Dichlorodioxomolybdenum(VI) complexes bearing oxygen-donor ligands as olefin epoxidation catalysts

abstract

Treatment of the solvent adduct [MoO2Cl2(THF)(2)] with either 2 equivalents of N,N-dimethylbenzamide (DMB) or 1 equivalent of N,N'-diethyloxamide (DEO) gave the dioxomolybdenum(VI) complexes [MoO2Cl2(DMB)(2)] (1) and [MoO2Cl2(DEO)] (2). The molecular structures of 1 and 2 were determined by single-crystal X-ray diffraction. Both complexes present a distorted octahedral geometry and adopt the cis-oxo, trans-Cl, cis-L configuration typical of complexes of the type [MoO2X2(L)n], with either the monodentate DMB or bidentate DEO oxygen-donor ligands occupying the equatorial positions trans to the oxo groups. The complexes were applied as homogeneous catalysts for the epoxidation of olefins, namely cis- cyclooctene (Cy), 1-octene, trans-2-octene, a-pinene and (R)-(+)-limonene, using tert-butylhydroperoxide (TBHP) as oxidant. In the epoxidation of Cy at 55 degrees C, the desired epoxide was the only product and turnover frequencies in the range of ca. 3150-3200 mol mol(Mo)(-1) h(-1) could be reached. The catalytic production of cyclooctene oxide was investigated in detail, varying either the reaction temperature or the cosolvent. Complexes 1 and 2 were also applied in liquid-liquid biphasic catalytic epoxidation reactions by using an ionic liquid of the type [C(4)mim][X] (C(4)mim = 1-n-butyl-3-methylimidazolium; X = NTf2, BF4 or PF6] as a solvent to immobilise the metal catalysts. Recycling for multiple catalytic runs was achieved without loss of activity.

keywords

PHOSPHINE OXIDE LIGANDS; BIDENTATE LEWIS-BASE; CRYSTAL-STRUCTURES; MOLECULAR-STRUCTURE; ADDITION-COMPOUNDS; MOLYBDENUM(VI) COMPLEXES; DIOXOMOLYBDENUM(VI)-BIPYRIDINE COMPLEXES; SPECTROSCOPIC CHARACTERIZATION; ORGANOMOLYBDENUM(VI); REACTIVITY

subject category

Chemistry

authors

Oliveira, TSM; Gomes, AC; Lopes, AD; Lourenco, JP; Paz, FAA; Pillinger, M; Goncalves, IS

Groups

G1 - Porous Materials and Nanosystems

Projects

Use of molecular containers to modify metallocene-based catalysts (PTDC/QEQ-SUP/1906/2012)

Desulfurization of diesel using green heterogeneous oxidative catalytic processes (PTDC/EQU-EQU/121677/2010)

CICECO - Aveiro Institute of Materials (UID/CTM/50011/2013)

acknowledgements

We acknowledge funding by FEDER (Fundo Europeu de Desenvolvimento Regional) through COMPETE (Programa Operacional Factores de Competitividade). National funding through the FCT (Fundacao para a Ciencia e a Tecnologia) within the projects FCOMP-01-0124-FEDER-029779 (FCT ref. PTDC/QEQ-SUP/1906/2012, including research grants to A.C.G. (ref. BPD/UI89/4864/2014) and T.S.M.O.) and FCOMP-01-0124-FEDER-020658 (FCT ref. PTDC/EQU-EQU/121677/2010) is thanked. This work was developed in the scope of the project CICECO - Aveiro Institute of Materials (FCT ref. UID/CTM/50011/2013), financed by national funds through the FCT/MEC and co-financed by FEDER under the PT2020 Partnership Agreement. The FCT and CICECO are acknowledged for financial support towards the purchase of the single-crystal diffractometer.