N-Heterocyclic Carbene Transfer from Gold(I) to Palladium(II

Oct 29, 2009 - (f) Barluenga , J.; Vicente , R.; Barrio , P.; López , L. A.; Tomás , M.; Borge , J. J. Am. Chem. Soc. 2004, 126, 14354. [ACS Full Text...
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Organometallics 2009, 28, 6957–6962 DOI: 10.1021/om900776j

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N-Heterocyclic Carbene Transfer from Gold(I) to Palladium(II) Shiuh-Tzung Liu,*,† Chun-I Lee,† Ching-Feng Fu,† Chang-Hong Chen,† Yi-Hung Liu,† Cornelis J. Elsevier,‡ Shei-Ming Peng,† and Jwu-Ting Chen*,† †

Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, Republic of China, and Van’t Hoff Institute of Molecular Sciences, University of Amsterdam, Amsterdam, The Netherlands

‡

Received September 7, 2009

N-Heterocyclic carbene gold(I) complexes [(L)AuCl] [L = 1,3-diethyl-4,5-dihydroimidazol-2-ylidene (3a); 1,3-dibenzyl-4,5-dihydroimidazol-2-ylidene (3c); 1,3-dipicolyl-4,5-dihydroimidazol-2-ylidene (3d); 1,3-diethylimidazol-2-ylidene (5a); and 1-methylthiomethyl-3-mesitylimidazol-2-ylidene (10)] react with [(PhCN)2PdCl2] to give the corresponding palladium complexes, and the reactions are promoted by the addition of triphenylphosphine. This study demonstrates that the carbene moiety can be transferred from Au(I) to Pd(II) for the first time.

Introduction Carbene transfer from a metal carbene complex to another metallic center represents an interesting approach that provides pragmatic accesses for the preparation of various new transition metal carbene complexes. Two approaches for the cabene transfer between metal ions are frequently encountered, and their starting materials are pentacarbonylmetal carbenes and silver carbenes, respectively.1 The first example of a carbene ligand transfer from molybdenum to iron complexes was reported by Fischer and Beck.2 Since then, the carbene ligands in group VI metal carbonyl carbene complexes have been transferred to iron,3 cobalt,4 rhodium,5

iridium,6 nickel,5e,f,7 palladium,5a,b,8,9 platinum,5a,b,8 copper,5b,7b,14 silver,5b and gold.5b,8,11,12 On the other hand, the reaction of imidazolium salts with Ag2O provides the corresponding Ag(I) carbenes directly, which can undergo transmetalation with various metal ions such as Ru(II), Ru(III), Ru(IV), Ni(II), Pd(II), Pt(II), Rh(I), Rh(III), Ir(I), Ir(III), Cu(I), and Au(I) to generate the corresponding carbene species.13 To the best of our knowledge, there is no precedented report concerning carbene transfer reaction from gold(I) to the other metal ion. Herein we describe the first example of a procedure for the carbene transfer from gold(I) to palladium(II).

Results and Discussion

*Corresponding authors. E-mail: [email protected]; [email protected]. (1) (a) Nolan, S. P., Ed. N-Heterocyclic Carbenes in Synthesis; WileyVCH: Weinheim, Germany, 2006. (b) Glorius, F. N-Heterocyclic Carbenes in Transition Metal Catalysis; Springer: Berlin, 2007. (c) Liddle, S. T.; Edworthy, I. S.; Arnold, P. L. Chem. Soc. Rev. 2007, 36, 1732. (d) K€uhl, O. Chem. Soc. Rev. 2007, 36, 592. (e) Dragutan, V.; Dragutan, I.; Delaude, L.; Demonceau, A. Coord. Chem. Rev. 2007, 251, 765. (f) Arnold, P. L.; Pearson, S. Coord. Chem. Rev. 2007, 251, 596. (g) Liu, S.-T.; Reddy, K. R. Chem. Soc. Rev. 1999, 315. (h) Gomez-Gallego, M.; Manche~no, M. J.; Sierra, M. A. Acc. Chem. Res. 2005, 38, 44. (2) Fischer, E. O.; Beck, H.-J. Angew. Chem., Int. Ed. Engl. 1970, 9, 72. (3) Fischer, E. O.; Beck, H.-J.; Kreiter, C. G.; Lynch, J.; Muller, J.; Winkler, E. Chem. Ber. 1972, 105, 162. (4) Jordi, L.; Moret o, J. M.; Ricart, S.; Vi~ nas, J. M.; Mejias, M.; Molins, E. Organometallics 1992, 11, 3507. (5) (a) Liu, S.-T.; Hsieh, T.-Y.; Lee, G.-H.; Peng, S.-M. Organometallics 1998, 17, 993. (b) Ku, R.-Z.; Huang, J.-C.; Cho, J.-Y.; Kiang, F.-M.; Reddy, K. R.; Chen, Y.-C.; Lee, K.-J.; Lee, J.-H.; Lee, G.-H.; Peng, S.-M.; Liu, S.-T. Organometallics 1999, 18, 2145. (c) Barluenga, J.; Vicente, R.;  L opez, L. A.; Rubio, E.; Tomas, M.; Alvarez-R ua, C. J. Am. Chem. Soc. 2004, 126, 470. (d) Barluenga, J.; Vicente, R.; Lopez, L. A.; Tomas, M. J. Organomet. Chem. 2006, 691, 5642. (e) Barluenga, J.; Vicente, R.; Barrio, P.; L opez, L. A.; Tomas, M. J. Am. Chem. Soc. 2004, 126, 5974. (f) Barluenga, J.; Vicente, R.; Barrio, P.; Lopez, L. A.; Tomas, M.; Borge, J. J. Am. Chem. Soc. 2004, 126, 14354. (6) (a) Chang, Y.-H.; Fu, C.-F.; Liu, Y.-H.; Peng, S.-M.; Chen, J.-T.; Liu, S.-T. Dalton Trans 2009, 861. (b) Chang, Y.-H.; Fu, C.-F.; Liu, Y.-H.; Peng, S.-M.; Elsevier, C. J.; Chen, J.-T.; Liu, S.-T. Dalton Trans. 2009, 6991. (7) (a) Barluenga, J.; Barrio, P.; L opez, L. A.; Tomas, M.; Garcı´ a Granda, S.; Alvarez-R ua, C. Angew. Chem., Int. Ed. 2003, 42, 3008. (b) del Amo, J. C.; Manche~ no, M. J.; Gomez-Gallego, M.; Sierra, M. A. Organometallics 2004, 23, 5021.

