Syntheses and Studies of the Linear Tri- and Pentanuclear Ruthenium Complexes
Date Issued
2006
Date
2006
Author(s)
Kuo, Ching-Kuo
DOI
zh-TW
Abstract
The syntheses of oligo-α-pyridylamino ligands and their linear trinuclear and pentanuclear ruthenium complexes are reported. This thesis concerns in three aspects: First, owing to difference of oxidation of trinuclear ruthenium complexes, metal-metal interaction of these complexes are studied carefully. Second, while the axial ligands of triruthenium complex are replaced by redox-active ferrocenyl (Fc) groups, electrochemical results reveal that there is electronic communication within the triruthenium complex. Then, the electronic effect is investigated by varying the axial ligands of triruthenium complexes. The effects of donor/acceptor modifications in electrochemistry are also investigated. Third, the linear pentanuclear ruthenium complex and linear pentanuclear mixed-metal (Ni2+ and Ru2+) complexes have been synthesized and characterized by X-ray analysis.
The results are summarized as follows: The neutral, one-, and two-electron oxidized linear trinuclear ruthenium complexes [Ru3(μ3-dpa)4Cl2](BF4), [Ru3(μ3-dpa)4Cl2](BF4)2, [Ru3(μ3-dpa)4(CN)2], and [Ru3(μ3-dpa)4(CN)2](BF4) (dpa = the anion of dipyridylamine) have been synthesized and characterized by various spectroscopic techniques. Cyclic voltammetric and spectroelectrochemical studies on the neutral and oxidized complexes are reported. These complexes undergo three successive metal centered one electron transfer processes. X-ray structural studies reveal a symmetrical Ru3 unit for these complexes. While the metal–metal bond distances only slightly change, the metal–axial ligand lengths exhibit a significant decrease upon oxidation of the neutral complex. The electronic configuration of Ru3 unit changes as the chloride axial ligands are replaced by the stronger “π-acid” cyanide
axial ligands. Magnetic measurements and 1H NMR spectra indicate that[Ru3(μ3-dpa)4Cl2] and [Ru3(μ3-dpa)4Cl2](BF4)2 are in a spin state of S = 0 and [Ru3(μ3-dpa)4Cl2](BF4), [Ru3(μ3-dpa)4(CN)2], and [Ru3(μ3-dpa)4(CN)2](BF4) in spin states of S = 1/2, 1, and 3/2, respectively. These results are consistent with M.O. calculations. A series of triruthenium complexes with arylacetylide axial ligands
[Ru3(μ3-dpa)4(C2X)2](BF4)y (X = Fc, y = 0 (2A); X = Ph, y = 0 (2B); X = PhOCH3, y = 1 (2C); X = PhC5H11, y = 1 (2D); X = PhCN, y = 0 (2E); X = PhNO2, y = 0 (2F) ) have been synthesized. The crystal structures show that the Ru-Ru bond lengths (2.3304(9)-2.3572(5) Å) of these compounds
are longer than those of [Ru3(μ3-dpa)4Cl2] (Ru-Ru=2.2537(1) Å). This is ascribed to the formation of the stronger π-backbonding from metal to axial ligand weakens the Ru-Ru interactions and a bond order is reduced in the triruthenium unit. Cyclic voltammetry and differential pulse
voltammetry show that compound 2A exhibits electronic coupling between the two ferrocenyl units with ΔE1/2 close to 100 mV. Compounds 2B-2F display three triruthenium-based reversible one-electron redox couples, two oxidations and one reduction, and the electrode potentials shift upon varying substituents. A linear relationship is observed when the Hammett constants are plotted against the redox potentials.
The first linear pentanuclear metal complex with the second-row transition metal, [Ru5(μ5-tpda)4Cl2]+[(Ru2(μ-OAc)4)2Cl3]- (3A) (tpda = the dianion of N,N'-bis(α-pyridyl)-2,6-diaminopyridine), has been synthesized. The linear penta-nuclear mixed-metal complexes with nickel and ruthenium, [Ni3Ru2(μ5-tpda)4(NCS)2] (3B) and [Ni3Ru2(μ5-tpda)4(NCS)2](BF4) (3C), have also been synthesized. In complex 3A, The bond lengths of Ru(1)-Ru(2) and Ru(2)-Ru(3) are 2.2922(8)Å and 2.2832(6)Å, respectively. The bond angles of Ru(1)-Ru(2)-Ru(3) and Ru(2)-Ru(3)-Ru(2A) are 178.77(3)° and 180.00(3)°, respectively. The linear counter anion has been formed owing to the charge balance of the complex and suitable packing size during recrystallization. Complex 3C was obtained by adding suitable oxidizing reagent in complex 3B. According to some identification (IR, electronic
absorption spectrum, electrochemistry, and OTTLE), we can ensure the existence of complex 3C.
Subjects
分子導線
釕
推拉電子
氧化
molecular wire
ruthenium
electron donor/acceptor
oxidation
Type
thesis
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