Facile Synthesis of (Phosphine)- and (N-heterocyclic Carbene)Gold(I

Jan 6, 2009 - Department of Chemistry, Case Western Reserve University, Cleveland, Ohio 44106, Creative Chemistry, LLC, Cleveland Ohio, 44106, and Dep...
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Organometallics 2009, 28, 795–801

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Facile Synthesis of (Phosphine)- and (N-heterocyclic Carbene)Gold(I) and Silver(I) Azide Complexes David V. Partyka,‡ Thomas J. Robilotto,† James B. Updegraff III,† Matthias Zeller,§ Allen D. Hunter,§ and Thomas G. Gray*,† Department of Chemistry, Case Western ReserVe UniVersity, CleVeland, Ohio 44106, CreatiVe Chemistry, LLC, CleVeland Ohio, 44106, and Department of Chemistry, Youngstown State UniVersity, Youngstown, Ohio 44555 ReceiVed June 9, 2008

Two general protocols for the synthesis of N-heterocyclic carbene- or phosphine-ligated gold(I) and silver(I) azide complexes have been developed. The first utilizes thallium(I) acetylacetonate, followed by treatment with trimethylsilyl azide, while the second protocol exploits the relative weakness of d10 metal-oxygen bonds in the reaction of metal(I) acetate with trimethylsilyl azide. Both methods give products in high yield, but only the metal(I) acetate/trimethylsilyl azide method proceeds to completion for an N-heterocyclic carbene-ligated silver(I) acetate. The successful application of this method to silver(I) suggests that this nonaqueous protocol may have general applicability to late transition element or main group acetate precursors. Eight new complexes are reported, of which six are metal azides; four have been crystallographically characterized. Products have been characterized by vibrational and multinuclear NMR spectroscopies and combustion analysis. The synthesis methods described here provide useful alternatives for the syntheses of azide complexes in cases where protic solvents cannot be used. Introduction The copper-catalyzed Huisgen cycloaddition of azides and terminal alkynes has gained much attention for its unarguable utility. This reaction is one prototype of what Kohl, Finn, and Sharpless1 term click chemistry. It is modular, has wide scope, and is high-yielding and simple to undertake, among other criteria. Copper(I) salts catalyze the reaction for terminal acetylenes,2 and copper(I) alkynyls, possibly polarized by π-coordination of a second Cu+ ion,3 are held to be critical intermediates in the reaction. Cycloaddition reactions of metal azide complexes, or of metal alkynyls with organic azides, have attracted less study.4,5 Numerous metal azide complexes are known, and the azide ligand can bind terminally or in any of several bridging geometries.6 Azidogold complexes are especially varied:7 the species [Au(N3)2]-, [Au(N3)4]-, R3PAuN3, and (R3P)3AuN3 are readily preparable,8-11 although salts of the homoleptic com* Corresponding author. E-mail: [email protected]. † Case Western Reserve University. ‡ Creative Chemistry, LLC. § Youngstown State University. (1) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem., Int. Ed. 2001, 40, 2004–2021. (2) Tornøe, C. W.; Christensen, C.; Meldal, M. J. Org. Chem. 2002, 67, 3057–3064. (3) Ahlquist, M.; Fokin, V. V. Organometallics 2007, 26, 4389–4391. (4) Beck, W.; Burger, K.; Fehlhammer, W. P. Chem. Ber. 1971, 104, 1816–1825. (5) Aureggi, V.; Sedelmeier, G. Angew. Chem., Int. Ed. 2007, 46, 8440– 8444. (6) Dori, Z.; Ziolo, R. F. Chem. ReV. 1973, 73, 247–254. (7) Stra¨hle, J. In Gold: Progress in Chemistry, Biochemistry and Technology; Schmidbaur, H., Ed.; John Wiley & Sons: Chichester, U.K., 1999; pp 311-348. (8) Beck, W.; Feldl, K.; Schuierer, E. Angew. Chem., Int. Ed. Engl. 1965, 249. (9) Beck, W.; Fehlhammer, W. P.; Po¨llmann, E.; Schuierer, E.; Feldl, K. Chem. Ber. 1967, 100, 2335–2361.

plexes are explosive.12 (Phosphine)gold(I) azides undergo (1,3)dipolar cycloaddition reactions with nitriles, isonitriles, and carbon disulfide to yield tetrazolato and thiotetrazolato complexes, respectively.13-15 We have shown that (triphenylphosphine)gold(I) azide reacts with terminal alkynes to yield the C-bound tautomer of the corresponding gold(I) triazolate.16 The same complexes can be accessed from reaction of (phosphine)gold(I) alkynyl complexes with trimethylsilyl azide in methanol. Under these reaction conditions, the N-Si bond is hydrolyzed, and the final complex is protonated rather than silylated. Such cycloaddition reactions hold promise as one means of metalating terminal alkynes. With the emergence of click chemistry, these are now available in greater profusion and variety than ever before. Accordingly, we have sought to develop new d10 metal azide complexes for reaction with alkynes and other dipolarophiles. We describe two reaction protocols that realize (phosphine)- or (N-heterocyclic carbene)MI azide complexes (M ) Ag, Au) in high yields. Syntheses and spectroscopic characterization are discussed for eight new compounds, six of which are azide complexes. The new compounds are expected to be useful synthons for reaction chemistry that proceeds from azide precursors. (10) Beck, W.; Fehlhammer, W. P. Angew. Chem., Int. Ed. Engl. 1967, 6, 169–170. (11) Wehlan, M.; Thiel, R.; Fuchs, J.; Beck, W.; Fehlhammer, W. P. J. Organomet. Chem. 2000, 613, 159–169. (12) Klapo¨tke, T. M.; Krumm, B.; Galvez-Ruiz, J.-C.; No¨th, H. Inorg. Chem. 2005, 44, 9625–9627. (13) Ziolo, R. F.; Thich, T. A.; Dori, Z. Inorg. Chem. 1972, 11, 626– 631. (14) Beck, W.; Burger, K.; Fehlhammer, W. P. Chem. Ber. 1971, 104, 1816–1825. (15) Fehlhammer, W. P.; Dahl, L. J. Am. Chem. Soc. 1972, 94, 3370– 3377. (16) Partyka, D. V.; Updegraff, J. B., III; Zeller, M.; Hunter, A. D.; Gray, T. G. Organometallics 2007, 26, 183–186.

