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From insertion of rhodium acetate paddlewheels into functionalized7-azaindole hydrogen-bonded dimers to infinite architectures†

Dmitry Pogozhev, Stephane A. Baudron* and Mir Wais Hosseini*

Received 2nd March 2011, Accepted 4th May 2011DOI: 10.1039/c1dt10359h

In order to take advantage of the peculiar mode of interaction consisting in the combination ofhydrogen and coordination bonding displayed by the 7-azaindole core towards tetraacetatepaddlewheel type complexes, a series of new derivatives, bearing peripheral interacting sites at theposition 3, have been prepared and their self-assembly into dimeric H-bonded species was established inthe solid state. Furthermore, the heterochelate mode of binding was exploited both in the solid stateand in solution using [Rh2(OAc)4] paddlewheel to generate discrete capped complexes resulting fromthe coordination of the pyridyl nitrogen atom to the axial position of the Rh(II) cations and hydrogenbonding between the pyrrolic NH and an oxygen atom of one of the equatorial acetate groups. Theextension to infinite hybrid networks was achieved using derivatives bearing self complementaryH-bond donor and acceptor groups such as a carboxylic moiety.

Introduction

Over the last two decades, the design and preparation of periodicextended architectures called molecular networks1 have beenattracting considerable attention. For the design of these giantarchitectures which may be regarded as hypermolecules, moleculartectonics2 based on combinations of complementary buildingblocks or tectons3 capable of mutual interconnection appears to bean efficient approach.4 Among various structural characteristicsdefining molecular networks such as their dimensionality andgeometry, the search for new assembling strategies resultingfrom the number of components, their modes of interactionand their sequence, is a matter of current interest. Although themajority of cases reported are usually based on a single type ofattractive interaction such as van der Waals contacts,5 hydrogen6

or coordination bonding,7 examples of combined interactions havebeen also reported.8 For the latter case, two strategies may beconsidered. The first one is based on the one-pot preparation ofperiodic architectures combining at least two different interac-tion modes. For the second strategy, allowing the hierarchicalconstruction of molecular networks, the use of differentiatedinteractions and their sequence are key features.9 With respect tothe second strategy, the 7-azaindole (7-azaH) moiety (Scheme 1)appeared to us as an interesting platform. Indeed, the latter offersthe possibility of exploiting its simultaneous coordination andH-bonding propensity giving rise to a heterochelate mode ofinteraction (Scheme 1, left) for the design of metallatectons bearing

Laboratoire de Chimie de Coordination Organique, UMR CNRS 7140,Universite de Strasbourg, F-67000, Strasbourg, France. E-mail: sbaudron@unistra.fr, hosseini@unistra.fr; Fax: +33 368851325; Tel: +33 368851325† CCDC reference numbers 815819–815825. For crystallographic data inCIF or other electronic format see DOI: 10.1039/c1dt10359h

Scheme 1 Most common coordination modes of 7-azaindole (left) and7-azaindolate (right).

at the position 3 peripheral interacting groups allowing thusthe construction of extended architectures through self-assemblyprocesses.

The nitrogen based heterocyclic molecule 7-azaindole(Scheme 1) has received considerable interest not only for itspharmaceutical applications,10–11 but also for its rich coordinationchemistry.12–20 Indeed, both 7-azaindole and its conjugate base,7-azaindolate (7-aza-), (Scheme 1) have been shown to form avariety of complexes with metal cations. Neutral 7-azaH offersboth a coordinating pyridyl group and H-bond donor site of theNH type. Thus, such a ligand may be regarded as a heterochelatecombining two distinct types of interactions. Indeed, upon ligationto a M-X fragment, hydrogen bonding between the NH groupand the anion X- is observed in all structurally characterized (7-azaH)MX complexes (Scheme 1, left).17–19 For 7-azaindolate, amonoanionic ligand, in principle, at least, two coordination modes(m or h2) with metal cations may be envisaged (Scheme 1, right).However, owing to the bite angle between the two N atoms, withthe exception of a mononuclear complex formed with europium,16

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all other complexes reported are polynuclear species resulting fromm-h1:h1 coordination mode, i.e. the anionic ligand bridges twometal centres.13–15 In particular, paddlewheel type complexes havebeen reported with Cu, Mo, Nb, Re and W for example.13

Interestingly, for the paddlewheel type complexes formed be-tween 7-azaH and bimetallic [M2(O2CR)4]n+ (M = CuII, RhII, n =0; M = RuII/III, n = 1; R = CH3, C2H5) species,17 the double modeof interaction (Scheme 2a), i.e. formation of a coordination bondbetween the pyridyl moiety of 7-azaH and the axial position ofthe metal cations and hydrogen bond between the NH group andone of the oxygen atoms of the equatorial carboxylate groups,is observed (Scheme 2a). One might draw an analogy betweenthe binuclear complex (Scheme 2c) and the self-complementaryhydrogen bonded dimers (Scheme 2b).20 In other words, thecoordination to the [M2(O2CR)4]n+ paddlewheel can thus beregarded as an expanded version of the hydrogen bonded dimersobserved for the free ligands.

