Versatile, Selective, and Switchable Coordination Modes of Pincer

Nov 13, 2009 - Elaine M. Schuster, Mark Botoshansky and Mark Gandelman*. Schulich ... Theodore R. Helgert , T. Keith Hollis , Allen G. Oliver , Henry ...
0 downloads 0 Views 2MB Size
Download PDF
Organometallics 2009, 28, 7001–7005 DOI: 10.1021/om900827g

7001

Versatile, Selective, and Switchable Coordination Modes of Pincer Click Ligands Elaine M. Schuster, Mark Botoshansky, and Mark Gandelman* Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Technion City, Haifa 32000, Israel Received September 24, 2009

Ligands possessing multiple complexation modes are an interesting class of compounds. Here we report that our recently established pincer click ligands (PCLs), prepared by copper-catalyzed cycloaddition of azides to alkynes, exhibit unique versatility in coordination ability. Nitrogens of the triazole-based backbone can actively participate in metal ligation rather than being a spectator backbone. Under selection of the reaction conditions these ligands can selectively acquire either bi- or tridentate coordination upon reaction with a metal precursor. Both palladium and platinum complexes with different coordination modes were prepared and fully characterized including X-ray analysis. Moreover, the “rollover switch” of kinetically preferred bidentate complexes to the thermodynamically controlled tridentate species is demonstrated.

Introduction Chelating ligands with multiple binding modes are an interesting and versatile class of compounds that are of great potential for catalytic applications, materials science, and supramolecular chemistry.1,2 Such ligands with ambidentate character can often be coordinated to a metal center in a selective manner by modification of metal choice or its oxidation state, ligand set, or reaction conditions. Particularly attractive is the ability to selectively interconvert complexes of different binding modes of the same ligand, which is of great interest for the design of molecular switches, logic gates, sensors, etc.3 Tridentate pincer-type ligands have found a variety of valuable applications and, as such, represent a valuable target for synthesis and studies.4 The pincer structure affords its metal complex a high stability, which is widely attributed to the protective, sheltered environment in which the metal is situated. The realization that pincer ligands offer both a unique, highly protective environment for the coordinated metal center and facility to fine-tune the steric and electronic properties of

the metal center has generated extensive research into the use of these complexes for catalysis, mechanistic studies, isolation of elusive species, and materials science.5 We recently reported a novel combinatorial approach toward the synthesis of triazole-based tridentate ligands.6 This methodology is based upon the Cu(I)-catalyzed [2þ3] cycloaddition of azides and alkynes, decorated with donor arms, to form triazole as the main tool for ligand assembly (Scheme 1).7 Utilization of the triazole pattern for adaptable ligand construction has received increasing interest in recent years.8 In our methodology, this type of ligand construction provided a triazole-based pincer frame with two donor arms in 1,4-positions; the relatively acidic triazole hydrogen allows for metal insertion to form tridentate complexes. The initial library of aryl-substituted donors (P, N, and S) was recently expanded to include bulky, electron-donating alkylsubstituted phosphines, which further expanded the range of ligands accessible by this route.9 We discovered significant differences between the triazole-based pincer complexes as

*To whom correspondence should be addressed. E-mail: chmark@tx. technion.ac.il. (1) Burmeister, J. L. Coord. Chem. Rev. 1990, 105, 77. (2) (a) Marzilli, L. G.; Summers, M. F.; Zangrando, E.; BrescianiPahor, N.; Randaccio, L. J. Am. Chem. Soc. 1986, 108, 4830. (b) Chi, K.-W.; Addicott, C.; Arif, A. M.; Stang, P. J. J. Am. Chem. Soc. 2004, 126, 16569. (c) Teo, P.; Koh, L. L.; Hor, T. S. A. Inorg. Chem. 2003, 42, 7290. (d) Chi, K.-W.; Addicott, C.; Moon, M.-E.; Lee, H. J.; Yoon, S. C.; Stang, P. J. J. Org. Chem. 2006, 71, 6662. (e) Zelikovich, L.; Libman, J.; Shanzer, A. Nature 1995, 374, 790. (f) Kalny, D.; Elhabiri, M.; Moav, M.; Vaskevich, A.; Rubinstein, I.; Shanzer, A.; Albrecht-Gary, A.-M. Chem. Commun. 2002, 1426. (3) Balzani, V., Credi, A.; Venturi, M. Molecular Devices and Machines, 2nd ed.; Wiley-VCH: New York, 2008. (4) van Koten, G.; Albrecht, M. Angew. Chem., Int. Ed. 2001, 40, 3750. (b) van der Boom, M. E.; Milstein, D. Chem. Rev. 2003, 103, 1759. (5) (a) Singleton, J. T. Tetrahedron 2003, 59, 1837. (b) MoralesMorales, D. Rev. Quim. Mex. 2004, 48, 338. (c) Vigalok, A.; Milstein, D. Acc. Chem. Res. 2001, 34, 798.

