Reactions of [Fe(cp)(CO)2Cl](cp =η-cyclopentadienyl) with 3-methylbut-2-enoic acid and its methyl ester. X-Ray crystal and molecular structure of bis[dicarbonyl(η-cyclopentadienyl)(3-methylbut-2-enoato)iron(II)]hydrogen hexafluoroantimonate and µ-chloro-bis[dicarbonyl(η-cyclopentadienyl)iron(II)] hexafluoroantimonate

Abstract

Reaction of [Fe(cp)(CO)₂Cl](cp =η-C₅H₅) with AgSbF₆ in the presence of Me₂CCHCOOH affords red [Fe(cp)(CO)₂(Me₂CCHCOOH)][SbF₆] with binding through the OH oxygen atom or orange [{Fe(cp)(CO)₂(Me₂CCHCOOH)}₂H][SbF₆]. The ester Me₂CCHCOOMe gives [Fe(cp)(CO)₂(Me₂CCHCOOMe)][SbF₆] for which i.r. studies imply binding through the carbonyl oxygen atom of the ester group. The spectroscopic properties of these compounds are discussed. The X-ray structure of [{Fe(cp)(CO)₂(Me₂CCHCOOH)}₂H][SbF₆] has been determined. Crystal data: monoclinic, a= 29.901 (2), b= 7.495(2), c= 14.006(2)Å, β= 100.65(1)°, space group C2/c, and Z= 4. The cation contains a centre of symmetry and is regarded as being made up of two Fe(cp)(CO)₂ units each bound to a carbonyl oxygen atom of a symmetrical (Me₃CCHCOO)₂H unit, with the two non-co-ordinated oxygen atoms hydrogen bonded together. The short O(9)⋯ O(9′) distance [2.406(9)Å] is indicative of a symmetrical hydrogen bond. The coplanarity of the two acid groups suggests some double bond delocalisation. In CH₂Cl₂, the compound [Fe(cp)(CO)₂(Me₂CCHCOOH)][SbF₆] slowly gives [{Fe(cp)(CO)₂}₂Cl][SbF₆] for which the X-ray crystal structure shows an angle of 119.4(2)° at the bridging chlorine atom. The crystals of the complex are monoclinic, space group P2₁/c, with a= 13.805(4), b= 12.301(3), c= 12.457(3)Å, and β= 111.88(2)°. The structure was solved via the heavy-atom method and refined to an R value of 0.053 for 4 540 observed diffractometer data.