Article pubs.acs.org/Organometallics
Imidazolyl-PTA Derivatives as Water-Soluble (P,N) Ligands for Ruthenium-Catalyzed Hydrogenations Donald A. Krogstad,*,† Antonella Guerriero,‡ Andrea Ienco,‡ Gabriele Manca,‡ Maurizio Peruzzini,*,‡ Gianna Reginato,‡ and Luca Gonsalvi*,‡ †
Concordia College at Moorhead, 334F Ivers, Moorhead, Minnesota 56562, United States Consiglio Nazionale delle Ricerche, Istituto di Chimica dei Composti Organometallici (ICCOM-CNR), Via Madonna del Piano 10, 50019 Sesto Fiorentino (Firenze), Italy
‡
S Supporting Information *
ABSTRACT: The first imidazolyl “upper-rim” derivatives of 1,3,5-triaza-7-phoshaadamantane (PTA), namely, 1-methylimidazolyl-(1,3,5-triaza-7-phosphatricyclo[3.3.1.13,7]dec-6-yl)methanol (2, PTA-CH(1-MeIm)OH) and bis(1-methylimidazolyl)(1,3,5triaza-7-phosphatricyclo[3.3.1.13,7]dec-6-yl)methanol (3, PTAC(1-MeIm)2OH), were synthesized in fair yields by reaction of PTA-Li with 1-methyl-2-imidazole carboxyaldehyde and bis(N-methylimidazole-2-yl) ketone, respectively. Compounds 2 and 3 exhibit higher water solubility than most upper-rim derivatives of PTA. The two ligands reacted cleanly with [Ru(η 6-p-cymene)Cl2]2 in refluxing CHCl3 to form κ 2-P,N[(η 6-p-cymene)Ru{PTA-CH(1-MeIm)OH}Cl]Cl (8) and κ 2P,N -[(η 6-p-cymene)Ru{PTA-C(1-MeIm)2OH}Cl]Cl (9). Ligands phenyl(1,3,5-triaza-7-phosphatricyclo[3.3.1.1 3,7]dec-6-yl)methanol (PZA) and 4′-dimethylaminophenyl(1,3,5-triaza-7-phosphatricyclo[3.3.1.1 3,7]dec-6-yl)methanol (PZA-NMe2) were also used to coordinate to Ru, and the corresponding κ 1-P -[(η 6-p-cymene)Ru(PZA)Cl2] (6) and κ 1-P -[(η 6-p-cymene)Ru(PZANMe2)Cl2] (7) were isolated and characterized. The ability of the ligands to coordinate in κ 1-P vs κ 2-P,E (E = O, N) modes was established by NMR experiments and complemented by DFT calculations. The X-ray crystal structure of the iodide analogue of 7 was obtained. Complexes 6−9 were tested as catalysts for acetophenone reduction using different hydrogen sources under mild conditions, and preliminary results are here described.
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dmoPTA9 and PTN(R) (R = Me, Et, Ph)10 (Chart 1). Due to the rigid structure and spatial arrangement of the heteroatoms,
INTRODUCTION The need for more sustainable chemical processes, for example by using water as a reaction medium instead of toxic organic solvents, is attracting attention from both academia and industry.1 From this point of view, the development of a library of versatile water-soluble ligands with easily tunable electronic, steric, and coordinating properties would be highly desirable.2,3 Bifunctional ligands containing for example P and N donor atoms are of great interest in the realms of coordination and organometallic chemistry because of their possible hemilabile behavior in their transition metal complexes.4 The bond between a soft metal and a hard base (N) is often weak enough to cause this moiety to reversibly dissociate and open a coordination site thus available for the activation of reagents in the coordination sphere of the metal.5,6 P,N ligands have thus been employed in metal-catalyzed hydroxylations, allylic substitutions, hydrogenations, hydrosilylations, hydroborations, carbonylations, hydroformylation, and many coupling reactions, usually run in organic solvents.7 To date, only a limited number of water-soluble aminophosphine ligands are known.2 Some of the few are 1,3,5-triaza7-phosphaadamantane (PTA)3a,8 and its derivatives including © 2011 American Chemical Society
Chart 1
PTA8a,11 and dmoPTA9 have not been reported to behave as κ 2-P,N chelating ligands but as κ 1-P and bridging μ-P,N Received: September 26, 2011 Published: November 3, 2011 6292
dx.doi.org/10.1021/om200896g | Organometallics 2011, 30, 6292−6302
Organometallics
Article
ligands. PTA has also been observed to bind κ 1-N,12 and dmoPTA to bind κ 2-N,N.9 PTN(R), however, has been reported to bind in both κ 1-P and κ 2-P,N modes.10,13 Rh complexes with both binding motifs have recently been synthesized by some of us and used as effective hydroformylation and hydrogenation catalysts under aqueous and biphasic conditions.13b Recently, κ 2-P,N -[(η 6-p-cymene)Ru{PTN(Me)}Cl]Cl (1) was proven to have antimetastatic activity toward ovarian cancer cells.14 These studies clearly illustrated that water-soluble P,N systems have great potential in both catalysis and medicinal fields. Frost et al. have derivatized PTA in the 6-position by reacting it with n-BuLi to form the very useful synthon PTA-Li.15 PTALi has then been used to prepare a library of PTA “upper-rim” derivatives by reacting it with PPh2Cl, CO2, ketones, and aldehydes.16−18 In particular, we have recently reported on the synthesis of phenyl(1,3,5-triaza-7-phosphatricyclo[3.3.1.1 3,7]dec-6-yl)methanol (PZA)17 and its p-dimethylamino analogue (PZA-NMe2, Chart 1),18 whose Ir(I) complexes were recently proven to be effective catalysts for the hydrogenation of ketones and α,β-unsaturated carbonyl substrates.18 Following on our interest in this field, we used PTA-Li to prepare two new water-soluble phosphines that incorporate N -methyl imidazole functionalities. The coordination chemistry of these ligands toward [Ru(η 6-p-cymene)Cl2]2, as well as that of PZA and PZA-NMe2, has been studied. It was found by a combination of NMR experiments and DFT calculations that the imidazole systems preferentially bind as κ 2-P,N chelates and thereby may behave as bifunctional P,N ligands under catalytic conditions. The abilities of the above-mentioned Ru(II) complexes to catalyze the hydrogenation of acetophenone with a variety of hydrogen sources and conditions were explored, and the obtained results are here reported.
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Aldrich and purified by recrystallization from n-pentane under N2. 1,3,5-Triaza-7-phosphaadamantane-6-yl lithium (PTA-Li),18 PZA,17 PZA-NMe2,18 [Ru(η 6-p-cymene)Cl2]2,19 and bis(N-methylimidazole2-yl) ketone20 were prepared as described in the literature and the latter further purified by recrystallization from THF under N 2. Compound water-solubilities were quantified by the addition of water via a 100 μL Hamilton microsyringe to a 100 mg sample of the phosphine or a 50 mg sample of the Ru complex in a Schlenk flask under slow stirring, in a thermostated bath kept at 20 °C until complete dissolution of the solids. For example, in a typical trial, 310 μL of water was required to dissolve 100 mg of 2 and a 160 μL aliquot was required for a 50 mg sample of 8. Caution: PTA-Li is a highly pyrophoric compound that readily combusts when exposed to air. Synthesis of 1-Methylimidazolyl(1,3,5-triaza-7phosphatricyclo[3.3.1.13,7]dec-6-yl)methanol (2, PTA-CH(1MeIm)OH). A 50 mL Schlenk flask was charged with PTA-Li (2.10 g, 12.88 mmol) and THF (20 mL) and cooled to −70 °C. A separate 50 mL Schlenk flask was charged with 1-methyl-2-imidazolecarboxaldehyde (1.71 g, 15.40 mmol) and THF (15 mL) at −70 °C. The aldehyde solution was then added to the stirred PTA-Li slurry under N2 over a 3 min period. After stirring for 30 min at −70 °C, the reaction was allowed to warm to room temperature. After 12 h, the reaction mixture was quenched by the dropwise addition of H2O (0.65 mL), resulting in an orange suspension. After evaporation of the solvents and addition of CHCl3, the orange slurry was dried with Na2SO4, then filtered through Celite. Evaporation of the solvent gave an orange residue, which was purified by column chromatography (R f = 0.17, eluent: methanol), to give a pale yellow solid, which was recrystallized from THF (10 mL)/benzene (20 mL) as an off-white powder. Yield: 1.40 g (40.7% based on PTA-Li). S(H2O)20 °C = 320 g/L. The product is formed as a mixture of two diastereoisomers (1:1 ratio), which may be enriched in one of the two diastereoisomers as follows: 300 mg of the crude product was combined with acetone (35 mL) under N 2 and filtered hot. The resulting solution was then put into the freezer at −20 °C for 12 h. After this time, the mother liquor was decanted off, leaving 122 mg of a white powder containing the two diastereoisomers in 15:1 ratio. Spectroscopic data for 2 (major diastereoisomer, values for minor diastereoisomer are reported in parentheses when distinguishable): 1H NMR (400.13 MHz, CDCl3): δ (ppm) 6.84 (7.00) (d, 3JHH = 1.1 Hz, 1H, H4-Im); 6.81 (6.89) (d, 3JHH = 1.1 Hz, 1H, Im, H5-Im); 5.29 (5.31) (pst, 3JHH = 7.7 Hz, 1H, PCHCH ImOH); 4.75 (AB system, 2JHAHB = 13.7 Hz, 1H, NCH2N); 4.62 (AB system, 2 JHAHB = 13.7 Hz, 1H, NCH2N); 4.50−4.42 (m, 3H, NCH2N + PCHN); 4.26−4.20 (m, 2H, NCH2N); 4.15−4.00 (m, 2H, PCH2N); 3.90−3.80 (m, 2H, PCH2N); 3.74 (3.81) (s, 3H, Me-Im). 