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An analogue of the mitochondrial calcium uniporter (MCU) inhibitor Ru265 containing axial ferrocenecarboxylate ligands is reported. This new complex exhibits enhanced cellular uptake compared to the parent compound Ru265.

A new method to tune solubility of ZrMOPs via node-modification.

Camphorsultam-based lithium enolates referred to colloquially as Oppolzer enolates are examined spectroscopically, crystallographically, kinetically, and computationally to ascertain the mechanism of alkylation and the origin of the stereoselectivity. Solvent- and substrate-dependent structures include tetramers for alkyl-substituted enolates in toluene, unsymmetric dimers for aryl-substituted enolates in toluene, substrate-independent symmetric dimers in THF and THF/toluene mixtures, HMPA-bridged trisolvated dimers at low HMPA concentrations, and disolvated monomers for the aryl-substituted enolates at elevated HMPA concentrations. Extensive analyses of the stereochemistry of aggregation are included. Rate studies for reaction with allyl bromide implicate an HMPA-solvated ion pair with a (+)Li(HMPA)(4) counterion. Dependencies on toluene and THF are attributed to exclusively secondary shell (medium) effects. Aided by density functional theory (DFT) computations, a stereochemical model is presented in which neither chelates nor the lithium gegenion serve roles. The stereoselectivity stems from the chirality within the sultam ring and not the camphor skeletal core.

SCS pincer ligands have an interesting combination of strong-field and weak-field donors, a coordination environment that is also present in the nitrogenase active site. Here, we explore the electronic structures of iron(II) and iron(III) complexes with such a pincer ligand, bearing a monodentate phosphine, thiolate S donor, amide N donor, ammonia, or CO. The ligand scaffold features a proton-responsive thioamide site, and the protonation state of the ligand greatly influences the reduction potential of iron in the phosphine complex. The N–H bond dissociation free energy, derived from a square scheme, is 56 ± 2 kcal/mol. EPR spectroscopy and SQUID magnetometry measurements show that the iron(III) complexes with S and N as the fourth donors have an intermediate spin (S = 3/2) ground state with large zero field splitting, and X-ray absorption spectra show high Fe–S covalency. The Mössbauer spectrum changes drastically with the position of a nearby alkali metal cation in the iron(III) amido complex, and DFT calculations explain this phenomenon through a change between having the doubly-occupied orbital as d(z)2 or d(yz), as the former is more influenced by the nearby positive charge.

The quest for homoleptic Cr TEMPO species has led to the preparation of pseudo-pentagonal planar (η2-TEMPO)2CrX (X = Cl, TEMPO), with perturbations from TEMPO(−) lone pairs at roughly 0°, 90°, 135°, 225° and 270°.

We examine the effects of fusing two benzofurans to s-indacene (indacenodibenzofurans, IDBFs) and dicyclopenta[b,g]naphthalene (indenoindenodibenzofurans, IIDBFs) to control the strong antiaromaticity and diradical character of these core units. Synthesis via 3-functionalized benzofuran yields syn-IDBF and syn-IIDBF. syn-IDBF possesses a high degree of paratropicity, exceeding that of the parent hydrocarbon, which in turn results in strong diradical character for syn-IIDBF. In the case of the anti-isomers, synthesized via 2-substituted benzofurans, these effects are decreased; however, both derivatives undergo an unexpected ring-opening reaction during the final dearomatization step. All the results are compared to the benzothiophene-fused analogues and show that the increased electronegativity of oxygen in the syn-fused derivatives leads to enhancement of the antiaromatic core causing greater paratropicity. For syn-IIDBF increased diradical character results from rearomati-zation of the core naphthalene unit in order to relieve this paratropicity.

The mitochondrial calcium uniporter (MCU) is a transmembrane protein that resides on the inner membrane of the mitochondria and mediates calcium uptake into this organelle. Given the critical role of mitochondrial calcium trafficking in cellular function, inhibitors of this channel have arisen as tools for studying the biological relevance of this process and as potential therapeutic agents. In this study, four new analogues of the previously reported Ru-based MCU inhibitor [ClRu(NH

Aldehyde and ketone hydrosilylation turnover frequencies of up to 330 s−1 have been achieved using a phosphine-substituted aryl diimine cobalt catalyst.

