Copper-catalyzed hydrophosphinations of styrenes in water at room temperature

Article abstract of DOI:10.1039/c4dt00993b

Copper-catalyzed hydrophosphinations of styrenyl systems in water, at room temperature is herein reported, enabled by our 'designer' surfactant TPGS-750-M. This is an attractive alternative to the more common Pd and Pt catalyzed versions.

Full text of DOI:10.1039/c4dt00993b

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Copper-catalyzed hydrophosphinations of
styrenes in water at room temperature†
Cite this: Dalton Trans., 2014, 43,
13196
Nicholas A. Isley, Roscoe T. H. Linstadt, Eric D. Slack and Bruce H. Lipshutz*
Received 3rd April 2014,
Accepted 15th July 2014
Copper-catalyzed hydrophosphinations of styrenyl systems in water, at room temperature is herein
reported, enabled by our ‘designer’ surfactant TPGS-750-M. This is an attractive alternative to the more
common Pd and Pt catalyzed versions.
DOI: 10.1039/c4dt00993b
www.rsc.org/dalton
temperature are oftentimes comparable to those observed in
traditional organic solvents.10 In addition to these virtues of
Introduction
Organophosphines are fundamentally important to many micellar catalysis, we focused on a base metal as catalyst that
aspects of synthetic organic chemistry. Representative appli- is inexpensive, nontoxic, and environmentally friendly: copper.
cations include ligands for metal-catalyzed transformations,1 Recently, Corma and co-workers reported the first catalytic use
biologically active substances, advanced materials, and build- of copper in hydrophosphinations of styrenes.11 Nonetheless,
ing blocks of supramolecular chemistry.2 Adding the elements the scope of the chemistry was limited, as only mono-substi-
of P–H across an olefin is an efficient and direct way of acces- tuted and activated substrates participated, with only moderate
sing organophosphines in terms of atom-economy, addressing yields. High catalyst loadings of a relatively expensive copper
one of the twelve-principles of green chemistry3 and paving source were needed,12 and high temperatures were required.
the way for more sustainable methods. Both Pd and Pt One major limitation was that α-substituted styrenes were
(others4) have been reported to catalytically activate P–H bonds functionalized in very poor yields.
to facilitate addition across activated olefins, but the catalyst
Herein, we report a very mild, copper-catalyzed strategy for
loading is not economically practical for industrial use, as the addition of diphenylphosphine to activated mono- and di-
both Pd and Pt are precious metals.4 Alternatively, Zr,4b Yb,4c substituted olefins containing functionalized aromatic/hetero-
Fe,4d Ca,5 and K5-catalyzed hydrophosphinations were recently aromatic systems (Scheme 1).
reported.5 Microwave-assisted, solvent-free, and metal-free
Initial optimization was done on α-methyl styrene, as this
have also been reported,6 but the phosphine source was oxi- was a difficult substrate in the published study by Corma11
dized prior to the reaction, thus adding an extra step to reduce (Table 1). A variety of copper sources was screened, with
the phosphine before it becomes of value again, e.g., as a Cu(OAc)2·H2O giving the best results, as well as being in
ligand for transition-metal catalysis.
A greener and less costly alternative has been pursued
employing micellar catalysis, enabled by our “designer” surfac-
tant TPGS-750-M. This technology allows for reactions to take
place in water, and usually at room temperature.7 Upon dissol-
ution of typically two weight percent of this amphiphile in
water, the surfactant spontaneously self-aggregates into nano-
meter-sized micelles.8 The reaction occurs within their lipo-
philic cores, providing an environment for water-insoluble
substrates and catalysts.9 Moreover, due to the high concentration
of reactants within these nanoreactors, reaction rates at room
Department of Chemistry & Biochemistry, University of California, Santa Barbara,
CA 93106, USA. E-mail: lipshutz@chem.ucsb.edu
†Dedicated to a great colleague and friend, William C. Kaska, on the occasion of
Scheme 1 Comparison between 2 wt% TPGS-750-M/H2O and organic
his 80th birthday.
solvent.