(8) Kessler, F.; Szesni, N.; Maass, C.; Hohberger, C.; Weibert, B.; Fischer, H. J. Organomet. Chem. 2007, 692, 3005. (9) (a) Sierra, M. A.; Manche~ no, M. J.; Saez, E.; del Amo, J. C. J. Am. Chem. Soc. 1998, 120, 6812. (b) Sierra, M. A.; del Amo, J. C.; Manche~no, M. J.; Gomez-Gallego, M. J. Am. Chem. Soc. 2001, 120, 6812. (c) Albeniz, A. C.; Espinet, P.; Manrique, R.; Perez-Mateo, A. Angew. Chem., Int. Ed. 2002, 41, 2363. (10) (a) Barluenga, J.; L opez, L. A.; L€ ober, O.; Tomas, M.; Garcı´ a Granda, S.; Alvarez-R ua, C.; Borge, J. Angew. Chem., Int. Ed. 2001, 40, 3392. (b) Barluenga, J.; Barrio, P.; Vicente, R.; Lopez, L. A.; Tomas, M. J. Organomet. Chem. 2004, 689, 3793. (11) Fischer, E. O.; B€ ock, M. J. Organomet. Chem. 1985, 287, 279. (12) Fa~ nanas-Mastral, M.; Aznar, F. Organometallics 2009, 28, 666. (13) (a) Lin, I. J. B.; Vasam, C. S. Coord. Chem. Rev. 2007, 251, 642. (b) Garrison, J. C.; Youngs, W. J. Chem. Rev. 2005, 105, 3978, and references therein. (c) Wang, H. M. J.; Lin, I. J. B. Organometallics 1998, 17, 972. (14) (a) Lee, C. K.; Vasam, C. S.; Huang, T. W.; Wang, H. M. J.; Yang, R. Y.; Lee, C. S.; Lin, I. J. B. Organometallics 2006, 25, 3768. (b) De Fremont, P.; Scott, N. M.; Stevens, E. D.; Ramnial, T.; Lightbody, O. C.; Macdonald, C. L. B.; Clyburne, J. A. C.; Abernethy, C. D.; Nolan, S. P. Organometallics 2005, 24, 6301.

r 2009 American Chemical Society

Published on Web 10/29/2009

Preparation of Saturated and Unsaturated NHC Gold(I) Complexes. Both saturated and unsaturated NHC complexes of gold(I) can be prepared by carbene transfer reactions either from tungsten complexes 2 or from silver complexes 5 with [(Me2S)AuCl] (Scheme 1). The saturated tungsten NHC complexes 2 were prepared by the direct

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Scheme 1. Preparation of Saturated NHC Gold(I) Complexes

