Revisiting the Potential of Group VI Inorganic Precatalysts for the Ethenolysis of Fatty Acids through a Mechanochemical Approach.

The utilization of biobased feedstocks to prepare useful compounds is a pivotal trend in current chemical research. Among a varied portfolio of naturally available starting materials, fatty acids are abundant, versatile substrates with multiple applications. In this context, the ethenolysis of unsaturated fatty acid esters such as methyl oleate is an atom-economical way to prepare functional C10 olefins with a biobased footprint. Despite the existence of a variety of metathesis catalysts for the latter process, there is a lack of readily available, efficient, and inexpensive catalytic systems based on earth-abundant metals (Mo, W) whose preparation does not require sophisticated syntheses and manipulations. Here, a systematic exploration of homogeneous and heterogeneous inorganic Mo, W (oxy)halides shows that MoOCl4, while inactive as a homogeneous species, forms active and selective silica-supported ethenolysis precatalysts able to reach equilibrium conversion of methyl oleate within a few minutes upon activation with SnMe4. Such heterogeneous MoOCl4-based precatalysts were easily accessed through mechanochemical solvent-free procedures and found to contain, upon characterization by elemental analysis and Raman spectroscopy, isolated (≡SiO)Mo(=O)Cl3 units or polymeric silica-supported [-O(≡SiO)nMoCl4-nO-]m (n = 1, 2) complexes depending on the molybdenum loading. The former isolated species exhibited a higher catalytic performance. The developed heterogeneous precatalysts could be applied to the ethenolysis of various substrates, including polyunsaturated fatty acid esters and industrial fatty acid methyl ester (FAME) mixtures from palm oil transesterification.

Catalytic Strategies for the Cycloaddition of CO2 to Epoxides in Aqueous Media to Enhance the Activity and Recyclability of Molecular Organocatalysts.

The cycloaddition of CO2 to epoxides to afford versatile and useful cyclic carbonate compounds is a highly investigated method for the nonreductive upcycling of CO2. One of the main focuses of the current research in this area is the discovery of readily available, sustainable, and inexpensive catalysts, and of catalytic methodologies that allow their seamless solvent-free recycling. Water, often regarded as an undesirable pollutant in the cycloaddition process, is progressively emerging as a helpful reaction component. On the one hand, it serves as an inexpensive hydrogen bond donor (HBD) to enhance the performance of ionic compounds; on the other hand, aqueous media allow the development of diverse catalytic protocols that can boost catalytic performance or ease the recycling of molecular catalysts. An overview of the advances in the use of aqueous and biphasic aqueous systems for the cycloaddition of CO2 to epoxides is provided in this work along with recommendations for possible future developments.

Enhancing the Catalytic Performance of Group I, II Metal Halides in the Cycloaddition of CO2 to Epoxides under Atmospheric Conditions by Cooperation with Homogeneous and Heterogeneous Highly Nucleophilic Aminopyridines: Experimental and Theoretical Study.

Compared to metal-organic complexes and transition-metal halides, group I metal halides are attractive catalysts for the crucial cycloaddition reaction of CO2 to epoxides as they are ubiquitously available and inexpensive, have a low molecular weight, and are not based on (potentially) endangered metals, especially for the case of sodium and potassium. Nevertheless, given their low intrinsic catalytic efficiency, they require the assistance of additional catalytic moieties. In this work, we show that by exploiting the high nucleophilicity of opportunely designed aminopyridines, catalytic systems based on alkaline metals can be formed, which allow the cycloaddition of CO2 to epoxides to proceed under atmospheric pressure at moderate temperatures. Importantly, the aminopyridine nucleophiles can be applied in their heterogenized form, leading to a recyclable catalytic system. An investigation of the reaction mechanism by density functional theory calculations shows that metal halide complexes and nucleophilic pyridines can work as a dual cooperative catalytic system where the use of aminopyridines leads to lower energy barriers for the opening of the epoxide ring, and halide-adducts are involved in the subsequent steps of CO2 insertion and ring closure.