A Chromium(II) Tetracarbene Complex Allows Unprecedented Oxidative Group Transfer

Area of Science:

• Organometallic Chemistry
• Inorganic Chemistry
• Catalysis

Background:

• Low-valent chromium complexes are versatile in oxidative group transfer reactions.
• Understanding the reactivity of chromium(II) is crucial for developing new catalytic processes.
• The synthesis and characterization of novel chromium species are of significant interest.

Purpose of the Study:

• To investigate oxidative group transfer reactions of a highly electronically unsaturated Cr(II) complex.
• To synthesize and characterize new chromium complexes, including rare oxidation states and species.
• To explore the scope and limitations of these reactions with various oxidants.

Main Methods:

• Synthesis of a square planar Cr(II) complex supported by a macrocyclic tetracarbene ligand.
• Reactions of the Cr(II) complex with trimethylamine N-oxide (Me3NO) and various organic and silyl azides.
• Characterization of the resulting chromium complexes using spectroscopic and analytical techniques.
• Exploration of reductive group transfer from a Cr(IV)-imido complex.

Main Results:

• Formation of a stable Cr(IV)-oxo complex from the reaction with Me3NO.
• Synthesis of metallotetrazenes with less bulky organic azides (p-tolyl, n-octyl).
• Generation of Cr(IV)-imido complexes with sterically demanding azides (mesityl, adamantyl).
• Isolation of the first linearly bridging nitrido chromium species using TMS-azide.
• Observation of reductive group transfer from a Cr(IV)-imido complex, yielding organic products like aziridines.

Conclusions:

• The study demonstrates the rich reactivity of the Cr(II) complex in oxidative group transfer reactions.
• It provides access to rare chromium species, including Cr(IV)-imidos, Cr(IV)-oxos, metallotetrazenes, and bridging nitridos.
• This work represents a detailed investigation into chromium-mediated oxidative group transfer reactions using a single ligand scaffold.