Dichlorobis(triphenylphosphine)nickel(II) refers to a pair of
metal phosphine complexes with the formula NiCl
2 6H5)3">(C6H5)3sub>2. The compound exists as two isomers, a paramagnetic dark blue solid and a diamagnetic red solid. These complexes function as
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 for
organic synthesis.
[Montgomery, J. Science of Synthesis Georg Thiene Verlag KG, Vol. 1, p 11, CODEN: SSCYJ9]
Synthesis and structure
The blue isomer is prepared by treating hydrated nickel chloride with
triphenylphosphine
Triphenylphosphine (IUPAC name: triphenylphosphane) is a common organophosphorus compound with the formula P(C6H5)3 and often abbreviated to P Ph3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists ...
in alcohols or glacial acetic acid:
:NiCl
2•6H
2O + 2 PPh
3 → NiCl
2(PPh
3)
2 + 6 H
2O
When allowed to crystallise from chlorinated solvents, the tetrahedral isomer converts to the square planar isomer.
The square planar form is red and diamagnetic. The phosphine ligands are
trans
Trans- is a Latin prefix meaning "across", "beyond", or "on the other side of".
Used alone, trans may refer to:
Arts, entertainment, and media
* Trans (festival), a former festival in Belfast, Northern Ireland, United Kingdom
* ''Trans'' (fil ...
with respective Ni-P and Ni-Cl distances of 2.24 and 2.17 Å. The blue form is paramagnetic and features tetrahedral Ni(II) centers. In this isomer, the Ni-P and Ni-Cl distances are elongated at 2.32 and 2.21 Å.
As illustrated by the title complexes, tetrahedral and square planar isomers coexist in solutions of various four-coordinated nickel(II) complexes. Weak field ligands, as judged by the
spectrochemical series
A spectrochemical series is a list of ligands ordered by ligand "strength", and a list of metal ions based on oxidation number, group and element. For a metal ion, the ligands modify the difference in energy Δ between the d orbitals, called the l ...
, favor tetrahedral geometry and strong field ligands favor the square planar isomer. Both weak field (Cl
−) and strong field (PPh
3) ligands comprise NiCl
2(PPh
3)
2, hence this compound is borderline between the two geometries.
Steric effect
Steric effects arise from the spatial arrangement of atoms. When atoms come close together there is a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape ( conformation) and reactivity of ions ...
s also affect the equilibrium; larger ligands favoring the less crowded tetrahedral geometry.
Applications
The complex was first described by
Walter Reppe
Walter Julius Reppe (29 July 1892 in Göringen – 26 July 1969 in Heidelberg) was a German chemist. He is notable for his contributions to the chemistry of acetylene.
Education and career
Walter Reppe began his study of the natural sciences ...
who popularized its use in
alkyne trimerisation
In organic chemistry, an alkyne trimerisation is a +2+2nbsp; cycloaddition reaction in which three alkyne units () react to form a benzene ring. The reaction requires a metal catalyst. The process is of historic interest as well as being applic ...
s and
carbonylation
Carbonylation refers to reactions that introduce carbon monoxide into organic and inorganic substrates. Carbon monoxide is abundantly available and conveniently reactive, so it is widely used as a reactant in industrial chemistry. The term carbony ...
s. Dichlorobis(triphenylphosphine)nickel(II) is a catalyst in
Suzuki reaction
The Suzuki reaction is an organic reaction, classified as a cross-coupling reaction, where the coupling partners are a boronic acid and an organohalide and the catalyst is a palladium, palladium(0) complex. It was first published in 1979 by Akira ...
s, although usually inferior in terms of activity.
See also
*
Bis(triphenylphosphine)palladium(II) chloride
*
Bis(triphenylphosphine)platinum(II) chloride
References
{{reflist
Nickel complexes
Triphenylphosphine complexes
Chloro complexes