Enabling a bioinspired N,N,N-copper coordination motif through spatial control in UiO-67: synthesis and reactivity.

Metal-organic frameworks (MOFs) featuring zirconium-based clusters are widely used for the development of functionalized materials due to their exceptional stability. In this study, we report the synthesis of a novel N,N,N-ligand compatible with a biphenyl dicarboxylic acid-based MOF. However, the resulting copper(I) complex exhibited unexpected coordination behaviour, lacking the intended trifold coordination motif. Herein, we demonstrate the successful immobilization of a bioinspired ligand within the MOF, which preserved its crystalline and porous nature while generating a well-defined copper site. Comprehensive spectroscopic analyses, including X-ray absorption, UV/Vis, and infrared spectroscopy, were conducted to investigate the copper site and its thermal behaviour. The immobilized ligand exhibited the desired tridentate coordination to copper, providing access to a coordination motif otherwise unattainable. Notably, water molecules were also found to coordinate to copper. Upon heating, the copper centre within the MOF exhibited reversible dehydration, suggesting facile creation of open coordination sites. Furthermore, the copper site displayed reduction at elevated temperatures and subsequent susceptibility to oxidation by molecular oxygen. Lastly, both the molecular complexes and the MOF were evaluated as catalysts for the oxidation of cyclohexane using hydrogen peroxide. This work highlights the successful immobilization of a bioinspired ligand in a zirconium-based MOF, shedding light on the structural features, thermal behaviour, and catalytic potential of the resulting copper sites.

Symmetry Breaking and Autocatalytic Amplification in Soai Reaction Confined within UiO-MOFs under Heterogenous Conditions.

Symmetry breaking is observed in the Soai reaction in a confinement environment provided by zirconium-based UiO-MOFs used as crystalline sponges. Subsequent reaction of encapsulated Soai aldehyde with Zn(i-Pr)2 vapour promoted absolute asymmetric synthesis of the corresponding alkanol. ATR-IR and NMR confirm integration of aldehyde into the porous material, and a similar localization of newly formed chiral alkanol after reaction. Despite the confinement, the Soai reaction exhibits significant activity and autocatalytic amplification. Comparative catalytic studies with various UiO-MOFs indicate different outcomes in terms of enantiomeric excess, handedness distribution of the product and reaction rate, when compared to pristine solid Soai aldehyde, while the crystalline MOF remains highly stable to action of Zn(iPr)2 vapour. This is an unprecedented example of absolute asymmetric synthesis using MOFs.

Structural Elucidation, Aggregation, and Dynamic Behaviour of N,N,N,N-Copper(I) Schiff Base Complexes in Solid and in Solution: A Combined NMR, X-ray Spectroscopic and Crystallographic Investigation.

A series of Cu(I) complexes of bidentate or tetradentate Schiff base ligands bearing either 1-H-imidazole or pyridine moieties were synthesized. The complexes were studied by a combination of NMR and X-ray spectroscopic techniques. The differences between the imidazole- and pyridine-based ligands were examined by 1H, 13C and 15N NMR spectroscopy. The magnitude of the 15Nimine coordination shifts was found to be strongly affected by the nature of the heterocycle in the complexes. These trends showed good correlation with the obtained Cu-Nimine bond lengths from single-crystal X-ray diffraction measurements. Variable-temperature NMR experiments, in combination with diffusion ordered spectroscopy (DOSY) revealed that one of the complexes underwent a temperature-dependent interconversion between a monomer, a dimer and a higher aggregate. The complexes bearing tetradentate imidazole ligands were further studied using Cu K-edge XAS and VtC XES, where DFT-assisted assignment of spectral features suggested that these complexes may form polynuclear oligomers in solid state. Additionally, the Cu(II) analogue of one of the complexes was incorporated into a metal-organic framework (MOF) as a way to obtain discrete, mononuclear complexes in the solid state.

Kinetic relationship in parallel autocatalytic amplifications of pyridyl alkanol and chiral trigger pyrimidyl alkanol.

Experimental and kinetic analysis of a chemical system combines autocatalytic amplification of 2-alkynyl-5-pyrimidyl alkanol 2 and 6-alkynyl-3-pyridyl akanol 4 in which 2 acts as a chiral trigger and 4 being the subsequent autocatalyst. Starting from a very low initial ee, both alkanols are produced with high enantiopurity in one single cycle. This provides insight into a dual nonlinear amplification of chirality observed with amplifying trigger 2 and accelerated amplification of autocatalyst 4. These kinetic studies reveal a five-fold magnitude superior amplification rates of 4 associated with trigger's enantiopurity at the outset.

Strongly visible light-absorbing metal-organic frameworks functionalized by cyclometalated ruthenium(ii) complexes.

