PUBLICATIONS

Abstract. Alcohols and aryl carboxylic acids are among the most commercially abundant, synthetically versatile, and operationally convenient building blocks in organic chemistry. Despite their widespread availability, the direct formation of C(sp³)–C(sp²) bonds from these functional groups remains a challenge. Recently, our group developed robust protocols to harness alcohols as alkyl radical precursors, but the activation of aryl acids remains relatively unexplored. Herein, we describe the merger of N-heterocyclic carbene (NHC)-mediated deoxygenation and nickel-mediated decarbonylation of aryl acids toward C(sp³)–C(sp²) bond formation. The utility of this method is demonstrated through the synthesis of a diverse range of aryl–alkyl cross-coupled products and the late-stage functionalization of complex molecules, including drugs, natural products, and biomolecules.

Abstract. We report the photogeneration and characterization of an open-shell, terminal iron nitrido (^EmL)Fe(N) using a sterically encumbered dipyrrin ligand environment. The Fe–N distance in the solid-state, zero-field ⁵⁷Fe Mössbauer spectrum, and computational analysis are consistent with a triplet electronic ground state of the iron nitrido. Notably, the attenuation of Fe–N multiple bond character through occupying π*_Fe–N enables (i) primary C(sp³)–H amination, (ii) H₂ cleavage, (iii) aromatic C–C cleavage, and (iv) photocatalytic N-atom transfer reactivity. These modes of reactivity have not previously been observed in low-spin Fe(N) analogues.

Abstract. A comprehensive educational strategy designed to make small-molecule crystallography more accessible for students at various academic levels is described. By integrating hands-on laboratory visits, structured courses and advanced application training, we cultivate a deep understanding of fundamental crystallographic concepts while fostering practical skills. This strategy also aims to inspire novice learners, building their confidence and interest in structural science. Our approach demystifies complex concepts through real-world examples and interactive case-learning modules, enabling students to proficiently apply crystallography in their research. The resulting educational impact is evident in numerous publications from undergraduates, scholarship awards to graduates and successful independent research projects, highlighting the effectiveness of our programme in inspiring the next generation of chemical crystallographers.

Abstract. Anomalous X-ray diffraction (AXD) and neutron diffraction can be used to crystallographically distinguish between metals of similar electron density. Despite the use of AXD for structural characterization in mixed metal clusters, there are no benchmark studies evaluating the accuracy of AXD toward assessing elemental occupancy in molecules with comparisons with what is determined via neutron diffraction. We collected resonant diffraction data on several homo and heterometallic clusters and refined their anomalous scattering components to determine metal site occupancies. Theoretical resonant scattering terms for Fe⁰, Co⁰, and Zn⁰ were compared against experimental values, revealing theoretical values are ill-suited to serve as references for occupancy determination. The cluster featuring distinct cation and anion metal compositions [CoCp₂*][(^tbsL)Fe₃(μ³–NAr)] was used to assess the accuracy of different f′ references for occupancy determination (f′_theoretical ± 15–17%; f′_experimental ± 10%). This methodology was applied toward calculating the occupancy of three different clusters: (^tbsL)Fe₂Zn(py) (6), (^tbsL)Fe₂Zn(μ³–NAr)(py) (7), and [CoCp*₂][(^tbsL)Fe₂Zn(μ³–NAr)] (8). The first two clusters maintain 100% Fe/Zn site isolation, whereas 8 showed metal mixing within the sites. The large crystal size of 8 enabled collection of neutron diffraction data which was compared against the results found with AXD. The ability of AXD to replicate the metal occupancies as determined by neutron diffraction supports the AXD occupancy methodology developed herein. Furthermore, the advantages innate to AXD (e.g., smaller crystal sizes, shorter collection times, and greater availability of synchrotron resources) versus neutron diffraction further support the need for its development as a standard technique.

