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. [Davies, M. L. H. Green, and D. M. P. Mingos. “Nucleophilic addition to organotransition metal cations containing unsaturated hydrocarbon ligands.” Tetrahedron (1978), 34, 3047-3077.] 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 vs closed polyenes. Acyclic polyenes include polyenes.

*Rule 3A. Even acyclic polyene ligands add nucleophiles at a terminal position.
*Rule 3B. Even acyclic polyene ligands add nucleophiles at the terminal carbon occurs only for highly electrophilic metals, otherwise attack occurs at an internal site.

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