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Abstract
New robust and air-stable ruthenium(II) indenylidene
second-generation precatalysts with unsymmetrical N-heterocyclic carbene
(NHC) ligands were synthesized. These complexes were studied using
ring-closing metathesis (RCM) of diethyl diallylmalonate (<b>5</b>; DEDAM) as a model substrate. Two new complexes containing OMe and
NMe<sub>2</sub> groups in the NHC ligand, namely [1-(2,4,6-trimethylphenyl)-3-(2-methoxybenzyl)-2-imidazolidinylidene]dichloro(3-phenyl-1<i>H</i>-inden-1-ylidene)(tricyclohexylphosphine)ruthenium(II)
(<b>4a</b>) and [1-(2,4,6-trimethylphenyl)-3-(2-<i>N,N</i>-dimethylaminobenzyl)-2-imidazolidinylidene]dichloro(3-phenyl-1<i>H</i>-inden-1-ylidene)(tricyclohexylphosphine)ruthenium(II)
(<b>4b</b>), show increased activity in comparison to the parent
[1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene]dichloro(3-phenyl-1<i>H</i>-inden-1-ylidene)(tricyclohexylphosphine)ruthenium(II)
(Umicore <b>M2</b>). Interestingly, the complex [1-(2,4,6-trimethylphenyl)-3-(2-thiomethylbenzyl)-2-imidazolidinylidene]dichloro(3-phenyl-1<i>H</i>-inden-1-ylidene)(tricyclohexylphosphine)ruthenium(II)
(<b>4c</b>), bearing a SMe substituent, showed very low activity
in the model RCM reaction with diethyl diallylmalonate (<b>5</b>). Application of the active complexes for metathesis reactions with
a broad spectrum of olefins in commercial-grade solvents in air was
examined
