The preparation and characterization of benzocyclobutenylidene-, naphtho[b]cyclobutenylidene-, and η2-benzocyclobutadiene-η5-cyclopentadienyldicarbonyliron hexafluorophosphate

Article abstract of DOI:10.1016/S0022-328X(00)91528-6

The preparation and characterization of the first isolable cationic mononuclear complexes bearing a η²-cyclobutadienoid ligand or a carbene ligand lacking heteroatom stabilization are described. The reaction between 1-bromo-benzocyclobutene and Na[η⁵-C₅H₅(CO)₂Fe] (NaFp) afforded η¹-1-benzocyclobutenyl-η⁵-cyclopentadienyldicarbonyliron (III). Treatment of III with trityl hexafluorophosphate gave benzocyclobutenylidene-η⁵-cyclopentadienyldicarbonyliron hexafluorophosphate (V). Naphtho [b] cyclobutenylidene-η⁵-cyclopentadienyldicarbonyliron hexafluorophosphate (VI) was formed in an analogous manner. Both V and VI gave 1,1-disubstituted cyclobutenes when treated with nucleophilic reagents. η²-Benzocyclobutadiene-η⁵-cyclopentadienyldicarbonyliron hexafluorophosphate, (XIX), which was prepared by the oxidation of bis-1,2-(η⁵-cyclopentadienyldicarbonyliron)benzocyclobutene by trityl hexafluorophosphate, afforded trans-1,2-disubstituted benzocyclobutenes when treated with nucleophilic reagents. The η²-benzocyclobutadiene ligand of XIX was displaced by I- and trapped as the Diels--Alder adduct by 1,3-diphenylisobenzofuran.