(6) Schuster, E. M.; Botoshansky, M.; Gandelman, M. Angew. Chem., Int. Ed. 2008, 47, 4555. (7) (a) Meldal, A.; Tornoee, C. W. Chem. Rev. 2008, 108, 2952. (b) Rostovtsev, V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B. Angew. Chem., Int. Ed. 2002, 41, 2596. (c) Tornoee, C. W.; Christensen, C.; Meldal, M. J. Org. Chem. 2002, 67, 3057. (8) (a) Liu, D.; Gao, W.; Dai, Q.; Zhang, X. Org. Lett. 2005, 7, 4907. (b) Dai, Q.; Gao, W.; Liu, D.; Kapes, L. M.; Zhang, X. J. Org. Chem. 2006, 71, 3928. (c) Detz, R. D.; Heras, S.; de Gelder, R.; van Leeuwen, P. W. N. M.; Hiemstra, H.; Reek, J. N. H.; van Maarseveen, J. H. Org. Lett. 2006, 8, 3227. (d) Dolhem, F.; Johansson, M. J.; Antonsson, T.; Kann, N. J. Comb. Chem. 2007, 9, 477. (e) Detz, R. D.; Delville, M. M. E.; Hiemstra, H.; van Maarseveen, J. H. Angew. Chem., Int. Ed. 2008, 47, 3777. (f) van Assema, S. G. A.; Tazelaar, C. G. J.; Bas de Jong, G.; van Maarseveen, J. H.; Schakel, M.; Lutz, M.; Spek, A. L.; Slootweg, J. C.; Lammertsma, K. Organometallics 2008, 27, 3210. (g) Rheingold, A. L.; Liable-Sands, L. M.; Trofimenko, S. Angew. Chem., Int. Ed. 2000, 39, 3321. (h) Mindt, T. L.; Schweinsberg, C.; Brans, L.; Hagenbach, A.; Abram, U.; Tourwe, D.; Garcia-Garayoa, E.; Schibli, R. ChemMedChem 2009, 4, 529. (i) Janssen, M.; M€uller, C.; Vogt, D. Adv. Synth. Catal. 2009, 351, 313. (9) Schuster, E. M.; Nisnevich, G.; Botoshansky, M.; Gandelman, M. Organometallics 2009, 28, 5025.

r 2009 American Chemical Society

Published on Web 11/13/2009

pubs.acs.org/Organometallics

7002

Organometallics, Vol. 28, No. 24, 2009

Schuster et al.

Scheme 1. Assembly of PCLs and Formation of Pd-Based Complexes

Scheme 2. Formation of Pt Complex 3 Figure 1. X-ray structure of a molecule of 3. Hydrogen atoms are omitted for clarity.

compared with their phenyl-based counterparts, both in catalytic activity and in their coordination chemistry. This new class of ligands demonstrates a modifiable coordination mode: under certain conditions, the nitrogens of the triazolebased backbone do not behave as innocent bystanders. In this paper, we report the selective formation of either bidentate or tridentate complexes upon reaction of these ligands with both palladium and platinum precursors. It should be noted that this is the first example of Pt complexes with pincer click ligands. A selective “switch” from bidentate-totridentate mode of coordination via C-H bond cleavage is demonstrated. Thus, our triazole-based system represents an intriguing example of “rollover” cyclometalation, which mainly has been demonstrated for bipyridine-derived and related complexes in both solution and gas phase.10

Figure 2. Phenyl-based pincer 4. Table 1. Selected bond lengths [A˚] and angles [deg] of Molecule 3 Pt(1)-C(25) Pt(1)-P(2) P(1)-Pt(1)-P(2) C(25)-Pt(1)-P(1) P(2)-Pt(1)-Cl(1)

