Enantiopure C1-symmetric N-Heterocyclic Carbene Ligands from Desymmetrized meso-1,2-Diphenylethylenediamine: Application in Ruthenium-Catalyzed Olefin Metathesis

Abstract

Abstract:In order to design improved chiral ruthenium catalysts for asymmetric olefin metathesis, enantiomeric catalysts incorporating C 1 -symmetric N-Heterocyclic carbenes (NHC) ligands with syn-related substituents on the backbone were synthesized starting from meso-1,2-diphenylethylenediamine. The absolute configuration of the enantiomers of the desymmetrized meso diamine was assigned by optical rotation analysis and in silico calculations, and was found to be maintained in their respective ruthenium catalysts by comparison of the relative electronic circular dichroism (ECD) spectra. The catalytic behaviour of the enantiomeric ruthenium complexes was investigated in model asymmetric metathesis transformations and compared to that of analogous complexes bearing C 1 -symmetric NHC ligands with an anti backbone. Modest enantioselectivities were registered and different catalyst properties depending on the nature of stereochemical relationship of substituents on the backbone were observed.

In a Quest for Selectivity Paired with Activity: A Ruthenium Olefin Metathesis Catalyst Bearing an Unsymmetrical Phenanthrene‐Based N‐Heterocyclic Carbene

“…[41] uNHCs were also used by Paradiso et al in an investigation of backbones terich inderence influence on the reactivity of ruthenium alkylidene complexes ( Figure 1, L13-A,C). [42][43][44][45] N-Cyclohexyl derivative was succesfullyu sed in alternating ringopeningm etathesis polymerisation (AROMP), [46] similarly to that previously published by the Plenio group N-pentiptycenyl ruthenium complex. [47] In line with the trend of investigating uNHC as ligandsf or olefin metathesis, our group published as eries of works on Naralkyl-N'-aryl NHC-based complexes.T hese provedu seful as olefin-metathesis precatalysts, not only,i ns tandard conditions under an argon atmosphere, but also in commercial grade nondegassed solvents (Figure 1, L10-B).…”

“…uNHCs were also used by Paradiso et al. in an investigation of backbone steric hinderence influence on the reactivity of ruthenium alkylidene complexes (Figure , L13‐A , C ) . N ‐Cyclohexyl derivative was succesfully used in alternating ring‐opening metathesis polymerisation (AROMP), similarly to that previously published by the Plenio group N ‐pentiptycenyl ruthenium complex …”

Expanding the Family of Hoveyda–Grubbs Catalysts Containing Unsymmetrical NHC Ligands

“…The catalytic performances of enantiomerically pure catalysts 12a – c were also evaluated in asymmetric metathesis transformations and compared to those of catalyst 10b . The asymmetric ring-closing metahesis (ARCM) of achiral trienes 44 and 45 (Scheme ) and the asymmetric ring-opening cross-metathesis (AROCM) of meso -norbornene derivative 48 with styrene (Scheme ) were chosen as model reactions.…”

Synthetic Approaches to Chiral Non-C 2-symmetric N-Heterocyclic Carbene Precursors

“…In 2007, Collins and co-workers applied this reaction sequence to (R,R)-1,2-di-tert-butylethylenediamine, which gave access to an imidazolinium salt with methyl/2-isopropylphenyl substituents 56e; 24 they obtained a library of similar structures in 2009. 25 Finally, in 2015 Ciogli, Grisi, and co-workers 26 used meso-1,2-diphenylethylenediamine as a useful building block, which underwent Buchwald-Hartwig coupling with 2-isopropylphenyl bromide to give a racemic mixture that was separated by HPLC to give single enantiomers. These underwent reductive amination with cyclohexanone and subsequent cyclization under classical conditions to give imidazolinium salts 56h,i in good overall yields.…”