Search for: All records

Praseodymium in the +5 oxidation state is a long-sought connection between lanthanide, early-transition and actinide metal redox chemistries. Unique among the lanthanide series, evidence for molecular pentavalent praseodymium species has been observed in the gas phase and noble gas matrix isolation conditions. Here we report the low-temperature synthesis and characterization of a molecular praseodymium complex in the formal +5 oxidation state, [Pr5+(NPtBu3)4][X−] (where tBu = tert-butyl and X− = tetrakis(pentafluorophenyl)borate or hexafluorophosphate). Single-crystal X-ray diffraction, solution-state spectroscopic, solution magnetometric, density functional theory and multireference wavefunction-based methods indicate a highly multiconfigurational singlet ground state. An inverted ligand field drives this unique electronic structure, which establishes a critical link in understanding the bonding of high-valent metal complexes across the periodic table. 

Materials made from covalently cross-linked polymer networks are ubiquitous in everyday life but are difficult to process at the end of their life cycle. Therefore, it is essential to design materials with sustainability in mind to reduce the detrimental effects of plastic waste buildup. Functionalized triazines such as 1,3,5-triazine-2,4,6-triamine (melamine), hexamethylolmelamine (HMM), and hexakis(methoxymethyl)melamine (HMMM) are key components of robust thermosets, adhesives, and coatings. We combine HMM and HMMM with an alkoxysilane to produce transparent thermosets with remarkable glass adhesion. The dynamicity of silyl ether bonds in the network makes the materials susceptible to methanolysis, enabling the recovery of HMMM and the substrate. A combination of solution- and solid-phase techniques is used to elucidate both gelation and degradation pathways. 

Abstract The imidophosphorane ligand, [NP^tBu₃]⁻(^tBu=tert‐butyl), enables isolation of a pseudo‐tetrahedral, tetravalent praseodymium complex, [Pr⁴⁺(NP^tBu₃)₄] (1‐Pr), which is characterized by a suite of physical characterization methods including single‐crystal X‐ray diffraction, electron paramagnetic resonance, and L₃‐edge X‐ray near‐edge spectroscopies. Variable‐temperature direct‐current magnetic susceptibility data, supported by multiconfigurational quantum chemical calculations, demonstrate that the electronic structure diverges from the isoelectronic Ce³⁺analogue, driven by increased crystal field. The four‐coordinate environment around Pr⁴⁺in1‐Pr, which is unparalleled in reported extended solid systems, provides a unique opportunity to study the interplay between crystal field splitting and spin‐orbit coupling in a molecular tetravalent lanthanide within a pseudo‐tetrahedral coordination geometry. 

Here we report the synthesis and characterization of diiron complexes containing triaryl N₄and N₂S₂ligands derived fromo-phenylenediamine. 

Renewable 1,3-butadiene (1,3-BD, C4H6) was synthesized from the tandem decyclization and dehydration of biomass-derived tetrahydrofuran (THF) on weak Brønsted acid zeolite catalysts. 1,3-BD is a highly solicited monomer for the synthesis of rubbers and elastomers. Selective conversion of THF to 1,3-BD was recently measured on phosphorus-modified siliceous zeolites (P-zeosils) at both high and low space velocities, albeit with low per-site catalytic activity. In this work, we combined kinetic analyses and QM/MM calculations to evaluate the interaction of THF with the various Brønsted acid sites (BAS) of Boric (B), Phosphoric (P), and Sulfuric (S) acid modified silicalite-1 catalysts toward a dehydra-decyclization pathway to form 1,3-BD. Detailed kinetic measurements revealed that all three catalysts exhibited high selectivity to 1,3-BD ca. 64–96% in the order of S-MFI > P-MFI > B-MFI at a given temperature (360 °C). Notably, the S-MFI maintained a selectivity >90% for all evaluated process conditions. The computational results suggested that the nature of the Brønsted acid sites and the adsorption energetics (relative THF-acid site interaction energies) are distinct in each catalyst. Additionally, the protonation of THF can be improved with the addition of a water molecule acting as a proton shuttle, particularly in S-MFI. Overall, S-containing zeosils exhibited the ability to control reaction pathways and product distribution in dehydra-decyclization chemistry optimization within microporous zeolites, providing another alternative weak-acid catalytic material.