Tris(trimethylsilyl)amine as a synthetic building block

From antimony trichloride and tris(trimethylsilyl)amine, a nitridoantimone cubane-type cluster can be formed almost quantitatively at –60 °C.^[14]

Ketones can be trifluoromethylated in the presence of P₄-t-Bu and nonamethyltrisilazane under mild conditions in yields of up to 84% with the inert fluoroform (HCF₃, HFC-23).^[15]

The monomer trichloro(trimethylsilyl)-phosphoranimine Cl₃P=NSiMe₃ is formed from tris(trimethylsilyl)amine and phosphorus pentachloride in hexane at 0 °C,

Synthese von Trichlor(trimethylsilyl)phosphoranimin

which can be polymerized to linear polydichlorophosphazenes with defined molecular weights and polydispersities.^[16]

The cyclic trimer (NPCl₂)₃ hexachlorocyclotriphosphane is predominantly formed from tris(trimethylsilyl)amine and phosphorus pentachloride in boiling dichloromethane (about 40 °C) among other oligomers which gives upon heating over 250 °C high molecular weight, little defined polydichlorophosphazenes.

Synthese von Hexachlorcyclotriphosphan

Nitrogen trifluoride NF₃ (which is used, inter alia, for the plasma etching of silicon wafers) is obtainable from tris(trimethylsilyl)amine and fluorine at –40 °C in acetonitrile, suppressing the formation of nitrogen and tetrafluorohydrazine, which are produced as undesirable by-products during the standard synthesis of nitrogen trifluoride from ammonia or ammonium fluoride.^[17]

Synthese von NF₃

Tris(trimethylsilyl)amine intermediate in chemical nitrogen fixation

The technical nitrogen fixation was made possible by the Haber-Bosch process, in which nitrogen is converted into ammonia by reductive protonation in the presence of iron catalysts under high pressures (> 150 bar) and temperatures (> 400 °C). In chemical nitrogen fixation (i.e., the transformation of atmospheric nitrogen under normal conditions into reactive starting materials for chemical syntheses, usually also ammonia), tris(trimethylsilyl)amine plays an important role in the so-called reductive silylation, since it is hydrolyzed with water to ammonia.

${\displaystyle {\ce {{N2}+{6e^{-}}->[{\ce {Catalyst:}}\ {\ce {Mo}},\ {\ce {Fe}},\ {\ce {Co}}]}}{\begin{cases}{\ce {->[{\ce {H+}}]}}&{\ce {2NH3}}\\{}\\{\ce {->[{\ce {R3Si-X}}][-\,{\ce {X-}}]}}&{\ce {2N(SiR3)3}}\end{cases}}}$

As early as 1895 it was observed that metallic lithium reacts with nitrogen to lithium nitride at room temperature.^[18] In 1972, K. Shiina observed that lithium (as an electron donor) forms with trimethylsilyl chloride under darkening tris(trimethylsilyl)amine in the presence of chromium(III) chloride as a catalyst at room temperature with the nitrogen used for inerting.^[2]

${\displaystyle {\ce {N2 + 6Me3SiCl + 6}}\,{\color {NavyBlue}{\ce {Li}}}\ {\ce {->[{\ce {CrCl3}}] 2N(SiMe3)3 + 6}}\,{\color {NavyBlue}{\ce {Li}}}{\ce {Cl}}}$

More recently, for the reductive silylation of N₂, sodium has been used instead of lithium as the electron donor and molybdenum^[19] and iron compounds^[3] (such as pentacarbonyl iron or ferrocenes^[20]) as catalysts, up to 34 equivalents of N(Me₃Si)₃ could be obtained per iron atom in the catalyst.

${\displaystyle {\ce {N2 + 6Me3SiCl + 6}}\,{\color {Red}{\ce {Na}}}\ {\ce {->[{\ce {Fe-catalyst}}] 2N(SiMe3)3 + 6}}\,{\color {Red}{\ce {Na}}}{\ce {Cl}}}$

With a molybdenum-ferrocene complex as catalyst, a turnover number of up to 226 could be achieved.^[21]

${\displaystyle {\color {Red}{\ce {N2}}}+{\color {NavyBlue}{\ce {Me3Si}}}{\ce {{Cl}+Na->[{\ce {Mo/Fe-catalyst}}.][{\ce {RT}} \atop (1\ {\ce {atm}})]}}\ {\color {Red}{\ce {N}}}{\color {NavyBlue}{\ce {(Me3Si)3}}}}$

The catalytic productivity of the catalysts for chemical nitrogen fixation developed so far is, despite intensive research,^[22] still by magnitude smaller than, for example, the modern polymerization catalysts of the metallocene type or enzymes.