alkylation of 1 with the corresponding alkyl halide in the presence of sodium hydride.5b In particular, reaction of 1 with 2-picolyl chloride in the presence of sodium hydride under refluxing conditions yielded 2d as yellow solids. The isolated complexes 2a-c have similar spectral data to those reported previously.5b Complex 2d is an air-stable, yellow solid. The 13C NMR signal for the carbene carbon atom of 2d (213.9 ppm) is located in the characteristic range reported for other analogous metal-NHC complexes, whereas the 1H NMR spectrum exhibits the 6H-pyridinyl proton signal at 9.15 ppm (coordination shift = 0.6 ppm), indicating the coordination of the pyridinyl-nitrogen to the tungsten atom. The carbonyl stretching wavenumbers of 2d occur in the range 2000-1800 cm-1, which is in accord with a tetracarbonyl species. These spectral data conclude that the pyridinyl-carbene ligand behaves as bidentate, not tridentate in 2d. Carbene transfer from tungsten to gold(I) has been reported by Fischer and Bock in the reaction of [(CO)5Wd C(R0 )NR2] with HAuCl4.11 In an early work, we have also demonstrated that reactions of [(NHC)W(CO)5] with [(Me2S)AuCl] could provide biscarbene gold(I) complexes [{(NHC)2Au}Cl]. With a similar procedure, the gold(I) carbene complexes 3a-d are formed directly via the reaction of 2a-d with 1 equiv of [(Me2S)AuCl] (Scheme 1). Typically, a mixture of 2a and an equal molar amount of [(Me2S)AuCl] in CH2Cl2 in dichloromethane at room temperature under ambient conditions readily caused a color change to deep green, indicating the formation tungsten clusters.5b The desired Au(I) carbene complexes were isolated as white solids after chromatographic purification. The transmetalation route using a NHC-silver complex has proved to be useful in the preparation of a variety of unsaturated NHC complexes.13 In this study, we employed this method to prepare the unsaturated NHC gold species as depicted in Scheme 2. First, reaction of the imidazolium salts 4a,b with an excess of Ag2O in dichloromethane afforded the corresponding NHC-silver complexes 5a,b. The NMR spectral data of 5a,b are essentially similar to those reported in the literature.14 Successive reaction of 5a,b with [(Me2S)AuCl] in dichloromethane at room temperature provided 6a, b in excellent yields. Furthermore, the unsymmetric carbene gold complex was prepared by a similar route (Scheme 3). Thus, reaction of the mesityl-substituted imidazole 7 with R-chlorodimethyl sulfide provided the imidazolium salt 8, which was subsequently reacted with silver oxide to yield the silver carbene complex 9. A similar procedure was employed for the reaction of 9 with [(Me2S)AuCl] to yield the desired gold complex 10. All gold carbene complexes in this work are white solids. Conductivity measurement of gold carbene complexes in dichloromethane shows that these complexes are essentially nonelectrolytic. In addition, mass spectra indicate that one carbene moiety is coordinated to the metal center. These observations

Scheme 2. Preparation of Unsaturated NHC Gold(I) Complexes

suggest the formulation of these complexes to be [(NHC)AuCl]. Indeed, the characteristic downfield signal for the coordinated carbene carbon atom is in the region 191-194 ppm for 2a-d and 169-176 ppm for 5a,b (Table 1), which are typical values for gold NHC complexes.5b,15 The coordination of chloride toward the metal center is evidenced by the infrared absorption at 330-345 cm-1, which is characteristic for the stretching frequency of Au-Cl (Table 1).16 Carbene Transfer from Au(I) to Pd(II). Initially, attempts on the carbene transfer reactions of 3a with [(COD)PdCl2] or [(Ph3P)2PdCl2] were investigated, but failed. In both instances, the reactions did not proceed at all; the gold carbene complex was recovered. However, reaction of 3a with 1.5 molar equiv of [(C6H5CN)2PdCl2] in CH2Cl2 at ambient temperature went smoothly to yield 11a in 35% isolated yield, which was proved to be a chloride-bridged dinuclear palladium carbene complex, and some other unidentified species. When the reaction was carried out in the presence of 1 molar equiv of PPh3, the complex 11a could be collected as the sole product, which can be characterized by NMR determination.5a The formulation of 11a was confirmed by both 1H and 13C NMR observation.5a However, the addition of an excess of phosphine may hinder the carbene transfer, presumably due to the competitive formation of [(Ph3P)2PdCl2]. In this context it is worth mentioning that the presence of phoshine in the reaction of 3a and [(PhCN)2PdCl2] does not provide the formation of any phoshine-substituted carbene palladium species such as 12. However, the coordination of triphenylphosphine toward Au(I), yielding [(Ph3P)AuCl], and the formation of 11a were acheived (eq 1). To our best knowledge, this observation demonstrates the first example of carbene transfer from Au(I) to Pd(II).

To test the generality of such a unique carbene transfer, other gold(I) carbene complexes, 3b-d, 5a,b, and 10, were also studied. Similar to 3a, reactions of 3c or 3d with (15) De Fremont, P.; Scott, N. M.; Stevens, E. D.; Nolan, S. P. Organometallics 2005, 24, 2411. (16) Ieda, H.; Fujiwara, H.; Fuchita, Y. Inorg. Chim. Acta 2001, 319, 203.

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Scheme 3. Preparation of Unsymmetric NHC Gold(I) Complexes

Table 1. Selected Spectral Data of Gold(I) Complexesa complex 3a 3b 3c 3d 5a 5b 10 a

1 H NMR -N-CHn-CHn-N-

13 C NMR C(NHC)-Au

IR ν(Au-Cl) (cm-1)b

3.62 3.61 3.45 3.67 6.95 7.15 7.41 and 6.93

191.6 192.8 192.3 193.7 169.5 175.5 172.1

332 335 330 331 331 341 338

carbene transfer reaction from 10 to Pd(II) went smoothly to yield the (C,S)-chelation complex 15. Complex 15 can also be prepared by a typical procedure via the carbene transfer from Ag(I) to Pd(II). Thus, reaction of 9 with [(COD)PdCl2] yielded 15 in 70% isolated yield.

