Dominique Armspach

Bucky Ligands: Synthesis, Ruthenium(II) Complexes, and Electrochemical Properties

Oligopyridine ligands with attached methanofullerene C60units have been prepared (e.g., 1) and their coordination behaviour investigated. The electrochemical properties of the resulting ruthenium(II) complexes are also described.

Boron-rich metallodendrimers—mix-and-match assembly of multifunctional metallosupramolecules

A dendritic system based upon a pentaerythritol unit bearing pendant 2,2′:6′,2″-terpyridine metal-binding domains is described; tetranuclear complexes bearing pendant carborane units are reported.

Confining Phosphanes Derived from Cyclodextrins for Efficient Regio- and Enantioselective Hydroformylation**

Two confining phosphane ligands derived from either α- or β-cyclodextrin produce singly P(III) -ligated metal complexes with unusual coordination spheres. High-pressure NMR studies have revealed that rhodium hydride complexes of the same type are also formed under hydroformylation conditions. This unique feature strongly favors the formation of the branched aldehyde at the expense of the linear one with high enantioselectivity in the rhodium-catalyzed hydroformylation of styrene.

Carbaborane-functionalised 2,2′:6′,2″-terpyridine ligands for metallosupramolecular chemistry: Syntheses, complex formation, and the crystal and molecular structures of 4′-( ortho -carboranyl)-2,2′:6′,2″-terpyridine and 4′-( ortho -carboranylpropoxy)-2,2′:6′,2″-terpyridine

Abstract A series of functionalised 2,2′:6′,2″-terpyridine ligands, each with a closo -1,2-C 2 B 10 H 10 R (R=H or Si t BuMe 2 ) substituent in the 4′ position, either directly or indirectly attached to the heterocyclic ring, has been prepared; two members of the series, 4′-(3- ortho -carboranylpropoxy)-2,2′:6′,2″-terpyridine ( 4 ) and 4′-( ortho -carboranyl)-2,2′:6′,2″-terpyridine ( 7 ) have been characterised by X-ray crystallography. The reaction of ligand ( 7 ) with alcohols results in the boron decapping of the closo- cage and yields a Zwitter-ionic nido -cluster-functionalised ligand. Analogous changes to the carbaborane cage have been observed in complexes in which the terpyridine domain is coordinated to ruthenium(II). However, decapping does not occur if a Si t BuMe 2 -protected carbaborane cage is incorporated into the terpyridine ligands.

Regioselective Double Capping of Cyclodextrin Scaffolds

Four different regioselective double capping reactions were applied either to α- or β-cyclodextrin (CD) scaffolds. The first, which relied on the use of a rigid, bulky dialkylating reagent containing two trityl-like subunits, gave access to an A,B,D,E-tetrafunctionalised β-CD regioisomer in large scale reactions. Two further capping reactions, involving the dianions PhP(2-) and S(2- , led to the synthesis of new C(1)-symmetrical β-cyclodextrins in which pairs of neighbouring glucose units are linked by very short spacers. The last double capping reaction described allowed the high-yield preparation of unprecedented α- and β-cyclodextrins containing two sulfate handles. Proximal capping turned out to be favoured for each of the above difunctional reagents. The structural characterisation of the capped species was achieved by thorough NMR investigations as well as by single-crystal X-ray diffraction studies.

Dicobalt cluster functionalized 2,2′:6′,2″-terpyridine ligands and their ruthenium(II) complexes

Abstract A series of 2,2′:6′,2″-terpyridine (tpy) ligands functionalized in the 4′-position with alkyne substituents has been prepared and characterized. Treatment of these ligands with [RuCl3(tpy)] yields complexes with pendant alkyne groups which then readily react with Co2(CO)8 to give novel compounds containing both cluster and classical coordination motifs. The new compounds are characterized by mass spectrometric and spectroscopic methods, and the single crystal structure of [Ru(tpy)(4′-HCCCH2Otpy)][PF6]2 is reported.

Regioselective opening of proximally sulfato-capped cyclodextrins.

Sulfato groups capping one or two pairs of adjacent glucose units in methylated cyclodextrin (CD) derivatives have been found to undergo regioselective opening with various nucleophiles; the reported methodology opens the way to the efficient synthesis of tridifferentiated α- and β-cyclodextrins that constitute key starting materials for the preparation of heteropolydentate cavitands.

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

Forty years after Venanzis 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.

Phosphinocyclodextrins as confining units for catalytic metal centres. Applications to carbon–carbon bond forming reactions

Summary The capacity of two cavity-shaped ligands, HUGPHOS-1 and HUGPHOS-2, to generate exclusively singly phosphorus-ligated complexes, in which the cyclodextrin cavity tightly wraps around the metal centre, was explored with a number of late transition metal cations. Both cyclodextrin-derived ligands were assessed in palladium-catalysed Mizoroki–Heck coupling reactions between aryl bromides and styrene on one hand, and the rhodium-catalysed asymmetric hydroformylation of styrene on the other hand. The inability of both chiral ligands to form standard bis(phosphine) complexes under catalytic conditions was established by high-pressure NMR studies and shown to have a deep impact on the two carbon–carbon bond forming reactions both in terms of activity and selectivity. For example, when used as ligands in the rhodium-catalysed hydroformylation of styrene, they lead to both high isoselectivity and high enantioselectivity. In the study dealing with the Mizoroki–Heck reactions, comparative tests were carried out with WIDEPHOS, a diphosphine analogue of HUGPHOS-2.

Non-conventional coordination of cavity-confined metal centres

WIDEPHOS, 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.