Exploring metal carbamates as precursors for the synthesis of metal-organic frameworks

In the synthesis of metal-organic frameworks (MOFs), the choice of the metal precursor plays a key role because of the influence that it can exert on the crystallization kinetics. The present work explores the use of metal-carbamato complexes for the synthesis of benchmark MOFs, namely HKUST-1 and UiO-66. Cu2(O2CNEt2)4·2NHEt2 and Zr(O2CNEt2)4, prepared using straightforward CO2 fixation reactions starting from the corresponding metal chlorides and diethylamine, were employed as metal precursors for MOF formation. The synthesis conditions, including the solvent, temperature, and ligand protonation degree, were systematically investigated, revealing metal carbamates as highly reactive precursors due to their prompt release of CO2 and amine upon reaction with protic species, i.e., the polycarboxylic linkers. This property of metal carbamates allowed us to identify room temperature protocols to achieve MOFs with comparable properties to those obtained using traditional metal precursors. Subsequent optimization of the reaction conditions led to the design of a one-pot synthetic strategy for HKUST-1, starting directly from copper(II) chloride and diethylamine under a CO2 atmosphere. The MOFs were characterized using various techniques, including powder X-ray diffraction, N2 sorption analysis, 1H nuclear magnetic resonance spectroscopy, and CHN elemental analysis, and compared to reference samples prepared according to literature procedures.

Diiron Aminocarbyne Complexes with NCE− Ligands (E = O, S, Se)

Diiron μ-aminocarbyne complexes [Fe2Cp2(NCMe)(CO)(μ-CO){μ-CN(Me)(R)}]CF3SO3 (R = Xyl, [1aNCMe]CF3SO3; R = Me, [1bNCMe]CF3SO3; R = Cy, [1cNCMe]CF3SO3; R = CH2Ph, [1dNCMe]CF3SO3), freshly prepared from tricarbonyl precursors [1a–d]CF3SO3, reacted with NaOCN (in acetone) and NBu4SCN (in dichloromethane) to give [Fe2Cp2(kN-NCO)(CO)(μ-CO){μ-CN(Me)(R)}] (R = Xyl, 2a; Me, 2b; Cy, 2c) and [Fe2Cp2(kN-NCS)(CO)(μ-CO){μ-CN(Me)(CH2Ph)}], 3 in 67–81% yields via substitution of the acetonitrile ligand. The reaction of [1aNCMe–1cNCMe]CF3SO3 with KSeCN in THF at reflux temperature led to the cyanide complexes [Fe2Cp2(CN)(CO)(μ-CO){μ-CNMe(R)}], 6a–c (45–67%). When the reaction of [1aNCMe]CF3SO3 with KSeCN was performed in acetone at room temperature, subsequent careful chromatography allowed the separation of moderate amounts of [Fe2Cp2(kSe-SeCN)(CO)(μ-CO){μ-CN(Me)(Xyl)}], 4a, and [Fe2Cp2(kN-NCSe)(CO)(μ-CO){μ-CN(Me)(Xyl)}], 5a. All products were fully characterized by elemental analysis, IR, and multinuclear NMR spectroscopy; moreover, the molecular structure of trans-6b was ascertained by single crystal X-ray diffraction. DFT calculations were carried out to shed light on the coordination mode and stability of the {NCSe-} fragment.

