A Resorcin[4]arene-Based Phosphite-Phosphine Ligand for the Branched-Selective Hydroformylation of Alkyl Alkenes

Synthesis of a chelating phosphite-phosphine ligand from a tris(quinoxaline) extended resorcin[4]arene and its application in the rhodium-catalyzed hydroformylation of terminal alkyl alkenes are reported. Rhodium complexes are formed within the cavity of the macrocycle and branched-selective hydroformylation of 1-octene with a b/l ratio of 5.9 has been achieved at 60 °C under 1:1 H2/CO (20 bar).

Synthesis, Resolution, and Absolute Configuration of a Phosphine-Based Hemicryptophane Cage with an Endo Phosphorus Lone Pair and Formation of the Corresponding Gold Complex

The synthesis, characterization, and chiroptical properties of a new class of hemicryptophanes combining a phosphine moiety and a cyclotriveratrylene unit are reported. The synthesis was short and efficient. The racemic mixture of the cage was resolved by chiral high-performance liquid chromatography (HPLC), giving access to enantiopure molecular cages, whose absolute configurations could be assigned by electronic circular dichroism (ECD) spectroscopy. These new phosphines were then reacted with gold in order to make the corresponding enantiopure gold complexes. The X-ray structure reveals an endohedral functionalization of the cage with the gold metal entrapped in the heart of the cavity, leading to a Vbur of 58%. Moreover, the chirality of the cyclotriveratrylene unit was found to control the chiral arrangement of the aryl group linked to the phosphorus atom, located at the opposite side of the cavity.

Structural and conformational analysis of a biaryl phosphine integrating a calix[4]arene cavity. Can the phosphorus atom behave as an introverted donor?

The conformational preference of a cavity-based biaryl phosphine, namely 5-(2-diphenylphosphinyl-phenyl)-25,26,27,28-tetrapropyloxycalix[4]arene (L) has been investigated by density functional theory calculations. The analysis showed that the barrier to rotation about the C-C axle of the biaryl unit is only 10.7 kcal mol^-1, this rendering possible access to conformers of two types, those in which the P lone pair sits at the cavity entrance and points to the calixarene interior, others with a more open structure where the P atom is located outside the cavity. As revealed by a single crystal X-ray diffraction study, the biaryl phosphine appears virtually as an atropisomer in the solid state in which the phosphorus atom lies totally out of the cavity defined by the four phenoxy rings.

Synthesis of a rhodium(III) dinitrogen complex using a calix[4]arene-based diphosphine ligand

The synthesis and characterisation of the rhodium(III) dinitrogen complex [Rh(2,2'-biphenyl)(CxP₂)(N₂)]⁺ are described, where CxP₂ is a trans-spanning calix[4]arene-based diphosphine and the dinitrogen ligand is projected into the cavity of the macrocycle.

Probing the Importance of Host Symmetry on Carbohydrate Recognition

The design of molecular cages with low symmetry could allow for more specific tuning of their properties and better mimic the unsymmetrical and complex environment of protein pockets. However, the added value of lowering symmetry of molecular receptors has been rarely demonstrated. Herein, C₃ - and C₁ -symmetrical cages, presenting the same recognition sites, have been synthesized and investigated as hosts for carbohydrate recognition. Structurally related derivatives of glucose, galactose and mannose were found to have greater affinity to the receptor with the lowest symmetry than to their C₃ -symmetrical analogue. According to the host cavity modelling, the C₁ symmetry receptor exhibits a wider opening than its C₃ -symmetrical counterpart, providing easier access and thus promoting guest proximity to binding sites. Moreover, our results show the high stereo- and substrate selectivity of the C₁ symmetry cage with respect to its C₃ counterpart in the recognition of sugars.

Diametric calix[6]arene gold(I) catalysts for intramolecular cyclopropanations of 1,6-dienynes

We report a solid-state structural investigation of diametric calix[6]arene-based phosphine gold(I) cavitands which are characterised by two specific, different 1,2,3-alternate conformations in solution and in the solid state. The effect of the specific orientation of phosphines, with respect to macrocycles, was studied in intramolecular cyclopropanation of 1,6-dienynes. The general applicability of these catalysts was disclosed, delivering a family of polycycles with high yields and functional group tolerance.

A cavity-shaped cis-chelating P,N ligand for highly selective nickel-catalysed ethylene dimerisation

The presence of a permethylated α-cyclodextrin (α-CD) cavity in a chelating P,N ligand promotes exclusive formation of 1 : 1 ligand/metal complexes. In MX₂ complexes, one of the two halido ligands is forced to reside inside the CD hollow while the second one is pointing outside. Unlike its cavity-free analogue, a Ni(II) complex of the CD ligand is a highly selective precatalyst for ethylene dimerisation (96% C₄ selectivity with up to 95% of 1-butene within the C₄ fraction).

Diametric calix[6]arene-based phosphine gold(I) cavitands

We report the synthesis and characterization, in low polarity solvents, of a novel class of diametric phosphine gold(I) cavitands characterized by a 1,2,3-alternate geometry. Preliminary catalytic studies were performed on a model cycloisomerization of 1,6-enynes as a function of the relative orientation of the bonded gold(I) nuclei with respect to the macrocyclic cavity.

Mimicking Enzymes: Taking Advantage of the Substrate-Recognition Properties of Metalloporphyrins in Supramolecular Catalysis

The present review describes the most relevant advances dealing with supramolecular catalysis in which metalloporphyrins are employed as substrate-recognition sites in the second coordination sphere of the catalyst. The kinetically labile interaction between metallo­porphyrins (typically, those derived from zinc) and nitrogen- or oxygen-containing substrates is energetically comparable to the non-covalent interactions (i.e., hydrogen bonding) found in enzymes enabling substrate preorganization. Much inspired from host–guest phenomena, the catalytic systems described in this account display unique activities, selectivities and action modes that are difficult to reach by applying purely covalent strategies.

Frustrated Behavior of Lewis/Brønsted Pairs inside Molecular Cages

Different endohedrally functionalized cages were designed to investigate the effects of the size and shape of molecular cavities on the frustrated behavior of Lewis/Brønsted acid-base pairs and on catalytic activities....