10.1021/om800536f CCC: $40.75  2009 American Chemical Society Publication on Web 01/06/2009

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Experimental Abbreviations: SIPr: 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazolin-2-ylidene; XPhos: 2′,4′,6′-triisopropyl-2-biphenyl)dicyclohexylphosphine. (SIPr)AgCl17 and (SIPr)AuCl18 were synthesized according to literature methods. The phosphine-ligated gold(I) chlorides used to synthesize 1-3 were prepared according to the literature procedure.19 All solvents and reagents were used as received. Microanalyses (C, H, and N) were performed by Quantitative Technologies, Inc. NMR spectra (1H, 13C{1H}, and 31P{1H}) were recorded on a Varian AS-400 spectrometer operating at 399.7, 161.8, and 100.5 MHz, respectively. Caution! Metal azide complexes are potentially explosiVe, and appropriate precautions should be taken. Although we haVe not experienced incidents with the present compounds, metal azides should be protected from heat and percussion. Reaction with acids may release toxic hydrazoic acid. ProtectiVe eyewear and protectiVe clothing are essential. [(PCy2(2-biphenyl))AuN3] (1). In 20 mL of toluene was suspended [(PCy2(o-biphenyl))AuCl] (151 mg, 0.26 mmol), and to this suspension was added thallium(I) acetylacetonate (97 mg, 0.32 mmol). The resultant suspension was stirred under nitrogen for 24 h. The suspension was then filtered though celite, yielding a clear filtrate. To the filtrate was added 70 µL (0.53 mmol) of trimethylsilyl azide and 4 mL of methanol, which, upon addition, formed a white precipitate. The suspension was then stirred for 16 h. The suspension was filtered through celite, resulting in a clear filtrate, which was evaporated to near dryness and then triturated with pentane. This resulted in the formation of a white crystalline precipitate. The white solid was collected, washed three times with 50-mL portions of pentane, and vacuum-dried. Yield: 133 mg (87%). 1H NMR (C6D6): δ 7.66 (td, 1H, 2′-biphenyl, J ) 1.6, 7.2 Hz), 7.52 (t, 2H, 2′-biphenyl, J ) 7.6 Hz), 7.13 (dd, 2H, 2′-biphenyl, J ) 1.2, 8.0 Hz,), 6.95-7.08 (m, 4H, 2′-biphenyl), 0.71-1.72 (m, 22H, C6H11) ppm. 13C NMR (C6D6): δ 132.36-132.57 (m), 130.38 (d, J ) 2.1 Hz), 129.41 (s), 127.39 (d, J ) 6.4 Hz), 127.14 (d, J ) 7.8 Hz), 36.23 (d, J ) 33.6 Hz), 30.73 (s), 29.12 (s), 26.58 (s), 26.44 (d, J ) 5.1 Hz), 26.26 (s), 25.34 (s) ppm. 31P NMR (C6D6): δ 37.8 (s) ppm. IR (KBr, cm-1): 2055 (νas: NdNdN, vs), 1286 (νs: NdNdN, w) cm-1. Anal. Calcd for C24H31AuN3P: C, 48.90; H, 5.30; N, 7.13. Found: C, 49.17; H, 5.53; N, 6.78. [(PCy2(2′-methyl-2-biphenyl))AuN3] (2). In 8 mL of toluene was suspended [(PCy2(2′-methylbiphenyl))AuCl] (87 mg, 0.15 mmol), and to this suspension was added thallium(I) acetylacetonate (63 mg, 0.21 mmol). The resultant suspension was stirred under nitrogen for 48 h. The suspension was then filtered though celite, yielding a clear filtrate. To the filtrate was added 40 µL (0.30 mmol) of trimethylsilyl azide and 2 mL of methanol, which, upon addition, formed a white precipitate. The suspension was then stirred for 16 h. The suspension was filtered through celite, resulting in a clear filtrate, which was rotary evaporated to near dryness and triturated with pentane. This resulted in the formation of a white crystalline precipitate. The white solid was collected, washed three times with 50-mL portions of pentane, and vacuum-dried. Yield: 73 mg (82%). 1 H NMR (C6D6): δ 7.62-7.71 (m, 2H, 2′-methylbiphenyl), 7.31 (td, 1H, 2′-methylbiphenyl, J ) 1.6, 7.2 Hz,), 6.94-7.22 (m, 4H, 2′-methylbiphenyl), 6.87-6.92 (m, 1H, 2′-methylbiphenyl), 1.98 (s, 3H, CH3), 0.68-1.82 (m, 22H, C6H11) ppm. 13C NMR (C6D6): 149.70 (d, J ) 13.0 Hz), 140.59 (d, J ) 5.2 Hz), 135.77 (s), 132.45 (d, J ) 7.6 Hz), 132.23 (d, J ) 3.8 Hz), 131.28 (s), 130.83 (d, J (17) de Fre´mont, 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, 6301–6309. (18) de Fre´mont, P; Scott, N.M.; Stevens, E. D.; Nolan, S. P Organometallics 2005, 24, 2411–2418. (19) Partyka, D. V.; Robilotto, T. J.; Zeller, M.; Hunter, A. D.; Gray, T. G. Organometallics 2008, 27, 28–32.

