Gold(I) Complexes of Conformationally Constricted Chiral Ferrocenyl

Simon A. Herbert , Dominic C. Castell , Jonathan Clayden , and Gareth E. Arnott. Organic Letters 2013 15 (13), 3334-3337. Abstract | Full Text HTML | ...
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Gold(I) Complexes of Conformationally Constricted Chiral Ferrocenyl Phosphines Elena M. Barreiro,† Diego F. D. Broggini,‡ Luis A. Adrio,† Andrew J. P. White,† Rino Schwenk,‡ Antonio Togni,*,‡ and King Kuok (Mimi) Hii*,† †

Department of Chemistry, Imperial College London, Exhibition Road, South Kensington, London SW7 2AZ, U.K. Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, ETH Zürich, CH-8093, Zürich, Switzerland

‡

S Supporting Information *

ABSTRACT: The preparation of two new chiral, enantiopure, and conformationally constrained phosphocin and 1,5-diphosphocin, incorporating two ferrocenyl units, is described. The gold(I) chloride complexes of these ligands and (S)-(R)-PPFOMe were prepared, and their structures, in solution and solid states, are compared. Abstraction of the chloride anion by the addition of silver salt of either toluenesulfonate or chiral BINOLphosphates generates active catalysts for the intramolecular cyclization of 6-methyl-1,1-diphenylhepta-4,5-dien-1-ol, where up to 47% ee can be obtained. Match and mismatch effects between chiral ligands and counteranions are highlighted.

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INTRODUCTION Chiral ferrocenylphosphine ligands were first described by Kumada and Hayashi in 1974.1,2 Boosted by their commercial availability,3 they have been extensively studied in asymmetric reactions4−8 and many industrial processes,9 resulting in the production of the herbicide (S)-metolachlor, the largest commercial application of asymmetric catalysis.10 On the other hand, the development of gold catalysis for stereoselective organic synthesis is a highly topical area of research in recent years, particularly for the activation of unsaturated carbon−carbon bonds toward C−C and C−X bond formations.11,12 Early work by Hayashi and Togni included the application of ferrocenylphosphine−gold(I) complexes to aldol reactions of isocyanoalkanoates with aldehydes to afford oxazolines in high enantioselectivities.13−15 Since then, they have also been used in C−C bond-forming processes, such as the addition of isocyanoacetates to N-sulfonylimines,16 alkoxycyclization of enynes,17 and cyclodimerization of dialkynes.18 However, more recent reports of enantioselective gold catalysis are dominated by the use of chiral diphosphine ligands, while the use of nonchelating ligands for asymmetric catalysis is restricted to sterically bulky NHCs 19 and phosphoramidites.20−22 In this paper, we will report the coordination chemistry of three structurally similar chiral ferrocenylphosphines, L1, L2, and L3, to gold (Figure 1). The resultant complexes will be evaluated in the intramolecular cyclization of a γ-allenol (6-methyl-1,1-diphenylhepta-4,5-dien1-ol, 6).

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Figure 1. Chiral mono- and diphosphine ligands used in this work. synthetic and recrystallization purposes were distilled under Ar (THF from Na/benzophenone; CH2Cl2, MeOH, EtOH, and acetonitrile from CaH2; pentane, hexane, toluene, and Et2O from Na/K) at ETH Zürich, or by passing through solvent purification towers under N2 over molecular sieves (Imperial College London). 31 P, 13C, and 1H NMR spectra were measured in the stated solvent using the following instruments: ETH Zürich: Bruker Avance 250 [frequency in MHz: 31P, 101.26; 13C, 62.90; 1H, 250.14] or Bruker Avance 300 [frequency in MHz: 31P, 121.49; 13C, 75.47; 1H, 300.13] or Bruker Avance 400 [frequency in MHz: 31P, 161.98; 13C, 100.61; 1 H, 400.13] or Bruker Avance DPX500 [frequency in MHz: 31P, 202.46; 13C, 125.75; 1H, 500.23] at room temperature. Imperial College London: Bruker AVANCE 400 [frequency in MHz: 31P, 161.9; 13C, 100.6; 1H, 400.3]. Chemical shifts are reported in δ (parts per million), referenced to TMS for 1H/13C, and 85% H3PO4 for 31P. J values are given in hertz. Multiplicity is abbreviated to s (singlet), d (doublet), dd (double doublet), t (triplet), q (quartet), dq (double quartet), tq (triple quartet), and m (multiplet). Melting points were recorded using an Electrothermal Gallenhamp apparatus and were uncorrected. Chiral HPLC was performed on Gilson and HewlettPackard HPLC systems, each equipped with a variable-wavelength UV detector set at 210 nm and autoinjectors with 10 μL loops, using a

EXPERIMENTAL SECTION

General Procedures. All reactions with air- or moisture-sensitive materials were carried out under Ar or N2 using standard Schlenk techniques or in a glovebox (under N2). The solvents used for © 2012 American Chemical Society

Received: March 19, 2012 Published: May 2, 2012 3745

dx.doi.org/10.1021/om300222k | Organometallics 2012, 31, 3745−3754

Organometallics

Article

Daicel Chiralcel OJ-H column (250 × 4.6 mm). Mass spectra (MS) were recorded on either a Micromass Autospec Premier or a VG Platform II spectrometer using EI or FAB+ techniques. Elemental analyses were carried out by the Science Technical Support Unit at London Metropolitan University. Crystal structure determination of L2-BH3 and L3 was performed at ETH, while those of the gold complexes were carried out at Imperial College London. Unless otherwise stated, all chemical reagents and precursors were procured from commercial sources and used without purification. (S)(R)-PPF-OMe (L1) was obtained as a gift to the Hii research group by Sigma-Aldrich, while (R)-(+)-[1-(dimethylamino)ethyl]ferrocene (4) was provided by SOLVIAS AG to the Togni group and was recrystallized with tartaric acid according to the reported literature procedure.23 6-Methyl-1,1-diphenylhepta-4,5-dien-1-ol (6) was synthesized by the literature procedure.24 Preparation of L2 and L3. 1,1″-Carbonyl-bis[(2S)-2-[(1R)-1(dimethylamino)ethyl]ferrocene], 2. A solution of n-BuLi (1.53 M in hexane, 9.7 mL, 14.9 mmol) was added at −78 °C to a solution of 1bromo-(S)-2-[(R)-1-(dimethylamino)ethyl]ferrocene 1 (5 g, 14.9 mmol) in THF (200 mL). After stirring for 2 h, diethyl carbonate (0.91 mL, 7.4 mmol) was added. After warming to r.t. overnight, the solution was treated with TBME (200 mL). The organic layer was washed with saturated NaHCO3 (2 × 200 mL) and brine (2 × 200 mL) and dried (MgSO4). Evaporation of the solvent yielded a crude product that was purified by flash chromatography (hexane/EtOAc, 5/ 1 to 1/1 containing 2% NEt3) and recrystallization from CH2Cl2/ hexane: 2.87 g (71%). Red crystals. δH (250 MHz, CDCl3): 4.74 (2H, q, J = 7.0, CHMe), 4.56 (2H, dd, J = 2.6, 1.5, CHCp), 4.42 (2H, dd, J = 2.6, 1.3, CHCp), 4.28 (2H, t, J = 2.6, CHCp), 4.12 (10H, s, Cp), 2.13 (12H, s, NMe2), 1.50 (6H, d, J = 6.8, CHMe). δC (62.9 MHz, CD2Cl2): 203.6 (CO), 93.7 (CCp), 80.4 (CCp), 70.7 (Cp), 70.5 (CCp), 70.1(CCp), 67.7(CCp), 54.5 (CHMe), 40.4 (NMe2), 13.9 (CHMe). m/z (HR-MALDI): 453.1 ([MH+ − 2NMe2], 100%). Anal. Calcd. for C29H38N2OFe2: C, 64.47; H, 6.72; N, 5.18. Found: C, 64.42; H, 6.83; N, 5.12%. 2,2″-Methylenebis[(1R)-1-[(1R)-1-(dimethylamino)ethyl]ferrocene], 3. A solution of 2 (2.5 g, 4.63 mmol) in THF (80 mL) was slowly added to a suspension of LiAlH4 (0.70 g, 18.5 mmol) in THF (200 mL). After stirring for 1 h at r.t., AlCl3 (2.46 g, 18.5 mmol) was added and the mixture was stirred for an additional 2 h. The solution was treated with sat. aq NaHCO3 (200 mL), and the aqueous layer was extracted with Et2O (3 × 150 mL). The combined organic layers were washed with saturated NaHCO3 (2 × 200 mL) and brine (2 × 200 mL) and dried (MgSO4). Evaporation of the solvent yielded a crude product that was purified by recrystallization from CH2Cl2/ hexane: 1.92 g (79%). Orange crystals. δH (250 MHz, CDCl3): 4.38 (2H, m, CHCp), 4.01 (10H, s, Cp), 4.01 (2H, m, CHCp), 4.00 (2H, q, J = 7.0, CHMe), 3.93 (2H, t, J = 2.2, CHCp), 3.57 (2H, m, CH2), 2.24 (12H, s, NMe2), 1.34 (6H, d, J = 7.0, CHMe). δC (62.9 MHz, CD2Cl2): 89.4 (CCp), 89.3 (CCp), 69.2 (Cp), 69.2 (CHCp), 65.6 (CHCp), 65.3 (CHCp), 56.3 (CHMe), 39.5 (NMe2), 25.5 (CH2), 8.3 (CHMe). m/z (HR-MALDI): 437.1 ([M+ − NMe2 − HNMe2], 100%). Anal. Calcd.. for C29H38N2Fe2: C, 66.18; H, 7.28; N, 5.32. Found: C, 66.02; H, 7.36; N, 5.15%. (2R,3R,7R,8R)-2,8-Dimethyl-1-cyclohexyl-diferroceno-[c,f ]-phosphocin, L2. The aminophosphine 3 (1.82 g, 3.46 mmol) was dissolved in degassed glacial acetic acid (30 mL), to which a solution of cyclohexylphosphine (0.471 M in acetic acid, 7.7 mL, 3.63 mmol) was added, and the mixture was stirred at 75 °C until no starting material was detected (31P NMR; 3 h). Evaporation of the solvent yielded a crude product that was purified by flash chromatography (hexane/ Et2O, 1:1) and recrystallization from hexane: 1.16 g (61%). Orange powder. δH (250 MHz, toluene-d8): δ 4.16 (1H, m, CHCp), 3.99 (5H, s, Cp), 3.99 (1H, m, CHCp), 3.97 (5H, s, Cp), 3.97 (1H, m, CHCp), 3.94 (1H, m, CHCp), 3.90 (1H, t, J = 2.4, CHCp), 3.67 (1H, m, CHCp), 3.46 (2H, AB spin system, CH2), 2.72 (1H, quintet, J = 7.0, CHMe), 2.23 (1H, q, J = 7.7, CHMe), 1.85 (1H, m, Cy), 1.68 (2H, m, Cy), 1.60 (1H, m, Cy), 1.56 (3H, dd, JHP = 17.6, J = 7.0, CHMe), 1.45 (1H, m, Cy), 1.33 (3H, dd, JHP = 18.4, J = 7.7, CHMe), 1.28 (1H, m, Cy), 1.20 (1H, m, Cy), 1.16 (1H, m, Cy), 1.16 (3H, m, Cy). δC (62.9 MHz,