13C{1H} NMR (100.61 MHz, CDCl3): δ 148.24 (146.04) (d, 3JCP = 4.1 Hz, C 2Im); 126.56 (127.47) (s, C 4-Im); 122.22 (122.10) (s, C 5-Im); 76.33 (76.01) (d, 3JCP = 1.1 Hz, NCH2N); 74.02 (74.00) (d, 3JCP = 2.6 Hz, NCH2N); 69.05 (61.11) (d, 2JCP = 9.3 Hz, CHOH); 67.52 (66.44) (d, 3 JCP = 2.2 Hz, NCH2N); 63.32 (63.72) (d, 1JCP = 21.0 Hz, PC HN); 51.25 (50.71) (d, 1JCP = 20.1 Hz, PCH2N); 47.63 (47.39) (d, 1JCP = 25.1 Hz, PCH2N); 33.21 (33.04) (s, Me-Im). 31P{1H} NMR (161.98 MHz, CDCl3): δ −103.39 (−104.65) (s); Anal. Found (calcd) for C11H18N5OP (267.27 g mol−1): C, 49.41 (49.43); H, 6.85 (6.79); N, 26.26 (26.21). IR (KBr, cm−1): ν(O−H) 3397 (sh); ν (CN) 1654. ESI-MS observed: m/z 268.19 (100) [M+ + 1]. Synthesis of Bis(1-methylimidazolyl)(1,3,5-triaza-7phosphatricyclo[3.3.1.13,7]dec-6-yl)methanol (3, PTA-C(1-MeIm)2OH). A 100 mL Schlenk flask was charged with PTA-Li (0.49 g, 3.00 mmol) and THF (15 mL) and put into an alcohol/liquid nitrogen bath at −70 °C. A 100 mL Schlenk flask was charged with bis(Nmethylimidazole-2-yl) ketone (0.65 g, 3.42 mmol) and THF (15 mL) kept at −70 °C. The ketone slurry was added to the PTA-Li under N2 over 1 min. Over the next 30 min, the reaction changed from a brown slurry to a slightly cloudy, gold-colored solution. The reaction was allowed to warm to room temperature. After 12 h, the clear, orange solution was quenched by the dropwise addition of H2O (0.3 mL), resulting in an orange suspension. The solvents were removed in vacuo, and the product was combined with CHCl3. The orange
EXPERIMENTAL SECTION
General Methods. All manipulations were carried out under a purified N2 atmosphere with use of standard Schlenk techniques unless otherwise noted. Elemental analyses were carried out at the University of Florence, Italy, by using a Perkin-Elmer 2400 series II elemental analyzer. Electrospray mass spectrometry (ESI-MS) analyses were carried out at the University of Florence, Italy, on a LCQ Orbitrap mass spectrometer (ThermoFischer, San Jose, CA, USA) equipped with a conventional ESI source by direct injection of the sample solution and are reported in the form m/z (intensity relative to base = 100). Infrared spectra were measured in CH2Cl2 solution or in KBr pellets on a Perkin-Elmer FT-IR Spectrum BX II instrument. GC analyses were performed on a Shimadzu GC-17A gas chromatograph (with a chiral column Lipodex-E Macherey-Nagel) equipped with a flame ionization detector (50 m, 0.25 mm i.d., 0.40 mm o.d.). Hydrogenation reactions were performed either with a magnetically stirred home-built stainless steel autoclave with sample carousel (100 mL) at room temperature or with a Parr autoclave (100 mL) with mechanical stirring and external digital controller. 1 H, 13C{1H}, and 31P{1H} NMR spectra were recorded on a Bruker Avance II 300 spectrometer (operating at 300.13, 75.47, and 121.50 MHz, respectively) and a Bruker Avance II 400 spectrometer (operating at 400.13, 100.61, and 161.98 MHz, respectively) at room temperature. The 13C and 31P spectra were run with proton decoupling, and 31P spectra are reported in ppm relative to an external 85% H3PO4 standard, with positive shifts downfield. 13C and 1H NMR spectra are reported in ppm relative to residual solvent resonances with positive shifts downfield. Solvents were distilled and dried prior to use. Doubly distilled water was used. Column chromatography purification was performed using glass columns (10−50 mm wide) and silica gel (230−400 mesh particle size). 1-Methyl-2-imidazolecarboxaldehyde was obtained from 6293
dx.doi.org/10.1021/om200896g | Organometallics 2011, 30, 6292−6302
Organometallics
Article
Found (calcd) for C15H22N7O2P (363.35 g mol−1): C, 49.85 (49.58); H, 6.22 (6.10); N, 26.05 (26.98). IR (KBr, cm −1): ν(O−H) 3283 sh; ν(CN) 1597; ν(PO) 1146. ESI-MS (MeOH): observed m/z 364.17 (100) [M+ + 1]. Synthesis of κ 1-P -[(η 6-p-cymene)RuCl2(PZA)] (6). [(η 6-pcymene)RuCl2]2 (0.22 g, 0.36 mmol) was dissolved under nitrogen in dry, degassed CH2Cl2 (13 mL). The solution of PZA (0.19 g, 0.72 mmol, two diastereomers, ratio 1:1) in CH2Cl2 (7 mL) was added dropwise, and the reaction was left under stirring at room temperature for 1 h. The volume was then reduced to approximately 10 mL, and diethyl ether (15 mL) added to precipitate the product. The solid was isolated and washed with cold ether to afford a reddish-orange powder (0.26 g, 63% yield based on the PZA ligand), containing the two diastereoisomers in 1:2 ratio. S(H2O)20 °C = 2.7 g/L. Data for 6 are as follows (major diastereoisomer, values for minor isomer are reported in parentheses). 1H NMR (400.13 MHz, CDCl3): δ (ppm) 7.41−7.30 (m, 5H, Ar); 5.65−5.51 (m, 3H, p-cymene); 5.47−5.40 (m, 1H, CHOH); 5.22−5.19 (m, 1H, p-cymene); 4.87−4.14 (m, 11H, 3 × NCH2N, 2 × PCH2N, PCHN); 2.82−2.77 (m, 1H, CHMe2); 2.20 (2.11) (s, 3H, p-cymene CH3); 1.30 (1.25) (d, 1JHH = 4.9 (2.3) Hz, 3H, CH-Me2); 1.28 (1.23) (d, 1JHH = 4.9 (2.3) Hz, 3H, CH-Me2). 13 C{1H} NMR (100.61 MHz, CDCl3): δ 141.09 (141.52) (d, 3JCP = 9.1 Hz, Ar); 128.53 (127.99) (s, Ar); 128.16 (127.12) (s, Ar); 126.69 (126.28) (s, Ar); 108.53 (106.83) (s, CCH-Me2); 99.86 (96.48) (s, C-CH3); 89.69 (88.66) (s, CH p-cymene); 87.52 (88.42) (s, CH p-cymene); 83.64 (85.70) (s, CH p-cymene); 83.49 (85.07) (s, CH p-cymene); 75.88 (75.47) (s, NCH2N); 73.54 (73.97) (s, NCH2N); 72.12 (s, C HOH); 69.72 (68.71) (d, 1JCP = 9.4 Hz, PC HN); 67.51 (65.70) (d, 3JCP = 4.6 Hz, NCH2N); 54.72 (51.25) (d, 2JCP = 12.8 Hz, PCH2N); 45.50 (d, 1JCP = 18.8 Hz, PCH2N); 31.10 (30.80) (s, CCHMe2); 22.54 (22.36) (s, CCH-Me2); 22.49 (22.03) (s, CCH-Me2); 19.03 (18.50) (s, C-CH3). 31P{1H} NMR (161.97 MHz, CDCl3): δ −40.32 (−28.71) (s). Anal. Calcd for C23H32Cl2N3OPRu (569.47 g mol−1). Anal. Found (calcd): C 48.31 (48.51); H 5.45 (5.66); N 7.40 (7.38). IR (KBr, cm−1): ν(OH) 3372 (br, s); ν(arom) 1446. Synthesis of κ 1-P -[(η 6-p-cymene)RuCl2{(SR,RS)(PZA-NMe2)}] (7). Dry, degassed CH2Cl2 (25 mL) was added under nitrogen to a Schlenk tube charged with ligand (SR,RS)(PZA-NMe2) (0.20 g, 0.65 mmol) and [(η 6-p-cymene)RuCl2]2 (0.20 g, 0.33 mmol). The resulting clear red solution was stirred for 2 h at room temperature. The solvent was reduced to about half of the initial volume, and upon addition of 15 mL of cold n-pentane, a reddish-pink precipitate was formed. This was filtered under nitrogen and washed with few drops of cold n-pentane, yielding a reddish-pink powder (0.22 g, 56% yield based on the PZA-NMe2 ligand). S(H2O)20 °C = 1.4 g/L. 1H NMR (300.13 MHz, CD2Cl2): δ (ppm) 7.26 (d, 1JHH = 8.7 Hz, 2H, Ar); 6.75 (d, 1JHH = 8.7 Hz, 2H, Ar); 5.65−5.54 (m, 3H, p-cymene); 5.38−5.30 (m, 1H, CH OH); 5.23 (d, 1JHH = 5.9 Hz, 1H, p-cymene); 4.65−4.35 (m, 9H, 3 × NCH2N + 1 × PCH2N + PCHN); 4.25−4 0.15(m, 2H, PCH2N); 2.97 (s, 6H, N(CH3)2); 2.79 (sept, 1JHH = 6.9 Hz, 1H, CHMe2); 2.19 (s, 3H, p-cymene CH3); 1.32 (d, 1JHH = 6.9 Hz, 3H, CHMe2); 1.30 (d, 1JHH = 6.9 Hz, 3H, CH-Me2). 13C{1H} NMR (75.47 MHz, CD2Cl2): δ 150.38 (s, Ar); 128.90 (d, 3JCP = 8.2 Hz, Ar); 127.51 (s, Ar); 112.17 (s, Ar); 108.10 (d, JCP = 2.7 Hz, CCH-Me2); 99.41 (s, C-CH3); 89.66 (d, JCP = 4.5 Hz, CH p-cymene); 87.55 (d, JCP = 5.6 Hz, CH p-cymene); 83.76 (s, CH p-cymene); 83.48 (d, JCP = 3.7 Hz, CH p-cymene); 75.84 (br s, NCH2N); 73.60 (d, 3JCP = 6.6 Hz, NCH2N); 71.63 (d, 3JCP = 2.6 Hz, CHOH); 69.57 (d, 1JCP = 9.5 Hz, PC HN); 67.43 (d, 3JCP = 7.4 Hz, NCH2N); 54.78 (d, 1JCP = 13.5 Hz, PCH2N); 45.25 (d, 1JCP = 18.8 Hz, PCH2N); 40.34 (s, N(CH3)2); 31.02 (s, CCH-Me2); 22.23 (s, CCH-Me2); 22.15 (s, CCH-Me2); 18.66 (s, C-CH3). 31P{1H} NMR (121.50 MHz, CD2Cl2): δ −40.35 (s). Anal. Found (calcd) for C25H37Cl2N4OPRu (612.54 g mol−1): C 48.96 (49.02); H 5.98 (6.09); N 9.02 (9.15). IR (KBr, cm −1): ν(OH) 3383 (br, s); ν(arom) 1611 (m), 1521 (m). Synthesis of κ 1-P -[(η 6-p-cymene)RuI2{(SR,RS)(PZA-NMe2)}] (7-I). Following the synthetic procedure described above for 7 and using [(η 6-p-cymene)RuI2]2 (70 mg, 0.09 mmol) in place of the chloride analogue, the corresponding κ 1-P complex 7-I was obtained in ca. 60% yield (based on the PZA-NMe2 ligand). S(H2O)20 °C = 0.5 g/L.
