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Journal of Organometallic Chemistry 700 (2012) 154e159

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Journal of Organometallic Chemistry

journal homepage: www.elsevier .com/locate/ jorganchem

trans Bis-N-heterocyclic carbene bis-acetylide palladium(II) complexes

Michael Koch, Jai Anand Garg, Olivier Blacque, Koushik Venkatesan*

Institute of Inorganic Chemistry, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland

a r t i c l e i n f o

Article history:Received 4 October 2011Received in revised form25 November 2011Accepted 2 December 2011

Keywords:AlkynesPalladiumN-Heterocyclic carbenesLuminescence

* Corresponding author. Tel.: þ41 44 6354694; fax:E-mail address: venkatesan.koushik@aci.uzh.ch (K

0022-328X/$ e see front matter � 2011 Elsevier B.V.doi:10.1016/j.jorganchem.2011.12.002

a b s t r a c t

A series of square planar trans bis-N-heterocyclic carbene palladium(II) bis(acetylide) complexes of thetype [(iPr2-bimy)2Pd(C^CeR)2] (bimy ¼ benzimidazolin-2-ylidene) (R ¼ C6H5, C6H4F, C6H4OMe, SiMe3,C4H3S, C5H4N, C6H4C^CC6H5 and 1-pyrene) were prepared by the addition of the corresponding lithiumacetylides to the starting (iPr2-bimy)2PdBr2 complex in good to modest yields. The molecular structuresof (iPr2-bimy)2Pd(C^CeC6H5)2 (1) and [(iPr2-bimy)2Pd(C^CeSiMe3)2] (4) were determined by single-crystal X-ray diffraction studies. UV/vis absorption studies reveal significant spectral changes depend-ing on the nature of the acetylide ligands bound to the palladium center.

� 2011 Elsevier B.V. All rights reserved.

1. Introduction

Organometallic complexes with trans s-alkynyl ligands areintensively investigated due to their utilization as buildingblocks in the synthesis of new dinuclear or oligonuclearrigiderod complexes that can have potential applications in thefield of electronic materials [1e4]. Particularly, the developmentof metal alkyne complexes and polymers with unusual opto-electronic properties has aroused great interest due to theirrecently found applications in the field of organic light emittingdiodes and photovoltaics [5e9]. The systematic tunability ofsuch complexes can afford building blocks that can be utilizedfor the development of non-linear optical (NLO) [10e12],luminescent, conductive [13] and magnetic materials [14]. Inthis context, phosphines as ligands had been successfullyutilized in the development of wide range of rigid-rodcomplexes [15e18]. Platinum(II) and palladium(II) alkynyl-based conjugated polymers and oligomers have attractedmuch interest because of their long-lived 3IL (intra ligand) and3MLCT (metal-to-ligand charge transfer) emissions [19e23]. Theluminescence properties of some of the platinum(II) andpalladium(II)-containing polymers with phosphines as thespectator ligands and with different heterocyclic organicspacers and their photophysical properties have been studied[24e31]. Recently, a series of monodisperse oligomers of thiskind has been investigated and these oligomers were found to

þ41 44 6356803.. Venkatesan).

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be luminescent in fluid solution at room temperature. Thephotovoltaic properties of platinum-containing alkynyl poly-mers with low band-gap organic spacers were also investigatedby different groups [24e31]. In comparison to the phosphineligands, the N-heterocyclic carbenes (NHCs) ligands areconsidered to form relatively robust metalecarbon bond incomplexes. Very recently, the groups of Bielawski and Albrechttook advantage of this property to obtain metal complexesbridged by NHC ligands to obtain oligonuclear complexes andpolymers containing metal carbene fragment in the main chainof the repeat unit [32e39]. In an alternative approach, metalcarbene complexes bearing acetylide ligands can be utilized asa novel way to prepare multinuclear complexes with a metalcarbene fragment in the back bone of the repeat unit, since thecarbene ligands bound to a metal center can give rise to inter-esting photophysical and redox properties. Particularly, incor-poration of NHC ligand, a strong s-donor and poor p-acceptor,into the cyclometallated Ir(III) and Pt(II) complexes has recentlybeen utilized as a strategy by other groups and our group tobroaden the energy gap by shortening the ligand p-conjuga-tions without sacrificing the structural rigidity [40e48]. In quitecontrast to these reports, work on the Pd(II) complexes isunknown. A systematic approach is pursued in order tounderstand the effect of different alkynes on the ground-stateand excited state properties of Pd(II) NHC complexes. Hereinwe report the synthesis and characterization of a new class ofpalladium(II) trans-bis(carbene) bis(acetylide) complexes. Tothe best of our knowledge this is the first report of palladium(II)bis(NHC) complexes bearing acetylide ligands.

