Design and Assembly of a Chiral Metallosalen-Based Octahedral Coordination Cage for Supramolecular Asymmetric Catalysis.

Supramolecular containers featuring both high catalytic activity and high enantioselectivity represent a design challenge of practical importance. Herein, it is demonstrated that a chiral octahedral coordination cage can be constructed by using twelve enantiopure Mn(salen)-derived dicarboxylic acids as linear linkers and six Zn4 -p-tert-butylsulfonylcalix[4]arene clusters as tetravalent four-connected vertices. The porous cage features a large hydrophobic cavity (≈3944 Å3 ) decorated with catalytically active metallosalen species and is shown to be an efficient and recyclable asymmetric catalyst for the oxidative kinetic resolution of racemic secondary alcohols and the epoxidation of olefins with up to >99 % enantiomeric excess. The cage architecture not only prevents intermolecular deactivation and stabilizes the Mn(salen) catalysts but also encapsulates substrates and concentrates reactants in the cavity, resulting in enhanced reactivity and enantioselectivity relative to the free metallosalen catalyst.

Metallosalen modified carbon nitride a versatile and reusable catalyst for environmentally friendly aldehyde oxidation.

The development of environmentally friendly catalysts for organic transformations is of great importance in the field of green chemistry. Aldehyde oxidation reactions play a crucial role in various industrial processes, including the synthesis of pharmaceuticals, agrochemicals, and fine chemicals. This paper presents the synthesis and evaluation of a new metallosalen carbon nitride catalyst named Co(salen)@g-C3N4. The catalyst was prepared by doping salicylaldehyde onto carbon nitride, and subsequently, incorporating cobalt through Schiff base chemistry. The Co(salen)@g-C3N4 catalyst was characterized using various spectroscopic techniques including Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Infrared Spectroscopy (IR), and Thermogravimetric Analysis (TGA). Furthermore, after modification with salicylaldehyde, the carbon nitride component of the catalyst exhibited remarkable yields (74-98%) in oxidizing various aldehyde derivatives (20 examples) to benzoic acid. This oxidation reaction was carried out under mild conditions and resulted in short reaction times (120-300 min). Importantly, the catalyst demonstrated recyclability, as it could be reused for five consecutive runs without any loss of activity. The reusable nature of the catalyst, coupled with its excellent yields in oxidation reactions, makes it a promising and sustainable option for future applications.

Highly Stable Chiral Zirconium-Metallosalen Frameworks for CO2 Conversion and Asymmetric C-H Azidation.

The engineering of highly stable metal-organic frameworks (MOFs) will unveil the intrinsic potential of these materials for practical applications, especially for heterogeneous catalyzes. However, it is fairly challenging to rationally design robust MOFs serving as highly effective and reusable heterogeneous catalysts. Here, for the first time, we report the construction of four robust UiO-type chiral zirconium-metallosalen frameworks, denoted ZSF-1-4. Single-crystal X-ray-diffraction reveals that the frameworks consist of twelve-connected Zr6O8 clusters with privileged chiral metallosalen ligands anchored at ideal positions, generating confined chiral cages that enable synergistic activation. Unlike UiO-68 that is highly sensitive to aqueous solutions, ZSF-1-4 exhibit excellent chemical stability in aqueous solutions with a wide range of pH owing to the abundant hydrophobic groups within metallosalen ligands. These features render ZSF-1 and ZSF-2 to be excellent recycled heterogeneous catalysts for the conversion of imitated industrial CO2 with epoxides into cyclic carbonates with the highest reported turnover numbers in Zr-MOFs. With regard to asymmetric catalysis, ZSF-3 and ZSF-4 can effectively catalyze C-H azidation reaction in water medium with ee value up to 94%. Moreover, these robust ZSFs can be further extended to other analogues with various metal centers through demetallization-remetallization strategy, which renders them to be an excellent platform for broader fields.

Thermal Stability and Fire Properties of Salen and Metallosalens as Fire Retardants in Thermoplastic Polyurethane (TPU).

This study deals with the synthesis and evaluation of salen based derivatives as fire retardants in thermoplastic polyurethane. Salens, hydroxysalens and their first row transition metal complexes (salen-M) were synthesized (Copper, Manganese, Nickel and Zinc). They were then incorporated in thermoplastic polyurethane (TPU) with a loading as low as 10:1 weight ratio. The thermal stability as well as the fire properties of the formulations were evaluated. Thermogravimetric analysis (TGA) showed that different coordination metals on the salen could induce different decomposition pathways when mixed with TPU. The Pyrolysis Combustion Flow Calorimetry (PCFC) results showed that some M-salen have the ability to significantly decrease the peak heat release rate (-61% compared to neat TPU) and total heat released (-63% compared to neat TPU) when formulated at 10:1 wt % ratio in TPU. Mass Loss Cone Calorimetry (MLC) results have shown that some additives (salen-Cu and salen-Mn) exhibit very promising performance and they are good candidates as flame-retardants for TPU.