Can μ₄-Alkyne and μ₃-Alkenyl Ligands Be Considered as Six- and Five-Electron Donors, Respectively?

Abstract

EHMO calculations have revealed that alkynes bridging four metal atoms are four-electron-donor ligands and that alkenyl groups bridging three metal atoms are three-electron-donor ligands. Therefore, the answer to the title question is "no". The clusters that contain these ligands have large HOMO-LUMO gaps, despite being electronically unsaturated (according to the EAN rules). These are the conclusions of the present contribution, which tries to shed light on the hitherto existing controversy about the number of electrons that these ligands contribute to the metal clusters that hold them.

The synthesis and reactivity of some indenyl and bis-indenyl ruthenium carbonyl complexes

“…However, the bonding of the benzenoid with the Ru(3)Ru(4)Ru(5)Ru(6) butterfly metal core may best be regarded as similar to that found in similar tetranuclear butterfly clusters and hence is not electron-deficient [19]. To the best of our knowledge, this is the first example of such a bonding mode exhibited by the indenyl ligand.…”

Reactivity of Alkynes Containing α‐Hydrogen Atoms with a Triruthenium Hydrido Carbonyl Cluster: Alkenyl versus Allyl Cluster Derivatives

“…[16] Despite being an open triangular cluster, its electron count is 48 and thus disobeys the EAN rules (EAN = effective atomic number). [17] Trimetallic …”

Reactions of μ3‐Alkenyl Triruthenium Carbonyl Clusters with Alkynes: Synthesis of Trinuclear μ‐//‐Alkyne, μ‐Vinylidene, and μ‐Dienoyl Derivatives

“…Such ligands have only been found in [Os 3 (μ‐H)(μ 3 ‐ κ 2 ‐CF 3 CCHCF 3 )(CO) 10 ],10 [WRu 2 Cp*(μ‐NPh)(μ 3 ‐ κ 2 ‐CF 3 CCHCF 3 )(CO) 7 ],11 [Ru 3 {μ 3 ‐NS(O)MePh}(μ 3 ‐ κ 2 ‐RCCHR)(μ‐CO)(CO) 7 ],3a and in some derivatives of compound 1 4–6. Curiously, despite being open (two RuRu bonds) trinuclear clusters, [Ru 3 {μ 3 ‐NS(O)MePh}(μ 3 ‐ κ 2 ‐RCCHR)(μ‐CO)(CO) 7 ] and the μ 3 ‐alkenyl derivatives of compound 1 are 48‐electron species 12. 13…”