Diastereoselective Synthesis of Phosphinyl Peptides via Rh-Catalyzed 1,4-Addition in Coparticipation of a P-Chiral Moiety and Difluorphos.

The asymmetric Rh-catalyzed 1,4-addition of aryl/heteroaryl moieties to α,ß-unsaturated esters was achieved in high diastereoselectivity via the coparticipation of a P-chiral phosphinyl moiety at Cß to the prochiral center and (R)- or (S)-Difluorphos. This methodology expands the synthetic toolbox available for the preparation of structurally diverse chiral phosphinyl peptides.

From Coordination to π-Hole Chemistry of Transition Metals: Metalloporphyrins as a Case of Study.

Herein we have evidenced the formation of favorable π-hole Br⋅⋅⋅metal noncovalent interactions (NCIs) involving elements from groups 9, 11 and 12. More in detail, M (M=Co2+, Ni2+, Cu2+ and Zn2+) containing porphyrins have been synthesized and their supramolecular assemblies structurally characterized by means of single crystal X-ray diffraction and Hirshfeld surface analyses, revealing the formation of directional Br⋅⋅⋅M contacts in addition to ancillary hydrogen bond and lone pair-π bonds. Computations at the PBE0-D3/def2-TZVP level of theory revealed the π-hole nature of the Br⋅⋅⋅M interaction. In addition, the physical nature of these NCIs was studied using Quantum Chemistry methodologies, providing evidence of π-hole Spodium and Regium bonds in Zn2+ and Cu2+ porphyrins, in addition to unveiling the presence of a π-hole for group 9 (Co2+). On the other hand, group 10 (Ni2+) acted as both electron donor and acceptor moiety without showing an electropositive π-hole. Owing to the underexplored potential of π-hole interactions in transition metal chemistry, we believe the results reported herein will be useful in supramolecular chemistry, organometallics, and solid-state chemistry by i) putting under the spotlight the π-hole chemistry involving first row transition metals and ii) unlocking a new tool to direct the self-assembly of metalloporphyrins.

Solvent-Switchable Remote C-H Activation via 1,4-Palladium Migration Enables Site-Selective C-P Bond Formation: A Tool for the Synthesis of P-Chiral Phosphinyl Imidazoles.

Solvent-switchable and site-selective phosphorylation of imidazoles at the C2 or C5 position of the imidazole ring was achieved via 1,4-palladium migration. P-Chiral tert-butyl(aryl)phosphine oxides were cross-coupled to 1-(2-bromophenyl)-1H-imidazoles with high enantiospecificity, thereby leading to a novel class of chiral imidazole-based phosphine oxides. As proof of concept, reduction of an analogue yielded the corresponding P-chiral 2-phosphinyl imidazole ligand, which was shown to induce high enantioselectivity in the formation of axially chiral molecules synthesized via Pd-catalyzed Suzuki-Miyaura cross-coupling.

Vibrational dynamics as an essential determinant of the thermal stability of zinc zeolitic imidazolate lattices.

Thermal stability and kinetics of zeolitic imidazolate frameworks (ZIFs) are crucial for their applications as energetic materials. Here, the effect of microscopic vibrational dynamics on the thermal stability of ZIFs is demonstrated by using simple tools. Specifically, we explored the thermal kinetics based on Flynn-Wall-Ozawa and Kissinger's methods. The study comprises a combination of structure-related effects such as topology, density, and alkyl substitution with respect to vibrational dynamics in ZIFs. The results exhibit a linear correlation between the vibrational dynamics of the linkers and activation energy, I.E. stabilization of ZIFs, in the polymorphic Zn(EtIm)2 series. At the same time, thermal destabilization was observed with the growing alkyl chain and was further probed by IR spectroscopy.

In situ monitoring of mechanochemical MOF formation by NMR relaxation time correlation.

In this paper, we present a new approach to monitoring mechanochemical transformations, based on a magnetic resonance (MR) method in which relaxation time correlation maps are used to track the formation of the popular metal-organic framework (MOF) materials Zn-MOF-74 and ZIF-8. The two-dimensional (2D) relaxation correlation measurement employed yields a spectrum which visually and analytically identifies different 1H environments in the sample of interest. The measurement is well-suited to analyzing solid mixtures, and liquids, in complex systems. Application in this work to monitoring MOF formation shows changes in signal amplitudes, and their MR lifetime coordinates, within the 2D plots as the reaction progresses, confirming reaction completion. This new measurement provides a simple way to analyse solid-state reactions without dissolution, and there is a logical pathway to benchtop measurement with a new generation of permanent magnet-based MR instruments. The methodology described permits measurement in an MR compatible milling container, which may be directly transferred from the shaker assembly to the MR magnet for in situ measurement of the entire reaction mixture.

Supramolecular "baking powder": a hexameric halogen-bonded phosphonium salt cage encapsulates and functionalises small-molecule carbonyl compounds.

