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. Author manuscript; available in PMC: 2009 Apr 1.
Published in final edited form as: J Organomet Chem. 2008 Apr;693(8-9):1674–1682. doi: 10.1016/j.jorganchem.2008.01.026

Cyclic (Alkyl)(amino)carbene Gold(I) complexes

A Synthetic and Structural Investigation

Guido D Frey 1, Rian D Dewhurst 1, Shazia Kousar 1, Bruno Donnadieu 1, Guy Bertrand 1,*
PMCID: PMC2394856  NIHMSID: NIHMS47569  PMID: 19343084

Abstract

A series of mono- and dicarbene gold(I) complexes of types Au(CAAC)(Cl) [CAAC = cyclic (alkyl)(amino)carbene] (1) and [Au(CAAC)2]+[X]- (X = Cl, AuCl2) (2) have been prepared through reaction of AuCl(SMe2) with free carbenes a-e, and structurally characterized by single X-ray diffraction studies (1a, 1b, 2d, 2e). In addition two new free cyclic (alkyl)(amino)carbenes (c and e) have been synthesized.

Keywords: Stable Carbenes, Carbene Complexes, Gold

Following the discovery of the first stable derivatives [1,2], singlet carbenes have received considerable attention as ligands for transition metals [3,4]. Carbenes feature a strong σ-donating ability, and strongly bind metal centers of high and low oxidation states [5]. Additionally, the possibility to tune their electronic and steric properties by variation of substituents [6], make carbenes versatile ligands for transition metal catalysts [7]. Since the Au(I) catalyzed asymmetric aldol reaction was published in the late 1980s [8], the use of Au(I) complexes in catalysis has received a lot of attention [9,10]. The first NHC substituted neutral and cationic gold(I) complexes were published in 1989 [11], and their application in catalysis stated in 2003 [12].

We have already reported the synthesis and isolation of well-defined cyclic (alkyl)(amino)carbenes (CAAC) [13a], their use for the activation of small molecules [13b-d], their properties as ligand for transition metals [13e,f], and recently the preparation of a CAAC gold(I) complex, which allows for the catalytic formation of allenes, starting from enamines and alkynes [14]. This manuscript describes the synthesis and characterization of a series of Au(I) complexes, featuring one or two CAACs, depending on the bulkiness of the carbene ligand.

The free carbenes (a-e) including the new ones (c and e) were readily prepared by deprotonation with LDA of the corresponding iminium salts; the latter were synthesized using the hydroiminiumation route [15] as shown in Scheme 1.

Scheme 1.

Scheme 1

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Synthesis of carbenes a-e.

The gold complexes 1a-d were then cleanly prepared by stirring the free carbenes a-d overnight in darkness in THF with AuCl(SMe2), the same procedure used for the corresponding NHC complexes [16]. After removing the solvent under vacuum and washing with hexanes, the remaining residue was extracted with CH2Cl2 or CHCl3. All complexes 1a-d were isolated as colorless analytically pure microcrystalline material in good yields (Scheme 2). They are readily soluble in most common polar solvents (CH2Cl2, CHCl3, THF), sparingly in diethyl ether and insoluble in hexanes. Single crystals of complexes 1a and 1b, suitable for X-ray diffraction studies (Fig. 1), were obtained by slow evaporation of the solvent (CH2Cl2 or CHCl3). Complexes 1a-d are slightly unstable when exposed to incandescent light (giving gold metal) but thermally stable in the solid state at room temperature over several months. The 13C NMR signals for the carbene carbon atom of gold complexes 1a-d (1a, 237.1; 1b, 239.9; 1c, 236.4; 1d, 235.0 ppm) are shifted toward high field compared to those observed for the corresponding free carbenes a-d (309-322 ppm).

Scheme 2.

Scheme 2

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Synthesis of mono substituted CAAC Au(I) complexes 1a-d.

Fig. 1.

Fig. 1

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Ball and Stick plots of complexes 1a and 1b in the solid state. Hydrogen atoms are omitted for clarity. Some pertinent metric parameters are given in Table 1.

Under the same reaction conditions, a different behavior was observed for carbene e. In this case the reaction of a stoichiometric amount of e with AuCl(SMe2) did not afford the expected mono-carbene gold complex (similar to 1a-d), but the cationic dicarbene gold complex 2e with AuCl2- as counteranion (Scheme 3), as demonstrated by a single crystal X-ray diffraction study (Fig. 2). The different nature of 2e, compared to 1a-d, is also apparent from the 13C NMR spectra, since the carbene carbon gives a signal at 249.7 ppm, some 10-14 ppm downfield compared to those observed for 1a-d. This result suggests that a disproportion reaction occurs, as already observed for related NHC-silver complexes [12,17,18]. Indeed, we found that all attempts to recrystallize complex 1d from a CD2Cl2 solution over several days also led to the homoleptic gold carbene complex 2d, with chloride as counteranion, as shown by an X-ray single crystal structure (Fig. 2). Here again, the 13C NMR signal for the carbene carbon of 2d appeared at lower field (251.2 ppm) than that observed for 1d (235.0 ppm).

Scheme 3.

Scheme 3

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Synthesis of homoleptic dicarbene Au(I) complexes 2d and 2e.

Fig. 2.

Fig. 2

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Ball and Stick plots of complexes 2d and 2e in the solid state. Hydrogen atoms are omitted for clarity. Some pertinent metric parameters are given in Table 1.