Abstract. Carbon capture can mitigate point-source carbon dioxide (CO₂) emissions, but hurdles remain that impede the widespread adoption of amine-based technologies. Capturing CO₂ at temperatures closer to those of many industrial exhaust streams (>200°C) is of interest, although metal oxide absorbents that operate at these temperatures typically exhibit sluggish CO₂ absorption kinetics and instability to cycling. Here, we report a porous metal–organic framework featuring terminal zinc hydride sites that reversibly bind CO₂ at temperatures above 200°C—conditions that are unprecedented for intrinsically porous materials. Gas adsorption, structural, spectroscopic, and computational analyses elucidate the rapid, reversible nature of this transformation. Extended cycling and breakthrough analyses reveal that the material is capable of deep carbon capture at low CO₂ concentrations and high temperatures relevant to postcombustion capture.

Media Coverage.
“Heat up to catch carbon” Science
“This MOF is hot to go” C&EN Chemical & Engineering News
“Breakthrough in capturing 'hot' CO₂ from industrial exhaust” Berkeley News, ChemEurope
“Breakthrough in capturing 'hot' CO₂ from exhaust” AAAS, Mirage, Science Daily, Tiisys[Japanese]
“UC Berkeley chemists discover method to capture CO₂ at high temperatures” The Daily Californian
“UC Berkeley scientists unveil breakthrough ‘hot’ CO₂ capture technology” The University Network
“Metal–organic framework captures carbon dioxide at industrially relevant temperatures” ChemistryWorld
“Scientists develop new material that could help solve major issue in Earth's atmosphere” The Cool Down
“Scientists develop breakthrough technology for high-temperature CO₂ capture” The Pinnacle Gazette
“Carbon removal at extreme temperatures: porous material can capture 'hot' CO₂” TechExplorer
“Reaction activation energy high? It’s okay. High has its perks” X-MOL [Mandarin]
“New material captures carbon dioxide from super-hot industrial exhaust” Knowridge
“Capturing hot carbon dioxide from industry for storage and reuse” Pump Industry
“Metal–organic framework to catch hot CO₂ from flue gas” Chemistry & Industry
“This sponge captures CO₂ as it leaves factories” Futura Sciences [French]
“MOF captures hot CO₂ from industrial exhaust streams” The Engineer
“Carsch research shows new frontiers in carbon capture” UT Austin
“CO₂ capture at high temperatures using MOFs” Chem Station [Japanese]
“Molecules of the Year 2024” C&EN Chemical & Engineering News
“Now that’s some hot carbon capture” COSMOS
“US university develops material to capture CO₂ from high-temperature factory” NIKKEI [Japanese]

A recorded lecture on this manuscript is available at the following link (https://www.youtube.com/watch?v=zho3E-Uy1ao), presented by Kurtis at the 2025 Award Symposium for the International Adsorption Society.

Abstract. Porous solids can accommodate and release molecular hydrogen readily, making them attractive for minimizing the energy requirements for hydrogen storage relative to physical storage systems. However, H₂ adsorption enthalpies in such materials are generally weak (−3 to −7 kJ/mol), lowering capacities at ambient temperature. Metal–organic frameworks with well-defined structures and synthetic modularity could allow for tuning adsorbent–H₂ interactions for ambient-temperature storage. Recently, Cu_2.2Zn_2.8Cl_1.8(btdd)₃ (H₂btdd = bis(1H-1,2,3-triazolo-[4,5-b],[4′,5′-i])dibenzo[1,4]dioxin; Cu^I-MFU-4l) was reported to show a large H₂ adsorption enthalpy of −32 kJ/mol owing to π-backbonding from Cu^I to H₂, exceeding the optimal binding strength for ambient-temperature storage (−15 to −25 kJ/mol). Toward realizing optimal H₂ binding, we sought to modulate the π-backbonding interactions by tuning the pyramidal geometry of the trigonal Cu^I sites. A series of isostructural frameworks, Cu_2.7M_2.3X_1.3(btdd)₃ (M = Mn, Cd; X = Cl, I; Cu^IM-MFU-4l), was synthesized through postsynthetic modification of the corresponding materials M₅X₄(btdd)₃ (M = Mn, Cd; X = CH₃CO₂, I). This strategy adjusts the H₂ adsorption enthalpy at the Cu^I sites according to the ionic radius of the central metal ion of the pentanuclear cluster node, leading to −33 kJ/mol for M = Zn^II (0.74 Å), −27 kJ/mol for M = Mn^II (0.83 Å), and −23 kJ/mol for M = Cd^II (0.95 Å). Thus, Cu^ICd-MFU-4l provides a second, more stable example of optimal H₂ binding energy for ambient-temperature storage among reported metal–organic frameworks. Structural, computational, and spectroscopic studies indicate that a larger central metal planarizes trigonal Cu^I sites, weakening the π-backbonding to H₂.