slurry was dried with Na2SO4 and filtered through Celite, and the resulting orange solution was evaporated to dryness. The orange residue was extracted with Et2O under N2 (5 × 50 mL), and the combined solutions were evaporated to dryness, leaving a pale yellow residue. Yield: 0.62 g (59.7% based on PTA-Li). S(H2O)20 °C = 78 g/L. The residue was recrystallized from hot Et2O under N2 to produce white microcrystals after sitting overnight at −20 °C. Data for 3 are as follows. 1H NMR (400.13 MHz, CD2Cl2): δ (ppm) 6.94 (d, 3JHH = 1.1 Hz, 1H, H4-Im); 6.90 (d, 3JHH = 1.1 Hz, 1H, H4-Im′); 6.87 (d, 3JHH = 1.1 Hz, 1H, H5-Im); 6.83 (d, 3JHH = 1.1 Hz, 1H, H5-Im′); 6.24 (br s, 1H, OH ); 5.55 (br d, 3JHP= 1.3 Hz, 1H, NCH2N); 4.77 (br d, 1JHP = 13.6 Hz, 1H, PCH N); 4.66 (AB system, 2JHAHB= 13.2 Hz, 1H, NCH2N); 4.60 (AB system, 2JHAHB= 13.2 Hz, 1H, NCH2N); 4.4−4.5 (m, 3H, NCH2N); 4.0−4.15 (m, 3H, PCH2N); 3.83 (m, 1H, PCH2N); 3.49 (s, 3H, Me-Im); 3.35 (s, 3H, Me-Im′). 13C{1H} NMR (100.61 MHz, CD2Cl2): δ 147.48 (d, 3JCP = 4.1 Hz, C 2-Im); 145.26 (s, C 2-Im′); 125.44 (s, C 4-Im); 124.55 (s, C 4-Im′); 124.20 (s, C 5-Im); 124.11 (s, C 5-Im′); 78.49 (d, 2JCP= 8.1 Hz, COH); 77.77 (s, NCH2N); 74.24 (d, 3JCP = 1.5 Hz, NCH2N); 67.49 (d, 3JCP= 3.3 Hz, NCH2N); 62.30 (d, 1JCP = 24.4 Hz, PC HN); 51.94 (d, 1JCP = 19.6 Hz, PCH2N); 49.13 (d, 1JCP = 23.7 Hz, PCH2N); 34.40 (s, Me-Im); 33.18 (s, MeIm′). 31P{1H} NMR (161.98 MHz, CD2Cl2): δ −97.55 (s). Anal. Found (calcd) for C15H22N7OP (347.37 g mol−1): C, 51.04 (51.87); H, 6.31 (6.38); N, 28.39 (28.23). IR (KBr, cm −1): ν(O−H) 3250 (sh); ν(CN) 1634. ESI-MS (MeOH): observed m/z 348.14 (100) [M+ + 1]. Synthesis of OPTA-CH(1-MeIm)OH (4). PTA-CH(1-MeIm)OH (2) (40 mg, 0.15 mmol) was dissolved in D2O (1 mL) in the air. The clear solution was then combined with 35% H2O2 (20 μL), transferred to a 5 mm NMR tube, and analyzed by NMR spectroscopy. According to the 31P spectrum, the phosphine was quantitatively converted into its oxide. The solvent was then removed under vacuum at 30 °C. The resulting white residue was washed with acetone (3 × 5 mL) and dried in vacuo. Yield: 24 mg (55.9% based on PTA-CH(1MeIm)OH). S(H2O)20 °C = 80 g/L. Spectroscopic data for 4 (major diastereoisomer, values for minor diastereoisomer are reported in parentheses when distinguishable). 1H NMR (400.13 MHz, D2O): δ (ppm) 6.94 (6.92) (d, 3JHH = 1.1 Hz, 1H, H4-Im); 6.81 (d, 3JHH = 1.2 Hz, 1H, H5-Im); 5.57 (vt, 3JHH ≈ 3JHP = 9.0 Hz, 1H, CHOH); 4.62 (m, 1H, PCHN); 4.1−4.3 (m, 6H, NCH2N); 3.95 (br d, 2JHP = 14.2 Hz, 1H, PCH2N); 3.88−3.81 (m, 3H, PCH2N); 3.64 (3.61) (s, 3H, MeIm). 13C{1H} NMR (100.61 MHz, D2O): δ 145.42 (d, 3JCP = 10.0 Hz, C 2-Im); 126.28 (126.54) (s, C 4-Im); 123.62 (123.04) (s, C 5-Im); 72.44 (d, 3JCP = 5.6 Hz, NCH2N); 70.31 (d, 3JCP = 8.9 Hz, NCH2N); 66.10 (66.52) (d, 1JCP = 52.0 Hz, PC HN); 65.03 (d, 2JCP = 11.5 Hz, CHOH); 64.65 (60.98) (s, NCH2N); 53.19 (d, 1JCP = 54.0 Hz, PCH2N); 50.41 (d, 1JCP = 52 Hz, PCH2N); 32.74 (32.53) (s, Me-Im). 31 1 P{ H} NMR (161.98 MHz, D2O): δ 0.59 (−0.48) (s), Anal. Found (calcd) for C11H18N5O2P (283.27 g mol−1): C, 46.35 (46.64); H, 6.37 (6.40); N, 24.45 (24.72). IR (KBr, cm−1): ν(O−H) 3317(sh); ν(P O) 1152. ESI-MS (MeOH): observed m/z 284.25 (100) [M+ + 1]. Synthesis of OPTA-C(1-MeIm)2OH (5). By following the same procedure as described for 4, PTA-C(1-MeIm)2OH (3) (32 mg, 0.09 mmol) was quantitatively converted into its oxide according to 31 P NMR. After evaporation and an absolute ethanol wash, a white powder was collected. Yield: 26 mg (76.7% based on PTA-C(1MeIm)2OH). S(H2O)20 °C = 66.7 g/L. Data for 5 are as follows. 1H NMR (400.13 MHz, D2O): δ (ppm) 6.92 (s, 1H, H4-Im); 6.90 (s, 1H, H4-Im′); 6.84 (s, 1H, H5-Im); 6.79 (s, 1H, H5-Im′); 5.57 (br d, 1JHH = 14.0 Hz, 1H, NCH2N); 4.47 (br d, 1JHP= 14.0 Hz, 1H, PCH N); 4.34 (vt, 3JHH ≈ 3JHP = 12.2 Hz, 1H, NCH2N); 4.21−4.14 (m, 2H, NCH2N + 1H AB system NCH2N); 4.08 (AB system, 1JHAHB= 13.6 Hz, 1H, NCH2N); 3.75−3.95 (m, 2H, PCH2N); 3.65−3.75 (m, 2H, PCH2N); 3.10 (s, 3H, Me-Im); 2.90 (s, 3H, Me-Im′). 13C{1H} NMR (100.61 MHz, D2O): δ 144.64 (d, 3JCP = 6.7 Hz, C 2-Im); 143.99 (s, C 2-Im′); 125.43 (s, C 4-Im); 125.17 (s, C 4-Im′); 125.14 (s, C 5-Im); 125.04 (s, C 5-Im′); 75.78 (d, 3JCP = 2.2 Hz, NCH2N); 74.03 (d, 3JCP = 4.4 Hz, NCH2N); 70.40 (d, 3JCP = 8.1 Hz, NCH2N); 68.34 (d, 1JCP = 53.0 Hz, PCHN); 65.17 (d, 2JCP = 13.7 Hz, COH); 53.92 (d, 1JCP = 52.0 Hz, PCH2N); 52.74 (d, 1JCP = 56.0 Hz, PCH2N); 33.17 (s, Me-Im); 32.67 (s, Me-Im′). 31P{1H} NMR (161.98 MHz, D2O): δ −0.20 (s). Anal. 6294
dx.doi.org/10.1021/om200896g | Organometallics 2011, 30, 6292−6302
Organometallics
Article
X-ray-quality crystals were obtained as red needles by addition of EtOH to a CH2Cl2 solution of the complex. 1 H NMR (300.13 MHz, CDCl3): δ (ppm) 7.25 (d, 1JHH = 8.7 Hz, 2H, Ar); 6.73 (d, 1JHH = 8.7 Hz, 2H, Ar); 5.67 (d, 1JHH= 5.8, 1H, p-cymene); 5.63−5.55 (m, 2H, p -cymene); 5.45 (dd, 1JHH = 7.3 Hz, 3 JHP = 9.6 Hz, 1H, CH OH); 5.36 (d, 1JHH= 5.8 Hz, 1H, p-cymene); 4.82−4.42 (m, 9H, 3 × NCH2N + 1 × PCH2N + PCHN); 4.16−4.04 (m, 2H, PCH2N); 3.64 (d, 1JHH= 5.6 Hz, 1H, OH ); 3.19 (sept, 1JHH = 5.0 Hz, 1H, CH-Me2); 2.96 (s, 6H, N(CH3)2); 2.45 (s, 3H, p-cymene CH3); 1.31 (d, 1JHH = 6.9 Hz, 3H, CH-Me2); 1.30 (d, 1JHH = 6.9 Hz, 3H, CH-Me2). 13C{1H} NMR (100.61 MHz, CDCl3): δ 150.35 (s, Ar); 128.11 (d, 3JCP = 6.1 Hz, Ar); 127.68 (s, Ar); 112.32 (s, Ar); 112.01 (d, JCP= 3.1 Hz, CCHMe2); 101.28 (s, C-CH3); 89.27 (d, JCP = 3.1 Hz, CH p-cymene); 87.60 (d, JCP = 3.3 Hz, CH p-cymene); 83.93 (s, CH p-cymene); 84.80 (d, JCP = 2.8 Hz, CH p -cymene); 76.20 (d, 3 JCP = 2.5 Hz, NCH2N); 73.32 (d, 3JCP = 5.0 Hz, NCH2N); 71.50 (d, 3 JCP = 2.2 Hz, CHOH); 70.22 (d, 1JCP = 7.5 Hz, PC HN); 67.72 (d, 3 JCP = 5.6 Hz, NCH2N); 59.62 (d, 1JCP = 11.7 Hz, PCH2N); 54.20 (d, 1 JCP = 17.0 Hz, PCH2N); 40.53 (s, N(CH3)2); 31.95 (s, CCH-Me2); 23.71 (s, CCH-Me2); 22.15 (s, CCH-Me2); 20.71 (s, C-CH3). 