NMR in CDCl3. ppm. b CsI.

(PhCN)2PdCl2 in the presence of 1 equiv of PPh3 in CH2Cl2 provided 11c and 13a, respectively. Complex 11c is a known species and was characterized by 1H and 13C NMR spectroscopies.5a The 1H NMR spectrum of 13a exhibits the 6H-pyridinyl proton signal at δ 9.40 (coordination shift = 0.9 ppm), indicating the coordination of the pyridinyl-nitrogen to the palladium atom. The proton spectrum of 13a also showed only one set of signals (δ 5.09) for the methylene units in the bridging pyridinyl and imidazole rings, supporting the presence of equivalent pyridinyl groups on the molecule, as expected for a structure in which the carbene ligand forms a pincer-type complex with palladium. Mass spectrometry also supported the proposed structure. Electrospray MS gave a clear ion at m/z 393.0 Da, which corresponds to the formula [(carbene)Pd35Cl]þ. Further confirmation of the formulation comes from the crystal structure of its hexafluorophosphate salt 13b, which was obtained via the anion metathesis. It should be noted that another synthetic approach leading to 13a can be achieved by the direct transfer reaction of 2d with [(COD)2PdCl2], i.e., the carbene transfer from tungsten to palladium.

In contrast with these cases, the analogous reaction of 3b gave complicated mixtures of palladium black and other unidentified species. It appears that reaction of 11b with Pd(II) may undergo other reaction pathways. Besides the saturated NHC complexes, gold complexes with an unsaturated carbene moiety are also investigated. Like complex 3a, the NHC ligand on complex 6a readily transfers to the palladium to yield 14 in 73% yield, but complex 6b remains intact. Presumably, the steric bulkiness of the substituents on the NHC hinders the transformation. Another example of this kind of transformation is illustrated with complex 10. With a NHC bearing a thioether donor,

Crystallography. For the pincer-type complex, yellow crystals of 13b were subsequently isolated, which proved suitable for X-ray crystallography. The ORTEP plot (Figure 1) shows the palladium atom with slightly distorted squareplanar coordination bonded to carbene and two pyridinyl nitrogen donors. The metallacycles are strongly puckered, as evidenced by the dihedral angles N(1)-C(1)-Pd(1)-N(4) (31.7°) and N(2)-C(1)-Pd(1)-N(3) (29.1°). These compare well to those observed in related pincer Pd(II) carbene complexes. The Pd-C(carbene) bond length is 1.936(2) A˚, which is normal for Pd-C(carbene) bonds. Selected bond lengths and angles are given in Table 2, and all are in the expected range. Complex 15 was isolated as light yellow crystals, and X-ray crystal structure confirms the formation of a (C,S)chelation complex (Figure 2). Selected bond distances and angles are shown in Table 3. Complex 15 adopts a slightly distorted square geometry around the palladium atom, where the carbene carbon [C(3)] and the sulfur donor [S(1)] constitute a five-membered ring with the metal atom. The resulting bite angle is 84.99(6)o. All bond lengths and angles of 15 are in the normal range as compared with those of the related species. The different trans influence of carbene vs sulfur donors is shown by the difference in the Pd-Cl bond distances [2.3033(6) vs 2.3456(6) A˚].

Summary In this work, we discover that gold(I) complexes with N-heterocyclic carbenes [(L)AuCl] can transfer NHC to [(PhCN)2PdCl2] to generate NHC palladium complexes with the promotion of triphenylphosphine. Although palladium carbene complexes can be obtained via several approaches, a carbene moiety transfer from Au(I) to Pd(II) leading to the formation of palladium carbene complexes is unprecedented. Further utilization of this type of carbene complexes and kinetics for the carbene transfer reactions are under investigation.

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Figure 2. ORTEP plot of 15 (drawn with 30% probability ellipsoids; labels for the phenyl group are omitted for clarity).

Figure 1. ORTEP plot of the cationic portion of 13b (drawn with 30% probability ellipsoids; labels for the pyridinyl rings are omitted for clarity). Table 2. Selected Bond Distances (A˚) and Bond Angles (deg) Pd(1)-C(1) Pd(1)-Cl(1) Pd(1)-N(3) Pd(1)-N(4) C(1)-N(1) C(1)-N(2) C(2)-C(3)

1.936(2) 2.3688(5) 2.066(2) 2.054(2) 1.321(3) 1.313(3) 1.523(3)

N(4)-Pd(1)-N(3) C(1)-Pd(1)-Cl(1) C(1)-Pd(1)-N(4) C(1)-Pd(1)-N(3) Pd(1)-C(1)-N(1) Pd(1)-C(1)-N(2)

174.92(6) 176.78(6) 87.15(8) 87.87(8) 123.9(2) 124.7(2)

