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Aminophosphine

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In organophosphorus chemistry, aminophosphines are compounds with the formula R3−nP(NR2)n where R is a hydrogen or organic substituent, and n = 0, 1, or 2. At one extreme, the parents H2PNH2 and P(NH2)3 are lightly studied and fragile. At the other extreme, tris(dimethylamino)phosphine (P(NMe2)3) is commonly available. Intermediate members are known, such as Ph2PN(H)Ph. Aminophosphines are typically colorless and reactive to oxygen. Aminophosphines are pyramidal at the phosphorus.[1]

Parent members

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Structure of P(NMe2)3.
The aminophosphine called the Verkade base is a superbase.

The fundamental aminophosphines have the formulae PH3−n(NH2)n (n = 1, 2, or 3). Fundamental aminophosphines can not be isolated in a practical quantities but have been examined theoretically. H2NPH2 is predicted to be more stable than the P(V) tautomer HN=PH3.[2]

Secondary amines are more straightforward. Trisaminophosphines are made by treating phosphorus trichloride with secondary amines:

PCl3 + 6 HNMe2 → (Me2N)3P + 3 [H2NMe2]Cl

Aminophosphine chlorides

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Structure of Me2NPCl2.

The amination of phosphorus trihalides occur sequentially, with each amination proceeding slower than before:[3]

PCl3 + 2 HNMe2 → Me2NPCl2 + [H2NMe2]Cl
Me2NPCl2 + 2 HNMe2 → (Me2N)2PCl + [H2NMe2]Cl

With bulky amines like diisopropylamine, the selectivity for the monosubstitution improves.[4] Commercially available aminophosphine chlorides include dimethylaminophosphorus dichloride and bis(dimethylamino)phosphorus chloride.

Related aminophosphine fluorides compounds are available from trifluorophosphine. The diphosphine MeN(PF2)2 is prepared from methylamine:

2 PF3 + 3 MeNH2 → MeN(PF2)2 + 2 [MeNH3]F

Me(PF2)2 is used as a bridging ligand in organometallic chemistry.

Substituted aminophosphines are generally prepared from organophosphorus chlorides and amines. The method is used to prepare ligands for homogeneous catalysis.[5] Chlorodiphenylphosphine and diethylamine react to give an aminophosphine:[1][6]

Ph2PCl + 2 HNEt2 → Ph2PNEt2 + [H2NEt2]Cl

Primary amines react with phosphorus(III) chlorides give aminophosphines with acidic α-NH centers:[7]

Ph2PCl + 2 H2NR → Ph2PN(H)R + [H3NR]Cl

Reactions

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Protonolysis

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The P-N bond is susceptible to attack by protic reagents. Alcoholysis occurs readily:

Ph2PNEt2 + ROH → Ph2POR + HNEt2

The P-N bond reverts to the chloride upon treatment with anhydrous hydrogen chloride:

Ph2PNEt2 + 2 HCl → Ph2PCl + [H2NEt2]Cl

Similarly, transamination is used in the conversion of one aminophosphine to another:

P(NMe2)3 + R2NH ⇌ P(NR2)(NMe2)2 + HNMe2

With tris(dimethylamino)phosphine is a reactant, the equilibrium can be driven by evaporation of dimethylamine.[8]

Since the P-NR2 bond is not attacked by Grignard reagents, aminophosphine chlorides are useful reagents in the preparation of unsymmetrical tertiary phosphines. Illustrative is the conversion of dimethylaminophosphorus dichloride to chlorodimethylphosphine:[9]

2 MeMgBr + Me2NPCl2 → Me2NPMe2 + 2 MgBrCl
Me2NPMe2 + 2 HCl → ClPMe2 + Me2NH2Cl

Illustrative also is the chemistry of 1,2-bis(dichlorophosphino)benzene, a versatile precursor to diphosphine ligands, is prepared using aminophosphine reagents. It is prepared from 1,2-dibromobenzene via lithiation and treatment with (Et2N)2PCl (Et = ethyl). This route gives C6H4[P(NEt2)2]2, which is treated with hydrogen chloride:[10]

C6H4[P(NEt2)2]2 + 8 HCl → C6H4(PCl2)2 + 4 Et2NH2Cl

Conversion to phosphenium salts

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Diaminophosphorus chlorides and tris(dimethylamino)phosphine are precursors to phosphenium ions of the type [(R2N)2P]+:[11]

R2PCl + AlCl3 → [R2P+]AlCl4−
P(NMe2)3 + 2 HOTf → [P(NMe2)2]OTf + [H2NMe2]OTf

Oxidation and quaternization

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Typical aminophosphines undergo oxidation to the oxide. Alkylation, e.g. by methyl iodide, gives the phosphonium cation.