31P{1H} NMR (121.50 MHz, CDCl3): δ −51.91 (s). Anal. Found (calcd) for C25H37I2N4OPRu (795.44 g mol−1): C 37.86 (37.75); H 4.86 (4.69); N 7.32 (7.04). IR (KBr, cm−1): ν(OH) 3411 (br, s); ν(arom) 1615 (m), 1522 (m). Synthesis of κ 2-P,N-[(η 6-p-cymene)Ru{PTA-CH(1-MeIm)OH}Cl]Cl (8). A flame-dried 100 mL Schlenk flask was charged with [(η 6p-cymene)RuCl2]2 (76 mg, 0.12 mmol), the diastereomerically enriched ligand 2 (77 mg, 0.29 mmol), and CHCl3 (25 mL). The clear red solution was heated to 60 °C for 5 h under N2. The resulting dark brown solution was filtered through Celite, and the volume was reduced to approximately 10 mL under vacuum. Et2O was added dropwise to produce a tan powder, which was collected under N 2, washed with Et2O, and dried in vacuo. Yield: 122 mg (85.9% based on Ru). S(H2O)20 °C = 320 g/L. Spectroscopic data for 8 (major diastereoisomer, values for minor diastereoisomer are reported in parentheses when distinguishable): 1H NMR (400.13 MHz, CDCl3): δ (ppm) 7.76 (br s, 1H, H4-Im); 6.93 (7.03) (br s, 1H, H5-Im); 6.05 (6.13) (AB system, JHAHB = 5.5 Hz, 1H, p-cymene); 5.98 (AB system, JHAHB = 5.5 Hz, 1H, p-cymene); 5.80 (5.72) (br s, 1H, p-cymene); 5.55 (br s, 1H, p-cymene); 5.54−5.43 (m, 2H, NCH2N); 5.22 (br d, 1H, CHOH); 4.78 (br d, 1H, PCHN); 4.60 (m, 3H, NCH 2N); 4.51 (AB system, JHAHB = 14.0 Hz, 1H, PCH2N); 4.40 (ad, 1H, PCH2N); 4.28 (AB system, JHAHB = 14.0 Hz, 1H, PCH2N); 4.10 (br d, 3JHP = 15.0 Hz, 1H, PCH2N); 4.02 (s, 3H, Me-Im); 3.47 (br s, 1H, PCH2N); 2.68 (m, 1H, CH-Me2); 1.81 (1.93) (s, 3H, p-cymene CH3); 1.29 (d, 3JHH = 6.7 Hz, 3H, CH-Me2); 1.19 (d, 3JHH = 6.7 Hz, 3H, CH-Me2). 13C{1H} NMR (100.61 MHz, CDCl3): δ 149.53 (s, C 2-Im); 134.64 (132.90) (s, C 4-Im); 122.22 (s, C 5-Im); 105.47 (s, C-CH3); 100.17 (s, CCH-Me2); 98.05 (d, JCP = 6.7 Hz, CH p-cymene); 95.60 (d, JCP = 7.0 Hz, CH p-cymene); 82.79 (s, CH p-cymene); 81.75 (s, CH p-cymene); 76.51 (d, 3JCP = 2.6 Hz, NCH2N); 74.17 (d, 3JCP = 6.3 Hz, NCH2N); 68.18 (d, 2JCP = 9.2 Hz, CHOH); 66.72 (s, NCH2N); 59.22 (d, 1JCP= 13.0 Hz, PC HN); 54.50 (d, 1JCP = 14.0 Hz, PCH2N); 52.56 (d, 1JCP = 19.0 Hz, PCH2N); 35.23 (s, Me-Im); 30.63 (s, CCH-Me2); 23.81 (s, CCHMe2); 20.89 (s, CCH-Me2); 18.50 (s, CCH3). 31P{1H} NMR (161.98 MHz, CDCl3): δ −26.37 (−22.88) (s). Anal. Found (calcd) for C21H32N5Cl2OPRu (573.4 g mol−1): C, 43.50 (43.98); H, 5.44 (5.62); N, 12.17 (12.21). IR (CH2Cl2, cm−1): ν(O−H) 3370 (sh); ν(CN) 1604. Synthesis of κ 2-P,N -[(η 6-p-cymene)Ru{PTA-C(1-MeIm)2OH}Cl]Cl (9). Following the same procedure as described for 8, the reaction of [(η 6-p-cymene)RuCl2]2 (75 mg, 0.12 mmol) and PTAC(1-MeIm)2OH (3) (102 mg, 0.29 mmol) produced a brown powder. Yield: 114 mg (71.4% based on Ru). S(H2O)20 °C = 170 g/L. Data for 9: 1H NMR (400.13 MHz, CD2Cl2): δ (ppm) 7.41 (s, 1H, H4-Im); 6.97 (s, 1H, H5-Im); 6.86 (s, 1H, H4-Im′); 6.81 (s, 1H, H5-Im′); 6.08 (AB system, JHAHB= 6.3 Hz, 1H, p-cym); 6.02 (AB system, JHAHB = 6.3 Hz, 1H, p-cymene); 5.57 (br s, 1H, p-cymene); 5.56 (br s, 1H, p-cymene); 5.29 (AB system, 2JHAHB = 13.5 Hz, 1H, NCH2N); 4.65−4.55 (m, 4H, NCH2N + 1H AB system NCH2N); 4.48 (br d, 2 JHP = 13.3 Hz, 1H, PCHN); 4.30 (AB system, JHAHB = 14.5 Hz, 1H,
PCH2N); 4.23 (s, 3H, Me-Im); 4.24−4.14 (m, 2H, PCH2N); 4.02 (AB system, JHAHB= 14.5 Hz, 1H, PCH2N); 3.01 (s, 3H, Me-Im′); 2.80 (sept, J = 6.9 Hz, 1H, CH-Me2); 2.05 (s, 3H, p-cymene CH3; 1.36 (d, 3 JHH = 6.8 Hz, 3H, CH-Me2); 1.27 (d, 3JHH = 6.8 Hz, 3H, CH-Me2). 13 C{1H} NMR (100.61 MHz, CD2Cl2): δ 150.39 (s, C 2-Im); 144.64 (d, 3JCP = 7.0 Hz, C 2-Im′); 134.73 (s, C 4-Im); 127.31 (s, C 4-Im′); 123.96 (s, C 5-Im); 122.82 (s, C 5-Im′); 107.63 (s, C-CH3); 105.67 (s, CCH-Me2); 96.86 (d, JCP = 5.9 Hz, CH p-cymene); 95.69 (d, JCP = 7.4 Hz, CH p-cymene); 82.14 (s, CH p-cymene); 81.53 (s, CH p-cymene); 78.48 (s, NCH2N); 76.85 (d, 3JCP = 3.3 Hz, NCH2N); 74.07 (d, 3JCP = 6.7 Hz, NCH2N); 68.23 (d, 2JCP = 9.3 Hz, COH-Im2); 64.47 (d, 1JCP = 14.1 Hz, PC HN); 54.14 (d, 1JCP = 22.9 Hz, PCH2N); 52.85 (d, 1JCP = 19.3 Hz, PCH2N); 36.78 (s, Me-Im); 36.65 (s, Me-Im′); 31.20 (s, CCH-Me2); 22.48 (s, CCH-Me2); 22.08 (s, CCH-Me2); 19.28 (s, C-CH3). 31P{1H} NMR (161.98 MHz, CD2Cl2): δ −19.77 (s). Anal. Found (calcd) for C25H36N7Cl2OPRu (653.6 g mol−1): C, 45.88 (45.94); H, 5.65 (5.55); N, 15.08 (15.01). IR (CH 2Cl2, cm−1): ν(O− H) 3284 (sh); ν (CN) 1606. X-ray Diffraction Data for κ 1-P -[(η 6-p-cymene)RuI2{(SR,RS)(PZA-NMe2)}] (7-I). X-ray data collections for compound 7-I were carried out at room temperature by using a CCD diffractometer equipped with Mo Kα radiation (0.71073 Å). The program CrysAlis CCD21 and CrysAlis RED22 were used for data collection and reduction, respectively. Absorption correction was applied through the program ABSPACK. The structure was solved by using the direct methods in Sir9723 and refined with SHELXL24 by using the fullmatrix least-squares method for all the available F 2 data. All of the nonhydrogen atoms were refined anisotropically, and the H atoms bonded to the carbon atoms were fixed in calculated positions and refined isotropically with thermal factors 20% larger (50% for the H of the methyl groups) than the atom to which they are bound. The hydrogen atom of the OH group was located in the Fourier difference map, and its coordinate was freely refined. All calculations were performed under the WINGX package.25 The molecular drawings were made by using ORTEP-III for Windows.26 Catalytic Hydrogenation Tests. Two different setups were used, depending on whether the tests were run at room temperature or higher. In the first case, up to seven 3 mL vials were charged under a protective nitrogen atmosphere with each precatalyst (7.0 × 10−3 mmol), base, substrate, 2 mL of solvent, and a micro stir bar. The vials were then transferred to the autoclave, which was flushed with H 2 for 10 min, then pressurized to 30 bar. After stirring at room temperature for the chosen time, the autoclave was depressurized and an aliquot of the reaction mixture (0.1 mL) was diluted with methanol (0.4 mL) and analyzed by GC; in the case of water as solvent, the products were extracted from the aqueous phase with dichloromethane, and the organic phase was analyzed by GC. In the second case, when heating was required, a 100 mL Parr autoclave was charged under nitrogen with precatalyst (2.6 × 10−2 mmol), base, substrate, and 40 mL of solvent, flushed with H2 for 10 min, then pressurized to 30 bar, stirred by mechanical stirring, and heated to the desired temperature by an external temperature controller (thermocouple). At the end of the test, the pressure was released and an aliquot of the reaction mixture (2 mL) was diluted in methanol (6 mL) and analyzed by GC; in the case of water, the aqueous phase was extracted with ethylacetate and analyzed by GC. Each test was repeated twice to check for reproducibility.
