Tris(trimethylsilyl)amine

Early attempts to prepare tris(trimethylsilyl)amine from ammonia and trimethylchlorosilane (TMS-Cl) were unsuccessful even at temperatures of 500 °C and in the presence of the base pyridine.{{citation|surname1=R.O. Sauer|periodical=J. Am. Chem. Soc.|title=Derivatives of the methylchlorosilanes. I. Trimethylsilanol and its simple ethers|volume=66|issue=10|pages=1707–1710|date= 1944|doi=10.1021/ja01238a030}}{{citation|surname1=R.O. Sauer, R.H. Hasek|periodical=J. Am. Chem. Soc.|title=Derivatives of the methylchlorosilanes. IV. Amines|volume=68|issue=2|pages=241–244|date= 1946|doi=10.1021/ja01206a028}} The reaction of ammonia and trimethylchlorosilane stops at the stage of the doubly silylated product bis(trimethylsilyl)amine (usually referred to as hexamethyldisilazane, HMDS).

File:HMDS-Synthese.svg

Tris(trimethylsilyl)amine is obtained by reaction of the sodium salt of hexamethyldisilazane - from hexamethyldisilazane and sodium amide or from hexamethyldisilazane, sodium and styrene - with trimethylchlorosilane in 80% yield.{{citation|surname1=U. Wannagat, H. Niederprüm|periodical=Chem. Ber.|title=Beiträge zur Chemie der Silicium-Stickstoff-Verbindungen, XIII. Silylsubstituierte Alkaliamide|volume=94|issue=6|pages=1540–1547|date= 1961|language=German|doi=10.1002/cber.19610940618}}

:$\backslash begin\{matrix\}\{\}\backslash \backslash$

\ce{[(CH3)3Si]2NH ->[+\ce{NaNH2}][-\ce{NH3}] NaN[Si(CH3)3]2 ->[+\ce{ClSi(CH3)3}][-\ce{NaCl}] N[Si(CH3)3]3}\\

{}\end{matrix}

The lithium salt of hexamethyldisilazane - from hexamethyldisilazane and butyllithium{{citation|surname1=E.H. Amonoo-Neizer, R.A. Shaw, D.O. Skovlin, B.C. Smith, J.W. Rosenthal, W.L. Jolly|editor-surname1=H.F. Holtzlow|title=Lithium Bis(trimethylsilyl)amide and Tris(trimethylsilyl)amine, in Inorganic Syntheses|volume=8|publisher=John Wiley & Sons, Inc.|publication-place=Hoboken, NJ, USA|pages=19–22|isbn=9780470131671|date= 1966|doi=10.1002/9780470132395.ch5}} or from hexamethyldisilazane and phenyllithium - reacts with trimethylchlorosilane only in yields of 50-60% to tris(trimethylsilyl)amine.

The reaction of lithium nitride with trimethylchlorosilane can be carried out as a one-pot reaction in THF with 72% yield.{{citation|surname1=W.L. Lehn|periodical=J. Am. Chem. Soc.|title=Preparation of tris(trimethylsilyl)- and tris(trimethylstannyl)amines|volume=86|issue=2|pages=305|date= 1964|doi=10.1021/ja01056a057}}

:Li3N + 3Me3SiCl -> N(Me3Si)3 + 3LiCl

Tris(trimethylsilyl)amine is a colorless, crystalline{{Sigma-Aldrich|Aldrich|360120|Name= Tris(trimethylsilyl)amine 98% |Datum=28. Dezember 2016}}{{Alfa|L04361|Name=Nonamethyltrisilazane| Datum=28. Dezember 2016}} or waxy{{citation|surname1=C.R. Krüger, H. Niederprüm, M. Schmidt, O. Scherer|editor-surname1=H.F. Holtzlow|title=Sodium Bis(trimethylsilyl)amide and Tris(trimethylsilyl)amine, in Inorganic Syntheses|volume=8|publisher=John Wiley & Sons, Inc.|publication-place=Hoboken, NJ, USA|pages=15–19|isbn=9780470131671|date= 1966|doi=10.1002/9780470132395.ch5}} solid which is stable to water and bases.{{citation|surname1=U. Wannagat, H. Niederprüm|periodical=ZAAC|title=dreifach silylierte Amine|volume=308|issue=1–6|pages=337–351|date= 1961|language=German|doi=10.1002/zaac.19613080135}} Alcohols or acids though cleave the Si-N-bond under formation of ammonia.

