Palladium(II) 9,10-phenanthrenequinone N-substituted thiosemicarbazone/semicarbazone complexes as efficient catalysts for N-arylation of imidazole

Abstract

A series of palladium complexes, [PdCl(L 1-4 )] (1-4) (L 1 = 9,10-phenanthrenequinone thiosemicarbazone, L 2 = 9,10-phenanthrenequinone methylthiosemicarbazone, L 3 = 9,10-phenanthrenequinone phenylthiosemicarbazone and L 4 = 9,10-phenanthrenequinone semicarbazone), have been synthesized and characterized by elemental analyses, UV-Vis, FT-IR, 1 H and 13 C NMR and ESI-Mass spectroscopic methods. The catalytic efficiency of the synthesized complexes was examined against N-arylation of imidazole. The system works well with the electron-rich, -neutral, and -deficient aryl halides to afford the products in good to excellent yields. Sterically congested aryl halides and heteroaryl halides have also been used as substrates to provide N-arylated heterocycles. In addition, this methodology can be applicable to other substrates with N-containing heterocycles.

Transition Metal—Catalyzed Cross Coupling Reactions

“…Aryl bromides and iodides gave good conversions in the reaction with primary or secondary amines in either dioxane at 100 N-arylation of heterocycles can been achieved by using a palladium catalyst derived from 9,10phenanthrenequinone thiosemicarbazones 37 (Figure 7) as well as the corresponding semicarbazone as reported by Anitha et al [138]. The ligand in these complexes is tridentate monoanionic and the most efficient one in initial screening experiments was that derived from phenanthrenequinone N- N-arylation of heterocycles can been achieved by using a palladium catalyst derived from 9,10phenanthrenequinone thiosemicarbazones 37 (Figure 7) as well as the corresponding semicarbazone as reported by Anitha et al [138]. The ligand in these complexes is tridentate monoanionic and the most efficient one in initial screening experiments was that derived from phenanthrenequinone N-Scheme 38.…”

“…Apart from the aforementioned monophosphine complexes, a recent study reports the synthesis of a cationic Pd thiosemicarbazone complex 23 (R = OCH3; see in Figure 4) containing a diphosphine which, apart from catalysing the Suzuki-Miyaura reaction (see above) was also found to be effective in the Buchwald-Hartwig arylation [117]. Aryl bromides and iodides gave good conversions in the reaction with primary or secondary amines in either dioxane at 100 N-arylation of heterocycles can been achieved by using a palladium catalyst derived from 9,10phenanthrenequinone thiosemicarbazones 37 (Figure 7) as well as the corresponding semicarbazone as reported by Anitha et al [138]. The ligand in these complexes is tridentate monoanionic and the most efficient one in initial screening experiments was that derived from phenanthrenequinone N- N-arylation of heterocycles can been achieved by using a palladium catalyst derived from 9,10phenanthrenequinone thiosemicarbazones 37 (Figure 7) as well as the corresponding semicarbazone as reported by Anitha et al [138].…”

N‐Arylation of Imidazoles: An Overview

“…Further they found that this palladium (II) complexes was found efficient in the synthesis of N-aryl imidazoles. [51] To standardise the reaction condition, an initial reaction was carried out between imidazole and iodobenzene using various bases and solvents. Excellent formation of product was obtained in shorter reaction time, when 9,10phenanthrenequinone methylthiosemicarbazone (0.75 M%) was used as catalyst in presence of KOH as base in DMSO 110°C for 10 h (Scheme 28).…”

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

“…The ligand in these complexes is tridentate monoanionic and the most efficient one in initial screening experiments was that derived from phenanthrenequinone N- N-arylation of heterocycles can been achieved by using a palladium catalyst derived from 9,10phenanthrenequinone thiosemicarbazones 37 ( Figure 7) as well as the corresponding semicarbazone as reported by Anitha et al [138]. The ligand in these complexes is tridentate monoanionic and the most efficient one in initial screening experiments was that derived from phenanthrenequinone N- N-arylation of heterocycles can been achieved by using a palladium catalyst derived from 9,10-phenanthrenequinone thiosemicarbazones 37 ( Figure 7) as well as the corresponding semicarbazone as reported by Anitha et al [138]. The ligand in these complexes is tridentate monoanionic and the most efficient one in initial screening experiments was that derived from phenanthrenequinone N-methylthiosemicarbazone.…”