The complex [MnCl

Dinuclear manganese hydride complexes of the form [Mn

Herein, we report a bulky variant of a bis-benzimidazole carboxylate ligand. The five-position of the benzimidazole groups were substituted with tertiary butyl groups with the intention of preventing bis-ligation and oligomerization, as was observed in other studies using similar ligands. Unfortunately, even with the bulkier substituents, the new ligand still formed a bis-ligated structure. Although the new ligand did not afford the desired mono-ligated species under the conditions studied here, the preparation of the new ligand and coordination compounds provides an added design principle in the ongoing efforts of preparing structurally faithful 2-histidine-1-carboxylate model ligands in biomimetic chemistry.

Advances in radical-based catalytic reactions have created a demand for understanding their mechanistic underpinnings. Here, we present the isolation, structural elucidation, and theoretical analysis of a catalytically relevant charge-transfer species formed between the azidyl radical and (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO). The unusual bond angles and pancake bonding between these two fragments highlight the weak bonding interactions present in this complex. This X-ray structure validates computational predictions as well as mechanistic proposals of TEMPO-mediated radical azidation reactions.

The preparation of a series of dibenzo- and tetrabenzo-fused fluoreno[3,2-b]fluorenes is disclosed, and the diradicaloid properties of these molecules are compared with those of a similar, previously reported series of anthracene-based diradicaloids. Insights on the diradical mode of delocalization tuning by constitutional isomerism of the external naphthalenes has been explored by means of the physical approach (dissection of the electronic properties in terms of electronic repulsion and transfer integral) of diradicals. This study has also been extended to the redox species of the two series of compounds and found that the radical cations have the same stabilization mode by delocalization that the neutral diradicals while the radical anions, contrarily, are stabilized by aromatization of the central core. The synthesis of the fluorenofluorene series and their characterization by electronic absorption and vibrational Raman spectroscopies, X-ray diffraction, SQUID measurements, electrochemistry, in situ UV-vis-NIR absorption spectroelectrochemistry, and theoretical calculations are presented. This work attempts to unify the properties of different series of diradicaloids in a common argument as well as the properties of the carbocations and carbanions derived from them.

Poly(pivalolactone) (PPVL) is a crystalline polyester with attractive physical and mechanical properties; however, prohibitively expensive syntheses of pivalolactone have thwarted efforts to produc...

Ru-PNN pincer catalysts of the general form [{PNN}Ru(H)(Cl)(CO)] can dehydrogenate alcohols through inner- and outer-sphere mechanisms, but determining the favored path is challenging. To address t...

High-energy resolution fluorescence-detected Cu K-edge X-ray absorption spectroscopy (XAS) and single-crystal polarized XAS data are presented toward refining the assignments of bands assigned as excitations from Cu 1s to ligand-localized molecular orbitals. These have been previously dubbed "XAS-metal-ligand charge transfer" (XAS-MLCT) bands. Data are presented for a series of [Cu(xbpy)2]n+ complexes (xbpy = 2,2'-bipyridine (1n+), 4,4'-bisamino-2,2'-bipyridine (2n+), and 4,4'-dimethoxy-2,2'-bipyridine (3n+); n = 1 and 2). Dipolar dependencies of these "XAS-MLCT" bands in both Cu1+ and Cu2+ species lead to reassignment of these features as owing their intensities primarily to Cu 1s → Cu 4p excitations. The transition densities are Cu-localized, highlighting that XAS-MLCT features in Cu XAS spectra are not "charge transfer" transitions but rather quasi-atomic transitions. Although scrutiny of the acceptor orbitals supports assignment as Cu 1s → ligand π* transitions, it ultimately appears that while the ligand orbital energetics govern the positions of these bands the intensity is conferred through a small degree of metal 4p mixing into otherwise ligand-dominated acceptor molecular orbitals.

