Shedding light on the use of Cu(ii)-salen complexes in the A³ coupling reaction

Abstract

One air stable Cu(ii)-salen complex compound enables the generation of propargylamines. Mechanistic details, scope and limitations of this protocol are presented.

Structural and Electronic Control of the Bidentate 1‐(2‐pyridyl)benzotriazole Ligand in Copper Chemistry with Application to Catalysis in the A3 Coupling Reaction

“…On the basis of evidence from our recent studies, [26] we performed a series of reactions to gain mechanistic insights. The synthesis of 5 cca in the presence of a radical trap (TEMPO, 10 mol % based on aldehyde; Table 4, entry 3) afforded the desired product (Figure S42 of the Supporting Information), and thus excluded the formation of a radical species.…”

“…1 H NMR, 13 C NMR, HRMS (ESI‐FTMS) and LCMS spectra are reported for the propargylamines synthesized for the first time. 1 H NMR spectra are presented for the already reported propargylamines [26] …”

Room-Temperature Cu(II) Radical-Triggered Alkyne C–H Activation

“…14,24 For the second series, inspired by pioneering research on galactose oxidase and the use of Cu(II)-radical based complexes, 25−27 we showed that a reusable Cu(II) complex, built from a tetradentate N 2 O 2 salen-based ligand, promoted alkyne C−H activation at room temperature, within 72 h, or 0.5 h at elevated temperature. 23 Mechanistic and theoretical studies suggested a radical-based and single-electron transfer (SET) mechanism. Based on this evidence, we hypothesized that fine-tuning of the salen ligand and its respective Cu(II) complex would be key for an optimized C−H activation protocol.…”

Breaking the symmetry: C1-salans with (N–H) backbones

“…We recently reported that Cu(II) C2-salan and C2-salen based complexes promote A 3 coupling reactions in open air. 25 In order to expand this study, our first effort was to break the symmetry and modify the ligand scaffold in the C2-salan complexes. The simplest route towards Non-Symmetric C1-Salan Ligands (NSSL) containing secondary diamine (N-H) backbones is the reduction of the corresponding C1-salen (Scheme 1, E).…”

“…We have previously shown that C2-Cu(II)-Salen and Cu(II)salan complexes enable the A 3 coupling transformation at room temperature in open air without the need for any additives. 25 Spurred by the success of these efforts, the catalytic activity of the non-symmetric complexes in the synthesis of a simple propargylamine was investigated. Under the given experimental conditions (see ESI), the Cu(II) complexes performed moderately with 1 H-NMR conversions ranging from 27-55% (Table S15).…”