Heteroleptic Copper(I) Pseudorotaxanes Incorporating Macrocyclic Phenanthroline Ligands of Different Sizes.

A series of copper(I) pseudorotaxanes has been prepared from bis[2-(diphenylphosphino)phenyl] ether (POP) and macrocyclic phenanthroline ligands with different ring sizes (m30, m37, and m42). Variable-temperature studies carried out on the resulting [Cu(mXX)(POP)]+ (mXX = m30, m37, and m42) derivatives have revealed a dynamic conformational equilibrium due to the folding of the macrocyclic ligand. The absorption and luminescence properties of the pseudorotaxanes have been investigated in CH2Cl2. They exhibit metal-to-ligand charge-transfer emission with photoluminescence quantum yields (PLQYs) in the range 20-30%. The smallest system [Cu(m30)(POP)]+ shows minimal differences in spectral shape and position compared to its analogues, suggesting a slightly distorted coordination environment. PLQY is substantially enhanced in poly(methyl methacrylate) films (∼40-45%). The study of emission spectra and excited-state lifetimes in powder samples as a function of temperature (78-338 K) reveals thermally activated delayed fluorescence, with sizable differences in the singlet-triplet energy gap compared to the reference compound [Cu(dmp)(POP)]+ (dmp = 2,9-dimethyl-1,10-phenanthroline) and within the pseudorotaxane series. The system with the largest ring ([Cu(m42)(POP)]+) has been tested as emissive material in OLEDs and affords bright green devices with higher luminance and greater stability compared to [Cu(dmp)(POP)]+, which lacks the macrocyclic ring. This highlights the importance of structural factors in the stability of electroluminescent devices based on Cu(I) materials.

Unconventional Synthesis of a CuI Rotaxane with a Superacceptor Stopper: Ultrafast Excited-State Dynamics and Near-Infrared Luminescence.

A CuI bis-phenanthroline rotaxane was prepared by using the [2+2] cycloaddition-retroelectrocyclization (CA-RE) reaction to graft a bulky dicyanoquinodimethane (DCNQ) stopper. The electronic properties were investigated with electrochemical and photophysical techniques, in parallel with three reference compounds, namely, the DCNQ derivative alone, the DCNQ-based phenanthroline ligand, and an analogue CuI complex lacking the DCNQ moiety. In all the systems containing the DCNQ unit, the lowest electronic excited states are centered thereon, with the singlet level (S1 ) located at about 1.0 eV, as suggested by TDDFT calculations. Accordingly, in the DCNQ-equipped rotaxane, the typical metal-to-ligand charge-transfer luminescence of the CuI center is totally quenched. Ultrafast transient absorption and emission studies show that, in the rotaxane, the final sink of photoinduced processes is the lowest singlet state of the DCNQ moiety (S1 ), which exhibits strong charge-transfer character and a lifetime of 0.4 ps. Its deactivation leads to population of another excited state with a lifetime of 1.3 ps, which can be the related triplet state (T1 ) or a vibrationally hot level (hot-S0 ). Notably, S1 also shows stimulated fluorescence in the near-infrared (NIR) region between 1100 and 1500 nm, corroborating the TDDFT prediction. This unusual finding opens up the study of ultrashort-lived NIR luminescence in organic donor-acceptor systems.

From Chemical Topology to Molecular Machines (Nobel Lecture).

To a large extent, the field of "molecular machines" started after several groups were able to prepare, reasonably easily, interlocking ring compounds (named catenanes for compounds consisting of interlocking rings and rotaxanes for rings threaded by molecular filaments or axes). Important families of molecular machines not belonging to the interlocking world were also designed, prepared, and studied but, for most of them, their elaboration was more recent than that of catenanes or rotaxanes. Since the creation of interlocking ring molecules is so important in relation to the molecular machinery area, we will start with this aspect of our work. The second part will naturally be devoted to the dynamic properties of such systems and to the compounds for which motions can be directed in a controlled manner from the outside, that is, molecular machines. We will restrict our discussion to a very limited number of examples which we consider as particularly representative of the field.