1.908(30) 2.348(13) 159.7(3) 82.2(9) 99.3(3)

Pt(1)-Cl(1) Pt(1)-P(1) C(25)-Pt(1)-Cl(1) C(25)-Pt(1)-P(2) P(1)-Pt(1)-Cl(1)

2.401(15) 2.261(11) 177.3(9) 79.0(9) 99.7(3)

Scheme 3. Formation of Bidentate Complexes 5a-da

Results and Discussion The tridentate pincer-type coordination ability of our ligands upon reaction with Pd precursors under heating and in the presence of base was previously demonstrated in our laboratories (Scheme 1).6,9 Our interest in Pt-based catalysis promoted exploration of these new ligands with platinum precursors. Gratifyingly, heating PCP ligand 2 with (COD)PtCl2 (COD = cyclooctadiene) in the presence of triethylamine resulted in selective formation of PCPplatinum chloride complex 3 (Scheme 2). This complex was fully characterized by multinuclear NMR. The 31P{1H} NMR spectrum of compound 3 exhibits two doublets at δ=38.13 and 28.58 ppm with JPP =445 Hz, a typical P-P trans coupling. The 195Pt-P satellites for both doublets with JPPt = 2813 and 3084 Hz, respectively, clearly indicate coordination of both phosphine arms to the platinum center. The structure of 3 was confirmed by X-ray analysis. Single (10) For representative examples in solution, see: (a) Nord, G.; Hazell, A. C.; Hazell, R. G.; Farver, O. Inorg. Chem. 1983, 22, 3429. (b) Spellane, P. J.; Watts, R. J.; Curtis, C. J. Inorg. Chem. 1983, 22, 4060. (c) Braterman, P. S.; Heat, G. H.; Mackenzie, A. J.; Noble, B. C.; Peacock, R. D.; Yellowlees, L. J. Inorg. Chem. 1984, 23, 3425. (d) Zucca, A.; Droppin, A.; Cinellu, M. A.; Stoccoro, S.; Minghetti, G.; Manassero, M. Organometallics 2002, 21, 783. (e) Minghetti, G.; Stoccoro, S.; Cinellu, M. A.; Soro, B.; Zucca, A. Organometallics 2003, 22, 4770. For mechanistic studies of rollover metalation in gas phase, see: Butschke, B.; Schlangen, M.; Schr€oder, D.; Schwarz, H. Chem.;Eur. J. 2008, 14, 11050.

a Conditions: 5, MCl2 = K2PdCl4 or (TMEDA)PdCl2; 6, MCl2 = (COD)PdCl2.

monoclinic crystals suitable for X-ray analysis were obtained by slow diffusion of ether into a DMF solution of 3. The platinum atom is located in the center of a distorted squareplanar structure with the chloride group occupying a position trans to the carbon atom of the triazole (Figure 1). The two phosphine groups are located in a mutual trans position with a P-Pd-P angle of 159.65. Interestingly, the analogous phenyl-substituted phosphine ligand arms in the phenylbased counterpart 411 (Figure 2) are twisted out of the plane with a torsional angle P2-C7-C2-C1 of 33°,12 as compared to the analogous angle P1-C27-C26-C25 in our triazolebased ligand of 10°. This lack of planarity in complex 4 is likely in order to release strain of metal-containing rings, imposed by the geometry of substitution in the six-membered (11) Bennett, M. A.; Jin, H.; Willis, A. C. J. Organomet. Chem. 1993, 451, 249. (12) For crystallographic details of 4, see: Fischer, S.; Wendt, O. F. Acta Crystallogr. Sect. E 2004, E60, m69.

