pop

egaD. F.

Ruthenium sandwich compounds

coOPallymatat tcomelemo

te ECEdecadarticulhe caseis of sbasedthe fuention

properties of the ligands, or inclusion of other metal centers. Thesynthesis of bimetallic pincer derivatives is a relatively new andinteresting research area since it allows the combining of the abovementioned aspects into one system. The possibility of tuning thecatalytic properties by addition of a second metal in the aromatic

2.1. Materials and reagents

All reactions were carried out under inert atmosphere (dini-trogen or argon) using conventional Schlenk glassware, all solventswere dried using established procedures and distilled under dini-trogen prior to use. The [MCl(POCOP)] pincer complexes weresynthesized according to the published procedures (1a [6], 1b [7],1c [8] and 1d [9]), using the M(II) chlorides without any previoustreatment. Anhydrous nickel(II) chloride, 4-(dimethylamino)

* Corresponding author. Tel.: 52 55 56224515; fax: 52 55 56162203.

Contents lists available at

Journal of Organom

sev

Journal of Organometallic Chemistry 716 (2012) 103e109E-mail addresses: ronan@servidor.unam.mx, ronan@unam.mx (R. Le Lagadec).the analogous PCP phosphine ligands. Besides, such POCOPcomplexes maintain the same characteristics of thermal robustnessand, in many catalytic procedures show increased reactivity whencompared to their phosphine counterparts [2]. The permanentsearch for higher reactivity and/or selectivity in catalytic reactionshas led to the design of new catalyst or the modication of theexisting ones in order to achieve these goals, and pincer complexesare no exception. As a result, modications and tuning of theirstructures have been focused on either the electronic or the spatial

2COP)(C2H4)], where Cp0 1,2,4-C5H2(tBu)3 and POCOP C6H3e2,6-(OPtBu2)2 [5]. In thepresentwork,wewish to reporton the facile andgeneral synthesis of a new family of group 10 metals POCOP pincercomplexes modied by p-coordination of the [CpRu] fragment tothe aromatic backbone. Structural and electrochemical features arediscussed.

2. Experimental1. Introduction

Metal complexes with tridentaattracted much attention in the laststability and tunability, this being psuch as homogeneous catalysis [1]. TPOCOP phosphinite pincer ligandssynthesis of the phosphinite ligandsnation of resorcinol derivatives andophosphines, is easier than the conv0022-328X/$ e see front matter 2012 Elsevier B.V.http://dx.doi.org/10.1016/j.jorganchem.2012.06.011pincer ligands havee because of their higharly important in areasof the complexes withpecial interest, as theon the initial deproto-rther addition to chlor-al procedure to prepare

backbone of a pincer complex is very attractive, even more if thesecond metal can participate in the catalytic cycle in a synergeticmanner. However, relatively few methods for the synthesis ofbimetallic complexes by p-coordination of a second metal to thearomatic ring of tridentate ECE ligands have been reported. Most ofthe procedures are based on the substitution by the electrophilicmoieties [(C5R5)Fe] to form metallocene-based pincer complexes[3], or [(C5R5)Ru] on arene-based PCP, NCN and SCS pincer deriv-atives [4]. To our knowledge, only one example of bimetallic POCOPcomplex has been prepared, starting from [Cp0Fe]I and [Ir(PO-Group 10 metal complexesFacile synthesis of heterobimetallic comruthenium moiety and group 10 POCOP

Noel ngel Espinosa-Jalapa, Simn Hernndez-OrtInstituto de Qumica, UNAM, Circuito Exterior s/n, Ciudad Universitaria, 04510 Mxico

a r t i c l e i n f o

Article history:Received 31 May 2012Received in revised form7 June 2012Accepted 8 June 2012

Keywords:POCOP pincer complexesHeterobimetallic complexes

a b s t r a c t

A series of heterobimetallicthe aromatic ring of POCstructures were unequivocmoiety and the POCOP arosolution clearly showed thboth faces of the pincerisopropyl substituents. Thecompared with that of the

journal homepage: www.elAll rights reserved.unds from the cyclopentadienyl-incer complexes

, David Morales-Morales, Ronan Le Lagadec*

, Mexico

mplexes have been prepared by p-coordination of the [CpRu] fragment topincer complexes of nickel, palladium and platinum. Their moleculardetermined by single-crystal X-ray diffraction, exhibiting the rutheniumic ring forming sandwich like species. The analysis in the solid state and inhe coordination occurs in an orthogonal fashion and, as a consequence,plexes become non equivalent, thus conferring diastereotopicity to thectrochemical behavior of the new bimetallic complexes was studied andnometallic POCOP pincer precursors.

