Synthesis and Reactivity of Electroactive Carbon Sulfide Ligands and Studies on Modifications of Nucleic Acids

Date of Award

2001

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Institution Granting Degree

University of Illinois at Urbana-Champaign

Cedarville University School or Department

Science and Mathematics

First Advisor

Thomas B. Rauchfuss

Keywords

Pure sciences, electroactive, carbon sulfide, ligands, nucleic acids, tetrathiooxalate

Abstract

The beginning of the thesis focuses on the synthesis and interconversion of two anionic carbon sulfide ligands, namely C2 S4 2- (tetrathiooxalate, TTO) and C4 S6 2- . The synthesis of TTO was accomplished by using a modified electrochemical apparatus and a new method for purification. A reliable route to analytically pure C4 S62- was accomplished by a two-step synthesis involving oxidation of TTO. Electrochemical studies of both free ligandsdemonstrate similarities between the two species.

The reaction of TTO and C4 S62- with metal carbonyls was investigated. Some limitations of TTO as a ligand were discovered. Reaction of W(S2 C2 Ph2 ) 2 (CO)2 with TTO gave an electrochemically active ditungsten species, and reaction with C4 S62- showed degradation of C4 S62- into C2 S4n- .

Synthesis of TTO complexes of transition metals was accomplished by using (Cp*MCl2 )2 , M = Rh and Ir, to give Cp*2 M 2 Cl2 (μ-C2 S4 ) complexes. The non-innocent redox nature of C2 S42- within these metal complexes was monitored structurally; specifically, the reduction of M2 C2 S42- to M2 C2 S44- was observed and characterized. This was the first system to show the conversion of a TTO-complex to an ethylenetetrathiolate complex. The analogous complex Cp*2 Rh2 Cl2 (μ-C 4 S6 ) was also synthesized.

Cp*2 Rh2 (μ-C2 S4 ) was used as a building block to create larger ensembles with new bonding modes of C 2 S4 . The electrochemical behavior of Cp*2 Rh 2 (μ-C2 S4 ) led to the discovery of a tetrarhodium species, [Cp*4 Rh4 (C2 S4 )2]2+ . The ability of the bridging C2 S 44- to donate electrons was probed by reaction of Cp*2 Rh2 (μ-C2 S4 ) with [Cp*Ru(NCCH 3 )3 ]+ and [Cp*Rh(NCCH3 )3 ] 2+ to give [Cp*3 Rh2 Ru(C2 S4 )] + and [Cp*6 Rh6 (C2 S4 ) 2 ]4+ , respectively.

Finally, a separate study into the selective selenization of nucleic acid oligonucleotides was pursued. By using the soluble Se-transfer agent (i -PrC5 H4 )2 TiSe5 in a new method with solid-phase phosphoramidite oligonucleotidesynthesis, a mono-, di-, tri-, and tridecanucleotide of DNA with one phosphoroselenoate modification as well as a dinucleotide of RNA modified with one phosphoroselenoate were synthesized. The utility of phosphate backbone modifications in nucleic acid chemistry has been pursued for phosphorothioates and may now be studied for selenium analogues.

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