Research on the one-electron reduced analogue of NO, namely nitroxyl (HNO/NO–), has revealed distinguishing properties regarding its utility as a therapeutic. However, the fleeting nature of HNO requires the design of donor molecules. Metal nitrosyl (MNO) complexes could serve as potential HNO donors. The synthesis, spectroscopic/structural characterization, and HNO donor properties of a {CoNO}8 complex in a pyrrole/imine ligand frame are reported. The {CoNO}8 complex [Co(LN4PhCl)(NO)] (1) does not react with established HNO targets such as FeIII hemes or Ph3P. However, in the presence of stoichiometric H+1 behaves as an HNO donor. Complex 1 readily reacts with [Fe(TPP)Cl] or Ph3P to afford the {FeNO}7 porphyrin or Ph3P=O/Ph3P=NH, respectively. In the absence of an HNO target, the {Co(NO)2}10 dinitrosyl (3) is the end product. Complex 1 also reacts with O2 to yield the corresponding CoIII-η1-ONO2 (2) nitrato analogue. This report is the first to suggest an HNO donor role for {CoNO}8 with biotargets such as FeIII-porphyrins.

The reactivity of free NO (NO(+), NO(•), and NO(-)) with thiols (RSH) is relatively well understood, and the oxidation state of the NO moiety generally determines the outcome of the reaction. However, NO/RSH interactions are often mediated at metal centers, and the fate of these species when bound to a first-row transition metal (e.g., Fe, Co) deserves further investigation. Some metal-bound NO moieties (particularly NO(+), yielding S-nitrosothiols) have been more thoroughly studied, yet the fate of these species remains highly condition-dependent and, for M-NO(-), an unexplored field. Herein, we present an overview of thiol reactions with metal nitrosyls that result in N-O bond activation, ligand substitution on {MNO} fragments, and/or redox chemistry. We also present our results pertaining to the thiol reactivity of nonheme {FeNO}(7/8) complexes [Fe(LN4(pr))(NO)](-/0) (1 and 2) and the noncorrin {CoNO}(8) complex [Co(LN4(pr))(NO)] (3), an isoelectronic analogue of the {FeNO}(8) complex 1. Among other products, the reaction of 1 with p-ClPhSH affords [Fe2(μ-SPh-p-Cl)2(NO)4](-) (anion of 6), a reduced Roussin's red ester (rRRE), which was characterized by Fourier transform infrared (FTIR), UV-vis, electron paramagnetic resonance (EPR), and X-ray diffraction. Similarly, the reaction of 1 with glutathione in buffer affords the corresponding rRRE, which has also been spectroscopically characterized by EPR and UV-vis. The oxidation states of the metals and nitrosyls both contribute to the complex nature of these interactions, and as such, we discuss the varying product distribution accordingly. These studies shed insight into the products that may form through MNO/RSH interactions that lead to NOx activation and {MNO} redox.

In an effort to discover potential alternatives to the anti-cancer drug cisplatin, the synthesis of gold(III) polypyridyl coordination complexes was pursued. Specifically, this report describes the synthesis and characterization of a series of 2,9-dialkyl-1,10-phenanthroline (Rphen) gold(III) coordination complexes (R = n-butyl, sec-butyl, and tert-butyl). Due to the steric hindrance imparted by the alkyl substituents, these ligands do not react with HAuCl4 to form square-planar gold(III) dichloride complex ions, as is the case with 1,10-phenanthroline, but instead form salts comprised of [AuCl(4)](-) anions and protonated 2,9-dialkylphenanthroline cations (compounds 1 and 2). In an effort to facilitate direct binding between the substituted phenanthroline and the gold(iii) metal center, reactions were carried out between the ligand and NaAuCl4 in the presence of a Ag(I) salt. The precipitation of one equivalent of AgCl afforded the formation of neutral, distorted square-pyramidal gold(iii) trichloride complexes (compounds 3 and 4). Primary or secondary substitutions at the alpha carbon of the alkyl substituent allow direct metal-ligand coordination, whereas a tertiary substituent inhibits chelation and results only in the formation of a salt comprised of a protonated phenanthroline cation and a [AuCl2]- anion (compound 5). Compounds 1-4 have been characterized by 1H NMR, UV/vis, IR spectroscopy, and X-ray crystallography.

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