: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Photocatalyzed and photosensitized chemical processes have seen growing interest recently and have become among the most active areas of chemical research, notably due to their applications in fields such as medicine, chemical synthesis, material science or environmental chemistry. Among all homogeneous catalytic systems reported to date, photoactive copper(I) complexes have been shown to be especially attractive, not only as alternative to noble metal complexes, and have been extensively studied and utilized recently. They are at the core of this review article which is divided into two main sections. The first one focuses on an exhaustive and comprehensive overview of the structural, photophysical and electrochemical properties of mononuclear copper(I) complexes, typical examples highlighting the most critical structural parameters and their impact on the properties being presented to enlighten future design of photoactive copper(I) complexes. The second section is devoted to their main areas of application (photoredox catalysis of organic reactions and polymerization, hydrogen production, photoreduction of carbon dioxide and dye-sensitized solar cells), illustrating their progression from early systems to the current state-of-the-art and showcasing how some limitations of photoactive copper(I) complexes can be overcome with their high versatility.

Photoactive Copper Complexes: Properties and Applications.

Atom transfer radical addition (ATRA) reactions are linchpin transformations in synthetic chemistry enabling the atom-economic difunctionalization of alkenes. Thereby a rich chemical space can be accessed through smart combinations of simple starting materials. Originally, these reactions required toxic and hazardous radical initiators or harsh thermal activation and thus, the recent resurgence and dramatic evolution of photocatalysis appeared as an attractive complement to catalyze such transformations in a mild and energy-efficient manner. Initially, this technique relied primarily on complexes of precious metals, such as ruthenium or iridium, to absorb the visible light. Hence, copper photocatalysis rapidly developed into a powerful alternative, not just from an economic point of view. Originally considered to be disadvantageous as a pathway for deactivation by quenching their excited state, the dynamic nature of Cu-complexes enables them to undergo facile ligand exchange and thus opens up special opportunities for transformations utilizing their inner-coordination sphere. Moreover, the ability of Cu(II), representing a persistent radical, to capture incipient radicals offers the possibility to access heretofore elusive two-component, but also three-component, ATRA reactions, not feasible with ruthenium or iridium catalysts. In this regard, the idea of using Cu(I)-substrate assemblies as active photocatalysts is an emerging field to achieve such 3-component coupling reactions even under enantioselective control, which is reflected by an increasing number of reports being covered in this review.

Copper-photocatalyzed ATRA reactions: concepts, applications, and opportunities.

Phosphine Evaluation on a New Series of Heteroleptic Copper(I) Photocatalysts with dpa Ligand [Cu(dpa)(P,P)]BF4

The intermediacy of alkoxy radicals in cerium-catalyzed C-H functionalization via H-atom abstraction has been unambiguously confirmed. Catalytically relevant Ce(IV)-alkoxide complexes have been synthesized and characterized by X-ray diffraction. Operando electron paramagnetic resonance and transient absorption spectroscopy experiments on isolated pentachloro Ce(IV) alkoxides identified alkoxy radicals as the sole heteroatom-centered radical species generated via ligand-to-metal charge transfer (LMCT) excitation. Alkoxy-radical-mediated hydrogen atom transfer (HAT) has been verified via kinetic analysis, density functional theory (DFT) calculations, and reactions under strictly chloride-free conditions. These experimental findings unambiguously establish the critical role of alkoxy radicals in Ce-LMCT catalysis and definitively preclude the involvement of chlorine radical. This study has also reinforced the necessity of a high relative ratio of alcohol vs Ce for the selective alkoxy-radical-mediated HAT, as seemingly trivial changes in the relative ratio of alcohol vs Ce can lead to drastically different mechanistic pathways. Importantly, the previously proposed chlorine radical-alcohol complex, postulated to explain alkoxy-radical-enabled selectivities in this system, has been examined under scrutiny and ruled out by regioselectivity studies, transient absorption experiments, and high-level calculations. Moreover, the peculiar selectivity of alkoxy radical generation in the LMCT homolysis of Ce(IV) heteroleptic complexes has been analyzed and back-electron transfer (BET) may have regulated the efficiency and selectivity for the formation of ligand-centered radicals.

Identification of Alkoxy Radicals as Hydrogen Atom Transfer Agents in Ce-Catalyzed C-H Functionalization.

Four new mixed ligand Cu(I) complexes bearing methoxycarbonyl imidoyl-indazole and bis[2-(diphenylphosphino)-phenyl]ether (POP) ligands were synthesized and characterized by variable-temperature NMR, FT-IR, EA and HRMS. For three of them, the molecular structures were obtained by X-ray diffraction analysis. The electrochemical and absorption–emission properties of all the complexes were investigated by using cyclic voltammetry, UV-Vis spectroscopy, and spectrofluorometric measurements in a CH2Cl2 solution at room temperature and in different solid-state matrices. In addition, quantum chemical computations were performed to gain insight into their electronic and photophysical properties. The complexes showed an MLCT band, which is more influenced by the position of the electron-withdrawing methoxycarbonyl substituent in the indazole ring rather than by the π-extension introduced by the alkene moiety. Besides, all the complexes were found to be weak emitters in the CH2Cl2 solution while they were brighter emitters in the solid-state.

Heteroleptic Cu(I) complexes bearing methoxycarbonyl-imidoylindazole and POP ligands – an experimental and theoretical study of their photophysical properties

Iron(III)-Light-Induced Homolysis: A Dual Photocatalytic Approach for the Hydroacylation of Alkenes Using Acyl Radicals via Direct HAT from Aldehydes

Influence of the thermal stability of ammonium perchlorate in presence of heteroleptic Copper (I) complexes bearing ethane-1,2-diimine and biphosphines

Marco A. Henriquez

Papers

Phosphine Evaluation on a New Series of Heteroleptic Copper(I) Photocatalysts with dpa Ligand [Cu(dpa)(P,P)]BF4

Heteroleptic Cu(I) complexes bearing methoxycarbonyl-imidoylindazole and POP ligands – an experimental and theoretical study of their photophysical properties

Iron(III)-Light-Induced Homolysis: A Dual Photocatalytic Approach for the Hydroacylation of Alkenes Using Acyl Radicals via Direct HAT from Aldehydes

Influence of the thermal stability of ammonium perchlorate in presence of heteroleptic Copper (I) complexes bearing ethane-1,2-diimine and biphosphines