X. Ribas/M. Costas (QBIS-UdG)

Supramolecular Fullerene Sponges as Catalytic Masks for Regioselective Functionalization of C60

Isomer-pure poly-functionalized fullerenes are required to boost the development of fullerene chemistry in all fields. On a general basis, multi-adduct mixtures with uncontrolled regioselectivity are obtained, and the use of chromatographic purification is prohibitively costly and time consuming, especially in the production of solar cells. Single-isomer poly-functionalized fullerenes are only accessible via stoichiometric, multistep paths entailing protecting-unprotecting sequences. Herein, a nanocapsule is used as a supramolecular tetragonal prismatic mask to exert full control on the reactivity and the equatorial regioselectivity of Bingel-Hirsch cyclopropanation reactions of a confined C ₆₀ guest. Thus, equatorial bis-, tris-, and tetrakis-C ₆₀ homo-adducts are exclusively obtained in a stepwise manner. Furthermore, isomer-pure equatorial hetero-tetrakis-adducts or hetero- Th-hexakis-adducts are synthesized at will in one-pot synthesis for the first time. This work provides a synthetically valuable path to produce a plethora of new pure-isomer poly-functionalized C ₆₀-based compounds as candidates for testing in solar cell devices and biomedical applications.

Cyclometalated Gold(III) Complexes: Noticeable Differences between (N,C) and (P,C) Ligands in Migratory Insertion

Gold(III) complexes are garnering increasing interest for opto-electronic, therapeutic and catalytic applications. But so far, very little is known about the factors controlling their reactivity and the very influence of the ancillary ligand. This article reports the first comprehensive study on this topic. The reactivity of a cationic (N,C) gold(III) complex, namely 1A, towards ethylene has been thoroughly studied and compared with that of the related (P,C) complex 1C. A cationic gold(III) complex 5A resulting from double insertion of ethylene was selectively obtained. Complex 5A was found to be remarkably stable. It was trapped with chloride and fully characterized. In marked contrast to that observed with 1C, no β-H elimination or linear-to-branched rearrangement of the alkyl chain occurred with 1A. The energy profile for the reactions of 1A with ethylene has been comprehensively investigated computationally, and the influence of the ancillary ligand has been precisely delineated. Because nitrogen is a weaker donor than carbon (and phosphorus), the (N,C) ligand is very electronically dissymmetric, much more than the (P,C) ligand. This makes the two reactive sites at gold quite different, which noticeably influences the competition between migratory insertion and β-H elimination, and actually changes the outcome of the olefin insertion at gold. This study provides valuable insight into the influence of ancillary ligands on gold(III) reactivity, something critical to further develop Au(III) and Au(I)/Au(III) catalysis.

Carboxylate-Assisted Formation of Aryl-Co(III) Masked-Carbenes in Cobalt-Catalyzed C-H Functionalization with Diazo Esters

Herein we describe the synthesis of a family of aryl-Co(III)-carboxylate complexes and their reactivity with ethyl diazoacetate. Crystallographic, full spectroscopic characterization, and theoretical evidence of unique C-metalated aryl-Co(III) enolate intermediates is provided, unraveling a carboxylate-assisted formation of aryl-Co(III) masked-carbenes. Moreover, additional evidence for an unprecedented Co(III)-mediated intramolecular S_N2-type C–C bond formation in which the carboxylate moiety acts as a relay is disclosed. This novel strategy is key to tame the hot reactivity of a metastable Co(III)-carbene and elicit C–C coupling products in a productive manner.

Isolation of Key Organometallic Aryl-Co(III) Intermediates in Cobalt- Catalyzed C(sp2)−H Functionalizations and New Insights into Alkyne Annulation Reaction Mechanisms

The selective annulation reaction of alkynes with substrates containing inert C−H bonds using cobalt as catalyst is currently a topic attracting significant interest. Unfortunately, the mechanism of this transformation is still relatively poorly understood, with little experimental evidence for intermediates, although an organometallic Co(III) species is generally implicated. Herein, we describe a rare example of the preparation and characterization of benchtop-stable organometallic aryl-Co(III) compounds (NMR, HRMS, XAS, and XRD) prepared through a C(sp2)−H activation, using a model macrocyclic arene substrate. Furthermore, we provide crystallographic evidence of an organometallic aryl-Co(III) intermediate proposed in 8-aminoquinoline-directed Co-catalyzed C−H activation processes. Subsequent insights obtained from the application of our new organometallic aryl-Co(III) compounds in alkyne annulation reactions are also disclosed. Evidence obtained from the resulting regioselectivity of the annulation reactions and DFT studies indicates that a mechanism involving an organometallic aryl-Co(III)-alkynyl intermediate species is preferred for terminal alkynes, in contrast to the generally accepted migratory insertion pathway.

Sponge-like molecular cage for purification of fullerenes

A supramolecular nanocage synthesized by metal-directed self-assembly, which encapsulates fullerenes of different sizes and exclusively extract pure C60 from a solid sample of cage charged with a mixture of fullerenes is described

Aryl-Copper(III)-Acetylides as Key Intermediates in Csp2-Csp Model Couplings under Mild Conditions

The reactivity of a well-defined aryl-CuIII species with p-R-phenylacetylenes (R=NO2, CF3, H) is reported and it is found that facile reductive elimination from a putative aryl-CuIII-acetylide species occurs at room temperature to afford the C(aryl.)-C(sp) coupling species (IR), which in turn undergo an intramolecular reorganisation to afford final heterocyclic products containing 2H-isoindole or 1,2-dihydroisoquinoline substructures.