Peter C. Ford

The structural complexity and chemical heterogeneity of lignin present a formidable barrier to its use as a sustainable replacement for petroleum-derived aromatics. Here, we report a robust, earth-abundant copper/nitroxyl catalytic system that achieves the aerobic oxidative funneling of crude, non-pre-fractionated reductive catalytic fractionation (RCF) lignin oil into a single, high-value platform chemical: 2,6-dialkoxybenzoquinone. This transformation operates via a cooperative proton-coupled electron transfer (PCET) mechanism to cleave robust aromatic–aliphatic C–C bonds under mild aerobic conditions (O2 or open air). Using various alcohols as both solvent and nucleophile, the reaction provides modular access to a library of 2,6-dialkoxybenzoquinones in up to 86% isolated yield from model monomers/dimers and an impressive 27 wt % yield (gram product per gram lignin) directly from high-S poplar wood lignin oil (62 mol % convergent yield based on the S-phenol equivalents in the lignin oil). Crucially, we demonstrate that these tunable biomass-derived quinones serve as highly versatile synthons for advanced chemical synthesis to access precursors of bioactive natural product (scutellarein), organic electronics (TCNQ-type acceptors), platform building blocks (1,4-cyclohexanediol), cross-coupling reactions, and a modified high-performancepolyether ether ketone (PEEK) polymer. This work establishes a bridge connecting raw biomass fractionation to diverse applications in synthetic chemistry and materials science.

Described are multiple approaches using density functional theory to probe the acid catalyzed aquation of the hexaammineruthenium(II) cation (Ru(NH₃)₆²⁺ + H₃O⁺ → Ru(NH₃)₅(H₂O)²⁺ + NH₄⁺) reported initially by Taube and co-workers. These computations support the proposal that the initial step is protonation of the Ru(II) center and/or the metal-NH₃ bond, thereby activating the latter toward dissociation. DFT analysis was also carried out for the hypothetical acid-mediated aquation of the isoelectronic hexaamminerhodium(III) complex, Rh(NH₃)₆³⁺. The computations suggest a key mechanistic difference for the latter pathway, namely that protonation of the NH₃ occurs late in a reaction coordinate involving dissociation of the Rh-NH₃ with no direct interaction of H⁺ with the metal center. Furthermore, while the calculated activation energy is considerably higher in the latter case, the calculations suggest that protonation could play an important role in such ligand substitution reactions.

We report the synthesis and characterization of a family of mixed-valent dinickel complexes, formally Ni₂³⁺, featuring a naphthyridine-based PNNP^iPr pincer ligand (PNNP^iPr = 2,7-bis(di-iso-propylphosphino-methyl)-1,8-naphthyridine). The mixed valent Ni₂³⁺ complexes, [Ni₂(μ-Br)₂PNNP^iPr]₂[NiBr₄] (1), [Ni₂(κ²-OAc)₃PNNP^iPr] (2), and [Ni₂(κ²-OPiv)₃PNNP^iPr] (3), were synthesized from the addition of two equivalents of a nickel(II) salt followed by an additional equivalent of Ni(COD)₂ (COD = cyclooctadiene) to the PNNP^iPr ligand. The delocalized Ni₂³⁺ mixed valence assignment was corroborated by single-crystal X-ray diffraction, electron paramagnetic resonance, and magnetic susceptibility measurements. In addition to these measurements, the presence of the Ni-Ni bond and symmetrical structure qualifies these complexes as Class III mixed valence in the Robin-Day classification scheme. Cyclic voltammetry experiments used to characterize the redox properties of these complexes exhibited a metal-centered, quasi-reversible couple associated with the Ni₂(II,II)/Ni₂(I,II) reduction event, with E_1/2 values ranging from -0.83 V to -1.05 V vs (C₅H₅)₂Fe^+/0 in acetonitrile for the series. Further tracking by UV-vis spectroscopy showed that the mixed-valent and (PNNP^iPr)Ni₂(II,II) complexes can be interconverted through either chemical oxidation or reduction using ferrocenium tetrafluoroborate ([(C₅H₅)₂Fe][BF₄]) or cobaltocene ((C₅H₅)₂Co), respectively.

