Two hydrogen-bond-cross-linked molybdenum (VI) network polymers: synthesis, crystal structures and cyclooctene epoxidation with H2O2

Abstract

Two molybdenum (VI) hydrogen-bonded network polymers [MoO 2 F 4 ]Á(4,4 0 -H 2 bpd)(H 2 O) 2 (1) and [MoO 2 Cl 3 (H 2 O)]Á(4,4 0 -H 2 bpd)Cl (2) (bpd = bipiperidine) have been synthesized and examined as catalysts for epoxidation of cyclooctene. Complexes of the Mo compounds containing the bpd ligand are prepared and characterized by infrared spectroscopy, thermogravimetric and elemental analyses. They have been structurally characterized by single crystal X-ray diffraction analysis. The structures of both the complexes are shown to be comprised of molybdenum and two protonated N-ligand cations that have resulted in a crosslinked hydrogen-bonded network structure. These complexes are applicable as catalysts for the cis-cyclooctene epoxidation reactions with hydrogen peroxide as a source of oxygen and NaHCO 3 as a cocatalyst. It has been observed that the formation of the oxidant peroxymonocarbonate ion, HCO 4 -by hydrogen peroxide and bicarbonate enhances the epoxidation reaction. Both the complexes have exhibited a good activity and a very high selectivity for the formation of cyclooctene oxide.

Remote Charge Effects on the Oxygen-Atom-Transfer Reactivity and Their Relationship to Molybdenum Enzymes

“…The IR spectra of compound 2 exhibits ν as (MoO) and ν s (MoO) at 951 and 912 cm –1 , respectively, reflecting contributions from the [Tpm*MoO 2 Cl] + cation. For complex 1 , the ν as (MoO) and ν s (MoO) stretches appear at 944 and 905 cm –1 , respectively, with contributions from both the [Tpm*MoO 2 Cl] + cation and the [MoO 2 Cl 3 ] − anion. , Notably, ν­(MoO) values for the [Tpm*MoO 2 Cl] + cation in complexes 1 and 2 are only ∼2% greater than those for neutral Tp*MoO 2 Cl and fall into the typical range of asymmetric and symmetric MoO stretching frequencies that have been previously reported (Table ). For complex 2 , a very strong peak at 1071 cm –1 is assigned to the vibrational mode with Cl–O stretching character.…”

Stereochemistry of Complexes with Double and Triple Metal–Ligand Bonds: A Continuous Shape Measures Analysis

“…Experimental and normalized coordination polyhedra of [MoO 2 F 4 ] 2– (ihotop, left), trans -[WCMe(CO) 4 I] (imcbcw, center), and fac- [ReO 3 (Me 3 tacn)] (pidtol, right) …”

“…Since the metal atoms in these complexes are in the equatorial plane (the one that contains the two MO bonds), we analyze first the equatorial MO 2 L 2 group to check whether the distortion from the ideal octahedron within that plane corresponds to an off-center shift of the metal atom toward the O 2 edge that would leave a regular O 2 L 2 square (Figure b), or to a bond shortening distortion that approaches that edge to the metal, thus deforming the O 2 L 2 square to a trapezoid (Figure a). To illustrate this point we have chosen three examples of cis -dioxo complexes: [MoO 2 F 4 ] 2– (Figure 2), [MoO 2 Cl 2 (dmso) 2 ], and [MoO 2 Br 2 (dmso) 2 ] (Figure ), and the results are represented in Figure . All these examples show the same behavior in the equatorial plane: 0 ≈ S(L 4 , SP-4) < S(ML 4 , SP-4), indicating an off-center shift of the metal atom within a nearly regular square cage formed by the equatorial ligands (see Figure b and eq ).…”

1,1′-(4,4′-Bipiperidine-1,1′-diyl)bis(2,2,2-trifluoroethanone)

“…For applications of and structures related to 4,4 0 -bipiperidine compounds, see: Medina et al (1991); Li et al (2009); Wang et al (2007); Melchiorre et al (2001); Adams et al (2006); Angeloni & Orpen (2001); De las Casas Engel et al (2010). For a related synthesis, see: Schenck et al (2004).…”

“…Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT-Plus (Bruker, 2007); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL. The structures containing 4,4′-bipiperidine scaffold attract more interest as molecular spacer for sustaining functional diversity, which finds different applications in materials chemistry (Wang et al, 2007;Medina et al, 1991;Li et al, 2009;Adams et al, 2006;Angeloni & Orpen, 2001), Organocatalysis (De las Casas Engel et al, 2010) and pharmaceutical development (Melchiorre et al, 2001).…”