膦氧化物

氧化膦（英語：Phosphine oxide，也稱膦氧化物）是化學式為X₃P=O的含磷化合物。氧化膦可以是有機物或是無機物，當式中X為烷基或芳基時是有機磷化合物（如三苯基氧化膦），當式中X均為鹵素時是無機物（如三氯氧磷）^[1]。

結構與分類

氧化膦分子內的P-O鍵較短且有極性^[2]。學界對P=O鍵的成因曾有爭論，過去認為是氧上的孤對電子填充到磷d軌道上，形成了p-d反饋π鍵（該理論現在被用於解釋氧化胺的不穩定性），然而氧化膦的雙鍵事實上與酰基性質不同，計算化學的結果也並不支持此理論。也有研究用離子鍵X₃P⁺-O^-來解釋其短鍵長與極性。現在得到較為普遍共識的理論是分子軌道理論的解釋，該理論認為P=O鍵的特性是由於氧p軌道的一對孤對電子填充到P-X鍵上的反鍵軌道𝛔*，該理論受從頭計算法結果支持^[3]^[4]。

分子軌道理論描述的P=O鍵

叔氧化膦

叔氧化膦是最常見的氧化膦，其通式為R₃P=O，具四面體分子結構，叔氧化膦可以從叔膦氧化而來。

仲氧化膦

仲氧化膦衍生自仲膦（R₂PH），保持了四面體分子結構^[5]。仲氧化膦可以用作交叉偶聯的偶聯劑，也可用於合成手性膦配體，如二苯基氧化膦就是一種常見的市售仲氧化膦試劑^[6]。

仲氧化膦可以進一步氧化：

R₂P(O)H + H₂O₂ → R₂P(O)OH + H₂O

仲氧化膦的互變異構體為次亞膦酸（R₂POH）：

R₂P(O)H ⇌ R₂POH

伯氧化膦

伯氧化膦衍生自伯膦，具四面體分子結構。伯氧化膦會發生歧化，得到伯膦和次膦酸^[7]：

2 RP(O)H₂ → RP(O)(H)OH + 2 RPH₂

合成

氧化膦容易由有機膦的氧化合成，室溫下空氣中的氧氣就足以將它們完全轉化為對應的氧化膦：

R₃P + 1/2 O₂ → R₃PO

該反應通常是不可控的，因此會儘量在無空氣體系中處理膦。

鹼性較弱的膦，例如甲基二苯基膦可以使用過氧化氫氧化^[8]：

PMePh₂ + H₂O₂ → OPMePh₂ + H₂O

Wittig反應中會產生氧化膦副產物：

R₃P⁺CR'₂ + R"₂CO → R₃PO + R'₂C=CR"₂

氫氧化鏻的受熱分解會產生氧化膦：

[PPh₄]Cl + NaOH → Ph₃PO + NaCl + PhH

二鹵化磷(V)水解時會產生氧化膦^[9]：

R₃PCl₂ + H₂O → R₃PO + 2 HCl

氯代膦能水解產生對應的仲氧化膦，如二苯基氯化膦：

Ph₂PCl + H₂O → Ph₂P(O)H + HCl

去氧

實驗室中常用三氯矽烷來還原氧化膦，工業上則會使用光氣等試劑將氧化膦轉化成氯化三苯基一氯鏻（Ph₃PCl⁺Cl^-）後再單獨進行還原^[10] ^[11]。對於手性的氧化膦分子，去氧過程可以控制構型保持或反轉，例如三氯矽烷與三乙胺的去氧過程是利於構型反轉的，而沒有路易斯鹼的反應過程是利於構型保持的^[12]。

HSiCl₃ + Et₃N ⇋ SiCl₃⁻ + Et₃NH⁺

R₃PO + Et₃NH⁺ ⇋ R₃POH⁺ + Et₃N

SiCl₃⁻ + R₃POH⁺ → PR₃ + HOSiCl₃

此法的泛用有部分得益於三氯矽烷低廉的價格，除了三氯矽烷外，也可以使用其他全氯矽烷（或其聚合物）如六氯乙矽烷（英語：hexachlorodisilane）。與三氯矽烷相比，全氯聚矽烷和相應的氧化膦，如Si₂Cl₆或Si₃Cl₈，在苯或氯仿中的去氧反應產率更高。

R₃PO + Si₂Cl₆ → R₃P + Si₂OCl₆

2 R₃PO + Si₃Cl₈ → 2 R₃P + Si₃O₂Cl₈

母體

最簡單的氧化膦（H₃PO）性質不穩定，在氧氣與膦反應產物的質譜檢測中被檢測到^[13]，也能通過FT-IR在膦與臭氧的反應^[14]及膦、三氯氧釩和鉻酰氯反應的基質分離物中檢測到^[15]。據報道，通過白磷的電化學氧化，其能在水-乙醇溶液中相對穩定存在，並緩慢地歧化成膦和次磷酸^[16]。有研究報道了膦與一氧化氮在室溫下催化聚合成P_xH_y的過程，通過熱重分析質譜（TGA-MS）和衰減全反射傅里葉變換紅外光譜（ATR-FTIR）分析，認為該過程是由氧化膦中間體脫水自縮合發生的^[17]。