Partyka et al. ) 2.3 Hz), 129.92 (J ) 7.6 Hz), 128.53 (s), 127.11 (d, J ) 7.7 Hz), 125.89 (s), 125.38 (s), 124.88 (s), 37.67 (d, J ) 32.8 Hz), 34.84 (d, J ) 35.1 Hz), 30.74 (d, J ) 2.3 Hz), 30.54 (d, J ) 5.4 Hz), 29.56 (s), 28.71 (d, J ) 2.3 Hz), 26.90 (s), 26.75 (d, J ) 6.9 Hz), 26.38 (s), 26.24 (s), 25.69 (d, J ) 15.3 Hz), 20.99 (s) ppm. 31 P NMR (C6D6): δ 35.1 (s) ppm. IR (KBr, cm-1): 2058 (νas: NdNdN, -1 vs), 1288 (νs: NdNdN, w) cm . Anal. Calcd for C25H33AuN3P: C, 49.76; H, 5.51; N, 6.96. Found: C, 49.79; H, 5.33; N, 6.68. [(Xphos)AuN3](3).In8mLoftoluenewassuspended[(PCy2(2′,4′,6′triisopropylbiphenyl))AuCl] (51 mg, 0.072 mmol), and to this suspension was added thallium(I) acetylacetonate (36 mg, 0.12 mmol). The resultant suspension was stirred under nitrogen for 48 h. The suspension was then filtered though celite yielding a clear filtrate. To the filtrate was added 30 µL (0.23 mmol) of trimethylsilyl azide and 2 mL of methanol, which, upon addition, formed a white precipitate. The suspension was then stirred for 16 h. The suspension was filtered through celite, resulting in a clear filtrate, which was rotary evaporated to near dryness and triturated with pentane. This resulted in the formation of a white crystalline precipitate. The white solid was collected, washed three times with 50 mL portions of pentane, and vacuum-dried. Yield: 40 mg (77%). 1 H NMR (C6D6): δ 7.51 (s, 2H, 2′,4′,6′-triisopropylbiphenyl), 7.14-7.18 (m, 1H, 2′,4′,6′-triisopropylbiphenyl), 6.94-7.05 (m, 3H, 2′,4′,6′-triisopropylbiphenyl), 3.32 (sep, 1H, CH(CH3)2, J ) 6.8 Hz), 2.38 (sep, 2H, CH(CH3)2, J ) 6.8 Hz), 1.61 (d, 6H, CH(CH3)2, J ) 6.8 Hz), 1.50 (d, 6H, CH(CH3)2, J ) 6.8 Hz), 1.04 (d, 6H, CH(CH3)2, J ) 6.4 Hz), 0.79-1.80 (m, 22H, C6H11) ppm. 13C NMR (C6D6): δ 150.78 (s), 147.86 (d, J ) 14.5 Hz), 146.01 (s), 135.56 (d, J ) 6.1 Hz), 133.72, (d, J ) 7.6 Hz), 131.94 (d, J ) 3.1 Hz), 130.32 (d, J ) 2.3 Hz), 128.44 (s), 127.03 (d, J ) 6.8 Hz), 121.88 (s), 37.04 (s), 36.70 (s), 34.88 (s), 31.38 (s), 31.05 (d, J ) 2.3 Hz), 29.94 (s), 26.97 (d, J ) 13.7 Hz), 26.59 (d, J ) 30.0 Hz), 25.91 (s), 25.64 (s), 24.24 (s), 22.97 (s) ppm. 31P NMR (C6D6): δ 34.1 (s) ppm. IR (KBr, cm-1): 2056 (νas: NdNdN, vs), 1265 (νs: NdNdN, w) cm-1. Anal. Calcd for C33H49AuN3P: C, 55.38; H, 6.90; N, 5.87. Found: C, 55.60; H, 7.14; N, 5.61. [(SIPr)AuN3] (4) (Method A). In 5 mL of degassed CH2Cl2 was dissolved recrystallized (SIPr)AuCl (170 mg, 0.27 mmol), and to this was added 1.1 equiv of thallium(I) acetylacetonate (91 mg, 0.30 mmol). A white material immediately precipitated. The suspension was stirred for 1 h and filtered through Celite. To the filtrate via syringe was added trimethylsilyl azide (0.04 mL), and a milky white solid precipitated. This suspension was stirred for 2 min, and 0.05 mL methanol was added by syringe. This suspension was stirred for 6 h, filtered, the solvent removed by rotary evaporation, and the solid triturated with pentane, collected, and dried. Yield: 147 mg (86%). 1H NMR (CDCl3): δ 7.43 (t, 2H, J ) 7.6 Hz), 7.24 (d, 4H, J ) 7.6 Hz), 4.05 (s, 4H), 3.02 (sep, 4H, J ) 6.8 Hz), 1.39 (d, 12H, J ) 7.2 Hz), 1.33 (d, 12H, J ) 7.2 Hz) ppm. 13C NMR (C6D6): δ 194.66 (s, C carbene), 146.46 (s, CH aromatic), 133.87 (s, CH aromatic), 130.10 (s, CH aromatic), 124.65 (s, CH aromatic), 53.45 (s, CH imidazole), 28.96 (s, CH(CH3)2), 25.06 (s, CH(CH3)2), 24.10 (s, CH(CH3)2) ppm. IR (KBr, cm-1): 2048 (νas: NdNdN, vs), 1274 (νs: NdNdN, m) cm-1. Anal. Calcd. for C27H38AuN5: C, 51.51; H, 6.08; N, 11.12. Found: C, 52.06; H, 6.22; N, 10.59. [(SIPr)AuN3] (4) (Method B). SIPrAuCl (142 mg, 0.23 mmol) was suspended in benzene (10 mL), and to this suspension was added 1.05 equiv (40 mg, 0.24 mmol) of silver(I) acetate. The mixture was stirred for 2 h, and azidotrimethylsilane (3 equiv, 0.09 mL, 0.67 mmol) was added directly by syringe. The resultant mixture was stirred 12 h, and filtered, and the solvent was removed by rotary evaporation. This yielded only a small amount of product. The insoluble material (the material initially filtered out of the product suspension in benzene) was further extracted with dichloromethane and filtered. After the dichloromethane was removed by rotary evaporation, the residue was triturated with pentane. The