Abstract. High or enriched-purity O₂ is used in numerous industries and is predominantly produced from the cryogenic distillation of air, an extremely capital- and energy-intensive process. There is significant interest in the development of new approaches for O₂-selective air separations, including the use of metal–organic frameworks featuring coordinatively unsaturated metal sites that can selectively bind O₂ over N₂ via electron transfer. However, most of these materials exhibit appreciable and/or reversible O₂ uptake only at low temperatures, and their open metal sites are also potential strong binding sites for the water present in air. Here, we study the framework Cu^I-MFU-4l (Cu_xZn_5–xCl_4–x(btdd)₃; H₂btdd = bis(1H-1,2,3-triazolo[4,5-b],[4′,5′-i])dibenzo[1,4]dioxin), which binds O₂ reversibly at ambient temperature. We develop an optimized synthesis for the material to access a high density of trigonal pyramidal Cu^I sites, and we show that this material reversibly captures O₂ from air at 25 °C, even in the presence of water. When exposed to air up to 100% relative humidity, Cu^I-MFU-4l retains a constant O₂ capacity over the course of repeated cycling under dynamic breakthrough conditions. While this material simultaneously adsorbs N₂, differences in O₂ and N₂ desorption kinetics allow for the isolation of high-purity O₂ (>99%) under relatively mild regeneration conditions. Spectroscopic, magnetic, and computational analyses reveal that O₂ binds to the copper(I) sites to form copper(II)–superoxide moieties that exhibit temperature-dependent side-on and end-on binding modes. Overall, these results suggest that Cu^I-MFU-4l is a promising material for the separation of O₂ from ambient air, even without dehumidification.

Abstract. A detailed chemical understanding of H₂ interactions with binding sites in the nanoporous crystalline structure of metal–organic frameworks (MOFs) can lay a sound basis for the design of new sorbent materials. Computational quantum chemical calculations can aid in this quest. To set the stage, we review general thermodynamic considerations that control the usable storage capacity of a sorbent. We then discuss cluster modeling of H₂ ligation at MOF binding sites using state-of-the-art density functional theory (DFT) calculations, and how the binding can be understood using energy decomposition analysis (EDA). Employing these tools, we illustrate the connections between the character of the MOF binding site and the associated adsorption thermodynamics using four experimentally characterized MOFs, highlighting the role of open metal sites (OMSs) in accessing binding strengths relevant to room temperature storage. The sorbents are MOF-5, with no open metal sites, Ni₂(m-dobdc), containing Lewis acidic Ni(II) sites, Cu(I)-MFU-4l, containing π basic Cu(I) sites and V₂Cl_2.8(btdd), also containing π-basic V(II) sites. We next explore the potential for binding multiple H₂ molecules at a single metal site, with thermodynamics useful for storage at ambient temperature; a materials design goal which has not yet been experimentally demonstrated. Computations on Ca²⁺ or Mg²⁺ bound to catecholate or Ca²⁺ bound to porphyrin show the potential for binding up to 4 H₂; there is precedent for the inclusion of both catecholate and porphyrin motifs in MOFs. Turning to transition metals, we discuss the prediction that two H₂ molecules can bind at V(II)-MFU-4l, a material that has been synthesized with solvent coordinated to the V(II) site. Additional calculations demonstrate binding three equivalents of hydrogen per OMS in Sc(I) or Ti(I)-exchanged MFU-4l. Overall, the results suggest promising prospects for experimentally realizing higher capacity hydrogen storage MOFs, if nontrivial synthetic and desolvation challenges can be overcome. Coupled with the unbounded chemical diversity of MOFs, there is ample scope for additional exploration and discovery.