All complexes (1a, 1b, 2d, 2e) show the expected linear coordination of the two ligands at the gold atom [Ccarbene-Au-X angle (X = Cl, C) between 175.78(6) [1b] and 180 [2d, 2e] degrees] (Table 1), and are in agreement with the literature for gold(I) complexes [12,20-31]. The Au-Ccarbene bond lengths in 1a (1.987(9) Å) and 1b (1.983(2) Å) are comparable with those found in substituted NHC gold(I) chloro complexes [12,18-23], and suggest a single bond character, in good agreement with the strong σ-donor character of CAACs. The cationic complexes 2d and 2e have slightly longer Au-Ccarbene bond lengths [2.0321(11) and 2.033(4) Å, respectively] in the range observed for cationic dicarbene (NHC) gold(I) complexes [24-31]. For all four gold complexes (1a, 1b, 2d and 2e), no aurophilic interactions between the Au atoms were observed (>7.4 Å).

Table 1.

Pertinent bond distances and angles for complexes 1a, 1b, 2d, and 2e

Compound 1a 1b 2d 2e
Au-Ccarbene [Å] 1.987(9) 1.983(2) 2.0321(11) 2.033(4)
Ccarbene-N [Å] 1.259(11) 1.304(3) 1.304(2) 1.297(5)
Ccarbene-Cspiro [Å] 1.572(13) 1.531(3) 1.512(2) 1.506(5)
N-CMe2 [Å] 1.508(11) 1.525(2) 1.530(2) 1.529(5)
Cspiro-CH2 [Å] 1.534(13) 1.551(3) 1.548(2) 1.566(8)
CMe2-CH2 [Å] 1.527(12) 1.531(3) 1.540(2) 1.538(9)
Ccarbene-Au-X
(X = C, Cl) [°]		 178.6(2) 175.78(6) 180 180
N-Ccarbene-Cq [°] 108.8(8) 109.6(2) 109.99(10) 110.4(3)
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The steric hindrance and the flexibility of the carbene carbon substituents have a dramatic effect on the synthetic outcome of the complexation reactions at gold centers. When bulky and rigid substituents are present at carbon, LAuCl complexes 1a,b are isolated, whereas the use of the smaller non-substituted cyclohexyl and cyclohexylene groups (d, e) give rise to cationic di(carbene) complexes 2d,e. However, despite the presence of relatively small substituents, the non-spiro carbene c behaves as a and b; this is probably due to the higher flexibility of the substitution motive (or to an interaction between the metal and the benzene ring). Given the likelihood that di(carbene) complexes of type 2 are at least partially deactivated in terms of catalysis, these results give a first indication of the range of the substituents, which might allow CAAC gold complexes to find catalytic applications.

Experimental Section

All reactions were performed under an atmosphere of argon and solvents were dried over Na metal or CaH2. Reagents were of analytical grade, obtained from commercial suppliers and used without further purification. 1H NMR (300 MHz), and 13C{1H}NMR (75 MHz) spectra were obtained with a Bruker Avance 300 spectrometer at 298 K. 1H and 13C chemical shifts (δ) are reported in parts per million (ppm) relative to TMS and were referenced to the residual solvent peak. NMR multiplicities are abbreviated as follows: s = singlet, d = doublet, t = triplet, sept. = septet, m = multiplet, br = broad signal. Coupling constants (J) are reported in hertz (Hz). High-resolution fast atom bombardment (FAB) mass spectra were obtained at the UC Riverside Mass Spectrometry Laboratory. Melting points were measured with a Büchi melting point apparatus system (Dr. Tottoli). Free carbenes a, b, and d were prepared according to the literature [15].

