Organorhenium chemistry describes the compounds with Re−C bonds. Because
rhenium
Rhenium is a chemical element with the symbol Re and atomic number 75. It is a silvery-gray, heavy, third-row transition metal in group 7 of the periodic table. With an estimated average concentration of 1 part per billion (ppb), rhenium is one ...
is a rare element, relatively few applications exist, but the area has been a rich source of concepts and a few useful
catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
s.
General features
Rhenium exists in ten known oxidation states from −3 to +7 except −2, and all but Re(−3) are represented by organorhenium compounds. Most are prepared from salts of
perrhenate and related binary oxides.
[O. Glemser "Ammonium Perrhenate" in Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1476-85.] The halides, e.g.,
ReCl5 are also useful precursors as are certain oxychlorides.
A noteworthy feature of organorhenium chemistry is the coexistence of oxide and organic ligands in the same
coordination sphere
In coordination chemistry, the first coordination sphere refers to the array of molecules and ions (the ligands) directly attached to the central metal atom. The second coordination sphere consists of molecules and ions that attached in various ...
.
Carbonyl compounds
Dirhenium decacarbonyl is a common entry point to other rhenium carbonyls. The general patterns are similar to the related
manganese carbonyls. It is possible to reduce this dimer with sodium
amalgam
Amalgam most commonly refers to:
* Amalgam (chemistry), mercury alloy
* Amalgam (dentistry), material of silver tooth fillings
** Bonded amalgam, used in dentistry
Amalgam may also refer to:
* Amalgam Comics, a publisher
* Amalgam Digital
...
to Na
5">e(CO)5with rhenium in the formal oxidation state −1. Bromination of dirhenium decacarbonyl gives
bromopentacarbonylrhenium(I), then reduced with
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
and
acetic acid to
pentacarbonylhydridorhenium:
:Re
2(CO)
10 + Br
2 → 2 Re(CO)
5Br
:Re(CO)
5Br + Zn + HOAc → Re(CO)
5H + ZnBr(OAc)
Bromopentacarbonylrhenium(I) is readily decarbonylated. In refluxing water, it forms the triaquo cation:
:Re(CO)
5Br + 3 H
2O →
3(H2O)3">e(CO)3(H2O)3r + 2 CO
With
tetraethylammonium bromide
Tetraethylammonium bromide (TEAB) is a quaternary ammonium compound with the chemical formula C8H20N+Br−, often written as "Et4N+Br−" in the chemical literature. It has been used as the source of tetraethylammonium ions in pharmacological and ...
Re(CO)
5Br reacts to give the anionic tribromide:
:Re(CO)
5Br + 2 NEt
4Br →
4">Et4sub>2
3Br3">e(CO)3Br3+ 2 CO
Cyclopentadienyl complexes
One of the first
transition metal hydride
Transition metal hydrides are chemical compounds containing a transition metal bonded to hydrogen. Most transition metals form hydride complexes and some are significant in various catalytic and synthetic reactions. The term "hydride" is used loo ...
complexes to be reported was (C
5H
5)
2ReH. A variety of
half-sandwich compound
Half sandwich compounds, also known as piano stool complexes, are organometallic complexes that feature a cyclic polyhapto ligand bound to an MLn center, where L is a unidentate ligand. Thousands of such complexes are known. Well-known examples in ...
s have been prepared from (C
5H
5)Re(CO)
3 and (C
5Me
5)Re(CO)
3. Notable derivatives include the electron-precise oxide (C
5Me
5)ReO
3 and (C
5H
5)
2Re
2(CO)
4.
Re-alkyl and aryl compounds
Rhenium forms a variety of alkyl and aryl derivatives, often with pi-donor coligands such as oxo groups. Well known is
methylrhenium trioxide
Methylrhenium trioxide, also known as methyltrioxorhenium(VII), is an organometallic compound with the formula CH3ReO3. It is a volatile, colourless solid that has been used as a catalyst in some laboratory experiments. In this compound, rhenium h ...
("MTO"), CH
3ReO
3 a volatile, colourless solid, a rare example of a stable high-oxidation state metal alkyl complex. This compound has been used as a
catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
in some laboratory experiments. It can be prepared by many routes, a typical method is the reaction of Re
2O
7 and
tetramethyltin:
:Re
2O
7 + (CH
3)
4Sn → CH
3ReO
3 + (CH
3)
3SnOReO
3
Analogous alkyl and aryl derivatives are known. Although PhReO
3 is unstable and decomposes at –30 °C, the corresponding sterically hindered mesityl and 2,6-xylyl derivatives (MesReO
3 and 2,6-(CH
3)
2C
6H
3ReO
3) are stable at room temperature. The electron poor 4-trifluoromethylphenylrhenium trioxide (4-CF
3C
6H
4ReO
3) is likewise relatively stable. MTO and other organylrhenium trioxides catalyze oxidation reactions with
hydrogen peroxide
Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%â ...
as well as olefin metathesis in the presence of a Lewis acid activator. Terminal
alkynes yield the corresponding acid or ester, internal alkynes yield diketones, and
alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
s give epoxides. MTO also catalyses the conversion of
aldehyde
In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl grou ...
s and
diazoalkanes into an alkene.
[Hudson, A. "Methyltrioxorhenium" Encyclopedia of Reagents for Organic Synthesis. John Wiley & Sons: New York, 2002.]
Rhenium is also able to make complexes with
fullerene ligands such as Re
2(PMe
3)
4H
8(η
2:η
2C
60).
Further reading
* ''Synthesis of Organometallic Compounds: A Practical Guide'' Sanshiro Komiya Ed. S. Komiya, M. Hurano 1997.
* Pericles Stavropoulos, Peter G. Edwards, Geoffrey Wilkinson, Majid Motevalli, K. M. Abdul Malik and Michael B. Hursthouse "Oxoalkyls of rhenium-(V) and-(VI). X-Ray crystal structures of (Me
4ReO)
2Mg(thf)
4,
3SiCH2)4ReO">Me3SiCH2)4ReOsub>2Mg(thf)
2, Re
2O
3Me
6 and Re
2O
3(CH
2SiMe
3)
6" J. Chem. Soc., Dalton Trans., 1985, pp. 2167-2175.
References
{{ChemicalBondsToCarbon
Rhenium compounds
Organometallic compounds