2012 Elsevier B.V. All rights reserved.

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ier .com/locate/ jorganchem

ganopyridine, chlorodiisopropylphosphine and 1,3-benzenediol werepurchased from SigmaeAldrich Chemical and were used asreceived. Commercial ruthenium(III) chloride, palladium(II) chlo-ride and platinum(II) chloride were purchased from PressureChemical Co. The [CpRu(MeCN)3]PF6 complex was synthesizedaccording to the published procedure [10], using a 450 W Acemedium-pressure Hg lamp. For the electrochemical measurements,tetra-n-butylammonium hexauorophosphate (Aldrich) wasrecrystallized from water/methanol.

The 1H (300.53 MHz), 31P{1H} (121.5 MHz) and 13C{1H}(75.65 MHz) NMR spectra were recorded on a JEOL GX300 spec-trometer in CD2Cl2 or CDCl3. Chemical shifts (d) are in ppm downeld of TMS using the residual solvent as internal standard. Massspectra (FAB) were obtained using a JEOL JMS-SX102A instrumentwith m-nitrobenzyl alcohol as a matrix. Elemental analyses werecarried out on an Exeter Analytical CE-440 instrument analyzer.Electrochemical measurements were performed on a PC-interfacedpotentiostategalvanostat AUTOLAB PGSTAT 12. A three-electrodesetup was used with a BAS working glassy carbon electrode, Ag/AgCl reference electrode, and auxiliary Pt electrode. Before eachmeasurement, the working electrode was polished with a diamondpaste and rinsed with acetone and distilled water. All potentialscans were carried out at a scan rate of 100mV s1 in 3 mM acetonesolutions and 0.1 M of tetra-n-butylammonium hexa-uorophosphate as support analyte.

2.2. Crystallography

Suitable crystals were grown from CH2Cl2/diethyl ether for 2aecand were mounted on glass bers. In all cases, the X-ray intensitydata were measured at 298 K on a Bruker SMART APEX CCD-basedX-ray diffractometer system equipped with a Mo-target X-ray tube(0.71073A). The detector was placed at a distance of 4.837 cm fromthe crystals in all cases. A total of 1800 frames were collected witha scan width of 0.3 in u and an exposure time of 10 s/frame. Theframes were integrated with the Bruker SAINT software packageusing a narrow-frame integration algorithm [11]. The integration ofthe data was done using a monoclinic unit cell to yield a total of51,186, 24,898 and 25,005 reections for 2a, 2b and 2c respectively,to a maximum 2q angle of 50.00, of which 11,304 [R(int) 0.0824]for 2a, 5560 [R(int) 0.0335] for 2b and 5550 [R(int) 0.0646] for2c were independent. Analysis of the data showed in all casesnegligible decay during data collections. The structures were solvedby the Patterson method using the SHELXS-97 program [12]. Theremaining atoms were located via a few cycles of least squaresrenements and difference Fouriermaps using the space group P21/c with Z 8 for 2a and Z 8 for 2b and 2c. Hydrogen atoms wereadded at calculated positions and allowed to ride on the atoms towhich they are attached. Thermal parameters were rened forhydrogen atoms on the phenyl groups using a Ueq 1.2 A toprecedent atom in all cases. For all complexes, the nal cycle ofrenement was carried out on all non-zero data using SHELXTL andanisotropic thermal parameters for all non-hydrogen atoms. Thehexauorophosphate anion of 2aec, the cyclopentadienyl ring andthe isopropyl substituents of 2b and 2c are disordered and weremodeled in two major contributors and rened anisotropically.