References

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  1. ^ a b Mateo Alajarín; Carmen López-Leonardo; Pilar Llamas-Lorente (2005). "The Chemistry of Phosphinous Amides (Aminophosphanes): Old Reagents with New Applications". Top. Curr. Chem. Topics in Current Chemistry. 250: 77–106. doi:10.1007/b100982. ISBN 978-3-540-22498-3.
  2. ^ Sudhakar, Pamidighantam V.; Lammertsma, Koop (1991). "Nature of Bonding in Phosphazoylides. A Comparative Study of N2H4, NPH4, and P2H4". Journal of the American Chemical Society. 113pages=1899–1906 (6): 1899–1906. doi:10.1021/ja00006a005.
  3. ^ Morse, J. G.; Cohn, K.; Rudolph, R. W.; Parry, R. W. (1967). "Substituted Difluoro- and Dichlorophosphines". Inorganic Syntheses. Inorganic Syntheses. Vol. 22. pp. 147–156. doi:10.1002/9780470132418.ch22. ISBN 9780470132418.
  4. ^ Denmark, Scott; Ryabchuk, Pavel; Min Chi, Hyung; Matviitsuk, Anastassia (2019). "Preparation of a Diisopropylselenophosphoramide Catalyst and its Use in Enantioselective Sulfenoetherification". Organic Syntheses. 96: 400–417. doi:10.15227/orgsyn.096.0400. PMC 8439352. PMID 34526731.
  5. ^ Agbossou, Francine; Carpentier, Jean-François; Hapiot, Frédéric; Suisse, Isabelle; Mortreux, André (1998). "The aminophosphine-phosphinites and related ligands: Synthesis, coordination chemistry and enantioselective catalysis1Dedicated to the memory of Professor Francis Petit". Coordination Chemistry Reviews. 178–180: 1615–1645. doi:10.1016/S0010-8545(98)00088-5.
  6. ^ Smith, Craig R.; Mans, Daniel J.; RajanBabu, T. V. (2008). "(R)-2,2'-Binaphthoyl-(S,s)-Di(1-Phenylethyl) Aminophosphine. Scalable Protocols for the Syntheses of Phosphoramidite (Feringa) Ligands". Organic Syntheses. 85: 238–247. doi:10.15227/orgsyn.085.0238. PMC 2719905. PMID 19655040.
  7. ^ Fei, Zhaofu; Dyson, Paul J. (2005). "The chemistry of phosphinoamides and related compounds". Coordination Chemistry Reviews. 249 (19–20): 2056–2074. doi:10.1016/j.ccr.2005.03.014.
  8. ^ Schmidt, H.; Lensink, C.; Xi, S. K.; Verkade, J. G. (1989). "New Prophosphatranes: Novel intermediates to five-coordinate phosphatranes". Zeitschrift für Anorganische und Allgemeine Chemie. 578: 75–80. doi:10.1002/zaac.19895780109.
  9. ^ Burg, Anton B.; Slota, Peter J. (1958). "Dimethylaminodimethylphosphine". Journal of the American Chemical Society. 80 (5): 1107–1109. doi:10.1021/ja01538a023.
  10. ^ Reetz, Manfred T.; Moulin, Dominique; Gosberg, Andreas (2001). "BINOL-Based Diphosphonites as Ligands in the Asymmetric Rh-Catalyzed Conjugate Addition of Arylboronic Acids". Organic Letters. 3 (25): 4083–4085. doi:10.1021/ol010219y. PMID 11735590.
  11. ^ Cowley, A. H.; Kemp, R. A. (1985-10-01). "Synthesis and reaction chemistry of stable two-coordinate phosphorus cations (phosphenium ions)". Chemical Reviews. 85 (5): 367–382. doi:10.1021/cr00069a002. ISSN 0009-2665.
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