Cyclic [4]rotaxanes containing two parallel porphyrinic plates: toward switchable molecular receptors and compressors.

Twenty years ago, researchers considered the synthesis of simple rotaxanes a challenging task, but with the rapid development of this field, chemists now view these interlocking molecules as accessible synthetic targets. In a major advance for the field, researchers have developed transition metals or organic molecules as templating structures, making it easier to construct these molecular systems. In addition, chemists have found ways to introduce new functional groups, which have given these compounds new properties. Today researchers can also construct multirotaxanes consisting of several individual components, but the synthesis of the most complex structures remains challenging. This Account primarily discusses the cyclic [4]rotaxanes incorporating porphyrins that the Strasbourg group has synthesized and studied during the past few years. These cyclic [4]rotaxanes consist of two rigid rods threaded through the four rings of two molecules of a bis-macrocycle, and the synthetic strategy used for making them relies on the copper(I)-driven "gathering-and-threading" reaction. The formation of the threaded precursors was mostly quantitative, and the quadruple stoppering reaction leading to the target compound produces high yields because of the efficient copper-catalyzed azide-alkyne cycloaddition (CuAAC) or click chemistry reaction. These rotaxanes behave as receptors for various ditopic guests. We prepared and studied two types of molecules: (i) a rigid compound whose copper(I) complex has a well-defined shape, with high selectivity for the guest geometry and (ii) a much more flexible [4]rotaxane host that could act as a distensible receptor. The rigid [4]rotaxane was crystallized, affording a spectacular X-ray structure that matched the expected chemical structure. In addition, metalation or demetalation of the rigid [4]rotaxane induces a drastic geometric rearrangement. The metal-free compound is flat without a binding pocket, while the copper-complexed species forms a rectangle-like structure. The removal of copper(I) also expels any complexed guest molecule, and this process is reversible, making the rigid porphyrinic [4]rotaxane a switchable receptor. The rigid [4]rotaxane was highly selective for short, ditopic guests in its copper(I)-complexed form, but the flexible copper(I)-complexed [4]rotaxane proved to be a versatile receptor. Its conformation can adjust to the size of the guest molecule similar to the induced fit mechanism that some enzymes employ with substrates.

Contractile and extensible molecular figures-of-eight.

Two large rings, 66- (m-66) and 78-membered (m-78) rings, each one incorporating two pairs of transition-metal-complexing units, have been prepared. The coordinating fragments are alternating bi- and tridentate chelating groups, namely, 2,9-diphenyl-1,10-phenanthroline (dpp) and 2,2',2',6''-terpyridine (terpy) respectively. Both macrocycles form molecular figures-of-eight in the presence of Fe(II) , affording a classical bis-terpy complex as the central core. The larger m-78 ring can accommodate a four-coordinate Cu(I) center with the formation of a {Cu(dpp)2 }(+) central complex and a highly twisted figure-of-eight backbone, whereas m-66 is too small to coordinate Cu(I) . Macrocycle m-78 thus affords stable complexes with both Fe(II) and Cu(I) ; the ligand around the metal changes from (terpy)2 to (dpp)2 . This bimodal coordination situation allows for a large amplitude rearrangement of the organic backbone. When coordinated to preferentially octahedrally coordinated Fe(II) or Cu(II) , the height of the molecule along the coordinating axis of the tridentate terpy ligands is only about 11 Å, whereas the height of the molecule along the same vertical axis is several times as large for the tetrahedral Cu(I) complex. Chemically or electrochemically driven contraction and extension motions along a defined axis make this figure-of-eight particularly promising as a new class of molecular machine prototype for use as a constitutive element in muscle-like dynamic systems.

Interconversion between a vertically oriented transition metal-complexed figure-of-eight and a horizontally disposed one.

