Properties and Behavior of Tricarbonyl Manganese Scorpionate Complexes

Manganese tricarbonyl complexes have widely been studied for their ability to release carbon monoxide (CO) in the presence of light for potential applications in cancer therapy and in catalysis. Most studies focus on the kinetics and quantity of CO release and the overall impact on cell death. Far fewer studies identify the manganese intermediates and final products after decarbonylation. Identification of such products would be critical to improving reactivity and understanding potential (undesirable) side effects in future applications employing these CO releasing molecules (CORMs). Recently, nitrogen confused C-scorpionate ligands were introduced by the Gardinier group where a pyrazolyl ring is bound to the central methine by a ring carbon atom rather than the prototypical ring nitrogen. These new C-scorpionates offer desirable versatility into scorpionate ligand designs, allowing unprecedented control over ligand sterics, electronics, and even potential increases in either denticity or the number of metals ligands can bind (nuclearity). In this thesis the syntheses of a new nitrogen-confused C-scorpionate, PhL*, with two 3,5-dimethylpyrazolyl and an N-phenylpyrazolyl donor attached to a methine CH group is described. An improved synthesis of the dinucleating analogue, pz6L*, containing two similar C-scorpionate centers connected via a meta-phenylene linkage is also documented. Two known tetradentate C-scorpionates, L1 and L2, that have either a di(pyrazolyl)methyl (for L1) or bis(3,5-dimethylpyrazolyl)methyl (for L2) group bound to the 3-position of an N-(2-pyridylmethyl-)pyrazolyl moiety were also prepared. The coordination of these four C-scorpionae ligands to tricarbonylmanganese(I) trifluoromethanesulfonate (OTf) and subsequent decarbonylation chemistry was probed in attempts to isolate and characterize any mono- or dinuclear intermediates and to identify the manganese products. This latter pursuit required an investigation into the coordination chemistry of the ligands with manganese(II) trifluoromethanesulfonate. Despite the significant steric bulk of PhL* and pz6L*, homoleptic [Mn(PhL*)2](OTf)2 or [Mn2(u-pz6L*)2](OTf)2 were the ultimate products of decarbonylation. Half sandwich complexes of the type [LMn(solvent)3]n+ (n = 1, 2) could not be isolated for the tridentate ligands. However, the use of tetradentate ligands afforded both homoleptic and heterleptic species, the latter being stabilized by k4- coordination. Chemical decarbonylation with Me3NO permitted, for the first time, isolation and characterization of cis- dicarbonylmanganese(I) complexes