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Table 1 Optimization of Cu-catalyzed hydrophosphinations
Table 2 Hydrophosphinations of vinyl-substituted aromaticsa
Entry
1
Styrene
Product
Yieldb (%)
94
Entry Conditions
Conversiona
1
1.2 equiv. HPPh2, Cu(OAc)2·H2O (3 mol%), BDPb
65
(3 mol%)
2
3c
4
5
6
7
8
1.2 equiv. HPPh2, Cu(OAc)2·H2O (3 mol%)
2.2 equiv. HPPh2, Cu(OAc)2·H2O (3 mol%)
2.0 equiv. HPPh2, Cu(OAc)2·H2O (3 mol%)
1.2 equiv. HPPh2, Cu(OAc)2·H2O (10 mol%)
1.5 equiv. HPPh2, Cu(OAc)2·H2O (5 mol%)
1.2 equiv. HPPh2
67
>99
93
73
95
3
2
3
4
97
95
82
entry 3 and H2O as solvent
41
a Determined by GC of crude reaction mixture. b 1,2-Bis(diphenyl-
phosphino)-benzene. c Reaction time: 40 h.
expensive and air-stable. The presence of a ligand was found
to be unnecessary for high conversion using copper(II) acetate
(entries 1 vs. 2). The loading of both copper and diphenyl-
phosphine was varied to ultimately give complete conver-
sion in under 24 hours. The optimal levels were found to be
5 mol% of copper(II) acetate monohydrate and 1.5 equivalents
of diphenylphosphine (entry 6). A control experiment was also
conducted (entry 7) to ensure that copper is necessary to facili-
tate the desired transformation. Another control experiment
a Conditions: 1.5 equiv. HPPh2 5 mol% [Cu], 0.5 mL 2 wt% TPGS-750-
M/H2O, rt, 24 h, 0.25 mmol scale. b Isolated, chromatographically
purified.
was conducted in the absence of TPGS-750-M and only moder- derivative in very good yield, while the p-substituted electron-
ate conversion was observed (entry 8). rich methoxy analog 15 led to 15a in poor yield. The o-tolyl
Several electronically varied styrenes were evaluated in this derivative 16 only gave trace amounts of the desired product.
hydrophosphination (Table 2). The desired phosphorylated Lastly, an electron-poor example without α-substitution, acrylo-
products were oxidized in situ to their respective phosphine nitrile, was attempted and the desired product was obtained in
oxides, which are more easily isolated and characterized spectro- good yield (entry 6). In the composite, it appears that bulky
scopically. Both the p-chloro- and fluoro-substituted sty- substituents at or near the α-position severely hinder phos-
renes afforded the desired products in high yields (entries 1 phine addition, and electron-rich styrene systems suppress the
and 3). Additionally, an electron-rich olefin (entry 2) also led to extent of conversion. On the other hand, electron-deficient
the hydrophosphinated product in high yield, and the hetero- substrates are tolerated with and without α-substitution,
aromatic vinylpyridine, likewise, afforded the desired product suggesting that these educts are functioning as Michael accep-
in good yield (entry 4).
tors towards copper.
Next, various α-substituted styrenes were studied. Based on
In order to demonstrate the formation of a carbon–copper
our promising initial hydrophosphination of α-methylstyrene, bond as a potential intermediate, rigorous exclusion of light in
a wide scope of substrate compatibility was anticipated. deuterium oxide led to 17, with full incorporation of deuterium
Simple α-methylstyrene 6 underwent hydrophosphination in determined by low-resolution mass spectrometry (Scheme 2).
high isolated yield (Table 3). An electron-rich version 7 also After initial coordination of the olefin with copper (18), and
afforded the desired product in high yield (entry 2).
under a non-radical pathway, intermediate 19 is likely with the
The methyl moiety in substituted styrene 6 could be formation of a carbon–copper bond. The nucleophilic carbon–
replaced with a phenethyl residue, as in 10, or an OTBS group copper bond of 19 then reacts with deuterium oxide. Analogous
in 12. While the former gave product 10a in modest yield, the work involving addition of an H–B bond across styrenyl systems
latter gave only traces of 12a, with starting material being catalyzed by copper also demonstrated the likelihood of a
recovered. Switching a sterically larger phenyl for methyl group carbon–copper bond at the α-position,17 further supporting
(entry 8) also gave the product in modest yield along with intermediate 19.
recovered starting material. Heating the mixture increased the
yield to 70%. The methylene indanyl array (entry 4) yielded the conditions are not amenable to isolated alkenes and alkynes;
desired product, but also required mild heating to 50 °C.
however, the addition of phosphorous across ynoates and
Lastly, preliminary experiments demonstrate our developed
α-Aryl substituted styrenes in addition to 13 were also ynones does occur, although further screening is under study
explored. The m-CF3-substituted 14 afforded the desired to control selectivity and increase the level of conversion.
