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Trisoxazolinylborate ligand Trisoxazolinylborate ligand.jpg
Trisoxazolinylborate ligand

Tris(oxazolinyl)borate compounds are a class of tridentate ligands; often abbreviated ToR, where R is the substituent on the oxazoline ring. Most commonly the substituent is either a methyl, propyl, tert-butyl or hydrogen. The formation of anionic boron backbone with addition of a phenyl group on boron allows the ligand to strongly bind to the metal center. It results in a more robust complex. [1]


Tris(oxazolinyl)borates can be characterised as scorpionate ligands 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. [1]


Tris(4,4-dimethyl-2-oxazolinyl)phenyl borate (To ) ToM ligand.jpg
Tris(4,4-dimethyl-2-oxazolinyl)phenyl borate (To )
Tris(4S-isopropyl-2-oxazolinyl)phenylborate (To ) ToP ligand.jpg
Tris(4S-isopropyl-2-oxazolinyl)phenylborate (To )

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. [2] Later variants, such as tris(4S-isopropyl-2-oxazolinyl)phenylborate (ToP) have been prepared in an analogous manner. [3]

PhBCl2 + 3 Li(Oxaz-Me2) → PhB(Oxaz-Me2)3 + 3 LiCl

Complexes of ToR

The first coordination complexes 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 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. [4]

Preparation of (To )ZrCl3 ligand Preparation of ToMZrCl3.png
Preparation of (To )ZrCl3 ligand

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 by-products. In contrast, lithium halide byproducts from preparations employing LiToM can cause purification problems. [1]

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. [2] Coordination chemistry of iridium(I) centers with ToP has been shown by the preparation of [Ir(ToP)(COD)] (COD =1,5-C8H12) by the reaction of LiToP and 0.5 equivalent of [Ir(μ-Cl)(COD)]2. [3]

Preparation of (To )2Mg ligand Preparation of ToM2Mg.png
Preparation of (To )2Mg ligand


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. [2] Furthermore, tris(oxazolinyl)borate yttrium alkyl and amide compounds (ToMYR2) can be used as precatalysts for the cyclization of aminoalkenes. [5]

See also

Related Research Articles

Scorpionate ligand

The term scorpionate ligand refers to a tridentate ligand which would bind to a metal in a fac manner. The most popular class of scorpionates are the hydrotris(pyrazolyl)borates or Tp ligands. These were also the first to become popular. These ligands first appeared in journals in 1966 from the then little-known DuPont chemist of Ukrainian descent, Swiatoslaw Trofimenko. Trofimenko called this discovery "a new and fertile field of remarkable scope".

Anions that interact weakly with cations are termed non-coordinating anions, although a more accurate term is weakly coordinating anion. Non-coordinating anions are useful in studying the reactivity of electrophilic cations. They are commonly found as counterions for cationic metal complexes with an unsaturated coordination sphere. These special anions are essential components of homogeneous alkene polymerisation catalysts, where the active catalyst is a coordinatively unsaturated, cationic transition metal complex. For example, they are employed as counterions for the 14 valence electron cations [(C5H5)2ZrR]+ (R = methyl or a growing polyethylene chain). Complexes derived from non-coordinating anions have been used to catalyze hydrogenation, hydrosilylation, oligomerization, and the living polymerization of alkenes. The popularization of non-coordinating anions has contributed to increased understanding of agostic complexes wherein hydrocarbons and hydrogen serve as ligands. Non-coordinating anions are important components of many superacids, which result from the combination of Brønsted acids and Lewis acids.

Titanocene dichloride Chemical compound

Titanocene dichloride is the organotitanium compound with the formula (η5-C5H5)2TiCl2, commonly abbreviated as Cp2TiCl2. This metallocene is a common reagent in organometallic and organic synthesis. It exists as a bright red solid that slowly hydrolyzes in air. It shows antitumour activity and was the first non-platinum complex to undergo clinical trials as a chemotherapy drug.

Tris(pentafluorophenyl)borane Chemical compound

Tris(pentafluorophenyl)borane, sometimes referred to as "BCF", is the chemical compound (C
. It is a white, volatile solid. The molecule consists of three pentafluorophenyl groups attached in a "paddle-wheel" manner to a central boron atom; the BC
core is planar. It has been described as the “ideal Lewis acid” because of its high thermal stability and the relative inertness of the B-C bonds. Related fluoro-substituted boron compounds, such as those containing B−CF
groups, decompose with formation of B-F bonds. Tris(pentafluorophenyl)borane is thermally stable at temperatures wide over 200 °C, resistant to oxygen and water-tolerant.

Organoactinide chemistry

Organoactinide chemistry is the science exploring the properties, structure and reactivity of organoactinide compounds, which are organometallic compounds containing a carbon to actinide chemical bond.

Lithium bis(trimethylsilyl)amide Chemical compound

Lithium bis(trimethylsilyl)amide is a lithiated organosilicon compound with the formula LiN(SiMe3)2. It is commonly abbreviated as LiHMDS (lithium hexamethyldisilazide - a reference to its conjugate acid HMDS) and is primarily used as a strong non-nucleophilic base and as a ligand. Like many lithium reagents, it has a tendency to aggregate and will form a cyclic trimer in the absence of coordinating species.

