P4-t-Bu
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3D model (JSmol) |
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| ChemSpider | |
| ECHA InfoCard | 100.157.699 |
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PubChem CID |
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CompTox Dashboard (EPA) |
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| Properties | |
| (CH3)3C−N=P(−N=P(−N(CH3)2)3)3 | |
| Molar mass | 633.732 g·mol−1 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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P4-t-Bu is a readily accessible chemical from the group of neutral, peralkylated sterically hindered polyaminophosphazenes, which are extremely strong bases but very weak nucleophiles, with the formula (CH3)3C−N=P(−N=P(−N(CH3)2)3)3. "t-Bu" stands for tert-butyl (CH3)3C–. "P4" stands for the fact that this molecule has 4 phosphorus atoms. P4-t-Bu can also be regarded as tetrameric triaminoiminophosphorane of the basic structure H−N=P(−NH2)3. The homologous series of P1 to P7 polyaminophosphazenes[1][2] of the general formula with preferably methyl groups as R1, a methyl group or tert-butyl group as and even-numbered x between 0 and 6 (P4-t-Bu: R1 = Me, R2 = t-Bu and x = 3)[3] has been developed by Reinhard Schwesinger; the resulting phosphazene bases are therefore also referred to as Schwesinger superbases.[4][5]
![{\displaystyle {\ce {[(R_{2}^{1}N)_{3}P=N-]_{\mathit {x}}-(R_{2}^{1}N)_{3\!-{\mathit {x}}}P=NR2}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/dd5464ed17d043fbe22eb8eb03446d3211ce9119)
The convergent synthesis of P4-t-Bu[6] is derived from phosphorus pentachloride (1) and leads in branch [A] to the well-characterized aminotris via the non-isolated chlorine (dimethylamino)phosphonium chloride (2)[2] via [(Dimethylamino)phosphonium tetrafluoroborate (3) and further via [A2] to the liquid iminotris (dimethylamino) phosphorane[7](4)
| [A] |
![{\displaystyle {\begin{matrix}{}\\\underbrace {\ce {PCl5}} _{(1)}\ {\ce {->[{\ce {Me2NH}}]}}\underbrace {\left[{\ce {(Me2N)3{\overset {\oplus }{P}}-Cl.{\overset {\ominus }{C}}l}}\right]} _{(2)}\ {\ce {->[1.\ {\ce {NH3}}][2.\ {\ce {NaBF4}}]}}\ \underbrace {\ce {(Me2N)3{\overset {\oplus }{P}}-NH2.{\overset {\ominus }{B}}F4}} _{(3)}\\{}\end{matrix}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/934831033e3d3a948ab3ad1435b54d3955156102)
![{\displaystyle \underbrace {\ce {(Me2N)3{\overset {\oplus }{P}}-NH2.{\overset {\ominus }{B}}F4}} _{(3)}\ {\ce {->[{\ce {KOMe}}]}}\ \underbrace {\ce {(Me2N)3P=NH}} _{(4)}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/f770d8ef6ebd14dd05f206b5a5834c39af323aaf)
and in branch [B] with phosphorus pentachloride and tert-butylammonium chloride to tert-butylphosphorimide trichloride (5)[8]
| [B] |
![{\displaystyle \underbrace {\ce {PCl5}} _{(1)}\ {\ce {->[t{\text{-}}{\ce {Bu-{\overset {\oplus }{NH3}}.{\overset {\ominus }{Cl}}}}]}}\ \underbrace {t{\text{-}}{\ce {Bu-N=PCl3}}} _{(5)}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/d9273434d7f39954c83fec9f0e179ee064ad1afe)
The reaction [C] of excess (4) with (5) yields the hydrochloride of the target product P4-t-Bu (6) in 93% yield
| [C] |
![{\displaystyle \scriptstyle {\begin{matrix}{}\\\underbrace {\ce {7(Me2N)3P=NH}} _{(4)}\ +\ \underbrace {t{\text{-}}{\ce {Bu-N=PCl3}}} _{(5)}\ {\ce {->}}\ \underbrace {{\ce {[(Me2N)3P=N]3P=N{\overset {\oplus }{H}}-}}t{\text{-}}{\ce {Bu.{\overset {\ominus }{Cl}}}}} _{(6)}\ {\ce {->[{\ce {NaBF4}}]}}\ \underbrace {{\ce {[(Me2N)3P=N]3P=N{\overset {\oplus }{H}}-}}t{\text{-}}{\ce {Bu.{\overset {\ominus }{B}}F4}}} _{(7)}\ {\ce {->[{\ce {KOMe/NaNH2}}]}}\ \underbrace {{\ce {[(Me2N)3P=N]3P=N{\overset {\oplus }{H}}-}}t{\text{-}}{\ce {Bu}}} _{(8)}\\{}\end{matrix}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/480a005659a30c7e3dd9eea70be5e9723311a768)
which is also converted into the tetrafluoroborate salt (7) from which the free base (8) can be obtained almost quantitatively with potassium methoxide/sodium amide[2] or with potassium amide in liquid ammonia.[9] The transfer of the hygroscopic and readily water-soluble hydrochlorides and the liquid free bases into the tetrafluoroborates, which are difficult to solubilize in water, facilitate the handling of the substances considerably.
 | [D] |
The relatively uncomplicated convergent synthesis with easily accessible reactants and very good yields of the intermediates make P4-t-Bu an interesting phosphazene superbase.[10]
