Nucleophilic abstraction is a type of an

organometallic 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 ...

reaction which can be defined as a

nucleophilic attack In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they a ...

on a

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 ...

which causes part or all of the original ligand to be removed from the metal along with the

nucleophile In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...

.Spessard, Gary; Miessler, Gary (2010).''Organometallic Chemistry: Second Edition''. pp. 285-289

Alkyl abstraction

While nucleophilic abstraction of an

alkyl group In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl group is derived from a cy ...

is relatively uncommon, there are examples of this type of reaction. In order for this reaction to be favorable, the metal must first be

oxidized Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

because reduced metals are often poor

leaving group In organic chemistry, a leaving group typically means a Chemical species, molecular fragment that departs with an electron, electron pair during a reaction step with heterolysis (chemistry), heterolytic bond cleavage. In this usage, a ''leaving gr ...

s. The oxidation of the metal causes the M-C bond to weaken, which allows for the nucleophilic abstraction to occur. G.M. Whitesides and D.J. Boschetto use the halogens Br₂ and I₂ as M-C cleaving agents in the following example of nucleophilic abstraction. It is important to note that the product of this reaction is inverted with respect to the stereochemical center attached to the metal. There are several possibilities for the

mechanism Mechanism may refer to: *Mechanism (economics), a set of rules for a game designed to achieve a certain outcome **Mechanism design, the study of such mechanisms *Mechanism (engineering), rigid bodies connected by joints in order to accomplish a ...

of this reaction which are shown in the following schematic. In path a, the first step proceeds with the oxidative addition of the

halogen The halogens () are a group in the periodic table consisting of six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and the radioactive elements astatine (At) and tennessine (Ts), though some authors would ...

to the metal complex. This step results in the oxidized metal center that is needed to weaken the M-C bond. The second step can proceed with either the nucleophilic attack of the halide ion on the

α-carbon In the nomenclature of organic chemistry, a locant is a term to indicate the position of a functional group or substituent within a molecule. Numeric locants The International Union of Pure and Applied Chemistry (IUPAC) recommends the use of n ...

of the alkyl group or reductive elimination, both of which result in the inversion of stereochemistry. In path b, the metal is first oxidized without the addition of the halide. The second step occurs with a nucleophilic attack of the α-carbon which again results in the inversion of stereochemistry.

Carbonyl abstraction

Trimethylamine N-oxide (Me₃NO) can be used in the nucleophilic abstraction of

carbonyl In organic chemistry, a carbonyl group is a functional group with the formula , composed of a carbon atom double bond, double-bonded to an oxygen atom, and it is divalent at the C atom. It is common to several classes of organic compounds (such a ...

. There is an nucleophilic attack of Me₃NO on the carbon of the carbonyl group which pushes electrons on the metal. The reaction then proceeds to kick out CO₂ and NMe₃. An article from the ''Bulletin of Korean Chemical Society'' journal showed interesting results where one iridium complex undergoes carbonyl abstraction while a very similar iridium complex undergoes

hydride In chemistry, a hydride is formally the anion of hydrogen (H−), a hydrogen ion with two electrons. In modern usage, this is typically only used for ionic bonds, but it is sometimes (and has been more frequently in the past) applied to all che ...

extraction.

Hydrogen abstraction

Nucleophilic abstraction can occur on a ligand of a metal if the conditions are right. For instance the following example shows the nucleophilic abstraction of H⁺ from an arene ligand attached to chromium. The

electron withdrawing An electron-withdrawing group (EWG) is a group or atom that has the ability to draw electron density toward itself and away from other adjacent atoms. This electron density transfer is often achieved by resonance or inductive effects. Electron-with ...

nature of the chromium allows for the reaction to occur as
facile
reaction.

Methyl abstraction

A Fischer carbene can undergo nucleophilic abstraction where a

methyl group 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 a ...

is removed. With the addition of a small abstracting agent, the abstracting agent would normally add to the carbene carbon. In this case however, the steric bulk of the abstracting agent that is added causes the abstraction of the methyl group. If the methyl group is replaced with ethyl, the reaction proceeds 70 times slower which is to be expected with a S_N2 displacement mechanism.

Silylium abstraction

A silylium ion is a silicon cation with only three bonds and a positive charge. The abstraction of the silylium ion is seen from the

ruthenium Ruthenium is a chemical element; it has symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is unreactive to most chem ...

complex shown below. In the first step of this mechanism one of the

acetonitrile Acetonitrile, often abbreviated MeCN (methyl cyanide), is the chemical compound with the formula and structure . This colourless liquid is the simplest organic nitrile (hydrogen cyanide is a simpler nitrile, but the cyanide anion is not class ...

groups is replaced by a silicon molecule where the bond between the silicon and the hydrogen is coordinating to the ruthenium. In the second step a

ketone In organic chemistry, a ketone is an organic compound with the structure , where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond C=O). The simplest ketone is acetone ( ...

is added for the nucleophilic abstraction of the silylium ion and the hydrogen is left on the metal.

α-Acyl abstraction

One example of nucleophilic abstraction of an α-acyl group is seen when MeOH is added to the following palladium complex. The mechanism follows a

tetrahedral In geometry, a tetrahedron (: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular Face (geometry), faces, six straight Edge (geometry), edges, and four vertex (geometry), vertices. The tet ...

intermediate which results in the methyl

ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

and the reduced palladium complex shown. The following year a similar mechanism was proposed where oxidative addition of an

aryl halide In organic chemistry, an aryl halide (also known as a haloarene) is an aromatic compound in which one or more hydrogen atoms directly bonded to an aromatic ring are replaced by a halide ion (such as fluorine F''−'', chlorine Cl−1,−3,−5, br ...

followed by migratory CO insertion and is followed by nucleophilic abstraction of the α-acyl by MeOH. One of the advantages of this intermolecular nucleophilic abstraction is the production of linear acyl derivatives. The intramolecular attack of these linear acyl derivatives gives rise to

cyclic compound A cyclic compound (or ring compound) is a term for a compound in the field of chemistry in which one or more series of atoms in the compound is connected to form a ring. Rings may vary in size from three to many atoms, and include examples where ...

s such as

lactone Lactones are cyclic carboxylic esters. They are derived from the corresponding hydroxycarboxylic acids by esterification. They can be saturated or unsaturated. Lactones are formed by lactonization, the intramolecular esterification of the corresp ...

s or

lactam A lactam is a Cyclic compound, cyclic amide, formally derived from an amino alkanoic acid through cyclization reactions. The term is a portmanteau of the words ''lactone'' + ''amide''. Nomenclature Greek_alphabet#Letters, Greek prefixes in alpha ...

s.R. F. Heck
Pure Appl. Chem., 1978, 50, 691

References

Inorganic chemistry Organometallic chemistry