Chelating η6-arene-η1-carbene ligands in ruthenium complexes

Abstract

N-Heterocyclic carbene (NHC) ruthenium complexes containing a chelating NHC-η6-arene ligand have been prepared and evaluated as precursors for ring opening metathesis polymerization (ROMP). The reaction of [RuCl2(p-cymene)]2 with electron-rich olefins of the bis(imidazolinylidene) type containing at least one arylmethyl-N chain (aryl: 2,4,6-trimethylphenyl, 3,4,5-trimethoxyphenyl) selectively leads, upon heating, to ruthenium(II) complexes 2 containing a chelating bridged carbene η6-arene ligand. The reaction of complexes containing an additional ROCH2CH2N group with AgOTf leads to ionic complexes 5 with a tridentate trifunctional carbene/arene/ether ligand. The X-ray structure of [RuCl2{η1-CN(CH2{η 6-C6H2Me3-2,4,6})CH 2CH2N(CH2{C6H2(OMe) 3-3,4,5})}] (2c) and that of the ionic ruthenium complex containing a trifunctional carbene/arene/ether ligand that provides ten electrons, [RuCl{η1-CN(CH2(η6-C6H 2Me3-2,4,6})CH2CH2N(CH 2CH2OCH3))][CF3SO3] (5e), have been determined. The precursors 2 in the presence of AgOTf and propargyl alcohol, in order to produce an allenylidene initiator, and complexes 5 in the presence of propargyl alcohol lead to ROMP of norbornene. It is shown that initial chloride abstraction is required and that the catalyst activity is increased by using mesityl-ruthenium precursors and coordinated branched ether complexes. © Wiley-VCH Verlag GmbH & Co. KGaA, 2007.