Scheme 2 Schematic representation of (7-azaH)MX metal complex (a),a 7-azaH hydrogen bonded dimer (b), a binuclear complex featuringboth coordination and H bonds (c) and a 1D network resulting frominterconnection of consecutive binuclear cores through a dihapto mode ofH-bonding (d).

Although paddlewheel type complexes and in particular[Rh2(OAc)4] have been exploited for the formation of supramolec-ular architectures,21–22 and the above mentioned interaction motifobserved with other amino functionalized nitrogen based hete-rocyclic ligands,23–24 to the best of our knowledge, the doublerecognition feature, which can be regarded as a heterochelate modeof interaction, has not been used for the formation of extendedarchitectures. This is probably related to the fact that, while thecoordination chemistry of 7-azaH has been widely investigated,the one of its functionalized derivatives, with the exception ofN-alkylated compounds,12 is almost unexplored. Introductionof an additional peripheral group at this position would leadto the formation of interesting functionalized complexes ormetallatectons,2–4 based on the heterochelate interaction. Suchderivatives would be interesting candidates for the sequentialconstruction of heterometallic architectures in the case of a

coordinating peripheral group,9,25 or hydrogen bonded networksin the case of a self-complementary hydrogen bonding peripheralmoiety (Scheme 2d).8 To address this issue, we report hereinon the synthesis, characterization and coordination chemistrytowards the [Rh2(OAc)4] paddlewheel unit of five 7-azaindolebased ligands 1–5 (Scheme 3) bearing a peripheral p-benzonitrile,a tricyanovinylene group, a 5-phenyldipyrrin, a m- or p-benzoicacid group respectively.

Scheme 3 Functionalized 7-azaindole derivatives 1–5 and their precur-sors and hydrogen assignments.

Results and discussion

Design of the ligands

Compounds 1–5 are 7-azaindole derivatives bearing peripheralinteraction sites at position 3. While ligand 1 bears a nitrilegroup at the para position, compound 2 is equipped with atricyanovinylene moiety. Ligand 4 and 5, bearing a carboxylicacid unit, are positional isomers. Finally, compound 3 combinesthe 7-azaindole core with a dipyrrin unit. Whereas for compounds1 and 2, one would expect mainly a coordinating behaviour forthe peripheral group, for the other three ligands, owing to theself-complementary nature of the groups, one would also expectH-bonding in addition to coordination propensity.

Synthesis and characterization of the ligands

Ligand 1, 4 and 5 were prepared by the Pd-catalyzed Stille couplingbetween 1-tert-butyldimethylsilyl-3-trimethylstannyl-7-azaindole,6,26 and p-bromobenzonitrile (7) or m- (8) or p- (9) bromobenzoicacid methyl ester in 17, 48 and 29% yield respectively (Scheme 3).By analogy with the reported 3-tricyanovinylindole analogue,27

ligand 2 was prepared in 93% yield by reaction of TCNE with7-azaindole in the presence of pyridine (Scheme 3). Finally,

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the dipyrrin appended derivative 3 was prepared as previouslydescribed.20d

All reported ligands were characterized in solution by 1H- and13C-NMR and IR spectroscopy. In the case of 1 and 2, they werealso studied in the solid state by single-crystal X-Ray diffraction(Fig. 1).

Fig. 1 Structures of the H-bonded dimers formed by the self-complemen-tary ligands 1 (a) and 2 (b). For 1: N1—N2i = 2.897(2) A, N1–H1A—N2i =166.5◦; for 2: N1—N2ii = 2.890(2) A, N1–H1A—N2ii = 168.1◦. i = 1 - x,-y, -z; ii = -x, 3 - y, -z.

Crystal structure of ligands 1 and 2

Compounds 1 and 2 are self-complementary units offering both H-bond donor (NH) and acceptor (N) sites. In the solid state, unlikethe commercially available 7-azaindole which self-organizes intoa tetrameric unit,15 both compounds 1 (Fig. 1a) and 2 (Fig. 1b)form hydrogen-bonded dimers, as observed for other derivativesfunctionalized at the 3 position.20 Both compounds crystallize inthe monoclinic space group P21/c with one molecule in generalposition.