Article

Organometallics, Vol. 28, No. 24, 2009

7003

Figure 3. X-ray structure of molecules 5b and 5c. Hydrogen atoms are omitted for clarity.

phenyl ring of the backbone, as compared with our fivemembered triazole-based backbone in complex 3 (compare corresponding angles C1-C2-C7 = 117.4° in 4 vs C25-C26-C27=125° in 3). Selected bond lengths and bond angles of 3 are given in Table 1. During investigation of the mechanism of PCL-metal complex formation, we discovered that the triazole backbone of these ligands is not an innocent bystander and can coordinate to the metal center via the triazole nitrogens (Scheme 3). Moreover, PCL reactivity can be tuned, by modification of reaction conditions, to participate selectively in either bidentate or tridentate coordination modes to the metal. Triazole derivatives have recently found widespread use as transition metal ligands by coordination through nitrogen atoms.8,13 Thus, addition of either (CH3CN)2PdCl2, K2PdCl4, or (tmeda)PdCl2 (tmeda = tetramethylethylenediamine) to ligands 1a-d in DMF resulted in selective formation of the P-N bidentatate complexes 5 (Scheme 3). This product was obtained even in the presence of base when the reaction was performed at room temperature, and no coordination to the sulfide arm was observed. This indicates that the formation of bidentate complexes (rather than their tridentate counterparts) giving a relatively stable five-membered coordination ring is kinetically favored. In the case of P-S ligands 1, these products could be isolated in a quantitative yield. Single crystals of compounds 5b and 5c suitable for X-ray analysis were obtained by addition of THF to the reaction mixture. In both complexes, the palladium atom is located in the center of distorted square-planar structures, with the P and N coordinating atoms occupying mutual cis positions (Figure 3). The two chloride groups are mutually cis to one another; the chloride that is trans to the triazole nitrogen exhibits a shorter Pt-Cl bond length than that which is trans to the phosphorus atom due to the weaker trans influence of nitrogen. Selected bond lengths and bond angles for both 5b and 5c are given in Table 2. This bidentate coordination was observed also using Pt(II) precursors. Thus, reaction of 1b with (COD)PtCl2 at room (13) For selected examples in addition to those in ref 8, see: (a) Suijkerbuijk, B. M. J. M.; Aerts, B. N. H.; Dijkstra, H. P.; Lutz, M.; Spek, A. L.; van Koten, G.; Klein Gebbink, R. J. M. Dalton Trans. 2007, 1273. (b) Huffman, J. C.; Flood, A. H.; Li, Y. Chem. Commun. 2007, 2692. (c) Struthers, H.; Spingler, B.; Mindt, T. L.; Schibli, R. Chem.;Eur. J. 2008, 14, 6173. (d) Schweinfurth, D.; Hardcastle, K. I.; Bunz, U. H. F. Chem. Commun. 2008, 2203.

Table 2. Selected Bond Lengths [A˚] and Angles [deg] for Complexes 5b and 5c complex 5b N(1)-Pd(1) P(1)-Pd(1) Pd(1)-Cl(2) Pd(1)-Cl(1) N(1)-Pd(1)-P(1) Cl(1)-Pd(1)-Cl(2)

complex 5c 2.015(19) 2.220(21) 2.300(24) 2.358(22) 84.2(2) 94.4(1)

N(1A)-Pd(1A) Pd(1A)-P(1A) Pd(1A)-Cl(2A) Pd(1A)-Cl(1A) N(1A)-Pd(1A)-P(1A) Cl(2A)-Pd(1A)-Cl(1A)

2.034(19) 2.213(5) 2.358(9) 2.298(23) 83.1(2) 92.6(1)

Figure 4. X-ray structure of a molecule of 6b. Hydrogen atoms are omitted for clarity. Selected bond lengths [A˚] and angles [deg]: N1-Pt1 2.016(37), P1-Pt1 2.216(34), Pt1-Cl1 2.301(43), Pt1-Cl2 2.373(40), N1-Pt1-P1 81.98(20), Cl2-Pt1-Cl1 91.69(8).

temperature exclusively affords bidentate complex 6b in quantitative yield. The X-ray structure of 6b is similar to that of corresponding palladium analogues 5 and is represented in Figure 4. These bidentate kinetic products could be selectively “switched” to the thermodynamically favored tridentate complexes. For example, when complex 5a or 5b, obtained at room temperature in the presence of triethyl amine, is heated at 70 °C, the smooth conversion of bidentate species 5 to pincer-type complex 7 takes place. Apparently, at elevated temperatures, an efficient on/off coordination of palladium to the nitrogen donor of the triazole takes place followed by

7004

Organometallics, Vol. 28, No. 24, 2009

Scheme 4. Bidentate-to-Tridentate “Switch” and Pincer Complex Formation via Lithiation

Schuster et al.

