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The recent addition was a little rough, so I cut out some of it and plan to continue to work on it. If other editors feel that I am too harsh or have suggestions, leave a note here. Or just revert my edits.

At least to organometallic chemists, metallacycle has a very specific meaning They are supposed to be carbocycles where a metal replaces a carbon center. The usage is analogous to aza-, thia, and oxa- for carbon compounds where N, S, and O replace C.

IUPAC defines "metallacycloalkanes" as "Monocyclic compounds containing a metal atom and saturated carbon atoms as ring members" see [1]. Some larger topics C₄M rings with a Cp₂M vertex, the MC₆H₁₂ rings in ethylene trimerization. Alkyne trimerization I think involve metallacycles. The metallabenzene theme remains a niche area.

At least by my thinking, metallacrowns do not qualify (no M-C bonds). So maybe we should shift that topic to an independent article.-- Smokefoot ( talk) 23:03, 23 December 2009 (UTC) reply