First Dioxomolybdenum(VI) Complexes Containing Chiral Oxazoline Ligands: Synthesis, Characterization and Catalytic Activity

The cis-[MoO2(N,O)2] complexes containing chiral oxazoline ligands (N,O) [1: N,O = A, (4′R)-2-(4′-ethyl-3′,4′-dihydroxazol-2′-yl)phenolato; 2: N,O = B, (4′S)-2-(4′-isopropyl-3′,4′-dihydroxazol-2′-yl)phenolato] were synthesised and characterised, both in solution and in the solid state. These pseudo-octahedral neutral complexes were obtained as mixtures of diastereomers due to the chirality of the ligand and at the metal centre (Δ or Λ). Theoretical DFT calculations corroborate the isomer distribution. For complex 1, the two major diastereomers, Δ-N-cis-1 and Λ-N-trans-1, crystallised independently and the molecular structures were determined by single-crystal X-ray diffraction. NMR experiments at 800 MHz for 2 allowed the determination of the isomeric composition in solution. The product distribution depends on the coordinating nature of the solvent. Complexes 1 and 2 catalyse the oxidation of triphenylphosphane and styrene.