Palladium‐Based Catalysts Supported by Unsymmetrical XYC^–1 Type Pincer Ligands: C5 Arylation of Imidazoles and Synthesis of Octinoxate Utilizing the Mizoroki–Heck Reaction

Abstract

A series of new unsymmetrical (XYC–1 type) palladacycles (C1–C4) were designed and synthesized with simple anchoring ligands L1–4H (L1H = 2‐((2‐(4‐methoxybenzylidene)‐1‐phenylhydrazinyl)methyl)pyridine, L2H = N,N‐dimethyl‐4‐((2‐phenyl‐2‐(pyridin‐2‐ylmethyl)hydrazono)methyl)aniline, L3H = N,N‐diethyl‐4‐((2‐phenyl‐2‐(pyridin‐2‐ylmethyl)hydrazono)methyl) aniline and L4H = 4‐(4‐((2‐phenyl‐2‐(pyridin‐2‐ylmethyl)hydrazono) methyl)phenyl)morpholine H = dissociable proton). Molecular structure of catalysts (C1–C4) were further established by single X‐ray crystallographic studies. The catalytic performance of palladacycles (C1–C4) was explored with the direct Csp2–H arylation of imidazoles with aryl halide derivatives. These palladacycles were also applied for investigating of Mizoroki–Heck reactions with aryl halides and acrylate derivatives. During catalytic cycle in situ generated Pd(0) nanoparticles were characterized by XPS, SEM and TEM analysis and possible reaction pathways were proposed. The catalyst was employed as a pre‐catalyst for the gram‐scale synthesis of octinoxate, which is utilized as a UV‐B sunscreen agent.

Efficient Organoruthenium Catalysts for α‐Alkylation of Ketones and Amide with Alcohols: Synthesis of Quinolines via Hydrogen Borrowing Strategy and their Mechanistic Studies

“…1 H NMR (500 MHz, CDCl 3 ) δ 8.63 (d, J =4.2 Hz, 1H), 7.54–7.50 (m, 3H), 7.40–7.36 (m, 3H), 7.30 (t, J =8.0 Hz, 2H), 7.17 (dd, J =6.9, 5.2 Hz, 1H), 7.08 (d, J =7.9 Hz, 1H), 6.90 (t, J =7.2 Hz, 1H), 6.68 (d, J =8.9 Hz, 2H), 5.24 (s, 2H), 2.95 (s, 6H). 13 C NMR (101 MHz, CDCl 3 ) δ 156.64, 150.59, 149.95, 147.90, 137.29, 133.97, 129.27, 127.52, 124.84, 122.44, 120.86, 120.19, 114.38, 112.35, 52.16, 40.59 …”

“…calcd for C 23 H 26 N 4 : 77.06; H, 7.31; N, 15.63 found: C, 77.01; H, 6.99; N, 15.81 1 H NMR (500 MHz, CDCl 3 ) δ 8.63 (d, J =4.5 Hz, 1H), 7.54 (t, J =8.5 Hz, 1H), 7.49 (d, J =8.8 Hz, 2H), 7.40–7.35 (m, 3H), 7.30 (t, J =7.9 Hz, 2H), 7.19–7.15 (m, 1H), 7.08 (d, J =7.9 Hz, 1H), 6.90 (t, J =7.2 Hz, 1H), 6.63 (d, J =8.8 Hz, 2H), 5.24 (s, 2H), 3.35 (q, J =7.1 Hz, 4H), 1.15 (t, J =7.1 Hz, 6H). 13 C NMR (101 MHz, CDCl 3 ) δ 156.73, 149.93, 147.96, 137.25, 134.19, 129.25, 127.79, 122.40, 120.88, 120.06, 114.33, 111.61, 52.12, 44.55, 12.68 …”

Direct Arylation in the Presence of Palladium Pincer Complexes

“…In order to explain the reaction mechanism, the authors proposed the catalytic cycle displayed in Scheme 14. After the in situ generation of palladium(0) species A, oxidative addition with the aryl halide provided intermediate B, which underwent a ligand exchange with potassium pivalate to form intermediate C. Interaction with methylimidazole generated intermediate E via a CMD transition state (D), and after a reductive elimination step, the arylated product was released along with the Pd(0) species [139]. Scheme 14.…”

Immobilizing palladium on melamine‐functionalized magnetic nanoparticles: An efficient and reusable phosphine‐free catalyst for Mizoroki–Heck reaction

“…[ 8–10 ] However, the main drawbacks with these phosphine–Pd catalyst systems are related to the fact that most of the phosphine derived ligands are toxic, highly expensive and moisture and air sensitive. [ 11 ] To overcome these limitations, enormous efforts have been devoted to synthesize various nonphosphine‐based homogeneous catalytic systems with new types of ligands such as palladacycles, [ 12,13 ] N ‐heterocyclic carbine, [ 14 ] and pincer ligands. [ 15,16 ] However, these homogeneous catalyst systems, in general, suffer from some drawbacks such as contamination of final products with Pd species and limited reusability of expensive catalysts that is a challenging issue in large‐scale applications.…”