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.
Chromium hexacarbonyl is a chromium(0) organometallic compound with the formula Cr(CO)6. It is a homoleptic complex, which means that all the ligands are identical. It is a colorless crystalline air-stable solid, with a high vapor pressure.
Metal carbonyls are coordination complexes of transition metals with carbon monoxide ligands. Metal carbonyls are useful in organic synthesis and as catalysts or catalyst precursors in homogeneous catalysis, such as hydroformylation and Reppe chemistry. In the Mond process, nickel tetracarbonyl is used to produce pure nickel. In organometallic chemistry, metal carbonyls serve as precursors for the preparation of other organometallic complexes.
Dithiolene metal complexes are complexes containing 1,2-dithiolene ligands. 1,2-Dithiolene ligands, a particular case of 1,2-dichalcogenolene species along with 1,2-diselenolene derivatives, are unsaturated bidentate ligand wherein the two donor atoms are sulfur. 1,2-Dithiolene metal complexes are often referred to as "metal dithiolenes", "metallodithiolenes" or "dithiolene complexes". Most molybdenum- and tungsten-containing proteins have dithiolene-like moieties at their active sites, which feature the so-called molybdopterin cofactor bound to the Mo or W.
Methyllithium is the simplest organolithium reagent, with the empirical formula CH3Li. This s-block organometallic compound adopts an oligomeric structure both in solution and in the solid state. This highly reactive compound, invariably used in solution with an ether as the solvent, is a reagent in organic synthesis as well as organometallic chemistry. Operations involving methyllithium require anhydrous conditions, because the compound is highly reactive toward water. Oxygen and carbon dioxide are also incompatible with MeLi. Methyllithium is usually not prepared, but purchased as a solution in various ethers.
Dihydrogen complexes are coordination complexes containing intact H2 as a ligand. They are a subset of sigma complexes. The prototypical complex is W(CO)3(PCy3)2(H2). This class of compounds represent intermediates in metal-catalyzed reactions involving hydrogen. Hundreds of dihydrogen complexes have been reported. Most examples are cationic transition metals complexes with octahedral geometry.
Dithiete is an unsaturated heterocyclic compound that contains two adjacent sulfur atoms and two sp2-hybridized carbon centers. Derivatives are known collectively as dithietes or 1,2-dithietes. With 6 π electrons, 1,2-dithietes are examples of aromatic organosulfur compounds. A few 1,2-dithietes have been isolated; one (low-yielding) route is oxidation of a dithiolene complex. 3,4-Bis(trifluoromethyl)-1,2-dithiete is a particularly stable example.
In organometallic chemistry, a transition metal indenyl complex is a coordination compound that contains one or more indenyl ligands. The indenyl ligand is formally the anion derived from deprotonation of indene. The η5-indenyl ligand is related to the η5cyclopentadienyl anion (Cp), thus indenyl analogues of many cyclopentadienyl complexes are known. Indenyl ligands lack the 5-fold symmetry of Cp, so they exhibit more complicated geometries. Furthermore, some indenyl complexes also exist with only η3-bonding mode. The η5- and η3-bonding modes sometimes interconvert.
Organomolybdenum chemistry is the chemistry of chemical compounds with Mo-C bonds. The heavier group 6 elements molybdenum and tungsten form organometallic compounds similar to those in organochromium chemistry but higher oxidation states tend to be more common.
Rhodocene is a chemical compound with the formula [Rh(C5H5)2]. Each molecule contains an atom of rhodium bound between two planar aromatic systems of five carbon atoms known as cyclopentadienyl rings in a sandwich arrangement. It is an organometallic compound as it has (haptic) covalent rhodium–carbon bonds. The [Rh(C5H5)2] radical is found above 150 °C (302 °F) or when trapped by cooling to liquid nitrogen temperatures (−196 °C [−321 °F]). At room temperature, pairs of these radicals join via their cyclopentadienyl rings to form a dimer, a yellow solid.
Tetrakis[3,5-bis(trifluoromethyl)phenyl]borate is an anion with chemical formula [{3,5-(CF3)2C6H3}4B]−, which is commonly abbreviated as [BArF4]−, indicating the presence of fluorinated aryl (ArF) groups. It is sometimes referred to as Kobayashi's anion in honour of Hiroshi Kobayashi who led the team that first synthesised it. More commonly it is affectionately nicknamed "BARF." The BARF ion is also abbreviated BArF24−, to distinguish it from the closely related BArF−
20, [(C6F5)4B]−. However, for a small group of chemists, the anion is abbreviated as TFPB otherwise, short for Tetrakis[3,5-bis(triFluoromethyl)Phenyl]Borate.
