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

Multiple distinct oxidative group transfer reactions to low valent chromium were examined. Six new chromium complexes were prepared from a highly electronically unsaturated Cr­(II) square planar complex that was supported by a macrocyclic tetracarbene ligand. This complex’s reactivity with Me₃NO and disparate azides was investigated. The reaction with Me₃NO generated a highly stable Cr­(IV)-oxo complex. Less bulky organic azides such as <i>p</i>-tolyl and <i>n</i>-octyl azides gave rise to metallotetrazenes, while more sterically demanding mesityl and adamantyl azides generated Cr­(IV)-imido complexes. The reaction of the square planar Cr­(II) complex with TMS-azide yielded the first linearly bridging nitrido chromium species. Reductive group transfer was explored for a Cr­(IV)-imido complex, and organic products, such as aziridines, were formed after addition. Cr­(IV) imidos and oxos are quite rare, while tetrazenes and bridging nitridos are virtually unknown. This is the most detailed study on oxidative group transfer reactions using chromium based complexes on a single auxiliary ligand to date