Chelating η6‐Arene‐η1‐carbene Ligands in Ruthenium Complexes

Abstract

AbstractN‐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{η6‐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{η1‐CN(CH2{η6‐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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)