toluene-d8): 94.5 (d, JCP = 5.0, CCp), 89.8 (d, JCP = 6.9, CCp), 84.1 (s, CCp), 82.5 (s, CCp), 69.1 (s, Cp), 69.1 (s, CHCp), 68.8 (s, Cp), 67.7 (s, CHCp), 65.9 (s, CHCp), 65.5 (s, CHCp), 65.0 (s, CHCp), 64.7 (d, JCP = 2.5, CHCp), 34.6 (d, JCP = 22.2, CHCy), 32.8 (d, JCP = 22.2, CH2Cy), 29.4 (d, JCP = 5.2, CH2(Cy)), 29.4 (s, CH2), 28.8 (d, JCP = 23.2, CHMe), 27.3 (s, CH2(Cy)), 27.2 (d, JCP = 17.1, CH2(Cy)), 26.4 (s, CH2(Cy)), 26.1 (d, JCP = 19.4, CHMe), 20.4 (d, JCP = 23.8, CHMe), 19.3 (d, JCP = 29.7, CHMe). δP (101.26 MHz, toluene-d8): 39.1. m/z (HR-MALDI): 552.132 ([M+], 100%). Anal. Calcd. for C31H37PFe2: C, 67.42; H, 6.75; P, 5.61. Found: C, 67.33; H, 6.56; P, 5.63%. (2R,3R,7R,8R)-2,8-Dimethyl-1-cyclohexyl-diferroceno-[c,f ]-phosphocin-κP-borane, L2-BH3. To a solution of 100 mg (0.18 mmol) of L2 in 5 mL of THF, BH3·SMe2 was added dropwise (51 μL, 41 mg, 0.47 mmol). After stirring overnight at r.t., the solvent was evaporated, yielding a crude product that was purified by recrystallization from hexane (90 mg, 88%). Orange powder. δH (250 MHz, toluene-d8): 4.33 (1H, m, CHCp), 4.12 (1H, m, CHCp), 4.05 (5H, s, Cp), 4.04 (1H, t, J = 2.3, CHCp), 3.99 (5H, s, Cp), 3.97 (1H, m, CHCp), 3.93 (1H, m, CHCp), 3.69 (1H, t, J = 2.4, CHCp), 3.42 (2H, AB spin system, CH2), 3.92 (1H, dq, JHP = 14.3, 7.2, CHMe), 2.51 (1H, dq, JHP = 9.5, 7.7, CHMe), 2.12 (1H, m, Cy), 2.00−0.80 (13H, m, Cy and BH3), 1.77 (3H, dd, JHP = 14.7, 7.2, CHMe,), 1.33 (3H, dd, JHP = 15.0, 7.7, CHMe). δC (62.90 MHz, CDCl3): 69.5 (s, Cp), 69.1 (s, Cp), 69.0 (s, CHCp), 68.2 (s, CHCp), 66.9 (s, CHCp), 66.5 (s, CHCp), 66.4 (s, CHCp), 66.2 (s, CHCp), 32.2 (d, JCP = 24.3, CαHCy), 29.3 (s, CH2(Cy)), 28.6 (s, CH2(Cy)), 28.0 (d, JCP = 3.1, CH2(Cy)), 27.9 (d, JCP = 27.0, CHMe), 27.3 (d, JCP = 4.6, CH2(Cy)), 27.1 (d, JCP = 1.9, CH2(Cy)), 26.0 (s, CH2(Cy)), 24.1 (d, JCP = 26.6, CHMe), 16.8 (d, JCP = 4.2, CHMe), 16.1 (d, JCP = 3.8, CHMe). δP (101 MHz, CDCl3): 47.1 (br s, w1/2 = 125 Hz). Anal. Calcd. for C31H40BPFe2: C, 65.77; H, 7.12; P, 5.47. Found: C, 65.49; H, 7.28; P, 5.38%. Crystal Data for L2-BH3: C31H40BFe2P, M = 566.11, orthorhombic, P212121 (No. 19), a = 12.9833(2) Å, b = 18.9236(3) Å, c = 22.7786(2) Å, V = 5596.49(13) Å3, Z = 8, Dc = 1.344 g cm−3, μ(Mo Kα) = 1.112 mm−1, T = 293 K, red plates, Siemens SMART Platform; 13 297 independent measured reflections (Rint = 0.0374), F2 refinement, R1(obs) = 0.0401, wR2(all) = 0.0779, 10 548 independent observed absorption-corrected reflections [|Fo| > 3σ(|Fo|), 2θmax = 56°], 637 parameters. The absolute structure of L2-BH3 was determined by use of the Flack parameter [x+ = 0.038(10)]. CCDC 875937. 1,1″-(Phenylphosphinidene)bis[(2S)-2-[(1R)-1-(dimethylamino)ethyl]]ferrocene, 5. A solution of t-BuLi (1.55 M in pentane, 5.46 mL, 8.46 mmol) was added at −78 °C to a solution of R-(+)-[1(dimethylamino)ethyl]ferrocene 4 (2.16 g, 8.38 mmol) in Et2O (20 mL). After stirring for 30 min, the reaction mixture was warmed to r.t. and stirred for a further hour. The mixture was then cooled to −78 °C, and the dichlorophenylphosphine (0.57 mL, 0.75 g, 4.2 mmol) was added. After warming to r.t. overnight, the solution was treated with H2O. The organic layer was washed with H2O (3×) and brine (3×) and dried (MgSO4). Evaporation of the solvent afforded an orange oil, which was purified by flash chromatography on silica (Et2O/hexane, 2/1, containing 1% Et3N): 1.63 g (63%). δH (250 MHz, CDCl3): δ 7.70−7.66 (m, 2H, Ph), 7.29−7.21 (3H, m, Ph), 4.54 (1H, m, CHCp), 4.46 (1H, m, CHCp), 4.37 (1H, m, CHCp), 4.36 (1H, m, CHCp), 4.22 (1H, m, CHCp), 4.21 (1H, m, CHCp), 4.29 (1H, dq, J = 4.2, 6.8, CHMe), 3.98 (5H, s, Cp), 3.98 (1H, m, CHMe), 3.58 (5H, s, Cp), 2.31 (6H, s, NMe2), 1.66 (6H, s, NMe2), 1.48 (3H, d, J = 6.8, CHMe), 1.26 (3H, d, J = 6.8, CHMe). δP (101.26 MHz, CDCl3): −45.6 (s). (2S,4R,6R,8S)-4,6-Dimethyl-5-cyclohexyl-1-phenyl-diferroceno[b,g][1,5]diphosphocin, L3. The aminophosphine 4 (0.82 g, 1.32 mmol) was dissolved in degassed glacial acetic acid (12 mL). Cyclohexylphosphine was added as a solution (0.365 M in glacial acetic acid, 3.6 mL, 1.32 mmol), and the reaction mixture was stirred at 70 °C, until no starting material was detectable in the reaction aliquot (31P NMR). Evaporation of the solvent yielded a crude product that was purified by flash chromatography (hexane/Et2O, 1/1) and recrystallization from MeOH/hexane/CH2Cl2: 567 mg (66%). δH (500 MHz, toluene-d8): 7.85 (2H, m, Ph), 7.20 (2H, m, Ph), 7.08 (1H, m, Ph), 4.62 (1H, m, CHCp), 4.24 (1H, m, CHCp), 4.21 (1H, m, CHCp), 4.09 (1H, m, CHCp), 4.08 (5H, s, Cp), 4.05 (1H, m, CHCp), 3746