Lanthanides (Ln(3+)) are critical materials used for many important applications, often in the form of coordination compounds. Tuning the thermodynamic stability of these compounds is a general concern, which is not readily achieved due to the similar coordination chemistry of lanthanides. Herein, we report two 18-membered macrocyclic ligands called macrodipa and macrotripa that show for the first time a dual selectivity towards both the light, large Ln(3+) ions and the heavy, small Ln(3+) ions, as determined by potentiometric titrations. The lanthanide complexes of these ligands were investigated by NMR spectroscopy and X-ray crystallography, revealing the occurrence of a significant conformational toggle between a 10-coordinate Conformation A and an 8-coordinate Conformation B that accommodates Ln(3+) ions of different sizes. The origin of this selectivity pattern was further supported by density functional theory (DFT) calculations, which show the complementary effects of ligand strain energy and metal-ligand binding energy that contribute to this conformational switch. This work demonstrates how novel ligand design strategies can be applied to tune the selectivity pattern for the Ln(3+) ions.

The ability to alter optoelectronic and magnetic properties of molecules at a late stage in their preparation is in general a nontrivial feat. Here, we report the late-stage oxidation of benzothiop...

The synthesis of 1,2-dihydroquinolines by the hydrazine-catalyzed ring-closing carbonyl-olefin metathesis (RCCOM) of N-prenylated 2-aminobenzaldehydes is reported. Substrates with a variety of substitution patterns are shown. With an acid-labile protecting group on the nitrogen atom, in situ deprotection and autoxidation furnish quinoline. In comparison with related oxygen-containing substrates, the cycloaddition step of the catalytic cycle is shown to be slower, but the cycloreversion is found to be more facile.

Structural, spectroscopic, and reactivity studies are presented for an electron transfer series of copper hydroxide complexes supported by a tridentate redox-active ligand. Single crystal X-ray crystallography shows that the mononuclear [CuOH](1+) core is stabilized via intramolecular H-bonds between the H-donors of the ligand and the hydroxide anion when the ligand is in its trianionic form. This complex undergoes two reversible oxidation processes that produce two metastable “high-valent” CuOH species, which can be generated by addition of stoichiometric amounts of 1e(−) oxidants. These CuOH species are characterized by an array of spectroscopic techniques including UV–vis absorption, electron paramagnetic resonance (EPR), and X-ray absorption spectroscopies (XAS), which together indicate that all redox couples are ligand-localized. The reactivity of the complexes in their higher oxidation states toward substrates with modest O─H bond dissociation energies (e.g., 4-substitued-2,6-di-tert-butylphenols) indicates that these complexes act as 2H(+)/2e(−) oxidants, differing from the 1H(+)/1e(−) reactivity of well-studied [CuOH](2+) systems.

This work details the synthesis, characterization, and catalytic activity of reactive low-coordinate organozinc complexes. The complexes activate hydrogen and they appear to be more active in hydrogenation of ketones and imines than their tridentate pincer analogs. This is thought, in part, to be due to the lack of trailing third phosphorus arm present in previous work. DFT computations reveal a sigma-bond metathesis mechanism is comparable to an alternative aromatization/dearomatization metal-ligand cooperative mechanism.

Inclusion of a second nitrogen atom in the aromatic core of phosphorus-nitrogen (PN) heterocycles results in unexpected tautomerization to a nonaromatic form. This tautomerization, initially observed in the solid state through X-ray crystallography, is also explained by computational analysis. We prepared an electron deficient analogue (2 e) with a fluorine on the pyridine ring and showed that the weakly basic pyridine resisted tautomerization, providing key insights to why the transformation occurs. To study the difference in solution vs. solid-state heterocycles, alkylated analogues that lock in the quinoidal tautomer were synthesized and their different

Mn complexes with amino acid derived PN ligands were used in the catalytic transfer hydrogenation (TH) of ketone and chalcone substrates in 2-propanol with mild heating. Moreover, chalcones are red...