Abstract. Despite the myriad Cu-catalyzed nitrene transfer methodologies to form new C–N bonds (e.g., amination, aziridination), the critical reaction intermediates have largely eluded direct characterization due to their inherent reactivity. Herein, we report the synthesis of dipyrrin-supported Cu nitrenoid adducts, investigate their spectroscopic features, and probe their nitrene transfer chemistry through detailed mechanistic analyses. Treatment of the dipyrrin Cu^I complexes with substituted organoazides affords terminally ligated organoazide adducts with minimal activation of the azide unit as evidenced by vibrational spectroscopy and single crystal X-ray diffraction. The Cu nitrenoid, with an electronic structure most consistent with a triplet nitrene adduct of Cu^I, is accessed following geometric rearrangement of the azide adduct from κ¹-N terminal ligation to κ¹-N internal ligation with subsequent expulsion of N₂. For perfluorinated arylazides, stoichiometric and catalytic C–H amination and aziridination was observed. Mechanistic analysis employing substrate competition reveals an enthalpically-controlled, electrophilic nitrene transfer for primary and secondary C–H bonds. Kinetic analyses for catalytic amination using tetrahydrofuran as a model substrate reveal pseudo-first order kinetics under relevant amination conditions with a first-order dependence on both Cu and organoazide. Activation parameters determined from Eyring analysis (ΔH^‡ = 9.2(2) kcal mol⁻¹, ΔS^‡ = −42(2) cal mol⁻¹ K⁻¹, ΔG^‡_298K = 21.7(2) kcal mol⁻¹) and parallel kinetic isotope effect measurements (1.10(2)) are consistent with rate-limiting Cu nitrenoid formation, followed by a proposed stepwise hydrogen-atom abstraction and rapid radical recombination to furnish the resulting C–N bond. The proposed mechanism and experimental analysis are further corroborated by density functional theory calculations. Multiconfigurational calculations provide insight into the electronic structure of the catalytically relevant Cu nitrene intermediates. The findings presented herein will assist in the development of future methodology for Cu-mediated C–N bond forming catalysis.

Abstract. We assess the binding of C₂H₄ to the coordinately unsaturated copper(I) sites of the metal–organic frameworks Cu(I)-ZrTpmC* and Cu(I)-MFU-4l via ¹³C solid-state nuclear magnetic resonance spectroscopy, density functional theory (DFT), and natural localized molecular orbital analysis. Using these methods, forward-donation and back-donation contributions between C₂H₄ and the exposed Cu(I) are delineated, and high binding enthalpies are contextualized as a function of electronic changes upon site modification and adsorption. With the infrastructure for DFT and solid-state ¹³C NMR becoming more routine for scientists, we envision that these results will support the study of exposed electron-rich metal sites in a variety of chemical applications.

Abstract. Densifying hydrogen in a metal–organic framework (MOF) at moderate pressures can circumvent challenges associated with high-pressure compression. The highly tunable structural and chemical composition in MOFs affords vast possibilities to optimize binding interactions. At the heart of this search are the nanoscale characteristics of molecular adsorption at the binding site(s). Using density functional theory (DFT) to model binding interactions of hydrogen to the exposed metal site of cation-exchanged MFU-4l, we predict multiple hydrogen ligation of H₂ at the first coordination sphere of V(II) in V(II)-exchanged MFU-4l. We find that the strength of this binding between the metal site and H₂ molecules can be tuned by altering the halide counterion adjacent to the metal site and that the fluoride containing node affords the most favorable interactions for high-density H₂ storage. Using energy decomposition analysis, we delineate electronic contributions that enable multiple hydrogen ligation and demonstrate its benefits for hydrogen adsorption and release at modest pressures.