dx.doi.org/10.1021/om300222k | Organometallics 2012, 31, 3745−3754

Organometallics

Article

JCP = 28.8, Cy), 29.5 (d, JCP = 27.0, Cy), 27.1 (d, JCP = 13.1, CHMe), 26.9 (d, JCP = 7.9, CHMe), 26.6 (CH2), 25.8 (Cy), 20.8 (d, JCP = 9.2, CHMe), 20.1 (d, JCP = 8.3, CHMe). δP (CDCl3): 70.9. m/z (FAB): 784 (M+, 75%), 749 ([M − Cl]+, 40), 154 (100). Anal. Calcd. for C31H37AuPFe2Cl: C, 47.42; H, 4.72. Found: C, 47.30; H, 4.71%. Crystal Data for (L2)AuCl: C31H37AuClFe2P, M = 784.69, orthorhombic, P2121 21 (No. 19), a = 7.21077(17) Å, b = 18.2833(4) Å, c = 20.8090(5) Å, V = 2743.39(11) Å3, Z = 4, Dc = 1.900 g cm−3, μ(Mo Kα) = 6.554 mm−1, T = 173 K, yellow prisms, Oxford Diffraction Xcalibur 3 diffractometer; 6252 independent measured reflections (Rint = 0.0365), F2 refinement, R1(obs) = 0.0231, wR2(all) = 0.0332, 5755 independent observed absorptioncorrected reflections [|Fo| > 4σ(|Fo|), 2θmax = 58°], 325 parameters. The absolute structure of (L2)AuCl was determined by a combination of R-factor tests [R1+ = 0.0231, R1− = 0.0705] and by use of the Flack parameter [x+ = 0.000(3)]. CCDC 875940. (L3)Au2Cl2 was obtained from L3, as orange crystals (92%). mp 215 °C (dec.). δH (CDCl3): 7.77−7.59 (2H, m, Ph), 7.57−7.39 (3H, m, Ph), 5.26−5.09 (1H, m, CHCp), 4.83 (1H, dd, J = 4.6, 2.3 Hz, CHCp), 4.68−4.66 (1H, m, CHCp), 4.66−4.64 (1H, m, CHCp), 4.64− 4.62 (1H, m, CHCp), 4.49−4.46 (1H, m, CHCp), 4.34 (5H, s, Cp), 4.32 (5H, s, Cp), 2.69 (1H, dq, JHP = 13.7, J = 6.9, CHMe), 2.13 (1H, dq, JHP = 15.5, J = 7.8, CHMe), 1.92−185 (1H, m, Cy), 1.85−1.75 (2H, m, Cy), 1.71 (3H, dd, JHP = 19.0, J = 7.8, CHMe), 1.60−1.44 (2H, m, Cy), 1.34 (3H, dd, JHP = 19.4, J = 6.9, CHMe), 1.27−1.20 (3H, m, Cy), 1.20−1.09 (3H, m, Cy). δC (CDCl3): 133.8 (Ph), 133.4 (d, JCP = 13.9, Ph), 131.7 (Ph), 128.4 (d, JCP = 11.9, Ph), 94.1 (d, JCP = 4.1, CCp), 90.8 (CCp), 78.1 (d, JCP = 27.6, CCp), 77.2 (CCp), 75.3 (d, JCP = 21.3, CCp), 72.0 (Cp), 71.9 (CCp), 71.6 (d, JCP = 12.0, CCp), 70.7 (Cp), 70.6 (d, JCP = 6.1, CCp), 68.8 (CCp), 68.1 (CCp), 35.0 (d, JCP = 26.0, Cy), 32.8 (Cy), 31.0 (d, JCP = 26.6, CHMe), 28.3 (Cy), 26.6 (d, JCP = 10.7, Cy), 26.35 (d, JCP = 17.2, CHMe), 26.15 (d, JCP = 3.6, Cy), 25.23 (Cy), 23.10 (d, JCP = 10.0, CHMe), 22.08 (d, JCP = 9.2, CHMe). δP (CDCl3): 70.1, 24.4. m/z (FAB): 1110 ([M]+, 50%), 1075 ([M − Cl]+, 60), 154 (100). Anal. Calcd. for C36H40Au2P2Fe2Cl2: C, 38.91; H, 3.63. Found: C, 38.81; H, 3.64%. Crystal Data for (L3)Au2Cl2: C36H40Au2Cl2Fe2P2·0.5(CHCl3), M = 1170.84, monoclinic, P21 (No. 4), a = 11.9744(4) Å, b = 8.9423(3) Å, c = 18.3431(5) Å, β = 96.613(3)°, V = 1951.09(11) Å3, Z = 2, Dc = 1.993 g cm−3, μ(Mo Kα) = 8.571 mm−1, T = 173 K, orange blocky needles, Oxford Diffraction Xcalibur 3 diffractometer; 10 484 independent measured reflections (Rint = 0.0486), F2 refinement, R1(obs) = 0.0434, wR2(all) = 0.1101, 8310 independent observed absorption-corrected reflections [|Fo| > 4σ(|Fo|), 2θmax = 65°], 433 parameters. The absolute structure of (L3)Au2Cl2 was determined by a combination of R-factor tests [R1+ = 0.0434, R1− = 0.0694] and by use of the Flack parameter [x+ = 0.000(8), x− = 1.014(8)]. CCDC 875941. Synthesis of AgOTs. Ag2CO3 (0.5 equiv) was added in one portion to a solution of p-toluenesulfonic acid (1 equiv) in EtOH (5 mL). The resulting mixture was protected from light and stirred vigorously overnight. The mixture was filtered and concentrated under vacuum, to give AgOTs was as a white solid (98%). mp 220 °C (dec.). δH (DMSO-d6): 7.48 (2H, d, J = 8.0, tol), 7.12 (2H, d, J = 8.0, tol), 2.28 (3H, s, CH3). δC (DMSO-d6): 145.4, 138.0, 128.3, 125.6, 20.9. m/ z (FAB) 279 ([M]+, 2%), 260 (21), 154 (100), 136 (72), 107 (43). Anal. Calcd. for C7H7AgO3S: C, 30.13; H, 2.53. Found: C, 30.05; H, 2.55%. (S)-P*Ag was similarly prepared from Ag2CO3 and (S)-(+)-1,1′binaphthyl-2,2′-diyl hydrogen phosphate, as a white solid (87%). mp > 261 °C (dec.). δH (DMSO-d6): 8.07 (d, J = 8.8, 2H), 8.04 (d, J = 8.1, 2H), 7.45 (t, J = 7.9, 4H), 7.36−727 (m, 2H), 7.22 (d, J = 8.5, 2H). δC (DMSO-d6): 149.9 (d, JCP = 8.9), 132.0, 130.5, 130.0, 128.5, 126.2, 126.1, 124.6, 122.6, 121.7. δP (DMSO-d6): +5.1. m/z (FAB): 1019 ([M + Ag2]+, 12%), 911 ([M2]+, 16), 563 ([M + Ag]+, 65), 455 ([M]+, 100), 349 ([MH − Ag]+, 46), 268 (50). Anal. Calcd. for C20H12AgO4P: C, 52.74; H, 2.62. Found: C, 52.59; H, 2.61%. (R)-P*Ag was similarly prepared from Ag2CO3 and (R)-(-)-1,1′binaphthyl-2,2′-diyl hydrogen phosphate, as a white solid (90%). mp > 261 °C (dec.). δH (DMSO-d6): 8.08 (d, J = 8.8, 2H), 8.04 (d, J = 8.1, 2H), 7.46 (t, J = 7.5, 4H), 7.38−7.27 (m, 2H), 7.22 (d, J = 8.5, 2H). δC