Fig. 1. Molecular structure of complex 1 with a selective atomic numbering scheme.Thermal ellipsoids are drawn at 50% probability level. Hydrogen atoms and solventmolecules are omitted for clarity.

M. Koch et al. / Journal of Organometallic Chemistry 700 (2012) 154e159 155

2. Results and discussion

2.1. Syntheses of complexes

The (iPr2-bimy)2PdBr2 (precursor) complex was chosen asa precursor for the synthesis of the bis-acetylide complexes, sincebromide being a labile ligand, it was expected to be substituted ina facile fashion for another monoanionic ligand such as alkyne. Thepreparation of the starting material (precursor) was accomplishedby an already reported procedure [49]. Several methods are knownfor the substitution of the halides in metal complexes. One suchapproach was to substitute the bromide for alkynes to obtain thecorresponding bis-acetylide complex 1 by reaction of the precursorwith phenylacetylene under Sonogashira coupling conditions usingCH2Cl2/HNiPr2 in the presence of a catalytic amount of copperiodide [15]. However this reaction did not yield the expected bis-acetylide product and instead afforded a mixture of unidentifiableproducts. Hence we resorted to addition of lithium acetylide to theprecursor complex in THF at �78 �C. After the addition of thelithium phenylacetylide, the reaction mixture was stirred at roomtemperature for 12 h. Subsequent work-up and column chroma-tography on silica gel gave complex 1 as air and water stablecolorless crystals in 54% yield. Complex 1was fully characterized byNMR, IR spectroscopy and elemental analysis.

The 1H NMR showed the presence of three sets of new reso-nances for the aromatic protons of the phenyl acetylide between7.61 and 7.05 ppm and the 13C NMR spectrum of 1 exhibited twodistinct resonances for the metal bound acetylide ligand at 112.1(Ca) and 72.5 (Cb) ppm. In the IR spectra typical n(C^C) bands wereobserved at 2115 cm�1. The band positions were similar to those ofthe previously reported complexes. A total of eight palladium(II)complexes were synthesized according to the procedure describedabove and the compounds were isolated as slight yellow to color-less complexes in 36e84% yield. Scheme 1 shows the generalprocedure for the synthesis of complexes 1e8. Alkynes that werenot commercially available were readily synthesized by standardpalladium-catalyzed cross-coupling methods.

2.2. X-ray diffraction studies

The molecular structures of complexes 1 and 4 have been eluci-dated by single-crystal X-ray diffraction studies. The perspective

Scheme 1. Synthesis o

views of 1 and 4 are shown in Figs. 1 and 2, respectively. In bothcomplexes, the palladium atoms showed the expected square planarcoordination geometry with slight distortion, with theCacetyleneePdeCcarbene bond angles in the range of 87.04(8)�e92.96(10)�. It is conceivable that a slight distortion from an idealsquare planar arrangement could relieve steric interactions betweenbulky ligands. The bond distances of PdeCcarbene in 1 (2.021(3) Å) isslightly shorter than in 4 (2.036(2) Å), while the PdeCacetylene bond isslightly longer in 1 (2.031(3) Å) than in 4 (2.012(2) Å) (Table 1). ThePdeC bond lengths are within the range reported for palladium(II)bis-phosphine bis-acetylide complexes [25]. The bond lengthsbetween the acetylenic carbon atoms C1eC2 in 1 and C6eC7 in 4 are1.168(3) Å and 1.204(3) Å, respectively, and are similar to those foundin other palladium(II) bis(acetylide) complexes [25]. Further, the

f complexes 1e8.

Fig. 2. Molecular structure of complex 4 with a selective atomic numbering scheme.Thermal ellipsoids are drawn at 50% probability level. Hydrogen atoms and solventmolecules are omitted for clarity.

Fig. 3. Electronic absorption spectra of complexes precursor, 2, 3, 4 and 6 in CH2Cl2 atRT.

