Chelating eta(6)-arene-eta(1)-carbene ligands in ruthenium complexes

WOS: 000247937300038N-Heterocyclic carbene (NHC) ruthenium complexes containing a chelating NHC-eta(6)-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 eta(6)-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{eta(1)-CN(CH2{eta 6-C6H2Me3-2,4,6})CH2CH2N(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{eta(1)-CN(CH2{eta(6)-C6H2Me3-2,4,6})CH2CH2N(CH2CH2OCH3)}][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. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)