2.3. General procedure

In a typical experiment, 100 mg (0.23 mmol) of [CpRu(MeCN)3]PF6 and 0.27 mmol of pincer complex in 15 mL of dichloro-methane were stirred at room temperature for 3e4 days. Thesolution was directly passed through a short column of silica(70e230) and the uncoordinated pincer complex was rst

N.. Espinosa-Jalapa et al. / Journal of Or104removed eluting with dichloromethane. The dinuclear complexwas eluted with a dichloromethane/acetonitrile (80:20) solventmixture to afford a pale yellow fraction. This fraction wascollected and evaporated to dryness under vacuum. The residuewas dissolved in 5 mL of dichloromethane and crystallized byslow diffusion of diethylether.

2.3.1. Synthesis of 2aReaction time 3 days. Yield: 151mg, 88%. 1H NMR (CDCl3): d 6.06

(broad s, 3H, Hmeta and Hpara), 5.27 (s, 5H, Cp), 2.57 (m, 4H,CH(CH3)2), 1.44 (m, 24H, CH(CH3)2). 13C NMR (CDCl3): d 139.65 (vt,vJCP 11 Hz, Cortho), 97.10 (vt, vJCP 20 Hz, Cipso), 80.65 (s, Cpara)80.25 (s, Cp), 70.57 (vt, vJCP 11 Hz, Cmeta), 29.29 (vt, vJCP 10 Hz,CH(CH3)2), 27.29 (vt, vJCP 10 Hz, CH(CH3)2), 17.82 (vt, vJCP 2.3 Hz,CH(CH3)2), 17.21 (vt, vJCP 2.3 Hz, CH(CH3)2), 17.14 (s, CH(CH3)2),16.40 (s, CH(CH3)2). 31P{1H} NMR (CDCl3): d 194.71 (s,PiPr2), 144.36 (stp, JPF 713 Hz, PF6). FABMS: 601[(M H) PF6] (100%), 400 [(MH) (Ru Cp Cl PF6)](12%). Anal. Calcd. for C23H36ClF6NiO2P3Ru$0.4C4H10O: C, 38.06; H,5.19. Found: C, 38.43; H, 4.84.

2.3.2. Synthesis of 2bReaction time 4 days. Yield: 149 mg, 82%. 1H NMR (CD2Cl2):

d 6.10 (d, 3J 6 Hz, 2H, Hmeta), 5.98 (t, 3J 6 Hz, 1H, Hpara), 5.24 (s,5H, Cp), 2.59 (m, 4H, CH(CH3)2), 1.38 (m, 24H, CH(CH3)2). 13C NMR(CD2Cl2): d 137.61 (vt, vJCP 7.5 Hz, Cortho), 98.73 (vt, vJCP 2.3 Hz,Cipso), 80.25 (s, Cp and Cpara), 70.85 (vt, vJCP 5.3 Hz, Cmeta), 29.86(vt, vJCP 9.8 Hz CH(CH3)2), 28.58 (vt, vJCP 9.8 Hz, CH(CH3)2), 17.06(vt, vJCP 3.8 Hz, CH(CH3)2), 16.83 (s, CH(CH3)2), 16.72 (vt,vJCP 3.8 Hz, CH(CH3)2), 16.29 (s, CH(CH3)2). 31P{1H} NMR (CD2Cl2):d 196.25 (s, PiPr2), 144.46 (stp, JPF 712 Hz, PF6). FAB-MS: 649[(M H) PF6] (100%), 447 [(M H) (Ru Cp Cl PF6)](30%). Anal. Calcd. for C23H36ClF6O2P3PdRu: C, 34.77; H, 4.57.Found: C, 34.64; H, 4.32.

