Chemistry: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.
- 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
See also
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.
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