Synergic Effects Between N‑Heterocyclic Carbene and Chelating Benzylidene–Ether Ligands Toward the Initiation Step of Hoveyda–Grubbs Type Ru Complexes

Synergic effects between ancillary N-heterocyclic carbenes [(1,3-bis­(2,4,6-trimethylphenyl)-1,3-imidazoline-2-ylidene or 1,3-bis­(2,6-di<i>iso</i>propylphenyl)-1,3-imidazoline-2-ylidene] and chelating benzylidene–ether ligands were investigated by studying initiation rates and kinetic profiles of Hoveyda–Grubbs (HG) type Ru complexes. A newly designed Ru-benzylidene-oxazinone precatalyst <b>4</b> was compared with Grela and Blechert complexes bearing modified <i>iso</i>propyloxy chelating leaving groups and with the standard HG complex to understand how the ancillary and the leaving ligands interact and influence the catalytic activity