2.3.3. Synthesis of 2cReaction time 4 days. Yield: 158 mg, 78%. 1H NMR (CD2Cl2):

d 5.99 (d, 3J 6 Hz, satellites JHPt 15 Hz, 2H, Hmeta), 5.79 (t,3J 6 Hz,1H, Hpara), 5.09 (s, 5H, Cp), 2.62 (m, 4H, CH(CH3)2), 1.33 (m,24H, CH(CH3)2). 13C NMR (CD2Cl2): d 136.94 (vt, vJCP 7 Hz, Cortho),92.46 (vt, vJCP 4.5 Hz, Cipso), 80.43 (s, Cp), 79.51 (s, Cpara), 70.51 (vt,vJCP 5.3 Hz, Cmeta), 30.83 (vt, vJCP 15 Hz, CH(CH3)2), 29.52 (vt,vJCP 15 Hz, CH(CH3)2), 17.14 (vt, vJCP 3.0 Hz, CH(CH3)2), 17.05 (s,CH(CH3)2), 16.62 (s, CH(CH3)2), 16.57 (vt, vJCP 3.0 Hz, CH(CH3)2).31P{1H} NMR (CD2Cl2): d 183.2 (s, satellites JPPt 2914 Hz,PiPr2), 144.50 (stp, JPF 712 Hz, PF6). FAB-MS: 737[(M H) PF6] (35%), 497 [(M H) (Ru Cp Cl PF6)](45%). Anal. Calcd. for C23H36ClF6O2P3PtRu: C, 31.28; H, 4.11. Found:C, 31.19; H, 3.84.

3. Results and discussion

3.1. Synthesis

The cationic complex [CpRu(MeCN)3]PF6 is a readily availableprecursor to cyclopentadienylruthenium complexes due to thesubstitutional lability of the acetonitrile ligands [13]. Additionally,the high afnity of the [CpRu] fragment for arene rings has also ledto its applications in the synthesis of heterobimetallic complexes byp-coordination on aromatic substituents. Thus, the bimetalliccomplexes 2aec were prepared in a simple manner by reacting[CpRu(MeCN)3]PF6 with a slight excess of the corresponding POCOPpincer complex 1aec in dichloromethane at room temperature(Scheme 1). Isopropyl substituents were preferred over thecommonly used phenyl to avoid the formation of side-products.

metallic Chemistry 716 (2012) 103e109The reactions were monitored by 31P{1H} NMR, to nd that 3

days reaction time at room temperature are the minimum neces-sary for the reaction to produce good yields (80% or higher). Theresulting white solids corresponding to the bimetallic species arevery stable both in the solid state and in solution. When the reac-tion was carried out under reux of dichloroethane for 15 h,decomposition occurred and none of the desired reaction productscould be identied but only the remaining 1aec POCOP pincercompounds. This slow reactivity is likely to be more a consequenceof the steric congestion around the ruthenium center, than of theelectronic requirements for the p-coordination. The importance ofthe steric hindrance was further demonstrated by using the pincercomplex 1d bearing two bulky tBu substituents on the arene unit.Under the same reaction conditions as for the preparation of 2aec,no reaction occurred after 3 days (as monitored by 31P{1H} NMR)and compound 1d completely recovered. Steric effects are knownto be crucial in the h6-coordination of [(C5R5)Ru(MeCN)3] [14],and such steric control of the reactions has been used to increase

3.2. X-ray diffraction studies

Single crystals suitable for X-ray diffractionwere obtained for allnew heterobimetallic complexes by slow diffusion of diethyletherinto a dichloromethane solution. The molecular structures ofcompounds 2aec are isomorphous and unequivocally conrm theirheterobimetallic nature (Fig. 1). The structure of the nickel complex2a consists of 2 independentmolecules in the asymmetric unit (onlyone cation is shown in Fig. 1). Crystallographic data, relevant bonddistances and angles are summarized in Tables 1e3. The metalcenterof thepincermoiety lies intoa slightlydistorted squareplanarenvironment, two of the coordination sites being occupied by thephosphorous donor ligands in a mutually trans conformation, andthe organometallic MeCipso bond and the chloride ligand trans tothis connection completes the coordination sphere. In all complexesthe P(1)eMeP(2) and CipsoeMeCl angles are smaller than 180,which is typical for ECE-pincer complexes (see Fig. 2) [15].

Bond distances and angles are similar in all the three molecularstructures, except for the bonds around the metal in the pincercomponent, which slightly increases from Ni to Pd and Pt. Inter-estingly, coordination of the ruthenium fragment does not alter thedistances around the Ni, Pd or Pt centers, and they remain almostthe same for the new bimetallic species as in the monometallicPOCOP pincer precursors (Table 2). For the three complexes, thedistance between the ruthenium atom and the cyclopentadienylring is marginally longer than between the ruthenium atom andthe average plane of the arene ring (2a: 1.805A/1.806A and 1.716A/1.721 A, 2b: 1.828 A and 1.720 A, 2c: 1.816 A and 1.723 A,respectively).