SilVer(I) and Gold(I) Azide Complexes solid (which consisted of the material from both the benzene and dichloromethane filtrates) was dried and collected. This material had a 13C NMR spectrum identical with the product of Method A (same solvent) and was analytically pure. Yield: 130 mg (91%). Anal. Calcd. for C27H38AuN5: C, 51.51; H, 6.08; N, 11.12. Found: C, 51.54; H, 6.09; N, 10.92. [(SIPr)Ag(OAc)] (5). In 10 mL of benzene was suspended (SIPr)AgCl (238 mg, 0.45 mmol, this material was partially soluble), and to this was added 1.05 equiv of silver acetate (78 mg). This suspension was stirred for 2 h and filtered to remove a brown insoluble material, the solvent was removed by rotary evaporation, and the solid was triturated with pentane, collected, and dried. Yield: 186 mg (74%). 1H NMR (CDCl3): δ 7.30 (t, 2H, para-CH aromatic, J ) 8.0 Hz), 7.14 (d, 4H, meta-CH aromatic, J ) 8.0 Hz), 3.96 (s, 4H, imidazole C2H4), 2.96 (sep, 4H, CH(CH3)2, J ) 6.8 Hz), 1.70 (s, 3H, CO2CH3), 1.26 (d, 12H, CH(CH3)2, J ) 7.6 Hz), 1.24 (d, 12H, CH(CH3)2, J ) 7.6 Hz) ppm. 13C NMR (CDCl3): δ 207.78 (dd, C carbene, J(107/109Ag/13C) ) 252, 292 Hz), 178.10 (s, CO2CH3), 146.56 (s, CH aromatic), 134.60 (s, CH aromatic), 129.85 (s, CH aromatic), 124.57 (s, CH aromatic), 53.75 (d, CH imidazole, 3 J(Ag-C) ) 9 Hz), 28.84 (s, CH(CH3)2), 25.30 (s, CH(CH3)2), 23.98 (s, CH(CH3)2), 22.53 (s, CO2CH3) ppm. Anal. Calcd. for C29H41AgN2O2: C, 62.47; H, 7.41; N, 5.02. Found: C, 62.38; H, 7.47; N, 5.08. [(SIPr)AgN3] (6). In 5 mL of toluene was suspended (SIPr)AgOAc (58 mg, 0.10 mmol; this material was partially soluble), and to this was added 4 equiv of trimethylsilyl azide (0.056 mL). After the addition, it appeared that more undissolved material was present. This suspension was stirred for 10 h, the solvent removed by rotary evaporation, and the solid triturated with pentane, collected, and dried. Yield: 53 mg (94%). 1H NMR (CDCl3): δ 7.43 (t, 2H, para-CH aromatic, J ) 7.6 Hz), 7.26 (d, 4H, meta-CH aromatic, J ) 7.6 Hz), 4.07 (s, 4H, imidazole C2H4), 3.03 (sep, 4H, CH(CH3)2, J ) 6.8 Hz), 1.34 (d, 12H, CH(CH3)2, J ) 6.4 Hz), 1.33 (d, 12H, CH(CH3)2, J ) 6.4 Hz) ppm. 13C NMR (CDCl3): δ 206.97 (dd, C carbene, J(107/109Ag/13C) ) 239, 239 Hz), 146.44 (s, CH aromatic), 134.29 (s, CH aromatic), 130.08 (s, CH aromatic), 124.70 (s, CH aromatic), 53.83 (d, CH imidazole, 3J(Ag-C) ) 9 Hz), 28.82 (s, CH(CH3)2), 25.26 (s, CH(CH3)2), 23.97 (s, CH(CH3)2) ppm. IR (KBr, cm-1): 2035 (νas: NdNdN, vs), 1271 (νs: NdNdN, m) cm-1. Anal. Calcd. for C27H38AgN5: C, 60.00; H, 7.09; N, 12.96. Found: C, 59.75; H, 7.13; N, 12.77. [(XPhos)Ag(OAc)] (7). In 3 mL of toluene was dissolved XPhos (200 mg, 0.42 mmol), and this solution was added dropwise to silver(I) acetate (68 mg, 0.41 mmol). The suspension quickly became a colorless solution and was stirred for 12 h, filtered to remove a brown insoluble material, and the solvent was removed by rotary evaporation. The residue was triturated with pentane to liberate a colorless solid, which was collected and dried. Yield: 206 mg (79%). 1H NMR (CDCl3): δ 7.63-7.67 (m, 1H, CH aromatic), 7.44-7.50 (m, 2H, CH aromatic), 7.24-7.28 (m, 1H, CH aromatic), 7.14 (s, 2H, CH aromatic), 2.96 (sep, 1H, paraCH(CH3)2, J ) 6.8 Hz), 2.26 (sep, 2H, ortho-CH(CH3)2, J ) 6.8 Hz), 1.93 (s, 3H, CO2CH3), 1.33 (d, 6H, CH(CH3)2, J ) 7.2 Hz), 1.31 (d, 6H, CH(CH3)2, J ) 6.8 Hz), 1.15-2.03 (m, 22H, C6H11), 0.94 (d, 6H, CH(CH3)2, J ) 6.8 Hz) ppm. 31P{1H} NMR (CDCl3): δ 15.3 (dd, 1J(107Ag-P) ) 653 Hz, 1J(109Ag-P) ) 754 Hz) ppm. Anal. Calcd. for C35H52AgO2P: C, 65.31; H, 8.14. Found: C, 65.14; H, 8.17. [(XPhos)AgN3] (8). In 5 mL of toluene was dissolved 7 (43 mg, 0.067 mmol), and to this solution 3 equiv (0.027 mL, 2.02 mmol) of trimethylsilyl azide was added. The resultant solution was stirred 12 h and filtered, and the solvent was removed by rotary evaporation. Pentane was added to the residue, and the mixture was placed in a freezer. After several hours, a crystalline solid had separated, which was collected and dried. Yield: 40 mg (96%). 1H NMR (CDCl3): δ 7.60-7.66 (m, 1H, CH aromatic), 7.46-7.53 (m,