We report a hexameric supramolecular cage assembled from the components of a Wittig-type phosphonium salt, held together by charge-assisted halogen bonds. The cage reliably encapsulates small polar molecules, including aldehydes and ketones, to provide host-guest systems where components are pre-formulated in a near-ideal stoichiometry for a mechanochemical base-activated Wittig olefination. These pre-formulated solids represent a proof-of-principle for a previously not reported supramolecular design of solid-state reactivity in which the host for molecular inclusion also acts as a complementary reagent for the subsequent chemical transformation of an array of guests. The host-guest solid-state complexes can act as supramolecular surrogates to their Wittig olefination vinylbromide products in a Sonogashira-type coupling that enables one-pot mechanochemical conversion of an aldehyde to an enediyne.

Three-in-One: Dye-Volatile Cocrystals Exhibiting Intensity-Dependent Photochromic, Photomechanical, and Photocarving Response.

Cocrystallization of a cis-azobenzene dye with volatile molecules, such as pyrazine and dioxane, leads to materials that exhibit at least three different light-intensity-dependent responses upon irradiation with low-power visible light. The halogen-bond-driven assembly of the dye cis-(p-iodoperfluorophenyl)azobenzene with volatile halogen bond acceptors produces cocrystals whose light-induced behavior varies significantly depending on the intensity of the light applied. Low-intensity (<1 mW·cm-2) light irradiation leads to a color change associated with low levels of cis → trans isomerization. Irradiation at higher intensities (150 mW·mm-2) produces photomechanical bending, caused by more extensive isomerization of the dye. At still higher irradiation intensities (2.25 W·mm-2) the cocrystals undergo cold photocarving; i.e., they can be cut and written on with micrometer precision using laser light without a major thermal effect. Real-time Raman spectroscopy shows that this novel photochemical behavior differs from what would be expected from thermal energy input alone. Overall, this work introduces a rational blueprint, based on supramolecular chemistry in the solid state, for new types of crystalline light-responsive materials, which not only respond to being exposed to light but also change their response based on the light intensity.

Effect of Photoinitiators Doped in PDMS for Femtosecond-Laser Writing: Characterization and Outcomes.

Herein, we have characterized in depth the effect of femtosecond (fs)-laser writing on various polydimethylsiloxane (PDMS)-based composites. The study combines systematic and nanoscale characterizations for the PDMS blends that include various photoinitiators (organic and inorganic agents) before and after fs-laser writing. The results exhibit that the photoinitiators can dictate the mechanical properties of the PDMS, in which Young's modulus of PDMS composites has higher elasticity. The study illustrates a major improvement in refractive index change by 15 times higher in the case of PDMS/BP-Ge [benzophenone (BP) allytriethylgermane] and Irgacure 184. Additional enhancement was achieved in the optical performance levels of the PDMS composites (the PDMS composites of Irgacure 184/500, BP-Ge, and Ge-ATEG have a relative difference of less than 5% in comparison with pristine PDMS), which are on par with glasses. This insightful study can guide future investigators in choosing photoinitiators for particular applications in photonics and polymer chemistry.

In situ study of Au nanoparticle formation in a mechanochemical-aging-based method.

As we strive to perform chemical transformations in a more sustainable fashion, enabling solid-state reactions through mechanochemistry has emerged as a highly successful approach. Due to the wide-ranging applications of gold nanoparticles (AuNPs), mechanochemical strategies have already been employed for their synthesis. However, the underlying processes surrounding gold salt reduction, nucleation and growth of AuNPs in the solid state are yet to be understood. Here, we present a mechanically activated aging synthesis of AuNPs, through a solid-state Turkevich reaction. Solid reactants are only briefly exposed to input of mechanical energy before being aged statically over a period of six weeks at different temperatures. This system offers an excellent opportunity for an in situ analysis of both reduction and nanoparticle formation processes. During the aging period, the reaction was monitored using a combination of X-ray photoelectron spectroscopy, diffuse reflectance spectroscopy, powder X-ray diffraction and transmission electron microscopy, to gain meaningful insights into the mechanisms of solid-state formation of gold nanoparticles. The acquired data allowed for the establishment of the first kinetic model for solid-state nanoparticle formation.

The Effect of Linker-to-Metal Energy Transfer on the Photooxidation Performance of an Isostructural Series of Pyrene-Based Rare-Earth Metal-Organic Frameworks.

The tetratopic linker, 1,3,6,8-tetrakis(p-benzoic acid)pyrene (H4 TBAPy) along with rare-earth (RE) ions is used for the synthesis of 9 isostructures of a metal-organic framework (MOF) with shp topology, named RE-CU-10 (RE = Y(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III), and Lu(III)). The synthesis of each RE-CU-10 analogue requires different reaction conditions to achieve phase pure products. Single crystal X-ray diffraction indicates the presence of a RE9 -cluster in Y- to Tm-CU-10, while a RE11 -cluster is observed for Yb- and Lu-CU-10. The photooxidation performance of RE-CU-10 analogues is evaluated, observing competition between linker-to-metal energy transfer versus the generation of singlet oxygen. The singlet oxygen produced is used to detoxify a mustard gas simulant 2-chloroethylethyl sulfide, with half-lives ranging from 4.0 to 5.8 min, some of the fastest reported to date using UV-irradiation and < 1 mol% catalyst, in methanol under O2 saturation.