A large ring containing two pairs of transition metal-complexing fragments with alternating bi- and tridentate chelates has been shown to behave as a bimodal figure-of-eight. When coordinated to a preferentially octahedrally coordinated Fe(II) or Cu(II) center, the height of the molecule along the coordinating axis of the tridentate ligands (vertical on the drawing) is only ∼11 Å, whereas the height of the molecule along the same vertical axis is several times as large for the complex of the tetrahedrally coordinated copper(I) center. This new type of molecular machine-prototype could be used as constitutive element in muscle-like dynamic systems.

Transition-metal-complexed catenanes and rotaxanes: from dynamic systems to functional molecular machines.

Transition metal-based catenanes and rotaxanes constitute a specific class of mechanically interlocked molecules whose metal centers are essential both as templates in the construction of the compounds and for their ability to induce large-amplitude motions. In the present chapter we will first present a historical perspective of the field of interlocking compounds in general, in relation to molecular machines, starting with old work dating back to the 1980s and 1990s. Copper was shown many years ago to be the metal of choice for synthesizing the compounds via a template approach and for setting the molecules in motion using a redox signal (Cu(II)/Cu(I)). In a second paragraph, we will discuss various rotaxanes able to undergo a pirouetting motion of the axis within the threaded ring. Two families of such molecules will be mentioned: (1) a porphyrin-containing [2]rotaxane whose pirouetting motion is induced by a chemical reaction and (2) electrochemically driven systems. In this second category of [2]rotaxanes, the rate of motion could be dramatically increased by gradually modifying structural parameters and, in particular, by making the metal center less and less hindered by its surrounding ligands. The third section will be devoted to molecular shuttles and muscles, both families of compounds being reminiscent of linear machines such as biological muscles. By replacing the classical 2,9-diaryl-1,10-phenanthroline chelate (highly shielding and hindering) used by our group since the 1980s by an endocyclic but non-sterically hindering 3,3'-biisoquinoline derivative, the shuttling rate was increased in spectacular fashion, demonstrating the importance of steric factors in transition metal-based molecular machines. The same 3,3'-biisoquinoline motif was also used in the elaboration of a three-station shuttle, leading to long-distance (>20 Å) transport of a ring along the axis on which it is threaded. Finally, porphyrin-containing [3]rotaxanes and [4]rotaxanes, the latter displaying an overall cyclic structure, will be discussed and shown to behave as adjustable and switchable receptors. The synthesis of such compounds is a particularly challenging task in itself. In addition, the new receptors display fascinating properties such as, in particular, their ability to compress various guests and to expel them from their binding site using a chemical signal.

Combining topological and steric constraints for the preparation of heteroleptic copper(I) complexes.

Heteroleptic copper(I) complexes have been prepared from a macrocyclic ligand incorporating a 2,9-diphenyl-1,10-phenanthroline subunit (M30) and two bis-phosphines, namely bis[(2-diphenylphosphino)phenyl] ether (POP) and 1,3-bis(diphenylphosphino)propane (dppp). In both cases, the diphenylphosphino moieties of the PP ligand are too bulky to pass through the 30-membered ring of M30 during the coordination process, hence the formation of C2v-symmetrical pseudo-rotaxanes is prevented. When POP is used, X-ray crystal structure analysis shows the formation of a highly distorted [Cu(M30)(POP)](+) complex in which the POP ligand is only partially threaded through the M30 unit. This compound is poorly stable as the Cu(I) cation is not in a favorable coordination environment due to steric constraints. By contrast, in the case of dppp, the bis-phosphine ligand undergoes both steric and topological constraints and adopts a nonchelating coordination mode to generate [Cu2(M30)2(µ-dppp)](BF4)2. This compound exhibits metal-to-ligand charge transfer (MLCT) emission characterized by a very large Stokes' shift (≈200 nm) that is not attributed to a dramatic structural distortion between the ground and the emitting states but to very weak MLCT absorption transitions at longer wavelengths. Accordingly, [Cu2(M30)2(µ-dppp)](BF4)2 shows unusually high luminescence quantum yields for Cu(I) complexes, both in solution and in the solid state (0.5 and 7 %, respectively).

NIR dual luminescence from an extended porphyrin. Spectroscopy, photophysics and theory.

