Catalytic oxidation of internal and terminal alkenes by oxidoperoxidomolybdenum(VI) and dioxidomolybdenum(VI) complexes

Impact of POM's coordination mode and Mo-hybrid constituents on the binding, stability, and catalytic properties of hybrid (pre)catalysts

The assembly of MoVIO2 2+ and methoxy-substituted salicylaldehyde nicotinoyl hydrazone ligands afforded two classes of hybrid polyoxometalates (POMs). In the Class I architectures, [MoO2(HL1-3)(D)]2[Mo6O19]·xCH3COCH3 (D = CH3COCH3 or H2O, x = 0 or 2, and L1-3 = ligands bearing the OMe group at position 3, 4 and 5, respectively), the main driving force for self-assembly is the electrostatic interaction between the components. Class II architectures are composed of a POM anion covalently linked to two Mo-complex units through the terminal Ot or bridging μ2-OPOM oxygen atoms, as found in Lindqvist-based hybrids [{MoO2(HL1-3)}2Mo6O19]·xCH3CN (x = 0 or 2) and the asymmetrical β-octamolybdate-based hybrid [{Mo2O4(HL2)(H2L)}{MoO2(HL2)}2Mo8O26]·CH3CN·H2O. Quantum chemical calculations were applied to evaluate the impact of the POM hybrid constituents on the hybrid-type stability, showing that it strongly depends on the ligand substituent position and ancillary ligand nature. Hybrids were tested as catalysts for cyclooctene epoxidation using tert-butyl hydroperoxide (TBHP in water or decane) and with or without the addition of acetonitrile (CH3CN) as an organic solvent. The catalytic results provided by the use of TBHP in decane are the best ones and classify all the prepared catalysts as very active, with the conversion of cyclooctene >90%, and high selectivity towards epoxide, >80%. We also examined the influence of the ligand structure, POM's hybrid type, and coordination mode on the Mo-hybrid activity and selectivity.

Preparative and Catalytic Properties of MoVI Mononuclear and Metallosupramolecular Coordination Assemblies Bearing Hydrazonato Ligands

A series of polynuclear, dinuclear, and mononuclear Mo(VI) complexes were synthesized with the hydrazonato ligands derived from 5-methoxysalicylaldehyde and the corresponding hydrazides (isonicotinic hydrazide (H2L1), nicotinic hydrazide (H2L2), 2-aminobenzhydrazide (H2L3), or 4-aminobenzhydrazide (H2L4)). The metallosupramolecular compounds obtained from non-coordinating solvents, [MoO2(L1,2)]n (1 and 2) and [MoO2(L3,4)]2 (3 and 4), formed infinite structures and metallacycles, respectively. By blocking two coordination sites with cis-dioxo ligands, the molybdenum centers have three coordination sites occupied by the ONO donor atoms from the rigid hydrazone ligands and one by the N atom of pyridyl or amine-functionalized ligand subcomponents from the neighboring Mo building units. The reaction in methanol afforded the mononuclear analogs [MoO2(L1-4)(MeOH)] (1a-4a) with additional monodentate MeOH ligands. All isolated complexes were tested as catalysts for cyclooctene epoxidation using tert-butyl hydroperoxide (TBHP) as an oxidant in water. The impact of the structure and ligand lability on the catalytic efficiency in homogeneous cyclooctene epoxidation was elucidated based on theoretical considerations. Thus, dinuclear assemblies exhibited better catalytic activity than mononuclear or polynuclear complexes.

New bis[MoO2] and [MoO(O2)] compounds: An artificial enzyme with peroxidase activity against o-phenylenediamine and dopamine

In this study, two binuclear dioxido- and oxidoperoxido molybdenum (VI) complexes, [{Mo^VIO₂}₂(L)(H₂O)₂] 1 and [{Mo^VIO(O₂)}₂(L)(H₂O)₂] 2, were synthesized. Complex 1 was obtained through a 1:2 reaction of ligand I with MoO₂(acac)₂, while complex 2 was synthesized in situ by reacting MoO₃ with H₂O₂ in a 1:2 ratio. The structures and characteristics of the complexes were examined employing several techniques such as elemental (CHN) analysis, spectroscopy (FT-IR, UV-Vis, ¹H, and ¹³CNMR), and thermal study (TGA). SC-XRD analysis of complex 1a revealed that the molybdenum central atom adopts an octahedral geometry and is bonded to phenolic oxygen, enolate oxygen, and azomethine nitrogen atoms. Powder X-ray diffraction was used to determine the purity of the bulk material, and the results were compared to single crystal data. Computational calculations were performed using density functional theory (DFT) at the B3LYP/6-31G(d, p) level of theory for the ligand and the LANL2DZ level of theory for the complexes, yielding geometry optimized structures that were then employed in frequency and NMR-calculations. These theoretical findings were compared to the experimental results and showed a good correlation. Furthermore, the complexes exhibited peroxidase-like activity in the presence of hydrogen peroxide as evidenced by the oxidation of o-phenylenediamine and dopamine.