The activation of dioxygen by Fe(II)(Me(3)TACN)(S(2)SiMe(2)) (1) is reported. Reaction of 1 with O(2) at −135 °C in 2-MeTHF generates a thiolate-ligated (peroxo)diiron complex Fe(III)(2)(O(2))(Me(3)TACN)(2)(S(2)SiMe(2))(2) (2) that was characterized by UV–vis (λ(max) = 300, 390, 530, 723 nm), Mössbauer (δ = 0.53, |ΔE(Q)| = 0.76 mm s(−1)), resonance Raman (RR) (ν(O–O) = 849 cm(−1)), and X-ray absorption (XAS) spectroscopies. Complex 2 is distinct from the outer-sphere oxidation product 1(ox) (UV–vis (λ(max) = 435, 520, 600 nm), Mössbauer (δ = 0.45, ΔE(Q) = 3.6 mm s(−1)), and EPR (S = 5/2, g = [6.38, 5.53, 1.99])), obtained by one-electron oxidation of 1. Cleavage of the peroxo O–O bond can be initiated either photochemically or thermally to produce a new species assigned as an Fe(IV)(O) complex, Fe(IV)(O)(Me(3)TACN)(S(2)SiMe(2)) (3), which was identified by UV–vis (λ(max) = 385, 460, 890 nm), Mössbauer (δ = 0.21, |ΔE(Q)| = 1.57 mm s(−1)), RR (ν(Fe(IV)=O) = 735 cm(−1)), and X-ray absorption spectroscopies, as well as reactivity patterns. Reaction of 3 at low temperature with H atom donors gives a new species, Fe(III)(OH)(Me(3)TACN)(S(2)SiMe(2)) (4). Complex 4 was independently synthesized from 1 by the stoichiometric addition of a one-electron oxidant and a hydroxide source. This work provides a rare example of dioxygen activation at a mononuclear nonheme iron(II) complex that produces both Fe(III)–O–O–Fe(III) and Fe(IV)(O) species in the same reaction with O(2). It also demonstrates the feasibility of forming Fe/O(2) intermediates with strongly donating sulfur ligands while avoiding immediate sulfur oxidation.

Pseudoephedrine-derived dianionic Myers enolates were generated using sodium diisopropylamide (NaDA) in THF solution. The reactivities and selectivities of the disodium salts largely mirror those of the dilithium salts but without the requisite large excesses of inorganic salts (LiCl) or mandated dilute solutions. The disodium salts require careful control of temperature to preclude deleterious aggregate aging effects traced to changes in the aggregate structure and intervening O-alkylations. Structural studies and density functional theory (DFT) computations show a dominant highly symmetric polyhedron quite different from the lithium analogue. No enolate-NaDA mixed aggregates are observed with excess NaDA. Rate studies show an alkylation mechanism involving an intervening tetramer-monomer pre-equilibrium followed by rate-limiting alkylation of tetrasolvated monomers. DFT computations were conducted to explore the possible influences on stereochemistry. A crystal deriving from samples aged at ambient temperature contains six dianionic subunits and two monoanionic (alkoxide-only) subunits. A new preparation of concentrated solutions of NaDA in THF solution is described.

The synthesis and reactivity of a new trimetallic complex Ti(NP)4Ni2 (NP = 2-diphenylphosphinopyrrolide) (3) is reported. Single-crystal X-ray diffraction and X-ray absorption studies point to a un...