Abstract. We report that exposing the dipyrrin complex (^EMindL)Cu(N₂) to air affords rapid, quantitative uptake of O₂ in either solution or the solid-state to yield (^EMindL)Cu(O₂). The air and thermal stability of (^EMindL)Cu(O₂) is unparalleled in molecular copper-dioxygen coordination chemistry, attributable to the ligand flanking groups which preclude the [Cu(O₂)]¹⁺ core from degradation. Despite the apparent stability of (^EMindL)Cu(O₂), dioxygen binding is reversible over multiple cycles with competitive solvent exchange, thermal cycling, and redox manipulations. Additionally, rapid, catalytic oxidation of 1,2-diphenylhydrazine to azoarene with the generation of hydrogen peroxide is observed, through the intermittency of an observable (^EMindL)Cu(H₂O₂) adduct. The design principles gleaned from this study can provide insight for the formation of new materials capable of reversible scavenging of O₂ from air under ambient conditions with low-coordinate Cu^I sorbents.

Abstract. Palladium 2-di­cyclo­hexyl­phosphanyl-2′,6′-diisopropoxybiphenyl (Pd–RuPhos) catalysts demonstrate high catalytic activity for Negishi cross-couplings of sterically hindered aryl halides, for Suzuki–Miyaura cross-couplings of tosyl­ated olefins, and for Buchwald–Hartwig amination of sterically hindered amines. The solid-state structure of the free RuPhos ligand, C₃₀H₄₃O₂P, is reported herein for the first time. RuPhos crystallizes in a triclinic cell containing two independent mol­ecules of the phosphine without any lattice solvent. Pertinent bond metrics and comparisons to other phosphine ligands are presented. The structure of RuPhos will be of assistance in the use of this ligand in the design of cross-coupling catalysts.

Media Coverage.
“Chem-145 undergraduates publish papers on novel crystals” Harvard Chemistry and Chemical Biology. Prepared Fall 2020 (CHEM145, experimental inorganic chemistry).

Abstract. The dichromium Pacman complex (^tBudmx)Cr₂Cl₂·C₄H₁₀O (1) [(^tBudmx)H₂ is a di­­methylxanthene-bridged cofacial (bis)dipyrrin, C₄₉H₅₈N₄O] was synthesized by salt metathesis using anhydrous CrCl₂ and previously reported (^tBudmx)K₂. Treament of 1 with two equivalents of the reductant potassium graphite afforded K₂(^tBudmx)Cr₂Cl₂(thf)₃·0.5C₄H₁₀O·0.5C₄H₈O (thf is tetrahydrofuran, C₄H₈O) (2), with both potassium ions intecalated between the pyrrolic subunits. Comparison of the solid-state structures for 1 and 2 reveals minimal changes in the primary coordination sphere of each Cr ion, with notable elongation of the dipyrrin C–C and C–N bonds upon reduction, consistent with computational support for a ligand-based reduction.

Media Coverage.
“Chem-145 undergraduates publish papers on novel crystals” Harvard Chemistry and Chemical Biology. Prepared Fall 2020 (CHEM145, experimental inorganic chemistry).

Abstract. Dicopper complexes templated by dinucleating, pacman dipyrrin ligand scaffolds (^Mesdmx, ^tBudmx: dimethylxanthine-bridged, cofacial bis-dipyrrin) were synthesized by deprotonation/metalation with mesitylcopper (CuMes; Mes: mesityl) or by transmetalation with cuprous precursors from the corresponding deprotonated ligand. Neutral imide complexes (^Rdmx)Cu₂(μ²-NAr) (R: Mes, ^tBu; Ar: 4-MeOC₆H₄, 3,5-(F₃C)₂C₆H₃) were synthesized by treatment of the corresponding dicuprous complexes with aryl azides. While one-electron reduction of (^Mesdmx)Cu₂(μ²-N(C₆H₄OMe)) with potassium graphite initiates an intramolecular, benzylic C–H amination at room temperature, chemical reduction of (^tBudmx)Cu₂(μ²-NAr) leads to isolable [(^tBudmx)Cu₂(μ²-NAr)]⁻ product salts. The electronic structures of the thermally robust [(^tBudmx)Cu₂(μ²-NAr)]^0/– complexes were assessed by variable-temperature electron paramagnetic resonance spectroscopy, X-ray absorption spectroscopy (Cu L_2,3/K-edge, N K-edge), optical spectroscopy, and DFT/CASSCF calculations. These data indicate that the formally Class IIIA mixed valence complexes of the type [(^Rdmx)Cu₂(μ²-NAr)]⁻ feature significant NAr-localized spin following reduction from electronic population of the [Cu₂(μ²-NAr)] π* manifold, contrasting previous methods for engendering iminyl character through chemical oxidation. The reactivity of the isolable imido and iminyl complexes are examined for prototypical radical-promoted reactivity (e.g., nitrene transfer and H-atom abstraction), where the divergent reactivity is rationalized by the relative degree of N-radical character afforded from different aryl substituents.