4.01 (5H, s, Cp), 3.87 (1H, m, CHCp), 2.84 (1H, dq, JHP = 6.9, J = 6.8, CHMe), 2.06 (1H, q, JHP = 7.8, CHMe), 1.84 (1H, m, Cy), 1.75 (2H, m, Cy), 1.67 (1H, m, Cy), 1.45 (1H, m, Cy), 1.45 (3H, dd, JHP = 18.4, J = 7.8, CHMe), 1.34 (1H, m, Cy), 1.33 (1H, m, Cy), 1.28 (3H, dd, JHP = 17.1, J = 6.8, CHMe), 1.23 (3H, m, Cy), 1.19 (1H, m, Cy). δC (125.75 MHz, toluene-d8): 135.9 (d, JCP = 25.9, Ph), 134.2 (d, JCP = 20.6, Ph), 128.1 (s, Ph), 127.6 (d, JCP = 6.4, Ph), 99.9 (dd, JCP = 8.4, 6.4, C2b), 94.1 (dd, JCP = 7.5, 5.5, C2a), 77.3 (d, JCP = 53.0, C5b), 75.0 (d, JCP = 30.4, C5a), 74.0 (dd, JCP = 21.0, JCP = 0.9, C1b), 72.5 (d, JCP = 4.1, C1a), 70.7 (s, Cp), 69.6 (s, Cp), 69.4 (d, JCP = 12.1, C4b), 69.1 (d, JCP = 7.8, C4a), 68.5 (m, C3a), 67.7 (d, JCP = 4.6, C3b), 34.4 (d, JCP = 22.6, Cy), 33.4 (d, JCP = 22.6, Cy), 29.6 (d, JCP = 24.0, CHMe), 29.5 (d, JCP = 4.6, Cy), 27.9 (d, JCP = 4.8, Cy), 27.6 (d, JCP = 13.3, Cy), 26.8 (d, JCP = 0.9, Cy), 25.0 (d, JCP = 18.3, CHMe), 21.5 (d, JCP = 20.8, CHMe), 21.1 (d, JCP = 23.1, CHMe). δP (202.46 MHz, toluene-d8): 39.5, −19.1. Anal. Calcd. for C36H40P2Fe2: C, 66.89; H, 6.23. Found: C, 66.64; H, 6.42%. Crystal Data for L3: C36H40Fe2P, M = 646.32, monoclinic, P21 (No. 4), a = 8.8418(2) Å, b = 10.4886(3) Å, c = 16.5551(4) Å, V = 1529.73(7) Å3, Z = 2, Dc = 1.403 g cm−3, μ(Mo Kα) = 1.077 mm−1, T = 293 K, red cubes, Siemens SMART Platform; 5501 independent measured reflections (Rint = 0.0316), F2 refinement, R1(obs) = 0.0365, wR2(all) = 0.0931, 4582 independent observed absorption-corrected reflections [|Fo| > 3σ(|Fo|), 2θmax = 53°], 363 parameters. The absolute structure of L3 was determined by use of the Flack parameter [x+ = −0.030(15)]. CCDC 875938. General Procedure for the Synthesis of Gold(I)−Chloride Complexes. Thiodiglycol (3 equiv) was added dropwise to an icecold solution of NaAuCl4·H2O (1 equiv) in water. When the orange solution turned to transparent, a solution of the appropriate phosphine (1 equiv for L1 and L2, 0.5 equiv for L3) in CHCl3 was added and the mixture was allowed to stir for 3 h. The organic layer was separated, dried over MgSO4, and filtered. Ethanol was added, and the mixture was put it into the freezer (−20 °C), whereupon the requisite gold complex crystallizes. (L1)AuCl was obtained from (S)-(R)-PPF-OMe, as orange crystals (95%). mp 123−125 °C. δH (CDCl3): 7.77−7.35 (10H, m, Ph), 5.27 (1H, q, J = 6.3, CHMe), 4.69−4.66 (1H, m, CHCp), 4.40 (1H, t, J = 2.4, CHCp), 4.24 (5H, s, Cp), 3.80 (1H, dd, J = 3.8, 2.4, CHCp), 2.91 (3H, s, OMe), 1.54 (3H, d, J = 6.3, CHMe). δC (CDCl3): 135.1 (d, JCP = 14.0, Ph), 133.5(d, JCP = 14.0, Ph), 132.1 (Ph), 131.7 (Ph), 131.4 (d, JCP = 2.3, Ph), 131.0 (Ph), 129.0 (d, JCP = 11.8, Ph), 128.6 (d, JCP = 12.1, Ph), 93.8 (d, JCP = 8.1, CH), 74.3 (d, JCP = 6.0, CCp), 74.0 (d, JCP = 3.1, CCp), 71.3 (d, JCP = 7.1, CCp), 71.1 (Cp), 70.2 (d, JCP = 7.5, CCp), 69.4 (Cp), 55.7 (OMe), 17.0 (CHMe). δP (CDCl3): +24.6. m/z (FAB): 661 (M+, 62%), 473 (57), 154 (100). Anal. Calcd. for C25H25AuOPFeCl: C, 45.36; H, 3.78. Found: C, 45.32; H, 3.81%. Crystal Data for (L1)AuCl: C25H25AuClFeOP, M = 660.69, orthorhombic, P21 2121 (No. 19), a = 11.18245(8) Å, b = 12.26925(8) Å, c = 17.17066(11) Å, V = 2355.82(3) Å3, Z = 4, Dc = 1.863 g cm−3, μ(Cu Kα) = 18.268 mm−1, T = 173 K, yellow plates, Oxford Diffraction Xcalibur PX Ultra diffractometer; 4610 independent measured reflections (Rint = 0.0324), F2 refinement, R1(obs) = 0.0183, wR2(all) = 0.0433, 4445 independent observed absorptioncorrected reflections [|Fo| > 4σ(|Fo|), 2θmax = 145°], 271 parameters. The absolute structure of (L1)AuCl was determined by a combination of R-factor tests [R1+ = 0.0183, R1− = 0.0476] and by use of the Flack parameter [x+ = 0.000(6), x− = 1.013(6)]. CCDC 875939. (L2)AuCl was obtained from L2, as orange crystals (89%). mp 160 °C (dec.). δH (CDCl3): 4.41−4.39 (1H, m, CHCp), 4.29 (1H, t, J = 2.5, CHCp), 4.25−4.22 (1H, m, CHCp), 4.15 (5H, s, Cp), 4.12−4.11 (1H, m, CHCp), 4.08 (1H, t, J = 2.5, CHCp), 4.04 (5H, s, Cp), 3.94−3.90 (1H, m, CHCp), 3.78 (1H, d, J = 16.6, CH2), 3.59 (1H, d, J = 16.6, CH2), 3.01 (1H, dq, JHP = 13.9, J = 6.9, CHMe), 2.48 (1H, dq, JHP = 15.1, J = 7.6, CHMe), 2.02−1.95 (1H, m, Cy), 1.69 (3H, dd, JHP = 19.1, J = 6.9, CHMe), 1.54 (3H, dd, JHP = 18.9, J = 7.6, CHMe), 1.54− 1.53 (4H, m, Cy), 1.30−1.11 (6H, m, Cy). δC (CDCl3): 89.9 (CCp), 85.5 (CCp), 85.0 (CCp), 82.4 (CCp), 69.9 (CCp), 69.8 (Cp), 69.4 (Cp), 68.9 (CCp), 67.3 (CCp), 67.0 (CCp), 66.4 (CCp), 61.3 (d, JCP = 8.8, CCp), 35.3 (Cy), 34.5 (d, JCP = 25.7, Cy), 33.5 (d, J = 2.4, Cy), 30.9 (d, 3747

