Pentakis(methoxycarbonyl)cyclopentadiene chemistry. Part 6. Some first-row transition-metal derivatives: crystal and molecular structures of [Fe{C5(CO2Me)5}2(MeOH)2], [Co{C5(CO2Me)5}2(OH2)2], and [Cu{C5(CO2Me)5}2(MeOH)2]

Abstract

Bivalent transition-metal derivatives of pentakis(methoxycarbonyl)cyclopentadiene have been obtained, which contain Mn, Fe, Co, Ni, or Cu : the latter is the first cyclopentadienyl complex of copper(II). These complexes are soluble in water or alcohols to give solutions containing [C₅(CO₂Me)₅]^– anions and solvated M²⁺ cations. Structural studies of the Fe and Cu complexes show the metal ion to be octahedrally co-ordinated by two solvent molecules, and two pairs of chelating carbonyl oxygens from each C₅(CO₂Me)₅ anion; the two salts, trans-[M{C₅(CO₂Me)₅}₂(MeOH)₂](M = Fe or Cu) are isomorphous, monoclinic, space group P2₁/c with a∼ 8.3, b∼ 20.2, c∼ 11.9 Å, β∼ 108°, and Z= 2, with the molecule lying on a crystallographic centre of symmetry. For the iron(II) salt, Fe–O[C₅(CO₂Me)₅] are 2.065(3) and 2.050(2)Å and Fe–O(MeOH) 2.151(2)Å, while in the copper(II) salt, Cu–O[C₅(CO₂Me)₅] are 1.946(2) and 1.962(2)Å and Cu–O(MeOH) 2.314(3)Å. The cobalt hydrate analogue, [Co{C₅(CO₂Me)₅}₂(OH₂)₂] has also been studied structurally and the molecule lies on a two-fold axis in space group C2/c with a= 17.151(7), b= 14.722(5), c= 15.026(6)Å, β=108.65(3)°, and Z= 4. The Co–OH₂bond is 2.054(4)Å; Co–O[C₅(CO₂Me)₅] are 2.043(4) and 2.068(4)Å. Residuals are 0.039, 0.044, and 0.043 respectively for the Fe, Cu, and Co complexes from 2 075, 3 018, and 1 430 ‘observed’ reflections. Unlike the iron and copper derivatives, the cobalt(II) complex is cis.