Reduction in the Presence of Olefins

The formation of olefin complexes may occur during reduction of transition metal compounds in the presence of alkenes. Reducing agents may be compounds introduced to the reaction medium, the solvent, or the olefin itself. Preparation of complexes possessing the composition Rh2Cl2(olefin)4 may serve as an example of reductions by alkenes  

Reactions with propene and allyl alcohol occur in a similar way. Analogous complexes containing cycloheptene, cyclooctene, 1,5-COD, norbornene, and norbornadiene are also formed from rhodium trichloride in aqueous ethyl alcohol however, the reaction stoichiometry for these olefins was not established. It is possible that the oxidation of alcohol occurs. For the preparation of rhodium and iridium complexes with cycloolefins of the formula [M2Cl2(olefin)4], the best results are obtained if aqueous ethyl or isopropyl alcohol is used as the solvent  

IrCl3(IrCl4) + cyclooctene--- °°295k ---- [Ir2Cl2(cyclooctene)4] 

The complexes AuCl(olefin) and Au2Cl4(olefm) ( = 1-3) are formed from AuCls, H[AuCl4], or Na[AuCl4] as a result of oxidation of excess olefin. Ketones, 1,2-dioles, jS-chloroalcohols, or chloroalkanes are the oxidation products. 

The following reducing agents are also utilized N2H4, SO2, CO, and organome-tallic aluminum compounds, such as AIR3 (R = Me, Et, Bu, etc.) and Al(OR) R3.  

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