A Comparative Study of Molybdenum Carbonyl and Oxomolybdenum Derivatives Bearing 1,2,3-Triazole or 1,2,4-Triazole in Catalytic Olefin Epoxidation

abstract

The molybdenum(0)-carbonyl-triazole complexes [Mo(CO)(3)(L)(3)] [L = 1,2,3-triazole (1,2,3-trz) or 1,2,4-triazole (1,2,4-trz)] have been prepared and examined as precursors to molybdenum(VI) oxide catalysts for the epoxidation of cis-cyclooctene. Reaction of the carbonyl complexes with the oxidant tert-butyl hydroperoxide (TBHP) (either separately or in situ) gives oxomolybdenum(VI) hybrid materials that are proposed to possess one-dimensional polymeric structures in which adjacent oxo-bridged dioxomolybdenum(VI) moieties are further linked by bidentate bridging triazole (trz) ligands. A pronounced ligand influence on catalytic performance was found and the best result (quantitative epoxide yield within 1 h at 70 degrees C) was obtained with the 1,2,3-triazole oxomolybdenum(VI) hybrid. Both molybdenum oxide-triazole compounds displayed superior catalytic performance in comparison with the known hybrid materials [MoO3(trz)(0.5)], which have different structures based on organic-inorganic perovskite-like layers. With aqueous H2O2 as the oxidant instead of TBHP, all compounds were completely soluble and active. A pronounced ligand influence on catalytic performance was only found for the hybrids [MoO3(trz)(0.5)], and only the 1,2,4-trz compound displayed reaction-induced self-precipitation behavior. An insight into the type of solution species that may be involved in the catalytic processes with these compounds was obtained by separately treating [MoO3(1,2,4-trz)(0.5)] with excess H2O2, which led to the crystallization of the complex (NH4)(1.8)(H3O)(0.2)[Mo2O2((2)-O)(O-2)(4)(1,2,4-trz)]H2O. The single-crystal X-ray investigation of this complex reveals an oxo-bridged dinuclear structure with oxodiperoxo groups being further linked by a single triazole bridge.

keywords

TERT-BUTYL HYDROPEROXIDE; DIOXOMOLYBDENUM(VI) COMPLEXES; COORDINATION CHEMISTRY; HYDROTHERMAL SYNTHESIS; CRYSTAL-STRUCTURES; OXIDATION; MONONUCLEAR; PRECURSORS; TAUTOMERISM; REACTIVITY

subject category

Biochemistry & Molecular Biology; Chemistry

authors

Nogueira, LS; Neves, P; Gomes, AC; Amarante, TA; Paz, FAA; Valente, AA; Goncalves, IS; Pillinger, M

Groups

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

Projects

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

Sistemas ativados por estímulos para a terapia com monóxido de carbono (SASCOT)

Conversao catalitica de olefinas derivadas da biomassa (BiOle_AcidOxCat)

acknowledgements

This work was carried out with the support of CICECO-Aveiro Institute of Materials-POCI-01-0145-FEDER-007679 (Foundation for Science and Technology (FCT) Ref. UID/CTM/50011/2013), the CENTRO 2020 Regional Operational Program (Project CENTRO-01-0145-FEDER-028031), and the COMPETE 2020 Operational Thematic Program for Competitiveness and Internationalization (POCI-01-0145-FEDER-030075), co-financed by the European Union (EU) through the European Regional Development Fund under the Portugal 2020 Partnership Agreement, and by national funds through the FCT in its state budget component (OE). The FCT and the EU are acknowledged for a PhD grant to L.S.N. (PD/BD/109666/2015), and post-doctoral grants to P.N. (SFRH/BPD/110530/2015), A.C.G. (SFRH/BPD/108541/2015) and T.R.A. (SFRH/BPD/97660/2013), co-funded by MCTES and the European Social Fund through the program POPH of QREN.