Article pubs.acs.org/Organometallics
Synthesis of P‑CPh3 Substituted Spirooxaphosphirane Complexes: Steric Effects Dominate the Product Formation Rainer Streubel,* Philip Junker, Andreas W. Kyri, and Gregor Schnakenburg Institut für Anorganische Chemie, Rheinische Friedrich-Wilhelms-Universität Bonn, Gerhard-Domagk-Straße 1, 53121 Bonn, Germany S Supporting Information *
ABSTRACT: The reaction of Li/Cl phosphinidenoid pentacarbonyltungsten complex 2 with cyclobutanone and 3oxetanone led to new, stable spirooxaphosphirane complexes 3 and 4. In contrast, formation of O−H insertion products 5 and 6 was the preferred reaction pathway in case of cyclopentanone and cyclohexanone; this is in contrast to spirooxaphosphirane complex formation with sterically less demanding P-substituents. All complexes have been characterized by heteronuclear NMR spectroscopy and single crystal X-ray analysis in case of 3 and 4.
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using Ti(III) reagents is of particular interest as it had opened a new route to end-on phosphaalkene complexes.8 In 2012, Li/Cl phosphinidenoid complexes5c were employed for the first time in the synthesis of [2,n]-spirooxaphosphirane complexes V having P-Cp* substituent, but synthesis of complexes with the [2,3]-spiro ring represented a challenge as they could not be isolated and/or fully characterized. Herein, a study on steric effects of a Li/Cl phosphinidenoid complex having a sterically more demanding P-substituent (R = CPh3) on the formation of spirooxaphosphirane complexes is reported. Focus was put on ketones with and without an additional oxygen atom in the ring as well as different ring sizes (4−6) in case of the latter.
piroheterocycles, e.g., containing epoxide (oxirane) I, II, and/or aziridine units III (Scheme 1), are present in
Scheme 1. Spiro Derivatives of Epoxides I,II, Aziridines III, and Oxaphosphirane Complexes Va
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RESULTS AND DISCUSSION Chlorine/lithium exchange in complex 1, using tert-butyllithium in the presence of 12-crown-4 at low temperature, led to Li/Cl phosphinidenoid complex12 2 which reacted in situ with cyclobutanone, cyclopentanone, cyclohexanone, and 3oxetanone, undergoing two different reaction pathways depending on the ring size of the ketone (Scheme 2). In case of the reaction with cyclobutanone and 3-oxetanone, the spirooxaphosphirane complexes 3 and 4 were formed. Remarkably, the reaction with 3-oxetanone showed a much higher selectivity (about 98% according to 31P{1H} NMR signal integration), while the reaction with cyclobutanone also yielded 36% of an unknown side-product with a chemical shift of 88.9 ppm (1JW,P = 263.3 Hz, 1JP,H = 300.4 Hz) in the 31P{1H} NMR spectrum. For cyclopentanone and cyclohexanone a different reaction occurred, and instead of the [2 + 1]-cycloaddition to form spirooxaphosphirane complexes, an O−H insertion took place. The latter, most probably resulted from the presence of the enol form, thus yielding alkoxyphosphane complexes 5 and 6 in
a
R denotes an organic substituent; the dashed line in V indicates various ring sizes. E indicates a heteroatom other than phosphorus.