Metal acetylacetonates are coordination complexes derived from the acetylacetonate anion (CH
3COCHCOCH−
3) and metal ions, usually transition metals. The bidentate ligand acetylacetonate is often abbreviated acac. Typically both oxygen atoms bind to the metal to form a six-membered chelate ring. The simplest complexes have the formula M(acac)3 and M(acac)2. Mixed-ligand complexes, e.g. VO(acac)2, are also numerous. Variations of acetylacetonate have also been developed with myriad substituents in place of methyl (RCOCHCOR′−). Many such complexes are soluble in organic solvents, in contrast to the related metal halides. Because of these properties, acac complexes are sometimes used as catalyst precursors and reagents. Applications include their use as NMR "shift reagents" and as catalysts for organic synthesis, and precursors to industrial hydroformylation catalysts. C
5H
7O−
2 in some cases also binds to metals through the central carbon atom; this bonding mode is more common for the third-row transition metals such as platinum(II) and iridium(III).
Trifluoromethylation in organic chemistry describes any organic reaction that introduces a trifluoromethyl group in an organic compound. Trifluoromethylated compounds are of some importance in pharmaceutical industry and agrochemicals. Several notable pharmaceutical compounds have a trifluoromethyl group incorporated: fluoxetine, mefloquine, Leflunomide, nulitamide, dutasteride, bicalutamide, aprepitant, celecoxib, fipronil, fluazinam, penthiopyrad, picoxystrobin, fluridone, norflurazon, sorafenib and triflurazin. A relevant agrochemical is trifluralin. The development of synthetic methods for adding trifluoromethyl groups to chemical compounds is actively pursued in academic research.
Transition-metal allyl complexes are coordination complexes with allyl and its derivatives as ligands. Allyl is the radical with the connectivity CH2CHCH2, although as a ligand it is usually viewed as an allyl anion CH2=CH−CH2−, which is usually described as two equivalent resonance structures.
Transition metal nitrile complexes are coordination compounds containing nitrile ligands. Because nitriles are weakly basic, the nitrile ligands in these complexes are often labile.
Magnesocene, also known as bis(cyclopentadienyl)magnesium(II) and sometimes abbreviated as MgCp2, is an organometallic compound with the formula Mg(η5-C5H5)2. It is an example of an s-block main group sandwich compound, structurally related to the d-block element metallocenes, and consists of a central magnesium atom sandwiched between two cyclopentadienyl rings.
A transition metal phosphido complex is a coordination complex containing a phosphido ligand (R2P, where R = H, organic substituent). With two lone pairs on phosphorus, the phosphido anion (R2P−) is comparable to an amido anion (R2N−), except that the M-P distances are longer and the phosphorus atom is more sterically accessible. For these reasons, phosphido is often a bridging ligand. The -PH2 ion or ligand is also called phosphanide or phosphido ligand.
Inverted ligand field theory (ILFT) describes a phenomenon in the bonding of coordination complexes where the lowest unoccupied molecular orbital is primarily of ligand character. This is contrary to the traditional ligand field theory or crystal field theory picture and arises from the breaking down of the assumption that in organometallic complexes, ligands are more electronegative and have frontier orbitals below those of the d orbitals of electropositive metals. As we move to the right of the d-block and approach the transition-metal - main group boundary, the d orbitals become more core-like, making their cations more electronegative. This decreases their energies and eventually arrives at a point where they are lower in energy than the ligand frontier orbitals. Here the ligand field inverts so that the bonding orbitals are more metal-based, and antibonding orbitals more ligand-based. The relative arrangement of the d orbitals are also inverted in complexes displaying this inverted ligand field. This has consequences in our understanding of accessible metal oxidation states, and the reactivity of complexes exhibiting ILFT.
Iron bis(diethyldithiocarbamate) is a coordination complex with the formula [Fe(S2CNEt2)2]2 where Et = C2H5. A red solid, it is representative of several ferrous dithiocarbamates with diverse substituents in place of ethyl. In terms of structure, the species is dimeric, consisting of two pentacoordinate iron(II) centers. It is isostructural with [Zn(S2CNEt2)2]2, which in turn is similar to zinc bis(dimethyldithiocarbamate).
