Published on Web 10/22/2008
2,3-Diphosphino-1,4-diphosphonium Ions Yuen-ying Carpenter,† C. Adam Dyker,† Neil Burford,*,† Michael D. Lumsden,‡ and Andreas Decken§ Department of Chemistry, Dalhousie UniVersity, Halifax, NS, B3H 4J3, Canada, Atlantic Region Magnetic Resonance Center, Dalhousie UniVersity, Halifax, NS, B3H 4J3, Canada, and Department of Chemistry, UniVersity of New Brunswick, Fredericton, NB, E3A 6E2, Canada Received July 28, 2008; E-mail:
[email protected] Abstract: Salts of the first crystallographically characterized chlorophosphinophosphonium ions have been prepared, and their reaction with Ph3P results in reductive coupling of the chlorophosphine centers to give the first acyclic 2,3-diphosphino-1,4-diphosphonium ions, representing a key framework in the development of catena-phosphorus chemistry. These new salts of general formula [R3P-PR′-PR′-PR3][OTf]2 are also obtained in a one-pot diastereoselective reaction of a dichlorophosphine, a tertiary phosphine, and trimethylsilyltrifluoromethanesulfonate. The structural and spectroscopic features of the new dications complement those of the known diphosphonium and 2-phosphino-1,3-diphosphonium dications. Quantitative ligand exchange reactions are observed when derivatives of [Ph3P-PR′-PR′-PPh3][OTf]2 are combined with Me3P, demonstrating the coordinative nature of the phosphine-phosphonium P-P bonds and implicating a bonding model involving the diphosphenium dication acceptor. The observed solid state structures have been interpreted in the context of computational studies.
Introduction
The strong homoatomic bond is a feature of phosphorus chemistry that has been highlighted in discussion of the diagonal relationship with carbon but has yet to be fully exploited. In this context, a diverse and extensive catena-phosphorus chemistry is evolving that is made possible by versatile synthetic methods for new catenated cationic frameworks.1-8 Derivatives of phosphinophosphonium i,2 diphosphonium ii,9-12 1,3-diphosphino-2-phosphonium iii,5,13 and 2-phosphino-1,3-diphosphonium iv14 cations represent the prototypical examples of acyclic
catena-phosphorus cations that have been isolated and comprehensively characterized, and other P-P bonded cationic frameworks have been reported.15 We now report the application of a new reductive coupling reaction and a ligand exchange reaction as high yield synthetic approaches to the first examples of acyclic 2,3-diphosphino-1,4-diphosphonium ions v.8 In addition, counterintuitive conformational features that are observed in the solid state structures are rationalized using computational models.
†
Department of Chemistry, Dalhousie University. Atlantic Region Magnetic Resonance Center, Dalhousie University. University of New Brunswick. (1) Burford, N.; Cameron, T. S.; Ragogna, P. J.; Ocando-Mavarez, E.; Gee, M.; McDonald, R.; Wasylishen, R. E. J. Am. Chem. Soc. 2001, 123, 7947–7948. (2) Burford, N.; Ragogna, P. J.; McDonald, R.; Ferguson, M. J. Am. Chem. Soc. 2003, 125, 14404–14410. (3) Burford, N.; Ragogna, P. J. Dalton Trans. 2002, 4307–4315. (4) Burford, N.; Ragogna, P. J.; McDonald, R.; Ferguson, M. J. Chem. Commun. 