M. Koch et al. / Journal of Organometallic Chemistry 700 (2012) 154e159156

molecular packing in the crystal structures of these complexesshowed no Pd/Pd interactions, the shortest intermolecular Pd/Pddistance is 7.8076(2) Å in 1 and 9.1177(2) Å in 4. Concentrationdependent absorption studies of all the complexes in CH2Cl2(cz10�6e10�4M�1dm�3) didnot changeeither thepeakmaximaorgenerate additional low-energy band confirming the absence ofPd/Pd interactions in solution.

2.3. UV/vis absorption studies

Fig. 3 shows the absorption spectra for complexes 1e8. Table 2summarizes the photophysical data of the compounds. The elec-tronic absorption spectra of complexes in dichloromethane solu-tion showed an intense band at ca. 250e325 nm for complexes 1(Fig. 4), 2, 3, 4 and 6 (Fig. 3) and at ca. 250e400 nm for complexes 5,7 and 9 (Fig. 4) with absorption coefficients in the order of

Table 1Selected bond distances (Å) and angles (�) data of complexes 1 and 4.

1

Pd(1)eC(1) 2.031(3) C(1)eC(2) 1.168(3)Pd(1)eC(9) 2.021(3) C(2)eC(3) 1.460(4)C(9)eN(1) 1.346(3) C(9)eN(2) 1.363(3)

C(2)eC(1)ePd(1) 174.8(2) C(9)ePd(1)eC(1) 92.96(10)C(1)eC(2)eC(3) 176.1(3) C(9)ePd(1)eC(9i) 180.00(6)C(9)ePd(1)eC(1i) 87.04(10) N(1)eC(9)ePd(1) 126.3(2)

4

Pd(1)eC(11) 2.036(2) C(6)-C(7) 1.204(3)Pd(1)eC(6) 2.012(2) C(7)eSi(2) 1.815(2)C(11)eN(1) 1.354(2) C(11)eN(2) 1.358(2)C(7)eSi(2) 1.815(2)

C(7)eC(6)ePd(1) 174.9(2) C(11)ePd(1)eC(6) 91.37(8)C(6)eC(7)eSi(2) 174.9(2) C(11)ePd(1)eC(24) 177.63(8)

10�4e10�5 dm3 mol�1 cm�1. The dependence of the absorptionmaxima at ca. 285 nm in relation to the acetylide ligands wasstudied. While the difference in the absorption maxima are barelydiscernible for 1 (Fig. 4), precursor, 2, 3, 4, 6 (Fig. 3), additionalbands were observed for complexes 5, 7 and 8 (Fig. 4) at lowerenergies. Moreover, this systematic bathochromic shift was in linewith the increase in p-conjugation (6 < 7 < 8). The band around285 nm in the absorption spectra of the complexes showed slightnegative solvatochromic behavior in the range of 3 nm along withthe other higher energy bands which corresponds to the carbeneligand and acetylide-based intra ligand transitions. As the electrondonating nature of acetylide increases, it is expected that theenergies of nonbonding and weakly p bonding metal orbitals willincrease leading to the observed red shifts in the complexes. Theobservation that the low-energy absorptions of complexes 5, 7 and8 are red shifted relative to its trans-(iPr2-bimy)2PdBr2 (precursor)and are very close to that of the ethynyl ligands suggested that theyare likely to be ligand-centered pep* transitions with metalperturbation. However, there is no significant difference in theabsorption coefficients between the alkynyl complexes and thestarting dibromo complex. This is also quite consistent with ourrecent work on cis bis-carbene platinum(II) bis(acetylide)complexes, where the transitions are predominantly due to theintra ligand charge transfer character.

Complexes 1e8 in degassed solvents showed no observableluminescence at room temperature (RT), while the 77 K spectrumfor these compounds showed resolvable vibronic components ofthe emission. The influence of the acetylide variation on theemission energies is evident from Table 2. The extent of observedshifts are greater than those seen in the absorption spectra with

Table 2Photophysical data for compounds 1e8.

Complex lmax [nm] (emax/M�1 cm�1) lmax (77 K, 2-MeTHF)

Precursor 283 (44,900), 277 (46,600) e

1 285 (48,200), 279 (45,600) 423 nm2 285 (49,000), 278 (43,900) 422 nm3 285 (43,900), 278 (41,900) 423 nm4 284 (48,500); 278 (46,900) 428 nm5 285 (49,700), 279 (44,900) 423 nm6 285 (43,300), 278 (44,900) 425 nm7 316 (43,800), 297 (47,000) 362 nm8 358 (38,800), 345 (40,200), 281 (51,900) 404 nm

Fig. 4. Electronic absorption spectra of complexes 1, 5, 7 and 8 in CH2Cl2 at RT.

