Marco Fusè

Vibrational circular dichroism and chiroptical properties of chiral Ir(III) luminescent complexes

The octahedral ionic Ir(iii) complex with a dual stereogenic centre of general formula Δ,Λ-(R,S)-[(ppy)2Ir(Me-Campy)]X, where ppy = 2-phenylpyridine and Me-Campy = 2-methyl-5,6,7,8-tetrahydroquinolin-8-amine, and the complex Λ-(R,S)-[(ppy)2Ir(H-Campy)]X, where ppy = 2-phenylpyridine, H-Campy = 8-amino-5,6,7,8-tetrahydroquinolines and X(-) = Cl(-) as a counterion in both cases, have been characterized by vibrational circular dichroism (VCD), which turns out to be efficacious in diastereomeric discrimination. Moreover, the single crystal X-ray structure of the complex Δ-(R)-[(ppy)2Ir(Me-Campy)]Cl is reported here. Density functional theory (DFT) calculations allow us to conclude that the most important doublet feature in the VCD spectra is associated with a clear vibrational exciton structure located on the two dissymmetrically disposed phenylpyridine ligands. The features in the VCD spectra associated with the (R) or (S)-central chirality configuration are identified and commented on. DFT calculations provide also the interpretation of electronic circular dichroism (ECD) spectra. Finally, circularly polarized luminescence (CPL) spectra are presented as an additional chiroptical characterization of these luminescent iridium complexes.

Simple 1,3-diamines and their application as ligands in ruthenium(II) catalysts for asymmetric transfer hydrogenation of aryl ketones

In this research work simple unsymmetrical 1,3-diamines were studied. The synthesis of the diamines started from non-commercial available compounds. S-5a and S,S-5c were obtained by biocatalysis with non conventional yeast, Rhodotorula rubra MIM 147, with excellent 99% e.e. and d.e. up to 90%. Different approaches of synthesis were applied to the same backbone to study both the steric and electronic effects of the ligands. The reactivity of the corresponding ruthenium complexes was evaluated in the asymmetric hydrogen transfer reduction of acetophenone as a standard substrate and of other different aryl ketones, highlighting the flexibility of the six membered chelating ring. A screening of the reaction conditions indicated aqueous media in the presence of HCOONa as a hydrogen donor to be the best system for overcoming the lack of stereocontrol thus allowing us to obtain 56% e.e. in the reduction of acetophenone with the complex in which the ligand was diamine 1, revealed as the best in terms of reactivity and stereoselectivity also in the reduction of the other different aryl ketones, in particular for α-tetralone, i (63% e.e.).

Evaluation of Chemical Diversity of Biotinylated Chiral 1,3‐Diamines as a Catalytic Moiety in Artificial Imine Reductase

The possibility of obtaining an efficient artificial imine reductase was investigated by introducing a chiral cofactor into artificial metalloenzymes based on biotin–streptavidin technology. In particular, a chiral biotinylated 1,3‐diamine ligand in coordination with iridium(III) complex was developed. Optimized chemogenetic studies afforded positive results in the stereoselective reduction of a cyclic imine, the salsolidine precursor, as a standard substrate with access to both enantiomers. Various factors such as pH, temperature, number of binding sites, and steric hindrance of the catalytic moiety have been proved to affect both efficiency and enantioselectivity, underlining the great flexibility of this system in comparison with the achiral system. Computational studies were also performed to explain how the metal configuration, in the proposed system, might affect the observed stereochemical outcome.

Diving into Chemical Bonding: An Immersive Analysis of the Electron Charge Rearrangement through Virtual Reality: Diving into Chemical Bonding: An Immersive Analysis of the Electron Charge Rearrangement through Virtual Reality

An integrated environment for the analysis of chemical bonding based on immersive virtual reality is presented. Using a multiscreen stereoscopic projection system, researchers are cast into the world of atoms and molecules, where they can visualize at a human scale the electron charge rearrangement (computed via state‐of‐the‐art quantum‐chemical methods) occurring on bond formation throughout the molecular region. Thanks to specifically designed features, such a virtual laboratory couples the immediacy of an immersive experience with a powerful, recently developed method yielding quantitative, spatially detailed pictures of the several charge flows involved in the formation of a chemical bond. By means of two case studies on organometallic complexes, we show how familiar concepts in coordination chemistry, such as donation and back‐donation charge flows, can be effectively identified and quantified to predict experimental observables.

Computational simulation of vibrationally resolved spectra for spin-forbidden transitions

In this computational study, we illustrate a method for computing phosphorescence and circularly polarized phosphorescence spectra of molecular systems, which takes into account vibronic effects including both Franck-Condon and Herzberg-Teller contributions. The singlet and triplet states involved in the phosphorescent emission are described within the harmonic approximation, and the method fully takes mode-mixing effects into account when evaluating Franck-Condon integrals. Spin-orbit couplings, which are responsible for these otherwise forbidden phenomena, are accounted for by means of a relativistic two-component time-dependent density functional theory method. The model is applied to two types of chiral systems: camphorquinone, a rigid organic system that allows for an extensive benchmark, and some members of a class of iridium complexes. The merits and shortcomings of the methods are discussed, and some perspectives for future developments are offered.

Towards the SMART workflow system for computational spectroscopy

Is it possible to convert highly specialized research in the field of computational spectroscopy into robust and user-friendly aids to experiments and industrial applications? What kind of tools should be created to increase the interactions between researchers with different backgrounds and push towards new frontiers in computational chemistry? The outstanding advances in computational spectroscopy and the wide availability of computational and analytical tools are paving the route toward the study of problems that were previously difficult or impossible to solve and enable the imagination of even more ambitious targets for fundamental and applied research. The combination of new computer- and data-centric technologies is transforming data analysis from an uncommon and retrospective practice into a proactive process of strategic decision and action. This paper starts from these premises and proposes a perspective for a new cyberinfrastructure aimed at integrating developments in theory, algorithms and software with new tools for workflow management, data mining and visualization. We make a case for this approach by means of a few examples that deal with unmanageable types of data in molecular modelling and results obtained using different unsupervised learning algorithms.

Cascade Reaction by Chemo- and Biocatalytic Approaches to Obtain Chiral Hydroxy Ketones and anti 1,3-Diols

Abstract A chemo‐ and biocatalytic cascade approach was applied for the stereoselective synthesis of hydroxy ketones and the corresponding 1,3‐diols. A new class of tridentate N,N,O ligands was used with copper(II) complexes for the asymmetric β‐borylation of α,β‐unsaturated compounds. The complex containing ligand L5 emerged as the best performer, and it gave the organoborane derivatives with good ee values. The corresponding keto–alcohol compounds were then bioreduced by yeasts. The biotransformation set up with Rhodotorula rubra allowed (R)‐keto–alcohols and (S,S)‐diols to be obtained with up to 99 % ee and up to 99 % de in favor of the anti enantiomers.