2003, 2066–2067. (5) Burford, N.; Dyker, C. A.; Decken, A. Angew. Chem., Int. Ed. 2005, 44, 2364–2367. (6) Burford, N.; Dyker, C. A.; Lumsden, M. D.; Decken, A. Angew. Chem., Int. Ed. 2005, 44, 6196–6199. (7) Weigand, J. J.; Burford, N.; Lumsden, M. D.; Decken, A. Angew. Chem., Int. Ed. 2006, 45, 6733–6737. (8) Preliminary Communication: (a) Dyker, C. A.; Burford, N.; Lumsden, M. D.; Decken, A. J. Am. Chem. Soc. 2006, 128, 9632–9633. (9) Romakhin, A. S.; Palyutin, F. M.; Ignat’ev, Yu., A.; Nikitin, E. V.; Kargin, Yu., M.; Litvinov, I. A.; Naumov, V. A. IzV. Akad. Nauk. SSSR, Ser. Khim. 1990, 3, 664–669. (10) Kilian, P.; Slawin, A. M. Z.; Woollins, J. D. Dalton Trans. 2006, 2175– 2183. (11) Schomburg, D.; Bettermann, G.; Ernst, L.; Schmutzler, R. Angew. Chem., Int. Ed. Engl. 1985, 24, 975–976. (12) Alder, R. W.; Ganter, C.; Harris, C. J.; Orpen, A. G. Chem. Commun. 1992, 1170–1172. (13) Krossing, I. Dalton Trans. 2002, 500–512. ‡ §
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Synthetic Procedures and Characterization Data General. Unless otherwise specified, reactions were carried out in a glovebox under an inert N2 atmosphere. Solvents were dried on a MBraun solvent purification system and stored over 4 Å molecular sieves unless otherwise specified. MeCN was purchased anhydrous from Aldrich and used as received, Et2O was dried by refluxing over Na/benzophenone and distilled before use, and CHCl3 was degassed by three freeze-pump-thaw cycles and stored over molecular sieves for 24 h before use. Deuterated solvents were purchased from Aldrich or Cambridge Isotope Laboratories and used as received (CD3CN, CD3NO2 in ampoules) or stored over molecular sieves for 24 h prior to use (CDCl3). [Ph3P-PPhCl][OTf], [1a][OTf]; [Ph3P-PPh-PPh-PPh3][OTf]2, [4a][OTf]2; and [Me3PPPh-PPh-PMe3][OTf]2, [4′a][OTf]2, were prepared as described in the preliminary communication.8 CyPCl2 was prepared according to literature methods.16 Me2PCl and MePCl2 were purchased from (14) Schmidpeter, A.; Lochschmidt, S.; Karaghiosoff, K.; Sheldrick, W. S. Chem. Commun. 1985, 1447–1448. (15) Dyker, C. A.; Burford, N. Chem. Asian J. 2008, 3, 28–36. (16) Weferling, N. Z. Z. Anorg. Allg. Chem. 1987, 548, 55–62. 10.1021/ja805911a CCC: $40.75 2008 American Chemical Society
2,3-Diphosphino-1,4-diphosphonium Ions
Strem and used as received. Ph3P, iPrPCl2, tBuPCl2, and Me3P (1.0 M solution in toluene) were purchased from Aldrich and used as received. Ph2PCl, PhPCl2, EtPCl2, and Me3SiOTf were purchased from Aldrich and purified by vacuum distillation prior to use. GaCl3 was purchased from Strem and sublimed under static vacuum prior to use. Solution 1H, 13C, and 31P NMR spectra were collected at room temperature on Bruker AC-250 (5.9 T) and Bruker Avance 500 (11.7 T) NMR spectrometers. Chemical shifts are reported in ppm relative to trace protonated solvent (1H), to perdeuterated solvent (13C), or to an external reference standard (31P, 85% H3PO4). NMR spectra of reaction mixtures were obtained by transferring an aliquot of the bulk solution to a 5 mm NMR tube. These tubes were flame sealed, or capped and sealed with Parafilm. All reported 31P{1H} NMR parameters for second-order spin systems were derived by iterative simulation of experimental data obtained at both fields (31P Larmor frequencies of 101.3 and 202.6 MHz) using gNMR, version 4.0.17 Typically, the higher field experimental spectrum was used to find the spin system parameters, and the lower field data was subsequently used to ensure the parameters were valid at both fields. Difference calculations between simulated and experimental spectra were produced with Bruker Topspin, version 2.0,18 using data at 202.6 MHz. The signs of the P-P coupling constants reported in Table 2 and Table 3 have been established by assigning the 1JPP coupling constants as negative.19,20 Product distributions for in situ reaction mixtures were assessed by integration of assigned signals in the 31P NMR spectra. 