Four different ruthenium(ii) complexes were incorporated into the metal-organic framework (MOF) UiO-67 using three different synthetic strategies: premade linker synthesis, postsynthetic functionalization, and postsynthetic linker exchange. One of these complexes was of the type (N-N)3Ru2+, and three of the complexes were of the type (N-N)2(N-C)Ru+, where N-N is a bipyridine-type ligand and N-C is a cyclometalated phenylpyridine-type ligand. The resulting materials were characterized by PXRD, SC-XRD (the postsynthetic functionalization MOFs), N2 sorption, TGA-DSC, SEM, EDS, and UV-Vis spectroscopy, and were digested in base for subsequent 1H NMR analysis. The absorption profiles of the MOFs that were functionalized with cyclometalated Ru(ii) complexes extend significantly further into the visible region of the spectrum compared to the absorption profiles of the MOFs that were functionalized with the non-cyclometalated reference, (N-N)3Ru2+.

Cyclometalated ruthenium complexes with carboxylated ligands from a combined experimental/computational perspective.

The syntheses and characterization of nine new cyclometalated ruthenium complexes are reported. These structures consist of Ru(ii) with bipyridine and phenylpyridine ligands which are substituted with ester or carboxylate groups. Two of the complexes were extensively studied and their properties were compared to those of two previously reported structures. The identities of the compounds were confirmed by NMR, HR-MS and single crystal XRD, and the electronic properties were investigated by UV-Vis spectroscopy. DFT and TD-DFT calculations showed that the intense absorbances in the visible region of the spectrum of these cyclometalated complexes are due to electronic excitations to virtual orbitals located on the carboxylated ligands. These results indicate that the compounds are promising candidates as sensitizers for more efficient photocatalysis with sunlight. Further, the carboxylate groups should facilitate their use as linkers in metal-organic frameworks.

Asymmetric Autocatalysis as a Relay for Remote Amplification of Chirality of Target Molecules Used as Triggers.

Nearly racemic target molecules are enantiomerically enriched through an asymmetric autocatalytic relay for a remote amplification of chirality. Target alkynols with very low initial ee act as chiral triggers for asymmetric amplification of the Soai autocatalyst, which in turn enables the formation of the same alkynols with greater enantiomeric purity. Additionally, the stereochemical correlation between the trigger/target and autocatalyst molecules is discussed.

On the dichotomic reactivity of lithiated styrene oxide: a computational and multinuclear magnetic resonance investigation.

A multinuclear magnetic resonance investigation, supported by density functional theory calculations, has been synergically used to investigate the configurational stability, reactivity and aggregation states of alpha-lithiated styrene oxide in THF at 173 K. NMR studies on alpha-lithiated [alpha,beta-(13)C(2)]styrene oxide (also in an enantiomerically enriched form) proved that in THF this oxiranyllithium is mainly present as a solvated monomeric species in equilibrium with a complex mixture of stereoisomeric dimeric aggregates, as well as with bridged and tetrameric aggregates. The fact that some C(alpha)-Li bonds are partially broken in some stereoisomers reduces their symmetry and complicates the NMR spectra: two diastereoisomers each having a pair of diastereotopic carbon atoms slowly inverting at the lithium atom in absence of tetramethylethylenediamine (TMEDA) have been detected. A ((13)C,(7)Li)-HMQC experiment to correlate (7)Li and (13)C resonances of the various aggregates has been performed for the first time. From natural bond analysis, the monomeric aggregate was proven to have a lower carbenoid character with respect to bridged O-coordinated dimeric aggregates. The employment of suitable experimental conditions in terms of concentration, temperature and the presence or not of TMEDA are crucial to mitigate at the best the "carbene-like" reactivity of lithiated styrene oxide toward intermolecular C-Li insertions, eliminative dimerisation reactions and ring-opening reactions. A two-step mechanism for the deprotonation of styrene oxide by sBuLi in THF has been proposed and discussed as well as competitive side reactions.

Asymmetric autocatalytic Mannich reaction in the presence of water and its implication in prebiotic chemistry.

An enantioselective process in which the chiral Mannich product acts as a catalyst for its own replication was observed to occur under various conditions in the presence of water.

Aminophosphonates as organocatalysts in the direct asymmetric aldol reaction: towards syn selectivity in the presence of Lewis bases.

Chiral alpha-aminophosphonates have been synthesized and their performance was evaluated as organocatalysts in the direct asymmetric aldol reaction. High enantioselectivities (up to 99% ee) were achieved for a range of substituted cyclohexanones and benzaldehydes. Several organic bases, such as DBU, DBN, and TMG, were used together with the alpha-aminophosphonates in the aldol reactions and were found to favor syn-selectivity.