Carbene c

2,6-Diisopropylaniline (5.00 mL, 4.70 g, 26.5 mmol) was added at room temperature to a reaction flask containing molecular sieves (15 g) and a hexane solution (50 mL) of 2-methyl-3-(p-isopropylphenyl)propionaldehyde (5.84 mL, 5.55 g, 29.2 mmol). The reaction mixture was stirred for 18 h. The molecular sieves were removed by filtration, and the hexane was removed in vacuo. After removal of the excess 2,6-diisopropylaniline by short path distillation at 170°C under vacuum, imine ca was obtained as a light yellow oil. Yield: 6.52 g (70%). 1H NMR (CDCl3) δ 7.57 (d, 3J = 4.5 Hz, 1H, NCH), 7.22 (br, 4H, Har), 7.12 (br, 3H, Har), 3.11-2.74 (m, 6H, CH(CH3)2 + CH2 + CHCHCH3), 1.30 (d, 3J = 6.6 Hz, 9H, CH(CH3)2 + CHCHCH3), 1.12 (d, 3J = 6.8 Hz, 12H, CH(CH3)2). 13C{1H}NMR (CDCl3) δ 170.1 (NCH), 148.7 (C q), 146.4 (Cq), 137.1 (Cq), 136.7 (Cq), 128.9 (CH), 126.3 (CH), 123.8 (CH), 122.6 (CH), 41.7 (NCHCH), 39.6 (CH2), 33.7 (CH), 27.4 (CH(CH3)2), 24.1 (CH), 23.4 (CH(CH3)2), 23.3 (CH(CH3)2), 17.4 (CHCH3). FAB-HRMS calcd for C25H36N [M+H]+:m/z 350.2848; found 350.2852. A solution of ca (6.52 g, 18.7 mmol) was added slowly to a solution of LiNMe2 (1.00 g, 19.6 mmol) in Et2O (20 mL). The mixture was allowed to warm to room temperature, and then stirred for two hours. 3-chloro-2-methyl-1-propene (2.03 g, 2.19 mL, 22.4 mmol) was added slowly under stirring to this solution. After stirring for 2h, all volatiles were removed in vacuo. Hexanes (20 mL) were added and the suspension was filtered. The solvent was evaporated to give compound cb as an oil. Yield: 6.71 g (89%). 1H NMR (CDCl3) δ 7.72 (s, 1H, NCH), 7.27-7.06 (m, 7H, Har), 4.95 (s, 1H, CH), 4.82 (s, 1H, CH), 2.95 (s, 2H, CH2), 2.86 (sept., 3J = 6.8 Hz, 3H, CH(CH3)2), 2.43 (d, 2J = 13.8 Hz, 1H, CH2), 2.31 (d, 2J = 13.8 Hz, 1H, CH2), 1.84 (s, 3H, CH3), 1.31 (s, 3H, CH3), 1.27 (d, 3J = 6.8 Hz, 6H, CH(CH3)2), 1.12 (d, 3J = 6.8 Hz, 12H, CH(CH3)2). 13C{1H} NMR (CDCl3) δ 172.4 (NCH), 148.7 (Cq), 146.8 (Cq), 142.4 (Cq), 137.4 (Cq), 135.1 (Cq), 130.9 (CH), 126.1 (CH), 123.9 (CH), 122.9 (CH), 115.5 (CH2), 46.4 (CH2), 44.9 (Cq), 44.5 (CH2), 33.8 (CH3), 27.5, 25.5, 24.2, 23.6, 22.6. FAB-HRMS calcd for C29H42N [M+H]+: m/z 404.3317; found 404.3314. To a solution of cb (6.71 g, 16.63 mmol) in acetonitrile (10 mL) was added a solution of HCl in Et2O (2M, 20.7 mL, 41.6 mmol). The vessel was sealed, and heated to 80 °C for 14h. The acetonitrile was removed, and the residue was extracted twice with boiling toluene (20 mL). After cooling to room temperature, the suspension was filtered, washed with toluene and dried to obtain cc (X = HCl2-) as a white solid. Yield: 5.74 g (72%). 