or tridentate coordination mode. Namely, triazole nitrogens could participate in complexation rather than being a spectator backbone of the ligand. Moreover, we can selectively prepare bidentate or tridentate complexes by selection of reaction conditions. The kinetically controlled bidentate complexes can be “switched” via rollover C-H cleavage to the thermodynamically preferred tridentate ones quite simply. We also reported both tridentate and bidentate platinum complexes. The bidentate complexes of ligand 1 formed with P-M-N coordination leave the sulfide arm free; which could conceivably be exploited to form either hetero- or homobimetallic complexes upon addition of a second metal center. Studies on applications of these ligands in the formation of bimetallic complexes as well as application of the prepared new Pd- and Pt-based compounds to catalytic transformations are currently underway in our laboratories.

Experimental Section

Scheme 5. Reaction of Ligand 8 with Pd Precursor

phosphine arm rotation (around the C1-C2 bond in 5b, for instance), C-H bond cleavage, and sulfide-arm coordination to afford compound 7. The overall switch represents a “rollover” cyclometalation process, which has found appreciable interest with regard to metal-assisted C-H bond activation.10 Alternatively, we found that tridentate complex 7 could be prepared by independent direct synthesis. Thus, ligand 1 is selectively lithiated at the triazole carbon by butyllithium at -78 °C (Scheme 4). The abstracted proton is relatively acidic, and the resulting compound is presumably stabilized by chelation of Li to the neighboring sulfide arm. These species formed in situ are trapped with a Pd(II) precursor, leading, via transmetalation, to selective formation of pincer complexes 7.14 Such selective behavior is not observed with PCP ligands bearing two phosphine arms. Complicated mixtures of intermediates are obtained upon addition of ligand 2 to Pd(II) or Pt(II) precursors at room temperature. These mixtures are fully converted to the tridentate pincer-type complex as a single product upon heating with triethyl amine. Additionally, reaction of PCN ligand 8 with a Pd(II) precursor at room temperature without the presence of an external base gave a mixture of both bidentate and tridentate complexes, presumably using the pyridine moiety as an internal base. Again, this mixture is smoothly converted to the tridentate complex when heated in the presence of excess triethyl amine. In conclusion, we have demonstrated that our pincer click ligands possess ambidentate character in either a bidentate (14) A similar lithiation-transmetalation approach was used for preparation of a ruthenium NCN-based complex (NCN = [C6H3(CH2NMe2)2-2,6]-): Sutter, J.-P.; James, S. L.; Steenwinkel, P.; Karlen, T.; Grove, D. M.; Veldman, N.; Smeets, W. J. J.; Spek, A. L.; van Koten, G. Organometallics 1996, 15, 941.