31P NMR integrations are approximate, but are estimated to be accurate to within (10% for identical coordination numbers or (20% otherwise.21 Letter designations for the phosphorus spin systems have been assigned by calculating the ratio |∆ν/J|, where ∆ν is the difference in 31P chemical shifts in Hz, and using a value of 10 at the lower field as the threshold between a first and second order letter designation. Infrared spectra were collected on samples prepared as nujol mulls between CsI plates using a Bruker Vector FT-IR spectrometer. Peaks are reported in wavenumbers (cm-1) with ranked intensities in parentheses, where a value of one corresponds to the most intense peak in the spectrum. Melting points were obtained on samples flame-sealed in glass capillaries under dry nitrogen using an Electrothermal apparatus. Chemical analyses were performed on selected compounds by Canadian Microanalytical Services Ltd., Delta, British Columbia, Canada. Unless otherwise stated, crystals for single crystal X-ray diffraction studies were obtained by vapor diffusion at room temperature. Samples were dissolved in a minimal amount (1-2 mL) of a polar solvent in a 5 mL vial placed within a capped 20 mL vial containing ∼5 mL of a less polar solvent (solvents are indicated in the text as polar/nonpolar pairs). After deposition of crystals, the solvent was carefully removed using a pipet and the crystals were coated with Paratone oil. Single crystal X-ray diffraction data were collected using a Bruker AXS P4/SMART 1000 diffractometer. All measurements were made with graphite monochromated Mo KR radiation. The data were reduced (SAINT)22 and corrected for absorption (SADABS)23 and were corrected for Lorentz and polarization effects. The structures were solved by direct methods and expanded using Fourier techniques. Full matrix least-squares refinement was carried out on F2 data using the program (17) Budzelaar, P. H. M. gNMR for Windows, 4.0; Cherwell Scientific Publishing Limited: Oxford, UK, 1997. (18) Topspin for Windows, 2.0, patchlevel 5; Bruker Biospin GmbH: Germany, 2006. (19) Finer, E. G.; Harris, R. K. Prog. Nucl. Magn. Reson. Spectrosc. 1971, 6, 61–118. (20) Forgeron, M. A. M.; Gee, M.; Wasylishen, R. E. J. Phys. Chem. 2004, 108, 4895–4908. (21) Huynh, K.; Rivard, E.; LeBlanc, W.; Blackstone, V.; Lough, A. J.; Manners, I. Inorg. Chem. 2006, 45, 7922–7928. (22) SAINT 7.23A; Bruker AXS, Inc: Madison, Wisconsin, 2006. (23) Sheldrick, G. M. SADABS; Bruker AXS, Inc.: Madison, Wisconsin, 2004.