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Table 3 Hydrophosphinations of α-substituted styrenesa
Entry
1
Styrene
Product
Yieldb (%)
93
Scheme 2 Evidence of non-radical pathway during hydrophosphinations.
2
3
37
Trace
Conclusions
In conclusion, we have demonstrated the potential of micellar
catalysis to be applied to hydrophosphination reactions in
water, and in most cases, at room temperature. These compare
rather favorably with related conversions performed under tra-
ditional conditions using organic solvents. With simpler
styrene substrates, the isolated yields are high, and involve
mild conditions compared to literature procedures. While
this methodology works well for basic styrenes, the substrate
scope is limited to electron-poor and sterically unhindered
substrates.
4
5
Trace
48
6
7
8
79c
Experimental
General
Trace
44
Unless otherwise noted, all reactions were performed under an
atmosphere of argon. TPGS-750-M was synthesized by our pre-
viously reported procedure7 and dissolved in HPLC grade
water that had been thoroughly purged of oxygen using an
argon flow. Diphenylphosphine was used as received by Sigma-
Aldrich®. Analytical thin layer chromatography (TLC) was per-
formed using Silica Gel 60 F254 plates (Merck, 0.25 mm thick).
Flash chromatography was performed with glass columns
using Silica Flash® P60 (SiliCycle, 40–63 µm). For gas chromato-
graphy a HP-5 column (30 m × 0.250 mm, 0.25 micron,
Agilent Technologies) was employed for conversion analysis.
General temperature program: 50 °C for 5 min; heating rate
5 °C min−1; 280 °C for 10 min; split-inlet at 200 °C and
8.97 psi (H2, constant pressure) with 40 : 1 split ration, FID at
9
85d
10
11
6
1
290 °C. H and 13C spectra were recorded at 25 °C on a Varian
UNITY INOVA 400, 500, or 600 MHz instrument. Chemical
shifts in 1H NMR spectra are reported in parts per million
(ppm) on the δ scale from an internal standard of residual
chloroform (7.27 ppm). Data are reported as follows: chemical
shift, multiplicity (s = singlet, d = doublet, t = triplet, q =
quartet, p = pentet, sep = septet, m = multiplet, br = broad),
coupling constant in hertz (Hz), and integration. Chemical
shifts of 13C NMR spectra are reported in ppm from the
central peak of CDCl3 (77.23 ppm) on the δ scale. Chemical
shifts of 31P NMR spectra are reported in ppm and were
internally referenced using tetramethylsilane. High resolution
Trace
a Conditions: 1.5 equiv. HPPh2 5 mol% [Cu], 0.5 mL 2 wt% TPGS-750-
M/H2O, rt, 24 h, 0.25 mmol scale. b Isolated, chromatographically
purified. c Conditions: 2.0 equiv. HPPh2 5 mol% [Cu], 0.5 mL 2 wt%
TPGS-750-M/H2O, 50 °C, 48 h. d Conversion: determined by 1H NMR.
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mass analyses were obtained using a PE Sciex QStar Pulsar 1437, 1328, 1246, 1171, 1067, 905, 726, 649, 560, 510 cm−1
;
quadrupole/TOF instrument (API) for ESI, or a GCT Premier HRMS (ESI) calcd for C21H21O2PNa (M + Na)+: 359.1177;
TOF MS (Waters Corp) for FI. IR analysis was performed on found: 359.1162.
PerkinElmer FI-IR Spectrometer UATR Two and all samples
were neat.
(2-(4-Methoxyphenyl)propyl)diphenylphosphine oxide 7a.
White powder; 1H NMR (500 MHz, CDCl3): δ 7.77–7.72 (m,
Representative experimental procedure. Unless otherwise 2H), 7.67–7.62 (m, 2H), 7.52–7.44 (m, 4H), 7.41–7.36 (m, 2H)
noted all reactions were performed on a 0.25 mmol scale in a 7.05 (d, J = 15 Hz, 2H), 6.73 (d, J = 15 Hz, 2H), 3.76 (s, 3H),
5 mL microwave conical vial equipped with a septum and 3.34–3.29 (m, 2H), 2.61–2.57 (m, 1H), 1.36 (d, J = 10 Hz, 3H);
spin vane. First, Cu(OAc)2·H2O (2.5 mg, 0.0125 mmol) was 13C NMR (125 MHz, CDCl3): δ 158.0, 131.6, 131.4, 130.8, 130.7,
added to the vial and a septum attached. The vial was purged 130.53, 130.47, 128.6, 128.5, 128.4, 128.3, 127.6, 113.8, 55.2,
of any oxygen with an argon flow followed by the addition of 33.4, 23.6; 31P NMR (160 MHz, CDCl3, unreferenced): δ 30.4;
2 wt% TPGS-750-M/H2O (0.3 mL). Once the copper dissolved, IR (neat): 3054, 2930, 1588, 1516, 1437, 1375, 1244, 1161, 1071,
HPPh2 (65 μL, 70 mg, 0.375 mmol) was added. Upon the 958, 850, 822, 768 cm−1; HRMS (FI) calcd for C22H23O2P (M+):
addition of HPPh2, the solution became colored (red, brown, 350.1436; found 350.1447.