It is worth noting that, for the dipyrromethane precursor of 3,the same type of arrangement is observed in the solid state.20d

For both dimers, the geometrical parameters of the observedR2

2(8) motifs1b are similar. While, for compound 1, the benzonitrilegroup is tilted with respect to the heterocycle by 24.5◦, for 2, thetricyanovinylene group is almost coplanar with the 7-azaindolemoiety (dihedral angle = 3.0◦). In the latter case, owing to therather flat nature of the dimer, p-stacking with a 3.32 A distancebetween two adjacent dimeric units is observed.

Synthesis and crystal structures of discrete paddlewheels 10–12

As stated above, paddlewheel type complexes offer both two freecoordination sites at the apical positions of the two metal centresadopting a square based coordination geometry and H-bond

acceptor sites located on the O atoms of carboxylate ligands. Sinceazaindole derivatives 1–5 offer a coordinating site (N atom of thepyridyl moiety) as well as a H-bond donor unit (NH group of thefive membered ring), upon their coordination to the tetraacetatepaddlewheel, four isomers can be envisioned, two being achiral(Fig. 2a and 2b) and two enantiomers (Fig. 2c and 2d).

Fig. 2 Schematic representation of all four possible isomers result-ing from the chelation of the [Rh2(OAc)4] paddlewheel complex by7-azaH. Whereas isomers a and b possessing a centre and a plane ofsymmetry respectively are achiral, isomers c (K) and d (D) are chiral andenantiomers.

At room temperature, upon reaction in either DMF or THFof two equivalents of ligands 1–3 with [Rh2(OAc)4],28 complexes10–12 were obtained in 35 to 65% yield. All three complexes werecharacterized both in solution by classical methods and in thesolid state by X-ray single-crystal diffraction.

Crystals of 10 were obtained by slow diffusion of water vapourinto a DMF solution of the complex. Compound 10 crystallizes asa DMF solvate, (10)·(DMF)2, in the triclinic space group P1 withone complex on an inversion center and one solvent moleculein general position. Crystals of 11 (triclinic, P1) were obtainedupon diffusion of n-pentane vapour into a dioxane solution of thecomplex. The binuclear species 11 crystallizes as a dioxane solvate,(11)·(Dioxane)4, with one complex on an inversion center and twosolvent molecules in general positions. Crystals of (12)·(Dioxane)4

were obtained by diffusion of n-pentane vapour into a dioxanesolution of the complex. The complex 12 crystallizes in themonoclinic space group P21/n with one complex on an inversioncenter and two dioxane molecules in general positions. For allthree dimers, the Rh–Rh distance is similar to one reported forother paddlewheel type complexes.24 In all three cases, the axialpositions on the RhII cation are occupied by the pyridyl nitrogenatom of the 7-azaindole moieties (Fig. 3). The functionalized 7-azaindole unit and two acetate groups are coplanar, in contrastwith what is observed for the parent [Rh2(O2CC2H5)4(7-azaH)2]complex (dihedral angle of 8.2 and 23.5◦) and the rutheniumanalogue [Ru2(OAc)4(7-azaH)2](PF6) (dihedral angle of 43◦).17

The NH of the five membered heterocycle is hydrogen bondedto an oxygen atom of an equatorial acetate group (Fig. 3) aspreviously described for [Cu2(OAc)4(7-azaH)2] and [Cu2(OAc)2(7-aza)2(7-azaH)2] complexes.17b,c Only the centrosymmetric iso-mer (Fig. 2a and 3) has been obtained as for the parent

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Fig. 3 Crystal structure of complexes 10 (a), 11 (b) and 12 (c). Hydrogenatoms and solvent molecules have been omitted for clarity. Selected bondlengths (A) and angles (◦): for 10, Rh1–Rh1 = 2.4076(4); Rh1–N1 =2.279(2), N2—O2 = 2.795(3), N2–H2—O2 = 146.6; for 11, Rh1–Rh1 =2.4031(4), Rh1–N1 = 2.290(2), N2—O2 = 2.720(4), N2–H2—O2 = 147.5;for 12: Rh1–Rh1 = 2.4036(7); Rh1–N4 = 2.268(3), N3—O1 = 2.896(5),N3–H3—O1 = 143.4.

[M2(O2CR)4(7-azaH)2]n+ complexes.17 It is interesting to note thatthese ligands are polytopic and thus upon reaction with rhodiumacetate, both coordination poles do compete for ligation to theRhII cations. This is particularly relevant in the case of 3 sinceboth coordination poles comprise a nitrogen based heterocycleand a pyrrolic ring capable of hydrogen bonding. However, thetwo rings are fused in the 7-azaH moiety while they are free torotate in the dipyrrin unit and the two nitrogen atom are not inan N–C–N arrangement, giving a preferred interaction with the7-azaH group. This free rotation of the coordinating and hydrogenbonding rings in dipyrrin ligands has been recently used for theformation of [2 + 2] metallamacrocycles with silver cations.29

Behaviour in solution of complexes 11 and 12

Owing to a better solubility in organic solvents, only paddlewheels11 and 12 were studied in solution by 1H-NMR spectroscopywhich revealed that both species are stable in liquid media. Forthe complex 11 in acetone-d6, proton signals corresponding tothe 7-azaindole moiety are strongly deshielded when compared tofree ligand 2 (Fig. 4). As expected, the observed shifts are morepronounced for the hydrogen atoms Ha, Hb and Hc belonging tothe pyridyl ring of the ligand.