General Methods. Oxygen- and moisture-sensitive reactions were carried out under an atmosphere of purified nitrogen in a glovebox equipped with an inert gas purifier or by using standard Schlenk techniques. Dry Et3N was obtained by distillation from CaH2. Solvents were purified by passing through a column of activated alumina under inert atmosphere. All commercially available reagents were used as received, unless otherwise indicated. NMR spectra were recorded at 300 MHz/75 MHz (1H/13C NMR) in CDCl3 unless otherwise stated on a Bruker AVANCE 300 MHz spectrometer at 23 °C. Chemical shifts (δ) are reported in parts per million, and the residual solvent peak was used as an internal standard (CDCl3: δ 7.261/ 77.0, 1H/13C NMR). 31P NMR signals are in ppm and referenced to external 85% H3PO4. Data are reported as follows: chemical shift, multiplicity (s=singlet, d=doublet, t=triplet, q= quartet, p=pentet, m=multiplet, b=broad), integration, and coupling constant(s) (Hz). Compounds 7a,b and 9 are compared to the previously reported spectroscopic data for these species.6 Preparation of Complex 3. To a solution of 2 (21 mg, 0.045 mmol) in DMF (2 mL) was added a solution of (COD)PtCl2 (17 mg, 0.045 mmol) in DMF (2 mL) and triethyl amine (63 μL, 0.45 mmol). The reaction mixture was placed in a sealed vessel and heated to 70 °C for 18 h. The solvent was removed under reduced pressure, and the crude residue was washed with ether (3  3 mL) and extracted with toluene/THF. The combined extracts were evaporated to give 3 (32 mg, 100%) as a grayish solid. 31P{1H} NMR (121 MHz, CD2Cl2) δ: 38.13 (d, JPP=445 Hz, JPPt=2813 Hz), 28.58 (d, JPP=445 Hz, JPPt=3084 Hz). 1H NMR (500 MHz, CD2Cl2) δ: 7.96-7.92 (m, 8H, Ar), 7.58-7.51 (m, 12H, Ar), 5.27 (d, JHP=7.0 Hz, 2H, P-CH2-N), 3.83 (d, JHP= 10.5 Hz, 2H, P-CH2-C). 13C{1H} NMR (125 MHz, CD2Cl2) δ: 152.0 (d, Cipso) 135.0 (q, JCP=12.1 Hz), 133.8, 132.9, 131.2 (d, JCP=11.0 Hz), 130.9 (d, JCP=10.6 Hz), 54.5 (d, JCP=45.2 Hz, P-CH2-N), 32.1 (d, JCP = 41.2 Hz, P-CH2-C). MS-ESI: (M þ H)þ 695.0812 C28H25N3P2ClPt. General Procedure for the Preparation of Complexes 5. 5a: To a solution of 1a (15 mg, 0.032 mmol) in THF (1 mL) was added a solution of (CH3CN)2PdCl2 (8.4 mg, 0.032 mmol) in THF (1 mL). A pale yellow color indicated the formation of the bidentate complex. The solvent was removed under reduced pressure, and the crude residue was washed with ether (3  3 mL) and toluene (3  3 mL) and extracted with THF and DMF. The combined extracts were evaporated to give 18 mg (100%) as a white solid. 31P{1H} NMR (DMF-d7) δ: 48.3. 1H NMR (DMF-d7) δ: 8.42 (s, 1H, triazole-H), 8.0-7.95 (m, 4H, aromatic), 7.67-7.59 (m, 5H, aromatic), 7.43-7.29 (m, 4H, aromatic), 6.14 (s, 2H, CH2-S), 4.12 (d, JHP =13 Hz, CH2-P). 13 C{1H} NMR (DMF-d7) δ: 148.3 (d, JCP = 9 Hz), 133.6 (d, JCP=15 Hz), 132.4 (d, JCP=3.3 Hz), 131.9, 131.8, 129.5, 129.2

Article (d, JCP =12 Hz), 128.5, 127.9 (d, JCP =57 Hz), 123.9 (d, JCP = 14 Hz), 55.0 (s, CH2-S), 27.0 (d, JCP =30 Hz). 5b: 31P{1H} NMR (DMSO-d6) δ: 76.7. 1H NMR (DMSO-d6) δ: 8.25 (s, 1H, triazole-H), 7.32-7.43 (m, 5H, Ar), 6.02 (s, 2H, CH2-S), 3.27 (d, JHP = 11.4 Hz, CH2-P), 2.15-2.33 (m, 2H), 1.54-1.76 (m, 10H), 1.31-1.50 (m, 10H). 13C{1H} NMR (DMSO-d6) δ: 149.5 (d, JCP = 6.5 Hz, CAr), 131.8, 131.5, 129.7, 128.7, 123.1 (d, JCP = 11.4 Hz, CArH), 54.6 (CH2-S), 36.1, 33.3 (d, JCP =28.7 Hz, CH2-P), 31.1, 26.3 (d, JCP =14.4 Hz), 26.1 (d, JCP=10.3 Hz), 25.6. HRMS-ESI: (M þ H)þ 576.04 C22H31N3PSCl2Pd calcd mass 576.0388. Anal. Calcd: C, 45.65; H, 5.57. Found: C, 45.89; H, 5.61. 5c: 31P{1H} NMR (DMF-d7) δ: 42.3. 1H NMR (500 MHz, DMF-d7) δ: 8.50 (s, 1H, triazole-H), 8.03-8.01 (m, 2H), 7.87-7.84 (m, 3H), 7.74 (d, 2H), 7.55 (d, 2H), 7.43-7.40 (m, 2H), 7.30-7.27 (m, 2H), 6.34 (s, 2H, CH2-S), 3.91 (s, 6H, O-CH3), 3.80 (s, 2H, CH2-P). 13C{1H} NMR (125 MHz, DMF-d7) δ: 162.3, 138.4 (d, JCP =12 Hz), 136.6, 134.2, 133.3, 131.6 (d, JCP =10 Hz), 130.3, 122.7 (d, JCP =13 Hz), 114.1 (d, JCP=5.0 Hz), 69.3 (s, CH2-S), 57.7 (s, OCH3), 25.8 (d, JCP=108 Hz). Anal. Calcd: C, 45.99; H, 3.86. Found: C, 44.99; H, 3.55. 5d: 31P{1H} NMR (DMF-d7) δ: 83.4. 1H NMR (DMF-d7) δ: 8.45 (s, 1H, triazole-H), 7.37-7.52 (m, 5H, Ph), 6.17 (s, 2H, CH2-S), 3.37 (d, JHP=11.4 Hz, CH2-P), 2.53-2.65 (m, 2H, CH), 1.44 (dd, JHH = 7.12 Hz, JHP = 18.3 Hz, 6H, CH3), 1.17 (dd, JHH=6.84 Hz, JHP=16.7 Hz, 6H, CH3). 13C{1H} NMR (DMFd7) δ: 149.4 (d, JCP=7.05 Hz, CAr), 131.9, 129.4, 128.5, 123.3 (d, JCP = 12.5 Hz, CArH), 54.9 (CH2-S), 24.8 (d, JCP = 28.3, CHCH3), 17.8 (d, JCP=28.3 Hz, CH2-P), 17.4, 16.7. Anal. Calcd: C, 38.53; H, 4.85. Found: C, 39.84; H, 5.72. General Procedure for the Preparation of Compounds 6. 6a: To a suspension of (COD)PtCl2 in DMF (1 mL) was added a

