Divergent deazotation and nitrene group transfer pathways at cobalt phospha-triazene species

Abstract

Metal-nitrenes are critical intermediates in the incorporation of nitrogen functional groups, and a better understanding of the mechanism of their formation from the corresponding organoazide adducts is highly desirable. In this work, we demonstrate a new mode of organoazide deazotation at a phosphide-containing (PPP)Co scaffold. A dimeric cobalt species reacts with organoazides to furnish the corresponding cobalt(II) phosphazido complexes via selective [2 + 3] cycloaddition. This metal–ligand cooperative (MLC) transformation involves P–P bond cleavage along with Co–N_α and P–N_γ bond formation, revealing that the Co-phosphide site acts as an anchoring site for organoazide binding. The reduced Co(I) phosphazido complexes react with electrophiles such as B(C₆F₅)₃ and methylating reagents at the N_γ position to give the respective borane adduct and methyl species. The electrophilic functionalization of such anchored organoazide moieties leads to a significantly less delocalized azide moiety and elongation of the N_β–N_γ distance, rendering it susceptible toward thermolytic N_β–N_γ bond cleavage. The resulting nitrene moiety reacts with the phosphide moiety or with exogenous nitriles to form the respective iminophosphide or phospha-amidinate species. Such reactivity provides a new mode of organoazide activation via formation of a dialkyl phospha-triazene species, distinct from previous studies that primarily feature N_α–N_β bond cleavage.