Reported are stopped-flow kinetics studies of the hydrogen peroxide reaction with the water-soluble manganese(I) carbonyl complex. fac-[Mn(CO)₃(Br)(bpCO₂)]^2- (I, bpCO₂^2- = 2,2'-bipyridine-4,4'-dicarboxylate dianion) in alkaline solution. In an earlier study, the H₂O₂ oxidation of I was shown to be accompanied by the release of more than two equivalents of carbon monoxide. The stopped-flow studies here confirm the strongly pH dependence of the reaction rate, and a revised mechanism for this kinetics behavior is proposed. The larger interest in these systems derives from evaluating redox mechanisms for CO delivery from metal-based carbon monoxide releasing moieties (CORMs) under physiologically relevant conditions.

The endogenous reduction of nitrite to nitrosyl is drawing increasing attention as a protective mechanism against hypoxic injury in mammalian physiology and as an alternative source of NO, which is involved in a wide variety of biological activities. Thus, chemical mechanisms for this transformation, which are mediated by metallo proteins, are of considerable interest. The study described here examines the reactions of the biomimetic models Co(TTP)(NO₂) (TTP = meso-tetratolylporphyrinato dianion) and Mn(TPP)(ONO) (TPP = meso-tetraphenyl-porphyrinato dianion) in sublimated solid films with hydrogen sulfide (H₂S) and with ethanethiol (EtSH) at various temperatures from 77 K to room temperature using in situ infrared and optical spectroscopy. In both cases, the coordinated nitrite complex is eventually converted to the respective nitrosyl Co(TTP)(NO) and Mn(TPP)(NO); however, reaction at low temperature first gave a novel six-coordinate complex M(Por)(RSH)(nitrite). Warming these films in the presence of excess thiol resulted in the formation of the two nitrosyl complexes. Mass spectrometric analysis of volatile products and DFT computations of possible intermediates are reported, and potential mechanisms for reduction of the coordinated nitrite ions are discussed.

Five novel manganese (I) tricarbonyl complexes were synthesized by the reaction of Mn (CO)₅Br with quinoline‐2‐carboxaldehyde and different anilines. The IR, UV, and myoglobin results indicate that these complexes can be used as photoCORMs (photo photoinduced carbon monoxide releasing molecules) activated by red light. The visible range spectra display strong charge transfer (CT) bands, the maxima of which are sensitive to the ligand substituents. Density functional theory (DFT) and time‐dependent density functional theory (TDDFT) computations show that these CT transitions are admixtures of metal‐to‐ligand and aniline‐to‐quinoline charge transfers and that increasing the electron‐donating ability on the aniline functionality can lead to shifts in the absorption bands of the corresponding compounds to longer wavelengths and to enhanced band intensities, thus enhancing their photoactivity. Photolysis of these complexes in aerobic solution leads to CO photodissociation followed by oxidation of the Mn(I) center to Mn(II).

Hemes play key roles in enzymatic production of the nitric oxide by NO synthase and in conversion from inorganic nitrite. Here we report a hitherto unknown pathway of NO formation via thiol reduction of an iron porphyrin nitrate in the solid state.

Lignin-based syringol monomer, 2,6-dimethoxypropylphenol (DMPP), can be upgraded through two synthetic routes to multi-functional propylpyrogallol DMPPO. With three hydroxyl groups, DMPPO can serve as a renewable polymer building block. In this study, we describe the synthesis and characterization of DMPPO epoxide mixtures based on their synthesis methodology; one route uses HBr, another a greener methodology with Nb₂O₅ catalyst in water. Epoxy thermoset polymers using the two different epoxide preparations are synthesized, characterized, and contrasted. Optimization of reaction conditions, including temperature and catalyst concentration, to enhance the performance of epoxy thermosets is discussed. Through dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA), the thermo-mechanical behavior and thermal stability of the resulting epoxy thermoset networks are evaluated, shedding light on how structural differences impact performance.

The effects of the nitro-ruthenium porphyrin complex, RuNO ₂ TPyP, in lung cells using 2D and 3D cell culture models.