Thermal and photochemical interconversions of isomeric monocarbonyl η5-Cyclopentadienyl(η3-allyl)iron complexes
1976; Elsevier BV; Volume: 105; Issue: 1 Linguagem: Inglês
10.1016/s0022-328x(00)91977-6
ISSN1872-8561
AutoresRichard W. Fish, Warren P. Giering, David F. Marten, Myron Rosenblum,
Tópico(s)Catalysis and Oxidation Reactions
ResumoThe photolysis of η5-C5H5-η1-C3H5Fe(CO)2 at 10°C gives two stereoisomers of η5-C5H5-η3-C3H5Fe(CO). The less stable isomer (endo) thermally isomerizes to the more stable (exo) isomer with a moderate rate at ambient temperatures. Similarly the endo-η3-methallyliron complex isomerizes completely to the exo isomer with AG≠ = 24.1 kcal/mol. Photolyses of cis- and trans-1-substituted-η1allyliron compounds yield the syn- and anti-η3-allyliron isomers stereospecifically as a mixture of endo and exo stereoisomers. In all the cases examined the exo, syn stereoisomers are the thermodynamically most stable while the endo, anti are the least stable isomers. Approximate rates for the thermal interconversion of the different stereoisomers have been determined. Anti to syn conversion occurs at a rate comparable to endo to exo isomerization and implies a similar mechanism involving a η3 → η1 → η3 transformation. Theoretical arguments are presented to explain the apparent change in mechanism for endo and exo interconversion of Group VI and VIII η3-allyl complexes.
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