Organometallics, Vol. 28, No. 3, 2009 797 2H, CH aromatic), 7.22-7.30 (m, 3H, CH aromatic), 3.12 (sep, 1H, CH(CH3)2, J ) 6.8 Hz), 2.23 (sep, 2H, CH(CH3)2, J ) 6.8 Hz), 1.40 (d, 6H, CH(CH3)2, J ) 7.2 Hz), 1.29 (d, 6H, CH(CH3)2, J ) 7.2 Hz), 1.10-2.04 (m, 22H, C6H11), 0.95 (d, 6H, CH(CH3)2, J ) 6.8 Hz) ppm. 13C NMR (CDCl3): δ 150.58 (s), 147.06 (d, J ) 18.6 Hz), 145.59 (s, CH aromatic), 133.80 (d, J ) 8.8 Hz), 132.65 (d, J ) 6.7 Hz), 132.08 (d, J ) 5.9 Hz), 130.29 (s), 127.83 (d, J ) 4.2 Hz), 127.47 (d, J ) 4.2 Hz), 121.74 (s), 35.05 (dd, J ) 4.6, 19 Hz), 34.18 (s), 31.48 (s), 31.41 (s), 30.89 (s), 29.94 (m), 27.04 (d, J ) 13.9), 26.66 (d, J ) 12.7 Hz), 25.72 (s), 25.59 (s), 23.73 (s), 22.83 (s) ppm. 31P{1H} NMR (CDCl3): δ 17.2 (dd, 1J(107Ag-P) ) 611 Hz, 1J(109Ag-P) ) 705 Hz) ppm. IR (KBr, cm-1): 2023 (νas: NdNdN, vs), 1264 (νs: NdNdN, m) cm-1. Anal. Calcd. for C33H49AgN3P: C, 63.25; H, 7.88; N, 6.71. Found: C, 63.35; H, 8.13; N, 6.59. X-Ray Structure Determination. Products were crystallized by diffusion of pentane into saturated benzene or THF solutions. Single crystal X-ray data were collected on a Bruker AXS SMART APEX CCD diffractometer using monochromatic Mo KR radiation with the omega scan technique. The unit cells were determined using SMART20 and SAINT+.21 Data collection for all crystals was conducted at 100 K (-173.5 °C; see Table 1). All structures were solved by direct methods and refined by full matrix least-squares against F2 with all reflections using SHELXTL.22 Refinement of extinction coefficients was found to be insignificant. All nonhydrogen atoms were refined anisotropically. All hydrogen atoms were placed in standard calculated positions, and all hydrogen atoms were refined with an isotropic displacement parameter 1.2 times that of the adjacent carbon.