1H NMR (CD3CN) δ 9.39 (s, 1H, NCH), 7.59 (t, 3J = 7.7 Hz, 1H, Har), 7.44 (t, 3J = 6.8 Hz, 2H, Har), 7.34 (d, 3J = 7.7 Hz, 2H, Har), 7.28 (d, 3J = 7.7 Hz, 1H, Har), 6.13 (br s, 1H, HCl2), 3.47 (d, 3J = 14.0 Hz, 1H, CH2), 3.03 (d, 3J = 14.0 Hz, 1H, CH2), 2.96 (sept., 3J = 6.9 Hz, 1H, CH(CH3)2), 2.66 (sept., 3J = 6.7 Hz, 1H, CH(CH3)2), 2.64 (d, 2J = 14.0 Hz, 1H, CH2), 2.35 (d, 2J = 14.0 Hz, 1H, CH2), 2.15 (sept., 3J = 6.6 Hz, 1H, CH(CH3)2), 1.73 (s, 3H, CH3), 1.42 (s, 3H, CH3), 1.35 (d, 3J = 6.7 Hz, 3H, CH(CH3)2), 1.26 (d, 3J = 6.8 Hz, 6H, CH(CH3)2), 1.13 (m, 9H, CH3), 0.93 (s, 3H, CH3). 13C{1H}NMR (CD3CN) δ 192.8 (NCH), 149.3 (Cq), 145.6 (Cq), 145.0 (Cq), 134.7 (Cq), 132.6 (CH), 131.1 (CH), 129.7 (Cq), 127.7 (CH), 126.5 (CH), 125.9 (CH), 84.7 (NC(CH3)2), 55.3 (Cq), 44.1 (CH2), 43.8 (CH2), 34.4, 30.1, 29.8, 28.5, 27.6, 26.3, 24.2, 22.0, 21.8. FAB-HRMS calcd for C29H42N [M]+: m/z 404.3317; found 404.3317. To a Schlenk tube containing the iminium salt cc (X = HCl2-) (4.86 g, 10.20 mmol) and NaBPh4 (3.49 g, 10.20 mmol) was added methylene chloride (40 mL). The mixture was stirred for 1 h at room temperature and filtered afterwards through Celite (3 g). The solvent was removed in vacuo, and the residue was extracted twice with boiling hexanes. The hexanes extract was cooled to -20 °C, and the solution was decanted from the solid. The solid was dried in vacuo to yield cc (X = BPh4-) 5.31 g (72%) as a white powder. A solution of KHMDS (419 mg, 2.10 mmol) in THF (10 mL) was added slowly to a solution of cc (X = BPh4-) (500 mg, 1.05 mmol) in THF (10 mL) at -78 °C. The mixture was allowed to warm to room temperature, and stirred for 1h. The THF was removed and the residue was extracted with hexanes (10 + 5 mL), filtered and the hexanes was removed yielding colorless crystals of free carbene c. Yield: 236 mg (56%). 1H NMR (C6D6) δ 7.75 (m, 1H, Har), 7.38-7.20 (m, 6H, Har), 3.93 (sept., 3J = 6.9 Hz, 1H, CH(CH3)2), 3.80 (sept., J = 6.8 Hz, 1H, CH(CH3)2), 3.78 (d, J = 8.2 Hz, 1H), 3.60 (sept., 3J = 6.4 Hz, 1H, CH(CH3)2), 3.28 (d, J = 8.3 Hz, 1H, CH2), 2.87 (s, 3H, CH), 2.15 (d, 2J = 12.7 Hz, 1H, CH2), 1.79 (d, 2J = 12.7 Hz, 1H, CH2), 1.45 (d, 3J = 6.9 Hz, 3H, CH(CH3)2), 1.37 (d, 3J = 6.9 Hz, 3H, CH(CH3)2), 1.36 (s, 3H, CH(CH3)2), 1.36 (d, 3J = 6.6 Hz, 3H, CH(CH3)2), 1.29-1.25 (9H, CH(CH3)2), 1.19 (d, 3J = 6.9 Hz, 3H, CH(CH3)2). 13C{1H}NMR (C6D6) δ 313.0 (Ccarbene), 152.7 (Cq), 152.5 (Cq), 147.0 (Cq), 139.2 (Cq), 137.7 (Cq), 131.0 (CH), 127.6 (CH), 126.6 (CH), 124.8 (CH), 124.7 (CH), 80.7 (NC(CH3)2), 61.2 (Cq), 51.5 (CH2), 46.5 (CH2), 34.4, 30.1, 29.8, 28.5, 27.6, 26.3, 24.2, 22.0, 21.8.