M. Koch et al. / Journal of Organometallic Chemistry 700 (2012) 154e159 157

trends that are exactly quite the opposite. An hypsochromic shiftwas observed with greater conjugation which is quite contrary tothe behavior observed in the Pt(II) complexes previously investi-gated by our group [47].

2.4. Cyclic voltammetry studies

The cyclic voltammograms of all complexes showed similar redoxprofile. In DMF/0.1 M [nBu4][PF6], all complexes show an irreversibleoxidation wave between þ0.95 and þ0.82 V. A qualitative relation-ship between the oxidation potential of the alkyne complexes andelectronic nature of the alkynes was observed. In general, theoxidation potential was in a decreasing order [5 (820 mV) > 4(þ840 mV) > 3 (þ850 mV) z 7 (þ850 mV) > precursor(þ860 mV) > 6 (þ950 mV)] with the increasing electron richness ofthe acetylide ancillary ligands. The cyclic volatmmatery studies of 2showed no observable maxima.

3. Conclusions

We have isolated and structurally characterized the first transpalladium(II) bis-acetylide complexes with NHC ligands trans toeach other. The structural features from the crystal structures ofthese complexes were found to be closely related to the trans pal-ladium(II) bis-acetylide complexes bearing phosphine ligands. Incontrast to the previously reported Pt(II) bis-acetylide complexeswith NHC ligand that show phosphorescence at room temperature[47], these Pd(II) complexes exhibit luminescence only at 77 K. Thisdifference can be attributed to the ‘Heavy Metal’ effect present inPt(II) in comparison to the Pd(II) [42]. Deprotection of the trime-thylsilyl group in complex 4 and subsequent reaction with theappropriate organic and organometallic counterparts would openup access to oligonuclear complexes and polymers with highfunctionality, which is being currently pursued.

4. Experimental

4.1. Materials and methods

All manipulations requiring inert atmosphere were carried outusing standard schlenk techniques under dinitrogen. 1H, 13C{1H}and 19F NMR spectra were recorded on Bruker AV2-300 (300 MHz)or AV-500 (500 MHz) spectrometers. Chemical shifts (d) are re-ported in parts per million (ppm) referenced to tetramethylsilane (d

0.00) ppm using the residual proton solvent peaks as internalstandards (1H NMR experiments) or the characteristic resonancesof the solvent nuclei (13C NMR experiments). 19F NMR was refer-enced to CFCl3 (d 0.00) ppm. Coupling constants (J) are quoted inHertz (Hz) and the following abbreviations are used to describe thesignal multiplicities: s (singlet); d (doublet); t (triplet); q (quartet);m (multiplet); dm (doublet of multiplet). Proton and carbonassignments have been made using routine one and two dimen-sional NMR spectroscopies where appropriate. Infra-red (IR)spectra were recorded on a PerkineElmer 1600 Fourier Transformspectrophotometer using KBr pellet with frequencies (nmax) quotedin wavenumbers (cm�1). Elemental microanalysis was carried outwith Leco CHNS-932 analyzer. Mass spectra were run on a Fin-nigan-MAT-8400 mass spectrometer. TLC analysis was performedon precoated Merck Silica Gel 60F254 slides and visualized byluminescence quenching either at (short wavelength) 254 nm or(long wavelength) 365 nm. Chromatographic purification of prod-ucts was performed on a short column using silica gel 60, 230e400mesh using a forced flow of eluent. UV/vis measurements werecarried out on a PerkineElmer Lambda 19 UV/vis spectrophotom-eter. Emission spectra were acquired on Perkin Elmer spectropho-tometer using 450W Xenon lamp excitation by exciting at thelongest-wavelength absorption maxima. 77 K emission spectrawere acquired in frozen 2-methyltetrahydrofuran (2-MeTHF) glass.Cyclic voltammograms were obtained with BAS 100W voltam-metric analyzer. The cell was equipped with an Auworking and a Ptcounter electrode, and a non-aqueous reference electrode. Allsample solutions (DMF) were approximately 5 � 10�3 M insubstrate and 0.1 M in Bu4NPF6, and were prepared under nitrogen.Ferrocene was subsequently added and the calibration of voltam-mograms recorded. BAS 100W program was employed for dataanalysis. Melting points were measured on Mettler Toledo MP70melting point system. All starting materials were purchased fromcommercial sources and used as received unless stated otherwise.The solvents used for synthesis were of analytical grade. Thecompounds 4-methoxyphenylacetylene, 2-ethynylthiophene, 4-(phenylethynyl)phenylacetylene, were prepared according toliterature methods.