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SHELX97.24 Non-hydrogen atoms were refined anisotropically. Refinement details are summarized in Table 1. Preparation and Isolation. [Ph3P-PPh(Cl)][GaCl4], [1a][GaCl4]: PhPCl2 (27.1 µL, 0.20 mmol), was added to a stirred solution of Ph3P (52 mg, 0.20 mmol) and GaCl3 (39 mg, 0.22 mmol) in CH2Cl2 (1 mL). After 15 min, the 31P{1H} NMR spectrum of the reaction showed near quantitative formation of [1a][GaCl4] (94%) along with PhPCl2-GaCl3 (156 ppm). Attempted isolation by addition of Et2O yielded an oil. [Me3P-PPh(Cl)][OTf], [1′a][OTf]: Me3P (1.0 M in toluene, 2 × 100.0 µL, 0.20 mmol) was added to a stirred solution of PhPCl2 (27.1 µL, 0.20 mmol) and Me3SiOTf (39.8 µL, 0.22 mmol) in CH2Cl2 (0.80 mL). After 1.5 h, the 31P{1H} NMR spectrum of this reaction mixture showed quantitative formation of [1′a][OTf]. General Procedure for [Ph3P-PR′(Cl)][OTf], [1b-e][OTf]: R′PCl2 (0.20 mmol) was added to a stirring solution of Ph3P (52 mg, 0.20 mmol) in CH2Cl2 (0.5-1 mL) followed immediately by the addition of Me3SiOTf (39.8 µL, 0.22 mmol). Attempted isolation of [1c-e][OTf] by addition or vapor diffusion of Et2O yielded an oil. [Ph3P-PMe(Cl)][OTf], [1b][OTf]: After 1 h, the 31P{1H} NMR spectrum of the reaction showed quantitative formation of [1b][OTf]. Vapor diffusion of Et2O into this solution overnight at room temperature afforded colorless needle-like crystals that were washed with Et2O (2 × 1 mL) and dried in Vacuo. Yield (crystalline): 63 mg (64%), mp 117-119.5 °C; FT-IR: 3063 (19), 1586 (10), 1443 (5), 1260 (1), 1189 (20), 1144 (13), 1106 (15), 1029 (7), 996 (16), 891 (18), 873 (8), 751 (6), 725 (14), 690 (4), 637 (2), 573 (11), 545 (9), 506 (3), 460 (17), 301 (12). [Ph3P-PEt(Cl)][OTf], [1c][OTf]: Quantitative formation of [1c][OTf] was observed after 10 min by 31P{1H} NMR spectroscopy. [Ph3P-PiPr(Cl)][OTf], [1d][OTf]: [1d][OTf] was observed as broad resonances (82 ppm and 16 ppm) at 298 K in the 31P{1H} NMR spectrum of the solution after 1 h, together with iPrPCl2 (ca. 15%). Quantitative formation of [1d][OTf] was observed at 213 K. [Ph3P-PCy(Cl)][OTf], [1e][OTf]: [1e][OTf] was observed as broad resonances (76 ppm and 18 ppm) at 298 K in the 31P NMR spectrum of the reaction mixture after 1 h, together with CyPCl2 (ca. 23%). Quantitative formation of [1e][OTf] was observed at 202 K. [Me3P-PCy(Cl)][OTf], [1′e][OTf]: Me3P (1.0 M in toluene, 3 × 73.4 µL, 0.22 mmol) was added to a stirred solution of CyPCl2 (41.4 mg, 0.22 mmol) in CH2Cl2 (1 mL) yielding a white precipitate. Upon addition of Me3SiOTf (43.8 µL, 0.24 mmol), this solid redissolved and produced a white precipitate after 5 min of stirring. The 31P{1H} NMR spectrum of this reaction mixture after 1 h showed the presence of only [1′e][OTf]. [Ph3P-PtBu(Cl)][OTf], [1f][OTf]: A solution of Ph3P (105 mg, 0.40 mmol) in CH2Cl2 was added to a stirred solution of tBuPCl2 (64 mg, 0.40 mmol) in CH2Cl2 (total volume ca. 1 mL) followed immediately by the addition of Me3SiOTf (79.6 µL, 0.44 mmol). The 31P{1H} NMR spectrum (213 K) of the reaction mixture after 2 h was interpreted as a mixture of [1f][OTf] and tBuPCl2 (200.0 ppm). The 31P{1H} NMR spectrum (213 K) of the reaction mixture after 48 h indicated the presence of small amounts of [Ph3PCl][OTf] and [5f][OTf] ([Ph3P-PtBu-PtBu(Cl)][OTf], AMX spin system, not simulated, approximate shifts -2 ppm (t), 24 ppm (dd), and 112 ppm (dd)). [Ph3P-PtBuCl][GaCl4], [1f][GaCl4]: A mixture of Ph3P (52 mg, 0.20 mmol), tBuPCl2 (32 mg, 0.20 mmol) and GaCl3 (39 mg, 0.22 mmol) in CH2Cl2 (1 mL) was stirred for 1 h at room temperature, and the 31P{1H} NMR spectrum at 298 K was interpreted as a mixture of tBuPCl2-GaCl3 (184 ppm, 98%,) and [1f][GaCl4] (2%). J. AM. CHEM. SOC.
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Carpenter et al.