Results and Discussion Syntheses. Two synthetic protocols have been developed that afford azide complexes of the (phosphine)- and (N-heterocyclic carbene)silver(I) and gold(I) fragments. These appear in Scheme 1. Table 2 sets out the new compounds so generated; a numbering system is indicated. In method A (eq 1), the metal chloride precursor reacts with thallium(I) acetylacetonate and then with trimethylsilyl azide in methanol to yield the azide complex in two steps. In method B (eq 2), the acetate complex reacts directly with trimethylsilyl azide in a single step. Method A has been previously applied to the synthesis of Ph3PAuN3,16 and we find that the procedure extends to other azidogold(I) complexes. This reaction may conceivably proceed through an intermediate gold(I) acetylacetonate complex, which then reacts with trimethylsilyl azide or its hydrolysis product, hydrazoic acid. Despite repeated efforts, we have not obtained a satisfactory synthesis of silver complex 6 from method A. Although method A did produce 6, the reaction did not proceed to completion, and always yielded mixtures of 6 with (SIPr)AgCl, as determined by X-ray diffraction crystallography and elemental analysis. Silver(I) azide complexes 6 and 8 were obtained by reaction of acetate precursors 5 and 7 with trimethylsilyl azide in toluene (method B, eq 2). An advantage of method B is that trimethylsilyl azide and trimethylsilyl acetate can be easily removed using pentane. Surprisingly, trimethylsilyl azide has been used infrequently for the generation of metal(metalloid) azides.23,24 (20) Bruker AdVanced X-ray Solutions, SMART for WNT/2000 (Version 5.628); Bruker AXS, Inc.: Madison, WI, 1997-2002. (21) Bruker AdVanced X-ray Solutions, SAINT (Version 6.45); Bruker AXS, Inc.: Madison, WI, 1997-2003. (22) Bruker AdVanced X-ray Solutions SHELXTL (Version 6.10); Bruker AXS, Inc.: Madison, WI, 2000. (23) Neumueller, B.; Dehnicke, K. Z. Anorg. Allg. Chem. 2006, 632, 931–933. (24) Carmalt, C. J.; Cowley, A. H.; Culp, R. D.; Jones, R. A. Chem. Commun. 1996, 1453–1454.

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Table 1. Crystallographic Data for Complexes 1, 3, 4, and 6 1 formula fw cryst syst space group a, Å b, Å c, Å R, deg β, deg γ, deg cell volume, Å3 Z Dcalcd, Mg, m3 T, K µ, mm-1 F(000) cryst size, mm θmin,θmax, deg no. of reflns collected no. of indep reflns no. of refined params goodness-of-fit on F2a final R indicesb [I > 2σ(I)] R1 wR2 R indices (all data) R1 wR2

C24H31AuN3P 589.45 triclinic P 10.2546(4) 10.8364(4) 11.6070(4) 62.768(2) 82.646(2) 75.921(2) 1112.19(7) 2 1.760 100(2) 6.701 580 0.29 × 0.15 × 0.15 1.97, 27.50 20534 5040 262 1.070 0.0154 0.0357 0.0174 0.0376

3 C33H49AuN3P 715.69 monoclinic C2/c 18.161(3) 17.165(3) 22.038(4) 101.120(2) 6741(2) 8 1.410 100(2) 4.436 2896 0.33 × 0.24 × 0.08 1.65, 27.04 36453 6377 349 1.053 0.0230 0.0276 0.0559 0.0572

4

6

C27H38AuN5 629.59 triclinic P 9.980(3) 10.653(3) 12.658(3) 84.927(3) 79.645(3) 81.541(3) 1306.8(6) 2 1.600 100(2) 5.652 628 0.38 × 0.35 × 0.07 1.64, 27.05 14805 5637 306 1.077 0.0270 0.0703 0.0296 0.0722

C27H38AgN5 540.49 triclinic P 9.8617(16) 11.3600(19) 12.409(2) 85.612(2) 85.076(2) 85.354(2) 1377.1(4) 2 1.303 180(2) 0.754 564 0.32 × 0.28 × 0.28 1.65, 28.28 14094 6765 306 1.051 0.0319 0.0663 0.0426 0.0720

a GOF ) [Σw(Fo2 - Fc2)2/(n - p)]1/2; n ) number of reflections, p ) number of parameters refined. Fc2)2/ΣwFo4]1/2.

Figure 1. Thermal ellipsoid representation (100 K) of 1 showing 50% probability ellipsoids and a partial atom-labeling scheme. Hydrogen atoms have been omitted for clarity. Selected bond distances (Å) and bond angles (°): Au1-P1, 2.235(1); Au1-N1, 2.070(2); N1-N2, 1.141(3); N2-N3, 1.191(4); N1-Au1-P1, 177.99(6); Au1-N1-N2, 120.17(2); N1-N2-N3, 175.9(3). Scheme 1

Crystallography. Products 1, 3, 4, and 6 were characterized by X-ray diffraction crystallography. Metal centers in all four complexes show an essentially linear coordination geometry, with azide ligands bound terminally. The crystal structure of 1 (Figure 1) shows a linear geometry about gold(I); the phosphorus-gold-azide nitrogen angle is 177.99(6)°. The P-Au bond length (2.235(1) Å) is a near match to those of other gold(I) dialkylbiarylphosphines.19 The gold-nitrogen bond, at 2.070(2) Å, is similar to that of (triphenylphosphine)gold(I) azide, at 2.100(4) Å,25 and shorter than those in a (phosphine)gold(I) azadipyrromethene complex