4.2. Syntheses

4.2.1. General procedureUnder nitrogen 0.32 mmol of a 1.6 M n-BuLi solution in hexanes

was added to 0.32 mmol of the corresponding acetylene in THF(9 mL) cooled to �78 �C. The reaction mixture was stirred for30 min to obtain a slightly yellow to orange colored solution. Thesolution was allowed to warm up and was then added to a solutionof 0.14 mmol precursor in THF (15 mL) at �78 �C under nitrogen.The suspension was allowed to warm up to room temperature andstirred overnight to give an orange respectively brown solution. Thereaction was quenched with water and then extracted twice withdichloromethane (DCM). The organic layer was dried over anhy-drous Na2SO4 and then concentrated in vacuo. The brownish solidwas purified using column chromatography using 20% EtOAc inhexane as eluent. Recrystallization from CH2Cl2/pentane affordedthe trans-alkyne-complexes.

trans-[Pd(iPr-bimy)2(C^CeC6H5)2] (1). Yield: 54% (54 mg,0.075 mmol). Recrystallization from CH2Cl2/pentane gave tinywhite needles. 1H NMR (500 MHz, CDCl3, 20 �C): d (ppm)¼ 7.61 (m,4H, phenyleH), 7.56 (m, 4H, bimyeH), 7.38 (m, 2H, phenyleH), 7.22(m, 4H, bimyeH), 7.05 (m, 4H, phenyleH), 6.15 (sept.,3J(HeH) ¼ 7.1 Hz, 4H, CH(CH3)2), 1.88 (t, 3J(HeH) ¼ 7.1 Hz, 24H, CH3).13C{1H} NMR (125.8 MHz, CDCl3, 20 �C): d (ppm) ¼ 189.0 (Pd]C),133.4 (phenyleC), 132.8 (bimyeC), 130.8 (bimyeC), 125.2(phenyleC), 124.0 (phenyleC), 122.6 (bimyeC), 121.8 (phenyleC),

Table 3Crystallographic data for complexes 1 and 4.

1 4

Empirical formula C42H46N4Pd C36H54N4PdSi2Formula weight (g mol�1) 713.23 705.41Temperature (K) 183(2) 183(2)Wavelength (Å) 0.71073 0.71073Crystal system, space group Monoclinic, P 21/c Monoclinic, P 21/ca (Å) 11.4324(3) 10.8583(1)b (Å) 7.8076(2) 15.2011(1)c (Å) 21.7470(6) 25.3362(2)a (deg) 90 90b (deg) 104.914(3) 102.011(1)g (deg) 90 90Volume (Å3) 1875.74(9) 4090.39(6)Z, density (calcd) (Mg m�3) 2, 1.263 4, 1.145Abs coefficient (mm�1) 0.528 0.538F(000) 744 1488Crystal size (mm3) 0.15 � 0.11 � 0.05 0.45 � 0.31 � 0.11q Range (deg) 2.8e26.4 2.6e30.5Reflections collected 15,500 60,347Reflections unique 3776/Rint ¼ 0.056 12,500/Rint ¼ 0.024Completeness to q (%) 98.4 99.9Absorption correction Analytical AnalyticalMax/min transmission 0.98 and 0.95 0.945 and 0.851Data/restraints/parameters 2517/3/248 10,158/60/449Goodness-of-fit on F2 0.946 1.076Final R1 and wR2 indices [I > 2s(I)] 0.0377, 0.0647 0.0381, 0.1143R1 and wR2 indices (all data) 0.0815, 0.0722 0.0484, 0.1184Largest diff. peak and hole (e Å�3) 0.344, �0.377 1.022, �1.237

The unweighted R-factor is R1 ¼ PðFo� FcÞ=P Fo; I > 2sðIÞ and the weighted R-factor is wR2 ¼ fPðFo2 � Fc2Þ2=PwðFo2Þ2g1=2.