natural products1 and have been studied intensively by experimentalists as well as theoreticians2 as they show a vast number of interesting physical properties.3 In contrast, the field of phosphorus-containing spiroheterocycles is largely underdeveloped. Small-sized ring systems, having a higher ring strain, are becoming increasingly interesting as polymer precursors. In the case of monocyclic oxaphosphirane complexes IV, the synthetic breakthrough came with the advent of Li/Cl phosphinidenoid complexes4 as P1 building blocks due to their high reactivity toward aldehydes and ketones combined with functional group tolerance.4,5 For example, studies on acid-induced ring opening6 (i) and ring expansion7 (ii) have demonstrated that they are valuable building blocks for unusual heterocyclic P-ligands and, hence, deserve further investigations. Furthermore, the possibility to remove the ring oxygen atom via a reductive single electron transfer (SET) reaction © XXXX American Chemical Society
Received: May 31, 2017
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DOI: 10.1021/acs.organomet.7b00404 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics Scheme 2. Synthesis of Spirooxaphosphirane Complexes 3 and 4 and Acyclic Complexes 5 and 6
a rather unselective manner (5: 33% and 6: 62%); unfortunately, these could not be isolated. Regarding O−H insertions a similar outcome was observed previously for some acyclic ketones.13 Interestingly, complex 5 and 6 appeared in two isomeric forms in the 31P{1H} NMR spectrum, due to the stereogenic center at phosphorus, at 117.2 ppm (1JW,P = 283.1 Hz) and 117.3 ppm (1JW,P = 281.2 Hz) in a 37:63 ratio (5) and 108.1 ppm (1JW,P = 281.2 Hz) and 110.0 ppm (1JW,P = 280.2 Hz) in a 80:20 ratio (6). Complexes 3 and 4 were confirmed by singlecrystal X-ray analysis; for selected data, see Figures 1 and 2.
Figure 2. Molecular structure of complex 4. Ellipsoids set at 50% probability; hydrogen atoms omitted for clarity. Selected bond lengths (Å) and angles (deg): W−P 2.4983(6), P−O(1) 1.6639(18), P−C(5) 1.890(2), C(1)−C(2) 1.532(3), C(2)−C(3) 1.552(4), O(1)−P−C(1) 50.45(10), C(1)−O(1)−P 69.28(12), C(1)−C(2)−C(3) 88.47(19).
Scheme 3. Deoxygenation of Spirooxaphosphirane Complex 3
Figure 1. Molecular structure of complex 3. Ellipsoids set at 50% probability; hydrogen atoms omitted for clarity. Selected bond lengths (Å) and angles (deg): W−P 2.4834(19), P−O(1) 1.660(5), P−C(4) 1.907(8), C(1)−C(2) 1.523(10), C(2)−O(2) 1.458(9), O(1)−PC(1) 49.2(3), C(1)−O(1)−P 70.0(4), C(1)−C(2)−O(2) 90.3(6).
and 7 could not be separated due to very similar solubilities, and further attempts to use column chromatography were met with limited success due to their instability on the solid phase.
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To remove the oxygen atom of the oxaphosphirane ring and hence obtain a possibly interesting polymer precursor, complex 3 was reacted with zinc and trichlorocyclopentadienyltitanium(IV) which had been used before successfully.8a The selective deoxygenation of complex 3 took place to yield end-on phosphaalkene complex 7 (Scheme 3), but the reaction stopped at about 57% conversion of 3. 31 1 P{ H} NMR spectroscopy of the reaction mixture showed a signal at 195.3 ppm (1JW,P = 255.1 Hz) which is in the expected range for complex 7.8−11 Unfortunately, complexes 3
CONCLUSIONS It was demonstrated that reaction of a Li/Cl phosphinidenoid pentacarbonyltungsten complex (R = CPh3) with cyclobutanone and 3-oxetanone led to new and stable spirooxaphosphirane complexes. In contrast, sterically more demanding substrates such as cyclopentanone and cyclohexanone furnished preferentially O−H insertion products, which may stem from reaction of the corresponding enol forms present in solution. Evidence for oxaphosphirane deoxygenation and endB
