A Recyclable Chiral Ru Catalyst for Enantioselective Olefin Metathesis. Efficient Catalytic Asymmetric Ring-Opening/Cross Metathesis in Air

Abstract

Page 4955. Enantioselectivity values for non-UV active compounds 14a and 14b were measured by HPLC/ELSD methods. Subsequent investigations led us to determine that ELSD methods are unreliable in measuring ee values of these compounds. Through reliable alternative analysis methods, we have established that the above reactions proceed in 80 and 82% ee, respectively. The remaining enantioselectivities are correct as initially reported. For additional details, see: Van Veldhuizen, J. J.; Gillingham, D. G.; Garber, S. B.; Kataoka, O.; Hoveyda, A. H.

Asymmetric catalysis with N-heterocyclic carbenes as non-covalent chiral templates

“…NHCs can catalyse chemical bond synthesis because of several unique chemical characteristics: they are strong s-donors 1 and good Brønsted bases, and they have moderate p-acidity 9 . For metal catalysis, the strong s-donor nature of NHCs makes them excellent ligands for late transition metals for asymmetric olefin metathesis [10][11][12] , hydrogenation [13][14][15][16] and conjugate additions 17,18 . Typically, an NHC-mediated organocatalytic reaction proceeds through a mechanism similar to the thiamine diphosphate mechanism, wherein a highly nucleophilic acyl-anion equivalent is the key reaction intermediate and is generated by the addition of the NHC catalyst to an aldehyde 19,20 .…”

Catalysis and Organometallic Chemistry of Monometallic Species

“…166 Developments in metathesis reactions have occurred with the synthesis of new active ruthenium() catalysts. A N-heterocyclic carbene ligand containing a binaphthyl substituent induces excellent enantioselectivity for some ring-opening/cross metathesis reactions in air, 167 and a functionalised alkylidene incorporating a hemilabile ether moiety has been investigated for ring closing metathesis. 168 A DFT study on the mechanism of olefin metathesis using ruthenium() N-heterocyclic carbene complexes has also been investigated.…”

N-Heterocyclic carbenes as highly efficient ancillary ligands in homogeneous and immobilized metathesis ruthenium catalytic systems

“…[51][52][53] Both complexes 63 and 64 ingeniously use backbone stereogenicity to induce atropisomeric chirality in the unsymmetrical N-aryl substituents. Of these two chiral ruthenium benzylidene complexes, compound 64 showed a wide range of metathesis activity and a particularly high enantioselectivity in RCM of dienes.…”

“…This chiral complex proved to be a highly effective catalyst in promoting both asymmetric ring-closing (ARCM) and cross-metathesis (CM) as well as ring-opening metathesis (ROM). 53 An interesting panel of very active NHC homo-and heterobimetallic complexes containing Ru, Os, Rh and Ir, such as 40-44, resulted from selective ligand substitution in mono-or bisimidazolin-2-ylidene ruthenium complexes using appropriate chloro-bridged organometallic dimers [54][55][56] (Scheme 21). By contrast, 69-71 can be obtained preferentially from 26a (R = Cy) and the corresponding organometallic dimers, as reaction of 28a will lead to a mixture of bimetallic complexes with phosphane or NHC.…”