A similar behaviour is observed for 12 in CDCl3. Whencompared to the free ligand 3, while signals of the phenyldipyrringroup remains unaffected, those of the 7-azaH moiety are stronglydownfield shifted upon coordination to the paddlewheel complex(Fig. 5). These observations clearly indicate that, in solution andat room temperature, no shift in the coordination mode betweenthe 7-azaH and dipyrrin units occurs.

Fig. 4 1H-NMR spectra in acetone-d6 of ligand 2 (bottom) and thepaddlewheel complex 11 (top) showing downfield shifts of Ha, Hb, Hcand Hd hydrogen atoms. For assignment see Scheme 3.

Fig. 5 1H-NMR spectra in CDCl3 of ligand 3 (bottom) and the complex12 (top) showing that upon coordination to the paddlewheel complexwhile signals of the dipyrrin moiety remain unaffected, Ha, Hb, Hc andHd hydrogen atoms of the 7-azaH unit are strongly downfield shifted. Forassignment see Scheme 3.

Synthesis and crystal structures of infinite 1D networks 13 and 14

Crystals of the infinite 1D network 13 were obtained in 82%yield from 1-propanol upon slow evaporation. 13 crystallizes inthe triclinic space group P1 with one paddlewheel unit on aninversion center. Owing to the disorder observed for the solventmolecules, the SQUEEZE command was applied.30 As observedfor paddlewheel complexes 10–12 mentioned above (Fig. 3), hereagain the same type of interactions between the 7-azaH unit andrhodium acetate is obtained. The binuclear complex bearing at itsperiphery two self-complementary carboxylic acid groups orientedin a divergent fashion leads to a 1D hydrogen bonding networkwith the formation of the R2

2(8) motif. It is worth noting that,under the conditions used, neither coordination through O–Rhbond of the carboxylic acid to the axial position of the RhII cationsnor the substitution of equatorial acetate groups are observed. Thelatter point results from the inertness at room temperature of therhodium acetate complex towards carboxylate exchange processes.The prevalence of the nitrogen over the oxygen coordination to theaxial position of RhII centre might be explained by a better affinityof the metal cations for the pyridyl group and the simultaneousformation of H-bond. Although, as mentioned above (Fig. 2),in principle the chelation of the paddlewheel complex by 7-azaH derivatives might lead to four different isomers, for allthree discrete complexes 10–12, a centrosymmetric organisationis observed (Fig. 3). However, for the infinite networks based onachiral units, two possibilities based either on the syn (Fig. 2b) orthe anti (Fig. 2a) configuration may be envisaged (Fig. 8). In thecase of the network 13 (Fig. 6) again only the centrosymmetricanti isomer (Fig. 2a) is observed.

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Fig. 6 A portion of the structure of the 1D network 13 resulting from the formation of H-bonds in a dihapto mode between carboxylic units belongingto consecutive paddlewheel type units. C–H hydrogen atoms have been omitted for clarity. Selected bond lengths (A) and angles (◦): Rh1–Rh1 = 2.4072(3);Rh1–N1 = 2.263(2); N2—O6 = 2.834(3); N2–H2—O6 = 142.4; O2—O1i = 2.630(3); O2–H2A—O1i = 169.4. i = 1 - x, 1 - y, -z.

Crystals of the network 14 were obtained in 62% yield froma DEF/EtOH/H2O mixture. 14 crystallizes as a DEF solvate,14·(DEF)2, with one complex on an inversion center and a solventmolecule in general position. For the latter, the carbonyl groupis found to be disordered over two positions. The observedinteractions between the paddlewheel and the ligand 5 are similarto what is observed for 10–12 and for 13, i.e. chelation throughsimultaneous formation of coordination (N–Rh) and hydrogen(NH ◊ ◊ ◊ O) bonds. Again, as in the case of 13, for 14 a H-bonded 1Dnetwork (Fig. 7) with centrosymmetric organisation of the units isobtained (Fig. 8a). In marked contrast with what is observed for13, the self-complementary peripheral carboxylic groups in 14 donot interact directly through a dihapto mode of hydrogen bondingleading to the R2

2(8) motif but they rather form a tetramolecularR4

4(14) motif resulting from the insertion of two solvent moleculesbetween carboxylic moieties belonging to consecutive units.

