Reaction of tricarbonylcyclo-octatetraene-ruthenium and -iron with electrophilic dienophiles

Abstract

The electrophilic dienophiles (CF₃)₂C:C(CN)₂, trans-CF₃(CN)C:C(CN)(CF₃), and (CF₃)₂C:O react with tricarbonylcyclo-octatetraene-ruthenium and -iron to form 1 : 1 adducts, which on the basis of ¹H and ¹⁹F n.m.r. measurements, are formulated as arising by a (2 + 2)π reaction, i.e. a 1,2-addition reaction. In contrast, the highly reactive dienophile 4-phenyl-1,2,4-triazole-3,5-(2H,4H)-dione adds 1,4 to tricarbonylcyclo-octatetraene-iron, and the reaction of (CF₃)₂C:O with C₈H₈Fe(CO)₃ affords an organic ketone C₈H₈CO[(CF₃)₂CO]. The analogous ketone C₈H₈CO[(CF₃)₂CC(CN)₂] is formed by the reaction of C₈H₈[(CF₃)₂CC(CN)₂]Fe(CO)₃ with carbon monoxide, 1,2-diphenylphosphinoethane, and nitric oxide. Possible structures for these compounds are described. The mechanism of the 1,2-addition reactions is discussed.