However, the cyclopentadienyl and arene rings are not parallel,forming a dihedral angle of 7.30/7.11 for 2a, 4.77 for 2b and 5.14

Scheme 1. Synthetic route used for the preparation of heterobimetallic complexes2aec.

N.. Espinosa-Jalapa et al. / Journal of Organometallic Chemistry 716 (2012) 103e109 105the regiospecicity by using Cp* instead of Cp [4e].Fig. 1. ORTEP views of heterobimetallic complexes 2a, 2c and 2c. Thermal ellipsoids arepentadienyl substituents and PF6 anions are omitted for clarity.for 2c. It is noteworthy that the bond distances between thedrawn with 50% probability level. Hydrogen atoms, disordered isopropyl and cyclo-

Table 1Crystal structure data for complexes 2aec.

2a 2b 2c

Empirical formula C23H36ClF6NiO2P3Ru C23H36ClF6O2P3PdRu C23H36ClF6O2P3PtRuFormula weight 746.66 794.35 883.04Temperature (K) 298(2) 298(2) 298(2)Wavelength (A) 0.71073 0.71073 0.71073Crystal system Monoclinic Monoclinic MonoclinicSpace group P21/c P21/c P21/cUnit cell dimensions (in A and ) a 10.7590(9) a 7.7654(7) a 7.7807(5)

b 52.044(4) b 28.875(2) b 28.904(2)c 11.0207(9) c 13.5886(11) c 13.577(1)a 90 a 90 a 90b 92.562(2) b 96.246(10) b 96.344(1)g 90 g 90 g 90

Volume (A3) 6164.8(9) 3028.8(4) 3034.7(4)Z 8 4 4Density (mg/m3, Calcd.) 1.609Absorption coeff. (mm1) 1.399F(000) 3024Crystal size (mm) 0.32 0.15 0.04q range for data collection () 1.86e25.41Index ranges 12 h 12

62 k 6213 l 13

Reections collected 51,186Independent reections 11,304 [R(int) 0.0824]Absorption correction AnalyticalRenement method Full-matrix least-squares on F2

Data/restrains/parameters 11,304/1033/839Goodness of t on F2 0.878Final R indices [I > 2s(I)] R1 0.0527, wR2 0.0870R indices (all data) R1 0.1059, wR2 0.1005Largest diff. peak and hole (e A) 0.667 and 0.633

Table 2Comparison of selected bond distances [A] and angles [] in the monometallic pincer 1a

1a [6] (M Ni) 2a (M Ni)MeCipso 1.879(2) 1.865(6) 1.847(6)MeP(1) 2.1582(6) 2.1545(19) 2.1613(19)MeP(2) 2.1603(6) 2.1621(19) 2.1679(19)MeCl 2.1944(6) 2.163(2) 2.152(2)P(1)eMeP(2) 164.01(3) 163.70(8) 177.5(2)CipsoeMeCl 178.31(6) 176.79(19) 165.07(8)

Table 3Selected bond distances [A] and angles [] for the bimetallic complexes.

2a 2ba 2ca

Ru-Cp(plane) 1.805 1.806 1.828 1.816Ru-Cp(shortest) 2.129(9) 2.147(7) 2.178(6) 2.168(7)Ru-Cp 2.146(9) 2.147(8) 2.181(6) 2.173(6)Ru-Cp 2.156(10) 2.177(8) 2.189(6) 2.177(7)Ru-Cp 2.167(9) 2.180(8) 2.194(6) 2.178(7)Ru-Cp(longest) 2.169(9) 2.186(9) 2.197(6) 2.182(7)Ru-Cp(average) 2.1534 2.1674 2.1878 2.1756Ru-arene(plane) 1.716 1.721 1.720 1.723Ru-Cpara 2.159(7) 2.151(6) 2.174(3) 2.170(6)Ru-Cmeta 2.191(7) 2.183(6) 2.199(3) 2.192(6)Ru-Cmeta 2.197(7) 2.204(6) 2.207(3) 2.207(5)Ru-Cortho 2.231(6) 2.235(6) 2.227(3) 2.219(6)Ru-Cortho 2.238(6) 2.242(6) 2.266(3) 2.277(5)Ru-Cipso 2.312(6) 2.293(5) 2.261(3) 2.279(5)Ru-arene(average) 2.2213 2.218 2.2225 2.2243Ru-Cp(centroid)-C(shortest) 88.46 89.09 89.41 89.56Ru-Cp(centroid)-C(longest) 91.23 90.88 90.55 90.38Ru-arene(centroid)-Cpara 86.85 86.92 87.62 87.29Ru-arene(centroid)-Cipso 93.42 92.78 91.40* 91.93Cp(centroid)-Ru-arene(centroid) 177.49 176.72 178.17 177.43Cp(plane)-arene(plane) 7.11 7.29 4.77 5.14