Conclusions

In conclusion, the coordination chemistry towards the[Rh2(OAc)4] paddlewheel type complex of five 7-azaindole deriva-tives bearing at position 3 a p-benzonitrile (1), a tricyanovinylenegroup (2), a phenyldipyrrin (3), a m- (4) and p-benzoic acid(5) has been investigated. In the solid state, the free ligands1 and 2 self-organize into hydrogen bonded dimers with theR2

2(8) motif. In the presence of [Rh2(OAc)4] paddlewheel, ligands1–3 interact with the paddlewheel core through simultaneouscoordination of the pyridyl nitrogen atom to the axial positionsof RhII centres and H-bonding between the NH group and anoxygen atom of one of the four equatorial acetate moieties. Theabove mentioned heterochelation process was used to generateinfinite 1D H-bonded networks upon combining the [Rh2(OAc)4]

Fig. 8 Two possible supramolecular isomers upon coordination of[Rh2(OAc)4] to a 7-azaindole derivative bearing a peripheral self-com-plementary hydrogen bonding group. Only a projection is presented here,based on the two achiral isomers (see Fig. 2).

paddlewheel with derivatives 4 and 5. Indeed, upon interactionwith the paddlewheel complex, both compounds 4 and 5 bearinga peripheral self-complementary hydrogen bonding benzoic acidgroup lead to the formation of self-complementary metallatectonswhich self assemble into 1D networks either though direct H-bonding by a dihapto mode of recognition in the case of 4 or byinsertion of solvent molecules bridging consecutive units in thecase of 5. The construction of heterometallic infinite architecturesusing the above mentioned complexes combining the [Rh2(OAc)4]paddlewheel and ligands 1–5 with other metal centres is currentlyunder investigation.

Fig. 7 A portion of the structure of the 1D network 14 resulting from the interconnection of consecutive paddlewheel type units through DEF solventmolecules forming H-bonds with carboxylic moieties belonging to consecutive complexes. C–H hydrogen atoms have been omitted for clarity. Note thatonly one of the two positions of the carbonyl group of the DEF molecule is shown and that, owing to this disorder, the hydrogen atom of of the C( O)Hgroup has not been introduced in the structure refinement. Selected bond lengths (A) and angles (◦): Rh1–Rh1 = 2.4055(4); Rh1–N1 = 2.274(2); N2—O4 =2.781(3); N2–H2—O4 = 145.8; O1—O7Ai = 2.554(5); O1–H1A—O7Ai = 155.0; O2—C19ii = 3.536(5). i = 2-x, 1-y, 1-z; ii = x, 1+y, z.

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Experimental

Synthesis

The intermediate 6, ligand 3 and the [Rh2(OAc)4] paddlewheelcomplex were prepared as described.20d,26,28 Other commerciallyavailable reagents were used as received. All solvents were driedusing standard procedures. 1H- and 13C-NMR spectra wereacquired at 25 ◦C on a Bruker AV 300 with the deuterated solventas the lock and residual solvent as the internal reference. NMRchemical shifts d are given in ppm and referenced internally to theresidual solvent resonance. J values are given in Hz. Elementalanalyses were performed at the Service Commun d’Analyses,Universite de Strasbourg (France).

Ligand 1. A THF solution (50 mL) of 6 (1 g, 2.53 mmol), 4-bromo-benzonitrile 7 (0.69 g, 3.80 mmol), LiCl (0.21 g, 7.59 mmol)and (Ph3P)4Pd (0.2 g) was refluxed for 72 h under argon. Afteraddition of Et2O, the precipitate was filtered off and the solutionevaporated. The crude product was purified by column chromatog-raphy (SiO2, CHCl3/pentane: 1/3). The resulting product wasdissolved in THF and an HCl solution in dioxane (4 M, 10 mL)was added. The mixture was stirred for 1 h and the resultingprecipitate was filtered and washed with ether to afford 1 (0.092 g,16%). dH(300 MHz, DMSO-d6) 12.20 (s, 1H), 8.38 (dd, J 1.4 and8.4, 1H), 8.31 (dd, J 1.4 and 4.6, 1H), 8.15 (d, J 2.5, 1H), 7.96(d, J 8.2, 2H), 7.86 (d, J 8.2, 2H), 7.21 (dd, J 4.8 and 8.1, 1H).dC(75 MHz, DMSO-d6) 149.7, 143.8, 140.6, 133.2, 128.2, 126.8,126.6, 119.7, 117.4, 117.1, 113.0, 107.9. IR(ATR) n/cm-1 2218(CN). Found: C; 75.97; N, 19.17; H, 4.25%. C14H9N3 requires C,76.70; N, 19.17; H, 4.14%.

