Computational comparison of the kinetic stabilities of diamino- and diamidocarbenes in the 1,2-H shift reaction.

In this study, we performed several DFT, MP2, and BD(T) calculations on the 1,2-H shift reactions of two diaminocarbenes (1, 2) and a diamidocarbene (3) using the Gaussian 09 program. In Gaussian 09, the BD(T) method keyword requests a Brueckner doubles calculation including a perturbative triples contribution. Although N-heterocyclic carbenes (NHC) are typically known for their exceptional σ-donor abilities, recent studies have indicated that π-interactions also play a role in the bonding between NHCs and transition metals or BX3 (X = H, OH, NH2, CH3, CN, NC, F, Cl, and Br) (Nemcsok et al. Organomet 23:3640-3646, 2004, Esrafili. J Mol Model 18:2003-2011, 2012). In order to study the importance of π-interactions between carbenes and transition metals, Hobbs and co-workers (Hobbs et al. New J Chem 34:1295-1308, 2010) focused on the synthesis of NHCs with reduced-energy lowest unoccupied molecular orbitals. By introducing an oxalamide moiety into the heterocyclic backbone, they found the resulting carbene possessed higher electrophilicity than usual NHCs. According to our results, the N,N'-diamidocarbene should be more stable than the diaminocarbenes with respect to the 1,2-H shift reaction.