Metal dithiolenes [M(S2C2R2)n] have been studied for decades because of their interesting chemical and spectroscopic properties, which are related to the unusual electronic properties of the dithiolene ligand. The ligand-based reactivity of metal bisdithiolenes [M(S2C2R2)2] toward alkenes has been proposed for use in alkene purification schemes. According to the proposal, compounds Ni(S2C2R2)2 (R=CF3,CN) react with simple alkenes to form stable S,S-interligand adducts and the alkene can be released from the adduct by reduction. We showed that Ni(S2C2(CF3)2)2 reacts with ethylene and 1-hexene to form, preferentially, S,S-intraligand adducts, which rapidly decompose to inactive metal-containing materials and dihydrodithiins. However, the product selectivity can be significantly modified so that stable S,S-interligand adducts are obtained as dominant products by adding [Ni(S2C2(CF3)2)2]- to Ni(S2C2(CF3)2)2/alkene reaction mixtures. Mechanistic implications are discussed.
Next, the reactions of Pt(S2C2(CF3)2)2 with 2,3-dimethyl-1,3-butadiene are addressed. Prior to our report, only symmetry-allowed S,S-interligand adducts had been observed as products in the reactions between conjugated dienes and metal bisdithiolenes. We discovered a novel mode of diene binding, where two dienes bind to one dithiolene ligand of Pt(S2C2(CF3)2)2, in an C,S-intraligand fashion, forming a new chiral bisthioether ligand.
From bisdithiolenes, the focus shifts to new mixed-ligand molybdenum trisdithiolenes [Mo(S2C2(CF3)2)2(S2C6H4) and Mo(S2C6H4)2(S2C2(CF3)2)]. These complexes rapidly and cleanly bind ethylene, in an S,S-intraligand fashion, as predicted by MO arguments. The resulting intraligand adducts are sufficiently stable to be characterized, in contrast to the nickel bisdithiolene case. The metal-chelated dihydrobenzodithiin, formed upon ethylene addition, can be substituted with a variety of donor ligands, allowing access to new types of molybdenum dithiolenes. We have recently extended these studies to catalytic reactions: Mo(S2C2(CF3)2)2(S2C6H4) was used as a catalyst to form dihydrobenzodithiins from (S2C6H4)2 and a variety of alkenes, in the first example of dithiolene-based reactivity being exploited for carbon-heteroatom bond-forming catalysis.
Finally, the synthesis, characterization and redox reactivity of a new Fe2Ni bis-double-decker complex is described, demonstrating for the first time a sandwich complex of a metal bisdithiolene with both NiS2C2 rings in an η5 π-donating mode. For the radical cation, experimental and computation evidence indicates that the lone electron is delocalized over the entire molecule.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/24350 |
| Date | 21 April 2010 |
| Creators | Harrison, Daniel |
| Contributors | Fekl, Ulrich |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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