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RESULTS AND DISCUSSION Synthesis and Characterization of Water-Soluble Imidazolyl-Aminophosphines and Their Oxides. The monoimidazolyl “upper-rim”-functionalized PTA, 1′methylimidazolyl(1,3,5-triaza-7-phosphatricyclo[3.3.1.13,7]dec-6-yl)methanol (2, PTA-CH(1-MeIm)OH), and the bis-imidazolyl analogue bis-1′-methylimidazolyl(1,3,5-triaza-7-phosphatricyclo[3.3.1.13,7]dec-6-yl)methanol (3, PTA-C(1-MeIm)2OH) were respectively produced by combining a THF slurry of PTA-Li, obtained as recently described,18 with a solution of 1-methyl-2imidazolecarboxaldehyde or bis(N-methylimidazole-2-yl) ketone at
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Scheme 1. Synthesis of Ligands 2 and 3 and Their Oxides 4 and 5
−70 °C (Scheme 1). The resulting deep orange solutions were slowly warmed to room temperature, stirred overnight, and quenched with H2O. Upon removal of the solvent, 2 was purified by column chromatography, while 3 was purified via extraction and recrystallization with Et2O. Once isolated, compounds 2 and 3 were found to be air-stable solids that slowly oxidized in solution after several days. ESI-MS and elemental analysis data confirm the empirical formulas of compounds 2 and 3 as C11H18N5OP and C15H22N7OP, respectively. The presence of the OH moiety in the phosphines was identified via IR as each exhibited a broad stretching band near 3370 cm−1. The presence of two diastereomers in 2 was confirmed by 31P{1H} NMR, showing, as expected,16−18 two singlets at −103.39 and −104.65 ppm, respectively. Compound 3 consists of a pair of enantiomers; hence its spectrum contained only one singlet at −97.55 ppm. The diastereomeric mixture of 2 made the interpretation of its 1 H and 13C{1H} NMR spectra quite complicated. This mixture could be diastereomerically enriched by extraction and recrystallization from hot acetone, to a final 15:1 ratio based on integration of the 31P{1H} NMR singlets. The 1H spectrum of the enhanced system was still complicated by second-order effects. The presence of the imidazole fragment was clearly evident from the two doublets (3JHH = 1.1 Hz, 1H) at 6.84 and 6.81 ppm and the singlet with an integration of 3H at 3.74 ppm. These originated from the CHCH and NCH3 groups, respectively.27 The imidazole moiety was also observed in the 13 C{1H} spectrum, as the C atoms of the ring resonated at 148.24 (d, 3JCP = 4.1 Hz, NCNMe), 126.56 (s, NCCNMe), and 122.22 (s, NCCNMe) ppm. Additionally, the N−CH 3 carbon was observed as a singlet at 33.21 ppm. As for 2, the 1 H NMR spectrum of 3 was not first order in the region 3.8− 4.8 ppm, and the signals had significant overlaps. The imidazole protons, however, were quite informative. Two singlets (3H) were observed at 3.49 and 3.35 ppm for the NCH3 groups, while four doublets (JHH = 1.1 Hz, 1H) resonated at 6.94, 6.90, 6.87, and 6.83 ppm for the CHCH protons. These two distinct sets indicated that the two imidazolyl moieties were magnetically inequivalent due to the presence of the adjacent stereocenter. The presence of two inequivalent imidazole groups was further confirmed by the 13C{1H} NMR spectrum. Two singlets were observed at 34.40 and 33.18 ppm, corresponding to the C atoms of the NCH3 moieties. Additionally,
the C atoms of the two imidazole rings were observed as six separate signals at 147.48 (d, 3JCP = 4.1 Hz, NCNMe), 145.26 (s, NCNMe), 125.44 (s, NCCNMe), 124.55 (s, NCCNMe), 124.20 (s, NCCNMe), and 124.11 (s, NCCNMe) ppm. Although PTA is quite water-soluble (S(H2O)20 °C = 235 g/L),8 most of its upper-rim derivatives possess limited water solubility (S(H2O)20 °C = 3−14 g/L).16,17 It was hypothesized that the imidazole rings of compounds 2 and 3 could alleviate this problem, as the additional N atoms would enhance hydrogen bonding with water. As expected, both systems readily dissolved in water. Phosphine 2 had a solubility of 320 g/L, while 3 had a solubility of 78 g/L, the difference likely due to a different extension of the hydrogen bonding with the solvent.28 Solutions of 2 and 3 oxidized into OPTA-CH(1-MeIm)OH (4) and OPTA-C(1-MeIm)2OH (5), respectively, over several days when not under an inert atmosphere. This transformation was also readily accomplished by employing 35% H2O2 (Scheme 1). The oxidation was clearly observed in the IR spectra of 4 and 5 via PO stretches at 1152 and 1146 cm−1, respectively. The 31 1 P{ H} NMR spectrum of 4 exhibited two singlets at +0.59 and −0.48 ppm, as expected for its diastereomeric nature, while that of 5 displayed a single resonance at −0.20 ppm. A diastereomerically enriched sample (ca. 13:1) of 4 was produced by reacting H2O2 with an enhanced sample of 2. The 1H spectra of 4 and 5 largely mirrored those of their parent compounds. In terms of 5, this implied that the imidazole fragments were inequivalent. Compounds 4 and 5 were soluble in H2O (S(H2O)20 °C = 80 and 66.7 g/L, respectively), alcohols, and CH2Cl2. It was found, however, that 4 was insoluble in CHCl3. Hence, this solvent may be used to separate phosphine 2 from its oxide. Synthesis and Characterization of Ruthenium Complexes. Phosphines 2 and 3 have the potential to bind to transition metals in both monodentate κ 1-P (or κ 1-N) and chelating κ 2-P,N modes. Following on our interest in the coordination chemistry of PTA derivatives to Ru and the application of the resulting complexes in catalysis29 and as anticancer agents,29d,30 PZA, PZA-NMe2, 2, and 3 were allowed to react with [(η 6-p-cymene)RuCl2]2 (Scheme 2). PZA and PZA-NMe2 reacted cleanly with [(η 6-p-cymene)RuCl2]2 in CH2Cl2 at room temperature to form exclusively the neutral, three-legged piano stool compounds κ 1-P-[(η 6-pcymene)Ru(PZA)Cl2] (6) and κ 1-P -[(η 6-p-cymene)Ru(PZANMe2)Cl2] (7) (Scheme 2). 6296
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on the phosphine ligands.33 Similar considerations are valid for 13 C{1H} spectra of 8 and 9, both containing four different resonances for the carbon atoms of the arene ring in the range 81−98 ppm.34,35 The 1H and 13C data of the imidazole rings were important, as they indicated that the ligands were binding in the κ 2-P,N mode in 8 and 9 (see Tables 1 and 2). In the diastereomerically
Scheme 2. Synthetic Route to Ru Complexes 6−9
Table 1. 1H and 13C{1H} Chemical Shifts (ppm) and Coupling Constants (Hz) for the Imidazole Rings of 2 and 8 atom codea 2 4 5 NCH3 a
1
13
C{1H}, 2
H, 2
1
148.24 d (4.1) 126.56 s 122.22 s 33.21 s
6.84 d (1.1) 6.81 d (1.1) 3.74 s
13
H, 8
C{1H}, 8
149.53 134.64 122.22 35.23
7.76 br s 6.93 br s 4.02 s
s s s s
For atom code see Chart 2.
Table 2. 1H and 13 C{1H} Chemical Shifts (ppm) and Coupling Constants (Hz) for the Imidazole Rings of 3 and 9 atom codea
1
2
When the imidazolyl ligands 2 and 3 were reacted with the Ru precursor in CH2Cl2 at room temperature, the 31P{1H} NMR spectrum showed signals at −39.42, −35.21, −26.37, and −22.88 ppm in the case of 2 and singlets at −38.11 and −19.77 ppm for 3. As the upfield signals were in the region observed with compounds 6 and 7 (vide infra), we can assume that the signals at −39.42 and −35.21 ppm belong to the complexes obtained with the diastereomeric mixture of ligand 2 bound in the κ 1-P mode to Ru. Analogously, the signal at −38.11 ppm is likely due to a similar behavior of ligand 3. The 31P{1H} signal of PTN(R) has previously been reported to shift downfield upon changing from the κ 1-P and κ 2-P,N mode.13 Therefore, it was reasonable that the resonances −26.37 and −22.88 ppm were due to the κ 2-P,N product obtained with ligand 2 and the singlet at −19.77 ppm to that of ligand 3. All attempts to separate the mixture or to prepare the pure κ 1-P species by altering the reaction conditions have failed to date. As κ 2-P,N[(η 6-arene)Ru{PTN(Me)}Cl]Cl could be formed by refluxing the corresponding Ru arene dimer precursors with the P,N ligand in CHCl3,14 we reasoned that a similar behavior could be shown by our imidazolyl ligands. As expected, when 2 and 3 were refluxed with chloroform solutions of [(η 6-p-cymene)RuCl2]2, only complexes κ 2-P,N-[(η 6-p-cymene)Ru{PTA-CH(1-MeIm)OH}Cl]Cl (8) and κ 2-P,N -[(η 6-p-cymene)Ru{PTAC(1-MeIm)2OH}Cl]Cl (9) were obtained in good yields (Scheme 2).31 The 31P{1H} NMR spectrum of 8 contained two singlets at −26.37 and −22.88 ppm (CDCl3) in the same diastereomeric ratio of the P,N ligand, while in the case of 9 only one resonance at −19.77 ppm (CD2Cl2) was observed, as expected. The 1H NMR spectra of complex 8 obtained using a diastereomeric enriched sample of the ligand (15:1) and that of 9 both contained four resonances for the p-cymene ring protons in the range 5.5−6.1 ppm and two separate doublets due to CH3 groups at 1.29 (3JHH = 6.8 Hz) and 1.19 (3JHH = 6.6 Hz) ppm and 1.36 (3JHH = 6.9 Hz) and 1.27 (3JHH = 6.8 Hz) ppm, respectively.32,33 The same behavior was found also for κ 1-P complexes 6 and 7 due to the presence of two stereocenters
4 5 NCH3 a
13
H, 3
6.94 d (1.1) 6.90 d (1.1) 6.87 d (1.1) 6.83 d (1.1) 3.49 s 3.35 s
C{1H}, 3
147.48 d (4.1) 145.26 s 125.44 s 124.55 s 124.20 s 124.11 s 34.40 s 33.18 s
1
H, 9
7.41 6.86 6.97 6.81 4.23 3.01
s s s s s s
13
C{1H}, 9
150.39 s 144.64 d (7.0) 134.73 s 127.31 s 123.96 s 122.82 s 36.78 s 36.65 s
For atom code see Chart 2.
