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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 ...
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.
Tolman's rule states that, in a certain chemical reaction, the steps involve exclusively intermediates of 18- and 16 electron configuration. The rule is an extension of the 18-electron rule . This rule was proposed by American chemist Chadwick A. Tolman . [ 1 ]
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 formulae of many metal carbonyls can be inferred from the 18-electron rule. ... Perhaps the earliest application was the extraction ... the chemistry of metal ...
From the perspective of the 18-electron rule, the four ligands each provides two electrons, for a total of 16-electrons. As such the compound is coordinatively unsaturated , i.e. susceptible to binding substrates (alkenes and H 2 ).
Typically the chemistry of transition metal complexes is dominated by interactions between s and p molecular orbitals of the donor-atoms in the ligands and the d orbitals of the metal ions. 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 ...
These complexes are isoelectronic and, incidentally, both obey the 18-electron rule. The formal description of nitric oxide as NO + does not match certain measureable and calculated properties. In an alternative description, nitric oxide serves as a 3-electron donor, and the metal-nitrogen interaction is a triple bond. linear and bent M-NO bonds