Spectroscopic and photophysical properties of an extended Zn porphyrin with fused bis(tetraazaanthracene) arms including a 2,9-diphenyl-1,10-phenanthroline incorporated in a polyether macrocycle are investigated in solvents of different polarity pointing to the presence of two emitting singlet excited states. The absorption and emission features are identified and ascribed, on the basis of solvent polarity dependence, to a π-π* and to a charge transfer (CT) state, respectively. Whereas the intraligand π-π* transition is assigned to the intense absorption observed at 442-455 nm, the CT states contribute to the bands at 521-525 nm and 472-481 nm. The theoretical analysis of the absorption spectrum confirms the presence of two strong bands centered at 536 and 437 nm corresponding to CT and π-π* states, respectively. Weak CT transitions are calculated at 657 and 486 nm. Two emission maxima are observed in toluene at 724 nm from a (1)π-π* state and at 800 nm from a (1)CT state, respectively. (1)CT bands shift bathochromically by increasing the solvent polarity whereas the energy of the (1)π-π band is less affected. Likewise, the emission yield and lifetime associated with the low energy (1)CT band are strongly affected by solvent polarity. This is rationalized by a (1)π-π* → (1)CT internal conversion driven by solvent polarity, this process being competitive with the (1)π-π* to ground state deactivation channel. Time resolved absorption spectra indicate the presence of two triplet states, a short-lived one (nanoseconds range) and a longer lived one (hundreds of microsecond range) ascribed to a (3)π-π* and a (3)CT, respectively. For them, a conversion mechanism similar to that of the singlet excited states is suggested.

Photoexpulsion of surface-grafted ruthenium complexes and subsequent release of cytotoxic cargos to cancer cells from mesoporous silica nanoparticles.

Ruthenium(II) polypyridyl complexes have emerged both as promising probes of DNA structure and as anticancer agents because of their unique photophysical and cytotoxic properties. A key consideration in the administration of those therapeutic agents is the optimization of their chemical reactivities to allow facile attack on the target sites, yet avoid unwanted side effects. Here, we present a drug delivery platform technology, obtained by grafting the surface of mesoporous silica nanoparticles (MSNPs) with ruthenium(II) dipyridophenazine (dppz) complexes. This hybrid nanomaterial displays enhanced luminescent properties relative to that of the ruthenium(II) dppz complex in a homogeneous phase. Since the coordination between the ruthenium(II) complex and a monodentate ligand linked covalently to the nanoparticles can be cleaved under irradiation with visible light, the ruthenium complex can be released from the surface of the nanoparticles by selective substitution of this ligand with a water molecule. Indeed, the modified MSNPs undergo rapid cellular uptake, and after activation with light, the release of an aqua ruthenium(II) complex is observed. We have delivered, in combination, the ruthenium(II) complex and paclitaxel, loaded in the mesoporous structure, to breast cancer cells. This hybrid material represents a promising candidate as one of the so-called theranostic agents that possess both diagnostic and therapeutic functions.

Use of cleavable coordinating rings as protective groups in the synthesis of a rotaxane with an axis that incorporates more chelating groups than threaded macrocycles.

A new methodology allowing preparation of a linear "unsaturated" [3]rotaxane consisting of an axis incorporating more coordination sites than threaded rings was developed. It was based on the preliminary synthesis of a "saturated" [5]rotaxane consisting of a four-chelating site axis threaded through four macrocyclic components, two of them being cleavable rings incorporating a lactone function and the two others being "secure" non-cleavable rings. The stoppering reaction was based on click chemistry. Subsequently, cleavage and removal of the two lactone-containing macrocycles from the [5]rotaxane in basic medium afforded the desired "unsaturated" [3]rotaxane in quantitative yield.

Copper(I)-assembled [3]rotaxane whose two rings act as flapping wings.