M. Koch et al. / Journal of Organometallic Chemistry 700 (2012) 154e159158

112.1 (PdeC^C), 72.5 (PdeC^C), 66.1 (CH(CH3)2), 20.6 (CH3). IR(KBr, cm�1) nC^C ¼ 2115. Elemental analysis calcd for C42H46N4Pd:C, 70.72; H, 6.50; N, 7.86. Found: C, 70.83; H, 6.62; N, 7.82. m.p. edecomp <199 �C.

trans-[Pd(iPr-bimy)2(C^CeC6H4F)2] (2). Yield: 69% (72 mg,0.097mmol). Recrystallization from CH2Cl2/pentane gave yellowishwhite needles. 1H NMR (500MHz, CDCl3, 20 �C): d (ppm)¼ 7.62 (m,4H, phenyleH), 7.57 (m, 4H, bimyeH), 7.24 (m, 4H, bimyeH), 7.18(m, 4H, phenyleH), 6.96 (sept., 3J(HeH) ¼ 7.1 Hz, 4H, CH(CH3)2), 1.61(t, 3J(HeH) ¼ 7.1 Hz, 24H, CH3). 13C{1H} NMR (125.8 MHz, CDCl3,20 �C): d (ppm)¼ 186.2 (Pd]C), 158.3, 156.4 (1J(CeF)¼ 239 Hz, CeF),132.2 (bimyeC), 132.0 (phenyleC), 127.2 (bimyeC), 127.0(phenyleC), 122.9 (bimyeC), 97.8 (PdeC^C), 75.7 (PdeC^C), 66.1(CH(CH3)2), 31.7 (CH3). IR (KBr, cm�1) nC^C ¼ 2218. Elementalanalysis calcd for C42H44F2N4Pd: C, 67.33; H, 5.92; N, 7.48. Found: C,67.54; H, 5.98; N, 7.39. m.p. e decomp <193 �C.

trans-[Pd(iPr-bimy)2(C^Ce4-C6H4OMe)2] (3). Yield: 39%(42 mg, 0.055 mmol). Recrystallization from CH2Cl2/pentane gavea yellow solid. 1H NMR (500 MHz, CDCl3, 20 �C): d (ppm) ¼ 7.63 (m,4H, phenyleH), 7.54 (m, 4H, bimyeH), 7.25 (m, 4H, bimyeH), 6.73(m, 4H, phenyleH), 6.16 (sept., 3J(HeH) ¼ 7.1 Hz, 4H, CH(CH3)2), 3.52(s, 6H, OCH3), 1.88 (t, 3J(HeH) ¼ 7.1 Hz, 24H, CH3). 13C{1H} NMR(125.8 MHz, CDCl3, 20 �C): d (ppm) ¼ 182.6 (Pd]C), 157.4(phenyleCeOMe), 133.7 (bimyeC), 130.8 (phenyleC), 127.8(bimyeC), 122.1 (bimyeC), 116.1 (phenyleC), 113.0 (phenyleC),112.6 (PdeChC), 75.7 (PdeC^C), 54.1 (OCH3), 54.0 (CH(CH3)2),21.3 (CH3). IR (KBr, cm�1) nC^C ¼ 2120. Elemental analysis calcd forC44H50N4O2Pd: C, 68.34; H, 6.52; N, 7.25. Found: C, 68.56; H, 6.67;N, 7.29. m.p. e decomp <195 �C.

trans-[Pd(iPr-bimy)2(C^CeSiMe3)2] (4). Yield: 70% (69 mg,0.098 mmol). Recrystallization from CH2Cl2/pentane gave yellowprisms. 1H NMR (500 MHz, CDCl3, 20 �C): d (ppm) ¼ 7.61 (m, 4H,bimyeH), 7.21 (m, 4H, bimyeH), 6.00 (sept., 3J(HeH) ¼ 7.1 Hz, 4H,CH(CH3)2), 1.78 (d, 3J(HeH) ¼ 7.1 Hz, 24H, CH3), �0.20 (s, 18H,Si(CH3)3). 13C{1H} NMR (125.8 MHz, CDCl3, 20 �C): d (ppm) ¼ 179.7(Pd]C), 133.6 (bimyeC), 122.0 (bimyeC), 112.6 (PdeC^C), 60.8(PdeC^C), 53.9 (CH(CH3)2), 21.3 (CH3), 1.4 (Si(CH3)3). IR (KBr,cm�1) nC^C ¼ 2180. Elemental analysis calcd for C36H54N4PdSi2: C,61.29; H, 7.72; N, 7.94. Found: C, 61.40; H, 7.78; N, 7.93. m.p. edecomp <184 �C.

