title: Influences on the rotated structure of diiron dithiolate complexes: electronic asymmetry vs. secondary coordination sphere interaction.
abstract: In the pursuit of a "rotated" structure, and exploration of the influence of the aza nitrogen lone pair, the Fe(I)Fe(I) model complexes wherein two Fe(CO)(3-x)P(x) moieties are significantly twisted from the ideal configuration (torsion angle >30°) are reported. [Fe(2)(μ-S(CH(2))(2)N(i)Pr(X)(CH(2))(2)S)(CO)(4)(κ(2)-dppe)](2)(2+) (X = H, 4; Me, 5) prepared from protonation and methylation, respectively, of [Fe(2)(μ-S(CH(2))(2)N(i)Pr(CH(2))(2)S)(CO)(4)(κ(2)-dppe)](2), 1, possess Φ angles of 34.1 and 35.4° (av.), respectively. Such dramatic twist is attributed to asymmetric substitution within the Fe(2) unit in which a dppe ligand is coordinated to one Fe site in the κ(2)-mode. In the presence of the N···C(CO(ap)) interaction, the torsion angle is decreased to 10.8°, suggesting availability of lone pairs of the aza nitrogen sites within 1 is in control of the twist. Backbones of the bridging diphosphine ligands also affect distortion. For a shorter ligand, the more compact structure of [Fe(2)(μ-S(CH(2))(2)N(i)Pr(CH(2))(2)S)(μ-dppm)(CO)(4)](2), 7, is formed. Dppm in a bridging manner allows achievement of the nearly eclipsed configuration. In contrast, dppe in [Fe(2)(μ-S(CH(2))(2)N(i)Pr(CH(2))(2)S)(μ-dppe)(CO)(4)](2), 6, could twist the Fe(CO)(3-x)L(x) fragment to adopt the least strained structure. In addition, the NC(CO(ap)) interaction would direct the twist towards a specific direction for the closer contact. In return, the shorter N···C(CO(ap)) distance of 3.721(7) Å and larger Φ angle of 26.5° are obtained in 6. For comparison, 3.987(7) Å and 3.9° of the corresponding parameters are observed in 7. Conversion of (μ-dppe)[Fe(2)(μ-S(CH(2))(2)N(i)Pr(CH(2))(2)S)(CO)(5)](2), 2, to complex 1 via an associative mechanism is studied.
authors.affiliation: Institute of Chemistry, Academia Sinica, Nankang, Taipei 115, Taiwan.
authors.forename: Yu-Chiao
authors.initials: YC
authors.lastname: Liu
authors.forename: Ling-Kuang
authors.initials: LK
authors.lastname: Tu
authors.forename: Tao-Hung
authors.initials: TH
authors.lastname: Yen
authors.forename: Gene-Hsiang
authors.initials: GH
authors.lastname: Lee
authors.forename: Ming-Hsi
authors.initials: MH
authors.lastname: Chiang
mesh_terms: D018360:Crystallography, X-Ray; D055664:Electrochemical Techniques; D005290:Ferric Compounds / Q000737:chemistry*; D008024:Ligands; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry; D013438:Sulfhydryl Compounds / Q000737:chemistry*
chemical_list: D005290:Ferric Compounds; D008024:Ligands; D013438:Sulfhydryl Compounds; C002007:dithiol-iron(III)-sulfide complex; D009584:Nitrogen