dx.doi.org/10.1021/om300222k | Organometallics 2012, 31, 3745−3754

Organometallics

Article

Scheme 1. Preparation of Enantiopure Chiral Ferrocenyl Phosphines L2 and L3

Figure 2. 31P NMR spectra of L3 to gold (collected in CDCl3). (A) M/L ratio = 0; (B) M/L ratio = 2; (C) M/L ratio = 1, after 10 min; (D) M/L ratio = 1, after 1 h. (DMSO-d6): 149.8 (d, JCP = 8.4), 132.3, 131.0, 130.6, 128.9, 126.7, 126.5, 125.2, 122.7, 122.0. δP (DMSO-d6): +4.5. m/z (FAB): 1019 ([M + Ag2]+, 19%), 911 ([M2]+, 18), 563 ([M + Ag]+, 98), 455 ([M]+, 90), 349 ([MH − Ag]+, 78), 154 (100). Anal. Calcd. for C20H12AgO4P: C, 52.74; H, 2.64. Found: C, 52.93; H, 2.66%. Halide Abstraction. One equivalent of the requisite gold(I) chloride complex (L1)AuCl or (L2)AuCl was added to a solution of the silver salt AgOTs, (S)-P*Ag or (R)-P*Ag (1 equivalent) in CHCl3, and stirred for 12 h. The resultant suspension was centrifuged, and the decanted liquid was evaporated under vacuum to yield the required complex. Cationic complexes of (L3)Au2Cl2 were not isolated, but generated in situ, by mixing the gold complex with the corresponding silver complex, prior to catalytic reactions. (L1)AuOTs was obtained from AgOTs and (L1)AuCl, as an orange powder (98%). mp 70−72 °C. δH (CDCl3): 7.93 (2H, d, J = 8.2, Tol), 7.73−7.35 (10H, m, Ph), 7.25 (2H, d, J = 8.2, Tol), 5.31 (1H, q, J = 6.2, CH), 4.71−4.68 (1H, m, CHCp), 4.41−4.38 (1H, m, CHCp), 4.27 (5H, s, Cp), 3.78 (1H, dd, J = 3.7, 2.5, CHCp), 2.88 (3H, s, OMe), 2.39 (3H, s, Me), 1.55 (3H, d, J = 6.2, CHMe). δP (CDCl3): 19.4. m/z (FAB): 796 ([M]+, 10%), 746 (65), 473 (100). Anal. Calcd. for C32H32AuPFeO4S: C, 48.30; H, 4.03. Found: C, 48.28; H, 4.05%.

(L1)Au[(S)-P*] was obtained from (S)-P*Ag and (L1)AuCl, as an orange powder (99%). mp 123−125 °C. δH (CDCl3): 8.02−7.33 (22H, m, Ph), 5.24 (1H, q, J = 6.3, CH), 4.61−4.59 (1H, m, CHCp), 4.32−4.28 (1H, m, CHCp), 4.02 (5H, s, Cp), 3.65−3.61 (1H, m, CHCp), 2.90 (3H, s, OMe), 1.45 (3H, d, J = 6.3, Me). δP (CDCl3): 18.4, 8.8. m/z (FAB): 973 ([M]+, 8%), 746 (22), 593 (33), 473 (100). Anal. Calcd. for C45H37AuP2FeO5: C, 55.50; H, 3.80. Found: C, 55.69; H, 3.82%. (L1)Au[(R)-P*] was obtained from (R)-P*Ag and (L1)AuCl, as an orange powder (95%). mp 125−127 °C. δH (CDCl3): 7.88−7.35 (22H, m, Ph), 5.08 (1H, q, J = 6.2, CHMe), 4.62−4.58 (1H, m, CHCp), 4.37−4.32 (1H, m, CHCp), 4.21 (5H, s, Cp), 3.74−3.69 (1H, m, CHCp), 2.63 (3H, s, OMe), 1.33 (3H, d, J = 6.2, CHMe). δP (CDCl3): 18.5, 7.5. m/z (FAB): 746 (20), 625 (5) [M − C20H12PO4]+, 473 (60), 136 (68), 73 (100). Anal. Calcd. for C45H37AuP2FeO5: C, 55.50; H, 3.80%. Found: C, 55.45; H, 3.79%. (L2)AuOTs was obtained from AgOTs and (L2)AuCl, as a red solid (79%). mp 195 °C (dec.). δH (CDCl3): 7.78 (2H, d, J = 7.7, Tol), 7.19 (2H, d, J = 7.7, Tol), 4.70−4.66 (1H, m, CHCp), 4.44−4.39 (1H, m, CHCp), 4.34−4.30 (1H, m, CHCp), 4.22−4.20 (1H, m, CHCp), 4.20−4.18 (1H, m, CHCp), 4.17 (5H, s, Cp), 4.06 (5H, s, Cp), 3.96−3.91 (1H, m, CHCp), 3.75−3.69 (1H, m, CH2), 3.49−3.40 (1H, 3748

dx.doi.org/10.1021/om300222k | Organometallics 2012, 31, 3745−3754

Organometallics

Article

m, CH2), 3.05−2.87 (1H, m, CHMe), 2.62−2.42 (1H, m, CHMe), 2.37 (3H, s, Me), 1.78−1.72 (1H, m, Cy), 1.61−1.56 (3H, m, CHMe), 1.51 (3H, dd, JHP = 19.5, J = 7.7, CHMe), 1.30−1.06 (10H, m, Cy). δP (CDCl3): 68.6. m/z (FAB): 920 ([M]+, 3%), 749 ([M − C7H7SO3]+, 62), 627 (23), 315 (25), 154 (47), 55 ([Fe]+, 100). Anal. Calcd. for C38H44AuPFe2O3S: C, 49.59; H, 4.82. Found: C, 49.75; H, 4.80%. (L2)Au[(S)-P*] was obtained from (S)-P*Ag and (L2)AuCl, as a red solid (89%). mp 205 °C (dec.). δH (CDCl3): 8.11−7.39 (12H, m, Ph), 4.83 (1H, d, J = 20.2, CHCp), 4.70−4.66 (1H, m, CHCp), 4.43− 4.39 (1H, m, CHCp), 4.33−4.29 (1H, m, CHCp), 4.23−4.18 (5H, m, Cp), 4.09−4.06 (1H, m, CHCp), 4.03−3.97 (5H, m, Cp), 3.93−3.87 (1H, m, CHCp), 3.78−3.70 (1H, m, CH2), 3.51−3.38 (1H, m, CH2), 2.96−2.84 (1H, m, CHMe), 2.54−2.40 (1H, m, CHMe), 1.67−1.61 (1H, m, Cy), 1.60 (3H, dd, JHP = 13.4, J = 5.8, CHMe), 1.54−1.48 (3H, m, CHMe), 1.30−1.13 (10H, m, Cy). δP (CDCl3): 67.0, 8.1. m/z (FAB): 1096 ([M]+, 19%), 793 (85), 749 ([M − C20H12PO4]+, 27), 627(32), 55 ([Fe]+, 100). Anal. Calcd. for C51H49AuP2Fe2O4: C, 55.86; H, 4.50. Found: C, 55.69; H, 4.52%. (L2)Au[(R)-P*] was obtained from (R)-P*Ag and (L2)AuCl, as a red solid (92%). mp 207 °C (dec.). δH (CDCl3): 7.97−7.39 (12H, m, Ph), 4.84−4.80 (1H, m, CHCp), 4.46−4.42 (1H, m, CHCp), 4.28 (2H, t, J = 5.4, CHCp), 4.20 (5H, s, CHCp), 4.17−4.15 (1H, m, CHCp), 4.01 (5H, s, Cp), 3.95−3.90 (1H, m, CHCp), 3.79−3.72 (1H, m, CH2), 3.47−3.41 (1H, m, CH2), 2.85−2.76 (1H, m, CHMe), 2.31−2.19 (1H, m, CHMe), 1.70−1.65 (1H, m, Cy), 1.63−1.52 (3H, m, CHMe), 1.40 (3H, dd, JHP = 20.8, J = 7.0, CHMe), 1.30−1.07 (10H, m, Cy). δP (CDCl3): 66.6 (s), 8.6 (s). m/z (FAB): 1096 ([M]+, 3%), 793 (33), 749 ([M − C20H12PO4]+, 13), 627(48), 419 (73), 149 (95), 57 ([Fe]+, 100). Anal. Calcd. for C51H49AuP2Fe2O4: C, 55.86; H, 4.50. Found: C, 55.75; H, 4.53%. Typical Procedure for Catalytic Reactions. A screw-cap vial was charged with a magnetic stir bar and 6-methyl-1,1-diphenylhepta-4,5dien-1-ol (6), and toluene or DCE was added. The catalyst was added as a solid or in solution, and the vial was then left to stir in the dark. Conversions were monitored by TLC and/or NMR integration. Upon completion, the solvent was evaporated and the residue purified by column chromatography (hexanes/EtOAc, 9:1). 2-(2-Methylprop-1-en-1-yl)-4,4-diphenyltetrahydrofuran, 7: Obtained as a white solid. mp 51−52 °C. Rf = 0.83 (hexanes/EtOAc, 3:1). δH (CDCl3): 7.57−7.44 (4H, m), 7.32 (4H, m), 7.27−7.15 (2 H, m), 5.41 (1H, dq, J = 8.4, 1.2), 4.85 (1H, dd, J = 14.9, 8.4), 2.81−2.55 (2H, m), 2.17−2.01 (1H, m), 1.79 (3H, d, J = 0.8), 1.75 (3H, s), 1.65−1.76 (1H, m). δC (CDCl3) 147.3, 146.9, 135.5, 128.2, 128.0, 126.6, 126.5, 126.4, 126.0, 126.0, 87.9, 75.9, 39.4, 32.7, 25.9, 18.3. m/z (EI): 278 ([M]+, 15%), 222 (41), 180 (100). HPLC conditions: Chirapak OJ-H column, 0.5% IPA in n-hexane, 0.3 mL/min, tR (major) = 46.0 min, tR (minor) = 55.4 min. [α]25 D = +27.0° (47% ee, c = 1.0, CHCl3).