a Only one part of the disordered cyclopentadienyl group is considered.

N.. Espinosa-Jalapa et al. / Journal of Organometallic Chemistry 716 (2012) 103e1091061.742 1.9331.396 5.4051584 17120.34 0.22 0.14 0.34 0.18 0.061.66e25.39 1.67e25.359 h 9 9 h 934 k 34 34 k 3416 l 16 16 l 1624,898 25,005ruthenium atom and the different carbon atoms of the arene ringare quite disparate, the carbon atom in para position is much closerto the ruthenium center than the carbon atom supporting the h1-coordination (Cipso in Fig. 2), and the average difference betweenRu-Cpara and Ru-Cipso is about 0.12 A. This dissimilarity probablyreects the steric congestion between the Cp ligand and the bulkyisopropyl groups of the pincer moiety.

5560 [R(int) 0.0335] 5550 [R(int) 0.0646]Analytical AnalyticalFull-matrix least-squares on F2 Full-matrix least-squares on F2

5560/761/460 5550/767/4600.945 0.827R1 0.0273, wR2 0.0680 R1 0.0339, wR2 0.0522R1 0.0353, wR2 0.0703 R1 0.0557, wR2 0.05570.427 and 0.376 0.971 and 0.550

ec and the bimetallic 2aec complexes.

1b [7] (M Pd) 2b (M Pd) 1c [8] (M Pt) 2c (M Pt)1.974(6) 1.976(3) 1.984(3) 1.965(5)2.276(16) 2.2823(9) 2.2636(10) 2.2688(15)2.284(17) 2.2863(9) 2.2688(10) 2.2760(15)2.371(18) 2.3440(10) 2.3758(10) 2.3500(16)

160.380(6) 159.41(3) 161.20(4) 160.58(6)178.720(18) 176.86(9) 178.96(11) 177.35(3)

Fig. 2. Nomenclature used for the description of complexes 2aec.

2b (

N.. Espinosa-Jalapa et al. / Journal of Organometallic Chemistry 716 (2012) 103e109 1073.3. NMR studies

In solution, the 1H NMR and 13C{1H} NMR spectra of the bime-tallic derivatives clearly indicate that the pincer fragment hasbecome dissymmetric by effect of the coordination of the ruthe-

Fig. 3. 1H NMR spectrum of 1b (top) andnium moiety. For instance, the 1H NMR of 1b at room temperatureshows two AB systems of well-resolved multiplets for the axial and

Fig. 4. . 13C{1H} NMR spectra of 1a (top) and 2equatorial isopropyl groups whereas that of 2b shows a broadsystem of multiplets for the isopropyl groups (Fig. 3). Such splittingof the signals clearly indicates that p-coordination to rutheniumrenders the two faces of the pincer complex to be non equivalent.The aromatic protons of the h6-coordinated arene are found upeld

bottom), in CD2Cl2 at room temperature.shifted compared with the uncoordinated pincer complex. Theproton in the para position exhibits the higher shift (ca. 1.0 ppm

a (bottom), in CDCl3 at room temperature.

