Tetranuclear Palladacycles of 3-Acetyl-7-methoxy-2H-chromen-2-one Derived Schiff Bases: Efficient Catalysts for Suzuki–Miyaura Coupling in an Aqueous Medium

Abstract

Tetranuclear organopalladium­(II) complexes 1–3 and mononuclear complex 4 have been synthesized by the complexation of 3-acetyl-7-methoxy-2H-chromen-2-one derived Schiff bases with potassium tetrachloropalladate K2[PdCl4]. Structural confirmation for the complexes (1–3) has been achieved by single-crystal X-ray diffraction analysis. The ligands are found to bind with the palladium ion through its azomethine nitrogen, thiolate sulfur, and C4 carbon atom of the coumarin moiety subsequent to C–H activation. The monomeric nature of complex 4 was confirmed from its mass spectroscopic data. In complex 4, coordination occurred via the lactone oxygen, azomethine nitrogen, and thiolate sulfur atoms. Computational study has been used to determine the optimized molecular structures of the complexes. An explanation on the energies of their highest occupied and lowest unoccupied molecular orbital levels and their electronic spectra has also been provided on the basis of the theoretical calculations. A systematic study of the application of these complexes as catalysts in Suzuki–Miyaura coupling (SMC) has been done with different aryl halides and phenyl boronic acid in an aqueous medium. Optimization of the reaction indicated that complex 2 exhibits greater efficiency than other complexes. An appreciable yield of the coupled products was observed with the minimum use of catalyst (μmol), and the C–C coupling has been confirmed by GC/GC-MS. An interesting result of our catalyst is the coupling of four different chloroquinolines with phenyl boronic acid to afford the coupled products in good yields.

Thiosemicarbazone Complexes of Transition Metals as Catalysts for Cross-Coupling Reactions

“…Cationic complexes 23 of the type [Pd(dppe)L]NO3 (dppe = 1,2-bis(diphenylphosphino)ethane), where L is a bidentate thiosemicarbazone ligand derived from a p-substituted benzaldehyde were prepared by Thapa et al, and structurally characterised, confirming the formation of N,S-chelated 5membered rings (Figure 4) [117]. The authors hypothesised that, in view of the previously observed Dharani et al reported a series of palladium complexes 22 derived from 3-acetyl-7-methoxy-2H-chromen-2-one thiosemicarbazones (Figure 3) [115]. Three of the products (22a-c) proved to be tetranuclear complexes in which ligands are bonded via S, N, and C, cyclometallation having taken place by activation of the ortho-C-H bond.…”

“…They were found to have an initial size of 1.5-2.0 nm, but after successive runs they aggregated to larger particles with lower activity. Dharani et al reported a series of palladium complexes 22 derived from 3-acetyl-7-methoxy-2Hchromen-2-one thiosemicarbazones (Figure 3) [115]. Three of the products (22a-c) proved to be tetranuclear complexes in which ligands are bonded via S, N, and C, cyclometallation having taken place by activation of the ortho-C-H bond.…”

Chroman‐4‐one‐Based Amino Bidentate Ligand: An Efficient Ligand for Suzuki‐Miyaura and Mizoroki‐Heck Coupling Reactions in Aqueous Medium

“…[22] Recently, Rathinasabapathi Prabhakaran et al reported tetranuclear palladacycles of 3-acetyl-7-methoxy-2Hchromen-2-one derived Schiff bases, and was found that this complex is very effective for Suzuki-Miyaura coupling in an aqueous medium. [23] Based on the literature evidences, we herein synthesized amino chroman-4-one based amino ligands (L1-L10) and have shown uses in the Suzuki-Miyaura and the Mizoroki-Heck cross-coupling reactions with Pd(II)-salt in aqueous medium under mild reaction conditions.…”

Synthesis and X-ray Diffraction Study of thiosemicarbazone Palladacycles with dppm

“…On the one hand, they are useful in synthetic organic chemistry, as catalysts in many reactions with formation of C-C and C-N bonds [1][2][3][4][5][6].…”