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Scheme 2. Coordination Behavior of Gold(I) to L3

Figure 3. Crystal structure of (L1)AuCl. H atoms are omitted for clarity.

BuLi, followed by the addition of diethyl carbonate, coupled two ferrocenyl fragments via a carbonyl linkage, which was reduced to a methylene group by using lithium aluminum hydride. Finally, the dimethylamino groups were sequentially substituted by cyclohexylphosphine, to form the eightmembered phosphocin L2, which was isolated and purified as its borane adduct (L2-BH3). For the synthesis of the 1,5diphosphocin L3, the chiral ferrocenyl units were coupled via a phosphine moiety, by the reaction of lithiated 4 with dichlorophenylphosphine, to afford 5 in 63% yield, followed by cyclization under acidic conditions with cyclohexylphosphine, to furnish L3 in 61% yield. Formation of Au(I) Complexes. The reaction of L1 and L2 with (thiodiglycol)AuCl, in a metal-to-ligand (M/L) ratio of 1:1, furnished the corresponding gold(I) chloride complexes (L1)AuCl and (L2)AuCl, respectively, while the reaction of the gold precursor with L3 in a 2:1 ratio afforded the bimetallic complex (L3)Au2Cl2. The different electronic environments of the two donor atoms in L3 correspond well with their equivalents in L1 and L2, reflected by their distinctive 31P NMR chemical shifts, observed at −20.5 and +39.4 ppm for PPh and P-Cy moieties, respectively (Figure 2, spectrum A). As

RESULTS AND DISCUSSION

Three enantiopure mono- and diphosphocins containing planar-chiral ferrocenyl units and stereogenic carbons were chosen for this work (Figure 1). (S)-(R)-PPF-OMe (L1) was first reported as a highly enantioselective ligand for nickelcatalyzed asymmetric cross-coupling by Hayashi et al., where up to 95% ee can be attained, a significant achievement that is rarely superseded.25,26 Since then, it has been utilized with moderate success in asymmetric hydrosilylation of 1,3-dienes,27 intramolecular cyclization of 1,5-dienes,28 alkylation of allenes by malonates,29 Rh-catalyzed C−H/olefin coupling,30,31 and Pd-catalyzed α-arylation of amides.32 Rather surprisingly, the coordination chemistry of this ligand to gold has never been reported. Synthesis of Diferrocenyl(di)phosphocins L2 and L3. In an earlier project,33 mono- and diphosphines L2 and L3 have been prepared from lithiated derivatives of N,N-dimethyl-(S)-1ferrocenylethylamine (Scheme 1). Halide exchange of 1 with n3749

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Figure 4. Crystal structures for L2-BH3, L3, (L2)AuCl, and (L3)Au2Cl2. H atoms are omitted for clarity.

chelation of the diphosphocin or the formation of a “head-totail” polymer (where Au is bound to P1 and P2 simultaneously) will be expected to give rise to AB coupling patterns, but these were not observed in the 31P NMR spectrum. Molecular Structures. Single crystals of suitable quality for X-ray crystallography were obtained for L2-BH3, L3, and also all three isolated gold(I) complexes, (L1)AuCl, (L2)AuCl, and (L3)Au2Cl2, allowing direct comparisons of their coordination environments. In all cases, the complexes consist of gold nuclei with essentially linear geometries, with a maximum distortion of up to 6.6°. None of these complexes display noticeable intermolecular Au···Au interactions, and the absolute stereochemistry of all five structures was unambiguously determined from the X-ray data, using a combination of R-factor tests and the Flack parameter. Interaction between oxygen and gold is not evident in the gold(I) complex of (S)-(R)-PPF-OMe, (L1)AuCl (Figure 3), the measured Au···O distance [3.705(3) Å] is longer than the

expected, their coordination to gold caused a downfield shift to +24.4 and +70.1 ppm (Figure 2, spectrum B). To investigate preferential binding of the donor atoms to gold, the precursor was mixed with L3 in a 1:1 M/L ratio. Within 10 min of mixing, the binding of the cyclohexylphosphine moiety to gold was clearly indicated by the appearance of the slightly broadened 31 P resonance signal at +70.1 ppm. However, only a broad resonance signal was observed at +24.4 ppm (Figure 2, spectrum C), which sharpened up slowly over an hour (Figure 2, spectrum D). During this time, two minor 31P resonance signals were also observed at +29.0 and +68.2 ppm. Given the absence of resonances corresponding to uncoordinated P(III) species, this suggests that the binding of the gold to the L3 occurs initially with the formation of the oligomeric or polymeric (L3AuCl)n, in a homoleptic “head-to-head” coordination mode.34 The assembled structure is unstable, undergoing fast, reversible dissociation at the Au−PCy bond, followed by a slower Au−PPh cleavage (Scheme 2). The 3750

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Table 1. Selected Bond Lengths, Bond Angles, and Observed 31P NMR Resonances compound (L1)AuCl

bond lengths (Å)

bond angles (deg)

Au(1)−Cl(1) = 2.2867(9) Au(1)−P(1) = 2.2357(9)

P(1)−Au(1)−Cl(1) = 174.18(4) P(1)−C(1)−C(2) = 125.5(3) C(1)−C(2)−C(23) = 126.1(3) C(1)−C(2)−C(6) = 124.3(3), 124.6(2) C(2)−C(1)−C(15) = 124.4(2), 124.6(2) C(10)−C(14)−C(15) = 130.1(3), 130.7(2) C(8)−C(10)−C(14) = 128.4(2), 129.2(2) P(1)−Au(1)−Cl(1) = 177.93(3) C(1)−C(2)−C(6) = 124.7(3) C(2)−C(1)−C(15) = 124.5(3) C(10)−C(14)−C(15) = 130.7(3) C(8)−C(10)−C(14) = 129.1(3) P(1)−C(1)−C(2) = 132.5(3) C(1)−C(2)−C(6) = 125.9(3) C(14)−C(15)−C(19) = 129.0(3) P(1)−C(14)−C(15) = 134.5(3) P(1)−Au(1)−Cl(1) = 173.41(13) P(2)−Au(2)−Cl(2) = 178.61(9) P(1)−C(1)−C(2) = 128.0(7) C(1)−C(2)−C(6) = 126.0(8) C(14)−C(15)−C(19) = 129.7(8) P(1)−C(14)−C(15) = 131.6(6)

L2-BH3b

(L2)AuCl

Au(1)−Cl(1) = 2.2863(8) Au(1)−P(1) = 2.2379(8)

L3

(L3)Au2Cl2

a

Au(1)−Cl(1) = 2.273(3) Au(2)−Cl(2) = 2.285(3) Au(1)−P(1) = 2.235(2) Au(2)−P(2) = 2.229(2)

θ (deg)a 314.9

317.0

315.5

P(1) = 310.3 P(2) = 307.7

P(1) = 319.1 P(2) = 324.6

Sum of three C−P−C angles around each P donor. bThere are two unique structures in the unit cell for L2-BH3.

Table 2. 31P NMR Data of Cationic Gold Complexesa entry

AuCl

P*Ag

product

1 2

(L1)AuCl (L1)AuCl

AgOTs (R)-P*Ag

(L1)Au(OTs) (L1)Au(R-P*)

3

(L1)AuCl

(S)-P*Ag

(L1)Au(S-P*)

4 5

(L2)AuCl (L2)AuCl

AgOTs (R)-P*Ag

(L2)Au(OTs) (L2)Au(R-P*)

6

(L2)AuCl

(S)-P*Ag

(L2)Au(S-P*)

