Green-Davies-Mingos rules
Encyclopedia
In organometallic chemistry
, the Green–Davies–Mingos rules predict the regiochemistry for nucleophilic addition
to 18-electron metal complexes containing multiple unsaturated ligand
s. In general, complexation enhances the susceptibility of unsaturated hydrocarbon toward nucleophilic attack.
Organometallic chemistry
Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Since many compounds without such bonds are chemically similar, an alternative may be compounds containing metal-element bonds of a largely covalent character...
, the Green–Davies–Mingos rules predict the regiochemistry for nucleophilic addition
Nucleophilic addition
In organic chemistry, a nucleophilic addition reaction is an addition reaction where in a chemical compound a π bond is removed by the creation of two new covalent bonds by the addition of a nucleophile....
to 18-electron metal complexes containing multiple unsaturated ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
s. In general, complexation enhances the susceptibility of unsaturated hydrocarbon toward nucleophilic attack.
- Rule 1. Nucleophilic attack is preferred on even-numbered polyenes (even hapticityHapticityThe term hapticity is used to describe how a group of contiguous atoms of a ligand are coordinated to a central atom. Hapticity of a ligand is indicated by the Greek character 'eta', η. A superscripted number following the η denotes the number of contiguous atoms of the ligand that are bound to...
).
- Rule 2. Nucleophiles preferentially add to acyclic polyenes rather than cyclic polyenes.
- Rule 3A. Nucleophiles preferentially add to even-hapticity polyene ligands at a terminal position.
- Rule 3B. Nucleophiles add to odd-hapticity acyclic polyene ligands at a terminal position if the metal is highly electrophilic, otherwise they add at an internal site.