trans-[Pd(iPr-bimy)2(C^Ce2-thienyl)2] (5): Yield: 66% (67 mg,0.092 mmol). Recrystallization from CH2Cl2/pentane gave smallyellow needles. 1H NMR (500 MHz, CDCl3, 20 �C): d (ppm) ¼ 7.62(m, 4H, bimyeH), 7.23 (m, 4H, bimyeH), 6.70 (m, 6H, thienyleH),6.06 (sept., 3J(HeH) ¼ 7.1 Hz, 4H, CH(CH3)2), 1.85 (t,3J(HeH) ¼ 7.1 Hz, 24H, CH3). 13C{1H} NMR (125.8 MHz, CDCl3, 20 �C):d (ppm) ¼ 187.6 (Pd]C), 133.9 (bimyeC), 129.7 (thienyleC), 126.8(bimyeC), 126.2 (thienyleC), 126.1(thienyleC), 121.7 (bimyeC),112.5 (PdeC^C), 96.8 (PdeC^C), 54.1 (CH(CH3)2), 21.1 (CH3). IR(KBr, cm�1) nC^C ¼ 2086. Elemental analysis calcd forC38H42N4PdS2: C, 62.93; H, 5.84; N, 7.72. Found: C, 63.17; H, 6.03; N,7.62. m.p. e decomp <191 �C.

trans-[Pd(iPr-bimy)2(C^Ce4-pyridine)2] (6). Yield: 65% (65 mg,0.091 mmol). Recrystallization from CH2Cl2/pentane gave yellowpowder. 1H NMR (500 MHz, CDCl3, 20 �C): d (ppm) ¼ 8.56 (d,3J(HeH) ¼ 4.9 Hz, 2H, pyridyleH), 8.24 (m, 2H, pyridyleH), 7.64 (m,4H, pyridyleH), 7.26 (m, 4H, bimyeH), 6.90 (m, 4H, bimyeH), 6.04(sept., 3J(HeH) ¼ 7.1 Hz, 4H, CH(CH3)2), 1.88 (t, 3J(HeH) ¼ 7.1 Hz, 24H,CH3). 13C{1H} NMR (125.8 MHz, CDCl3, 20 �C): d (ppm) ¼ 184.8(Pd]C), 149.6 (pyridyleC), 134.7 (pyridyleC), 134.2 (bimyeC),126.0 (bimyeC), 122.6 (pyridyleC) 122.5 (bimyeC), 113.1(PdeC^C), 82.7 (PdeC^C), 58.8 (CH(CH3)2), 21.9 (CH3). IR (KBr,cm�1) nC^C ¼ 2093. Elemental analysis calcd for C40H44N6Pd: C,67.17; H, 6.20; N, 11.75. Found: C, 67.30; H, 6.27; N, 11.86. m.p. edecomp <198 �C.

trans-[Pd(iPr-bimy)2(C^CeC6H4eC^CeC6H5)2] (7). Yield: 56%(72 mg, 0.078 mmol). Recrystallization from CH2Cl2/pentaneafforded yellow compound. 1H NMR (500 MHz, CDCl3, 20 �C):d (ppm) ¼ 7.58 (m, 4H, bimyeH), 7.36 (m, 4H, phenyleH), 7.20 (m,4H, bimyeH), 7.02 (m, 8H, phenyleH), 6.93 (m, 2H, phenyleH), 6.13(sept., 3J(HeH) ¼ 7.1 Hz, 4H, CH(CH3)2), 1.86 (t, 3J(HeH) ¼ 7.1 Hz, 24H,CH3). 13C{1H} NMR (125.8 MHz, CDCl3, 20 �C): d (ppm) ¼ 189.0(Pd]C), 134.0 (phenyleC), 132.7 (bimyeC), 130.9 (phenyleC), 129.4(phenyleC), 129.1 (phenyleC), 128.6 (phenyleC), 127.7 (bimyeC),124.3 (phenyleC), 122.0 (bimyeC), 121.6 (phenyleC), 112.4(PdeC^C), 107.8 (PheC^CePh), 81.7 (PdeC^C), 54.0 (CH(CH3)2),21.2 (CH3). IR (KBr, cm�1) nC^C ¼ 2106. Elemental analysis calcd forC58H54N4Pd: C, 76.26; H, 5.96; N, 6.13. Found: C, 76.38; H, 6.01; N,6.09. m.p. e decomp <204 �C.

