Preparation and properties of dinuclear dioxomolybdenum(VI) complexes with ONO-ONO-type hexadentate Schiff base ligands

Preparation and properties of dinuclear cis-dioxomolybdenum(VI) complexes containing ONO-ONO-type hexadentate Schiff bases derived from 2,5-dihydroxyterephthalaldehyde and aminoalcohols in a 1:2 molar ratio are reported. When 2-amino-2methyl-1,3-propanediol was used as the aminoalcohol, the H-1 NMR spectrum of the complex showed two sets of resonances, indicating the presence of two isomers. The origin of the isomerism was elucidated by variable-temperature H-1 NMR spectroscopy and by comparing the H-1 NMR spectrum with those of the analogous dinuclear complexes derived from (1R,2S)- and (1S,2R)-norephedrine and with those of the corresponding mononuclear complexes. The Schiff base ligand derived from 2,5-dihydroxyterephthalaldehyde and 2-amino-2-methyl-1,3-propanediol contains two prochiral carbon atoms, which become chiral (R and S) upon coordination. The combination of these two chiral centers generates three stereoisomers, RR, SS, and RS (= SR), and the NMR characteristics were accounted for by these isomers. (C) 2000 Elsevier Science B.V. All rights reserved.