Experimental Section General Information. All reactions, manipulations, and purification steps were performed under a dry nitrogen atmosphere. Tetrahydrofuran was distilled under nitrogen from sodium benzophenone ketyl. Dichloromethane and acetonitrile were dried over CaH2 and distilled under nitrogen. Other chemicals and solvents were of analytical grade and were used after a degassing process. Tungsten carbene complex 1, 2a-c, 5a,b, and 1-mesitylimidazole were prepared according to the method reported previously.5a,14,17 Nuclear magnetic resonance spectra were recorded in CDCl3 on a Bruker AVANCE 400 spectrometer. Chemical shifts are given in parts per million relative to Me4Si for 1H and 13C NMR and relative to 85% H3PO4 for 31P NMR. Infrared spectra were measured on a Bomem DA 8.3 spectrometer as CsI pallets. Conductivity measurements were carried out at 25 °C on a YSI model 32 conductance meter. Complex 2d. A mixture of sodium hydride (prewashed with hexane 10 mL  2) (25 mmol) and 1 (0.5 g, 1.27 mmol) in anhydrous THF (20 mL) was stirred at room temperature for 8 h. 2-Picolyl chloride (0.86 g, 6.7 mmol) in THF was added to the above solution and then heated to reflux overnight. Upon cooling, the excess of NaH was slowly quenched by water and the organic portion was separated. The aqueous layer was extracted with dichloromethane (20 mL). The combined organic (17) Johnson, A. L.; Kauer, J. C.; Sharma, D. C.; Dorfman, R. I. J. Med. Chem. 1969, 12, 1024.

Table 3. Selected Bond Distances (A˚) and Bond Angles (deg) Pd(1)-C(3) Pd(1)-Cl(1) N(1)-C(3) N(1)-C(2) C(3)-Pd(1)-S(1) S(1)-Pd(1)-Cl(1) N(2)-C(3)-N(1)

1.977(2) 2.3033(6) 1.351(3) 1.442(3) 84.99(6) 176.95(2) 104.6(2)

Pd(1)-S(1) Pd(1)-Cl(2) N(2)-C(3) C(4)-C(5) C(3)-Pd(1)-Cl(1) C(3)-Pd(1)-Cl(2) C(3)-N(1)-C(5)

2.2640(6) 2.3456(6) 1.344(3) 1.330(3) 95.99(6) 171.02(6) 111.6(2)

portions were dried and concentrated. The residue was dissolved in dichloromethane. By addition of hexane, the desired complex precipitated out as yellow solids (0.43 g, 66%). 1H NMR (DMSO-d6, 400 MHz): δ 8.98 (m, 1H, Py-H), 8.51 (m, 1H, Py-H), 7.99 (m, 1H, Py-H), 7.78 (m, 1H, Py-H), 7.72 (m, 1H, PyH), 7.33 (m, 1H, Py-H), 7.26-7.29 (m, 2H, Py-H), 4.99 (s, 2H, -NCH2-Py), 4.70 (s, 2H, -NCH2-Py), 3.81-3.86 (m, 2H, imiH), 3.52-3.57 (m, 2H, imi-H). 13C NMR (DMSO-d6, 100.6 MHz): δ 218.8, 213.9, 213.5 (trans-CO, WdC and axial-CO), 203.2 (cis-CO), 158.0, 156.9, 156.6, 149.2, 139.1, 136.9, 125.4, 123.9, 122.4, 121.2, 55.6, 55.2, 51.3, 49.1. IR (KBr, νCO): 1992, 1862, 1811 cm-1. ESI-MS: calcd for (M þ H)þ C19H17N4O4W m/z = 549.1, found 549.1. Anal. Calcd for C19H16N4O4W: C, 41.63; H, 2.94; N, 10.22. Found: C, 41.61; H, 3.31; N, 10.05. Complex 3a. To a solution of 2a (149.8 mg, 0.33 mmol) in CH2Cl2 (1 mL) was added a dichloromethane solution (5 mL) of [(Me2S)AuCl] (108 mg, 0.36 mmol). The resulting mixture was stirred at room temperature for 10 min, and the solution turned a dark green color. The reaction mixture was concentrated and the residue was chromatographed on silica gel (15 g) with the elution of ethyl acetate/hexane (1:1). The fraction of the desired product was collected and concentrated to yield 3a as white solids (85.6 mg, 72%). IR: 332 cm-1 (Au-Cl). ΛM (1.0  10-3 mol dm-3, dichloromethane): 8 Ω cm2 mol-1. 1H NMR (CDCl3, 400 MHz): δ 3.66 (q, J = 7.2 Hz, 4H, -CH2CH3), 3.62 (s, 4H, imi-H), 1.19 (t, J = 7.2 Hz, 6H, -CH2CH3). 13C NMR (CDCl3, 100 MHz): δ 191.6 (AudC), 47.8, 45.4, 13.6. Anal. Calcd for C7H14AuClN2: C, 23.44; H, 3.93; N, 7.81. Found: C, 23.81; H, 4.23; N, 7.57. Complex 3b. The preparation procedure is similar to that for 2a: white powders (78%). IR: 335 cm-1 (Au-Cl). ΛM (1.0  10-3 mol dm-3, dichloromethane): 8 Ω cm2 mol-1. 1 H NMR (CDCl3, 400 MHz): δ 5.80 (m, 2H, -CH2-CHdCH2), 5.26 (d, J=14 Hz, 4H, -CH2-CHdCH2), 4.25 (d, J=6 Hz, 4H,

