A Dinuclear Oxoperoxomolybdenum(VI) Complex, [Mo2O6(OH)2(Pyridine Oxide Tetrazolate)2], Displaying the {MoO(O2)(μ-OH)2MoO(O2)}0 Core, and its Catalytic Performance in Olefin Epoxidation

abstract

The dinuclear oxoperoxomolybdenum(VI) complex [Mo2O6(OH)(2)(pto)(2)] (1), containing a rare example of a hydroxo-bridged {MoO(O-2)(mu-OH)(2)MoO(O-2)}(0) core, has been synthesized via the reaction of MoO3 with H2O2 and 5-(2-pyridyl-1-oxide)tetrazole (Hpto) and characterized by elemental analysis and ICP-OES, infrared and Raman spectroscopies, single crystal X-ray diffraction, nuclear magnetic resonance, and mass spectrometry. Compound 1 is an effective homogeneous catalyst for olefin epoxidation. The type of oxidant, namely tert-butyl hydroperoxide (TBHP) or H2O2, influences the catalytic performance. For cis-cyclooctene epoxidation, 1/TBHP led to 100% conversion after 4 h at 70 degrees C, and 1/H2O2 led to 80% conversion after 24 h at 70 degrees C. Catalyst recycling is feasible using an ionic liquid solvent with high affinity for the catalyst, and product separation via an extraction process. The catalytic potential of 1 was further explored for the chemical valorization of biomass-derived fatty acid methyl esters (FAMEs), namely C18-unsaturated methyl oleate and methyl linoleate derived from vegetable oils. The reaction of FAMEs/TBHP gave mainly epoxidized FAMEs (>97% selectivity at high conversions of 97-100%, at 70 degrees C). This catalyst is a rare example of a dinuclear organo-oxomolybdenum(VI) compound with the ability to epoxidize FAMEs.

keywords

DIOXOMOLYBDENUM(VI) COMPLEXES; MOLYBDENUM(VI) COMPLEXES; HYDROGEN-PEROXIDE; CRYSTAL-STRUCTURE; LIGANDS SYNTHESIS; OXO-MOLYBDENUM; OXIDATION; CYCLOOCTENE; 5-(2-PYRIDYL-1-OXIDE)TETRAZOLE; OCTAMOLYBDATE

subject category

Chemistry

authors

Nunes, MS; Neves, P; Gomes, AC; Mendes, RF; Paz, FAA; Lopes, AD; Da Silva, JP; Pillinger, M; Valente, AA; Gonçalves, IS

Groups

G1 - Porous Materials and Nanosystems
G4 - Renewable Materials and Circular Economy

Projects

CICECO - Aveiro Institute of Materials (UIDB/50011/2020)

CICECO - Aveiro Institute of Materials (UIDP/50011/2020)

Associated Laboratory CICECO-Aveiro Institute of Materials (LA/P/0006/2020)

acknowledgements

This work was developed within the scope of the project CICECO-Aveiro Institute of Materials (UIDB/50011/2020 (DOI: 10.54499/UIDB/50011/2020), UIDP/50011/2020 (DOI: 10.54499/UIDP/50011/2020), and LA/P/0006/2020 (DOI: 10.54499/LA/P/0006/2020)), financed by national funds through the FCT (Fundacao para a Ciencia e a Tecnologia)/MCTES (Ministerio da Ciencia, Tecnologia e Ensino Superior) (PIDDAC). This study received Portuguese national funds from the FCT through projects UIDB/04326/2020 (DOI: 10.54499/UIDB/04326/2020), UIDP/04326/2020 (DOI: 10.54499/UIDP/04326/2020), and LA/P/0101/2020 (DOI: 10.54499/LA/P/0101/2020) and from the operational programs CRESC Algarve 2020 and COMPETE 2020 through project EMBRC.PT ALG-01-0145-FEDER-022121. The authors acknowledge the support of the project with ref. 2023.14213.PEX, financed by national funds through the FCT/MCTES (PIDDAC). M.S.N. acknowledges the FCT for a Ph.D. grant (ref. 2021.06403.BD, DOI 10.54499/2021.06403.BD; State Budget, European Social Fund within the framework of PORTUGAL2020, namely through the Centro 2020 Regional Operational Program). A.C.G. (ref. CEECIND/02128/2017, DOI 10.54499/CEECIND/02128/2017/CP1459/CT0039) and R.F.M. (ref. CEECIND/00553/2017, DOI 10.54499/CEECIND/00553/2017/CP1459/CT0034) thank the FCT/MCTES for research positions funded through the Individual Call to Scientific Employment Stimulus.