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.

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.

<p dir="ltr">The use of redox non-innocent ligands to imbue third-row transition metal complexes with properties emulating those of their fourth- and fifth-row congeners has become an attractive strategy to overcome the limited resources and environmental implications associated with the latter class of metals. The tetra-imine macrocycle, TIM (2,3,9,10-tetramethyl-1,4,8,11-tetraza-cyclotetradeca-1,3,8,10-tetraene), which bears two sets of potentially redox-active α-diimine units, therefore, has been targeted as the ligand scaffold to investigate the structural and electronic properties of various organocobalt(III) complexes within this work.</p><p dir="ltr">First, the reaction between <i>trans</i>-[Co(TIM)Cl₂]⁺ and terminal alkynes (HC₂Ar), in the presence of triethylamine, yielded a series of mono- and bis-alkynyl Co^III(TIM) complexes, as discussed in Chapters 1 and 2. Interestingly, the use of electron-rich terminal alkynes (HC₂Y) favors the formation of products featuring a 1-aza-2-cobalt-cyclobutene unit. As detailed in Chapter 3, the <i>trans</i>-[Co(TIM')(HC=C)Y)Cl]⁺-type complexes (TIM' = the resulting derivative of TIM) were prepared through the addition of HC₂Y to <i>trans</i>-[Co(TIM)Cl₂]⁺ in the presence of KOH. The unprecedented involvement of the TIM ligand was verified crystallographically and through ¹H NMR and FT-IR spectroscopies. In Chapter 4, the properties and influences of the aza-cobalt-cyclobutene are further explored through UV-vis spectroelectrochemical studies on the constitutional isomers, <i>trans</i>-[Co(TIM)(C₂Fc)Cl]⁺ and <i>trans</i>-[Co(TIM')((HC=C)Fc)Cl]⁺ (Fc = ferrocene). Moreover, the reactivity of the Co^III center in the latter complexes is investigated via the reaction with KCN and AgOTf in CH₃CN.</p><p dir="ltr">In Chapter 5, a new facet of Co^III(TIM) reactivity is revealed through the reaction between <i>trans</i>-[Co(TIM)Cl₂]⁺ and HC₂Ar, in the presence of NaBH₄. The reaction generates both mono- and bis-alkenyl complexes along with products containing a 1-aza-2-cobalt-cyclopropane unit. The formation of the former class of products is postulated to proceed through a transient H-Co^III(TIM) intermediate, while the latter is believed to be accessed upon the reduction of an imine moiety within the TIM ligand. Moreover, the generation of the three-membered ring showcases another example of the non-innocent nature of the TIM ligand.</p>