氧化膦母體的球棍模型

參考文獻

^ D. E. C. Corbridge "Phosphorus: An Outline of its Chemistry, Biochemistry, and Technology" 5th Edition Elsevier: Amsterdam 1995. ISBN 0-444-89307-5.
^ D. B. Chesnut. The Electron Localization Function (ELF) Description of the PO Bond in Phosphine Oxide. Journal of the American Chemical Society. 1999, 121 (10): 2335–2336. doi:10.1021/ja984314m.
^ Gilheany, Declan G. No d Orbitals but Walsh Diagrams and Maybe Banana Bonds: Chemical Bonding in Phosphines, Phosphine Oxides, and Phosphonium Ylides. Chemical Reviews. 1994, 94 (5): 1339–1374. PMID 27704785. doi:10.1021/cr00029a008.
^ G. L. Miessler and D. A. Tarr 「Inorganic Chemistry」 3rd Ed, Pearson/Prentice Hall publisher, ISBN 0-13-035471-6.
^ Gallen, Albert; Riera, Antoni; Verdaguer, Xavier; Grabulosa, Arnald. Coordination Chemistry and Catalysis with Secondary Phosphine oxides. Catalysis Science & Technology. 2019, 9 (20): 5504–5561. doi:10.1039/C9CY01501A. hdl:2445/164459  .
^ Ackermann, Lutz. Catalytic Arylations with Challenging Substrates: From Air-Stable HASPO Preligands to Indole Syntheses and C-H-Bond Functionalizations. Synlett. 2007, 2007 (4): 0507–0526. doi:10.1055/s-2007-970744.
^ Horký, Filip; Císařová, Ivana; Štěpnička, Petr. A Stable Primary Phosphane Oxide and Its Heavier Congeners. Chemistry – A European Journal. 2021, 27 (4): 1282–1285. PMID 32846012. S2CID 221346479. doi:10.1002/chem.202003702.
^ Denniston, Michael L.; Martin, Donald R. Methyldiphenylphosphine Oxide and Dimethylphenylphosphine Oxide. Inorganic Syntheses. 1977, 17: 183–185. ISBN 9780470132487. doi:10.1002/9780470132487.ch50.
^ W. B. McCormack (1973). "3-Methyl-1-Phenylphospholene oxide". Org. Synth.; Coll. Vol. 5: 787.
^ Podyacheva, Evgeniya; Kuchuk, Ekaterina; Chusov, Denis. Reduction of phosphine oxides to phosphines. Tetrahedron Letters. 2019, 60 (8): 575–582. doi:10.1016/j.tetlet.2018.12.070.
^ van Kalkeren, Henri A.; van Delft, Floris L.; Rutjes, Floris P. J. T. Organophosphorus Catalysis to Bypass Phosphine Oxide Waste. ChemSusChem. 2013, 6 (9): 1615–1624. ISSN 1864-5631. PMID 24039197. doi:10.1002/cssc.201300368.
^ Klaus Naumann; Gerald Zon; Kurt Mislow. Use of hexachlorodisilane as a reducing agent. Stereospecific deoxygenation of acyclic phosphine oxides. Journal of the American Chemical Society. 1969, 91 (25): 7012–7023. doi:10.1021/ja01053a021.
^ Hamilton, Peter A.; Murrells, Timothy P. Kinetics and mechanism of the reactions of PH3 with O(3P) and N(4S) atoms. J. Chem. Soc., Faraday Trans. 1985, 2 (81): 1531–1541. doi:10.1039/F29858101531.
^ Withnall, Robert; Andrews, Lester. FTIR spectra of the photolysis products of the phosphine-ozone complex in solid argon. J. Phys. Chem. 1987, 91 (4): 784–797. doi:10.1021/j100288a008.
^ Kayser, David A.; Ault, Bruce S. Matrix Isolation and Theoretical Study of the Photochemical Reaction of PH3 with OVCl3 and CrCl2O2. J. Phys. Chem. A. 2003, 107 (33): 6500–6505. Bibcode:2003JPCA..107.6500K. doi:10.1021/jp022692e.
^ Yakhvarov, D.; Caporali, M.; Gonsalvi, L.; Latypov, S.; Mirabello, V.; Rizvanov, I.; Sinyashin, O.; Stoppioni, P.; Peruzzini, M. Experimental Evidence of Phosphine Oxide Generation in Solution and Trapping by Ruthenium Complexes. Angewandte Chemie International Edition. 2011, 50 (23): 5370–5373. PMID 21538749. doi:10.1002/anie.201100822.
^ Zhao, Yi-Lei; Flora, Jason W.; David Thweatt, William; Garrison, Stephen L.; Gonzalez, Carlos; Houk, K. N.; Marquez, Manuel. Phosphine Polymerization by Nitric Oxide: Experimental Characterization and Theoretical Predictions of Mechanism. Inorg. Chem. 2009, 48 (3): 1223–1231. PMID 19102679. doi:10.1021/ic801917a.