Organometallics, Vol. 28, No. 24, 2009

7005

solution of 1a (10 mg, 0.026 mmol) in DMF (1 mL). A bright yellow color indicated the formation of the bidentate complex. The solvent was removed under reduced pressure, and the crude residue was washed with ether (3  3 mL) and toluene (3  3 mL) and extracted with THF and CH2Cl2. The combined extracts were evaporated to give 6 as a white solid. 31P{1H} NMR (DMF-d7) δ: 22.2 (s, JPPt = 3646 Hz). 1H NMR (DMF-d7) δ: 8.63 (s, 1H, triazole-H), 8.17-8.13 (m, 5H), 7.78-7.52 (m, 10H), 6.33 (s, 2H, CH2-S), 4.13 (d, JHP = 11 Hz, CH2-P). 13 C{1H} NMR (DMF-d7) δ: 152.4, 135.3 (d, JCP = 156 Hz), 134.0 (d, JCP=3 Hz), 133.9, 133.7, 131.5, 131.0 (d, JCP=12 Hz), 130.4, 129.7 (d, JCP = 64 Hz), 126.0 (d, JCP = 13 Hz), 57.2 (s, C-CH2-S), 28.9 (d, JCP = 37.9 Hz, C-CH2-P). Anal. Calcd: C, 40.31; H, 3.08. Found: C, 39.18; H, 4.56. 6b: 31P{1H} NMR (81 MHz, DMF-d7) δ: 46.11 (s, JPPt=3482 Hz). 1H NMR (200 MHz, DMF-d7) δ: 8.55 (s, 1H, triazole-H), 7.68-7.56 (m, 5H, Ar), 6.30 (s, CH2-S), 3.36 (d, JHP =10 Hz, CH2-P), 2.52-2.33 (m, 4H), 1.94-1.45 (m, 18H). 13C{1H} NMR (200 MHz, DMF-d7) δ: 151.6, 132.0, 131.9, 129.7, 123.2, 55.2, 27.0, 26.9, 26.3, 26.0, 25.9, 25.7. MS-ESI: (M þ H)þ 665.1035 C22H31N3PSCl2Pt calcd mass 665.1001. Anal. Calcd: C, 39.58; H, 4.83. Found: C, 40.16; H, 5.13.

Acknowledgment. Financial support from Israel Science Foundation (Grant No. 1292/07) and The FIRST Program of the Israel Science Foundation (Grant No. 1514/07) is acknowledged. E.M.S. is a recipient of the Schulich Graduate Fellowship. Supporting Information Available: Crystallographic data are available free of charge via the Internet at http://pubs.acs.org.