Synthesis, Structural Elucidation, and Catalytic Properties in Olefin Epoxidation of the Polymeric Hybrid Material [Mo 3 O 9 (2-[3(5)- Pyrazolyl]pyridine)] n Tatiana R. Amarante, † Patrícia Neves, † Ana C. Gomes, † Mariela M. Nolasco, † Paulo Ribeiro-Claro, † Ana C. Coelho, † Anabela A. Valente, † Filipe A. Almeida Paz,* ,† Stef Smeets, ‡ Lynne B. McCusker, ‡ Martyn Pillinger, † and Isabel S. Gonc ̧ alves* ,† † Department of Chemistry, CICECO, University of Aveiro, Campus Universita ́ rio de Santiago, 3810-193 Aveiro, Portugal ‡ Laboratory of Crystallography, ETH Zü rich, CH-8093, Zü rich, Switzerland * S Supporting Information ABSTRACT: The reaction of [MoO 2 Cl 2 (pzpy)] (1) (pzpy = 2- [3(5)-pyrazolyl]pyridine) with water in an open reflux system (16 h), in a microwave synthesis system (120 °C, 2 h), or in a Teflon- lined stainless steel digestion bomb (100 °C, 19 h) gave the molybdenum oxide/pyrazolylpyridine polymeric hybrid material [Mo 3 O 9 (pzpy)] n (2) as a microcrystalline powder in yields of 72− 79%. Compound 2 can also be obtained by the hydrothermal reaction of MoO 3 , pzpy, and H 2 O at 160 °C for 3 d. Secondary products isolated from the reaction solutions included the salt (pzpyH) 2 (MoCl 4 ) (3) (pzpyH = 2-[3(5)-pyrazolyl]pyridinium), containing a very rare example of the tetrahedral MoCl 4 2− anion, and the tetranuclear compound [Mo 4 O 12 (pzpy) 4 ](4). Reaction of 2 with excess tert-butylhydroperoxide (TBHP) led to the isolation of the oxodiperoxo complex [MoO(O 2 ) 2 (pzpy)] (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 [Mo 3 O 9 (pzpy)], is formed by the connection of two very distinct components: a double ladder-type inorganic core reminiscent of the crystal structure of MoO 3 and 1D chains of corner-sharing distorted {MoO 4 N 2 } 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. ■ INTRODUCTION Among the various oxyhalides of molybdenum, dichlorodioxomolybdenum(VI), MoO 2 Cl 2 , has received much attention as a starting material for preparing numerous molybdenum compounds and as a catalyst in organic transformations. 1 Most of the synthetic chemistry has dealt with the synthesis of adducts with the general formula [MoO 2 Cl 2 (L) n ], where L is a mono- (n = 2) or bidentate (n = 1) ligand such as a nitrogen or oxygen-donating solvent molecule (e.g., tetrahydrofuran, dimethylsulfoxide, dimethylfor- mamide, acetonitrile), 2 2,2′-bipyridines, 3 phosphine oxides, 4 thio- and seleno-ethers. 5 The stability of these compounds toward moisture varies from quite stable in the case of the bipyridine adducts to extremely sensitive in the case of the thio- and seleno-ether complexes. Even for the most stable complexes the Mo−Cl bond is susceptible to hydrolysis. Thus, in the presence of residual or small amounts of water, [MoO 2 Cl 2 (L) n ] complexes have been shown to dimerize, leading to the isolation of dioxo(μ-oxo)molybdenum(VI) complexes with the general formula [Mo 2 O 4 (μ 2 -O)Cl 2 (L) n ]. 2c,6 Several higher nuclearity oxomolybdenum(VI) compounds have been isolated after the reaction of dichlorodioxomolybdenum(VI) complexes with excess water, namely the hexamolybdate isopolyanion in [(H 3 O)(18-crown- 6)] 2 [Mo 6 O 19 ](L=H 2 O in the precursor complex), 7 the octanuclear complex [Mo 8 O 22 (OH) 4 (di-tBu-bipy) 4 ] (di-tBu- bipy = 4,4′-di-tert-butyl-2,2′-bipyridine), 8 and the polymeric materials {[MoO 3 (bipy)][MoO 3 (H 2 O)]} n 9 (bipy = 2,2′- bipyridine) and [Mo 2 O 6 (HpypzA)] (HpypzA = [3-(pyridi- nium-2-yl)-1H-pyrazol-1-yl]acetate). 10 The hydrolysis and condensation of dichlorodioxomolybdenum(VI) complexes is therefore an interesting, yet still largely unexplored, pathway toward molybdenum oxide-based organic−inorganic hybrid materials, which are of interest due to their potential application Received: December 10, 2013 Published: February 12, 2014 Article pubs.acs.org/IC © 2014 American Chemical Society 2652 dx.doi.org/10.1021/ic403033j | Inorg. Chem. 2014, 53, 2652−2665