(d) D. Morales-Morales, Rev. Soc. Quim. Mex. 48 (2004) 338e346;(e) D. Morales-Morales, C.M. Jensen (Eds.), The Chemistry of Pincer

R.A. Toscano, J. Mol. Cat. A. Chem. 247 (2006) 124e129;

(c) S.A. Kuklin, A.M. Sheloumov, F.M. Dolgushin, M.G. Ezerniskaya,

ganodifference between 1 and 2), while the protons in the meta posi-tions show the smaller shift (ca. 0.45 ppm difference between 1 and2). The 13C{1H} NMR spectrum of the bimetallic complex 1a exhibitsa triplet (Jz 11 Hz) at ca. d 28 ppm for the methylene carbon and 2signals at ca. d 18 ppm (triplet, J z 2 Hz) and 17 ppm (singlet) forthe methyl carbons. These observed triplets are characteristic ofvirtual couplings generally observed in the NMR spectra of PCPpincer compounds [6]. With exception of the Cpara, the whole set ofsignals for the other carbon atoms of the arene ring also presentssuch virtual couplings with coupling constants (J) ranging from ca.11 Hz (Cortho and Cmeta) to ca. 20 Hz (Cipso) for 2a (virtual couplingconstants are slightly lower for 2b and 2c). From the 1H NMRspectra, it can be noted that upon coordination of the rutheniumthe signals belonging to the isopropyl substituents are split intotwo different sets, showing again their non-equivalence (Fig. 4).Similar features are observed for the NMR spectra of the rest of theanalogous compounds, with the additional satellites due to thecoupling with platinum for complexes 1c and 2c. In 31P{1H} NMR,the bimetallic derivatives show signals upeld shifted comparedwith the uncoordinated pincer complexes (Dd w 11 ppm (a) andw9 ppm for b and c). This shift is considered a consequence of theelectron-withdrawing properties of the [CpRu] group.

3.4. Electrochemistry

To study the inuence of the second metal center on the elec-tron density of the POCOP pincer complexes, cyclic voltammetry ofcompounds 1aec and 2aec was recorded in acetone. All oxidationpotentials discussed are relative to Ag/AgCl reference electrode (see2.1. for conditions). Nickel complex 1a exhibits a quasi-reversible,one electron wave at 1.26 V, which can be attributed to the Ni(II)/Ni(III) oxidation. Another irreversible feature appears at 1.99 V. Forthe palladium and platinum complexes, the voltammograms showtwo irreversible waves at 1.55 V and 1.91 V for 1b and 1.43 V and1.89 V for 1c. Due to the higher electronegativity of the oxygenatom, those potentials are more positive than those reported forrelated bimetallic PCP phosphine complexes [4a]. Irreversiblefeatures are also observed at very negative potentials 1.97 V(1a), 2.18 V (1b) and 1.88 V (1c). For 2a, the rst oxidation waveis shifted to 1.60 V, becoming almost irreversible, and the second to1.99 V. Compounds 2b and 2c show only one oxidation wave at2.08 V (same potential for both). In reduction, complex 2a showsone irreversible wave at 1.38 V, while 2b exhibits 3 new irre-versible waves at2.14 V,1.79 V and 1.50 V. Finally, compound 2chas two irreversible features at 2.14 V and 1.69 V. It has beenreported that [(C5R5)Ru(arene)] species give fully irreversible oneelectron reduction at very low potentials (Ered < 2.0 V vs. SCE inacetonitrile [16]). Such potentials are also observed in the cyclicvoltammograms of 2aec, and some features observed at verynegative values for 2aec are likely caused by the ruthenium center.Although the oxidation potentials do not correspond to reversibleprocesses and their interpretation is out of the reach of the presentwork, the observations reveal electronic interactions between thetwo metal centers that are consistent with the electron-withdrawing properties of the [CpRu] fragment, resulting ina less electron-rich POCOP-pincer metal center.

