Mechanistic Aspects of Copper‐Catalyzed Reactions

Larsson, Per‐Fredrik; Norrby, Per‐Ola; Woodward, Simon

doi:10.1002/9783527664573.ch12

Cited by 2 publications

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“…[ 30–31 ] After an initial formation of a precatalyst due to the affinity of the active Cu(I) catalyst for the unsaturated substrate [ 15,29–30,32–34 ] (see Scheme 2, III ), the cyclopropanation proceeds further via complexation of a metal and a carbene ( VI ), formed by expelling N 2 from the diazo compound ( V → VI ), which is considered as the rate determining step. [ 15 ] The ring closing step itself is known to proceed either via a one‐step concerted pathway ( VII ) as a direct‐carbene insertion, or via a two‐step process, proceeding by a metallocyclobutane intermediate ( VIII ), [ 29,32,35 ] depending on the diazo compound, the ligand (L n ) and the transition metal (M).…”

Section: Resultsmentioning

confidence: 99%

“…VI), which is considered as the rate determining step. [15] The ring closing step itself is known to proceed either via a one-step concerted pathway (VII) as a directcarbene insertion, or via a two-step process, proceeding by a metallocyclobutane intermediate (VIII), [29,32,35] depending on the diazo compound, the ligand (L n ) and the transition metal (M).…”

Section: Cu(i)-catalyzed Cyclopropanation Of Pi With Diazoacetatesmentioning

confidence: 99%

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Cyclopropanation of poly(isoprene) using NHC‐Cu(I) catalysts: Introducing carboxylates

Shinde

Michael

Rössle³

et al. 2020

Journal of Polymer Science

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The incorporation of functional groups into unsaturated polyolefine-polymers often represent a challenging task. Based on the known cyclopropanation of double bonds with diazoesters in the presence of metal-catalysts of low molecular weight compounds, we in this article develop an approach to decorate the polymer backbone of poly(diene)s with ester as well as carboxylic groups via cyclopropanation. Therefore, predominantly cis-1,4-poly(isoprene)s are converted with ethyl or tert-butyl diazoacetate using copper(I) N-heterocyclic carbene (NHC) catalysts, while focusing on the technically relevant cyclohexane as solvent. The application of commercially available NHC-Cu(I) catalysts results in modification degrees of 4-5%, while an increased solvent polarity, like dichloromethane, results in up to 17% modification. The resulting esters were further converted to the corresponding free carboxylic groups by deprotection using trifluoroacetic acid. Thus, an introduction of functional groups along the polymer backbone with a wide variety of application, like ionic interaction or hydrogen bonding motifs, was successfully demonstrated. Its potential for upscaling makes this approach feasible for an application in large-scale production processes, such as for manufacturing of modified synthetic rubbers.

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Section: Resultsmentioning

confidence: 99%

Section: Cu(i)-catalyzed Cyclopropanation Of Pi With Diazoacetatesmentioning

confidence: 99%

Cyclopropanation of poly(isoprene) using NHC‐Cu(I) catalysts: Introducing carboxylates

Shinde

Michael

Rössle³

et al. 2020

Journal of Polymer Science

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“…The copper-catalysed 1,4-addition of organometallics to enones is typically proposed to proceed via evolution of a π-enone complex, akin to 1, to a fleeting copper(III) intermediate (2) whose reductive elimination to product 3 is commonly proposed to be rate limiting (Scheme 1). 1,2 In Asymmetric Conjugate Addition (ACA) 1,2 versions of such reactions, this latter step also defines the stereochemistry in the 1,4-product. Identifying ligands (L) which reduce the transition state barrier to reductive elimination is a commonly understood concept in achieving fast catalysis.…”

Section: ■ Introductionmentioning

confidence: 99%

Mechanistic-Insight-Driven Rate Enhancement of Asymmetric Copper-Catalyzed 1,4-Addition of Dialkylzinc Reagents to Enones

et al. 2020

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Combination of [Cu(MeCN)4]TFA•TFAH (TFA = O2CCF3) with Feringa's phosphoramidite ligand (L A ) provides an exceptionally active (0.75 mol%) catalyst for asymmetric conjugate additions of ZnR2 (R = Et, Me at -40 to -80 o C) to enones. Kinetic and other studies of the addition of ZnEt2 to cyclohex-2-en-1-one indicate a transition state stoichiometry composition: (ZnEt2)3(enone)4Cu2(L A )3 that is generated by transmetalation from Et2Zn(enone)2. Catalyst genesis is significantly slower than turnover (which has limited previous attempts to attain useful kinetic data); in the initial stages varying populations of catalytically inactive, off-cycle, species are present. These issues are overcome by a double-dosing kinetic analysis protocol. A rest state of [L A Cu(Et)(µ-TFA)(µ-{(enone)(ZnEt)2(enolate)})CuL A2 ] + (through the equivalence of enolate = enone + ZnEt2) is Manuscript for Organometallics, Woodward and co-workers Page 2 of 19supported by DFT studies (ωB97X-D/SRSC). Rate determining ZnEt2(enone)2 transmetalation drives the exceptionally high catalytic activity of this system.

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Mechanistic Aspects of Copper‐Catalyzed Reactions

Cited by 2 publications

References 151 publications

Cyclopropanation of poly(isoprene) using NHC‐Cu(I) catalysts: Introducing carboxylates

Cyclopropanation of poly(isoprene) using NHC‐Cu(I) catalysts: Introducing carboxylates

Mechanistic-Insight-Driven Rate Enhancement of Asymmetric Copper-Catalyzed 1,4-Addition of Dialkylzinc Reagents to Enones

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