Mimics of Pincer Ligands: An Accessible Phosphine-Free N-(Pyrimidin-2-yl)-1,2-azole-3-carboxamide Framework for Binuclear Pd(II) Complexes and High-Turnover Catalysis in Water

Abstract

We report for the first time cyclic phosphine-free “head to tail” N,N,N pincer-like (pincer complexes mimicking) N-(pyrimidin-2-yl)-1,2-azole-3-carboxamide Pd­(II) complexes with deprotonated amide groups as high-turnover catalysts (TON up to 106, TOF up to 1.2 × 107 h–1) for cross-coupling reactions on the background of up to quantitative yields under Green Chemistry conditions. The potency of the described catalyst family representatives was demonstrated in Suzuki–Miyaura, Mizoroki–Heck, and Sonogashira reactions on industrially practical examples. Corresponding ligands could be synthesized based on readily available reagents through simple chemical transformations. Within the complex structures, a highly unusual 1,3,5,7-tetraza-2,6-dipalladocane frame could be observed.

Recent Expedition inPd‐CatalyzedSonogashira Coupling and Related Processes†

“…In 2020, Kletskov, Bumagin and Potkin reported N,N,N pincer‐ like palladacycle 15 for Sonogashira reactions of prop‐2‐yn‐1‐ol and methyl p ‐iodobenzoate at 20 °C with 0.1 mol% Pd (Figure 3). [ 80 ] Very recently, an aromatic triangular tri‐palladium complex 16 was disclosed by Maestri, Wang and Wu for Sonogashira coupling of aryl iodide (Figure 3; Table 2, entry 13). [ 81 ] Steric hindered (hetero)aryl iodides were successfully coupled.…”

Amino acid-derived bisphenolate palladium complexes as C–C coupling catalysts

“…24,25 These alternative catalysts utilise NHC and other N-, O-or S-donor ligands, including amide, diamine bisphenolate, hydrazone, salen as well as water-soluble sulfosalan ligands. [26][27][28][29][30][31][32][33][34] Despite the popularity of ABP complexes across the board of catalytic processes (featuring an expansive array of transition metals), studies investigating these ligands' coordination to Pd remain scarce. 35 handful of ABP ligands in combination with Pd precursors were reported to successfully catalyse the C-C coupling of phenylboronic acids and aryl bromides.…”

Heteroleptic Palladium(II) Complexes of Thiazolinyl‐picolinamide Derived N∩N∩N Pincer Ligand: An Efficient Catalyst for Acylative Suzuki Coupling Reactions

“…[13,33] However, late transition metal amido complexes have been found to be potential catalysts for many organic transformations including transfer hydrogenation to an unsaturated substrate and coupling reactions (Figure 1). [34][35][36][37][38][39][40][41][42][43][44][45][46] The intrinsic structure of the pincer ligands allows the development of late transition metal amido complexes and to explore their catalytic activities. [47,48] Palladium-catalyzed cross-coupling reactions are important and pioneering methodology for producing the C sp 2 À C sp 2 , C sp 2 À N and C sp 2 À O in the synthesis of industrially important valueadded molecules and other natural products, bioactive compounds, polymers, and materials.…”