Green–Davies–Mingos rules

In organometallic chemistry, the Green–Davies–Mingos rules predict the regiochemistry for nucleophilic addition to 18-electron metal complexes containing multiple unsaturated ligands.^[1] In general, complexation enhances the susceptibility of unsaturated hydrocarbon toward nucleophilic attack.

• Rule 1. Nucleophilic attack is preferred on even-numbered polyenes (even hapticity).

• Rule 2. Nucleophiles preferentially add to acyclic polyenes rather than cyclic polyenes.

• Rule 3A. Nucleophiles preferentially add to even-hapticity polyene ligands at a terminal position.
• Rule 3B. Nucleophiles add to odd-hapticity acyclic polyene ligands at a terminal position if the metal is highly electrophilic, otherwise they add at an internal site.

References

1. ^ Stephen G. Davies et al (1977). "Nucleophilic Addition to Organotransition Metal Cations Containing Unsaturated Hydrocarbon Ligands". Tetrahedron 34: 3047–3077. doi:10.1016/0040-4020(78)87001-X.