[1] D. E. C. Corbridge "Phosphorus: An Outline of its Chemistry, Biochemistry, and Technology" 5th Edition Elsevier: Amsterdam 1995. ISBN 0-444-89307-5.

[2] D. B. Chesnut. The Electron Localization Function (ELF) Description of the PO Bond in Phosphine Oxide. Journal of the American Chemical Society. 1999, 121 (10): 2335–2336. doi:10.1021/ja984314m.

[3] Gilheany, Declan G. No d Orbitals but Walsh Diagrams and Maybe Banana Bonds: Chemical Bonding in Phosphines, Phosphine Oxides, and Phosphonium Ylides. Chemical Reviews. 1994, 94 (5): 1339–1374. PMID 27704785. doi:10.1021/cr00029a008.

[4] G. L. Miessler and D. A. Tarr 「Inorganic Chemistry」 3rd Ed, Pearson/Prentice Hall publisher, ISBN 0-13-035471-6.

[5] Gallen, Albert; Riera, Antoni; Verdaguer, Xavier; Grabulosa, Arnald. Coordination Chemistry and Catalysis with Secondary Phosphine oxides. Catalysis Science & Technology. 2019, 9 (20): 5504–5561. doi:10.1039/C9CY01501A. hdl:2445/164459  .

[6] Ackermann, Lutz. Catalytic Arylations with Challenging Substrates: From Air-Stable HASPO Preligands to Indole Syntheses and C-H-Bond Functionalizations. Synlett. 2007, 2007 (4): 0507–0526. doi:10.1055/s-2007-970744.

[7] Horký, Filip; Císařová, Ivana; Štěpnička, Petr. A Stable Primary Phosphane Oxide and Its Heavier Congeners. Chemistry – A European Journal. 2021, 27 (4): 1282–1285. PMID 32846012. S2CID 221346479. doi:10.1002/chem.202003702.

[8] Denniston, Michael L.; Martin, Donald R. Methyldiphenylphosphine Oxide and Dimethylphenylphosphine Oxide. Inorganic Syntheses. 1977, 17: 183–185. ISBN 9780470132487. doi:10.1002/9780470132487.ch50.

[9] W. B. McCormack (1973). "3-Methyl-1-Phenylphospholene oxide". Org. Synth.; Coll. Vol. 5: 787.

[TL-10] Podyacheva, Evgeniya; Kuchuk, Ekaterina; Chusov, Denis. Reduction of phosphine oxides to phosphines. Tetrahedron Letters. 2019, 60 (8): 575–582. doi:10.1016/j.tetlet.2018.12.070.

[van_Kalkerenvan_Delft2013-11] van Kalkeren, Henri A.; van Delft, Floris L.; Rutjes, Floris P. J. T. Organophosphorus Catalysis to Bypass Phosphine Oxide Waste. ChemSusChem. 2013, 6 (9): 1615–1624. ISSN 1864-5631. PMID 24039197. doi:10.1002/cssc.201300368.

[12] Klaus Naumann; Gerald Zon; Kurt Mislow. Use of hexachlorodisilane as a reducing agent. Stereospecific deoxygenation of acyclic phosphine oxides. Journal of the American Chemical Society. 1969, 91 (25): 7012–7023. doi:10.1021/ja01053a021.

[13] Hamilton, Peter A.; Murrells, Timothy P. Kinetics and mechanism of the reactions of PH3 with O(3P) and N(4S) atoms. J. Chem. Soc., Faraday Trans. 1985, 2 (81): 1531–1541. doi:10.1039/F29858101531.

[14] Withnall, Robert; Andrews, Lester. FTIR spectra of the photolysis products of the phosphine-ozone complex in solid argon. J. Phys. Chem. 1987, 91 (4): 784–797. doi:10.1021/j100288a008.

[15] Kayser, David A.; Ault, Bruce S. Matrix Isolation and Theoretical Study of the Photochemical Reaction of PH3 with OVCl3 and CrCl2O2. J. Phys. Chem. A. 2003, 107 (33): 6500–6505. Bibcode:2003JPCA..107.6500K. doi:10.1021/jp022692e.

[16] Yakhvarov, D.; Caporali, M.; Gonsalvi, L.; Latypov, S.; Mirabello, V.; Rizvanov, I.; Sinyashin, O.; Stoppioni, P.; Peruzzini, M. Experimental Evidence of Phosphine Oxide Generation in Solution and Trapping by Ruthenium Complexes. Angewandte Chemie International Edition. 2011, 50 (23): 5370–5373. PMID 21538749. doi:10.1002/anie.201100822.

[17] Zhao, Yi-Lei; Flora, Jason W.; David Thweatt, William; Garrison, Stephen L.; Gonzalez, Carlos; Houk, K. N.; Marquez, Manuel. Phosphine Polymerization by Nitric Oxide: Experimental Characterization and Theoretical Predictions of Mechanism. Inorg. Chem. 2009, 48 (3): 1223–1231. PMID 19102679. doi:10.1021/ic801917a.

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