yellow, and orange). The color dissipated within a few to
(((2,3-Dihydro-1H-inden-1-yl)methyl)diphenylphosphine
10 min and the solution became cloudy and white. After the oxide) 9a. White powder; contained an unknown impurity not
dissipation of color, the substrate (0.25 mmol) was added via removable by chromatography (determined to be 95% pure by
syringe. The sides of the vial were subsequently washed with GC analysis); 1H NMR (500 MHz, CDCl3): 7.85–7.77 (m, 3H),
more 2 wt% TPGS-750-M/H2O (0.2 mL). The reaction was vig- 7.76–7.70 (m, 1H), 7.61–7.55 (m, 7H), 7.53–7.39 (m, 2H), 3.78
orously stirred for 24 h. The mixture was quenched with H2O2 (d, J = 11 Hz, 1H), 3.63–3.55 (m, 1H), 2.91–2.84 (m, 1H),
(0.2 mL, 30% aq.) and stirred at rt for 2 h. Note: The reaction 2.81–2.74 (m, 1H), 2.44 (dt, J = 10.5, 15 Hz), 2.30–2.34 (m, 1H),
mixture with products 4a, 5a, 7a, 11a, and 12a were cooled to 1.75–1.71 (m, 1H); 13C NMR (125 MHz, CDCl3): unable to
0 °C in an ice-bath before the addition of hydrogen peroxide clearly assign peaks due to impurity; 31P NMR (160 MHz,
and were only stirred for 30 min. Next Na2S2O3 (0.3 mL, CDCl3): δ 30.53; IR (neat): 3053, 3018, 2855, 1715, 1595, 1478,
sat. aq.) was added and the mixture stirred at rt. The mixture 1438, 1182, 1025, 748, 696, 561 cm−1; HRMS (EI) calcd for
was filtered through a pad of silica gel using 10% (v/v) C22H21OP (M+) 332.1330; found 332.01324.
MeOH–DCM. The mixture was then concentrated via rotary
evaporation and purified by flash chromatography using powder; H NMR (600 MHz, CDCl3): δ 8.00 (d, J = 7.8 Hz, 3H),
MeOH–DCM. 7.82 (dd, J = 7.2, 11.4 Hz, 4H), 7.59–7.52 (m, 5H), 7.51–7.46
(2,3-Diphenylbutyl)diphenylphosphine oxide 10a. White
1
Compounds 7, 8, and 9 were synthesized via a Tebbe reac- (m, 6H), 7.43 (t, J = 7.8 Hz, 2H), 4.16 (br m, J = 15.6 Hz, 2H),
tion from their respective ketone precursor by a procedure pre- 3.71–3.65 (m, 1H), 3.17–3.13 (m, 1H), (d, J = 7.2 Hz, 3H); 13C
viously reported.13 Compound 10 was synthesized from NMR (125 MHz, CDCl3): δ 157.1, 141.8, 133.8, 132.4, 131.4,
propiophenone through an α-arylation procedure14 followed 131.3, 129.4, 128.9, 128.8, 128.7, 128.1, 127.9, 43.7, 43.3, 32.0
by a Tebbe reaction13 previously published. Compounds 13, (1JCP = 281 Hz), 15.5; 31P NMR (160 MHz, CDCl3): δ 31.66; IR
14, 15, and 16 were synthesized by a previously published (neat): 3052, 2923, 2853, 1676, 1438, 1272, 1185, 1120, 741,
procedure.15
695, 523 cm−1; HRMS (FI) calcd for C28H27OP (M+): 410.1800;
Product’s 3a,16 4a,6 6a,11 11a.6 1H NMR spectral data found: 410.1819.
matched that previously reported.