enriched free ligand 2, the H4 proton resonance of the imidazole ring (Chart 2) was observed at 6.84 (d, 3JHH = 1.1 Hz) ppm. Chart 2
In 8, however, the corresponding signal was dramatically shifted downfield to 7.76 ppm (br s). This large shift was likely due to the close proximity of the proton to the N donor, as this H would encounter the greatest σ-effect.36 These data thus indicated that N3 was binding to the Ru center. This hypothesis was supported by the fact that only a slight shift was observed for H5 (Table 1). Similar results were seen in the 13C NMR. The C5 singlet was observed at the same resonance (122.22 ppm) for both the free ligand and the complex. However, a downfield shift was observed with C4. In the free ligand, C4 resonated at 126.56 ppm, while in the complex, its singlet was observed at 134.64 ppm. Similar dramatic chemical shift effects have previously been observed with other P-imidazole ligands and their κ 2-P,N complexes.33,36 6297
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[{Ru(η 6-C10H14)}2(Cl)3]+. The phosphorus atom binds to ruthenium in the κ 1-P mode with a Ru−P distance of 2.3416(16) Å. Regarding the adamantane cage, the P1−C1 distance is slightly longer than the other P−C distances, while there are no significant differences in the C−N distances. This feature was previously observed for other PZA cage structures.16−18 An intramolecular hydrogen bond between the OH group and one iodine atom (O1···I1 = 3.4698(45) Å) was present, similar to what was observed for [Cp*IrCl2(PZA)].17 Interestingly, in the crystal structure of the free PZA molecule, the OH group forms a strong intermolecular hydrogen bond with one nitrogen atom of the adamantane cage, forming a 1D infinite chain.18 Computational DFT Studies on κ 1-P vs κ 2-P,E (E = O, N) Coordination Behavior of Ligands to Ru. The lability of the chloride ligand in the polar solvents and the donor abilities of the oxygen and/or nitrogen atoms could, in principle, favor the formation of a κ 2-P,O or κ 2-P,N coordination mode. In order to gain more details on the geometric and energetic factors that govern the coordination mode around the Ru center, a theoretical investigation at the DFT/B3LYP level of theory was carried out. On the basis of a previous study, 18 all the possible coordination modes of PTA derivatives were investigated. No structural approximations were introduced, and the calculations were performed in chloroform solution, the same solvent used during the synthesis. As pointed out before, 18 for compound 7, four nitrogen atoms could in principle act as proton acceptors following hydroxyl group deprotonation, so six models were investigated: the first one with the coordination κ 1-P (7a), four related with the κ 2-P,O coordination with a variable proton acceptor (7b+: H on N1; 7c+: H on N2; 7d+: H on N3; 7e+: H on N4), and the last one with κ 2P,OH coordination (7f+). All of the structures were optimized and confirmed as minima by the frequencies calculations (see Supporting Information for details). In all conformers 7a−f+ the Ru atom displays an octahedral coordination environment with the Ru−cymene centroid distances in the range 2.21−2.34 Å and the Ru−Cl of 2.47 Å. In 7a, the proton of the OH group is involved in hydrogen bonding with one of the two coordinated chloride atoms [d(O−H‑‑‑Cl) ca. 2.2 Å]. The changes in the coordination modes of PTA derivatives did not strongly affect the remaining coordination environment of the Ru center, with the average Ru−O bond length of 2.1 Å. Only in 7f+ was an elongation of the Ru−O bond distance (ca. 0.13 Å) observed. This was likely due to a residual interaction of the bonded proton with the adjacent chloride (2.98 Å). In order to identify the most stable species in solution and the most probable protonation center, the relative energy of each conformer was evaluated together with the energy of the free chloride in chloroform solution. Among all the κ 2-P,O coordination isomers, the most stable free energies were associated with the conformers 7b+ and 7f+, with the latter more stable by ca. 8.7 kcal mol−1. Nevertheless, the most stable conformer was 7a, with an energy stabilization of 18.7 kcal mol−1 with respect to the system 7f+ + Cl−. The optimized structures of the conformers 7a, 7b+, and 7f+ are shown in Figure 2. The optimized structures of the remaining conformers are reported in the Supporting Information. The high energy difference between κ 1-P (7a) and the κ 2P,OH coordination (7f+) suggests that at room temperature only the former conformer is reasonably present in solution. In order to investigate all the possible products, the neutral κ 2-P,O
Similar spectroscopic changes were observed with the bisimidazole ligand and its Ru complex (Table 2). Since phosphine 3 contained two inequivalent imidazoles, two H4 doublets (3JHH = 1.1 Hz) were observed at 6.94 and 6.90 ppm. In the Ru complex 9, the corresponding signals were at 7.41 and 6.86 ppm. The substantial chemical shift change of only one signal indicated that one of the imidazole rings had coordinated via N3, while the other ring was not attached. Therefore, in this particular case, ligand 3 acted in a κ 2-P,N mode and not a tridentate κ 3-P,N,N fashion. This has previously been observed for other P,N,N ligands.37 The conclusions supported by NMR data indicating preferential κ 1-P binding of PZA and PZA-NMe2 and κ 2-P,N binding of 2 and 3 to Ru, respectively, have been substantiated by DFT calculations (vide infra). The Ru compounds 6−9 were found to be soluble in most halogenated hydrocarbons, alcohols, and water. In fact, the water solubilities of 6−9 were determined to be 2.7, 1.4, 320, and 170 g/L, respectively. The solubilities of 8 and 9 are substantially greater than those of related Ru(arene) complexes that contained upper-rim-derivatized PTA ligands, usually falling in the range 4−11 g/L. 16 This remarkable difference is likely due to the noncoordinating imidazole nitrogen atoms, which may undergo hydrogen bonding with H2O. X-ray Crystal Structure of κ 1-P -[(η 6-p-cymene)RuI2{(SR,RS)(PZA-NMe2)}] (7-I). Red needles of 7-I were obtained from the slow diffusion of dry ethanol in a CH2Cl2 solution of the complex. These were suitable for X-ray crystal diffraction. The X-ray crystal structure shows that the complex crystallizes in a centrosymmetric space group, and both the SR and RS isomers are present in the cell. Figure 1 shows an
Figure 1. ORTEP plot (ellipsoids drawn at 50% probability level) of complex 7-I; O−H···I hydrogen bonding shown as empty lines. Selected bond distances (Å) and angles (deg): Ru1−P1, 2.3416(16); Ru1−I1, 2.7375(8); Ru1−I2, 2.7398(8); Ru1−C17, 2.243(6); Ru1− C18, 2.196(6); Ru1−C19, 2.203(7); Ru1−C20, 2.288(6); Ru1−C21, 2.250(5); Ru1−C22, 2.192(6); P1−C1, 1.885(7); P1−C2, 1.845(7); P1−C3, 1.845(6); P1−Ru1−I1, 85.95(5); P1−Ru1−I2, 86.68(5); I1− Ru1−I2, 89.84(2).
ORTEP drawing with selected distances and angles in the caption. The geometry around the ruthenium atom in 7-I is an octahedron, where p-cymene occupies three coordination positions, while two iodine atoms (in cis position) and one PZA-NMe2 ligand occupy the other three sites. The Ru−C distances are between 2.192(6) and 2.288(6) Å, thus slightly longer than the corresponding distances 38 in the cation 6298
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Figure 2. Optimized structures and relative energies (kcal mol −1) for κ 1-P (7a), κ 2-P,O (7b+), and κ 2-P,OH (7f+) coordination modes. Color code: oxygen, red; nitrogen, blue; phosphorus, pink; chlorine, green; ruthenium, gray; carbon, black; hydrogen, white. The methyl substituents on the pcymene ring are omitted for clarity.
proton acceptor (8b+), κ 2-P,N (8c+), κ 2-P,OH (8d+), and κ 2P,O coordination without N protonation (8e). The optimized structures are reported in Figure 4.
coordination (7g), formed by the loss of a HCl molecule, was also considered, and the optimized structure is reported in Figure 3. The compound shares with the aforesaid complexes all the structural features with no significant differences.
Figure 3. Optimized structure and relative energy (kcal mol−1) for isomer κ 2-P,O (7g).
The comparison of 7g + HCl with 7f+ + Cl− shows a slight stabilization (less than 0.5 kcal mol−1) of the latter. Thus, at room temperature the κ 1-P coordination mode is confirmed as the only one available. When the temperature is increased, for example at reflux in chloroform (around 70 °C), both coordination modes could be active. When an imidazole unit was introduced in the “upper rim”, such as in compound 8, κ 1-P and two chelate coordination modes, i.e., κ 2-P,O and κ 2-P,N, can be expected. Calculations on compound 8 lead to the optimization of five different structures, namely, κ 1-P (8a), κ 2-P,O coordination with N1 as
Figure 4. Optimized structures and relative energies (kcal mol−1) for isomers κ 1-P (8a), κ 2-P,O (8b+), κ 2-P,N (8c+), κ 2-P,OH (8d+), and κ 2-P,O (8e). 6299
