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 Pd0 complexes derived from [Pd2(dvds)3]. The reaction of IPrCH2 and IMesCH2 with the Pd0 precursor [Pd2(dvds)3] resulted in the formation of abnormal N‐heterocyclic carbene complexes [(aIPrCH3)Pd(dvds)] (1) and [(aIMesCH3)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 MeIPrCH2 and mMeIMesCH2 (4) were shown not to undergo the isomerization observed in IPrCH2 and IMesCH2. N‐heterocyclic olefins (NHO) have been tested as ligands for electron‐rich Pd0‐fragments. This resulted in an unusual NHO to abnormal carbene (aNHC) isomerization, which afforded unique aNHC–Pd0 complexes. Quantum mechanical calculations support the observed transformation.