Table 1. Crystallographic Data (a) Crystallographic Data for Chlorophosphinophosphonium Triflate Salts
CCDC # Formula molecular weight (g/mol) crystal system space group color, habit a /Å b /Å c /Å R /° β /° γ /° V /Å3 T /K Z crystal size/mm3 µ/mm-1 2θmax /° reflections collected independent reflections Rint parameters R1a (I > 2σ(I)) wR2b (all data) GOFc ∆F max and min /e Å-3
[Ph3P-PPh(Cl]][OTf] [1a][OTf]8
[Ph3P-PMe(Cl)][OTf] [1b][OTf]
605574 C25H20ClF3O3P2S 554.86 monoclinic Pn colorless plate 10.0707(16) 8.8891(15) 14.166(2) 90 104.192(3) 90 1229.5(3) 173(1) 2 0.40 × 0.125 × 0.025 0.420 54.98 8149 4027 0.0256 396 0.0256 0.0630 1.031 0.309, -0.176
694816 C20H18ClF3O3P2S 492.79 triclinic P1j colorless plate 8.3728(10) 11.0797(13) 12.4662(15) 83.4150(10) 72.798(2) 85.040(2) 1095.8(2) 198(1) 2 0.50 × 0.30 × 0.10 0.461 54.98 7617 4767 0.0177 358 0.0347 0.0972 1.065 0.382, -0.228
(b) Crystallographic Data for Salts of 2,3-Diphosphino-1,4-diphosphonium Triflate Salts
CCDC # Formula molecular weight (g/mol) crystal system Space group color, habit A /Å B /Å C /Å R /° β /° γ /° V /Å3 T /K Z crystal size/mm3 µ/mm-1 2θmax /° reflections collected independent reflections Rint parameters R1a (I > 2σ(I)) wR2b (all data) GOFc ∆F max and min /e Å-3
[Ph3P-PPh-PPh-PPh3][OTf]2 [4a][OTf]28
[Ph3P-PMe-PMe-PPh3][OTf]2 [4b][OTf]2
[Ph3P-PEt-PEt-PPh3][OTf]2 [4c][OTf]2
[Me3P-PPh-PPh-PMe3][OTf]2 [4′a][OTf]28
[Me3P-PMe-PMe-PMe3][OTf]2 [4′b][OTf]2
605575 C10H24F6O6P4S2 1038.82 monoclinic P21/n Colorless plate 10.942(4) 20.769(7) 11.462(4) 90 113.120(6) 90 2395.7(15) 173(1) 2 0.45 × 0.275 × 0.075 0.318 55.00 16121 5349 0.0239 387 0.0499 0.1450 1.087 1.913, -0.409
694391 C40H36F6O6P4S2 914.69 monoclinic P21/c colorless rod 8.761(5) 27.114(17) 17.578(11) 90 96.807 90 4146(4) 173(1) 4 0.45 × 0.10 × 0.10 0.356 55.00 27998 9274 0.0583 525 0.0460 0.1070 1.007 0.457, -0.359
694390 C42H40F6O6P4S2 942.74 monoclinic C2/c colorless rod 15.5968(16) 14.5043(16) 19.895(2) 90 102.483(2) 90 4394.3(8) 173(1) 4 0.50 × 0.20 × 0.20 0.338 55.00 15089 4932 0.0263 272 0.0461 0.1282 1.069 0.820, -0.579
605576 C20H28F6O6P4S2 666.42 monoclinic P21/c colorless irregular 8.9520(14) 16.597(3) 10.0504(16) 90 101.328(3) 90 1464.1(4) 173(1) 2 0.60 × 0.40 × 0.20 0.473 55.00 9319 3253 0.0477 228 0.0479 0.1393 1.056 1.226, -0.466
694392 C10H24F6O6P4S2 542.29 monoclinic P21/c colorless irregular 12.431(2) 13.520(3) 13.883(3) 90 94.872(3) 90 2324.7(7) 198(1) 4 0.50 × 0.25 × 0.20 0.574 55.00 15518 5164 0.0380 261 0.0659 0.2112 1.177 0.806, -0.461
a R1 ) Σ | |Fo| - |Fc| |/Σ |Fo|. b wR2 ) (Σ[w(Fo2 - Fc2)2]/Σ[w(Fo4])1/2. c GOF ) [ Σw(|Fo| - |Fc|)2/(n - p)]1/2, where n ) number of reflections and p ) number of parameters.
