Ligand effects on bioinspired iron complexes /
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| Other Authors: | |
| Format: | Thesis eBook |
| Language: | English |
| Published: |
[College Station, Tex.] :
[Texas A&M University],
[2005]
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| Subjects: | |
| Online Access: | Link to OAK Trust copy |
| Abstract: | The synthesis of diiron thiolate complexes was carried out using two ligands that were expected to furnish improved catalytic activity, solubility in water, and stability to the metal complexes. The water-soluble phosphine 1,3,5-triaza-7-phosphaadamantane, PTA, coordinates to the Fe centers forming the disubstitutedcomplex ([mu]-pdt)[Fe(CO)₂PTA]₂, which presents one PTA in each iron in a transoid arrangement. Substitution of one CO ligand in the ([mu]-pdt)[Fe(CO)₃]₂ parent complex forms the asymmetric ([mu]-pdt)[Fe(CO)₃][Fe(CO)₂PTA]. Enhanced water solubility was achieved through reactions with electrophiles, H⁺ and CH₃⁺, which reacted with the N on the PTA ligand forming the protonated and methylated derivatives, respectively.The 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), IMes, was reacted with([mu]-pdt)[Fe(CO)₃]₂ yielding the asymmetric ([mu]-pdt)[Fe(CO)₃][Fe(CO)₂IMes], an electron rich, air stable complex that does not show reactivity with H⁺. Electrocatalytic production of hydrogen was studied for the all-CO, bis-PMe₃,mono- and di-PTA Fe¹Fe¹ complexes, as well as the PTA-protonated and -methylated derivatives. The all-CO species produce H₂, in the presence of the weak HOAc, at their second reduction event, Fe¹Fe⁰ [to] Fe⁰Fe⁰, that occurs at ca. -1.9 V, through an EECC mechanism. The mono- and di-substituted phosphine complexes present electrocatalytic production of H₂ from the Fe⁰Fe¹ redox state; this reduction takes placeat -1.54 V for ([mu]-pdt)[Fe(CO)₃][Fe(CO)₂PTA], and at ca. -1.8 for the disubstituted PMe₃ and PTA derivatives. A positive charge on the starting complex does not have an effect on the production of H₂. It was found that the protonated and methylated derivatives are not the catalytic species for H₂ production. At their first reduction event the neutral precursor forms, and catalysis occurs from the Fe¹Fe¹ complex in all cases.The possibility of enhanced catalytic activity in the presence of H₂O was explored by conducting electrochemical experiments in the mixed CH₃CN:H₂O solvent system for the PTA-substituted complexes. The reduction potential of the catalytic peak is shifted to more positive values by the presence of H₂O. The cyclic voltammogram of {([mu]-pdt)[Fe(CO)₂(PTA· H)]₂}²⁺ in CH₃CN:H₂O 3:1 shows the reduction of a more easily reduced species in the return scan. This curve-crossing event provides evidence for the ([eta]²-H₂)Fe¹¹ intermediate proposed in the ECCE mechanism. |
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| Item Description: | "Major Subject: Chemistry" Title from author supplied metadata (automated record created on Nov. , 09:45:50.) Vita. Abstract. Electronic resource. |
| Format: | Mode of access: World Wide Web. System requirements: World Wide Web access and Adobe Acrobat Reader. |
| Bibliography: | Includes bibliographical references. |