7 8

(L3)Au2Cl2 (L3)Au2Cl2

AgOTs 2 × (R)-P*Ag

(L3)Au(OTs) (L3)Au2(R-P*)2

9

(L3)Au2Cl2

2 × (S)-P*Ag

(L3)Au2(S-P*)2

ment did not reveal any other transannular interactions, nor any close allylic (A1,3) contact between the methyl substituents and the Cp ring. Hence, it is assumed that ring strain is mostly contained within distortions in bond lengths and angles in the eight-membered ring. In L2-BH3 (which crystallized with two independent complexes), this manifested itself in wider bond angles in one of the Cp rings (averaged C(8)−C(10)−C(14) and C(10)−C(14)−C(15) bond angles of 128.8° and 130.4°, respectively), while the corresponding angles in the other Cp ring are all very similar, ranging between 124.3(3) and 124.6(2) ° across both independent complexes. In comparison, for both of the Cp rings contained in L3, the equivalent bond angles are notably larger than 125°, being 125.9(3), 129.0(3), 132.5(3), and 134.5(3)° (Table 1). The θ values in L3 were found to be 310.3° and 307.7° for the PPh and PCy moieties, respectively. The latter increases to 317.0° in the BH3 adduct, in keeping with coordination of the phosphorus’ lone pair to boron. The boat−boat conformations are retained upon the coordination of gold(I) chloride to L2 and L3. The structural parameters of L2-BH3 and (L2)AuCl are very similar. The pyramidalization at P (θ = 315.5°) is only slightly smaller than that found in the BH3 adduct. As a result, there is little difference in the bond angles observed in L2-BH3 and (L2)AuCl. The coordination of AuCl to the highly strained L3, on the other hand, causes an increase in θ from 310.3° to 319.1° at P1, and from 307.7° to 324.6° at P2. This inevitably causes changes to the equivalent bond angles within the medium-sized ring; in this case, significant decreases in P(1)− C(1)−C(2) from 132.5(3)° to 128.0(7)°, and P(1)−C(14)− C(15) from 134.4(3)° to 131.6(6)°, were observed. Halide Abstraction. Metathesis reactions of (L1)AuCl and (L2)AuCl with the achiral and chiral silver salts AgOTs, (R)- or (S)-P*Ag, cause upfield shifts and a certain amount of broadening of the 31P resonance signals (Table 2). More significantly, observed chemical shifts are different between diastereomeric pairs (entries 2 vs 3, 5 vs 6, and 8 vs 9),

δP (ppm) +19.4 +18.5, +7.5 (br) +18.4, +8.8 (br) +68.6 +66.6, +8.6 (br) +67.0, +8.1 (br) +66.9, +18.2 +66.2, +19.9, +8.5 (br) +65.9, +17.3, +8.2 (br)

a

NMR samples prepared in CDCl3, using 85% H3PO4 as internal standard.

sum of their van der Waals radii. The crystal structure provides measurements of P(1)−C(1)−C(2) and C(1)−C(2)−C(23) angles of 125.5(3) and 126.1(3)°, respectively, and the sum of three C−P−C angles (θ) provided a value of 314.87° (which is within the expected range for similar R3P−Au−Cl complexes35), which set a useful benchmark (vide infra). The X-ray crystal structures of L2-BH3 and L3 revealed a (somewhat flattened) boat−boat conformation in both compounds, with the exocyclic P−C bonds in pseudoaxial positions (Figure 4). These conformations are retained in solution, as indicated by the observation of distinct chemical shifts and coupling patterns in their 1H NMR spectra. A 1HNOESY experiment performed with L3 confirmed the boat− boat endo−endo conformation of the eight-membered diphosphocin ring, by the observation of NOE cross-peaks between the P-Ph and P-Cy substituents (Supporting Information). Barring these close contacts, the NOE experi3751

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Figure 5. 31P NMR spectra of addition of (S)-P*Ag to (L3)Au2Cl2 (in CDCl3). (A) (S)-P*Ag; (B) (L3)Au2Cl2; (C) (L3)Au2Cl2 + (S)-P*Ag; (D) (L3)Au2Cl2 + 2 (S)-P*Ag.

Scheme 3. Intramolecular Cyclization of γ-Allenol

Characterization of these compounds was achieved by 1H NMR spectroscopy, FAB-MS, and elemental analysis. Attempts to isolate the corresponding complexes of L3 were unsuccessful. Asymmetric Catalysis. Given ongoing interests in our research laboratories on the development of ferrocenylphosphines38−40 and group 11 catalysts41−44 for stereoselective addition of X−H to CC bonds, the potential application of these gold(I) complexes as enantioselective catalysts was evaluated. To date, only axially chiral diphosphines have been reported to be highly selective ligands for the gold-catalyzed intramolecular addition of O−H or N−H to allenes.36,45−51 In our recent work on the development of silver catalysts for such reactions,52 2,2-diphenyl-substituted γ-allenol 6 was found to be one of the more challenging substrates and was thus chosen as the acyclic precursor in this study (Scheme 3, Table 3). With the three ferrocenyl-based ligands in hand, we will examine the effect of the various chiral components on the enantioselectivity of the reaction; the diphosphocin L3 can be regarded as a composite of L1 and L2, containing a relatively electrondeficient and sterically congested P1 substituted by three aromatic groups, and a sterically less congested, but more Lewis basic P2, substituted by three alkyl groups. As expected, the gold(I) sulfonate and phosphonate salts showed good to moderate catalytic activity in the cyclization of 6 under (sub)ambient conditions (≤room temperature), while the equivalent reactions with chloride salts did not afford any turnover. Preliminary studies were conducted with gold complexes in toluene at −40 °C using 2 mol % of the catalyst. Overall, the catalytic activity of comparative (L)AuX complexes decreases in the order: L1 > L3 > L2, which can be rationalized on the grounds of sterics (L1 vs L3) and electronic factors (L1 and L3 vs L2). Using the tosylate complex, complete conversions can be obtained with all three complexes, to afford the product with low enantioselectivities of between 10.5 and 18.5% (entries 1, 4,

Table 3. Catalytic Performance of the Cationic Gold(I) Complexesa entry

catalyst (mol %)

T (°C)

time (h)

% conversionb

% eec (±)d

1 2 3 4 5 6 7 8 9 10

(L1)Au(OTs) (2) (L1)Au(R-P*) (2) (L1)Au(S-P*) (2) (L2)Au(OTs) (2) (L2)Au(R-P*) (2) (L2)Au(S-P*) (2) (L3)Au2(OTs)2e (L3)Au2(R-P*)2e (L3)Au2(S-P*)2e (L3)Au2Cl(S-P*)f

−40 −40 −40 −40 −40 −40 −40 −40 −40 −40

20 48 50 48 48 72 48 48 48 48

100 100 100 100 62 32 100 100 100 100

10.5 (+) 4 (+) 47 (+) 11.5 (+) 9 (−) 25 (+) 18.5 (+) 7 (+) 31.5 (+) 22.5 (+)

a

See the Experimental Section for general reaction conditions. Determined by 1H NMR spectroscopy. cDetermined by chiral HPLC. dDetermined by polarimetry. eGenerated by mixing 1 mol % (L3)Au2Cl2 with 2 mol % Ag salt. fGenerated by mixing 1 mol % (L3)Au2Cl2 with 1 mol % Ag salt. b

suggestive of weak interactions between the counteranions and gold, by either a weak dative coordination or the formation of an ion pair.36,37 Addition of 1 equiv of the silver salt (S)-P*Ag (where P* = 1,1′-binaphthyl-2,2′-diyl phosphate) to (L3)Au2Cl2 led to an equal mixture of starting materials and the dicationic complex (Figure 5); that is, the extraction of the halide from the metal center occurs spontaneously and unselectively. The broadened peaks suggest that the interaction between the phosphate anion and gold is likely to be highly dynamic. (L1)AuX and (L2)AuX (where X = OTs, (R)-P*, (S)-P*) can be isolated as orange and red solids, respectively. 3752

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Foundation are also gratefully acknowledged (Ph.D. fellowships to D.F.D.B. and R.S.).

and 7). In comparison, complexes derived from the phosphate anions were less active. However, dramatic match−mismatch effects can be observed; the S enantiomer of the gold phosphate complex of L1 enhanced the ee of the product to 47%, while its R congener afforded only 4% (entries 2 and 3). Very interestingly, the use of the S enantiomer of the phosphate anion only slightly enhanced the stereoselectivity of the gold complexes of L2 (entries 4 and 6), while the incorporation of the mismatched R-phosphate resulted in lower and opposite stereoinduction (entries 5 and 6). In the case of L3, each of the gold metal centers was expected to behave independently; their reactivity tuned by the electronically and sterically different PR3 moieties that they are ligated to. In this regard, the incorporation of the additional PPh group in the eight-membered ring appeared to only slightly enhance the enantioselectivity achieved in (L3)Au2X2, compared to L2 (entries 4 vs 7, 5 vs 8, and 6 vs 9). Using a Au/ P* ratio of 2:1, the selectivity reduced from 31.5 to 22.5% (entries 9 and 10).

