Rahaman Ahibur, Ghosh Shishir, Unwin David G, Basak-Modi Sucharita, Holt Katherine B, Kabir Shariff E, Nordlander Ebbe, Richmond Michael G, Hogarth Graeme
Department of Chemistry, Jahangirnagar University , Savar, Dhaka 1342, Bangladesh ; Inorganic Chemistry Research Group, Chemical Physics, Center for Chemistry and Chemical Engineering, Lund University , P.O. Box 124, SE-22100 Lund, Sweden.
Department of Chemistry, Jahangirnagar University , Savar, Dhaka 1342, Bangladesh ; Department of Chemistry, University College London , 20 Gordon Street, London WC1H 0AJ, U.K.
Organometallics. 2014 Mar 24;33(6):1356-1366. doi: 10.1021/om400691q. Epub 2014 Mar 5.
The mixed-valence triiron complexes [Fe(CO) (PPh) (μ-edt)] ( = 0-2; edt = SCHCHS) and [Fe(CO)(κ-diphosphine)(μ-edt)] (diphosphine = dppv, dppe, dppb, dppn) have been prepared and structurally characterized. All adopt an arrangement of the dithiolate bridges, and PPh substitution occurs at the apical positions of the outer iron atoms, while the diphosphine complexes exist only in the dibasal form in both the solid state and solution. The carbonyl on the central iron atom is semibridging, and this leads to a rotated structure between the bridged diiron center. IR studies reveal that all complexes are inert to protonation by HBF·EtO, but addition of acid to the pentacarbonyl complexes results in one-electron oxidation to yield the moderately stable cations [Fe(CO)(PPh)(μ-edt)] and [Fe(CO)(κ-diphosphine)(μ-edt)], species which also result upon oxidation by [CpFe][PF]. The electrochemistry of the formally Fe(I)-Fe(II)-Fe(I) complexes has been investigated. Each undergoes a quasi-reversible oxidation, the potential of which is sensitive to phosphine substitution, generally occurring between 0.15 and 0.50 V, although [Fe(CO)(PPh)(μ-edt)] is oxidized at -0.05 V. Reduction of all complexes is irreversible and is again sensitive to phosphine substitution, varying between -1.47 V for [Fe(CO)(μ-edt)] and around -1.7 V for phosphine-substituted complexes. In their one-electron-reduced states, all complexes are catalysts for the reduction of protons to hydrogen, the catalytic overpotential being increased upon successive phosphine substitution. In comparison to the diiron complex [Fe(CO)(μ-edt)], [Fe(CO)(μ-edt)] catalyzes proton reduction at 0.36 V less negative potentials. Electronic structure calculations have been carried out in order to fully elucidate the nature of the oxidation and reduction processes. In all complexes, the HOMO comprises an iron-iron bonding orbital localized between the two iron atoms not ligated by the semibridging carbonyl, while the LUMO is highly delocalized in nature and is antibonding between both pairs of iron atoms but also contains an antibonding dithiolate interaction.
已制备并对混合价态的三铁配合物[Fe(CO)(PPh)(μ - edt)]（ = 0 - 2；edt = SCHCHS）和[Fe(CO)(κ - 二膦)(μ - edt)]（二膦 = dppv、dppe、dppb、dppn）进行了结构表征。所有配合物均采用二硫醇盐桥的排列方式，PPh取代发生在外层铁原子的顶端位置，而二膦配合物在固态和溶液中仅以双基底形式存在。中心铁原子上的羰基是半桥连的，这导致桥连二铁中心之间形成旋转结构。红外光谱研究表明，所有配合物对HBF·EtO的质子化反应呈惰性，但向五羰基配合物中加入酸会导致单电子氧化，生成中等稳定的阳离子[Fe(CO)(PPh)(μ - edt)]和[Fe(CO)(κ - 二膦)(μ - edt)]，这些物种也可通过[CpFe][PF]氧化得到。已对形式上为Fe(I)-Fe(II)-Fe(I)的配合物的电化学性质进行了研究。每个配合物都经历一个准可逆氧化过程，其电位对膦取代敏感，一般在0.15至0.50 V之间，不过[Fe(CO)(PPh)(μ - edt)]在 - 0.05 V时被氧化。所有配合物的还原过程都是不可逆的，并且同样对膦取代敏感，[Fe(CO)(μ - edt)]的还原电位为 - 1.47 V，膦取代配合物的还原电位约为 - 1.7 V。在其一电子还原态下，所有配合物都是将质子还原为氢气的催化剂，连续膦取代后催化过电位会增加。与二铁配合物[Fe(CO)(μ - edt)]相比，[Fe(CO)(μ - edt)]在负电位低0.36 V时催化质子还原。已进行电子结构计算以全面阐明氧化和还原过程的本质。在所有配合物中，最高占据分子轨道（HOMO）包含一个位于未被半桥连羰基配位的两个铁原子之间的铁 - 铁成键轨道，而最低未占据分子轨道（LUMO）本质上高度离域，在两对铁原子之间都是反键的，但也包含一个反键的二硫醇盐相互作用。