(2,2-Diphenylethyl)diphenylphosphine oxide 13a. White
(4-Fluorophenethyl)diphenylphosphine oxide 1a. White powder; 1H NMR (600 MHz, CDCl3): δ 7.54–7.02 (m, 20H), 4.68
1
powder; H NMR (600 MHz, CDCl3): δ 7.77 (dd, J = 7.8, 9 Hz, (m, 1H), 3.10 (m, 2H); 13C NMR (125 MHz, CDCl3): δ 143.9,
4H), 7.56–7.53 (m, 2H), 7.51–7.44 (m, 4H), 7.12 (dd, J = 5.4, 143.8, 131.3, 131.3, 130.7, 130.6, 130.4, 130.3, 128.5, 128.4,
9 Hz, 2H), 6.94 (t, J = 8.4 Hz, 2H), 2.92 (dt, J = 7.8, 12 Hz, 2H), 128.4, 128.3, 128.3, 127.8, 127.8, 126.8, 126.4, 125.8, 44.4, 36.7,
2.59–2.54 (m, 2H); 13C NMR (125 MHz, CDCl3): δ 133.5, 132.1, 36.3, 29.7; 31P NMR (160 MHz, CDCl3): δ 28.96; IR (neat): 3710,
132.0, 131.0, 130.9, 129.7, 129.6, 129.0, 128.9, 115.6, 115.5, 2922, 1731, 1436, 1176, 1055, 1033, 884, 742, 524, 508 cm−1
;
32.2 (1JCP = 277 Hz), 27.0; 31P NMR (160 MHz, CDCl3): δ 31.35; HRMS (FI) calcd for
C
26H23OP (M+): 382.1486; found:
IR (neat): 3378, 3066, 2925, 2854, 1719, 1601, 1510, 1438, 1182, 382.1499.
1124, 826, 696, 552 cm−1; HRMS (ESI) calcd for C20H18FOPNa
(M + Na)+: 347.0977; found: 347.0961.
Diphenyl(2-phenyl-2-(3-(trifluoromethyl)phenyl)ethyl)-phos-
phine oxide 14a. White powder; 1H NMR (600 MHz, CDCl3):
(4-Methoxyphenethyl)diphenylphosphine oxide 2a. White
δ 7.68–7.08 (m, 19H), 4.79 (m, 1H), 3.11 (m, 2H);
powder; 1H NMR (600 MHz, CDCl3): δ 7.77 (dd, J = 7.8, 13C NMR (125 MHz, CDCl3): δ 144.4, 143.3, 143.2, 130.6,
11.4 Hz, 4H), 7.55–7.52 (m, 2H), 7.50–7.47 (m, 4H), 7.08 (d, J = 130.6, 130.4, 130.4, 128.8, 128.6, 128.5, 128.4, 128.3, 128.3,
8.4 Hz, 2H), 6.80 (d, J = 8.4 Hz, 2H), 3.77 (s, 3H), 2.88 (dt, J = 127.6, 126.8, 124.5, 124.4, 123.4, 123.4, 44.3, 36.5, 36.0;
7.8, 12.6 Hz, 2H), 2.58–2.54 (m, 2H); 13C NMR (125 MHz, 31P NMR (160 MHz, CDCl3): δ 28.90; IR (neat): 3072, 2940,
CDCl3): δ 158.3, 133.4, 133.3, 132.6, 132.0, 131.0, 130.9, 129.2, 2891, 1592, 1437, 1327, 1175, 1114, 1075, 814, 687, 525 cm−1
;
128.9, 128.8, 114.2, 55.4, 32.3 (1JCP = 277 Hz), 26.8; 31P NMR HRMS (EI) calcd for C27H22F3OP (M+): 450.1360, found:
(160 MHz, CDCl3): δ 31.66; IR (neat): 2944, 2867, 1591, 1513, 450.1369.
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26, 2953–2956; (b) S.-C. Rosca, T. Roisnel, V. Dorcet,
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Conflict of interest
The authors declare no competing financial interests.
Acknowledgements
6 R. A. Stockland Jr., R. I. Taylor, L. E. Thompson and
P. B. Patel, Org. Lett., 2005, 7, 851–853.
Financial support provided by the NSF (CHE 0948479) is
warmly acknowledged with thanks.
7 For
micellar
catalysis
with
TPGS-750-M
see:
(a) B. H. Lipshutz and S. Ghorai, Aldrichimica Acta, 2012,
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