A new copper-complexed [3]rotaxane consisting of two coordinating 30-membered rings threaded by a two-binding-site axis has been prepared in good yield from relatively simple organic fragments. The main specificity of the system originates from the stoppering reaction, based on "click" chemistry, and thus from the presence of two triazole groups at positions next to the bidentate chelates of the axis central part. The geometry of the coordinating atoms belonging to the axis is such that the triazole groups can either be part of the coordinating fragments when the metal center is 5-coordinate or be not at all involved in coordination to the metal when the latter is 4-coordinate. To be more specific, when the two complexed metal centers are monovalent copper(I) centers, the triazoles are not included in the metal coordination sphere, whereas when the metal centers are Cu(II) or Zn(2+), the triazole groups are bound to the metals. This is easily explained by the fact that Cu(I) is preferably 4-coordinate and Cu(II) and Zn(2+) are 5-coordinate. The interconversion between both situations (4- or 5-coordinate) can be quantitatively induced by metal exchange (Cu(I)/Zn(2+)) or by a redox process (Cu(II)/Cu(I)). It leads to important geometrical changes and in particular to a strong modification of the angle between the two rings. As a consequence, the two threaded rings undergo a motion which is reminiscent of a wing-flapping movement similar to that of birds. This flapping motion is fast and quantitative. It should lead to new functional molecular machines in the future.

The beauty of knots at the molecular level.

What makes a given object look beautiful to the observer, be it in the macroscopic world or at the molecular level? This very general question will be briefly addressed at the beginning of this essay, in relation to contemporary molecular chemistry and biology, leading to the general statement that, most of the time, beauty is tightly connected to function as well as to the cultural background of the observer. The main topic of the present article will be that of topologically non-trivial molecules or molecular ensembles and the fascination that such species have exerted on molecular or solid state chemists. Molecules with a graph identical to Kuratowski's K5 or K3,3 graphs are indeed highly attractive from an aesthetical viewpoint, but perhaps even more fascinating and beautiful are molecular knots. A general discussion will be devoted to these compounds, which are still considered as exotic species because of the very limited number of efficient synthetic strategies leading to their preparation. Particularly efficient are templated approaches based either on transition metals such as copper(I) or on organic groups able to form hydrogen bonds or acceptor-donor stacks. A particularly noteworthy property of knots, and in particular of the trefoil knot, is their topological chirality. The isolation of both enantiomers of the trefoil knot (31) could be achieved and showed that such species have fascinating chiroptical properties. Finally, various routes to more complex and beautiful knots than the trefoil knot, which is the simplest non-trivial knot, will be discussed in line with the remarkable ability of transition metals to gather and orient in a very precise fashion several organic components in their coordination spheres, thus leading to synthetic precursors displaying geometries which are perfectly well adapted to the preparation of the desired knots or links.

A flexible copper(I)-complexed [4]rotaxane containing two face-to-face porphyrinic plates that behaves as a distensible receptor.

A new cyclic [4]rotaxane composed of two flexible bis-macrocycles and two rigid axles is described. Each bis-macrocycle consists of two rings attached to antipodal meso positions of a central Zn porphyrin through single C-C bonds. Each ring incorporates a 2,9-diphenyl-1,10-phenanthroline chelation site. The axles contain two coplanar bidentate sites derived from the 2,2'-bipyridine motif. The building blocks were assembled by using a one-pot threading-and-stoppering reaction, which afforded the [4]rotaxane in 50% yield. The "gathering-and-threading" effect of copper(I) was utilised in the formation of a [4]pseudorotaxane, which was immediately converted to the corresponding [4]rotaxane by a quadruple CuAAC stoppering reaction. The rotaxane contains two face-to-face zinc porphyrins, which allowed the coordination of ditopic guest substrates. The rotaxane host showed remarkable flexibility and was able to adjust its conformation to the guest size. It can be distended and accommodate rod-like guests of 2.6 to 15.8 Å in length.

[2]Catenanes built around octahedral transition-metal complexes that contain two intertwined endocyclic but non-sterically hindering tridentate ligands.

