HAPTOTROPIC SHIFTS IN (C5H5)FE AND MN(CO)(3) COMPLEXES OF 4H-CYCLOPENTA[DEF]PHENANTHRENE (CPPH) - X-RAY CRYSTAL-STRUCTURE AND NMR FLUXIONALITY OF (ETA(1)-CPP)MN(CO)(3)(PET(3))(2)

The favored pathways for the haptotropic shifts from (eta(6)-cpp)ML(n) to (eta(5)-cpp)ML(n), where cppH is 4H-cyclopenta[def]phenanthrene an d ML(n) = Fe(C5H5) or Mn(CO)(3), have been investigated by means of ex tended Huckel molecular orbital calculations, and energy hypersurfaces for these processes have been obtained. These data suggest the interm ediacy of an exocyclic (eta(3)-cpp)ML(n) species, stabilized by the pr esence of a naphthalene-type 10 pi aromatic system. In an attempt to g enerate (eta(3)-cpp)Fe(CO)(C5H5), the corresponding (eta(1)-cpp)Fe(CO) (2)(C5H5) complex was prepared and allowed to decompose; the major pro ducts were [(C5H5)Fe(CO)(2)](2) and the cpp trimer, C15H8(C15H9)(2), 2 0, that was shown to adopt a rigid geometry with C-2 symmetry. Treatme nt of (eta(5)-cpp)Mn(CO)(3) with triethylphosphine yields (eta(1)-cpp) Mn(CO)(3)(PEt(3))(2), 23, which exhibits hindered rotation about the C (4)-Mn bond with a barrier of 16.5 kcal mol(-1). The molecule [(eta(6) -cppH)Fe(C5H5)]PF6, 2b, and also the manganese complex 23 have been ch aracterized by X-ray crystallography. The relevance of these (and othe r literature data) to the mechanisms of haptotropic shifts are discuss ed.