Consequences of the electronic tuning of latent ruthenium-based olefin metathesis catalysts on their reactivity.

Karolina Żukowska,Eva Pump,Aleksandra E Pazio,Luigi Cavallo,Christian Slugovc,Krzysztof Woźniak

doi:10.3762/bjoc.11.158

Abstract

Two ruthenium olefin metathesis initiators featuring electronically modified quinoline-based chelating carbene ligands are introduced. Their reactivity in RCM and ROMP reactions was tested and the results were compared to those obtained with the parent unsubstituted compound. The studied complexes are very stable at high temperatures up to 140 °C. The placement of an electron-withdrawing functionality translates into an enhanced activity in RCM. While electronically modified precatalysts, which exist predominantly in the trans-dichloro configuration, gave mostly the RCM and a minor amount of the cycloisomerization product, the unmodified congener, which preferentially exists as its cis-dichloro isomer, shows a switched reactivity. The position of the equilibrium between the cis- and the trans-dichloro species was found to be the crucial factor governing the reactivity of the complexes.

Highlights

Olefin metathesis is a catalytic process during which C–C double bonds are exchanged [1]
The present work introduced two ruthenium-based olefin metathesis catalysts/initiators featuring electronically modified quinoline-based chelating carbene ligands. Their reactivity in ring-closing metathesis (RCM) and ring-opening metathesis polymerization (ROMP) reactions was tested and results were set in comparison to those obtained with the parent compound, bearing the unsubstituted quinoline-based chelating carbene
Electronic modification of the quinoline moiety changes the position of the trans–cis equilibrium as shown experimentally and theoretically

Summary

Introduction

Olefin metathesis is a catalytic process during which C–C double bonds are exchanged [1]. Both compounds 12 and 13 were used in a carbene exchange reaction with compound 1 conducted in toluene at 80 °C (see Scheme 3), releasing the desired complexes 14 and 15 as trans-dichloro isomers in good yields. The formyl-substituted complex 15 underwent isomerization, but only a mixture of 11% cis-15 and 89% trans-15 was obtained (cf Supporting Information File 1).

Results

Conclusion