b

R1 ) Σ(|Fo - Fc|)/ΣFo; wR2 ) [Σw(Fo2 -

reported recently, at 2.2349(12) and 2.2448(12) Å.26 The azide ligand binds terminally to gold in a bent geometry, and the Au-N1-N2 angle is 120.17(2)°. A close approach occurs between gold and two carbon atoms of the phosphine biaryl substituent: Au1-C7 ) 3.057(2) Å, Au1-C12 ) 3.122(2) Å. Such interactions have been observed previously for gold(I) compounds19 where the distance between gold and the aryl ipso carbon, or one of the two ortho carbons, lies within van der Waals contact. The Kochi hapticity27 calculated for the pendant phenyl ring of 1 is 1.80. The crystal structure of 3 appears in Figure 2. Here the phosphine ligand is a triisopropyl-substituted derivative of that in 1. Again the geometry about gold is nearly linear, and metrical parameters are similar to those of 1. The hapticity calculated for the flanking triisopropylphenyl ring is 1.86. Carbon atoms C19 and C24 are within van der Waals contact distance with gold. Interatomic distances are Au-C19, 3.186(2) Å, and Au-C24, 3.234(2) Å. A thermal ellipsoid projection of gold complex 4 appears in Figure 3a. Silver complex 6 is isostructural; it appears as Figure S1 of the Supporting Information. Essentially, linear 2-fold coordination prevails in both. Inspection of metal-carbon and metal-nitrogen bond distances affirms Schmidbaur and coworkers’ conclusion28 that gold(I) is smaller than silver(I). Metal-carbon bond lengths suggest that the azide ligand exerts a similar, or perhaps greater trans-influence to chloride; metal-phosphorus bond lengths in 1 and 3 lead to the same conclusion. As is usual for these hindered carbene ligands,29,30 the best-fit planes of the 2,6-diisopropylphenyl benzene rings (25) Beck, W.; Klapo¨tke, T. M.; Klu¨fers, P.; Keamers, G.; Riena¨cker, C. M. Z. Anorg. Allg. Chem. 2001, 627, 1669–1674. (26) Teets, T. S.; Partyka, D. V.; Esswein, A. J.; Updegraff, J. B., III; Zeller, M.; Hunter, A. D.; Gray, T. G. Inorg. Chem. 2007, 46, 6218–6220. (27) Vasilyev, A. V.; Lindeman, S. V.; Kochi, J. K. Chem. Commun. 2001, 909–910. (28) Bayler, A.; Schier, A.; Bowmaker, G. A.; Schmidbaur, H. J. Am. Chem. Soc. 1996, 118, 7006–7007. (29) Dı´ez-Gonza´lez, S.; Nolan, S. P. Coord. Chem. ReV. 2007, 251, 874– 883.

SilVer(I) and Gold(I) Azide Complexes

Organometallics, Vol. 28, No. 3, 2009 799

Table 2. (Phosphine) and (N-Heterocyclic carbene)MI Azide Complexes (M ) Ag, Au), Isolated Yields, and Designation of Compounds

Figure 2. Thermal ellipsoid representation (100 K) of 3 showing 50% probability ellipsoids and a partial atom-labeling scheme. Hydrogen atoms have been omitted for clarity. Selected bond distances (Å) and bond angles(°): Au1-P1, 2.2279(7); Au1-N1, 2.057(2); N1-N2, 1.171(3); N2-N3, 1.156(3); N1-Au1-P1, 173.08(6); Au1-N1-N2, 124.3(2); N1-N2-N3, 175.0(3).

Multinuclear NMR spectroscopy (either 31P or 13C) of the donor atom trans to the azide ligand is diagnostic of product formation. Table 4 compares the 31P chemical shifts of azide complexes 1-3 and 8 to those of their precursors in the same solvents. Chemical shifts differ by at least 1.9 ppm in all cases. Silver complex 8 shows clearly resolved doublets from coupling of 31P to the spin-1/2 nuclides 107Ag (51.8% abundance) and 109 Ag (48.2%). Similarly, in N-heterocyclic carbene complexes 5 and 6, coupling between the carbene carbon and silver elicits a pair of doublets with a coupling constant of ca. 240 Hz, similar to previously measured 13C(carbene)-107/109Ag coupling constants.

Conclusion

a

A ) Scheme 1, eq 1; B ) Scheme 1, eq 2.

are nearly orthogonal to the trigonal plane of the carbene carbon. The packing diagrams of 4 and 6 suggest an intermolecular hydrogen-bonding interaction between a methylene hydrogen of the carbene and the terminal azide nitrogen of a neighboring complex. A similar interaction was encountered for a twocoordinate copper acetate complex of the unsaturated carbene analogue.31 There, an interaction occurs between a backbone methine proton and the dangling (unligated) acetate oxygen of a neighbor. Spectroscopic Characterization. New metal azide complexes were characterized by infrared and NMR spectroscopy. Table 3 collects frequencies of symmetric and antisymmetric stretching vibrations. The more intense antisymmetric stretching mode falls within the range 2023-2058 cm-1, whereas symmetric stretch frequencies range from 1264-1288 cm-1. All such frequencies are in regions normally found for terminal metal azide complexes.32 (30) Hahn, F. E.; Jahnke, M. C. Angew. Chem., Int. Ed. 2008, 47, 3122– 3172. (31) Mankad, N.; Gray, T. G.; Laitar, D. S.; Sadighi, J. P. Organometallics 2004, 23, 1191–1193.