Sodium tetraphenylborate Chemical compound

Sodium tetraphenylborate is the organic compound with the formula NaB(C6H5)4. It is a salt, wherein the anion consists of four phenyl rings bonded to boron. This white crystalline solid is used to prepare other tetraphenylborate salts, which are often highly soluble in organic solvents. The compound is used in inorganic and organometallic chemistry as a precipitating agent for potassium, ammonium, rubidium, and cesium ions, and some organic nitrogen compounds.

Dimethylphenylphosphine Chemical compound

Dimethylphenylphosphine is an organophosphorus compound with a formula P(C6H5)(CH3)2. The phosphorus is connected to a phenyl group and two methyl groups, making it the simplest aromatic alkylphosphine. It is colorless air sensitive liquid. It is a member of series (CH3)3-n(C6H5)2P that also includes n = 0, n = 2, and n = 3 that are often employed as ligands in metal phosphine complexes.

Organobismuth chemistry

Organobismuth chemistry is the chemistry of organometallic compounds containing a carbon to bismuth chemical bond. Applications are few. The main bismuth oxidation states are Bi(III) and Bi(V) as in all higher group 15 elements. The energy of a bond to carbon in this group decreases in the order P > As > Sb > Bi. The first reported use of bismuth in organic chemistry was in oxidation of alcohols by Challenger in 1934 (using Ph3Bi(OH)2). Knowledge about methylated species of bismuth in environmental and biological media is limited.

Oxazoline Chemical compound

Oxazoline is a five-membered heterocyclic chemical compound containing one atom each of oxygen and nitrogen. It was likely first synthesized in 1884 but it was not until 5 years later that Siegmund Gabriel correctly assigned the structure. It was named in-line with the Hantzsch–Widman nomenclature and is part of a family of heterocyclic compounds, where it exists between oxazole and oxazolidine in terms of saturation.

Organogold chemistry is the study of compounds containing gold–carbon bonds. They are studied in academic research, but have not received widespread use otherwise. The dominant oxidation states for organogold compounds are I with coordination number 2 and a linear molecular geometry and III with CN = 4 and a square planar molecular geometry. The first organogold compound discovered was gold(I) carbide Au2C2, which was first prepared in 1900.

Organoplatinum chemistry is the chemistry of organometallic compounds containing a carbon to platinum chemical bond, and the study of platinum as a catalyst in organic reactions. Organoplatinum compounds exist in oxidation state 0 to IV, with oxidation state II most abundant. The general order in bond strength is Pt-C (sp) > Pt-O > Pt-N > Pt-C (sp3). Organoplatinum and organopalladium chemistry are similar, but organoplatinum compounds are more stable and therefore less useful as catalysts.

Dichlorotris(triphenylphosphine)ruthenium(II) Chemical compound

Dichlorotris(triphenylphosphine)ruthenium(II) is a coordination complex of ruthenium. It is a chocolate brown solid that is soluble in organic solvents such as benzene. The compound is used as a precursor to other complexes including those used in homogeneous catalysis.

Metal bis(trimethylsilyl)amides

Metal bis(trimethylsilyl)amides are coordination complexes composed of a cationic metal with anionic bis(trimethylsilyl)amide ligands and are part of a broader category of metal amides.

The dehydrogenative coupling of silanes is a reaction type for the formation of Si-Si bonds. Although never commercialized, the reaction has been demonstrated for the synthesis of certain disilanes as well as polysilanes. These reactions generally require catalysts.

Dehydrogenation of amine-boranes or dehydrocoupling of amine-boranes is a chemical process in main group and organometallic chemistry wherein dihydrogen is released by the coupling of two or more amine-borane adducts. This process gained some interests due to the potential of using amine-boranes for hydrogen storage.

Brookharts acid Chemical compound

Brookhart's acid is the salt of the diethyl ether oxonium ion and tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BAr′4). It is a colorless solid, used as a strong acid. The compound was first reported by Volpe, Grant, and Brookhart in 1992.


Trisoxazolines are a class of tridentate, chiral ligands composed of three oxazoline rings. Despite being neutral they are able to form stable complexes with high oxidation state metals, such as rare earths, due to the chelate effect. The ligands have been investigated for molecular recognition and their complexes are used in asymmetric catalysts and polymerisation.

Nickel(II) precatalysts are a type of catalyst used in organic reactions. Many transformations are catalyzed by nickel in organometallic chemistry and in organic synthesis. Many of these transformations invoke a low valent (generally Ni(0)) species as the active catalyst. Unfortunately, unlike its counterpart, Pd(0), Ni(0) catalysts are predominantly confined to the glovebox due to their high instability to air and water, with the most common Ni(0) catalyst being Ni(cod)2. Additionally, Ni(cod)2 is more expensive than many Ni(II) salts and the quality varies significantly amongst suppliers. To make nickel catalysis more accessible and amenable to synthesis and industrial purposes, the use of air-stable Ni(II) precursors has emerged as an important development in this area of research. This page describes the more commonly employed nickel(II) precatalysts, their synthesis for those not commercially available, and the methods for their reduction to Ni(0) complexes.

Transition metal nitrile complexes Class of coordination compounds containing nitrile ligands (coordinating via N)

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