Alkaline anion exchange membranes (AAEMs) are an important component of alkaline exchange membrane fuel cells (AEMFCs), which facilitate the efficient conversion of fuels to electricity using nonplatinum electrode catalysts. However, low hydroxide conductivity and poor long-term alkaline stability of AAEMs are the major limitations for the widespread application of AEMFCs. In this paper, we report the synthesis of highly conductive and chemically stable AAEMs from the living polymerization of trans -cyclooctenes. A trans -cyclooctene–fused imidazolium monomer was designed and synthesized on gram scale. Using these highly ring-strained monomers, we produced a range of block and random copolymers. Surprisingly, AAEMs made from the random copolymer exhibited much higher conductivities than their block copolymer analogs. Investigation by transmission electron microscopy showed that the block copolymers had a disordered microphase segregation which likely impeded ion conduction. A cross-linked random copolymer demonstrated a high level of hydroxide conductivity (134 mS/cm at 80 °C). More importantly, the membranes exhibited excellent chemical stability due to the incorporation of highly alkaline-stable multisubstituted imidazolium cations. No chemical degradation was detected by 1 H NMR spectroscopy when the polymers were treated with 2 M KOH in CD 3 OH at 80 °C for 30 d.

This report details the synthesis and characterization of six new Mn(II) complexes coordinated to systematically varied 2,2',2''-nitrilotris(N-arylacetamidate) ligands (LR; R = NO2, Cl, Br, H, Me, and OMe). The complexes are synthesized as the di-tetramethylammonium salts [Me4N]2[MnLR(OAc)]. The nitro variant MnNO2 afforded crystals suitable for X-ray diffraction and its molecular structure is reported. We previously reported the crystal structures of FeNO2 and ZnNO2 and additionally report herein the synthesis and characterization of CoNO2. Using these four molecules, we conduct a brief comparison of the bond metrics to demonstrate that the primary difference governing structural changes is likely due to ionic crystal radii changes rather than electronic properties. The electrochemical properties of the MnR complexes were additionally explored with cyclic voltammetry, which revealed that the series is modulated by the various electronic substituents on the aryl groups of the ligands. The electrochemical studies also revealed, consistent with our previous report, that the acetate ligand on the MnR complexes is labile. Finally, a Hammett plot was constructed using the potentials obtained from cyclic voltammetry, which is compared with a few other similar transition metal complexes.

We report the first examples of the carbide ligand in (Cy3P)2Cl2Ru≡C (RuC) developing into a μ3 ligand toward metal centers. Conventionally, sterics exclude this coordination mode, but Fe2(CO)9 and Co2(CO)8 expel bridging CO ligands upon reaction with RuC to form trimetallic (Cy3P)2Cl2Ru═CFe2(CO)8 (RuCFe2) and (Cy3P)2Cl2Ru═CCo2(CO)7 (RuCCo2) complexes. Thus, the proximity offered by metal–metal associations in bimetallic carbonyl complexes allows the formation of trinuclear carbide complexes as verified by NMR, Mossbauer, and X-ray spectroscopic techniques.

The structures and reactivities of pseudoephedrine-derived dianionic Myers enolates are examined. A combination of NMR and IR spectroscopic, crystallographic, and computational data reveal that the homoaggregated dianions form octalithiated tetramers displaying S(4)-symmetric Li(8)O(8) cores and overall C(2) symmetry. Computational and isotopic labeling studies reveal strong N–Li contacts in the carboxamide enolate moiety. The method of continuous variations proves deceptive, as octalithiated tetrameric homoaggregates afford hexalithiated trimeric heteroaggregates. A lithium diisopropylamide–lithium enolate mixed aggregate is found to be a C(2)-symmetric hexalithiated species incorporating two enolate dianions and two lithium diisopropylamide (LDA) subunits. Structural and rate studies show that lithium chloride has little effect on the dynamics of the enolate homoaggregates but forms adducts of unknown structure. Rate studies of alkylations indicate that the aging of the aggregates can have effects spanning orders of magnitude. The LiCl–enolate adduct dramatically accelerates the reaction but requires superstoichiometric quantities owing to putative autoinhibition. Efforts and progress toward eliminating the requisite large excess of LiCl are discussed.

