The preparation and properties of dicarbonyl-h5-cyclopentadienyliron h2-vinyl ether and h2-ketene acetal complexes

Metallation of >-haloacetals wth sodium dicarbonyl-h⁵-cyclopentadienyl- ferrate (Fp^-) provides a convenient point of departure for the synthesis of alhyde -iron complexes (FpCHRCHO) and of h²-vinyl alcohol and vinyl ether cations Fp(CH₂=CHOR)]⁺. These latter complexes are shown to be best described as distorted dihapto cation. Treatment of FpCOCH₂OMe with strong acid leads to the ketene hemiacetal cation Fp(CH₂=C(OH)OMe)]⁺ rather than to the expected ketene complex. This substance, as well as the acetal cation Fp(CH₂=C(OMe)OEt)]⁺ prepared by alkylation of FpCH₂COOMe, may possess the structure of an h¹-metal complex incorporating a carboxonium ion. A correlation is shown to exist between the chemical shift of cyclopentadienyl protons and the average infrared carbonyl stretching frequency in a variety of Fp(olefin)⁺ FpR complexes.