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As for compound 7, in all the investigated conformers the octahedral coordination around Ru was maintained. In conformers 8a and 8c+ a hydrogen bond between the coordinated chloride and the OH was found (2.18 Å); however, in 8d+ hydrogen bonding seems unlikely [d(Cl‑‑‑H) = 2.8 Å]. When the energy differences were calculated, the κ 2-P,N coordination mode of 8c+ was ca. 14.3 kcal mol−1 more stable than the κ 2-P,O mode of 8d+. It is possible that the Ru preferentially binds to the imidazole N donor atom, due to the softer nature if compared to the OH group and adamantane N atoms. A slight further stabilization of compound 8c+ could be due to the presence of an intramolecular Cl---H−O hydrogen bond. Even though the most stable compound is 8c+, the comparison among the three κ 2-P,O coordination modes reveals that 8e is ca. 4.0 kcal mol−1 more stable than the parent 8d+. However, the energy comparison between κ 1-P and κ 2-P,N reveals only a very small stabilization of the former by ca. 6.7 kcal mol−1 with respect to the latter, suggesting that in solution both conformers can be present. The energy difference becomes even smaller when two imidazole substituents are introduced, as in complex 9. In fact, in such a compound, the stabilization energy difference between the κ 1-P (9a) and κ 2-P,N (9c+) coordination is only 4.0 kcal mol−1 (see Supporting Information for details). This is in good agreement with the experimental data, which show the presence of both coordination modes at room temperature. Furthermore, due to the small energy difference, it can be predicted that when the temperature is increased, the entropic contribution can be fundamental and the κ 2-P,N isomer (9c+) becomes predominant, as found experimentally in chloroform under reflux conditions. An intramolecular hydrogen bonding is present for 9c+, where the uncoordinated OH is involved in an interaction with one nitrogen atom of the PTA unit [d(O−H‑‑‑N)
= 1.9 Å]. Noteworthy is the fact that all efforts to optimize the geometry of κ 2-P,OH (9d+) failed. Thus, the metal center remained with a free coordination position, and in turn the metal−C(p-cymene) distances were found to decrease. The corresponding coordinative unsaturation around the Ru metal resulted in the particularly high energy of conformer 9d+ compared to 9c+ (ca. 17.5 kcal mol−1), leading to an isomer that is unlikely to form experimentally. Finally, the structure of a neutral κ 2-P,O isomer, 9e, resulting from formal elimination of HCl from 9a without N-protonation was also optimized. 9e was ca. −4.0 kcal mol−1 more stable than 9d+ and −2.9 kcal mol−1 than 9b+, but less stable by 13.4 kcal mol−1 than the 9c+/ Cl− couple. This suggested that, also in this case, OH group deprotonation must be followed by protonation at the N atom of the PTA moiety. Ruthenium-Catalyzed Hydrogenation Reactions. Ru complexes have a rich history as homogeneous catalysts for a variety of reactions, including the hydrogenation of carbonyl groups to alcohols.39−41 This reaction can be run either under transfer hydrogenation conditions,42 typically in i-PrOH in the presence of a strong base, or under a pressure of hydrogen. Mixed systems using transfer hydrogenation conditions under a pressure of hydrogen are also known.43 We tested compounds 6−9 as catalysts for CO bond reduction, mainly using acetophenone as a model substrate. The most relevant results are summarized in Table 3. From Table 3, it can be observed that all catalysts were active, although not rivaling the state-of-the-art bifunctional Ru catalysts,44 using the protocol involving H2 (30 bar), tBuOK, and iPrOH as solvent, giving conversions ranging from moderate to excellent depending on the precatalyst and reaction temperature. In the presence of the most active precatalyst, namely, complex 8 used as the 1:1 diastereomeric
Table 3. Hydrogenation of Acetophenone Catalyzed by 6−9 under a Pressure of H 2 in the Presence of Added Base run
catalyst
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
a
6 6a 6c 6c 7a 7c 7c 7c 7c,d 8a 8a 8a,d 8c 8c 8c 8c 8c,d 8c 8c 9a 9a 9c 9c
solvent i
PrOH PrOH i PrOH i PrOH i PrOH i PrOH H2O i PrOH i PrOH H2O i PrOH i PrOH i PrOH i PrOH i PrOH i PrOH i PrOH i PrOH H2O i PrOH H2O i PrOH i PrOH i
base
temperature (°C)
time (h)
conversion (%) b
BuOK BuOK t BuOK t BuOK t BuOK t BuOK KOH t BuOK t BuOK KOH t BuOK t BuOK t BuOK t BuOK t BuOK t BuOK t BuOK t BuOK KOH t BuOK KOH t BuOK t BuOK
25 25 60 80 25 60 60 80 80 25 25 25 40 40 40 60 60 60 60 25 25 60 80
4 4 4 4 4 4 4 4 4 4 4 4 1 4 4 1 4 4 4 4 4 4 4
15.85 26.06 45.98 95.31 2.01 48.49 25.41 92.94 95.89 4.88 84.14 82.04 94.82 97.91 89.71 100 98.4 100 38.19 3.48 0 53.02 96.91
cat/sub/base 1/250/5 1/250/50 1/250/5 1/250/5 1/250/50 1/250/5 1/250/10 1/250/5 1/250/5 1/100/50 1/250/5 1/250/5 1/250/5 1/500/5 1/1000/5 1/250/5 1/250/5 1/500/5 1/250/5 1/250/5 1/100/50 1/250/5 1/250/5
t t
a
Solvent, 2 mL; pH2, 30 bar; catalyst, 7.0 × 10−3 mmol. bConversions determined by GC based on pure samples. cSolvent, 40 mL; pH2, 30 bar; catalyst, 2.6 × 10−2 mmol. dAddition of one drop of Hg(0). 6300
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mixture, the reactions could be run with high efficiency at room temperature (run 11) or under very mild (40 °C) temperature conditions (runs 13−15). The catalyst load could be decreased from the standard 0.4% to as low as 0.1% without significant loss of activity. The homogeneous nature of the catalysis was proven by a standard Hg(0) poisoning test,45 showing very low decrease of activity under these conditions (runs 9, 12, 17). Disappointingly, only a maximum 38% conversion (run 19) was obtained using H2O/KOH/H2 in the presence of precatalyst 8 (1:250 catalyst to substrate ratio) at 60 °C. The catalysts were also tested for the reduction of 2cyclohexenone under the experimental conditions described in Table 3 (catalyst/substrate/base = 1:250:5). Only catalyst 8 gave good conversion (64.7%, 4 h, 25 °C), although the selectivity of the reaction was not excellent (cyclohexanone, 22.1%; 2-cyclohexenol, 1.0%; cyclohexanol, 41.6%). Acetophenone hydrogenation was also tested with catalysts 6−9 under standard transfer hydrogenation conditions, i. e., i PrOH/KOH at reflux (80 °C). Using catalyst/substrate ratios of 1:500, the κ 1-P compounds 6 and 7 gave conversions of 3.8% and 6.8% after 3 h. As these results compare well with conversions obtained in our hands using the ligand-free complex [(p-cymene)RuCl2]2 under the same conditions (4.2% conversion after 3 h), we can suggest that ligand decoordination may occur, leaving unknown Ru species to catalyze the hydrogenation reactions. On the other hand, compound 8 was quite effective, reaching ca. 73% conversion at 0.2% mol and 95% conversion at 1.0% mol catalyst loading after 3 h, respectively. Poor stability of complex 9 under the same conditions was deduced from the immediate darkening of the solution upon mixing the reagents, and no conversion was observed. Poor conversions (less than 5%) were observed using H2O/HCOONa as mild reducing protocol at 80 °C, accompanied by phosphine decoordination and oxidation as deduced by 31P{1H} NMR experiments run on aliquots of the reaction mixtures after the catalytic runs, giving signals at the same chemical shift values of isolated phosphine oxides (vide infra).
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conversions with catalyst loadings as low as 0.1%. More detailed structure−activity relationship and mechanistic studies are in progress.
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ASSOCIATED CONTENT * Supporting Information Cartesian coordinates for complexes 6−9; cif files, crystal data, and structure refinement for 7-I. This material is available free of charge via the Internet at http://pubs.acs.org. S
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AUTHOR INFORMATION Corresponding Author *E-mail:
[email protected];
[email protected];
[email protected].
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ACKNOWLEDGMENTS
The authors thank MATTM and DPM-CNR for financial support through PIRODE and EFOR projects. MIUR is thanked for support through PRIN 2009. GDRE project “Catalyse Homogène pour le Développement Durable (CH2D)” and COST Action CM0802 “PhoSciNet” are also thanked for funding mobility. L.G. thanks MAE for a JRP grant within the Executive Programme of Cooperation Italy-USA (2008−2010). D.A.K. thanks American Chemical Society Petroleum Research Fund (grant 49372-UFS) and Fulbright Research Scholarships (2009−2010) for partially supporting his stay at ICCOM CNR. A.I. and G.M. thank the ISCRA-CINECA HP grant “HP10BNL89W” for the computational time.
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DEDICATION Dedicated to our friend Prof. Christian Bruneau on the occasion of his 60th birthday.
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REFERENCES
(1) Handbook of Green Chemistry: Green Solvents; Anastas, P. T., Leitner, W., Jessop, P. G., Li, C.-J., Wasserscheid, P., Stark, A., Eds.; Wiley-VCH: Weinheim, Germany, 2010. (2) Shaughnessy, K. H. Chem. Rev. 2009, 109, 643−710. (3) Reviews of water-soluble phosphines and their applications have recently been published. (a) Bravo, J.; Bolaño, S.; Gonsalvi, L.; Peruzzini, M. Coord. Chem. Rev. 2010, 254, 555−607. (b) James, B. R.; Lorenzini, F. Coord. Chem. Rev. 2010, 254, 420−430. (c) Organic Reactions in Water: Principles, Strategies and Applications; Lindstroem, U. M., Ed.; Blackwell Publishing: Oxford, UK, 2007. (4) Jeffrey, J. C.; Rauchfuss, T. B. Inorg. Chem. 1979, 18, 2658−2666. (5) Bonnaventure, I.; Charette, A. B. J. Org. Chem. 2008, 73, 6330− 6340. (6) Several reviews have recently been written on this topic. (a) Grotjahn, D. B. Pure Appl. Chem. 2010, 82, 635−647. (b) Karaski, A. A.; Balueva, A. S.; Naumov, R. N.; Kulikov, D. V.; Spiridonova, Y. S.; Sinyahsin, O. G.; Hey-Hawkins, E. Phosphorus, Sulfur Silicon Relat. Elem. 2008, 183, 583−585. (c) Weng, Z.; Shihui, T.; Hor, T. S. A. Acc. Chem. Res. 2007, 40, 676−684. (d) Breit, B. Angew. Chem., Int. Ed. 2005, 44, 6816−6825. (7) (a) Lundgren, R. J.; Peters, B. D.; Alsabeh, P. G.; Stradiotto, M. Angew. Chem., Int. Ed. 2010, 49, 4071−4074. (b) Mazuela, J.; Paptchikhine, A.; Tolstoyt, P.; Pamies, O.; Dieguez, M.; Andersson, P. G. Chem.Eur. J. 2010, 16, 620−638. (c) Zhang, Y.; Han, Z.; Li, F.; Ding, K.; Zhang, A. Chem. Commun. 2010, 156−158. (d) Schulz, T.; Torborg, C.; Schaeffner, B.; Huang, J.; Zapf, A.; Kadyrov, R.; Boerner, A.; Beller, M. Angew. Chem., Int. Ed. 2009, 48, 918−921. (e) Han, Z.; Wang, Z.; Zhang, X.; Ding, K. Angew. Chem., Int. Ed. 2009, 48, 5345− 5349. (f) Wechler, D.; Stradiotto, M. Can. J. Chem. 2009, 87, 72−79.