Carbene e

2,6-Diisopropylaniline (10.00 mL, 9.40 g, 53 mmol) was added at room temperature to a reaction flask containing molecular sieves (15 g) and a hexane solution (50 mL) of 1-cyclohexene-1-carboxaldehyde (90%) (7.23 mL, 7.01 g, 64 mmol). The reaction mixture was stirred for 16 h. The molecular sieves were removed by filtration, and the hexane was removed In vacuo. Excess 2,6-diisopropylaniline was removed by short path distillation at 170°C under vacuum. The resulting oily residue was recrystallized from ethanol at low temperatures to afford N-Dipp-C-3-cyclohexene (ea) as white crystals. Yield: 11.296 g (79%). 1H NMR (CDCl3) δ 7.63 (d, 3J = 4.5 Hz, 1H, NCH), 7.16-7.06 (m, 3H, Har), 5.80 (s, 2H, CH), 2.96 (sept., 3J = 6.9 Hz, 2H, CH(CH3)2), 2.80-2.74 (m, 1H, NCHCH), 2.36-2.30 (m, 2H, CH2), 2.26-2.21 (m, 2H, CH2), 2.15-2.06 (m, 1H, CH2), 1.82-1.72 (m, 1H, CH2), 1.19 (d, 3J = 6.9 Hz, 12H, CH(CH3)2). 13C{1H}NMR (CDCl3) δ 168.8 (N CH), 149.2 (Co,ar), 136.6 (Ci,ar), 126.7 (CH), 125.3 (CH), 123.6 (CH), 122.4 (CH), 39.7 (NCHCH), 27.5 (CH), 27.4 (CH2), 25.2 (CH2), 24.2 (CH2), 23.2 (CH3). FAB-HRMS calcd for C19H28N [M+H]+: m/z 270.2222; found 270.2226. A solution of ea (8.80 g, 32.7 mmol) was added slowly to a solution of LDA (3.67 g, 34.3 mmol) in Et2O (20 mL). The mixture was allowed to warm to room temperature, and then stirred for two hours. 3-chloro-2-methyl-1-propene (3.55 g, 3.84 mL, 39.2 mmol) was added to this solution slowly under stirring. After stirring for 2h, all volatile compounds were removed under vacuo. The remaining residue was dried at 50 °C in vacuo to remove all traces of diethyl ether and diisopropylamine. Hexanes (20 mL) was added and the suspension was filtered. The solvent was evaporated to give eb as a pale yellow oil. Yield: 7.40 g (70%). 1H NMR (CDCl3) δ 7.62 (s, 1H, NCH 7.15-7.02 (m, 3H, Har), 5.75 (m, 2H, CH), 4.94 (s, 1H, CH), 4.80 (s, 1H, CH), 2.97 (sept., 3J = 6.9 Hz, 2H, CH(CH3)2), 2.52 (d, 2J = 16.4 Hz, 1H), 2.39 (s, 2H, CH2), 2.29-2.20 (m, 3H), 2.03-1.96 (m, 1H, CH2), 1.88-1.77 (m, 1H, CH2), 1.85 (s, 3H, CH3), 1.18 (d, 3J = 6.9 Hz, 6H, CH(CH3)2), 1.17 (d, 3J = 6.9 Hz, 6H, CH(CH3)2). 13C{1H}NMR (CDCl3) δ 171.2 CH), 149.2 (Co,ar), 142.0 (CCH2), 137.0 (Ci,ar), 126.4 (CH), 125.8 (CH), 124.1 (CH), 122.9 (CH), 115.6 (CCH2), 46.2 (CH2), 42.8 (NCHCq), 32.7 (CH2), 30.3 (CH2), 27.6 (CH), 25.4 (CH3), 23.8 (CH3), 23.3 (CH2). FAB-HRMS calcd for C23H34N [M+H]+: m/z 324.2691; found 324.2697. To a solution of eb (3.04 g, 9.44 mmol) in acetonitrile (10 mL) was added a solution of HCl in Et2O (2M, 9.44 mL, 18.82 mmol). The vessel was sealed, and heated to 90 °C for 16 h. The acetonitrile was removed, and the residue was extracted twice with boiling toluene (20 mL). After cooling to -20 °C, the suspension was filtered, washed with toluene and dried. ec with HCl2- as a counteranion was obtained as a white solid. Yield: 2.95 g (79%). m.p. 164-166 °C (dec.). 1H NMR (CD3CN) δ 12.88 (s, 1H, HCl2), 9.17 (s, 1H, NCH), 7.62 (t, 3J = 7.8 Hz, 1H, Hp,ar), 7.49 (d, 3J = 7.8 Hz, 2H, Hm,ar), 5.90 (m, 1H, CH), 5.78 (m, 1H, CH), 2.75 (m, 3H, CH(CH3)2 + CH2), 2.56-2.39 (m, 3H), 2.28-2.22 (m, 3H), 2.12-2.07 (m, 1H), 1.57 (s, 6H, C(CH3)2), 1.37 (d, 3J = 6.7 Hz, 6H, CH(CH3)2), 1.12 (d, 3J = 6.7 Hz, 6H, CH(CH3)2). 13C{1H}NMR (CD3CN) δ 192.5 (NCH), 145.4 (Co,ar), 132.7 (Cm,ar), 130.1 (Ci,ar), 128.1 (CH), 126.2 (CH), 123.0 (CH), 84.6 (NCq), 51.5 (NCHCq), 45.8 (CH2), 33.9 (CH2), 30.4 (CH2), 30.3 (CH3), 29.0 (CH), 28.5 (CH), 26.4 (CH3), 22.2 (CH3), 22.1 (CH3), 21.6 (CH2). FAB-HRMS calcd for C23H34N [M]+: m/z 324.2691; found 324.2699. To a Schlenk tube containing the iminium salt ec (2.95 g, 7.45 mmol) and NaBPh4 (2.55 g, 7.45 mmol) was added methylene chloride (40 mL). The mixture was stirred for 1 h at room temperature and filtered afterwards through Celite (3 g). The solvent was removed in vacuo, and the residue was extracted two times with boiling hexanes. The hexanes extract was cooled to -20 °C and the solution was decanted from the solid. The solid was dried in vacuo to yield 4.03 g (84%) of ec with BPh4- as counteranion as a white powder. A solution of KHMDS (250 mg, 1.26 mmol) in THF (6 mL) was added slowly to a solution of ec(BPh4-) (810 mg, 1.26 mmol) in THF (5 mL) at -78 °C. The mixture was allowed to warm to room temperature, and stirred for 2h. The THF was removed and the residue was extracted with toluene (10 + 5 mL), and filtered. After removal of the toluene, carbene e was isolated as colourless crystals. Yield: 265 mg (65%). 1H NMR (C6D6) δ 7.35-7.18 (m, 3H, Har), 5.77 (s, 2H, CH), 3.84 (sept., 3J = 6.7 Hz, 1H, CH(CH3)2), 3.82 (sept., J = 6.7 Hz, 1H, CH(CH3)2), 3.48 (td, J = 8.5 Hz, 3J = 7.0 Hz, 2H, CH2), 2.35-2.12 (m, 2H), 1.91 (d, J = 2.5 Hz, 2H), 1.79 (t, 3J = 6.3 Hz, 2H, CH2), 1.40 (s, 3H, C(CH3)2), 1.38 (s, 3H, C(CH3)2), 1.25 (d, 3J = 8.6 Hz, 12H, CH(CH)3)2). 13C{1H}NMR (C6D6) δ 311.0, 152.7, 152.6, 139.4, 136.0, 127.5, 127.4, 127.1, 124.6, 85.9, 63.0, 55.3, 40.0, 39.8, 35.0, 29.6, 29.5, 29.1, 29.0, 27.2, 27.1, 24.6, 23.7.