Sterically hindering bidentate chelates, such as 2,9-diphenyl-1,10-phenanthroline, form entwined complexes with copper(I) and other tetrahedrally coordinated transition-metal centres. To prepare octahedral complexes containing two entwined tridentate ligands and thus apply a strategy similar to that used for making catenanes with tetrahedral metal centres, the use of the classical terpy ligand (terpy=2,2':6',2''-terpyridine) appears to be attractive. In fact, 6,6''-diphenyl-2,2':6',2''-terpyridine (dp-terpy) is not appropriate due to strong "pinching" of the organic backbone by coordination to the metal and thus stable entwined complexes with this ligand cannot be obtained. Herein, we report the synthesis and coordination properties of a new family of tridentate ligands, the main features of which are their endocyclic nature and non-sterically hindering character. The coordinating fragment consists of two 8'-phenylisoquinolin-3'-yl groups attached at the 2 and 6 positions of a pyridine nucleus. Octahedral complexes containing two such entangled ligands around an octahedral metal centre, such as Fe(II) , Ru(II) or Co(III) , are highly stable, with no steric congestion around the metal. By using functionalised ligands bearing terminal olefins, double ring-closing metathesis leads to [2]catenanes in good yield with Fe(II) or Co(III) as the templating metal centre. The X-ray crystallography structures of the Fe(II) precursor and the Fe(II) catenane are also reported. These show that although significant pinching of the ligand is observed in both Fe(II) complexes, the system is very open and no steric constraints can be detected.

Stereochemistry of molecular figures-of-eight.

A trans isomer of a figure-of-eight (Fo8) compound was prepared from an electron-withdrawing cyclobis(paraquat-p-phenylene) derivative carrying trans-disposed azide functions between its two phenylene rings. Copper(I)-catalyzed azide-alkyne cycloadditions with a bispropargyl derivative of a polyether chain, interrupted in its midriff by an electron-donating 1,5-dioxynaphthalene unit acting as the template to organize the reactants prior to the onset of two click reactions, afforded the Fo8 compound with C(i) symmetry. Exactly the same chemistry is performed on the cis-bisazide of the tetracationic cyclophane to give a Fo8 compound with C(2) symmetry. Both of these Fo8 compounds exist as major and very minor conformational isomers in solution. The major conformation in the trans series, which has been characterized by X-ray crystallography, adopts a geometry which maximizes its C-H···O interactions, while maintaining its π···π stacking and C-H···π interactions. Ab initio calculations at the M06L level support the conformational assignments to the major and minor isomers in the trans series. Dynamic (1)H NMR spectroscopy, supported by 2D (1)H NMR experiments, indicates that the major and minor isomers in both the cis and trans series equilibrate in solution on the (1)H NMR timescale rapidly above and slowly below room temperature.

NIR emission of cyclic [4]rotaxanes containing π-extended porphyrin chromophores.

The photophysical properties of a Cu(I) [4]rotaxane 4(4+) and of the demetalated [4]rotaxane 3 have been determined and compared to those of the component Zn porphyrin 2. All samples emit in the NIR region (700-1200 nm). The luminescence from the interlocked structures is bathochromically shifted with respect to 2 and displays a lower emission quantum yield, much lower for 4(4+) than for 3. The occurrence of intra-molecular electron or energy transfer is excluded and the decrease in luminescence yield is discussed in terms of the energy gap law and of electronic interactions between components of the cyclic interlocked structure. In toluene a dual emission behavior, similar to that of 2, is observed for 3 and ascribed to the presence of two non-equilibrated excited states, π-π* and CT in nature with lifetimes of 0.80 and 0.14 ns, respectively.

Transition-metal-complexed cyclic [3]- and [4]pseudorotaxanes containing rigid ring-and-filament conjugates: synthesis and solution studies.