Adding Diversity to Diiron Aminocarbyne Complexes with Amine Ligands

The reactions of the diiron aminocarbyne complexes [Fe2Cp2(NCMe)(CO)(μ-CO){μ-CN(Me)(R)}]CF3SO3 (R = Me, 1aNCMe; R = Cy, 1bNCMe), freshly prepared from the tricarbonyl precursors 1a–b, with primary amines containing an additional function (i.e., alcohol or ether) proceeded with the replacement of the labile acetonitrile ligand and formation of [Fe2Cp2(NH2CH2CH2OR’)(CO)(μ-CO){μ-CN(Me)(R)}]CF3SO3 (R = Me, R’ = H, 2a; R = Cy, R’ = H, 2b; R = Cy, R’ = Me, 2c) in 81–95% yields. The diiron-oxazolidinone conjugate [Fe2Cp2(NH2OX)(CO)(μ-CO){μ-CN(Me)2}]CF3SO3, 3, was prepared from 1a, 3-(2-aminoethyl)-5-phenyloxazolidin-2-one (NH2OX) and Me3NO, and finally isolated in 96% yield. In contrast, the one pot reactions of 1a-b with NHEt2 in the presence of Me3NO gave the unstable [Fe2Cp2(NHEt2)(CO)(μ-CO){μ-CN(Me)(R)}]CF3SO3 (R = Me, 4a; R = Cy, 4b) as unclean products. All diiron complexes were characterized by analytical and spectroscopic techniques; moreover, the behavior of 2a–c and 3 in aqueous media was ascertained.

Kinetic Resolution of Azaarylethynyl Tertiary Alcohols by Chiral Brønsted Acid Catalysed Phosphine-Mediated Deoxygenation

A chiral Brønsted acid catalysed phosphine-mediated deoxygenation protocol is reported. This metal-free method provides a precise kinetic resolution platform for azaarylethynyl tertiary alcohols, which are a broad category of biologically and synthetically important azaarene derivatives. In addition to providing an efficient method for the first asymmetric preparation of these tertiary alcohols, the strategy facilitates the construction of azaaryl-functionalized allenes with good to excellent enantioselectivities. The high selectivity factors (s up to 235), broad substrate scope, and ability to convert azaaryl compounds into both chiral tertiary alcohols and allenes robustly underscore the efficiency and promising utility of this method. The practicability is further validated by the successful synthesis of deuterated allenes with high ee values and substantial incorporation of deuterium using inexpensive D₂ O as the deuterium source.

The choice of μ-vinyliminium ligand substituents is key to optimize the antiproliferative activity of related diiron complexes

Diiron vinyliminium complexes constitute a large family of organometallics displaying a promising anticancer potential. The complexes [Fe2Cp2(CO)(μ-CO){μ-η1:η3-C(R3)C(R4)CN(R1)(R2)}]CF3SO3 (2a-c, 4a-d) were synthesized, assessed for their behavior in aqueous solutions (D2O solubility, Log Pow, stability in D2O/Me2SO-d6 mixture at 37°C over 48 h) and investigated for their antiproliferative activity against A2780 and A2780cisR ovarian cancer cell lines and the nontumoral one Balb/3T3 clone A31. Cytotoxicity data collected for 50 vinyliminium complexes were correlated with the structural properties (i.e. the different R1-R4 substituents) using the partial least squares methodology. A clear positive correlation emerged between the octanol-water partition coefficient and the relative antiproliferative activity on ovarian cancer cell lines, both of which appear as uncorrelated to the cancer cell selectivity. However, the different effects played by the R1-R4 substituents allow tracing guidelines for the development of novel, more effective compounds. Based on these results, three additional complexes (4p-r) were designed, synthesized and biologically investigated, revealing their ability to hamper thioredoxin reductase enzyme and to induce cancer cell production of reactive oxygen species.

Non-precious metal carbamates as catalysts for the aziridine/CO2 coupling reaction under mild conditions

The catalytic potential of a large series of easily available metal carbamates (based on thirteen different non-precious metal elements) was explored for the first time in the coupling reaction between 2-aryl-aziridines and carbon dioxide, working under solventless and ambient conditions and using tetraalkylammonium halides as co-catalysts. The straightforward synthesis of novel [NbCl3(O2CNEt2)2], NbCl, and [NbBr3(O2CNEt2)2], NbBr, is reported. The niobium complex NbCl, in combination with NBu4I, emerged as the best catalyst of the overall series to convert aziridines with small N-alkyl substituents into the corresponding 5-aryl-oxazolidin-2-ones.