Complex 1a

A THF solution (5 mL) of free carbene a (666 mg, 1.75 mmol) was added to a THF solution (5 mL) of AuCl(SMe2) (500 mg, 1.71 mmol). The reaction mixture was stirred for 12 h at room temperature. The solvent was removed under vacuum, and the residue was washed with hexane (10 mL). The residue was extracted with methylene chloride (10 mL), and the solvent was removed under vacuum, affording complex 1a as a white solid (914 mg, 87% yield). Crystals suitable for X-ray diffraction study were obtained by slow evaporation of a CHCl3 solution. m.p. 124-125 °C. [α]D20 = 7.5° (CHCl3). 1H NMR (CDCl3) δ 7.42 (t, 3J = 7.1 Hz, 1H, Hp ar), 7.24 (d, 3J = 7.1 Hz, 2H, Hm ar), 3.16-2.89 (m, 2H), 2.83 (sept., 3J = 6.3 Hz, 1H, CH(CH3)2), 2.79 (sept,3J = 6.3 Hz, 1H, CH(CH3)2), 2.37 (d, 3J = 13.6 Hz, 1H), 2.12-1.99 (m, 2H), 1.95-1.83 (m, 2H), 1.80-1.72 (m, 1H), 1.44 (d, 3J = 6.7 Hz, 3H, CH(CH3)2), 1.39 (s, 3H, CH), 1.37 (d, 3J = 7.0 Hz, 3H, CH(CH3)2), 1.34 (d, 3J = 6.5 Hz, 3H, CH(CH3)2), 1.33 (s, 3H, CH3), 1.32 (d, 3J = 7.0 Hz, 3H, CH(CH3)2), 1.30-1.21 (m, 2H), 1.18 (d, 3J = 6.9 Hz, 3H, CH(CH3)2), 1.75-1.25 (m, 1H), 1.02 (d, 3J = 6.9 Hz, 3H, CH(CH3)2), 0.89 (d, 3J = 6.4 Hz, 3H, CH(CH3)2). 13C{1H}NMR (CDCl3 δ 237.1 (Ccarbene), 145.4 (Co,ar), 145.0 (Co,ar), 135.2 (Ci,ar), 129.8 (Cp,ar), 125.0 (Cm,ar), 124.9 (Cm,ar), 76.6 (C), 64.1 (C), 52.6 (CH2), 51.4 (CH), 49.8 (CH2), 35.6 (CH2), 30.3, 29.7, 29.7, 29.4, 29.0, 28.1, 27.5, 27.0, 25.2, 24.4 (CH2), 23.0, 22.9, 22.8, 20.2. FAB-HRMS (solvent CH3CN) calcd for C27H43AuN·CH3CN [M-Cl+CH3CN]+: m/z 619.3327; found 619.3303.

Complex 1b

Following the same experimental procedure as for 1a but free carbene b (640 mg, 1.69 mmol) and AuCl(SMe2) (475 mg, 1.61 mmol), complex 1b was isolated as a white solid (850 mg, 86% yield). Crystals suitable for an X-ray diffraction study were obtained by slow evaporation of a CHCl3 solution. m.p. 194-195 °C (dec.). 1H NMR (CDCl3 δ 7.37 (t, 3J = 7.7 Hz, 1H, Hp,ar), 7.20 (d, 3J = 7.7 Hz, 2H, Hm,ar), 4.00 (d, 2J = 12.9 Hz, 2H, CH2), 2.71 (sept., 3J = 6.7 Hz, 2H, CH), 2.32 (s, 2H), 2.12 (s, 1H), 2.02 (s, 1H), 1.98 (s, 1H), 1.92 (s, 3H), 1.78 (m, 6H), 1.39 (d, 3J = 6.7 Hz, 6H, CH(CH3)2), 1.31 (s, 6H, C(CH3)2), 1.26 (d, 3)J = 6.7 Hz, 6H, CH(CH3)2). 13C{1H}NMR (C6D6) δ 239.9 (Ccarbene), 144.8 (Co,ar), 135.2 (Ci,ar), 129.7 (Cp,ar), 125.0 (Cm,ar), 76.9 (Cq), 63.7 (Cq), 48.5 (CH2), 39.0 (CH2), 37.0, 35.2, 34.6 (CH2), 29.2, 29.1, 27.6, 27.1, 26.9, 23.1. FAB-HRMS (solvent CH3CN) calcd for C27H39AuN·CH3CN [M-Cl+CH3CN]+: m/z 615.3014; found 615.2990.

Complex 1c

Following the same experimental procedure as for 1a but free carbene c (254 mg, 0.63 mmol) and AuCl(SMe2) (186 mg, 0.63 mmol), complex 1c was isolated as a white solid (189 mg, 47% yield). 1H NMR (C6D6) δ 7.47 (t, 3J = 7.5 Hz, 1H, Har ), 7.39 (d, 3J = 7.4 Hz, 2H, Har), 7.31 (t, 3J = 7.3 Hz, 2H, Har), 7.25 (d, 3J = 7.5 Hz, 2H, Har), 3.52 (d, J = 13.6 Hz, 1H, CH2), 2.92 (sept., 3J = 7.0 Hz, 1H, CH(CH3)2), 2.82 (d, J = 14.2 Hz, 1H, CH2), 2.79 (m, 1H, CH(CH3)2), 2.39 (d, J = 13.2 Hz, 1H, CH2), 2.36 (sept., 3J = 7.0 Hz, 1H, CH(CH3)2), 2.00 (d, J = 13.7 Hz, 1H, CH2), 1.57 (s, 3H, CCH3), 1.35 (d, 3J = 6.5 Hz, 6H, CH(CH3)2), 1.30-1.18 (m, 15H, CH3), 1.07 (d, 3J = 6.8 Hz, 3H, CH(CH3)2). 13C{1H}NMR (C6D6) δ 236.4 Ccarbene), 147.8 (Cq), 145.7 (Cq), 145.3 (Cq), 135.5 (Cq), 131.4 (CH), 130.0 (CH), 126.4 (CH), 125.2 (CH), 125.0 (CH), 81.3 (NC(CH3)2), 60.2 (Cq), 46.1 (CH2), 44.2 (CH2), 34.3, 29.7, 29.4, 29.0, 28.6, 27.2, 26.8, 24.1, 23.9, 22.5, 22.3. FAB-HRMS (solvent CH3CN) calcd for C30H42AuN2 [MH-(Cl+CH3)+CH3CN]+: m/z 627.3014; found 627.3015.