From antimony trichloride and tris(trimethylsilyl)amine, a nitridoantimone cubane-type cluster can be formed almost quantitatively at –60 °C.{{citation|surname1=M. Rhiel, F. Weller, J. Pebler, K. Dehnicke|periodical=Angew. Chem.|title=[SbN(SbCl)₃(NSbCl₂)(NSiMe₃)₃·SbCl₃], ein ungewöhnlicher Nitridoantimonkomplex mit Heterocubanstruktur|volume=106|issue=5|pages=599–600|date= 1994|language=German|doi=10.1002/ange.19941060519|bibcode=1994AngCh.106..599R }}

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).{{citation|surname1=S. Okusu, K. Hirano, E. Tokunaga, N. Shibata|periodical=ChemistryOpen|title=Organocatalyzed trifluormethylation of ketones and sulfonyl fluorides by fluoroform under a superbase system|volume=4|pages=581–585|date= 2015|issue=5 |doi=10.1002/open.201500160|pmc=4608523|pmid=26491635}}

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

File:Synthese von Trichlor(trimethylsilyl)phosphoranimin.svg

which can be polymerized to linear polydichlorophosphazenes with defined molecular weights and polydispersities.{{Cite patent|country =US |number =5698664 |title=Synthesis of polyphosphazenes with controlled molecular weight and polydispersity |pubdate =1997-12-16 |fdate =1995-4-26 |inventor =H.R. Allcock, C.T. Morrissey, I. Manners, C.H. Honeyman | assign= The Penn State Research Foundation, University of Toronto}}

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.

File:Synthese von Hexachlorcyclotriphosphan.svg

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.{{Cite patent|country =US |number =8163262 |title=Method for production of nitrogen fluoride from trimethylsilylamines |pubdate =2012-4-24 |fdate =2011-1-4 |inventor =B. A. Omotowa}}

File:Bildung von Stickstofftrifluorid.svg

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.

:$\backslash ce\{\; \{N2\}\; +\; \{6e^-\}\; ->[\backslash ce\{Catalyst:\}\backslash \; \backslash ce\{Mo\},\backslash \; \backslash ce\{Fe\},\backslash \; \backslash ce\{Co\}]\}$

\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.{{citation|surname1=H. Deslandres|periodical=Comptes rendus|title=Absorption de l'azote par le lithium à froid|volume=121|pages=886–887|date= 1895|url=http://gallica.bnf.fr/ark:/12148/bpt6k3077p/f887.item.r=Deslandres.zoom}} 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.

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

More recently, for the reductive silylation of N₂, sodium has been used instead of lithium as the electron donor and molybdenum{{citation|surname1=Q. Liao, N. Saffon-Merceron, N. Mézailles|periodical=ACS Catal.|title=N₂ reduction into silylamine at tridentate phosphine/Mo center: catalysis and mechanistic study|volume=5|issue=11|pages=6902–6906|date= 2015|doi=10.1021/acscatal.5b01626}} and iron compounds (such as pentacarbonyl iron or ferrocenes{{citation|surname1=M. Yuki, H. Tanaka, K. Sasaki, Y. Miyake, K. Yoshizawa, Y. Nishibayashi|periodical=Nature Communications|title=Iron-catalyzed transformation of molecular dinitrogen into silylamine under ambient conditions|volume=3|pages=1254|date= 2012|doi=10.1038/ncomms2264|pmid=23212383 |bibcode=2012NatCo...3.1254Y |doi-access=free}}) as catalysts, up to 34 equivalents of N(Me₃Si)₃ could be obtained per iron atom in the catalyst.

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

With a molybdenum-ferrocene complex as catalyst, a turnover number of up to 226 could be achieved.{{citation|surname1=H. Tanaka|display-authors=etal|periodical=J. Am. Chem. Soc.|title=Molybdenum-Catalyzed Transformation of Molecular Dinitrogen into Silylamine: Experimental and DFT Study on the Remarkable Role of Ferrocenyldiphosphine Ligands|volume=133|issue=10|pages=3498–3506|date= 2011|doi=10.1021/ja109181n|pmid=21341772 }}

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

{\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,{{citation|surname1=Y. Nishibayashi|periodical=Inorg. Chem.|title=Recent progress in transition-metal-catalyzed reduction of molecular dinitrogen under ambient reaction conditions|volume=54|issue=19|pages=9234–9247|date= 2015|doi=10.1021/acs.inorgchem.5b00881|pmid=26131967 }} still by magnitude smaller than, for example, the modern polymerization catalysts of the metallocene type or enzymes.

{{Reflist}}

Category:Nitrogen(−III) compounds

Category:Trimethylsilyl compounds