By using the "gathering-and-threading" effect of copper(I) with rigid ring-and-string conjugates, daisy-chain-type [3]- and [4]pseudorotaxanes could be prepared in high yields. The organic fragment used consisted of a 2,9-diphenyl-1,10-phenanthroline (dpp)-containing ring attached to a coordinating filament capable of threading through the ring of another molecule by coordination to copper(I). The bidentate chelate introduced in the axis was also a 1,10-phenanthroline (phen) derivative with two methyl groups ortho to the nitrogen atoms of the phen unit. The organic component was prepared following a multistep strategy, one of the key steps being the attachment of the ring to the lateral axis. This connection was done by a condensation reaction between an ortho dione located at the back of a ring-incorporated phen and an aromatic aldehyde, which was the end-function of the thread. An oxazole nucleus was obtained after the condensation, which provided a rigid connection between the ring and the axis. In this way, the coordination axes of the ring-incorporated bidentate chelate and of the ligand belonging to the lateral filament were approximately orthogonal to one another. The design was such that the tetrameric complex, a [4]pseudorotaxane, seemed to be the most stable species, owing to the mutual geometrical arrangement of the filament and the ring. Various spectroscopic techniques, such as (1)H NMR spectroscopy, including DOSY, and electrospray ionization mass spectroscopy (ESI-MS), clearly demonstrated that a mixture of cyclic [3]- and [4]pseudorotaxane was obtained; the proportions of both components depended on concentration and temperature. Copper(I) was not the only metal center leading to the formation of cyclic pseudorotaxanes. A similar effect was observed with silver(I) as the templating metal: quantitative formation of threaded species was observed, with a higher proportion of trimer over tetramer than in the copper(I) case. Concentration and temperature effects were investigated for both series of Cu(I) - and Ag(I) -complexed threaded species showing that formation of the trimer was favored upon dilution or heating of the solution.

Synthesis of [5]rotaxanes containing bi- and tridentate coordination sites in the axis.

A new example of a linear [5]rotaxane has been synthesized by using the traditional "gathering-and-threading" approach but based on an unusual axle incorporating a symmetrical bis(bidentate) chelating fragment built on a 4,7-phenanthroline core. The stoppering reaction is particularly noteworthy since, instead of using a trivial bulky stopper as precursor to the blocking group, two semistoppered copper-complexed [2]pseudorotaxanes (namely [2]semirotaxanes) are used, which leads to the desired [5]rotaxane in good yield. The efficiency of the method relies on the use of "click" chemistry, with its very mild conditions, and on the protection by a transition-metal (copper(I)) of the various coordinating groups present in the fragments to be interconnected (terpy and bidentate chelating groups), thus inhibiting potential detrimental side reactions during the copper-catalyzed stoppering reaction. Since the external fragments and the central core of the system contain tri- and bidentate chelating units, respectively, the axle of the final [5]rotaxane incorporates two types of coordinating units: two external terpy groups (terpy: 2,2':6',2''-terpyridine) and two central bidentate ligands. Such a situation enables the system to tidy two different metals centers, and to localize them in a priori well-defined positions. This is what was observed when mixing the free ligand with a mixture of Zn(2+) and Li(+) : the zinc(II) ions were unambiguously shown to occupy the external sites, whereas the Li(+) cations were found in the central part of the [5]rotaxane. An X-ray diffraction study carried out on a [3]pseudorotaxane, the axis of which is similar to the central part of the [5]rotaxane axle, demonstrates that Zn(2+) is clearly five-coordinate, the fifth ligand being a counterion, even when the coordination site of the pseudorotaxane is designed for four-coordinate metals, which is in marked contrast with copper(I) or Li(+) .

Coordination chemistry-assembled porphyrinic catenanes.

Non covalent [2]catenanes were synthesized in high yield as kinetic products or as thermodynamic products after completion of an equilibrium. These sophisticated architectures were assembled in two steps, from an oblique bis-zinc(II) porphyrin and two different dipyridyl chelates, by using Cu(I)-N interactions to assemble acyclic complexes and Zn(II)-N interactions to generate rings. (1)H NMR including 2D COSY and ROESY experiments were used to characterize each compound. Spectrophotometric titrations highlight the influence of geometry in terms of distances and angles in non covalent coordinated assemblies. In fact, it was proved that a perfect fit leads to highly stable coordination chemistry-assembled species.