Complex 1d

Following the same experimental procedure as for 1a but free carbene d (331 mg, 1.02 mmol) and AuCl(SMe2) (294 mg, 1.00 mmol), complex 1d was isolated as a white powder. Yield: 221 mg (40%). 1H NMR (CD3CN) δ 7.51 (t, J = 7.7 Hz, 1H, Hp,ar), 7.36 (d, J = 7.7 Hz, 2H, Hm,ar), 2.85 (sept, 3J = 6.7 Hz, 2H, CH), 2.20 (s, 2H, CH2), 2.16-2.10 (m, 2H), 1.85-1.40 (m, 8H), 1.37 (s, 6H, C(CH)3)2), 1.35 (d, 3J = 6.7 Hz, 6H, CH(CH3)2), 1.32 (d, 3J = 6.7 Hz, 6H, CH(CH3)2). 13C{1H}NMR (CD3CN) δ 235.0 (Ccarbene), 145.3 (Co,ar), 134.3 (Ci,ar), 129.9 (Cp,ar), 125.0 (Cm,ar), 80.7 (C), 58.6 (C), 44.4 (CH2), 36.0 (CH2), 28.7, 26.1, 25.0 (CH2), 22.0, 21.4 (CH2). FAB-HRMS (solvent CH3CN) calcd for C23H35AuN·CH3CN [M-Cl+CH3CN]+: m/z 563.2701; found 563.2690.

Complex 2d

Complex 1d slowly rearranges in dichloromethane (48 h) to the dicarbene complex 2d. The dichloromethane was removed in vacuo to give a white powder. Crystals suitable for X-ray analysis were obtained by slow evaporation of a concentrated dichloromethane solution. Yield: 1.535 g (85%, relative to carbene d). m.p. 248-252 °C. 1H NMR (CD3CN) δ 750 (dd, 3J = 8.4 Hz, 3J = 7.0 Hz, 2H, Hp,ar), 7.39 (d, J = 7.0 Hz, 4H, Hm,ar), 2.71 (sept, 3J = 6.7 Hz, 4H, CH), 2.10 (s, 4H, CH2), 1.63-1.52 (m, 8H), 1.37 (s, 12H, C(CH3)2), 1.31 (br. s, 12 H, C(CH3)2), 1.26-1.21 (m, 24H, CH(CH3)2). 13C{1H}NMR (CD3CN) δ 252.2 (Ccarbene), 146.1 (Co,ar), 135.8 (Ci,ar), 131.1 (Cp,ar), 126.3 (Cm,ar), 82.7 (C), 60.2 (C), 45.3 (CH2), 36.3 (CH2), 29.8, 29.6, 27.3, 25.8 (CH2), 23.6, 22.2 (CH2). 13C NMR (CD2Cl2) δ 251.2 (Ccarbene), 145.0 (Co,ar), 134.6 (Ci,ar), 130.3 (Cp,ar), 125.3 (Cm,ar), 81.9 (C), 59.6 (C), 45.2 (CH2), 35.8 (CH2), 29.5, 29.0, 26.8, 25.1 (CH2), 23.9, 21.5 (CH). FAB-HRMS calcd for C46H70AuN2 [M]+: m/z 847.5200; found 847.5204.

Complex 2e

To a hexane solution (5 mL) of free carbene e (410 mg, 1.27 mmol) a hexane solution (5 mL) of AuCl(SMe2) (372 mg, 1.26 mmol) was added and stirred at room temperature for 14h. The hexane was removed by filtration and the residue was extracted twice with 5 mL dichloromethane. The dichloromethane was removed in vacuo to give a white powder. Crystals suitable for X-ray analysis were obtained by slow evaporation of a concentrated dichloromethane solution. Yield: 471 mg (67%). m.p. 148-152 °C (dec.). 1H NMR (CDCl3) δ 7.40 (t, 3J = 7.7 Hz, 2H, Hp,ar), 7.22 (d, 3J = 7.7 Hz, 4H, Hm,ar), 5.76 (m, 2H, CH), 5.63 (m, 2H, CH), 2.58 (m, 4H, CH(CH3)2), 2.50-2.38 (m, 2H), 2.18-2.03 (m, 8H), 1.94-1.78 (m, 2H), 1.73-1.57 (m, 4H), 1.39 (s, 6H, C(CH3)2), 1.34 (s, 6H, C(CH3)2), 1.26 (d, 3J = 6.6 Hz, 6H, CH(CH3)2), 1.25 (d, 3J = 6.5 Hz, 6H, CH(CH3)2), 1.14 (d, 3J = 6.7 Hz, 4H, CH(CH3)2), 1.02 (d, 3J = 6.6 Hz, 4H, CH(CH3)2), 0.92 (d, 3J = 6.6 Hz, 4H, CH(CH3)2). 13C{1H}NMR (CH2Cl2) δ 249.7 CH), 144.7 (Co,ar), 144.5 (Co,ar), 133.7 (Ci,ar), 130.1 (CHp,ar), 127.0 (CH), 126.9 (CH), 125.5 (CH), 125.4 (CH), 125.1 (CH), 125.0 (CH), 122.5 (CH), 122.4 (CH), 81.9 (NCq), 57.4 (NCHCq), 45.0 (CH2), 34.8 (CH2), 34.7 (CH2), 32.2 (CH2), 32.1 (CH2), 29.5 (CH3), 29.0 (CH3), 28.9 (CH), 28.8 (CH), 26.7 (CH3), 26.4 (CH3), 22.9 (CH3), 22.8 (CH3), 22.6 (CH3), 22.5 (CH3), 20.8 (CH2), 20.7 (CH2). FAB-HRMS calcd for CH4666AuN2 [M]+: m/z 843.4891; found 843.4891.