Ligand 2. A benzene (10 mL) solution of 7-azaindole (0.5 g,4.23 mmol) was added to a refluxing benzene solution (8 mL) ofTCNE (0.3 g, 2.34 mmol). The solution immediately turned black.Addition of few drops of pyridine resulted in the precipitation of agreen solid. The mixture was further refluxed for 2 h. The solutionwas then filtered and the solid washed with benzene and coldCHCl3 to afford 2 (0.48 g, 93% based on TCNE). dH(300 MHz,DMSO-d6) 13.78 (br s, 1H), 8.78 (s, 1H), 8.49 (dd, J 1.4 and4.5, 1H), 8.44 (dd, J 1.5 and 8.2, 1H), 7.45 (dd, J 4.5 and 8.2,1H). dC(75 MHz, DMSO-d6) 149.5, 146.5, 137.4, 133.5, 129.4,119.6, 117.1, 115.0, 114.3, 113.9, 107.7, 81.4. lmax(CH2Cl2)/nm(e/mol-1 L cm-1): 228 (14000), 281 (6000), 423 (8000), 478 (3000).IR(ATR) n/cm-1 2223 (CN). Found: C, 65.16; N, 31.62; H, 2.67%.C12H5N5 requires C, 65.75; N, 31.95; H, 2.30%.

Ligand 4. A THF solution (150 mL) of 6 (3.40 g, 8.60 mmol),3-bromo-benzoic acid methyl ester 8 (3.64 g 16.93 mmol), LiCl(1.28 g, 30.29 mmol) and (Ph3P)4Pd (0.2 g) was refluxed for 72 hunder argon. After evaporation, the residue was first dissolved ina minimum amount of MeOH and then an aq. NaHCO3 solution(150 mL) was added. The suspension was refluxed until dissolutionof the solid. The pH of the solution was adjusted to 3–5 by additionof an aq. HCl solution. Aq. NaHCO3 was added until pH 7–8 wasreached affording a white precipitate. After filtration, the solidresidue was washed with MeOH and Et2O to afford 4 as a whitepowder (0.99 g, 48%). dH(300 MHz, DMSO-d6) 13.06 (s, 1H),12.01 (s, 1H), 8.31–8.25 (m, 3H), 7.98–7.95 (m, 2H), 7.83(dt, J 1.5and 7.6, 1H), 7.56 (t, J 7.6, 1H), 7.19 (dd, J 4.7 and 7.9, 1H).dC(75 MHz, DMSO-d6) 167.9, 149.5, 143.5, 135.8, 132.1, 130.9,

129.6, 127.6, 127.2, 126.9, 124.8, 117.6, 117.0, 113.8. IR(ATR)n/cm-1 3144–2551 (OH), 1698 (C O), 1303 (C–O). Found: C,69.50; N, 11.37; H, 4.06%. C14H10N2O2 requires C, 70.58; N, 11.76;H, 4.23%. HRMS (ESI), m/z: [M + H]+ calcd for C14H11N2O2:239.082, found 239.080.

Ligand 5. Under argon, a THF (50 mL) solution of 6(1 g, 2.53 mmol), 4-bromo-benzoic acid methyl ester 9 (0.82 g,3.81 mmol), LiCl (0.321 g, 7.57 mmol) and (Ph3P)4Pd (0.1 g)was refluxed for 72 h. Addition of Et2O afforded a precipitatewhich was filtered. The filtrate was evaporated and the residuewas purified by chromatography (SiO2, CHCl3/pentane: 1/3).The isolated white powder was dissolved in a minimum amountof MeOH and mixed with an aq. NaHCO3 solution (100 mL).This suspension was refluxed until dissolution of the solid. Then,an aq. HCl solution was added until the pH reached 3–5. Aq.NaHCO3 was added to the solution until the pH reached 7–8.The resulting white precipitate was filtered off and was washedwith Et2O (100 mL) to afford 5 as a white powder (0.175 g, 29%).dH(300 MHz, DMSO-d6) 12.81 (s, 1H), 12.10 (s, 1H), 8.38 (d, J 7.8,1H), 8.30 (d, J 4.7, 1H), 8.06 (d, J 2.5, 1H), 7.99 (d, J 8.2, 2H), 7.88(d, J 8.2, 2H), 7.19 (dd, J 4.6 and 8.0, 1H). dC(75 MHz, DMSO-d6)167.7, 149.6, 143.6, 140.1, 130.4, 128.2, 127.9, 126.2, 125.7, 117.5,116.8, 113.7. IR(ATR) n/cm-1 3226 (OH), 1691 (C O), 1314 (C–O). Found: C, 69.24; N, 11.11; H, 4.26%. C14H10N2O2 requires C,70.58; N, 11.76; H, 4.23%. HRMS (ESI), m/z: [M + H]+ calcd forC14H11N2O2: 239.082, found 239.081.