Article -CH2-CHdCH2), 3.61 (s, 4H, imi-H). 13C NMR (CDCl3, 100 MHz): δ 192.8 (AudC), 131.9, 119.5, 53.3, 48.2. Anal. Calcd for C9H14AuClN2: C, 28.25; H, 3.69; N, 7.32. Found: C, 28.56; H, 4.00; N, 7.26. Complex 3c. The preparation procedure is similar to that for 2a: white solids (65%). IR: 330 cm-1 (Au-Cl). 1H NMR (CDCl3, 400 MHz): δ 7.42-7.28 (m, 10H, Ar-H), 4.85 (s, 4H, -CH2Ph), 3.45 (s, 4H, imi-H). 13C NMR (CDCl3, 100 MHz): δ 192.3 (AudC), 134.6, 128.9, 128.4, 128.1, 54.7, 48.0. Anal. Calcd for C17H18AuClN2: C, 42.29; H, 3.76; N, 5.80. Found: C, 42.67; H, 4.18; N, 5.63. Complex 3d. The preparation procedure is similar to that for 2a: white solids (23%). IR: 331 cm-1 (Au-Cl). ΛM (1.0  10-3 mol dm-3, dichloromethane): 4 Ω cm2 mol-1. 1H NMR (CDCl3, 400 MHz): δ 8.50 (d, 2H, Py-H, J=4.4 Hz), 7.66 (t, 2H, -Py, J= 7.6 Hz), 7.43 (d, 2H, Py-H, J = 7.6 Hz), 7.20 (t, 2H, Py-H, J = 4.4 Hz), 4.93 (s, 4H, -CH2Py), 3.67 (s, 4H, imi-H). 13C NMR (CDCl3, 100 MHz): δ 193.7 (AudC), 155.0, 149.5, 137.2, 123.0, 122.4, 56.0, 49.1. Anal. Calcd for C15H16AuClN4: C, 37.17; H, 3.33; N, 11.56. Found: C, 37.42; H, 3.01; N, 11.48. Complex 6a. A solution of 5a (148 mg, 0.47 mmol) in dichloromethane (1 mL) was added to a solution of [(Me2S)AuCl] (153.7 mg, 0.47 mmol) in dichloromethane (5 mL), and the resulting mixture was stirred at room temperature for 2 h. After filtration of silver salts and concentration of the filtrate, the residue was chromatographed on silica gel with elution of ethyl acetate. The desired complex was obtained as white solids (155.9 mg, 92%). IR: 331 cm-1 (Au-Cl). ΛM (1.0  10-3 mol dm-3, dichloromethane): 6 Ω cm2 mol-1. 1H NMR (CDCl3, 400 MHz): δ 6.95 (s, 2H, -imi-H), 4.18 (q, J=7 Hz, 4H, CH3CH2-), 1.43 (t, J= 7 Hz, 6H, CH3CH2-). 13C NMR (CDCl3, 100 MHz): δ 169.5 (AudC), 119.9, 46.4, 16.4. Anal. Calcd for C7H12AuClN2: C, 23.58; H, 3.39; N, 7.86. Found: C, 23.68; H, 3.60; N, 7.22. Complex 6b. The preparation procedure is similar to that for 5a: white solid (86%). IR: 341 cm-1 (Au-Cl). ΛM (1.0  10-3 mol dm-3, dichloromethane): 5 Ω cm2 mol-1. 1H NMR (CDCl3, 400 MHz): δ 7.48 (t, J = 7.8 Hz, 2H, Ar-H), 7.26 (d, J = 7.8 Hz, 2H, Ar-H),7.15 (s, 2H, imi-H), 2.54 (m, 4H, -CH), 1.32 (d, J = 7 Hz, 6H, -CH3), 1.19 (d, J = 7 Hz, 6H, -CH3). 13C NMR (CDCl3, 100 MHz): δ 175.5 (AudC), 145.6, 134.0, 130.7, 124.3, 123.1, 28.8, 24.4, 24.0. Anal. Calcd for C27H36AuClN2: C, 52.22; H, 5.84; N, 4.51. Found: C, 52.12; H, 6.02; N, 4.10. Compound 8. A mixture of imidazole 7 (0.5 g, 2.7 mmol) and chloromethyl methyl sulfide (1.15 g, 12 mmol) in anhydrous THF (10 mL) was heated to reflux for 24 h. Yellowish solids were collected and redissolved in CH2Cl2. Addition of ether to the solution gave 8 as white precipitates (0.7 g, 91%). 1H NMR (CDCl3, 400 MHz): δ 11.02 (s, 1H, im-H), 7.76 (s, 1H, im-H), 7.15 (s, 1H,im-H), 7.00 (s, 2H, Ar-H), 5.94 (s, 2H, -CH2-), 2.33 (s, 3H, p-Ar-Me), 2.30 (s, 3H, -SCH3), 2.07(s, 6H, o-Ar-Me). 13 C NMR (CDCl3, 100 MHz): δ 140.2, 137.1, 133.2, 129.9, 128.9, 123.0, 122.7, 51.8, 20.2, 16.7, 13.6. Anal. Calcd for C14H19ClN2S: C, 59.45; H, 6.77; N, 9.90. Found: C, 59.25; H, 6.62; N, 10.11. Complex 9. A mixture of 8 (0.1 g, 0.36 mmol) and Ag2O (0.1 g, 0.43 mmol) in CH3CN (10 mL) was stirred at room temperature in the dark for 24 h. The reaction mixture was filtered, and the solvent was removed under vacuum to give the crude product, which was washed with ether to give complex 9 as a gray-white solid (79 mg, 56%). 1H NMR (CDCl3, 300 MHz): δ 7.43 (s, 1H, imi-H), 7.00 (s, 1H, imi-H), 6.94 (s, 2H, Ar-H), 5.23 (s, 2H, -CH2-), 2.32 (s, 3H, p-Ar-Me), 2.10 (s, 3H, -SCH3), 1.95 (s, 6H, o-Ar-Me). 13C NMR (CDCl3, 100 MHz): δ 180.8, 139.0, 134.9, 134.2, 128.9, 123.0, 121.1, 54.1, 20.1, 17.2, 13.7. Anal. Calcd for C14H18AgClN2S: C, 43.15; H, 4.66; N, 7.19. Found: C, 42.95; H, 4.75; N, 7.38. Complex 10. A mixture of 9 (105.9 mg, 0.27 mmol) and [Me2SAuCl] (79.0 mg, 0.27 mmol) in anhydrous dichloromethane (10 mL) was stirred at room temperature under a nitrogen atmosphere for 4 h. After filtration of silver salts, the

