text: The parent metallacyclopentane has the formula LM(CH). Such compounds are intermediates in the metal catalysed dimerization, trimerization, and tetramerization of ethylene to give but-1-ene, hex-1-ene and oct-1-ene, respectively.  Metallacyclopentanes are invoked as intermediates in the evolution of heterogeneous alkene metathesis catalysts from ethylene and metal oxides.  Metallacyclopentane intermediates are proposed to isomerize to metallacyclobutanes, which then eliminate propylene giving the alkylidene.