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(1) Hayashi, T.; Yamamoto, K.; Kumada, M. Tetrahedron Lett. 1974, 15, 4405. (2) Hayashi, T.; Kumada, M. Acc. Chem. Res. 1982, 15, 395. (3) Thommen, M.; Blaser, H.-U. PharmaChem 2002, 1, 33. (4) Hayashi, T. Asymmetric catalysis with chiral ferrocenylphosphine ligands. In Ferrocene; Togni, A., Hayashi, T., Eds.; VCH: Weinheim, Germany, 1995; pp 105−142. (5) Dai, L.-X.; Tu, T.; You, S.-L.; Deng, W.-P.; Hou, X.-L. Acc. Chem. Res. 2003, 36, 659. (6) Barbaro, P.; Bianchini, C.; Giambastiani, G.; Parisel, S. L. Coord. Chem. Rev. 2004, 248, 2131. (7) Manoury, E.; Poli, R. Catal. Met. Complexes 2011, 37, 121. (8) Arrayas, R. G.; Adrio, J.; Carretero, J. C. Angew. Chem., Int. Ed. 2006, 45, 7674. (9) Blaser, H.-U.; Brieden, W.; Pugin, B.; Spindler, F.; Studer, M.; Togni, A. Top. Catal 2002, 19, 3. (10) Blaser, H.-U. Adv. Synth. Catal. 2002, 344, 17. (11) (a) Pradal, A.; Toullec, P. Y.; Michelet, V. Synthesis 2011, 1501. (b) Sengupta, S.; Shi, X. ChemCatChem 2010, 2, 609. (12) Hashmi, A. S. K.; Buehrle, M. Aldrichimica Acta 2010, 43, 27. (13) Ito, Y.; Sawamura, M.; Hayashi, T. J. Am. Chem. Soc. 1986, 108, 6405. (14) Togni, A.; Pastor, S. D. J. Org. Chem. 1990, 55, 1649. (15) Pastor, S. D.; Togni, A. Tetrahedron Lett. 1990, 31, 839. (16) Zhou, X.-T.; Lin, Y.-R.; Dai, L.-X.; Sun, J.; Xia, L.-J.; Tang, M.H. J. Org. Chem. 1999, 64, 1331. (17) Muñoz, M. P.; Adrio, J.; Carretero, J. C.; Echavarren, A. M. Organometallics 2005, 24, 1293. (18) Hashmi, A. S. K.; Hamzić, M.; Rominger, F.; Bats, J. W. Chem.Eur. J. 2009, 15, 13318. (19) Arnanz, A.; Gonzalez-Arellano, C.; Juan, A.; Villaverde, G.; Corma, A.; Iglesias, M.; Sanchez, F. Chem. Commun. 2010, 46, 3001. (20) Teller, H.; Fluegge, S.; Goddard, R.; Fuerstner, A. Angew. Chem., Int. Ed. 2010, 49, 1949. (21) Gonzalez, A. Z.; Benitez, D.; Tkatchouk, E.; Goddard, W. A., III; Toste, F. D. J. Am. Chem. Soc. 2011, 133, 5500. (22) Gorin, D. J.; Sherry, B. D.; Toste, F. D. Chem. Rev. 2008, 108, 3351. (23) Marquarding, D.; Klusacek, H.; Gokel, G.; Hoffmann, P.; Ugi, I. J. Am. Chem. Soc. 1970, 92, 5389. (24) Kolakowski, R. V.; Manpadi, M.; Zhang, Y.; Emge, T. J.; Williams, L. J. J. Am. Chem. Soc. 2009, 131, 12910. (25) Hayashi, T.; Mise, T.; Fukushima, M.; Kagotani, M.; Nagashima, N.; Hamada, Y.; Matsumoto, A.; Kawakami, S.; Konishi, M.; Yamamoto, K.; Kumada, M. Bull. Chem. Soc. Jpn. 1980, 53, 1138. (26) Hayashi, T.; Hayashizaki, K.; Kiyoi, T.; Ito, Y. J. Am. Chem. Soc. 1988, 110, 8153. (27) Ohmura, H.; Matsuhashi, H.; Tanaka, M.; Kuroboshi, M.; Hiyama, T.; Hatanaka, Y.; Goda, K.-i. J. Organomet. Chem. 1995, 499, 167. (28) Fujii, N.; Kakiuchi, F.; Yamada, A.; Chatani, N.; Murai, S. Chem. Lett. 1997, 26, 425. (29) Hiroi, K.; Kato, F.; Yamagata, A. Chem. Lett. 1998, 27, 397. (30) Kakiuchi, F.; Le Gendre, P.; Yamada, A.; Ohtaki, H.; Murai, S. Tetrahedron: Asymmetry 2000, 11, 2647. (31) Thalji, R. K.; Ellman, J. A.; Bergman, R. G. J. Am. Chem. Soc. 2004, 126, 7192. (32) Lee, S.; Hartwig, J. F. J. Org. Chem. 2001, 66, 3402. (33) Broggini, D. F. D. Ph.D. Thesis, Swiss Federal Institute of Technology, Zürich, Switzerland, 2003. ETH Dissertation No. 15041. (34) Berners-Price, S. J.; Sadler, P. J. Inorg. Chem. 1986, 25, 3822. (35) Cambridge Structural Database, version 5.33; February 2012 update. (36) Aikawa, K.; Kojima, M.; Mikami, K. Adv. Synth. Catal. 2010, 352, 3131.

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CONCLUSIONS The preparation and characterization of two conformationally constrained, diferrocenyl-derived (di)phosphocin ligands, and their gold(I) complexes, have been described. The application of these, as well as the gold(I) complex of the (S)-(R)-PPFOMe ligand (pioneered by Hayashi), in gold-catalyzed intramolecular addition of O−H to allene was examined. Low to moderate enantioselectivities can be achieved using tosylate and enantiopure phosphate as counterions, and match− mismatch effects were observed between the chirality of the phosphine ligand and the anion. On the basis of the results obtained so far, it is possible to draw the following conclusions: (1) The diferrocenyldiphosphocin ligand L3 behaves as a nonchelating diphosphine toward gold; (2) gold(I) complexes ligated by the more basic PR3 moiety is less active catalytically, even though it is sterically less hindered; (3) the incorporation of a chiral anion can have a profound influence on the level of enantioselectivity; and (4) observation of match−mismatch effects between different chiral counteranions suggests the close involvement of the anion in the stereodefining step. Thus, high enantioselectivity may be achieved by a judicious matching of the chiral ligand with a suitable counteranion.

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ASSOCIATED CONTENT

S Supporting Information *

Crystallographic information files (CIF) and copies of NMR spectra. This material is available free of charge via the Internet at http://pubs.acs.org.

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (A.T.), mimi.hii@imperial. ac.uk (K.K.H.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful to Fundación Barrié de la Maza and Xunta Galicia (Angeles Alvariñ o program) for the award of postdoctoral fellowships to E.M.B. and L.A.A., respectively. Support from ETH Zürich and the Swiss National Science 3753

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(37) Nguyen, B. N.; Adrio, L. A.; Barreiro, E. M.; Brazier, J. B.; Haycock, P.; Hii, K. K.; Nachtegaal, M.; Newton, M. A.; Szlachetko, J. Organometallics 2012, 31, 2395. (38) Togni, A.; Breutel, C.; Schnyder, A.; Spindler, F.; Landert, H.; Tijani, A. J. Am. Chem. Soc. 1994, 116, 4062. (39) Buergler, J. F.; Niedermann, K.; Togni, A. Chem.Eur. J. 2012, 18, 632. (40) Buergler, J. F.; Togni, A. Chem. Commun. 2011, 47. (41) Taylor, J. G.; Whittall, N.; Hii, K. K. M. Chem. Commun. 2005, 5103. (42) Taylor, J. G.; Whittall, N.; Hii, K. K. Org. Lett. 2006, 8, 3561. (43) Adrio, L. A.; Quek, L. S.; Taylor, J. G.; Hii, K. K. Tetrahedron 2009, 65, 10334. (44) Arbour, J. L.; Rzepa, H. S.; White, A. J. P.; Hii, K. K. Chem. Commun. 2009, 7125. (45) Hamilton, G. L.; Kang, E. J.; Mba, M.; Toste, F. D. Science 2007, 317, 496. (46) LaLonde, R. L.; Sherry, B. D.; Kang, E. J.; Toste, F. D. J. Am. Chem. Soc. 2007, 129, 2452. (47) Zhang, Z. B.; Liu, C.; Kinder, R. E.; Han, X. Q.; Qian, H.; Widenhoefer, R. A. J. Am. Chem. Soc. 2006, 128, 9066. (48) Zhang, Z. B.; Bender, C. F.; Widenhoefer, R. A. Org. Lett. 2007, 9, 2887. (49) Zhang, Z. B.; Widenhoefer, R. A. Angew. Chem., Int. Ed. 2007, 46, 283. (50) Zhang, Z.; Bender, C. F.; Widenhoefer, R. A. J. Am. Chem. Soc. 2007, 129, 14148. (51) Aikawa, K.; Kojima, M.; Mikami, K. Angew. Chem., Int. Ed. 2009, 48, 6073. (52) Arbour, J. L.; Rzepa, H. S.; Contreras-Garcia, J.; Adrio, L. A.; Barreiro, E. M.; Hii, K. K. Chem.Eur. J. 2012, accepted. DOI: 10.1002/chem.201200547.

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