Complex 10. In a tube (16 ¥ 1 cm), a DMF (5 mL) solution of1 (25 mg, 0.114 mmol) was mixed with a DMF solution (5 mL) of[Rh2(OAc)4] (25.2 mg, 0.057 mmol). Upon slow diffusion of water,red crystals of the desired complex 10 were obtained (35.5 mg,60%). IR(ATR) n/cm-1 2220(CN) 1437(COO-), 1591 (COO-).Found: C, 48.38; N, 11.04; H, 4.64%. C42H44N8O10Rh2 requiresC, 49.14; N, 10.91; H, 4.32%.

Complex 11. A solution of 2 (25.7 mg, 0.117 mmol) in THF(10 mL) was mixed with a THF solution (10 mL) of [Rh2(OAc)4](25.8 mg, 0.058 mmol). The solution was evaporated and theresidue was dissolved in dioxane. Red crystals were grown by slowdiffusion of n-pentane vapours into a dioxane solution of thecomplex (25.5 mg, 35%). dH(300 MHz, CDCl3) 11.84 (br s, 2H),9.23 (dd, J 1.0 and 5.1, 2H), 9.03 (dd, J 1.1 and 8.2, 2H), 8.88 (d,J 3.3, 2H), 7.81 (dd, J 5.2 and 8.4, 2H), 1.98 (s, 12H). dC(75 MHz,CDCl3) 192.6, 151.0, 147.8, 133.8, 133.2, 130.9, 120.8, 119.3, 114.0,113.5, 112.0, 108.0, 78.5, 24.2 ppm. dH(300 MHz, acetone-d6) 8.93(s, H), 8.59 (dd, J 1.5 and 8.1, 1H), 8.52 (dd, J 1.5 and 4.7, 1H), 7.48(dd, J 4.7 and 8.1, 1H), 2.05 (s, 6H). IR(ATR) n/cm-1 2224 (CN),1415 (COO-), 1588(COO-). The solvated nature of this compoundled to non-reproducible elemental analysis.

Complex 12. A THF solution (30 mL) of dipyrrin 3 (50 mg,0.149 mmol) was added to a THF solution (20 mL) of [Rh2(OAc)4](32.85 mg, 0.074 mmol). The reaction mixture was stirred for 5 minand the solvent was removed under vacuum. Red crystals weregrown by slow diffusion of n-pentane into a dioxane solution ofthe complex (71 mg, 65%). dH(300 MHz, CDCl3) 10.56 (s, 2H),9.07 (d, J 4.3, 2H), 8.62 (dd, J 1.0 and 7.9, 2H), 7.84–7.81 (m,4H), 7.71(d, J 2.4, 2H), 7.68 (t, J 1.1, 4H), 7.65–7.62 (m, 4H),7.57 (dd, J 5.1 and 7.9, 2H), 6.77(dd, J 1.0 and 4.2, 4H), 6.44 (dd,J 1.4 and 4.2, 4H), 2.00 (s, 12H). The signal of the pyrrolic NH

7408 | Dalton Trans., 2011, 40, 7403–7411 This journal is © The Royal Society of Chemistry 2011

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Table 1 Crystallographic data for 1–2, 10–12

1 2 (10)·(DMF)2 (11)·(Dioxane)4 (12)·(Dioxane)4

Formula C14H9N3 C12H5N5 C42H44N8O10Rh2 C48H54N10O16Rh2 C68H76N8O16Rh2

FW 219.24 219.21 1026.67 1232.83 1467.21Crystal system Monoclinic Monoclinic Triclinic Triclinic MonoclinicSpace group P21/c P21/c P1 P1 P21/na/A 10.4831(15) 8.9962(4) 8.0638(2) 8.8730(2) 8.7968(4)b/A 14.485(2) 5.4962(3) 11.2180(3) 10.5971(2) 36.9943(15)c/A 7.2366(11) 20.0699(8) 12.0060(3) 14.7313(3) 10.26665(4)a (◦) 78.2360(10) 107.5620(10)b (◦) 104.049(4) 99.713(2) 84.2670(10) 90.5040(10) 100.402(2)g (◦) 85.0210(10) 101.4450(10)V/A3 1066.0(3) 978.13(8) 1055.47(5) 1290.84(5) 3286.1(2)Z 4 4 1 1 2T/K 173(2) 173(2) 173(2) 173(2) 173(2)m/mm-1 0.085 0.098 0.850 0.719 0.577Refls. coll. 9130 6991 13745 28199 18888Ind. refls. (Rint) 3027 (0.0451) 2212 (0.0307) 4812 (0.0376) 7590 (0.0353) 7311 (0.0501)R1 (I > 2s(I))a 0.0567 0.0382 0.0344 0.0492 0.0605wR2 (I > 2s(I))a 0.1340 0.1032 0.0848 0.1363 0.1074R1 (all data)a 0.1243 0.0555 0.0434 0.0592 0.0885wR2 (all data)a 0.1641 0.1219 0.1064 0.1533 0.1199GOF 0.932 1.126 1.165 1.102 1.159

a R1 =∑‖F o| - |F c‖/

∑|F o|; wR2 = [

∑w(F o

2 - F c2)2/

∑wF o

4]1/2.