Abstract. Seventeen Cu complexes with formal oxidation states ranging from Cu^I to Cu^III are investigated through the use of multiedge X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations. Analysis reveals that the metal–ligand bonding in high-valent, formally Cu^III species is extremely covalent, resulting in Cu K-edge and L_2,3-edge spectra whose features have energies that complicate physical oxidation state assignment. Covalency analysis of the Cu L_2,3-edge data reveals that all formally Cu^III species have significantly diminished Cu d-character in their lowest unoccupied molecular orbitals (LUMOs). DFT calculations provide further validation of the orbital composition analysis, and excellent agreement is found between the calculated and experimental results. The finding that Cu has limited capacity to be oxidized necessitates localization of electron hole character on the supporting ligands; consequently, the physical d⁸ description for these formally Cu^III species is inaccurate. This study provides an alternative explanation for the competence of formally Cu^III species in transformations that are traditionally described as metal-centered, 2-electron Cu^I/Cu^III redox processes.

Media Coverage.
“Credit ligands for copper-complex chemistry” C&EN Chemical & Engineering News
“Copper comeuppance” Nature Chemistry Reviews

Abstract. Terminal copper-nitrenoid complexes have inspired interest in their fundamental bonding structures as well as their putative intermediacy in catalytic nitrene-transfer reactions. Here, we report that aryl azides react with a copper(I) dinitrogen complex bearing a sterically encumbered dipyrrin ligand to produce terminal copper nitrene complexes with near-linear, short copper–nitrenoid bonds [1.745(2) to 1.759(2) angstroms]. X-ray absorption spectroscopy and quantum chemistry calculations reveal a predominantly triplet nitrene adduct bound to copper(I), as opposed to copper(II) or copper(III) assignments, indicating the absence of a copper−nitrogen multiple-bond character. Employing electron-deficient aryl azides renders the copper nitrene species competent for alkane amination and alkene aziridination, lending further credence to the intermediacy of this species in proposed nitrene-transfer mechanisms.

Media Coverage.
“Break it up” Harvard Chemistry and Chemical Biology News
“How an elusive catalyst makes unusual reactions happen”Harvard Gazette
“Discovered architecture of a copper-nitrenoid complex could revolutionize synthesis” Phys, ScienceDaily,
“Discovered architecture of a copper-nitrenoid complex could revolutionize synthesis” LongRoom
“Big game hunting for a more versatile catalyst” 7^th Space, TechSite
“Catch it! Super active copper nitrenoid” X-MOL [Mandarin]
“Missing electrons reveal the true face of a new copper-based catalyst” CornellChronicle, ScienceDaily,
“Missing electrons reveal the true face of a new copper-based catalyst”Newswise, LongRoom
“Metalloenzyme mastery” ChemistryWorld

Abstract. The modulation of the reactivity of metal oxo species by redox inactive metals has attracted much interest due to the observation of redox inactive metal effects on processes involving electron transfer both in nature (the oxygen-evolving complex of Photosystem II) and in heterogeneous catalysis (mixed-metal oxides). Studies of small-molecule models of these systems have revealed numerous instances of effects of redox inactive metals on electron- and group-transfer reactivity. However, the heterometallic species directly involved in these transformations have rarely been structurally characterized and are often generated in situ. We have previously reported the preparation and structural characterization of multiple series of heterometallic clusters based on Mn₃ and Fe₃ cores and described the effects of Lewis acidity of the heterometal incorporated in these complexes on cluster reduction potential. To determine the effects of Lewis acidity of redox inactive metals on group transfer reactivity in structurally well-defined complexes, we studied [Mn₃MO₄], [Mn₃MO(OH)], and [Fe₃MO(OH)] clusters in oxygen atom transfer (OAT) reactions with phosphine substrates. The qualitative rate of OAT correlates with the Lewis acidity of the redox inactive metal, confirming that Lewis acidic metal centers can affect the chemical reactivity of metal oxo species by modulating cluster electronics.

