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UBC Theses and Dissertations

Charge transfer in conjugated organometallic materials Zhu, Yongbao

Abstract

This thesis examines factors which influence charge delocalization in conjugated organometallic materials. This delocalization is examined by electrochemical and spectroscopic characterization of model complexes, oligomers and polymers. The complex [c/5-Ru(dppm)₂(CsCFc) ₂]CuI (dppm = Ph₂PCH₂PPh₂, Fc = ferrocenyl) (52) is prepared by the coupling of FcC=CSn(n-Bu)₃ (60) and RuCl₂ (dppm) ₂ in the presence of excess Cul, while frans-Ru(dmpe) ₂ (C=CFc) ₂ (dmpe = Me₂PCH₂CH₂PMe₂) (54) is obtained from RuCl₂ (dmpe) ₂ and 60 using catalytic Cul. Removal of the coordinated Cul from 52 with excess P(OMe)₃ yields trans-Ru(dppm) ₂ (G=CFc) ₂ (53). The mono- and dications of both 52 - 54 and trans,trans,trans-Ru(PBu3) ₂ (CO)(L)(C=CFc) ₂ complexes (L = CO (55); py (56); P(OMe) ₃ (57)) are prepared by oxidation with FcPF6. All the neutral and oxidized species are characterized using UV-Vis-near-IR spectroscopy and cyclic voltammetry (CV). The data are interpreted according to the Hush model of electron transfer, and the results indicate that ruthenium bisacetylide bridges facilitate electronic interactions between the two terminal ferrocenyl groups. Charge delocalization between the Fem and Run centers in the oxidized species is enhanced when the ancillary ligands on the Ru center are electron donors and is lessened when the ligands are acceptors. Complexes trans-Ru(dppm) ₂ (Cl)(C=CR) (62a - c), trans-Ru(dppm) ₂ (GCR) ₂ (63a - c), and Fc-=-R (68a - e), Fc-=-R-=-Fc (69a - e) and R-Fc-R (40, 50 and 73) (R = 1 - 3 linked thiophene rings with various substituents) are prepared to elucidate electronic interactions between the metals and oligothienyl groups. The complexes are all redox-active due to the Ru[sup II/III] and Fe[sup II/III]couples and oligothiophene-based oxidations. The CVs of 62a – c and 63a - c show that the Ru[sup II/III] oxidation process becomes more reversible with an increase in the conjugation length of the oligothienyl group. Complexes 68a - e, 69a - e, 40,50 and 73 all contain a reversible Fe[sup II/III] oxidation wave and an irreversible oligothiophene-based wave. When oxidized past the oligothiophene-based oxidation potential, and by careful exclusion of water, the complexes with terminal bi- and terthienyl groups (50, 62b, 62c, 68c, 68e and 73) electropolymerize or dimerize, resulting in the deposition of an electrochemically active film on the electrode surface. The monocations 62c⁺ and 63c⁺ prepared in solution at -20 °C exhibit intense LMCT absorption bands at 500 - 700 nm and 900 - 1700 nm, indicative of significant charge derealization from the Ru[sup III] to the conjugated oligothienyl group. Electrochemical oxidation of the Fe[sup II] centers in the ferrocene-oligothiophene complexes yields the corresponding monocations and dications, which all have oligothiophene-to-Fe[sup III] charge-transfer transitions in the near-IR region. For each series, the energy and intensity of these low-energy transitions correlate to the difference in the oxidation potentials of the ferrocenyl and oligothienyl groups, showing that charge delocalization in these compounds is enhanced when the conjugated organic group and the metal are close in oxidation potential. The complex trans-RuCi₂(dppm)₂ (19) is converted to its cis isomer (59) at 20 °C in the presence of catalytic CuCl or Cul, and [{cw-RuCi₂(dppm)₂}₂Cu][CuCi₂] (74) is isolated when 19 or 59 reacts with excess CuCl. Addition of a small amount of 74 to a solution of 19 results in isomerization of 19 to 59. Complex 74 can be converted quantitatively to 59 by reaction with excess [(n-Bu)₄N]Cl or HC1 (aq). A mechanism for the catalytic isomerization of 19 to 59 and the formation of 74 is proposed on the base of in situ 3 1P NMR results.

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