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{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)

Synthesis and catalytic properties of novel ruthenium N-heterocyclic-carbene complexes

“…Values of d( 13 C carb ) are in the 198.5-201.5 ppm range and are similar to those found for other carbene complexes. These complexes show typical spectroscopic signatures, which are in line with those recently reported for other [RuCl 2 (mono-NHC)(arene)] complexes [28].…”

Heterocyclische Carbene – Synthese und Koordinationschemie

“…Diese lassen sich in situ deprotonieren und eignen sich zur Synthese von Metallkomplexen, obwohl die freien Carbenliganden nicht isoliert wurden. Gleiches gilt für N‐Allyl‐substituierte Imidazolium‐,55b, c, 153 Benzimidazolium‐94e und Benzothiazoliumsalze123a sowie N‐Benzyl‐funktionalisierte Imidazolidiniumsalze,55d,e deren Olefin‐ oder Arylfunktionen ebenfalls als Donorgruppen fungieren können. Die in Schema gezeigten N‐arylierten Liganden wurden von Danopoulos et al.…”

Transition Metal Complexes of Neutral eta1-Carbon Ligands

“…Although several other ruthenium-allenylidene complexes, including half-sandwich, five-and six-coordinate species, have proven to be active in RCM and ROMP of olefins, their efficiencies are in general lower than that showed by [RuCl (=C=C=CPh 2 )( 6 -p-cymene)(PCy 3 )][X] (X À = PF 6 À , TfO À ) and will not be commented on [142,146,154,155,164,217,[308][309][310]. The cross-olefin metathesis of cyclopentene with methyl acrylate using as catalyst the water soluble allenylideneruthenium(II) complex 28 (see Fig.…”