Exploring Mesoionic Imine-Carbodiimide (MII-CDI) Adducts: 1,3 H-Shift, N(I) Compounds and Guanidinate-Type Ligands

In this study, we report our recent findings on the synthesis and reactivity of a novel 1,2,3-triazolin-5-imine-type mesoionic imine-carbodiimide (MII-CDI) adduct. Unlike reported NHC-CDI adducts, formed by the reactions of N-heterocyclic carbene (NHC) with CDI, these zwitterionic compounds undergo a spontaneous 1,3-hydrogen shift (1,3-H shift), resulting in guanidine-type compounds. The mechanism of this 1,3-H shift has been investigated through quantum chemical calculations. The MII-CDI adduct serves as a valuable synthon for the synthesis of mesoionic carbene-acyclic diamino carbene (MIC-ADC)-based nitreone (N(I)) compounds. We have conducted a detailed investigation into the electronic properties, chemical reactivity, and electrochemical behavior of these nitreone (N(I)) compounds. Additionally, the potential of these MII-CDI adducts as guanidinate ligands is explored. Our investigations here display the distinct reactivities of MII in contrast to their N-heterocyclic imine (NHI) congeners.