Chiraphos is a
chiral
Chirality is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand", a familiar chiral object.
An object or a system is ''chiral'' if it is distinguishable from ...
diphosphine
Diphosphane, or diphosphine, is an inorganic compound with the chemical formula P2H4. This colourless liquid is one of several binary phosphorus hydrides. It is the impurity that typically causes samples of phosphine to ignite in air.
Propert ...
employed as a
ligand
In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...
in
organometallic chemistry
Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and so ...
. This bidentate ligand chelates metals via the two phosphine groups. Its name is derived from its description — being both ''chiral'' and a ''phosphine''. As a
C2-symmetric ligand, chiraphos is available in two enantiomeric forms, ''S'',''S'' and ''R'',''R'', each with C
2 symmetry.
Preparation
Chiraphos is prepared from ''S'',''S'' or ''R'',''R''-
2,3-butanediol
2,3-Butanediol is the organic compound with the formula (CH3CHOH)2. It is classified as a ''vic''-diol (glycol). It exists as three stereoisomers, a chiral pair and the meso isomer. All are colorless liquids. Applications include precursors to ...
, which are derived from commercially available ''S'',''S'' or ''R'',''R''-
tartaric acid
Tartaric acid is a white, crystalline organic acid that occurs naturally in many fruits, most notably in grapes, but also in bananas, tamarinds, and citrus. Its salt, potassium bitartrate, commonly known as cream of tartar, develops naturally i ...
; the technique of using cheaply available enantiopure starting materials is known as
chiral pool synthesis The chiral pool is a "collection of abundant enantiopure building blocks provided by nature" used in synthesis. In other words, a chiral pool would be a large quantity of common organic enantiomers. Contributors to the chiral pool are amino acids, s ...
. The diol is
tosylated and then the ditosylate is treated with
lithium diphenylphosphide
Lithium diphenylphosphide contains lithium and the organophosphorus anion with the formula (C6H5)2PLi. It is an air-sensitive solid that is used in the preparation of diphenylphosphino compounds. As an ether complex, the lithium salt is dark red ...
.
[{{cite journal, last1=Fryzuk, first1=M. D., last2=Bosnich, first2=B., authorlink2=Brice Bosnich, title=Asymmetric synthesis. Production of optically active amino acids by catalytic hydrogenation, journal=Journal of the American Chemical Society, volume=99, issue=19, year=1977, pages=6262–6267, pmid=893889, doi=10.1021/ja00461a014] The ligand was an important demonstration of how the conformation of the chelate ring can affect asymmetric induction by a metal catalyst. Prior to this work, in most chiral phosphines, e.g.,
DIPAMP
DIPAMP is an organophosphorus compound that is used as a ligand in homogeneous catalysis. It is a white solid that dissolves in organic solvents. Work on this compound by W. S. Knowles was recognized with the Nobel Prize in Chemistry. DIPAMP w ...
, phosphorus was the stereogenic center.
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References
Diphosphines
Phenyl compounds