DOI: 10.1021/acs.organomet.7b00404 Organometallics XXXX, XXX, XXX−XXX
Article
Organometallics
added under continuous stirring 0.28 mL (0.48 mmol, 1.7 mol/L) of tert-butyllithium at −80 °C (to form complex 2). After stirring for 30 min, 5 equiv of cyclobutanone (148 μL, 2.0 mmol) was added at −65 °C. The reaction mixture was allowed to warm up to −30 °C while stirring. Then, the reaction mixture was stirred for 2 h while maintaining the mixture at −30 °C. Afterward the reaction mixture was allowed to warm to ambient temperature while stirring overnight. The reaction was filtered using a small column (Ø 2 cm, 1 cm SiO2, r.t.) with diethyl ether (50 mL). After evaporation of the diethyl ether, the residue was washed with 1.5 mL of n-pentane at −30 °C, dissolved in diethyl ether again, and stored in the glovebox at r.t. to crystallize. Complex 4. Yield: 83 mg (31%); mp 126 °C (dec.); 1H NMR (500.1 MHz, C6D6, r.t.) δ = 1.31−1.43 (m, CH2), 1.45−1.56 (m, CH2), 1.66−1.82 (m, CH2), 1.84−2.02 (m, CH2), 2.19−2.38 (m, CH2), 2.41−2.62 (m, CH2), 6.94−7.01 (m, C6H5, para-H), 7.04−7.12 (m, C6H5, meta-H), 7.50−7.58 (m, C6H5, ortho-H). 13C{1H} NMR (75.5 MHz, CDCl3, r.t.) δ = 32.0 (s, CH2), 35.3 (d, 2JP,C = 3.5 Hz), 35.5 (d, 2JP,C = 1.5 Hz), 67.9 (d, 1JP,C = 9.8 Hz, spiro-C), 72.4 (d, 1JP,C = 19.9 Hz, C(C6H5)3), 127.9 (d, 5JP,C = 1.8 Hz, C6H5 (para-C)), 128.9 (d, 4JP,C = 0.6 Hz, C6H5 (meta-C)), 131.4 (d, 3JP,C = 7.3 Hz, C6H5 (ortho-C), 140.6 (d, 2JP,C = 2.4 Hz, C6H5 (Cquart), 195.8 (d, 2JP,C = 8.2 Hz, cis-CO), 197.1 (d, 2JP,C = 38.2 Hz trans-CO). 31P{1H} NMR (121.5 MHz, Et2O, r.t.) δ = 22.0 (ssat, 1JW,P = 302.1 Hz). MS (EI, 70 eV, 184W) m/z (%) = 667.9 (5) [M]+•, 639.9 (18) [M − CO]+, 583.9 (72) [M − CO − CO − CO]+, 344.1 (10) [M − W(CO)5, 243.1 (100) [CPh3]+. M(C28H21O6PW) = 669.28 g/mol. IR (ATR Diamond) ṽ [cm−1] = ν(CO): 2074.3 (s), 1986.2 (s), 1923.1 (vs). Elemental analysis for C28H21O6PW (669.28 g/mol): calcd: C 50.32%, H 3.17%; exp: C 50.62%, H 3.51%. Procedure for the Reaction of 2 with Cyclopentanone and Cyclohexanone. To a solution of complex 1 (67 mg, 0.1 mmol) and 12-crown-4 (16 μL, 0.1 mmol) in THF (2 mL), was slowly added 0.08 mL (0.14 mmol, 1.7 mol/L) of tert-butyllithium at −80 °C to form complex 2. After stirring for 30 min, 3 equiv of the ketone derivative, cyclopentanone (27 μL, 0.3 mmol), or cyclohexanone (23 μL, 0.1 mmol) was added at −50 °C. The reaction mixture was allowed to warm up while stirring. Complex 5. Yield: 33% of reaction mixture (according to 31P{1H} NMR integration). 31P{1H} NMR (121.5 MHz, THF, r.t.) δ = 117.2 (ssat, 1JW,P = 283.1 Hz), 117.3 (ssat, 1JW,P = 281.2 Hz); ratio 37:63. Complex 6. Yield: 62% of reaction mixture (according to 31P{1H} NMR integration). 31P{1H} NMR (121.5 MHz, THF, r.t.) δ = 108.1 (ssat, 1JW,P = 281.2 Hz), 110.0 (ssat, 1JW,P = 280.2 Hz); ratio 80:20. Procedure for the Reaction of 3 with Zinc/CpTiCl3. Complex 3 (67 mg, 0.1 mmol) was added to zinc (6.5 mg, 0.1 mmol) and CpTiCl3 (22 mg, 0.1 mmol) before adding THF (6 mL). The reaction mixture was stirred overnight for 24 h at ambient temperature. THF was removed in vacuo (10−2 mbar), and the product was extracted using diethyl ether (15 mL). Afterward, the diethyl ether was removed under vacuum (10−2 mbar), and the residue was washed with 2 mL of n-pentane at −30 °C. Complex 7. Yield: 50% of the product mixture (according to 31 1 P{ H} NMR integration). 31P{1H} NMR (121.5 MHz, THF, r.t.) δ = 195.3 ppm (1JW,P = 255.4 Hz).
