Tolman's 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] As stated above, Tolman's rule, even for reactions that proceed via 2e⁻ steps, is incorrect because many reactions involve configurations of fewer than 16 e⁻.

Many examples of homogeneous catalysis involving organometallic complexes involve shuttling of complexes between 16 and 18 electron configurations. 16-electron complexes often form adducts with Lewis bases and, if low-valent, undergo oxidative addition.

CH 3 I + cis -[Rh(CO) 2 I 2] - \to [(CH 3)Rh(CO) 2 I 3] -

Conversely, complexes of 18 electron configuration tend to dissociate ligands or undergo reductive elimination:

[Rh(PPh 3) 3 ClH 2 \to [Rh(PPh 3) 3 Cl + H 2

References[]

^ Tolman, C.A. (1972). "The 16 and 18 electron rule in Organometallic Chemistry and Homogeneous Catalysis". Chem. Soc. Rev. 1 (3): 337–353. doi:10.1039/CS9720100337.

[1] Tolman, C.A. (1972). "The 16 and 18 electron rule in Organometallic Chemistry and Homogeneous Catalysis". Chem. Soc. Rev. 1 (3): 337–353. doi:10.1039/CS9720100337.

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