[Me3P-PtBu(Cl)][OTf], [1′f][OTf]: Me3P (1.0 M in toluene, 2 × 100 µL, 0.20 mmol) was added to a stirred solution of tBuPCl2 (32 mg, 0.20 mmol) in CH2Cl2 (0.5-1 mL) followed immediately by the addition of Me3SiOTf (39.8 µL, 0.22 mmol) and the 31P{1H} NMR spectra of this solution showed nearly quantitative formation of [1′f][OTf]. [Me3P-PtBu(Cl)][GaCl4], [1′f][GaCl4]: Me3P (1.0 M in toluene, 220 µL, 0.22 mmol) was added to a stirred solution of tBuPCl2 15734
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(32 mg, 0.20 mmol) in CH2Cl2 (0.5 mL) followed immediately by the addition of GaCl3 (79.6 µL, 0.44 mmol) in CH2Cl2 (0.5 mL). After 1 h, the 31P{1H} NMR spectrum showed essentially quantitative formation of [1′f][GaCl4].
(24) Sheldrick, G. M. SHELXL-97, Program for crystal structure determination; University of Go¨ttingen: Germany, 1997.
2,3-Diphosphino-1,4-diphosphonium Ions Table 2.
31
P{1H} NMR Parameters for Phosphinophosphonium Triflate Saltsa
cation
a
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donor
acceptor
3a
Ph3P
PPh2
3b 3c 2a 2b 1a 1a 1′a 1b 1c 1d 1e 1′e 1f 1f 1′f 1′f
Me3P Cy3P Ph2(Cl)P Me2(Cl)P Ph3P Ph3P Me3P Ph3P Ph3P Ph3P Ph3P Me3P Ph3P Ph3P Me3P Me3P
PMe2 PCy2 PPh2 PMe2 PPh(Cl) PPh(Cl) PPh(Cl) PMe(Cl) PEt(Cl) PiPr(Cl) PCy(Cl) PCy(Cl) PtBu(Cl) PtBu(Cl) PtBu(Cl) PtBu(Cl)
anion
spin system
[OTf]2 [GaCl4]2 [OTf]5 [OTf]2 [GaCl4]35 [GaCl4]35 [OTf]8 [GaCl4] [OTf] [OTf] [OTf] [OTf] [OTf] [OTf] [OTf] [GaCl4] [OTf] [GaCl4]
31 PB or X [δ] (phosphonium)
31 PA[δ] (phosphine)
1 JPP [Hz] (T)
15 13 18 25 73 99 22 22 26 24 18 22 23 23 16 17 23 20
-10 -12 -60 -21 0 -33 55 55 46 61 76 72 65 76 90 98 95 94
n/a -340 -275 -361 -393 -340 -333 (213 K) -338 -305 -313 (202 K) n/a (203 K) -344 (213 K) -343 (202 K) -326 -390 (213 K) -398 -350 -356
s AB AX AX AX AX AB AB AB AX s AX AX AX AX AX AX AX
Data are reported for spectra obtained at 298 K unless otherwise indicated.
Table 3.
4a
31
P{1H} NMR Parameters at 101.3 MHz for 2,3-Diphosphino-1,4-diphosphonium Triflate Saltsa
8
4b
[Ph3P-PPh-PPh-PPh3] minor diastereomer [Me3P-PPh-PPh-PMe3]8 minor diastereomer [Ph3P-PMe-PMe-PPh3]
4′b 4c 4d 4e
[Me3P-PMe-PMe-PMe3] [Ph3P-PEt-PEt-PPh3] [Ph3P-PiPr-PiPr-PPh3] [Ph3P-PCy-PCy-PPh3]
4′a
solvent
δA
δB
CH2Cl2 CH2Cl2 MeCN MeCN CH2Cl2 MeCN MeCN MeCN MeCN CH2Cl2
-33 -42 -52 -56 -71 -67 -73 -53.6 -25.5 -34
24 22 25 23 26 32 26 24.1 22.2 20
1
JAA′
-124 not simulated -105 not simulated -278 not simulated -238 -276 -318 not simulated
JAB)1JA′B′
1
JA′B)2JAB′
2
3
JBB′
-343
69
51
-305
66
56
-282
78
62
-269 -297 -348
80 82 98
58 59 63
a All spectra are AA′BB′ spin systems, with parameters derived by iterative fitting of experimental data at 298 K. Minor diastereomer shifts could not be simulated and thus are approximate if given. Chemical shifts (δ) are given in ppm and coupling constants (J) in Hz.