on phosphaalkene formation was obtained (in case of 3) via reaction with Zn/CpTiCl3.
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EXPERIMENTAL SECTION
All reactions were carried out under an inert gas atmosphere using purified and dried argon and standard Schlenk techniques. Tetrahydrofuran, diethyl ether, and n-pentane were dried over sodium wire/benzophenone, CH2Cl2 over CaH2 and further purified by subsequent distillation. All ketones were distilled before usage. All NMR spectra were recorded on a Bruker AVI-300 (300.1 MHz for 1H, 75.5 MHz for 13C and 121.5 MHz for 31P), Bruker AVI-400 (400.1 MHz for 1H, 100.6 MHz for 13C and 162.0 MHz for 31P), Bruker AV III HD Prodigy 500 (500.2 MHz for 1H, 125.8 MHz for 13C and 202.5 MHz for 31P), and Bruker AV III HD Cryo 700 (700.4 MHz for 1H, 176.1 MHz for 13C and 283.5 MHz for 31P) spectrometer at 25 °C. The 1H and 13C NMR spectra were referenced to the residual proton resonances and the 13C NMR signals of the deuterated solvents, respectively, and 31P spectra were referenced to 85% H3PO4 as an external standard. Melting points were determined in one-side melted off capillaries using a Büchi Type S or a Carl Roth Type MPM-2 apparatus, they are uncorrected. Elemental analyses were carried out on a Vario EL gas chromatograph. Mass spectrometric data were collected on a Kratos MS 50 spectrometer using EI, 70 eV or a MAT 90 Thermo Finnigan sector instrument equipped with a LIFDI ion source. IR spectra of all compounds were recorded on a Thermo Nicolet 380 FT-IR spectrometer with an attenuated total reflection (ATR) attachment or a Bruker Alpha Diamond ATR FTIR spectrometer. The molecular structures in the single crystal were solved by direct methods refined by full-matrix least-squares technique in anisotropic approximation for non-hydrogen atoms using SHELXS97 and SHELXL9723 program packages. Hydrogen atoms were located from Fourier synthesis and refined isotropically. Crystallographic data for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre (CCDC) as CCDC nos. 1552552−1552554, which can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif. Synthesis of Complex 3. To a solution of complex 1 (334.5 mg, 0.5 mmol) and 12-crown-4 (80 μL, 0.5 mmol) in THF (10 mL), was slowly added 0.35 mL (0.6 mmol, 1.7 mol/L) of tert-butyllithium at −85 °C (to form complex 2) under continuous stirring. After stirring for 30 min, 3 equiv of 3-oxetanone (90 μL, 1.5 mmol) was added at −50 °C. The reaction mixture was allowed to warm to −20 °C while stirring. THF was then evaporated, and the products were extracted with diethyl ether (3 portions of 20 mL). After evaporation of the diethyl ether the remaining white/beige solid was dried in vacuo (10−2 mbar) for 1 h. Complex 3. Yield: 269 mg (81%); mp 172−173 °C; 1H NMR (300.1 MHz, CDCl3, r.t.) δ = 3.96 (ddd, 2JH,H = 9.9 Hz, 3JP,H = 6.2 Hz, 4 JH,H = 1.6 Hz, CH2), 4.26 (ddt, 2JH,H = 10.4 Hz, 3JP,H = 8.4 Hz, 4JH,H = 1.4 Hz, CH2), 4.84 (ddt, 2JH,H = 10.1 Hz, 3JP,H = 8.6 Hz, 4JH,H = 1.2 Hz, CH2), 5.02 (ddd, 2JH,H = 10.0 Hz, 3JP,H = 8.8 Hz, 4JH,H = 1.6 Hz, CH2), 7.41 (m, C6H5). 