CONCLUSIONS
In this study, the first imidazole derivatives of PTA, 1-methylimidazolyl(1,3,5-triaza-7-phosphatricyclo[3.3.1.1 3,7]dec-6-yl)methanol (2, PTA-CH(1-MeIm)OH) and bis(1-methylimidazolyl)(1,3,5-triaza-7-phosphatricyclo[3.3.1.13,7]dec-6-yl)methanol (3, PTA-C(1-MeIm)2OH) have been prepared, characterized, and shown to have water solubilities that far exceed most known upper-rim analogues, likely due to extensive hydrogen bonding in solution. It was shown that reaction of these ligands with [Ru(η 6-p-cymene)Cl2]2 in refluxing CHCl3 gave the chelate compounds κ 2-P,N -[(η 6-p-cymene)Ru(PTA-CH(1-MeIm)OH)Cl]Cl (8) and κ 2-P,N -[(η 6-p-cymene)Ru(PTA-C(1MeIm)2OH)Cl]Cl (9), in contrast with what is observed for potential (P,O) ligands such as PZA and PZA-NMe2, which form preferentially the κ 1-P species [(η 6-p-cymene)Ru(PZA)Cl2] (6) and [(η 6-p-cymene)Ru(PZA-NMe2)Cl2] (7). This experimental finding was explained by DFT calculations, pointing out the different coordination abilities and energy differences between all possible isomers, suggesting that the higher chelating properties of 2 and 3 may be due to the softer nature of the N atom on the imidazole ring compared to both O hydroxyl and adamantane cage N atoms. Compounds 6−9 were tested in base-assisted catalytic hydrogenation of acetophenone, with compound 8 outperforming the others both at room temperature and at 40 °C, giving complete 6301
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Organometallics
Article
(30) (a) Ang, W. H.; Casini, A.; Sava, G.; Dyson, P. J. J. Organomet. Chem. 2011, 696, 989−998. (b) Nowak-Sliwinska, P.; van Beijnum, J. R.; Casini, A.; Nazarov, A. A.; Wagnieres, G.; van den Bergh, H.; Dyson, P. J.; Griffioen, A. W. J. Med. Chem. 2011, 54, 3895−3902. (c) Vock, C. A.; Renfrew, A. K.; Scopelliti, R.; Juillerat-Jeanneret, L.; Dyson, P. J. Eur. J. Inorg. Chem. 2008, 1661−1671. (d) Dorcier, A.; Hartinger, C. G.; Scopelliti, R.; Fish, R. H.; Keppler, B. K.; Dyson, P. J. J. Inorg. Biochem. 2008, 102, 1066−1076. (31) The synthesis of κ 2-P,N -[(η 6-p-cymene)Ru(PZA-NMe2)Cl]Cl was attempted by carrying out the reaction in CHCl3 at reflux conditions. Monitoring the reaction by 31P{1H} NMR spectroscopy, it was observed that a mixture of 7 and a second product, with signals at −16.51 ppm, was obtained in 2:1 ratio after 24 h in all cases. Attempts to separate the two compounds by crystallization or column chromatography have not been successful so far. (32) Caballero, A.; Jalon, F. A.; Manzano, B. R.; Espino, G.; PerezManrique, M.; Mucientes, A.; Poblete, F. J.; Maestro, M. Organometallics 2004, 23, 5694−5706. (33) Hounjet, L. J.; Bierenstiel, M.; Ferguson, M. J.; McDonald, R.; Cowie, M. Inorg. Chem. 2010, 49, 4288−4300. (34) (a) de la Encarnacion, E.; Pons, J.; Yanez, R.; Ros, J. Inorg. Chim. Acta 2005, 358, 3272−3276. (b) Moldes, I.; de la Encarnacion, E.; Ros, J.; Alvarez-Larena, A.; Piniella, J. F. J. Organomet. Chem. 1998, 566, 165−174. (35) Jalil, M. A.; Yamada, T.; Fujinami, S.; Honjo, T.; Nishikawa, H. Polyhedron 2001, 627−633. (36) Jahil, M. A.; Fujinami, S.; Nishikawa, H. J. Chem. Soc., Dalton Trans. 1999, 3499−3505. (37) Liu, S.; Peloso, R.; Braunstein, P. Dalton Trans. 2010, 39, 2563− 2572. (38) Liu, L.; Zhanga, Q. F.; Leung, W. H. Acta Crystallogr. 2004, E60, m506−m508. (39) Several reviews have recently been written on this issue. (a) Modern Reduction Methods; Andersson, P. G., Munslow, I. J., Eds.; Wiley-VCH: Weinheim, Germany, 2008. (b) Asymmetric Synthesis, 2nd ed.; Christmann, M., P., G., Braese, S., Eds.; Wiley-VCH: Weinheim, Germany, 2008. (c) Ito, M.; Ikariya, T. Chem. Commun. 2007, 5134− 5142. (d) Hems, W. P.; Groarke, M.; Zanotti-Gerosa, A.; Grasa, G. A. Acc. Chem. Res. 2007, 40, 1340−1347. (40) (a) Baratta, W.; Rigo, P. Eur. J. Inorg. Chem. 2008, 26, 4041− 4053. (b) Handbook of Homogeneous Hydrogenation, Vol. 2; De Vries, J. G., Elsevier, C. J., Eds.; Wiley-VCH: Weinheim, Germany, 2007. (41) Clapham, S. E.; Hadzovic, A.; Morris, R. H. Coord. Chem. Rev. 2004, 248, 2201−2237. (42) (a) Mebi, C. A.; Nair, R. P.; Frost, B. J. Organometallics 2007, 26, 429−438. (b) Fekete, M.; Joo, F. Collect. Czech. Chem. Commun. 2007, 72, 1037−1045. (43) Malacea, R.; Manoury, E.; Poli, R. Coord. Chem. Rev. 2010, 254, 729−752, and references therein. (44) (a) Noyori, R.; Hashiguchi, S. Acc. Chem. Res. 1997, 30, 97− 102. (b) Yamakawa, M.; Ito, H.; Noyori, R. J. Am. Chem. Soc. 2000, 122, 1466−1478. (c) Noyori, R.; Ohkuma, T. Angew. Chem., Int. Ed. 2001, 40, 40−73. (d) Noyori, R. Angew. Chem., Int. Ed. 2002, 41, 2008−2022. (e) Sandoval, C. A.; Ohkuma, T.; Muniz, K.; Noyori, R. J. Am. Chem. Soc. 2003, 125, 13490−13503. (f) Ikariya, T.; Murata, K.; Noyori, R. Org. Biomol. Chem. 2006, 4, 393−406. (g) Sandoval, C. A.; Bie, F.; Matsuoka, A.; Yamaguchi, Y.; Hiroshi, N.; Li, Y.; Koichi, K.; Utsumi, N.; Tsutsumi, K.; Ohkuma, T.; Murata, K.; Noyori, R. Chem. Asian J. 2010, 5, 806−816. (45) (a) Whitesides, G. M.; Hackett, M.; Brainard, R. L.; Lavalleye, J.-P. P. M.; Sowinski, A. F.; Izumi, A. N.; Moore, S. S.; Brown, D. W.; Staudt, E. M. Organometallics 1985, 4, 1819−1830. (b) Hamlin, J. E.; Hirai, K.; Gibson, V. C.; Maitlis, P. M. J. Mol. Catal. 1982, 15, 337− 347. (c) Lin, Y.; Finke, R. G. Inorg. Chem. 1994, 33, 4891−4910.
(8) (a) Phillips, A. D.; Gonsalvi, L.; Romerosa, A.; Vizza, F.; Peruzzini, M. Coord. Chem. Rev. 2004, 248, 955−993. (b) Daigle, D. J. Inorg. Synth. 1998, 32, 40−45. (9) (a) Mena-Cruz, A.; Lorenzo-Luis, P.; Romerosa, A.; SerranoRuiz, M. Inorg. Chem. 2008, 47, 2246−2248. (b) Mena-Cruz, A.; Lorenzo-Luis, P.; Romerosa, A.; Saoud, M.; Serrano-Ruiz, M. Inorg. Chem. 2007, 46, 6120−6128. (10) (a) Assmann, B.; Angermaier, K.; Paul, M.; Riede, J.; Schmidbauer, H. Chem. Ber. 1995, 128, 891−900. (b) Assmann, B.; Angermaier, K.; Schmidbaur, H. J. Chem. Soc., Chem. Commun. 1994, 941−942. (c) Caporali, M.; Gonsalvi, L.; Zanobini, F.; Peruzzini, M. Inorg. Synth. 2010, 35, 96−101. (11) (a) Jaremko, L.; Kirillov, A. M.; Smolenski, P.; Pombeiro, A. J. L. Cryst. Growth Des. 2009, 9, 3006−3010. (b) Ruiz, M. S.; Romerosa, A.; Sierra-Martin, B.; Fernandea-Babbero, A. Angew. Chem., Int. Ed. 2008, 47, 8665−8669. (c) Lidrissi, C.; Romerosa, A.; Saoud, M.; Serrano-Ruiz, M.; Gonsalvi, L.; Peruzzini, M. Angew. Chem., Int. Ed. 2005, 44, 2568−2572. (12) Frost, B. J.; Bautista, C. M.; Huang, R.; Shearer, J. Inorg. Chem. 2006, 45, 3481−3483. (13) (a) Caporali, M.; Bianchini, C.; Bolaño, S.; Bosquain, S. S.; Gonsalvi, L.; Oberhauser, W.; Rossin, A.; Peruzzini, M. Inorg. Chim. Acta 2008, 361, 3017−3023. (b) Phillips, A. D.; Bolaño, S.; Bosquain, S. S.; Daran, J. C.; Malacea, R.; Peruzzini, M.; Poli, R.; Gonsalvi, L. Organometallics 2006, 25, 2189−2200. (14) Renfrew, A. K.; Phillips, A. D.; Egger, A. E.; Hartinger, C. G.; Bosquain, S. S.; Nazarov, A. A.; Keppler, B. K.; Gonsalvi, L.; Peruzzini, M.; Dyson, P. J. Organometallics 2009, 28, 1165−1172. (15) Wong, G. W.; Harkreader, J. L.; Mebi, C. A.; Frost, B. J. Inorg. Chem. 2006, 45, 6748−6755. (16) Wong, G. W.; Lee, W.-C.; Frost, B. J. Inorg. Chem. 2008, 47, 612−620. (17) Erlandsson, M.; Gonsalvi, L.; Ienco, A.; Peruzzini, M. Inorg. Chem. 2008, 47, 8−10. (18) Guerriero, A.; Erlandsson, M.; Krogstad, D. A.; Ienco, A.; Peruzzini, M.; Reginato, G.; Gonsalvi, L. Organometallics 2011, 30, 1874−1884. (19) Bennett, M. A.; Huang, T. N.; Matheson, T. W.; Smith, A. K. Inorg. Synth. 1982, 21, 74−78. (20) Carrion, M. C.; Jalon, F. A.; Manzano, B. R.; Rodriguez, A. M.; Sepulveda, F.; Maestro, M. Eur. J. Inorg. Chem. 2007, 3961−3973. (21) CrysAlis CCD, Version 1.171.34.41 (release 13-09-2010); Oxford Diffraction Ltd., CrysAlis171.NET. (22) CrysAlis RED, Version 1.171.34.41 (release 13-09-2010); Oxford Diffraction Ltd., CrysAlis171.NET. (23) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. C.; Polidori, G.; Spagna, R. J. Appl. Crystallogr. 1999, 32, 115−119. (24) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112−122. (25) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837−838. (26) Burnett, M. N.; Johnson, C. K. ORTEP-III; Oak Ridge National Laboratory: Oak Ridge, TN, USA, 1996. (27) For a brief discussion of the NMR spectroscopy of P-imidazole ligands see the following. (a) Jahil, M. A.; Yamada, T.; Fuginami, S.; Honjo, T.; Nashikawa, H. Polyhedron 2001, 20, 627−633. (b) Jahil, M. A.; Fujinami, S.; Senda, H.; Nishikawa, H. J. Chem. Soc., Dalton Trans. 1999, 1655−1662. (28) Krogstad, D. A.; Gohmann, K. E.; Sunderland, T. L.; Geis, A. L.; Bergamini, P.; Marvelli, L.; Young, V. G. Jr. Inorg. Chim. Acta 2009, 362, 3049−3055. (29) (a) Bolaño, S.; Ciancaleoni, G.; Bravo, J.; Gonsalvi, L.; Macchioni, A.; Peruzzini, M. Organometallics 2008, 27, 1649−1652. (b) Bosquain, S. S.; Dorcier, A.; Dyson, P. J.; Erlandsson, M.; Gonsalvi, L.; Laurenczy, G.; Peruzzini, M. App. Organomet. Chem. 2007, 21, 947−951. (c) Bolaño, S.; Gonsalvi, L.; Zanobini, F.; Vizza, F.; Bertolasi, V.; Romerosa, A.; Peruzzini, M. J. Mol. Catal. A 2004, 224, 61−70. (d) Akbayeva, D. N.; Gonsalvi, L.; Oberhauser, W.; Peruzzini, M.; Vizza, F.; Brüggeller, P.; Romerosa, A.; Sava, G.; Bergamo, A. Chem. Commun. 2003, 264−265. 6302
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