Formation of [Ph3P-PPh2][OTf], [3a][OTf], from [Ph3P-PPh(Cl)][OTf], [1a][OTf]: Addition of Ph2PCl (26.9 µL, 0.15 mmol) to a stirred solution of [1a][OTf], (83 mg, 0.15 mmol) in CH2Cl2 afforded partial conversion to [3a][OTf] and PhPCl2 (162 ppm) after 30 min (5:1 ratio of 3a:1a, as observed by 31P{1H} NMR spectroscopy). [Ph3P-PPh-PPh-PPh3][OTf]2, [4a][OTf]2: [4a][OTf]2 was prepared as described in the preliminary communication8 for analysis by solid state NMR spectroscopy on a Bruker Avance 400 (9.4 T) spectrometer. 31P CP/MAS NMR (162.0 MHz, 6.5 kHz spin rate, 4 mm rotor, ice cooled carrier gas): Major diastereomer δ ) 24 ppm, -40 ppm; Minor diastereomer δ ) 19 ppm, -31 ppm; [Ph3P-PMe-PMe-PPh3][OTf]2, [4b][OTf]2: MePCl2 (0.079 mL, 0.885 mmol) and Me3SiOTf (0.266 mL, 1.47 mmol) were added to a solution of Ph3P (0.35 g, 1.34 mmol) in CHCl3 (9 mL) in a 50 mL 1-necked bulb with a Teflon stopper. The mixture was degassed by three freeze-pump-thaw cycles and subsequently heated to reflux within the closed system by use of an oil bath (∼ 60 °C). After 4 days, the resulting white precipitate was filtered, washed with CHCl3 (1.5 mL) and dried in Vacuo. Crystals were obtained by vapor diffusion from CH3CN/Et2O. Yield (powder): 0.224 g (0.245 mmol, 55%). D.p. 225-237 °C; elemental analysis calc’d (found): %C 52.52 (52.79), %H 3.97 (3.98); 1H NMR (500.1 MHz, CD3CN, 298 K): δ ) 7.97 ppm (t, 3JHH ) 7.5 Hz, 6H), 7.90 ppm (m, 12H), 7.81 ppm (m, 12H), 0.76 ppm (m, 6H); 1H NMR (500.1 MHz, CD3NO2, 298 K): δ ) 8.03 ppm (m, 18H), 7.88 ppm (m, 12H), 0.95 ppm (m, 6H); 13C NMR (125.8 MHz, DEPTQ135, CD3NO2, 298 K): δ ) 136.0 ppm (s, +), 134.0 ppm (s, +), 131.1 ppm (m, +), 117.1 ppm (m, -), 0.0 ppm (m, +); FT-IR: 1439
(10), 1262 (1), 1223 (12), 1152 (7), 1103 (10), 1030 (4), 995 (14), 879 (15), 755 (9), 721 (8), 692 (5), 637 (2), 572 (13), 543 (6), 511 (3), 306 (16). [Me3P-PMe-PMe-PMe3][OTf]2, [4′b][OTf]2: Me3P (0.235 mL, 1.0 M in toluene, 0.235 mmol) was added dropwise to a stirred mixture of [Ph3P-PMe-PMe-PPh3][OTf]2, ([4b][OTf]2, 0.106 g, 0.116 mmol) in CH2Cl2 (3 mL). After stirring for 30 min, the white precipitate was collected by filtration, and washed with CH2Cl2 (1 mL). Recrystallization over 1 day, by vapor diffusion with CD3CN/ Et2O at -25 °C gave crystals that were washed with Et2O (2 × 1 mL), and dried in Vacuo, yield: 0.032 g (0.059 mmol, 51%); Mp 221-224 °C; elemental analysis calc’d (found): %C 22.15 (21.18), %H 4.46 (4.11); 1H NMR (500.1 MHz, CD3NO2, 298 K): δ ) 2.21 ppm (m, 18H), 1.93 ppm (m, 6H); 13C NMR (125.8 MHz, DEPTQ135, CD3NO2, 298 K): δ ) 7.78 ppm (m, +), -0.4 ppm (m, +); FT-IR: 1426 (14), 1260 (1), 1301 (13), 1225 (10), 1152 (5), 1029 (3), 966 (4), 901 (8), 861 (9), 809 (17), 768 (16), 758 (15), 680 (11), 636 (2), 573 (7), 517 (6). [Ph3P-PEt-PEt-PPh3][OTf]2, [4c][OTf]2: [1c][OTf] (1.0 mmol) was prepared in situ in a 50 mL 1-necked bulb containing 5 mL CHCl3. Me3SiOTf (100.0 µL, 0.55 mmol) and Ph3P (132 mg, 0.50 mmol, in ca. 2 mL CHCl3) were added, and the solution was degassed by three freeze-pump-thaw cycles and sealed at reduced pressure. This solution was heated at reflux (∼55 °C) in the closed system for 48 h. The supernatant was decanted from the resulting white precipitate, which was then washed with cold CH2Cl2 (-40 °C, 2 × 0.5 mL) and Et2O (2 × 1 mL). Addition of Et2O (∼4 mL) to the supernatant gave a white precipitate, which was isolated by decantation and washed with cold CH2Cl2. Colorless needle-like J. AM. CHEM. SOC.
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VOL. 130, NO. 46, 2008
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ARTICLES
Carpenter et al.
crystals were obtained by vapor diffusion from MeCN/Et2O, yield (powder): 0.249 g (53% based on EtPCl2), mp 201-203 °C; 1H NMR (500.1 MHz, CD3CN, 298 K): δ ) 7.91 ppm (vt, 6H, Ha), 7.85 ppm (vq, 12H, Hb), 7.74 ppm (vt, 12H, Hc), 1.93 ppm (m, 3H, He), 0.55 ppm (m, 6H, Hf); 13C NMR (125.8 MHz, DEPTQ135, CD3CN, 298 K): δ ) 136.91 ppm (s, +, Ca/b), 135.07 ppm (s, +, Ca/b), 132.06 ppm (t, +, Cc), 119.07 ppm (t, -, Cd), 14.26 ppm (t, -, Ce), 12.42 ppm (m, +, Cf); FT-IR: 1584 (15), 1439 (6), 1270 (1), 1224 (7), 1147 (4), 1101 (5), 1031 (2), 996 (11), 754 (10), 721 (12), 690 (8), 637 (3), 572 (14), 542 (9), 509 (13).
[Ph3P-PiPr-PiPr-PPh3][OTf]2, [4d][OTf]2: iPrPCl2 (36.0 µL, 0.29 mmol) and Me3SiOTf (58.1 µL, 0.32 mmol) were added to a solution of Ph3P (77 mg, 0.29 mmol) in CH2Cl2 (0.60 mL). After stirring for 1 h at room temperature, this solution was transferred to a vial containing 39 mg (0.15 mmol) Ph3P, followed by subsequent addition of Me3SiOTf with stirring (29.1 uL, 0.16 mmol). This solution was stirred for 5 days at room temperature, resulting in the precipitation of a white powder. This solid was isolated by filtration and washed with cold CH2Cl2 (-40 °C, 2 × 1 mL). Dissolution of this sparingly soluble powder in MeCN and removal of the solvent in Vacuo provided [4d][OTf]2 (45 mg). The supernatant was analyzed by 31P{1H} NMR spectroscopy and showed a mixture of [1d][OTf], [Ph3PCl][OTf] and a new AMX spin system (δA ) -35.7 ppm, δM ) 23.0 ppm, δX ) 96.5 ppm, 1 JAM ) -309 Hz, 1JAX ) -305 Hz, 2JMX ) 59 Hz), tentatively assigned to [Ph3P-PiPr-PiPrCl][OTf], [5d][OTf]. Slow evaporation of the supernatant and CH2Cl2 washes over 2 days yielded an additional 18 mg of [4d][OTf]2 as a semicrystalline material. In contrast, 31P{1H} NMR spectra of reactions performed in more dilute solutions (