trans-[Pd(iPr-bimy)2(C^Cepyrene)2] (8). Yield: 41% (55 mg,0.057 mmol). Recrystallization from CH2Cl2/pentane gave yellowpowder. 1H NMR (500 MHz, CDCl3, 20 �C): d (ppm) ¼ 8.21 (m, 2H,pyrenyleH), 8.12 (m, 8H, pyrenyleH), 7.81 (m, 2H, pyrenyleH), 7.62(m, 4H, pyrenyleH), 7.55 (m, 4H, bimyeH), 7.43 (m, 2H, pyrenyleH),7.23 (m, 4H, bimyeH), 6.21 (sept., 3J(HeH) ¼ 7.1 Hz, 4H, CH(CH3)2),1.82 (t, 3J(HeH) ¼ 7.1 Hz, 24H, CH3). 13C{1H} NMR (125.8 MHz, CDCl3,20 �C): d (ppm)¼ 183.1 (Pd]C), 132.8 (pyrenyleC), 131.9 (bimyeC),131.5 (pyrenyleC), 131.1 (pyrenyleC), 130.1 (pyrenyleC), 129.9(pyrenyleC), 128.4 (pyrenyleC), 128.0 (pyrenyleC), 127.8 (bimyeC),126.4 (pyrenyleC), 126.5 (pyrenyleC), 126.0 (pyrenyleC), 122.7(bimyeC), 122.2 (pyrenyleC), 120.0 (pyrenyleC), 112.8 (PdeC^C),81.9 (PdeC^C), 54.0 (CH(CH3)2), 21.2 (CH3). IR (KBr, cm�1)nC^C ¼ 2219. Elemental analysis calcd for C62H54N4Pd: C, 77.44; H,5.66; N, 5.83. Found: C, 77.65; H, 5.76; N, 5.73. m.p. e decomp<207 �C.

4.3. X-ray crystal structure determination for 1 and 4

Intensity data were collected at 183(2) K an Oxford Xcaliburdiffractometer (4-circle kappa platform, Ruby CCD detector, and

M. Koch et al. / Journal of Organometallic Chemistry 700 (2012) 154e159 159

a single wavelength Enhance X-ray source with MoKa radiation,l ¼ 0.71073 Å) [50]. The selected suitable single crystals weremounted using polybutene oil on the top of a glass fiber fixed ona goniometer head and immediately transferred to the diffrac-tometer. Pre-experiment, data collection, data reduction andanalytical absorption corrections [51] were performed with theOxford program suite CrysAlisPro [52]. The crystal structures weresolved with SHELXS-97 [53] using direct methods. The structurerefinements were performed by full-matrix least-squares on F2

with SHELXL-97 [53]. All programs used during the crystal struc-ture determination process are included in the WINGX software[54]. The program PLATON [55] was used to check the result of theX-ray analyses. In the crystal structure of 1, the molecule lies ona center of inversion, which led to refine only half of the molecule(the second part being reproduced by a symmetry operation). Oneisopropyl group is disordered over two sets of positions with site-occupancy factors of 0.425(11) and 0.575(11). In the crystal struc-ture of 4, one alkyne ligand C^CeSiMe3 is disordered over two setsof positions with site-occupancy factors of 0.748(4) and 0.252(4).Some restraints had to be used to correct the geometry and thermalparameters of the minor occupancy component and its corre-sponding atoms. All hydrogen positions were calculated after eachcycle of refinement using a riding model with CeH distances in therange 0.95e0.98 Å and Uiso(H) ¼ 1.2 or 1.5Ueq(C). No classichydrogen bonds were found in both crystal structures (Table 3).

Acknowledgments

This work was supported by the Swiss National Science Foun-dation NRP 62 Smart Materials Program (Grant No. 406240-126142). Support also from University of Zürich and H. Berke aregratefully acknowledged.

Appendix A. Supplementary material

CCDC 821700e821701 contain the supplementary crystallo-graphic data for this paper. These data can be obtained free ofcharge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

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