Ruthenium Catalysts Supported by Amino‐Substituted N‐Heterocyclic Carbene Ligands for Olefin Metathesis of Challenging Substrates

Abstract

N-Heterocyclic carbene (NHC) ligands IMesNMe2 and IMes(NMe2)2 derived from the well-known IMes ligand by substituting the carbenic heterocycle with one and two dimethylamino groups, respectively, were employed for the synthesis of second-generation Grubbs- and Grubbs-Hoveyda-type ruthenium metathesis precatalysts. Whereas the stability of the complexes was found to depend on the degree of dimethylamino-substitution and on the type of complex, the backbone-substitution was shown to have a positive impact on their catalytic activity in ring-closing metathesis, with a more pronounced effect in the second-generation Grubbs-type series. The new complexes were successfully implemented in a number of challenging olefin metathesis reactions leading to the formation of tetra-substituted C=C double bonds and/or functionalized compounds.

Synthesis of N-Sulfonyl- and N-Acylpyrroles via a Ring-Closing Metathesis/Dehydrogenation Tandem Reaction

“…The sulfonyl-and acyldiallylamines were prepared according to literature procedures. [17][18][19][20][21][22] Sulfonyl chloride, formyl chloride, diallylamine, and other reagents were purchased from commercial sources and used as received. High-resolution mass spectra were recorded by using an Electrothermal LTQ-Orbitrap mass spectrometer.…”

“…17 Yield: 138.7 mg (69%); yellow oil. Acyldiallylamines 1aa-vv; General Procedure [20][21][22] Et 3 N (126 mg, 1.25 mmol) was added dropwise to a stirred solution of diallylamine (107 mg, 1.10 mmol) in anhyd CH 2 Cl 2 (3.0 mL) at 0 °C. Then the appropriate formyl chloride (1.00 mmol) was slowly added to the mixture.…”

“…Compound 1gg was prepared according to a literature procedure. 22 Yield: 284.5 mg (87%); white solid; mp 50-51 °C.…”

Helicenes as Chirality‐Inducing Groups in Transition‐Metal Catalysis: The First Helically Chiral Olefin Metathesis Catalyst

“…The principle is illustrated herein for the example of asymmetric olefin metathesis. [5] Unfortunately,e nantioselectivities are normally low for this ligand design if the chiralN -substituent can freely rotatea round the CÀNb ond, [6] whereas higher levels of enantioselectivity are observed with multicyclic, [7] bidentate [8] or cyclometalated NHCs. Kineticd ata were acquired for benchmark test reactionsa nd compared to an achiral catalyst.…”

“…Asymmetric (or enantioselective) catalysis requires the presence of ac hiral ligand at the metal, which induces either directly or indirectly ad issymmetry aroundt he catalytically active center.F or as uccessfule nantioinduction,t he chiral informationn eeds to be embedded in as teeringl igand, whichi st ightly bound to the metal throughout the entire catalytic cycle. [5] Unfortunately,e nantioselectivities are normally low for this ligand design if the chiralN -substituent can freely rotatea round the CÀNb ond, [6] whereas higher levels of enantioselectivity are observed with multicyclic, [7] bidentate [8] or cyclometalated NHCs. [1,2] In most cases described so far,N HC-ligands have been chirally modified by introducing centers of chirality, either in the Nsubstituent or in the NHC-backbone ( Figure 1).…”