A pentanuclear Er (III) coordination cluster as a catalyst for selective synthesis of 1,2‐disubstituted benzimidazoles

Abstract

A new tridentate ligand (H 3 L) was prepared from the reaction of 6-formyl-2-(hydroxymethyl)-4-tert-butylphenol and 2-amino-4-nitrophenol. The ligand H 3 L and acetylacetone were treated with Er (NO 3 ) 3 Á5H 2 O, which resulted in the formation of a pentanuclear coordination cluster [Er 5 (LH) 4 (acac) 4 (μ 3 -O) (μ 3 -OH)(H 2 O) 2 ] . 5H 2 O (1) (acac = acetylacetonate). Five Er (III) ions are arranged in a nonlinear fashion in 1. Complex 1 was utilized as a catalyst towards the selective synthesis of 1,2-disubstituted benzimidazole derivativesinvolving o-phenylenediamine and different aldehydes. Yields of 1,2-disubstituted benzimidazole derivatives were in the range of 66%-91%. This study demonstrates the first-ever approach to employ a homo-and pentanuclear lanthanide coordination cluster for catalyzing the synthesis of 1,2-disubstituted benzimidazoles.

Field‐Induced SMM Behaviour of Tetranuclear Coordination Clusters with a Cubane [Ni4O4] Core

“…The aromatic protons are found in the expected region at 7.54-6.86 ppm. In the 13 C NMR spectra of H 3 L 2 , the azomethine carbon is observed at 162.6 ppm. The signals for t-butyl group appear at 31.8 and 34.3 ppm, whereas the signal for the hydroxymethyl group could be observed at 58.2 ppm.…”

“…The previously reported Schiff base ligand (H 3 L 1 ) was synthesized by reacting 2-amino-4-nitrophenol and 6-formyl-2-(hydroxymethyl)-4-tert-butylphenol following a reported procedure. [13] The ligand H 3 L 2 was synthesized by a condensation of 2-aminophenol and 6-formyl-2-(hydroxymethyl)-4-tertbutylphenol in methanol under reflux condition (Scheme 2). The ligand H 3 L 2 was isolated as an orange crystalline solid.…”

“…However, a partial solubility of the ligand was observed in dichloromethane (CH 2 Cl 2 ), and chloroform (CHCl 3 ). The ligand H 3 L 2 was fully characterized by FT-IR spectroscopy, mass spectrometry and 1 H, 13 C{ 1 H} NMR spectroscopy. The two tetranuclear coordination clusters, [Ni 4 (HL 1 ) 4 ] • H 2 O (1) and [Ni 4 (HL 2 ) 4 ] • 1.5 dmf (2) were synthesized by treating the ligands H 3 L 1 and H 3 L 2 , respectively with Ni(NO 3 ) 2 • 6H 2 O in dmf solvent using Et 3 N as a base (Scheme 3).…”

“…1 H NMR (400 MHz, DMSO-d 6 ) δ 14.06 (s, 1H, À OH at C-13), 9.76 (s, 1H, À OH at C-1), 8.96 (s, 1H, H-7), 7.54 (d, J = 2.6 Hz, 1H, ArH), 7.46 (d, J = 2.6 Hz, 1H, ArH), 7.36 (m, 1H, ArH), 7.10 (m, 1H, ArH), 6.95 (m, 1H, ArH), 6.86 (m, 1H, ArH), 5.10 (s, 1H, À OH at C-14), 4.58 (s, 2H, À CH 2 OH), (s, 9H, t Bu). 13 C NMR (100 MHz, DMSO-d 6 ) δ 162. 6, 156.5, 151.5, 140.6, 135.2, 129.7, 128.4, 128.3, 127.4, 120.1, 119.8, 118.2, 117.0, 58.2 (À CH 2 OH), 34.3 (À CMe 3 ), 31.8 (À CMe 3 ).…”

Syntheses and exploration of the catalytic activities of organotin(iv) compounds

“…The pro-ligand H 3 L was synthesized via the condensation reaction of 5-(tert-butyl)-2-hydroxy-3-(hydroxymethyl)benzaldehyde and 2-amino-5-nitrophenol in a 1 : 1 molar ratio using methanol as a solvent following our reported method (Scheme 2). 36 H 2 L was synthesized by the reaction of 5-(tert-butyl)-2-hydroxybenzaldehyde with 2-amino-5-nitrophenol under identical reaction conditions as for pro-ligand H 3 L (Scheme 2). The formation of the pro-ligands was confirmed by FT-IR spectroscopy, and 1 H and 13 C{ 1 H} NMR spectroscopy and verified with the reported data for H 3 L. 36 Compounds 1-6 were prepared by the reaction of the pro-ligands (H 3 L and H 2 L) with corresponding organotin(IV) chlorides Ph 2 SnCl 2 , (t-Bu) 2 SnCl 2 and (n-Bu) 2 SnCl 2 using Et 3 N as a base in methanol (Scheme 3).…”