Quinone Methide Intermediates with Ferrocene

“…Given our ongoing interest in functionalization of ferrocene derivatives based on the generation and subsequent trapping of highly electrophilic species, we posited that o ‐QMs could be intercepted by ferrocene through a Friedel–Crafts‐type reaction, thus delivering ferrocene derivatives featuring a phenolic moiety. Since, as stated before, phenol groups endow several ferrocene derivatives with therapeutic properties, our proposal was not only synthetically appealing, but also potentially relevant in the field of medicinal organometallic chemistry.…”