Synthesis, Characterisation and Catalytic Application of Oxidorhenium Complexes Bearing H-Spirophosphorane Ligands

Abstract

The coordination properties of the H-spirophosphorane ligands HP(OCMe₂CMe₂O)₂ (L1), HP(OCHMeCHMeO)₂ (L2) and HP(OCH₂CMe₂NH)₂ (L3) towards rhenium have been studied, and the complexes cis-[ReOCl₂{P(OCMe₂CMe₂O)OCMe₂CMe₂O}pic] (1a), cis- and trans-[ReOCl₂{P(OCMe₂CMe₂O)OCMe₂CMe₂O}lut] (2a and 2b), cis- and trans-[ReOBr₂{P(OCMe₂CMe₂O)OCMe₂CMe₂O}PPh₃] (3a and 3b), [nBu₄N][ReOCl₃{P(OCMe₂CMe₂O)OCMe₂CMe₂O}] (4), cis-[ReOCl₂{P(OCHMeCHMeO)OCHMeCHMeO}py] (5), and [ReOCl₃{P(OCH₂CMe₂NH)OCH₂CMe₂NH₂}] (6) have been prepared. The H-spirophosphoranes coordinate to the rhenium moiety as bidentate, ionic chelating ligands in 1–5 and as a molecular chelating ligand in 6. The chemical compositions of all the complexes were established by spectroscopic methods and the molecular structures of 1a, 2b, 3a, 3b, 5 and 6 were determined by single-crystal X-ray diffraction. It was proved that some of the complexes 1–6 and their previously obtained congeners are very good cocatalyst precursors for the oxidation of aldehydes using molecular oxygen as oxidant and N-hydroxyphthalimide as catalyst. The impact of the structures of the complexes on their catalytic activity was studied. The presence of spirophosphorane ligands in the structures seems to be essential for stabilising the active form of the cocatalyst.