Synthesis, Structural Elucidation, and Catalytic Properties in Olefin Epoxidation of the Polymeric Hybrid Material [Mo3O9(2-[3(5)-Pyrazolyl]pyridine)](n)

abstract

The reaction of [MoO2Cl2(pzpy)] (1) (pzpy = 2-[3(5)-pyrazolyl]pyridine) with water in an open reflux system (16 h), in a microwave synthesis system (120 degrees C, 2 h), or in a Teflon-lined stainless steel digestion bomb (100 degrees C, 19 h) gave the molybdenum oxide/pyrazolylpyridine polymeric hybrid material [Mo3O9(pzpy)](n) (2) as a microcrystalline powder in yields of 72-79%. Compound 2 can also be obtained by the hydrothermal reaction of MoO3, pzpy, and H2O at 160 degrees C for 3 d. Secondary products isolated from the reaction solutions included the salt (pzpyH)(2)(MoCl4) (3) (pzpyH = 2-[3(5)-pyrazolyl]pyridinium), containing a very rare example of the tetrahedral MoCl42- anion, and the tetranuclear compound [Mo4O12(pzpy)(4)] (4). Reaction of 2 with excess tert-butylhydroperoxide (TBHP) led to the isolation of the oxodiperoxo complex [MoO(O-2)(2)(pzpy)(4)] (5). Single-crystal X-ray structures of 3 and 5 are described. Fourier transform (FT)-IR and FT Raman spectra for 1, 4, and 5 were assigned based on density functional theory calculations. The structure of 2 was determined from synchrotron powder X-ray diffraction data in combination with other physicochemical information. In 2, a hybrid organic inorganic one-dimensional (1D) polymer, (1)(infinity)[Mo3O9(pzpy)], is formed by the connection of two very distinct components: a double ladder-type inorganic core reminiscent of the crystal structure of MoO3 and 1D chains of corner-sharing distorted {MoO4N2} octahedra. Compound 2 exhibits moderate activity and high selectivity when used as a (pre)catalyst for the epoxidation of cis-cyclooctene with TBHP. Under the reaction conditions used, 2 is poorly soluble and is gradually converted into 5, which is at least partly responsible for the catalytic reaction.

keywords

PHOSPHINE OXIDE LIGANDS; CRYSTAL-STRUCTURE; HYDROTHERMAL SYNTHESIS; DIOXOMOLYBDENUM(VI) COMPLEXES; MOLYBDENUM(VI) COMPLEX; MOLECULAR-STRUCTURE; PERFORMANCE; DERIVATIVES; DIOXO; DICHLORODIOXOMOLYBDENUM(VI)

subject category

Chemistry

authors

Amarante, TR; Neves, P; Gomes, AC; Nolasco, MM; Ribeiro-Claro, P; Coelho, AC; Valente, AA; Paz, FAA; Smeets, S; McCusker, LB; Pillinger, M; Goncalves, IS

Groups

G1 - Porous Materials and Nanosystems
G4 - Renewable Materials and Circular Economy
G6 - Virtual Materials and Artificial Intelligence

Projects

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

Centre for Research in Ceramics and Composite Materials - CICECO (LA0011: 2013-2014) (PEst-C/CTM/LA0011/2013)

acknowledgements

The Portuguese group is grateful to the Fundacao para a Ciencia e a Tecnologia (FCT), QREN, Fundo Europeu de Desenvolvimento Regional (FEDER), COMPETE, and the European Union for funding (R&D Projects No. PTDC/EQU-EQU/121677/2010 and No. PDTC/QUI-QUI/098098/2008 (FCOMP-01-0124-FEDER-010785)). The Swiss group thanks the Swiss National Science Foundation for funding. The Associate Laboratory CICECO (PEst-C/CTM/LA0011/2013) is acknowledged for continued support and funding. The FCT and the European Union are acknowledged for a postdoctoral Grant to P.N. (SFRH/BPD/73540/2010) cofunded by MCTES and the European Social Fund through the program POPH of QREN, and for a Ph.D. Grant to T.R.A. (SFRH/BD/64224/2009). We thank the Diamond Light Source (DLS) for access to beamline 111 (EE8234) that contributed to the results presented here, and also Dr. Stephen Thomson for help during the experiment. The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under Grant Agreement No. 226716. F.A.A.P. also wishes to thank Chevron (Richmond, CA, USA) for funding a research visit to ETH Zurich.