Counter Anion Effects on the Formation and Structural Transformations of Mo(vi)-Hydrazone Coordination Assemblies: Salts, Solvates, Co-Crystals, and Neutral Complexes

Complex salts [1H]X and [1H](XA)0.5·2MeOH, and co-crystals [1H]X·0.5VA (X = chloride or bromide, XA = chloranilate or bromanilate, VA = o-vanillin azine), comprising [MoO2(HL)(MeOH)]+ ([1H]+) cation (H2L = 3-methoxysalicylaldehyde isonicotinoyl hydrazone), were prepared either by solution-based synthesis or by mechanochemical synthesis. Whereas [1H]X salts were extremely sensitive to humidity, their stability could be reinforced by the azine incorporation into the complex network. Solvent-mediated transformations of [1H]X led to methanol co-ligand replacement and afforded complexes [MoO2(HL)X] (2Cl·MeOH, 2Cl, and 2Br·0.5MeCN). However, solvates [1H](XA)0.5·2MeOH, under the same conditions, gave stable complexes [1H](XA)0.5 in which methanol remained coordinated. The differences in the assembly’s behavior were attributed to the packing arrangements, the relative orientation of cations and anions, and interactions between them. Polymorph [MoO2(L)(MeOH)] (1), not attainable by other routes, was the only product when compounds [MoO2(HL)X] were treated with a weak base at low temperatures. Tetranuclear [MoO2(L)]4 and polynuclear [MoO2(L)]n (2) supramolecular isomers, concomitantly crystallized when the reaction was conducted solvothermally. All of the complexes were characterized using X-ray diffraction methods (SCXRD and PXRD), spectroscopic methods (ATR-IR and solution-state and solid-state MAS NMR), and elemental and thermal analyses. The cytotoxicity of the different types of compounds against THP-1 and HepG2 cells was also evaluated.

Discrete mononuclear and dinuclear compounds containing a MoO22+ core and 4-aminobenzhydrazone ligands: synthesis, structure and organic-solvent-free epoxidation activity

New aroylhydrazone molybdenum(vi) complexes have been synthesized, characterized and used as (pre)catalysts for epoxidation of cyclooctene using aqueous TBHP as the oxidant.

Molybdenum(vi) complexes of hemilabile aroylhydrazone ligands as efficient catalysts for greener cyclooctene epoxidation: an experimental and theoretical approach

The focus of this work was on the synthesis, characterization and catalytic activity of Mo(vi) complexes with hemilabile 2-aminobenzhydrazone ligands.

New polymeric, dimeric and mononuclear dioxidomolybdenum(vi) complexes with an ONO donor ligand: crystal structures, DFT calculations, catalytic performance and protein binding study of the ligand

Catalytic activity and BSA binding is reported.

Dioxotungsten(vi) complexes with isoniazid-related hydrazones as (pre)catalysts for olefin epoxidation: solvent and ligand substituent effects

The catalytic performances (activity and selectivity) of the mononuclear dioxotungsten(vi) complexes [WO₂(L^R)(D)] towards alkene epoxidation by tert-butyl hydroperoxide (TBHP) were investigated under different conditions.

Effect of N-based additive on the optimization of liquid phase oxidation of bicyclic, cyclic and aromatic alcohols catalyzed by dioxidomolybdenum(vi) and oxidoperoxidomolybdenum(vi) complexes

Catalytic potentials of [Mo^VIO₂]²⁺ and [Mo^VIO(O₂)]²⁺ complexes with dibasic tridentate ONO donor ligands for the oxidation of bicyclic, cyclic and aromatic alcohols in the presence of NEt₃ are reported.