Light-Induced Reactivity Switch at O2-Activating Bioinspired Copper(I) Complexes.

Using light to unveil unexplored reactivities of earth-abundant metal-oxygen intermediates is a formidable challenge, given the already remarkable oxidation ability of these species in the ground state. However, the light-induced reactivity of Cu-O2 intermediates still remains unexplored, due to the photoejection of O2 under irradiation. Herein, we describe a photoinduced reactivity switch of bioinspired O2-activating CuI complexes, based on the archetypal tris(2-pyridyl-methyl)amine (TPA) ligand. This report represents a key precedent for light-induced reactivity switch in Cu-O2 chemistry, obtained by positioning C-H substrates in close proximity of the active site. Open and caged CuI complexes displaying an internal aryl ether substrate were evaluated. Under light, a Cu-O2 mediated reaction takes place that induces a selective conversion of the internal aryl ether unit to a phenolate-CH2- moiety with excellent yields. This light-induced transformation displays high selectivity and allows easy postfunctionalization of TPA-based ligands for straightforward preparation of challenging heteroleptic structures. In the absence of light, O2 activation results in the standard oxidative cleavage of the covalently attached substrate. A reaction mechanism that supports a monomeric cupric-superoxide-dependent reactivity promoted by light is proposed on the basis of reactivity studies combined with (TD-) DFT calculations.

Spectroscopy of End-On Copper(II) Superoxido Complexes: A Wave Function-Based Analysis.

Wave function methods are employed to analyze the ground and low-lying excited states of bipyramid trigonal copper(II) superoxido complexes, up to their characteristic ligand to metal charge transfer band. Several multireference methods have been combined to provide new insights into the interpretation of their experimental absorption spectra. We show that the intraligand transition on the dioxygen leads to a dark state. Among the results, we shall highlight the finding of doubly excited states in the region of the d-d transitions and the subtle interplay between Cu(I) and Cu(II) in the ground and excited states. Some of these findings could be obtained only with multireference methods.

Mechanistic insight into cobalt-mediated [2 + 2 + 2]-cycloaddition reactions with γ-alkylidenebutenolide and γ-alkylidenebuterolactam as 2π partners.

The molecular complexity of recently reported cobalt(III) polycyclic complexes, resulting from an intramolecular formal (2 + 2 + 3) cycloaddition reaction on an enediyne containing a lactone moiety, has prompted us to computationally review the mechanisms of cobalt cycloaddition reactions with γ-alkylidenebutenolide or γ-alkylidenebuterolactam as 2π partners. Computed mechanisms are compared, leading to either cobalt(III)- or cobalt(I)-spiro complexes depending of both the nature of the reaction (intra- vs. intermolecular pathway) and the nature of the 2π partner (γ-alkylidenebutenolide vs. γ-alkylidenebuterolactam). These proposed mechanisms are supported by experiments, allowing us to report the synthesis and characterization of the predicted compounds.

Accurate computed singlet-triplet energy differences for cobalt systems: implication for two-state reactivity.

Accurate singlet-triplet energy differences for cobalt and rhodium complexes were calculated by using several wave function methods, such as MRCISD, CASPT2, CCSD(T) and BCCD(T). Relaxed energy differences were obtained by considering the singlet and triplet complexes, each at the minimum of their potential energy surfaces. Active spaces for multireference calculations were carefully checked to provide accurate results. The considered systems are built by increasing progressively the first coordination sphere around the metal. We included in our set two CpCoX complexes (Cp = cyclopentadienyl, X = alkenyl ligand), which have been suggested as intermediates in cycloaddition reactions. Indeed, cobalt systems have been used for more than a decade as active species in this kind of transformations, for which a two-state reactivity has been proposed. Most of the considered systems display a triplet ground state. However, in the case of a reaction intermediate, while a triplet ground state was predicted on the basis of Density Functional Theory results, our calculations suggest a singlet ground state. This stems from the competition between the exchange term (stabilising the triplet) and the accessibility of an intramolecular coordination (stabilising the singlet). This finding has an impact on the general mechanism of the cycloaddition reaction. Analogous rhodium systems were also studied and, as expected, they have a larger tendency to electron pairing than cobalt species.

A caged tris(2-pyridylmethyl)amine ligand equipped with a Ctriazole-H hydrogen bonding cavity.

A capped bioinspired ligand built from a tris(2-pyridyl-methyl)amine (TPA) unit and surmounted by a triazole-based intramolecular H-bonding secondary sphere was prepared. The resulting cage provides a well-defined cavity combining the hydrophobic nature with H-bonding properties. Its coordinating properties were explored using Zn(II) and Cu(II) metal ions.

Thermally Induced Synthesis of Anthracene-, Pyrene- and Naphthalene-Fused Porphyrins.

The synthesis of π-extended porphyrins containing anthracenyl moieties still represents an important challenge. Here, we report on the synthesis of a series of unsubstituted naphthyl-, pyrenyl- and anthracenyl-fused zinc porphyrin derivatives. To this aim, meso-substitued porphyrins are synthesized and the fusion of the PAHs (Polycyclic Aromatic Hydrocarbon) on the ß-positions are performed through thermally induced dehydro-aromatization. The fused zinc-porphyrin derivatives are fully characterized and their optical absorption and photoluminescence properties are reported. We also demonstrate that zinc can be removed from the porphyrin core, giving rise to pure C, H, N materials. This work constitutes the first step towards the synthesis of the fully-fused tetra-anthracenylporphyrin.