A new nonheme iron(II) complex, Fe(II)(Me(3)TACN)((OSi(Ph2))(2)O) (1), is reported. Reaction of 1 with NO((g)) gives a stable mononitrosyl complex Fe(NO)(Me(3)TACN)((OSi(Ph2))(2)O) (2), which was characterized by Mössbauer (δ = 0.52 mm s(−1), |ΔE(Q)| = 0.80 mm s(−1)), EPR (S = 3/2), resonance Raman (RR) and Fe K-edge X-ray absorption spectroscopies. The data show that 2 is an {FeNO}(7) complex with an S = 3/2 spin ground state. The RR spectrum (λ(exc) = 458 nm) of 2 combined with isotopic labeling ((15)N, (18)O) reveals ν(N-O) = 1680 cm(−1), which is highly activated, and is a nearly identical match to that seen for the reactive mononitrosyl intermediate in the nonheme iron enzyme FDPnor (ν(NO) = 1681 cm(−1)). Complex 2 reacts rapidly with H(2)O in THF to produce the N-N coupled product N(2)O, providing the first example of a mononuclear nonheme iron complex that is capable of converting NO to N(2)O in the absence of an exogenous reductant.

A permanently porous, three-dimensional metal–organic material formed from zero-valent metal nodes is presented. Combination of ditopic m-terphenyl diisocyanide, [CNArMes2]2, and the d10 Ni(0) precursor Ni(COD)2, produces a porous metal–organic material featuring tetrahedral [Ni(CNArMes2)4]n structural sites. X-ray absorption spectroscopy provides firm evidence for the presence of Ni(0) centers, whereas gas-sorption and thermogravimetric analysis reveal the characteristics of a robust network with a microdomain N2-adsorption profile.

Several C,X-chelate complexes of iron were generated via standard metathetical procedures. Treatment of FeCl2 and LnFeCl2 (L = Me2IPr, n = 1; PMe3, n = 2) with anionic equivalents o-LiCH2C6H4NMe2, o-LiCH2C6H4PPh2, and LiCH2PMe2 led to the preparation of [Fe(o-CH2C6H4NMe2)]2(κ-μ-CH2,N-o-CH2C6H4NMe2)2 (1, X-ray), [fac-Fe(κ-C,P-o-CH2C6H4PPh2)3][Li(TMEDA)2] (2, X-ray), (Me2IPr)Fe(CH2C6H4-o-NMe2)2 (3-C,N), [(Me2IPr)2Fe](μ-κ-C,P-CH2PMe2)2[Fe(κ-C,P-CH2PMe2)2] (4, X-ray), and (PMe3)2Fe(κ-C,P-CH2PMe2)2 (5). CH-Bond activation of cis-(Me3P)4FeMe2 with o-CH3C6H4PMe2 led to the generation of trans,cis-(PMe3)2Fe(κ-C,P-CH2C6H4-o-PMe2)2 (6). Exposure of these compounds to [Cp2Fe][PF6], a 1e− oxidant, or AdN3, here construed as a 2e− oxidant, led to degradation in all cases, usually with the generation of carbon-carbon coupled ligands as byproducts. The inability of these systems to permit access to higher iron oxidation states is discussed.

