Christiane Dietrich-Buchecker

Une nouvelle famille de molecules : les metallo-catenanes

Abstract A new strategy has been developed for synthesizing catenanes; it is based on a generalized template effect, as shown in Figure 1. The first example of a novel class of molecules, the metallo-catenanes , has been obtained in good yield : it contains copper (I) and macrocyclic phenanthroline derivatives.

Templated synthesis of interlocked macrocyclic ligands, the catenands. Preparation and characterization of the prototypical bis-30 membered ring system

Abstract We describe here the detailed template synthesis of a copper(I) catenate. Demetallation leads to the corresponding free ligand, a catenand. Both molecules are made of two interlocked 30 membered rings.

Rotaxanes and catenanes as prototypes of molecular machines and motors

In the course of the last 20 years, our view on rotaxanes and catenanes has completely changed. Copper(I)-templated strategies, in particular, have allowed us to prepare catenanes on a real preparative scale, in a few chemical steps from commercially available compounds. A particularly significant improvement was the introduction of the recently developed ring-closing metathesis reaction, using Grubbs catalyst. The dynamic properties of rotaxanes and catenanes has been exploited to construct molecular systems for which one component can be set in motion under the action of an external signal, while the other components can be considered as motionless (artificial molecular “machines ”and “motors ”). A particularly representative example is that of a rotaxane dimer, whose overall length can be controlled chemically: A metal exchange reaction (CuI/ZnII) triggers a reversible contraction/stretching process of the same molecular assembly, in a way reminiscent of the functioning of biological muscles.

Synthese de composes polyethers macrocycliques derives de la phenanthroline-1,10 diphenyl-2,9.

Abstract The macrocylic compounds (V) and (VI) have been synthesized in three steps from phenanthroline, with an overall yield of 35%. These new ligands contain two coordination sites whose electronic properties are drastically different : the phenanthroline subunit and the polyoxyethylene chain; the latter prevents ligands (V) or (VI) from forming analogues of bis-phenanthroline complexes of transition metals.

Absorption and luminescence properties of 1, 10-phenanthroline, 2, 9-diphenyl-1, 10-phenanthroline, 2,9-dianisyl-1, 10-phenanthroline and their protonated forms in dichloromethane solution

Addition of trifluoroacetic acid to CH2Cl2 solutions of 1, 10-phenanthroline (1), 2,9-diphenyl-1, 10-phenanthroline (2) and 2,9-dianisyl-1, 10-phenanthroline (3) causes strong changes in the absorption and fluorescence spectra at room temperature. The low-energy absorption bands move to the red, while isosbestic points are maintained. The intensity of the structured, short-lived ππ* fluorescence band decreases and a new, unstructured longer-lived fluorescence band arises at longer wavelength. The number of equivalents of acid needed to obtain 50% protonation in the ground state increases in the series 3 < 2 < 1. The spectral changes can be fully reversed by addition of base. The proton affinity in the singlet excited state is higher than that in the ground state (ΔpKa≈ 14 units for 3), but the protonation and deprotonation processes are too slow to compete with the excited-state decay. In a rigid CH2Cl2 matrix at 77 K the shift of the fluorescence band upon protonation is smaller than that observed at room temperature. The effect of protonation on the phosphorescence band, which can be observed in the rigid CH2Cl2 matrix at 77 K, is very small.

Synthesis of catenanes and molecular knots by copper(I)-directed formation of the precursors followed by ruthenium(II)-catalysed ring-closing metathesis

Abstract Catenanes and knots are fascinating molecular systems, but for several decades these compounds have been regarded as exotic species due to synthetic difficulties. We have proposed template strategies based on transition metals (mostly copper(I)), and this approach has allowed us to make a wide family of interlocking rings and knots in the course of the last 15 years. A very recent and practically important improvement now permits relatively easy preparation of some of these systems with, in some cases, almost quantitative yields. The key step is the ring-closing metathesis (RCM) of olefins, using the extremely efficient and mild catalysts developed by Grubbs et al. in the last few years, and consisting of ruthenium carbenes.

Interlocked and Knotted Rings in Biology and Chemistry

Catenanes are chemical entities consisting of two or more interlocked rings. Such systems, as well as knotted molecules, belong to a branch of chemistry which is related to mathematics, molecular biology and graphic art. Many endeavours have been made to build such topologicaly novel compounds. The statistical methods of preparation, although very simple to conceive and to attempt, are of little practical utility. The directed strategy, using the classical reactions of organic synthesis, offers an interesting alternative route to prepare interlocked ring systems. The most recent approaches, utilizing templated reactions either on transition metals or on organic electron donoracceptor pairs are certainly the most efficient ones for making catenanes. For instance, a gram-scale preparation of [3]-catenanes (two peripheral rings separately interlocked to a central cycle) has been achieved using the transition metal template approach. The metal is able to gather and pre-oriente the several fragments to be incorporated into the target molecule. Although knotted forms of DNA are relatively common, no synthetic molecular knot had been obtained until recently. Here again, the success of the synthetic approach relies on the use of transition metals as templating species. Multinuclear double-stranded helices are interesting intermediate compounds which should allow the preparation of molecular knots and catenanes of increasing topological complexity. The first molecular trefoil knot has only been synthesized and fully characterized recently, although theoretical discussions on chemical knots were published over thirty years ago.

Selective and efficient synthesis of di-, tri- and tetrasubstituted 1, 10-phenanthrolines

A general synthetic procedure for the preparation of multisubstituted phenanthrolines is presented. Bromination of 1, 10-phenanthroline at the 3 and 8 positions, followed by Suzuki coupling reaction and subsequent methylation afford the di-, tri and tetra- substituted phenanthrolines in good yields. These phenanthroline derivatives are useful building blocks in the construction of highly sophisticated molecular architectures. 1, 10-Phenanthrolines1–4b have been synthesized in good yields. Download full-size image

Cyclopropenes electrophiles—II : Synthese par photolyse de dimethyl-3,3 pyrazolenines

Abstract The photolysis of 3,3-dimethyl-3H-pyrazoles derived from 2-diazopropane and acetylenic esters and nitriles leads in good yields to electrophilic cyclopropenes Starting from acetylenic ketones, only the 4-keto-3H-pyrazoles give acylcyclopropenes, the photolysis of the 5-keto-derivatives leading mainly to vinylketenes.

Transition metals as assembling and templating species: From catenanes and knots to organized multi-porphyrins arrays

Absrrucr. New dicopper(1) knots have been synthesized as well as their face-to-face isomers. The knots range from 80 to 90-membered rings and their preparation yields depend crucially on structural parameters such as number of methylene fragments linking the two chelating units and length of the polyethyleneoxy unit used in the cyclization reaction. The best yield was obtained for an 84-membered knotted ring with a -(CH2)6connector : this relatively long fragment allows pronounced winding of the double helix precursor and is thus favorable to the knotting reaction. The X-ray structures of two dicopper trefoil knots are also presented and discussed. The transition metal-directed threading of a molecular fragment containing a central chelate and an end-attached gold(II1) porphyrin into a presynthesized coordinating ring affords a general precursor to a rotaxane-type structures. After threading, construction of the second porphyrin acting as an efficient stopper affords a copper(1) complexed [2]-rotaxane as well as a novel compartmental [3]-rotaxane.