Agostic complexes are coordination compounds where the σ bond of a ligand serves as the electron pair donor. Synthesis of copper(II)-tetraphenylporphine, a metal complex, from tetraphenylporphine and copper(II) acetate monohydrate. ... Electron atomic and molecular orbitals, showing among others the sigma bond of two s-orbitals and a sigma bond of two p-orbitals In chemistry, sigma bonds (σ-bonds) are bonds where there is no nodal plane containing the line segment between the two bonded species. ... In chemistry, a ligand is an atom, ion, or molecule (see also: functional group) that generally donates one or more of its electrons through a coordinate covalent bond to, or shares its electrons through a covalent bond with, one or more central atoms or ions (these ligands act as a...

One can view agostic interactions as the "third tier" of metal-ligand bonding:

Tier 1: To form classical Lewis acid-base adducts, ligands utilize nonbonded pairs of electrons. Werner chemistry is based on this type of interaction between a Lewis-acidic metal and a Lewis-basic ligand.

Tier 2: With the advent of organometallic chemistry, it became apparent that alkenes could serve as ligands via donation of electrons in π bonds. The classic example is Zeise's salt, in which ethylene is a ligand on a platinum atom.

Tier 3: Molecules lacking both lone pairs and π-bonds also interact with metals (and other Lewis acids), forming isolable complexes in some cases. The interaction entails "sharing" of the electrons in a σ bond with the metal. Such interactions can be described as 3-center, 2-electron bonds, familiar in the chemistry of boron hydrides, aluminium alkyls, and carbocations.

In chemistry, a Lewis acid can accept a pair of electrons and form a coordinate covalent bond, after the American chemist Gilbert Lewis. ... A Lewis base is any molecule or ion that can form a new covalent bond by donating a pair of electrons. ... It has been suggested that Organometallic compounds be merged into this article or section. ... The chemical structure of ethylene, the simplest alkene. ... Electron atomic and molecular orbitals, showing a Pi-bond at the bottom right of the picture In chemistry, pi bonds (Ï€ bonds) are bonds with a single nodal plane containing the line segment between the two atoms. ... ... Ethylene (or IUPAC name ethene) is the simplest alkene hydrocarbon, consisting of four hydrogen atoms and two carbon atoms connected by a double bond. ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Atomic mass 195. ... Diborane is a colorless gas at room temperature with a repulsive, sweet odor. ... This article needs copyediting (checking for proper English spelling, grammar, usage, etc. ... A carbocation is an ion with a positively-charged carbon atom. ...

Agostic bonding

The term "agostic bonding" is usually reserved to describe the complexation of the C-H bond of a hydrocarbon to a metal, however, the concept has been extended to include other ligands. The most famous extension is to the complexation of H₂ itself, illustrated in W(CO)₃(PPrⁱ₃)₂H₂.^[1] Silanes are also well-known to form such complexes. Hydrocarbons are refined at oil refineries and processed at chemical plants In chemistry, a hydrocarbon is any chemical compound that consists only of the elements carbon (C) and hydrogen (H). ... Silane is a chemical compound with chemical formula SiH4. ...

It is widely suspected that agostic bonding describes the interaction of hydrocarbons with metals and non-metals alike.^{[citation needed]} For these ligands, which in general do not possess a 'normal' Lewis basic site, to undergo (catalytic or stoichiometric) activation, the first interaction is an agostic interaction of the metal centre with one of the ligands σ-bonds, followed by a (heterolytic or homolytic) cleavage of the σ-bond (oxidative addition). A subtle example can be seen with some ruthenium-dihydrogen complexes, in which both (low valent) ruthenium-dihydrogen complexes and the (high valent) ruthenium-dihydrides can be observed.^{[citation needed]} In chemistry and biology, catalysis (in Greek meaning to annul) is the acceleration of the rate of a chemical reaction by means of a substance, called a catalyst, that is itself unchanged chemically by the overall reaction. ... In chemistry, stoichiometry is the study of the combination of elements in chemical reactions. ... Homolytic: a bond cleavage (lysis) in which two neutral species are produced ... Oxidative addition and reductive elimination are two important classes of reactions in organometallic chemistry. ... General Name, Symbol, Number Ruthenium, Ru, 44 Chemical series transition metals Group, Period, Block 8, 5, d Appearance silvery white metallic Atomic mass 101. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... A hydride is a compound of hydrogen with more electropositive elements. ...

Examples

• W(CO)₃(PPrⁱ₃)₂H₂.^[1]

Applications

• With the increased availability of natural gas as a feedstock, there is growing interest in the exploitation of agostic interactions between methane and metals.

• Agostic bonds sometimes play a role in catalysis by increasing 'rigidity' in transition states. One prominent example is Ziegler-Natta catalysis, where the highly electrophilic metal center has agostic interactions with the growing polymer chain.^{[citation needed]}

Natural gas is commonly referred to as gas. ...

References

1. ^ ^a b Kubas, G. J., "Metal Dihydrogen and σ-Bond Complexes", Kluwer Academic/Plenum Publishers: New York, 2001