is not observed. dC(75 MHz, CDCl3) 192.3, 148.7, 144.9, 143.6,140.8, 135.3, 131.8, 129.6, 129.1, 126.2, 122.9, 121.0, 120.3, 117.6,117.4, 116.2, 113.8, 24.2. lmax(CH2Cl2)/nm (e/mol-1 L cm-1): 228(94000), 269 (52000), 437 (40000), 458 (34000). IR(ATR) n/cm-1

1412 (COO-), 1592 (COO-). Found: C, 55.33; N, 7.99; H, 4.82%.C68H76N8O16Rh2 requires C, 55.66; N, 7.63; H, 5.22%.

Complex 13. A 1-propanol solution of 4 (25 mg, 0.105 mmol)and [Rh2(OAc)4] (22.2 mg, 0.052 mmol) was left to stand for twoweeks to afford red crystals of 13 (39.5 mg, 82%). IR(ATR) n/cm-1

3259 (OH), 1710 (C O), 1232 (C–O), 1440 (COO-), 1589(COO-).Found: C, 47.77; N, 6.80; H, 4.08%. C36H32N4O12Rh2 requires C,47.08; N, 6.10; H, 3.51%.

Complex 14. A DEF/EtOH/H2O: 3/2/2 solution of 5 (25 mg,0.105 mmol) and [Rh2(OAc)4] (22.2 mg, 0.052 mmol) was left tostand for two weeks. Red crystals, insoluble in common organicsolvents, were obtained (37.8 mg, 62%). IR(ATR) n/cm-1 3295(OH), 1720 (C O), 1221 (C–O), 1435 (COO-), 1582 (COO-).Found: C, 49.06; N, 7.07; H, 4.94%. C46H54N6O14Rh2 requires C,49.29; N, 7.50; H, 4.86%.

X-Ray diffraction

Data (Tables 1 and 2) were collected on a Bruker SMART CCDdiffractometer with Mo-Ka radiation. The structures were solvedusing SHELXS-97 and refined by full matrix least-squares on F 2

using SHELXL-97 with anisotropic thermal parameters for allnon hydrogen atoms.31 The hydrogen atoms were introduced atcalculated positions and not refined (riding model). In the case ofthe structure of 13, the SQUEEZE command was employed owingto the presence of highly disordered solvent molecules.30

CCDC 815819–815825 contain the supplementary crystal-lographic data for compounds 1–2 and 10–14. For crystal-lographic data in CIF or other electronic format see DOI:10.1039/c1dt10359h

Table 2 Crystallographic data for 13 and 14

13 14·(DEF)2

Formula C36H32N4O12Rh2 C46H54N6O14Rh2

FW 918.48 1120.78Crystal system Triclinic TriclinicSpace group P1 P1a/A 7.7872(2) 8.4005(2)b/A 11.7497(3) 10.4754(3)c/A 13.7757(4) 13.6491(4)a (◦) 110.5140(10) 77.8610(10)b (◦) 96.1150(10) 88.822(2)g (◦) 96.0720(10) 88.1780(10)V/A3 1159.85(5) 1173.53(6)Z 1 1T/K 173(2) 173(2)m/mm-1 0.766 0.777Refls. coll. 18223 17206Ind. refls. (Rint) 5262 (0.0290) 5351 (0.0364)R1 (I > 2s(I))a 0.0323 0.0309wR2 (I > 2s(I))a 0.0904 0.0768R1 (all data)a 0.0393 0.0389wR2 (all data)a 0.0933 0.0906GOF 1.035 1.190

a R1 =∑‖F o| - |F c|/

∑‖F o|; wR2 = [∑

w(F o2 - F c

2)2/∑

wF o4]1/2.

Acknowledgements

We thank the Universite de Strasbourg, the Institut Universitairede France, the Ministry of Education and Research, the C.N.R.S.and Marie Curie Est Actions FUMASSEC Network (ContractN◦ MEST-CET-2005-020992) for financial support.

Notes and references

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This journal is © The Royal Society of Chemistry 2011 Dalton Trans., 2011, 40, 7403–7411 | 7411

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