Trisoxazolinylborate
   HOME

TheInfoList



OR:

Tris(oxazolinyl)borate compounds are a class of tridentate
ligand In coordination chemistry, a ligand is an ion or molecule with a 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 el ...
s; often abbreviated ToR, where R is the
substituent In organic chemistry, a substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule. The suffix ''-yl'' is used when naming organic compounds that contain a single bond r ...
on the
oxazoline Oxazoline is a five-membered heterocyclic organic compound with the formula . It is the parent of a family of compounds called oxazolines (emphasis on plural), which contain non-hydrogenic substituents on carbon and/or nitrogen. Oxazolines are the ...
ring. Most commonly the substituent is either a
methyl In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula (whereas normal methane has the formula ). In formulas, the group is often abbreviated as ...
,
propyl In organic chemistry, a propyl group is a three-carbon alkyl substituent with chemical formula for the linear form. This substituent form is obtained by removing one hydrogen atom attached to the terminal carbon of propane. A propyl substituent ...
,
tert-butyl In organic chemistry, butyl is a four-carbon alkyl radical or substituent group with general chemical formula , derived from either of the two isomers (''n''-butane and isobutane) of butane. The isomer ''n''-butane can connect in two ways, giv ...
or
hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
. The formation of anionic boron backbone with addition of a
phenyl In organic chemistry, the phenyl group, or phenyl ring, is a cyclic group of atoms with the formula , and is often represented by the symbol Ph (archaically φ) or Ø. The phenyl group is closely related to benzene and can be viewed as a benzene ...
group on boron allows the ligand to strongly bind to the metal center. It results in a more robust complex. Tris(oxazolinyl)borates can be characterised as
scorpionate ligand In coordination chemistry, a scorpionate ligand is a tridentate (three-donor-site) ligand that binds to a central atom in a ''fac'' manner. The most popular class of scorpionates are the hydrotris(pyrazolyl)borates or Tp ligands. These were al ...
s and may be compared to tris(pyrazolyl)borate and trisoxazoline ligands. In bulky pyrazolylborate (Tp) derivatives, isomerization may occur via 1,2-shifts; additionally B–N bond cleavage is a common decomposition pathways for the Tp ligands. The oxazoline-based ligands with B-C linkages avoid these decomposition problems.


Synthesis

The first example of a trisoxazolinylborate ligand was tris(4,4-dimethyl-2-oxazolinyl)phenyl borate (ToM). This was prepared by a reaction of dichlorophenylborane with 3 equivalents of 2-lithio-4,4-dimethyl-2-oxazolide. Later variants, such as tris(4''S''-isopropyl-2-oxazolinyl)phenylborate (ToP) have been prepared in an analogous manner. : PhBCl2 + 3 Li(Oxaz-Me2) → PhB(Oxaz-Me2)3 + 3 LiCl


Complexes of ToR

The first
coordination complex A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ' ...
es made using ToM ligands were based around zirconium (IV), as the sterically bulky ligands were able to stabilise the highly reactive metal centers. ToMZr(IV) complexes were prepared by
salt metathesis A salt metathesis reaction (also called a double displacement reaction, double replacement reaction, or double decomposition) is a type of chemical reaction in which two ionic compounds in aqueous solution exchange their component ions to form two ...
using LiToM and TlToM and ZrCl4. The formed complex ToMZrCl3 was found to be quite robust and showed C3V symmetry in both solution and solid state. Lithium tris(4,4-dimethyl-2-oxazolin-2-yl) phenyl borate (LiToM) is used as a transfer agent. However TlToM frequently is as a more effective transfer agent than LiToM because of the higher solubility of the Tl salt and the insolubility of
thallium chloride Thallium(I) chloride, also known as thallous chloride, is a chemical compound with the formula TlCl. This colourless salt is an intermediate in the isolation of thallium from its ores. Typically, an acidic solution of thallium(I) sulfate is treate ...
by-products. In contrast, lithium halide byproducts from preparations employing LiToM can cause purification problems. Another example for the coordinating chemistry of ToM is the formation of ToMMgMe by the reaction of equimolar amounts of HToM and MgMe2(O2C4H8)2. In addition, the reaction of two equivalents of HToM with MgMe2(O2C4H8)2 gives the homoleptic ToM2Mg compound. This compound can also be obtained by the reaction between one equivalent of HToM and ToMMgMe revealing that Mg in ToMMgMe is an active center for the chemical reactions. According to 1H NMR spectroscopic data, ToM2Mg shows Cs symmetry. In these reactions HToM is used as the transfer agent. Coordination chemistry of iridium(I) centers with ToP has been shown by the preparation of r(ToP)(COD)(COD =1,5-C8H12) by the reaction of LiToP and 0.5 equivalent of r(μ-Cl)(COD)sub>2.


Catalysis

ToMMgMe is an effective precatalyst for the cross-dehydrocoupling of Si-H bonds in organosilanes and N-H bonds in amines to give Si-N bonds and H2. Furthermore, tris(oxazolinyl)borate yttrium alkyl and amide compounds (ToMYR2) can be used as precatalysts for the cyclization of aminoalkenes.


See also

* Trisoxazolines *
Trispyrazolylborate The trispyrazolylborate ligand, abbreviated Tp−, is an anionic Denticity, tridentate and tripodal ligand. Trispyrazolylborate refers specifically to the anion
B(C3N2H3)3 B, or b, is the second letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''bee'' (pronounced ), plural ''bees''. It represent ...
ˆ’. However, the term can also be used to refer to derivatives having s ...


References

{{reflist Oxazolines Ligands