Metallated cavitands (calixarenes, resorcinarenes, cyclodextrins) with internal coordination sites

International audienceAlthough quite common in nature, notably in metalloenzymes, the coordination of transition metals within a confined three dimensional environment has long been hampered by the lack of molecular receptors that may force ligand binding to take place internally. However, an increasing number of appropriate cavity-shaped molecules has become available over the years. Their modification with donor atoms has led to metalloreceptors that can not only bind substrates inside a well-defined hollow space, but which can also promote transformations of the confined guests. This article gives an overview of transition metal complexes capable of directing the binding of exogeneous ligands inside a molecular cavity. Special emphasis is placed on the stabilisation of unusual coordination modes and geometries as well as the role of the cavity in catalysis and metal-assisted molecular recognition

"Through-space" nuclear spin-spin couplings in ferrocenyl polyphosphanes: a new way of gathering structural information in constrained ligands by NMR

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Regioselective di- and tetra-functionalisation of γ-cyclodextrin using capping methodology.

International audienceAlkylation of γ-cyclodextrin with 3 equiv. of 1,3-bis[bis(4-tert-butylphenyl)chloromethyl]benzene, followed by permethylation afforded selectively a singly capped (A,B), as well as two doubly capped (A,B:D,E and A,B:E,F) methylated γ-CDs. Deprotection with HBF4 gave quantitatively the corresponding diols and tetrols, which constitute valuable starting compounds for further functionalisation

Non-conventional coordination of cavity-confined metal centres.

International audienceWIDEPHOS, a β-cyclodextrin cavitand bearing two introverted P(III) donor atoms, readily accommodates two converging Au-X fragments (X = Cl, Br, I). In the corresponding [(WIDEPHOS)(AuX)(2)] complexes, severe steric crowding within the cavity results in one of the P-Au-X rods deviating from linearity, as revealed by an X-ray diffraction study and unusual (31)P magnetic shielding of one of the two phosphorus signals. The cavitand ligand is also suited for hosting strained dipalladium moieties with a single chlorido bridge, thereby forming dynamic complexes in which ligand coordination to one of the metal centres occurs via an oschelating P,O-subunit

TRANSDIP: a trans-chelating ligand tailor-made for probing unusual Pd0 and PdII intermediates.

International audienceForty years after Venanzi's seminal studies on trans-spanning diphosphines, a cavity-shaped trans chelator (TRANSDIP) has been used to monitor the stepwise formation of a carbon-carbon bond on a palladium centre. Furthermore, the ligand, which incorporates a cyclodextrin subunit, enabled the synthesis of the first η(2)-dioxygen complex in which the M-O(2) unit is entrapped within a cavity