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filtrate was chromatographed on silica gel with elution of ethyl acetate. Upon concentration, complex 10 was obtained as white solids (113 mg, 87%). IR: 338 cm-1 (Au-Cl). 1H NMR (400 MHz CDCl3): δ 7.41 (d, J = 2 Hz, 1H, imi-H), 6.94 (s, 2H, Ar-H), 6.93 (d, J=2 Hz, 1H, imi-H), 5.35 (s, 2H, -CH2-), 2.31 (s, 3H, p-Ar-Me), 2.19 (s, 3H, -SCH3), 2.00 (s, 6H, o-Ar-Me). 13 C NMR (400 MHz CDCl3): δ 172.1 (Au-C), 139.8, 134.6, 134.3, 129.4, 123.3, 119.6, 53.9, 21.2, 17.9, 14.4. Anal. Calcd for C14H18AuClN2S: C, 35.12; H, 3.79; N, 5.85. Found: C, 34.89; H, 3.82; N, 5.59. Complex 11a. 1H NMR (CDCl3, 300 MHz): δ 4.22 (q, J = 7.3 Hz, 8H, -CH2-), 3.63 (s, 8H, imi-H), 1.37 (t, J =7.3 Hz, 12H, -CH3). These spectral data are consistent with the literature data.5a,b Complex 11c. 1H NMR (CDCl3, 300 MHz): δ 7.46-7.50 (m, 8H, Ar-H), 7.36-7.28 (m, 12H, Ar-H), 5.41 (s, 8H, -CH2Ph), 3.37 (s, 8H, imi-H). These spectral data are consistent with the literature data.5a,b Complex 13a. Method A. A mixture of 2d (30 mg, 5.5  10-2 mmol) and [(COD)PdCl2] (23.4 mg, 8.2  10-2 mmol) in CH2Cl2 (8 mL) was stirred at room temperature for 2 h. The reaction mixture was passed through Celite (2 g) to remove tungsten species, and the filtrate was concentrated. The residue was recrystallized in CH2Cl2/ether to yield yellow crystalline solids (13 mg, 55%). Method B. A mixture of 3d (10 mg, 2  10-2 mmol) and [(PhCN)2PdCl2] (12 mg, 3  10-2 mmol) in CH2Cl2 was stirred at 40 °C for 6 h. The reaction mixture was concentrated and chromatographed on silica gel with elution of hexane/ethyl acetate. A yellow band from the column was collected and concentrated to give 13a as yellow solids (6.2 mg). 1H NMR (CDCl3, 400 MHz): δ 9.40 (d, J=6 Hz, 2H, Py-H), 7.97 (dd, J= 8, 6 Hz, 2H, Py-H), 7.87 (d, J=8 Hz, 2H, Py-H), 7.42 (dd, J=8, 6 Hz, 2H, Py-H), 5.09 (s, 4H, -CH2Py), 4.33 (s, 4H, imi-H). 13C NMR (CDCl3, 100 MHz): δ 178.2 (MdC), 155.9, 153.6, 140.7, 126.3, 124.8, 52.9, 51.9. HR-ESI-MS calcd for C15H16N435Cl106Pd [M - Cl] m/z = 393.0096, found 393.0097. ΛM (1.0  10-3 mol dm-3, CH3OH): 63 S cm2 mol-1. Anal. Calcd for C15H16Cl2N4Pd: C, 41.93; H, 3.75; N, 13.04. Found: C, 41.73; H, 3.85; N, 13.25. Complex 13b. To a solution of 13a was added an excess of KPF6 in CH3CN. Upon stirring at room temperature for 2 h, the solvent was removed and the residue was extracted with CH2Cl2/H2O. The organic extract was dried and concentrated. Upon recrystallization from CH2Cl2/ether, the desired complex 13b was obtained as yellow crystalline solids (73%). 1H NMR (CDCl3, 400 MHz): δ 9.42 (d, J = 6 Hz, 2 H, Py-H), 7.97 (t, J = 7.8 Hz, 2H, Py-H), 7.62 (d, J = 7.8 Hz, 2H, Py-H), 7.43 (t, J = 6 Hz, 2H, Py-H), 4.80 (s, 4H, CH2-Py), 4.12 (s, 4H, imi-H). 13C NMR (CDCl3, 100.6 MHz): δ 178.2 (MdC), 155.9, 153.6, 140.7, 126.3, 124.8, 52.9, 51.9. 31P{1H} NMR (CDCl3, 162 MHz): δ -144.0 (sept, PF6, JFP = 712.8 Hz). Anal. Calcd for C15H16ClF6N4PPd: C, 33.42; H, 2.99; N, 10.39. Found: C, 33.28; H, 2.89; N, 10.18. Complex 14. The procedure is similar to that for 5a (method B) (61%). 1H NMR (CDCl3, 400 MHz): δ 6.91 (s, 4H, imi-H), 4.67 (q, J = 7 Hz, 8H, -CH2-), 1.63 (t, J = 7 Hz, 12H, -CH3). 13 C NMR (CDCl3, 100.6 MHz): δ 139.8 (MdC), 121.5, 46.1, 16.1. Anal. Calcd for C14H24Cl4N4Pd2: C, 27.88; H, 4.01; N, 9.29. Found: C, 27.68; H, 4.12; N, 9.08. Complex 15. Method A (transfer from Ag-carbene). A mixture of 9 (31.2 mg, 0.08 mmol) and [Pd(COD)Cl2] (23 mg, 0.08 mmol) in CH2Cl2 (3 mL) was stirred at room temperature in the dark for 24 h. The reaction mixture was filtered through Celite, and the filtrate was concentrated. The residue was washed with ether (2 mL  2) to give 15 as light yellow solids (25 mg, 73%). Method B. The procedure is similar to that for 5a (method B) (70% isolated yield). 1H NMR (400 MHz, CD3CN): δ 7.48 (s, 1H), 6.96 (m, 3H), 5.26 (d, 1H, J = 12.7 Hz), 4.95 (d, 1H, J = 12.7 Hz), 2.67 (s, 3H), 2.32 (s, 1H), 2.08 (s, 1H), 2.03 (s, 1H).

