(Dimethyl)dioxomolybdenum(VI) complexes: syntheses and catalytic applications

Abstract

Reaction of MoO 2Br 2S 2 complexes [S=THF, CH 3CN] with bidentate nitrogen donor ligands (L 2) leads to complexes of the type MoO 2Br 2L 2 in good yields, L 2=substituted bipyridylphenantroline, 1,4-R 2-diazabutadiene and bipyrimidine. Treatment of the latter complexes with Grignard reagents at low temperatures yields complexes of the general formula MoO 2(CH 3) 2L 2 and MoO 2(C 2H 5) 2(diphenylphenantroline). 1H NMR and IR data are comparatively indifferent to the ligand changes. The 95Mo NMR data of selected complexes reflect the donor capability of the organic ligands. Mass spectroscopy and temperature-dependent 95Mo NMR spectroscopy show a significant stability of the MoN bond. The compound MoO 2(CH 3) 2(bipyrimidine) was additionally examined by single crystal X-ray analysis. The catalytic activity of the MoO 2R 2L 2 complexes in olefin epoxidation with t-butyl hydroperoxide as oxidizing agent is strongly influenced by the nature of the ligand L and its steric bulk in the equatorial plane. The title complexes with a Mo(CH 3) 2 moiety are slightly less active in catalysis than the MoBr 2 precursor compounds. Increase of both reaction time and/or temperature lead to a significant increase in the product yield in all examined cases. At about 90°C catalyst decomposition hampers further product yield increase.