Homoleptic Diphosphacyclobutadiene Complexes [M(n⁴-P₂C₂R₂)₂]ˣ⁻ (M=Fe, Co; X=0, 1)
The preparation and comprehensive characterization of a series of homoleptic sandwich complexes containing diphosphacyclobutadiene ligands are reported. Compounds [K(crown-6)(thf)2] [Fe(Î·4-P2C2tBu2) 2] (K1), [K(crown-6)(thf)2] [Co(Î·4-P2C2tBu2) 2] (K2), and [K(crown-6)(thf)2] [Co(Î·4-P2C2Ad2) 2] (K3, Ad=adamantyl) were obtained from reactions of [K(crown-6)(thf)2][M(Î·4-C 14H10)2] (M=Fe, Co) with tBuCï£P (1, 2), or with AdCï£P (3). Neutral sandwiches [M(Î· 4-P2C2tBu2)2] (4: M=Fe 5: M=Co) were obtained by oxidizing 1 and 2 with [Cp2Fe]PF6. Cyclic voltammetry and spectro-electrochemistry indicate that the two [M(Î·4-P2C2tBu2) 2]-/[M(Î·4-P2C 2tBu2)2] moieties can be reversibly interconverted by one electron oxidation and reduction, respectively. Complexes 1-5 were characterized by multinuclear NMR, EPR (1 and 5), UV/Vis, and Mössbauer spectroscopies (1 and 4), mass spectrometry (4 and 5), and microanalysis (1-3). the molecular structures of 1-5 were determined by using X-ray crystallography. Essentially D2d-symmetric structures were found for all five complexes, which show the two 1,3-diphosphacyclobutadiene rings in a staggered orientation. Density functional theory calculations revealed the importance of covalent metal-ligand π bonding in 1-5. Possible oxidation state assignments for the metal ions are discussed. Fancy a sandwich? Homoleptic sandwich anions that contain diphosphacyclobutadiene ligands result from the reaction of anthracene metalates [Fe(Î·4-C 14H10)2]- and [Co(Î· 4-C14H10)2]- with phosphaalkynes. Electrochemical and preparative investigations of [M(Î·4-P2C2tBu2) 2]- (M=Fe, Co) revealed that these anions are readily oxidized to neutral derivatives [M(Î·4-P 2C2tBu2)2]. the electronic structures of the new sandwich complexes have been elucidated by using spectroscopic techniques and density functional theory calculations. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
R. Wolf and A. W. Ehlers and M. M. Khusniyarov and F. Hartl and B. Debruin and G. J. Long and F. Grandjean and F. M. Schappacher and R. Pöttgen and J. C. Slootweg and M. Lutz and A. L. Spek and K. Lammertsma, "Homoleptic Diphosphacyclobutadiene Complexes [M(n⁴-P₂C₂R₂)₂]ˣ⁻ (M=Fe, Co; X=0, 1)," Chemistry - a European Journal, Wiley-VCH Verlag, Jan 2010.
The definitive version is available at http://dx.doi.org/10.1002/chem.201001913
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