Organic azides are at the center of copper-catalyzed click chemistry, and metalloazide complexes are recognized synthons, especially in gold chemistry.16,33-37 Previous syntheses of gold azide complexes have relied on reaction of chlorogold precursors with excesses of LiN3, NaN3, or NEt4N3, often with heating, and often in protic solvents.35,36,38 Presented here are two alternatives that may find use with aprotic reaction media are strictly necessary or when heating is unacceptable. The new methods rely on the stability of the Si-O bond and on the (commercial) availability of trimethylsilyl azide. They parallel work by Haiges, Christe, and co-workers39,40 where homoleptic, early transition-element, and main group azide complexes are generated from fluorides and trimethylsilyl azide, with elimination of trimethylsilyl fluoride. Although an (N-heterocyclic carbene)gold(I) fluoride complex is accessible,41 it is photo(32) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part B: Applications in Coordination, Organometallic, and Bioinorganic Chemistry, 5th ed.; Wiley: New York, 1997, pp 124-126. (33) Stra¨hle, J. J. Organomet. Chem. 1995, 488, 15–24. (34) Kunkeley, H.; Vogler, A. Inorg. Chem. Commun. 2003, 6, 553– 554. (35) Beck, W.; Fehlhammer, W. P.; Po¨llmann, P.; Scha¨chl, H. Chem. Ber. 1969, 102, 1976–1987. (36) Beck, W.; Bauder, M.; Fehlhammer, W. P.; Po¨llmann, P.; Scha¨chl, H. Inorg. Nucl. Chem. Lett. 1968, 4, 143–146. (37) Beck, W. J. Organomet. Chem. 1990, 383, 143–160. (38) Nichols, D. I.; Charleston, A. S. J. Chem. Soc. A 1969, 2581–2583. (39) Haiges, R.; Boatz, J. A.; Bau, R.; Schneider, S.; Schroer, T.; Yousufuddin, M.; Christe, K. O. Angew. Chem., Int. Ed. 2005, 44, 1860– 1865. (40) Haiges, R.; Boatz, J. A.; Vij, A.; Gerken, M.; Schneider, S.; Schroer, T.; Yousufuddin, M.; Christe, K. O. Angew. Chem., Int. Ed. 2004, 43, 6676– 6680. (41) Laitar, D. S.; Mu¨ller, P.; Gray, T. G.; Sadighi, J. P. Organometallics 2005, 24, 4503–4505.

800 Organometallics, Vol. 28, No. 3, 2009

Partyka et al.

Figure 3. (a) Thermal ellipsoid representation (100 K) of 4 showing 50% probability ellipsoids and a partial atom-labeling scheme. Hydrogen atoms have been omitted for clarity. Selected bond distances (Å) and bond angles(°): (4) Au1-C1, 1.961(3); Au1-N3, 2.068(3); N1-N2, 1.187(5); N2-N3, 1.139(5); C1-Au1-N3, 175.29(11); N4-C1-N5, 108.6(3); N5-C1-Au1, 122.7(2); N4-C1-Au1, 128.3(2); N5-C1-N4, 108.6(3); Au1-N3-N2, 116.1(3); N1-N2-N3, 174.8(4). (b) Packing diagram of (4) showing an intermolecular interaction between N1 of one complex and the backbone C-H atom of a neighbor. Table 3. Asymmetric (νas) and Symmetric (νs) Stretching Frequencies for Azide-Bearing Productsa

a

compound

νas (cm-1)

νs (cm-1)

1 2 3 4 6 8

2055 2058 2056 2048 2035 2023

1286 1288 1265 1274 1271 1264

As KBr pellets.

sensitive; its synthesis is nontrivial, and there is no known phosphine analogue. Readier preparations of group 11 (phosphine)- and (carbene)MI azides were sought. Azide complexes of both silver(I) and gold(I) are procurable in 77% or better isolated yields. To our knowledge, the silver-containing products herein are the first heteroleptic silver azide complexes featuring a terminal (non-bridging) azide ligand.

Table 4. Comparison of 31P NMR Chemical Shifts: Products versus Starting Materialsa product

precursor

δP (ppm) of precursor

δP (ppm) of product

1 2 3 8d

PBHAuClb PBMeAuClc (XPhos)AuCl (XPhos)AgOAc (7)

44.6 38.6 36.0 15.3

37.8 35.1 34.1 17.2

a In C6D6, except 7 and 8 (CDCl3). b PBH ) dicyclohexyl(2-biphenyl)phosphine. c PBMe ) dicyclohexyl(2′-methyl-2-biphenyl)phosphine. d Pair of doublets; listed chemical shift is average chemical shift of all four observed resonances.

Although many metal azide complexes are explosive, we have not experienced mishaps with the compounds described here. The new complexes were always handled gingerly and in small quantities. We cannot oVeremphasize the importance of safe practices in manipulating these high-energy compounds.

SilVer(I) and Gold(I) Azide Complexes

Structural and spectroscopic characterization is presented here for six new azide complexes of silver(I) and gold(I). Dative interactions occur between the metal sites and dialkylbiarylphosphine supporting ligands. In an N-heterocyclic carbene complex, an intermolecular hydrogen-bonding interaction takes place between an azide terminal nitrogen atom and a carbene backbone sp3-C-H bond. 31P and carbene-carbon 13C NMR resonances provide spectroscopic indicators of product formation. The normal vibrational signatures of terminal azide complexes are present in these compounds, namely, an intense νas stretching node near 2050 cm-1 and a lesser νs peak near 1275 cm-1.

Acknowledgment. The authors thank the National Science Foundation (Grant CHE-0749086 to T.G.G.), the donors of

Organometallics, Vol. 28, No. 3, 2009 801

the Petroleum Research Fund, administered by the American Chemical Society (Grant 42312-G3 to T.G.G.), and Case Western Reserve University for support. T.J.R. acknowledges an Ohio Board of Regents Innovation Incentive Fellowship. The diffractometer at Case Western Reserve was funded by NSF grant CHE0541766; that at YSU was funded by NSF Grant 0087210, by the Ohio Board of Regents Grant CAP491, and by Youngstown State University. Supporting Information Available: Crystallographic data in CIF format; thermal ellipsoid projection of 6. This material is available free of charge via the Internet at http://pubs.acs.org. OM800536F