13C{1H} NMR (75.5 MHz, CDCl3, r.t.) δ = 67.4 (d, 2 JP,C = 7.8 Hz, CH2), 69.8 (d, 2JP,C = 24.8 Hz, CH2), 77.6 (d, 1JP,C = 1.9 Hz, C(C6H5)3), 80.7 (d, 1JP,C = 4.2 Hz, spiro-C), 128.3 (d, 5JP,C = 2.0 Hz, C6H5 (para-C)), 129.0 (d, 4JP,C = 0.7 Hz, C6H5 (meta-C)), 131.0 (d, 3JP,C = 7.6 Hz, C6H5 (ortho-C), 139.4 (d, 2JP,C = 2.5 Hz, C6H5 (Cquart), 194.5 (d, cis-CO), 196.0 (d, trans-CO). 31P{1H} NMR (121.5 MHz, CDCl3, r.t.) δ = 18.2 (ssat, 1JW,P = 305.7 Hz). MS (EI, 70 eV, 184 W) m/z (%) = 670.0 (0.06) [M]+•, 598.0 (0.06) [M − C3H4O2]+, 570.0 (0.07) [M − C3H4O2 − CO]+, 542.0 (0.04) [M − C3H4O2 − CO − CO]+, 514.0 (0.4) [M − C3H4O2 − CO − CO − CO]+, 426.9 (0.9) [M − CPh3]+, 243.1 (100) [CPh3]+. IR (ATR Diamond) ṽ [cm−1] = ν(CO): 2075.6 (s), 1998.0 (m), 1919.6 (vs). Elemental analysis for C27H19O7PW (670.26 g/mol): calcd: C 48.38%, H 2.86%; exp: C 48.42%, H 3.011%. (A chromium derivative, 3b, was also synthesized as such. The NMR spectra and crystallographic data can be found in the Supporting Information.) Synthesis of Complex 4. To a solution of complex 1 (268 mg, 0.4 mmol) and 12-crown-4 (64 μL, 0.4 mmol) in THF (8 mL), was slowly
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ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.7b00404. NMR spectra (1H, 13C{1H}, 31P{1H}) and crystallographic data of 3 (3a: M = W, 3b: M = Cr) and 4 (PDF) Accession Codes
CCDC 1552552−1552554 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
[email protected], or by contacting The C
DOI: 10.1021/acs.organomet.7b00404 Organometallics XXXX, XXX, XXX−XXX
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Organometallics Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Fax: +49(0)228 73-9616. ORCID
Rainer Streubel: 0000-0001-5661-8502 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We are grateful to the Deutsche Forschungsgemeinschaft (STR 411/26-3 and 29-3 and SFB 813) and the cost action cm1302 “SIPs” for financial support. We also acknowledge Prof. Dr. A. C. Filippou and Prof. D. Menche for the use of X-ray facilities and C. Rödde for the X-ray diffraction studies. We dedicate this manuscript to Prof. John Gladysz and Prof. Dr. G. Bertrand in honor of their respective 65th birthdays.
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REFERENCES
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DOI: 10.1021/acs.organomet.7b00404 Organometallics XXXX, XXX, XXX−XXX
