Tripodal Trimanganese(III) Complexes of New Unsymmetrical Pentadentate Ligands Derived from 2‐(Salicylideneamino)phenol: Syntheses, Crystal Structures and Properties

Abstract

Trinuclear manganese(III) complexes of new unsymmetrical pentadentate ligands, 6‐hydroxy‐2‐(2‐hydroxyphenyl)‐5‐(salicylideneamino)benzoxazole (H3L1) and 5‐(5,6‐benzosalicylideneamino)‐6‐hydroxy‐2‐(2‐hydroxynaphthyl)benzoxazole (H3L2), [Mn3(L1)3(CH3OH)3] (1) and [Mn3(L2)3(dmf)(CH3OH)(H2O)] (2) (dmf = N,N‐dimethylformamide), have been prepared. The structures of the ligands H3L1, H3L2 and complex 1 were determined by X‐ray crystallography, which revealed that the ligands have two distant chelating sites. The molecular structure of 1 is regarded as a tripodal pyramid with a cavity of about 3 Å diameter. Each MnIII ion is coordinated by ONO atoms from a tridentate Schiff base site and ON atoms from a benzoxazole site of two respective H3L1 ligands. The intramolecular Mn···Mn distances for 1 are in the range 8.0683–8.1791 Å, and the nearest intermolecular Mn···Mn distance, 5.7824(15) Å, is shorter than theintramolecular values. Magnetic measurements of 1 indicate that weak antiferromagnetic interactions (J = –0.2 cm–1, g = 2.0) are dominant in the trinuclear manganese(III) core. Cyclic voltammogram of 1 in dmf showed obscure redox couples assigned to two single‐electron transfer processes.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Versatile Chemical Transformations of Benzoxazole Based Ligands on Complexation with 3d-Metal Ions

“…According to the structure of HL1 and other literature examples ,,,, the oxazole cyclization can be expected; however, the presence of two di- tert -butyl aromatic rings suggests that only one moiety of expected Schiff base was cyclized. A similar case with unsymmetrical benzoxazole cyclization has been reported for the reaction of 2-hydroxybenzaldehyde and 4,6-diaminoresorcinol in methanol . On the other hand it has been reported that the condensation of DTBBQ with ethylenediamine or 2,2-dimethylpropylenediamine under aerobic conditions in acetonitrile only gives the symmetrical Schiff bases or their reduced amino form but no benzoxazole cyclization occurs in these conditions.…”

“…A similar case with unsymmetrical benzoxazole cyclization has been reported for the reaction of 2hydroxybenzaldehyde and 4,6-diaminoresorcinol in methanol. 43 On the other hand it has been reported that the condensation of DTBBQ with ethylenediamine or 2,2-dimethylpropylenediamine under aerobic conditions in acetonitrile only gives the symmetrical Schiff bases or their reduced amino form but no benzoxazole cyclization occurs in these conditions.…”

“…In this context and also regarding our interest in single-molecule magnets (SMM), we investigated the coordination ability of benzoxazoles formed by condensation/oxidation reaction between 3,5-di- tert -butyl- o -benzoquinone (DTBBQ) and amines. − We have previously reported that the reaction of ethanolamine with DTBBQ gives 5,7-di- tert -butyl-2-methylenhydroxylbenzoxazole. This ligand was formed in situ in a one pot reaction with a mixture of Cu(II) and Ln(III) salts to give [Ln 4 Cu 8 ] systems .…”

Mononuclear and polynuclear complexes with a side-off compartmental Schiff base

“…2a) or one ethanol moiety (Fig. 2b) These data offer additional examples to those already reported in the recent literature [31,32] of the versatility of the Schiff bases to rearrange the coordination moiety to accommodate better the different metal ions. The experimental conditions are certainly relevant in determining the ligand rearrangement or modifications and hence the complexation reaction and the configuration about the metal ion.…”

Crystal Structure of Dichloro{2-(quinolin-2-yl)-4H-benzo[d][1,3]oxazine}cobalt(II)

“…The formation of this ligand is thought to be due to the nucleophilic addition of benzyl alcohol to the imine carbon and the subsequent Co-catalyzed air oxidation, similar to the formation of benzoxazole from Schiff-base ligands containing phenol groups. 9,10 Since the benzo-1,3-oxazines flamework is expected to be applied as an antianginal and antirheumatic drug, 11,12 1 may contribute to the drug design. The crystal packing diagram of 1 is shown in Fig.…”