NHO to aNHC Isomerization at a Pd0-Center

N-heterocyclic carbenes (NHCs) are a highly important class of ligands in transition metal-mediated catalysis. Recently, a modification of the NHCs has received considerable interest, the N-heterocyclic olefins (NHOs) with an exocyclic methylene appended to the NHC. In here we investigated the propensity of NHOs to act as a ligands for Pd-0 complexes derived from [Pd-2(dvds)(3)]. The reaction of IPrCH2 and IMesCH(2) with the Pd-0 precursor [Pd-2(dvds)(3)] resulted in the formation of abnormal N-heterocyclic carbene complexes [(aIPrCH(3))Pd(dvds)] (1) and [(aIMesCH(3))Pd(dvds)] (2). DFT calculations were applied to study this isomerization and to reveal the bonding in 1 and 2. In addition, the backbone-methylated NHOs (IPrCH2)-I-Me and (mMe)IMesCH(2) (4) were shown not to undergo the isomerization observed in IPrCH2 and IMesCH(2).