B. de Bruin
- Homoleptic Diphosphacyclobutadiene Complexes [M(η(4)-P2C2R2)(2]x- (M = Fe, Co; x=0, 1)
- Chemistry - A European Journal
- Volume | Issue number
- 16 | 48
- Pages (from-to)
- Document type
- Faculty of Science (FNWI)
- Van 't Hoff Institute for Molecular Sciences (HIMS)
The preparation and comprehensive characterization of a series of homoleptic sandwich complexes containing diphosphacyclobutadiene ligands are reported. Compounds [K(crown-6)(thf)(2)[Fe(η(4)-P(2)C(2)tBu(2))(2)] (K1), [K(crown-6)(thf)(2)][Co(η(4)-P(2)C(2)tBu(2))(2)] (K2), and [K(crown-6)(thf)(2)][Co(eta(4)-P(2)C(2)Ad(2))(2)] (K3, Ad = adamantyl) were obtained from reactions of [K(crown-6)(thf)(2)][M(η(4)-C14H10)(2)] (M =Fe, Co) with tBuC P (1, 2), or with Ad P (3). Neutral sandwiches [M(η(4)-P(2)C(2)tBu(2))(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(η(4)-P(2)C(2)tBu(2))(2)](-)/[M(η(4)-P(2)C(2)tBu(2))(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 Mossbauer 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 D-2d-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 pi bonding in 1-5. Possible oxidation state assignments for the metal ions are discussed.
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