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The 18-electron rule is a chemical rule of thumb used primarily for predicting and rationalizing formulas for stable transition metal complexes, especially organometallic compounds. [1] The rule is based on the fact that the valence orbitals in the electron configuration of transition metals consist of five ( n −1)d orbitals, one n s orbital ...
In organometallic chemistry, the Green–Davies–Mingos rules predict the regiochemistry for nucleophilic addition to 18-electron metal complexes containing multiple unsaturated ligands. [1] The rules were published in 1978 by organometallic chemists Stephen G. Davies, Malcolm Green, and Michael Mingos.
The rule is an extension of the 18-electron rule. This rule was proposed by American chemist Chadwick A. Tolman. [1] However, there are exceptions to Tolman's rule, even for reactions that proceed via 2e − steps, because many reactions involve intermediates with fewer than 16 electrons.
The 18-electron rule is helpful in predicting the stabilities of organometallic complexes, for example metal carbonyls and metal hydrides. The 18e rule has two representative electron counting models, ionic and neutral (also known as covalent) ligand models, respectively. [7] The hapticity of a metal-ligand complex, can influence the electron ...
The s, p, and d orbitals of the metal can accommodate 18 electrons (see 18-Electron rule). The maximum coordination number for a certain metal is thus related to the electronic configuration of the metal ion (to be more specific, the number of empty orbitals) and to the ratio of the size of the ligands and the metal ion.
It has 6 d electrons to contribute to the electron count. The two bpy ligands are L-type ligand neutral ligands, thus contributing two electrons each. The two chloride ligands are anionic ligands, thus donating 2 electrons each to the electron count. The total electron count of RuCl 2 (bpy) 2 is 18, agreeing with the result of neural counting.
As is the case for many other η 1-allyl complexes, the monohapticity of the allyl ligand in this species is enforced by the 18-electron rule, since CpFe(CO) 2 (η 1-C 3 H 5) is already an 18-electron complex, while an η 3-allyl ligand would result in an electron count of 20 and violate the 18-electron rule.
Transition metal complexes have 9 valence orbitals, and 18 electrons will in turn fill these valences shells, creating a very stable complex, which satisfies the 18-electron rule. The cis-labilization of 18 e − complexes suggests that dissociation of ligand X in the cis position creates a square pyramidal transition state, which lowers the ...