1,2-DISUBSTITUTED [(ETA(6)-ARENE)CR(CO)(3)] COMPLEXES BY SEQUENTIAL NUCLEOPHILIC-ADDITION ENDO-HYDRIDE ABSTRACTION

Regioselective addition of organolithium compounds at the ortho positi on in oxazoline, imine, or hydrazone (eta(6)-arene)tricarbonyl chromiu m complexes afforded anionic [(eta(5)-cyclohexadienyl)Cr(CO)(3)] inter mediates. A single-crystal Xray structure determination of the product of the addition reaction of naphthyllithium with a phenyl oxazoline c omplex showed structural characteristics of an aza-enolate superimpose d on the predominant cyclohexadienyl structure. Reaction of the anioni c cyclohexadienyl complex with a trityl salt yielded 1,2-disubstituted [(eta(6)-arene)Cr-(CO)(3)] complexes. Labeling studies, carried out t o provide mechanistic details of the aromatization process, ruled out an isomerization/exo-hydride abstraction sequence but were in accord w ith a process involving endo-hydride abstraction.