Synthesis, X-ray structures, electrochemistry, magnetic properties, and theoretical studies of the novel monomeric [CoI2(dppfO2)] and polymeric chain [CoI2(μ-dppfO2)n]

Abstract

The new compound [Co(η⁵-C₅H₅)(dppf-P,P′)I]I, 1, was synthesised by the stoichiometric reaction of the Co(III) complex [Co(η⁵-C₅H₅)(CO)I₂], 2, with 1,1′-bis(diphenylphosphino)ferrocene (dppf) in CH₂Cl₂, and was characterised by multinuclear NMR spectroscopy. Exposure to air of THF or CH₂Cl₂ solutions of compound 1 gave, in an unexpected way, a polymeric chain comprising bridging 1,1′-bis(oxodiphenylphosphoranyl)ferrocene (dppfO₂) joining tetrahedral Co(II) units [CoI₂(μ-dppfO₂)]_n, 3. Attempts to obtain the polymeric chain 3 by the direct reaction of dppfO₂ with CoI₂, in CH₂Cl₂, gave instead the monomeric compound [CoI₂(dppfO₂)], 4, in which dppfO₂ is coordinated in a chelating mode. The structural characterisation of compounds 2, 3, and 4 was carried out by single crystal X-ray diffraction studies. The magnetic behaviour of [CoI₂(dppfO₂)] and [CoI₂(μ-dppfO₂)]_n was studied, and the results are consistent with tetrahedral S = 3/2 Co^II, possessing a ⁴A₂ ground state, and S = 0 Fe^II. In these compounds, Co^II negative zero field splittings were determined from an analysis of the magnetic susceptibility temperature dependence, with D/k = −13 and −14 K for CoI₂(dppfO₂) and [CoI₂(μ-dppfO₂)]_n, respectively. DFT calculations were performed in order to understand the electronic structure of [Co(η⁵-C₅H₅)(dppf-P,P′)I]I, 1, as well as that of the paramagnetic specie [CoI₂(dppfO₂)], 4. The [CoI₂(μ-dppfO₂)]_n chain was also analysed and found to behave very similarly to the monomeric iodine derivative 4. The calculations showed the unpaired electrons to be localized on the Co(II) centre in all these species. The rather complicated electrochemical behaviour exhibited by the dppf complex [Co^III(η⁵-C₅H₅)(dppf-P,P′)I]I and by [Co(dppfO₂)I₂] is discussed.