Seven rhenium(I) complexes of the general formula fac-[Re(CO)(3)(NN)(OH(2))](+) where NN = 2,2′-bipyridine (8), 4,4′-dimethyl-2,2′-bipyridine (9), 4,4′-dimethoxy-2,2′-bipyridine (10), dimethyl 2,2′-bipyridine-4,4′-dicarboxylate (11), 1,10-phenanthroline (12), 2,9-dimethyl-1,10-phenanthroline (13), or 4,7-diphenyl-1,10-phenanthroline (14), were synthesized and characterized by (1)H NMR spectroscopy, IR spectroscopy, mass spectrometry, and X-ray crystallography. With the exception of 11, all complexes exhibited 50% growth inhibitory concentration (IC(50)) values that were less than 20 μM in HeLa cells, indicating that these compounds represent a new potential class of anticancer agents. Complexes 9, 10, and 13 were as effective in cisplatin-resistant cells as wild-type cells, signifying that they circumvent cisplatin resistance. The mechanism of action of the most potent complex, 13, was explored further by leveraging its intrinsic luminescence properties to determine its intracellular localization. These studies indicated that 13 induces cytoplasmic vacuolization that is lysosomal in nature. Additional in vitro assays indicated that 13 induces cell death without causing an increase in intracellular reactive oxygen species or depolarization of the mitochondrial membrane potential. Further studies revealed that the mode of cell death does not fall into one of the canonical categories such as apoptosis, necrosis, paraptosis, and autophagy, suggesting that a novel mode of action may be operative for this class of rhenium compounds. The in vivo biodistribution and metabolism of complex 13 and its (99m)Tc analogue 13* were also evaluated in naïve mice. Complexes 13 and 13* exhibited comparable biodistribution profiles with both hepatic and renal excretion. High-performance liquid chromatography inductively coupled plasma mass-spectrometry (HPLC-ICP-MS) analysis of mouse blood plasma and urine post administration showed considerable metabolic stability of 13, rendering this potent complex suitable for in vivo applications. These studies have shown the biological properties of this class of compounds and demonstrated their potential as promising theranostic anticancer agents that can circumvent cisplatin resistance.

We report Ti-catalyzed radical formal [3+2] cycloadditions of N-acylaziridines and alkenes. This method provides an efficient approach to the synthesis of pyrrolidines, structural units prevalent in bioactive compounds and organocatalysts, from readily available starting materials. The overall redox-neutral reaction was achieved via a redox-relay mechanism, which harnesses radical intermediates for selective C-N bond cleavage and formation.

Nine bis(thiosemicarbazone) (BTSC) cobalt(III) complexes of the general formula [Co(BTSC)(L)(2)]NO(3) were synthesized, where BTSC = diacetyl bis(thiosemicarbazone) (ATS), pyruvaldehyde bis(thiosemicarbazone) (PTS), or glyoxal bis(thiosemicarbazone) (GTS) and L = ammonia, imidazole (Im), or benzylamine (BnA). These compounds were characterized by multinuclear NMR spectroscopy, mass spectrometry, cyclic voltammetry, and X-ray crystallography. Their stability in phosphate-buffered saline was investigated and found to be highly dependent on the nature of the axial ligand L. These studies reveal that complex stability is primarily dictated by the axial ligand following the sequence NH(3) > Im > BnA. The cellular uptake and cytotoxicity in cancer cells were also determined. Both the cellular uptake and cytotoxicity are significantly affected by the nature of the equatorial BTSC. Complexes of ATS are taken up much more effectively than those of PTS and GTS. The cytotoxicity of the complexes is correlated to that of the free ligand. Cell uptake and cytotoxicity was also determined under hypoxic conditions. Only minor differences in the hypoxia activity and uptake is observed. Treatment of the cancer cells with the copper-depleting agent tetrathiomolybdate decreases the cytotoxic potency of the complexes, indicating that they may operate via a copper-dependent mechanism. These results provide a structure-activity relationship for this class of compounds, which may be applied for the rational design of new cobalt(III) anticancer agents.

As part of the United Nations 2019 celebration of the periodic table of elements, we are privileged to present our studies with the element manganese in this Forum Article series. Catalysis with organomanganese(I) complexes has recently emerged as an important area with the discovery that pincer manganese(I) complexes that can activate substrates through metal-ligand cooperative mechanisms are active (de)hydrogenation catalysts. However, this rapidly growing field faces several challenges, and we identify these in this Forum Article. Some of our efforts in addressing these challenges include using alternative precursors to Mn(CO)5Br to prepare manganese(I) dicarbonyl complexes, the latter of which is usually a component of active catalysts. Specifically, the synthesis of a new bidentate phosphine-phenol ligand along with its corresponding coordination chemistry of five new manganese(I) complexes is described. The complexes having two phenol-phenolate moieties interact with the secondary coordination sphere to enable facile loss of the bromido ligand and even one of the CO ligands to afford manganese(I) dicarbonyl centers.