CATIONIC VINYLIDENE COMPLEXES - PREPARATION AND STRUCTURAL CHARACTERIZATION OF ETA-5-CYCLOPENTADIENYL)(2-METHYL-4,5-BIS(DIPHENYLPHOSPHINO)-2-PENTEN-3-YL)IRON (II) - BASE-INDUCED INTERLIGAND REACTION IN A VINYLIDENE COMPLEX

The cationic vinylidene complex [(Cp)Fe(dppe)(C=C(CH3)2|][SO3F] (la) (dppe = 1,2-bis(diphenylphosphino)-ethane), prepared by the methylation of (Cp)Fe(dppe)(C≡CCH3) (II), is smoothly deprotonated by potassium hydroxide or sodium bis(trimethylsilyl)amide. The exclusive product is (Cp) Fe[Ph2PCH2CH(PPh2C =C(CH3)2] (III), which contains a novel ferradiphospha[2.1.1]bicyclohexane ring system. This product was investigated by spectroscopic and crystal structure analysis: space group Cc, a = 14.738 (4) Å b = 12.471 (5) Å c = 16.982 (7) Å β = 106.17 (3)°, V = 2997 (4) Å3, Z = 4, ρclacd = 1 -268 g/cm3. Refinement on 1668 reflections with F02 > 3σ(F02) has yielded the final discrepancy indices R = 0.058 and Rw = 0.060. The bicyclic ring system shows geometric and spectroscopic features which indicate that significant torsional strain is present. The formation of III has been explained by the intermediacy of a zwitterionic complex containing both a deprotonated dppe ligand ([Ph2PCH2CHPPh2]) and a cationic vinylidene moiety. Subsequent intramolecular cyclization produces III. © 1979, American Chemical Society. All rights reserved.