4. Conclusion

In this report, the facile and general synthesis of a series ofrutheniumenickel, rutheniumepalladiumand rutheniumeplatinumh6,h1-bimetallic complexesof thePOCOPpincer type isdescribed. Thearenophilicity of the [CpRu] group was exploited to readily preparethe new compounds in very good yields (>80%), starting from the

N.. Espinosa-Jalapa et al. / Journal of Or108POCOP pincer derivatives. The comparison of the X-ray crystalA.S. Peregudov, P.V. Petrovskii, A.A. Koridze, Organometallics 25 (2006)5466e5476;(d) A.A. Koridze, A.M. Sheloumov, S.A. Kuklin, V.Y. Lagunova, I.I. Petukhova,F.M. Dolgushin, M.G. Ezerniskaya, A.S. Peregudov, P.V. Petrovskii,A.A. Macharashvili, R.V. Chedia, Russ. Chem. Bull. Int. Ed. 51 (2002)1077e1078;(e) A.A. Koridze, A.V. Polezhaev, S.V. Safronov, A.M. Sheloumov,F.M. Dolgushin, M.G. Ezernitskaya, B.V. Lokshin, P.V. Petrovskii,A.S. Peregudov, Organometallics 29 (2010) 4360e4368.

[4] (a) S. Bonnet, M. Lutz, A.L. Spek, G. van Koten, R.J.M. Gebbink, Organometallics27 (2008) 159e162;(b) S. Bonnet, J. Li, M.A. Siegler, L.S. von Chrzanowski, G. van Koten,J.M. Robertus, K. Gebbink, Chem. Eur. J. 15 (2009) 3340e3343;(c) S. Bonnet, J.H. van Lenthe, M.A. Siegler, A.L. Spek, G. van Koten,R.J.M.K. Gebbink, Organometallics 28 (2009) 2325e2333;(f) F. Estudiante-Negrete, S. Hernndez-Ortega, D. Morales-Morales, Inorg.Chim. Acta 387 (2012) 58e63;(g) D. Morales-Morales, Mini-Rev. Org. Chem. 5 (2008) 141e152;(h) V. Gmez-Bentez, O. Baldovino-Pantalen, C. Herrera-lvarez, R.A. Toscano,D. Morales-Morales, Tetrahedron Lett. 47 (2006) 5059e5062.

[3] (a) E.J. Farrington, E.V. Martinez, B.S. Williams, G. van Koten, J.M. Brown,Chem. Commun. (2002) 308e309;(b) A.A. Koridze, S.A. Kuklin, A.M. Sheloumov, F.M. Dolgushin, V.Y. Lagunova,I.I. Petukhova, M.G. Ezerniskaya, A.S. Peregudov, P.V. Petrovskii,E.V. Vorontsov, M. Baya, R. Poli, Organometallics 23 (2004) 4585e4593;Compounds, Elsevier, Amsterdam, 2007;(f) J.M. Serrano-Becerra, D. Morales-Morales, Curr. Org. Synth. 6 (2009)169e192.

[2] (a) M. Beller, A. Zapt, Synlett (1998) 792e793;(b) A. Zapt, M. Beller, Chem. Eur. J. 6 (2000) 1830e1833;(c) R.B. Bedford, S.M. Draper, P.N. Scully, S.L. Welch, New J. Chem. 24 (2000)745e747;(d) D. Morales-Morales, R. Redn, C. Yung, C.M. Jensen, Chem. Commun.(2000) 1619e1620;(e) R. Cern-Camacho, V. Gmez-Bentez, R. Le Lagadec, D. Morales-Morales,structures shows that the compounds are isomorphous and that onlyslight differences exist between the three bimetallic species. NMRstudies allowed showing that upon coordination of the rutheniummoiety, the two faces of the pincer complex become non equivalent,turning the P-isopropyl groups stereotopic. Electrochemical studiesconrmed the strongelectron-withdrawingproperties of the [CpRu]

group. Currently, extensive studies are underway in order to comparethe catalytic activity of these new bimetallic complexes with that oftheir parent pincer precursors in different organic transformationsincluding cross-couplings reactions, these results will be disclosed indue time.

Acknowledgements

We thank nancial support from DGAPA (PAPIIT ProjectsIN205209, IN204812 and IN201711-3) and CONACyT (Projects153151, CB2010-154732 and scholarship to N. A. E-J.). ElizabethHuerta Salazar is gratefully acknowledged for performing NMRmeasurements.

Appendix A. Supplementary material

CCDC 883827 (2a), CCDC 883828 (2b) and CCDC 883829 (2c)contain the supplementary crystallographic data for this paper.These data can be obtained free of charge from the CambridgeCrystallographic data Center via www.ccdc.cam.ac.uk/data_request/cif.

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