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Anal. Calcd for C14H19Cl2N2PdS: C, 39.69; H, 4.28; N, 6.61. Found: C, 39.49; H, 4.32; N, 6.61. Crystallography. Crystals suitable for X-ray determination were obtained for 13b and 15 by recrystallization at room temperature. Cell parameters were determined by a Siemens SMART CCD diffractometer. The structure was solved using the SHELXS-97 program18 and refined using the SHELXL-97 program19 by full-matrix least-squares on F2 values. Crystal data for 13b: C15H16ClF6N4PPd, Mw =539.14, triclinic, P1, a= 8.8533(2) A˚, b=10.3000(2) A˚, c=11.7433(3) A˚, R=69.643(2)°, β=84.810(2)°, γ=67.415(2)°, V=925.83(4) A˚3, Z=2, Dcalcd = 1.934 Mg/m3, F(000) = 532, 0.20  0.15  0.10 mm3, 2θ = 3.18-27.50°, 21 207 reflns collected, 4245 independent reflns [R(int) = 0.0233], full-matrix least-squares on F2, R1 = 0.0236, wR2 = 0.0833 [I > 2σ(I)], goodness of fit on F2 0.775. Crystal (18) Sheldrick, G. M.SHELXS-97. Acta Crystallogr., Sect. A: Found. Crystallogr. 1990, 46, 467 (19) Sheldrick, G. M. SHELXL-97; University of G€ottingen: G€ ottingen, Germany, 1997.

Liu et al. data for 15: C14H18Cl2N2PdS, Mw =423.66, monoclinic, P21/n, a = 8.0299(2) A˚, b = 17.8932(3) A˚, c = 12.3472(3) A˚, β = 108.238(2)°, V = 1684.93(7) A˚3, Z = 4, Dcalcd = 1.670 Mg/m3, F(000)=848, 0.25  0.15  0.10 mm3, 2θ=2.86-27.50°, 20 043 reflns collected, 3855 independent reflns [R(int) = 0.0345], fullmatrix least-squares on F2, R1 = 0.0233, wR2 = 0.0583 [I > 2σ(I)], goodness of fit on F2 1.039. Other crystallographic data are deposited as Supporting Information.

Acknowledgment. We thank the National Science Council (NSC97-2113-M-002-013-MY3) and the NSCNWO Project for their financial support. Supporting Information Available: Tables providing atomic positional parameters, bond distances and angles, anisotropic thermal parameters, and calculated hydrogen atom positions for complexes 13b and 15. A CIF file is also available. This material is available free of charge via the Internet at http:// pubs.acs.org.