Transition metal alkene complex

In organometallic chemistry, a transition metal alkene complex is a coordination compound containing one or more alkene ligands. The inventory is large. Such compounds are intermediates in many catalytic reactions that convert alkenes to other organic products. The simplest monoalkene is ethene. Many complexes of ethene are known, including Zeise's salt (see figure), Rh2Cl2(C2H4)4, Cp*2Ti(C2H4), and the homoleptic Ni(C2H4)3. Substituted monoalkene include the cyclic cyclooctene, as found in chlorobis(cyclooctene)rhodium dimer. Alkenes with electron-withdrawing groups commonly bind strongly to low-valent metals. Examples of such ligands are TCNE, tetrafluoroethylene, maleic anhydride, and esters of fumaric acid. These acceptors form adducts with many zero-valent metals. Butadiene, cyclooctadiene, and norbornadiene are well-studied chelating agents. Trienes and even some tetraenes can bind to metals through several adjacent carbon centers. Common examples of such ligands are cycloheptatriene and cyclooctatetraene. The bonding is often denoted using the hapticity formalism. Keto-alkenes are tetrahapto ligands that stabilize highly unsaturated low valent metals as found in (benzylideneacetone)iron tricarbonyl and tris(dibenzylideneacetone)dipalladium(0). File:Ni(cod)2.png|[[Bis(cyclooctadiene)nickel(0)]], a catalyst and source of "naked nickel." File:Zeise'sSalt.png|The first alkene complex, the anion in [[Zeise's salt]]. File:Rh2Cl2 coe 4.svg|[[Chlorobis(cyclooctene)rhodium dimer]], source of "RhCl". File: Crabtree.svg|[[Crabtree's catalyst]], a very active catalyst for hydrogenation. File: (benzylideneacetone)iron-tricarbonyl-2D-skeletal.png|(Benzylideneacetone)iron tricarbonyl, source of "Fe(CO)3". file:Fullerene 4.png|[[Et3P]2Pt]6(η2:η2:η2:η2:η2:η2-C60), a [[transition metal fullerene complex|fullerene complex]]. File:CHTMo(CO)3.png|Mo(C7H8)(CO)3, a complex of [[cycloheptatriene]].