Preparation of nanodiamond anchored on copper tannic acid as a heterogenous catalyst for synthesis of 1,4-benzodiazepines derivatives

In this research, a new and eco-friendly heterogeneous catalyst (ND@Tannicacid-Cu) was synthesized based on nanodiamond and copper tannic acid via esterification process. The as-prepared catalyst was characterized by Fourier transforms infrared spectroscopy (FT-IR), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and X-ray diffraction (XRD) methods. The catalytic efficacy of the intended catalyst was examined by one-step three-component reaction of 1,4-benzodiazepine derivatives from a mixture of ortho-phenylenediamine, aromatic aldehydes, and dimedone under mild conditions. In all instances, corresponding 2,4-benzodiazepines derivatives were synthesized with high efficiency, short reaction time, straightforward work up procedure, no requirement for column-chromatography, and cost-effective catalyst. The heterogeneous catalyst was easily recycled using fillers, and it can be reused for eight cycles without significantly diminishing its performance.

Synthesis and Structure-Activity Characterization of a Single-Site MoO2 Catalytic Center Anchored on Reduced Graphene Oxide

Molecularly derived single-site heterogeneous catalysts can bridge the understanding and performance gaps between conventional homogeneous and heterogeneous catalysis, guiding the rational design of next-generation catalysts. While impressive advances have been made with well-defined oxide supports, the structural complexity of other supports and the nature of the grafted surface species present an intriguing challenge. In this study, single-site Mo(═O)₂ species grafted onto reduced graphene oxide (rGO/MoO₂) are characterized by XPS, DRIFTS, powder XRD, N₂ physisorption, NH₃-TPD, aqueous contact angle, active site poisoning assay, Mo EXAFS, model compound single-crystal XRD, DFT, and catalytic performance. NH₃-TPD reveals that the anchored MoO₂ moiety is not strongly acidic, while Mo 3d_5/2 XPS assigns the oxidation state as Mo(VI), and XRD shows little rGO periodicity change on MoO₂ grafting. Contact angle analysis shows that MoO₂ grafting consumes rGO surface polar groups, yielding a more hydrophobic surface. The rGO/MoO₂ DRIFTS assigns features at 959 and 927 cm^-1 to the symmetric and antisymmetric Mo═O stretching modes, respectively, of an isolated cis-(O═Mo═O) moiety, in agreement with DFT computation. Moreover, the Mo EXAFS rGO/MoO₂ structural data are consistent with isolated (C-O)₂-Mo(═O)₂ species having two Mo═O bonds and two Mo-O bonds at distances of 1.69(3) and 1.90(3) Å, respectively. rGO/MoO₂ is also more active than the previously reported AC/MoO₂ catalyst, with reductive carbonyl coupling TOFs approaching 1.81 × 10³ h^-1. rGO/MoO₂ is environmentally robust and multiply recyclable with 69 ± 2% of the Mo sites catalytically significant. Overall, rGO/MoO₂ is a structurally well-defined and versatile single-site Mo(VI) dioxo heterogeneous catalytic system.