An Isolable Base‐Stabilized Diazosilenyl Cation

Abstract In contrast to the emerging chemistry of stable diazoalkenes, there are not yet any studies devoted to heavier silicon analogues, diazosilenes. Here, we report the synthesis of a base‐stabilized diazosilenyl cation 2 by the reaction of base‐stabilized C ‐phosphonio‐silyne 1 with N 2 O. This silicon analog of diazoalkenes 2 exhibits a remarkable stability thanks to the coordination of phosphine and phosphine oxide ligands at the cationic silicon center. In addition, DFT calculations predict that, due to a particular stabilizing effect of the electropositive silicon atom, for diazosilenes (R 2 Si=C=N 2 ), the presence of π‐donor substituents is not essential to prevent N 2 dissociation, contrary to carbon analogues. Interestingly, diazosilenyl cation 2 tends to isomerize into (silylene)(phosphonio)diazomethane 7 via a 1,2‐phosphine ligand migration and thus exhibits dual reactivity as a diazoalkene and as a diazo‐substituted silylene.