In
chemistry, salt-free reduction describes methodology for reduction of
metal halide
Metal halides are compounds between metals and halogens. Some, such as sodium chloride are ionic, while others are covalently bonded. A few metal halides are discrete molecules, such as uranium hexafluoride, but most adopt polymeric structures, s ...
s by
electron-rich
In chemistry, electron-rich is jargon that is used in multiple related meanings with either or both kinetic and thermodynamic implications:
*with regards to electron-transfer, electron-rich species have low ionization energy and/or are reducing ...
trimethylsilyl reagents. Traditional reductions of metal halides are accomplished with alkali metals, a process that cogenerates alkali metal salts. Using the salt-free reduction, the reduction of metal halides is accompanied by formation of neutral organic compounds that can be easily removed from the inorganic or organometallic product. In addition to the reduction of metal halides, the reagents associated with this methodology are applicable to
deoxygenation
Deoxygenation is a chemical reaction involving the removal of oxygen atoms from a molecule. The term also refers to the removal of molecular oxygen (O2) from gases and solvents, a step in air-free technique and gas purifiers. As applied to org ...
of organic substrates.
A typical reducing agent is N,N'-bis(trimethylsilyl)-4,4'-bipyridinylidene. Related
pyrazine
Pyrazine is a heterocyclic aromatic organic compound with the chemical formula C4H4N2. It is a symmetrical molecule with point group D2h. Pyrazine is less basic than pyridine, pyridazine and pyrimidine. It is a ''"deliquescent crystal or wax-l ...
- and
cyclohexadiene-based reagents have been developed. They are red or orange THF-soluble solids. The bipyridine reagent is produced by reduction of
4,4'-bipyridine in the presence of
trimethylsilyl chloride
Trimethylsilyl chloride, also known as chlorotrimethylsilane is an organosilicon compound (silyl halide), with the formula (CH3)3SiCl, often abbreviated Me3SiCl or TMSCl. It is a colourless volatile liquid that is stable in the absence of water. I ...
(Me = CH
3):
:
A typical reduction reaction is the conversion of
tungsten hexachloride
Tungsten hexachloride is the chemical compound of tungsten and chlorine with the formula WCl6. This dark violet blue species exists as a volatile solid under standard conditions. It is an important starting reagent in the preparation of tungst ...
to the tetrachloride using the silylated pyrazine reagent:
::{{chem2, Me3SiNC4Me4NSiMe3 + WCl6 + 2 thf -> NC4Me4N + 2 Me3SiCl + WCl4(thf)2
References
Chemical reactions
Redox