Crystal Structure Determination of compounds 1a, 1b, 2d and 2e

The Bruker X8-APEX X-ray diffraction instrument [32] with Mo-radiation was used for data collection. All data frames were collected at low temperature (T = 100 K) using an ω, φ-scan mode (0.3° ω-scan width, hemisphere of reflections) and integrated using a Bruker SAINTPLUS software package [33]. Intensity data were corrected for Lorentzian polarization. Absorption corrections were performed using the SADABS program [34]. The SIR92 [35] was used for solution. Direct methods of phase determination followed by some subsequent difference Fourier map led to an electron density map from which most of the non-hydrogen atoms were identified in the asymmetry unit of the unit cell. With subsequent isotropic refinement, all of the non-hydrogen atoms were identified. The Bruker SHELXTL software package [36] was used for structure refinement and difference Fourier maps. Atomic coordinates, isotropic and anisotropic displacement parameters of all the non-hydrogen atoms of compounds were refined by means of a full matrix least-squares procedure on F2. All H-atoms were included in the refinement in calculated positions riding on the C atoms. Drawing of molecules was performed using Ortep3 [37].Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-671264 [1a], CCDC-671265 [1b·(CHCl3)], CCDC-671266 [2d·4(CHCl3)], and CCDC-671267 [2e]. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: (+44)1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).

Table 2.

Crystallographic Data for 1a, 1b, 2d, and 2e

1a 1b·(CHCl3) 2d·4(CHCl3) 2e
Formula C27H43AuClN C28H40AuCl4N C50H74AuCl13N2 C46H66Au2Cl2N2
Fw 614.04 729.38 1360.92 1111.84
Color / habit colorless colorless colorless colorless
Crystal dimensions (mm3) 0.46×0.40×0.13 0.17×0.16×0.09 0.43×0.36×0.13 0.32×0.25×0.17
Crystal system Monoclinic Orthorhombic Triclinic Triclinic
Space Group P2(1) Pbca P-1 P-1
a (Å) 12.361(2) 15.6359(13) 10.1388(6) 9.2198(4)
b (Å) 12.268(2) 16.4652(12) 12.1156(7) 11.5608(5)
c (Å) 21.666(4) 22.5014(18) 12.7174(8) 12.1686(5)
α (°) 90.0 90.0 71.544(3) 62.4130(10)
β (°) 103.145(2) 90.0 84.588(3) 75.221(2)
γ (°) 90.0 90.0 75.268(3) 77.4290(10)
V (Å3) 3199.4(9) 5792.9(8) 1432.95(15) 1104.02(8)
Z 4 8 1 1
T (K) 100 100 100 100
Dcalcd (g cm-3) 1.275 1.673 1.577 1.672
μ (mm-1) 4.693 5.466 3.208 6.790
F(000) 1232 2896 1376 1096
θ Range (°)a) Index ranges (h, k, l) 1.92 - 33.14 -18<=h<=19, -16<=k<=18, -32<=l<=33 6.39 - 32.57 0<=h<=23, -19<=k<=7, -25<=l<=5 1.82 - 51.27 -21<=h<=20, -23<=k<=25, -27<=l<=27 1.92 - 32.57 -13<=h<=13, -17<=k<=16, -18<=l<=10
No. of rflns. collected 39186 6504 68429 10679
No. of indep. rflns. / Rint 19291 / 0.0410 4742 / 0.0250 29275 / 0.0258 7327 / 0.0139
No. of obsd. rflns. [I>2σ (I)] 17952 2828 28903 6929
No. of data / restraints / params 19291 / 455 / 560 4742 / 15 / 349 29275 / 0 / 308 7327 / 0 / 253
R1/wR2 [I>2σ(I)]a) R1 = 0.0572, wR2 = 0.1371 R1 = 0.0291, wR2 = 0.0406 R1 = 0.0391, wR2 = 0.1064 R1 = 0.0352, wR2 = 0.0924
R1/wR2 (all data)a) R1 = 0.0615, wR2 = 0.1387 R1 = 0.0653, wR2 = 0.0454 R1 = 0.0402, wR2 = 0.1075 R1 = 0.0372, wR2 = 0.0934
GOF (on F2)a) 1.194 0.787 1.036 1.255
Largest diff. peak and hole (e Å-3)a) 4.518 and -6.799 0.746 and -0.567 3.138 and -3.748 4.705 and -6.688
Open in a new tab
a)

Because of the very large θ angle, and as often observed for gold complexes, there are large electronic residuals close to gold in complexes 1a, 2d and 2e.

Acknowledgement

We are grateful to Vincent Lavallo for helpful assistance. We thank the NIH (R01 GM 68825) and RHODIA Inc. for financial support, the Alexander von Humboldt Foundation and the Higher Education Commission of Pakistan for a Fellowship to G.D.F. and S.K., respectively.

Footnotes

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