Tolman's rule

Tolman's Rule states that, in a certain chemical reactions, 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]

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.

CH₃I + cis-[Rh(CO)₂I₂]⁻ → [(CH₃)Rh(CO)₂I₃]⁻

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

[Rh(PPh₃)₃ClH₂ → [Rh(PPh₃)₃Cl + H₂

References

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

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