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