(Carbene)→SO2 Complexes: Ligand Stabilised Carbocyclic Carbenes (lsCCCs) are Better than N-Heterocyclic Carbenes

Abstract

Cyclic carbenes can form coordination complexes with SO2 (sulfur dioxide). Two N-heterocyclic carbene (NHC)→SO2 coordination complexes were reported along with their crystal structures. However, the computational analysis on the character of the coordination bond and its strength provided conflicting indications. There is a need to identify the properties which enhance the carbene→SO2 bond strength. In this work, Density Functional Theory (DFT) studies have been carried out to estimate the electronic, geometric and energetic parameters of several (NHC)→SO2 complexes. This work has been extended to carbocyclic carbene (CCC)→SO2, remote N-heterocyclic carbene (rNHC)→SO2, abnormal N-heterocyclic carbene (aNHC)→SO2, cyclic alkyl amino carbene (CAAC)→SO2, amido carbene (amNHC) →SO2 complexes. The results helped in identifying a set of ligand stabilised carbocyclic carbenes (lsCCCs), which can stabilise the donor→acceptor bonds between cyclic carbenes and SO2.