Three novel Bi(iii) complexes with in situ generated anilate ligands: unusual oxidation of cyclohexanedione to dihydroxy benzoquinone

Abstract

Three novel bismuth(III) complexes with in situ synthesized dihydroxybenzoquinone (anilic acid) ligands, namely [Bi(H₃dhbqdc)(H₂dhbqdc)]·2.5dmf (1), [Bi₂(mdhbqdc)(ox)₂(dmf)₄] (2) and [Bi₂(mdhbqdc)₂(ox)(dmf)₄] (3) (H₄dhbqdc = 3,6-dihydroxy-2,5-benzoquinone-1,4-dicarboxylic acid; H₂mdhbqdc = dimethyl 3,6-dihydroxy-2,5-benzoquinone-1,4-dicarboxylate, ox = oxalate, dmf = dimethyl formamide) were prepared under ambient conditions. 1 features 3-D diamond-like structure with 2-D channels filled by dmf molecules. 2 and 3 are geometrically different but topologically identical. 2 shows a brick-wall layer in which ratio of mdhbqdc to ox is 1 : 2 while 3 has a herringbone layer in which the ratio of mdhbqdc to ox is 2 : 1. Bismuth-assisted aerobic in situoxidation of dimethyl 1,4-cyclohexanedione-2,5-dicarboxylate (H₂dmchddc) gave H₂mdhbqdc, which underwent either ester hydrolysis to give H₄dhbqdc or carbon–carbon cleavage to form oxalate. Comparative experiments revealed that both Bi(III) and nitrate are important in the unusual oxidation. Possible reaction pathways for the formation of the dihydroxy benzoquinone (dhbq) ligands from their cyclohexanedione precursor were proposed.