Abstract. The dangler manganese center in the oxygen-evolving complex (OEC) of photosystem II plays an important role in the oxidation of water to dioxygen. Inspired by the structure of the OEC, we synthesized a series of site-differentiated tetra-manganese clusters [LMn₃(PhPz)₃OMn][OTf]_x (2: x = 2; 3: x = 1) that features an apical manganese ion—distinct from the others—that is appended to a trinuclear manganese core through an μ₄-oxygen atom bridge. This cluster design was targeted to facilitate studies of high-valent Mn-oxo formation, which is a proposed step in the mechanism for water oxidation by the OEC. Terminal Mn-oxo species—supported by a multinuclear motif—were targeted by treating 2 and 3 with iodosobenzene. Akin to our previously reported iron complexes, intramolecular arene hydroxylation was observed to yield the C–H bond oxygenated complexes [LMn₃(PhPz)₂(OArPz)OMn][OTf]_x (5: x = 2; 6: x = 1). The fluorinated series [LMn₃(F₂ArPz)₃OMn][OTf]_x (8: x = 2; 9: x = 1) was also synthesized to mitigate the observed intramolecular hydroxylation. Treatment of 8 and 9 with iodosobenzene results in intramolecular arene C–F bond oxygenation as judged by electrospray ionization mass spectrometry. The observed aromatic C–H and C–F hydroxylation is suggestive of a putative high-valent terminal metal-oxo species, and it is one of the very few examples capable of oxygenating C–F bonds.

Abstract. The selectivity of intramolecular C(sp²)−H versus C(sp²)−F bond oxygenation was examined with a new series of [LM₃(PhPz)₃OM′][OTf]₂ (M, M′=Fe or Mn) clusters. The distribution of metal centers within these clusters provided insight into how a single metal center (Fe vs. Mn) can control the selectivity of oxygenation chemistry. Although for iron (M=Fe, M′=Fe) essentially exclusive C(sp²)−F bond oxygenation was observed, with manganese (M=Fe or Mn, M′=Mn), C(sp²)−H oxygenation was preferred.

Abstract. Iodosobenzene adducts LFe₃(PhPz)₃OMn(^sPhIO)][OTf]_x (x=2 or 3; PhPz=phenylpyrazolate) on multinuclear scaffolds were synthesized and characterized. The reactivity of these rare adducts was investigated in light of remote redox state changes in a triiron core (Fe^III₂Fe^IIMn^II vs. Fe^III₃Mn^II), thereby highlighting significant reactivity differences (>10²) in oxygen atom transfer and C−H bond oxygenation.

Abstract. Synthetic model compounds have been targeted to benchmark and better understand the electronic structure, geometry, spectroscopy, and reactivity of the oxygen-evolving complex (OEC) of photosystem II, a low-symmetry Mn₄CaO_n cluster. Herein, low-symmetry Mn^IV₃GdO₄ and Mn^IV₃CaO₄ cubanes are synthesized in a rational, stepwise fashion through desymmetrization by ligand substitution, causing significant cubane distortions. As a result of increased electron richness and desymmetrization, a specific μ₃-oxo moiety of the Mn₃CaO₄ unit becomes more basic allowing for selective protonation. Coordination of a fifth metal ion, Ag⁺, to the same site gives a Mn₃CaAgO₄ cluster that models the topology of the OEC by displaying both a cubane motif and a “dangler” transition metal. The present synthetic strategy provides a rational roadmap for accessing more accurate models of the biological catalyst.

Abstract. Cp*W(O)₂(CH₂SiMe₃) (1) (Cp* = η⁵-pentamethylcyclopentadienyl) reacts with oxygen atom donors (e.g., H₂O₂, PhIO, IO₄^–) in THF/water to produce TMSCH₂OH (TMS = trimethylsilyl). For the reaction of 1 with IO₄^–, the proposed pathway for alcohol formation involves coordination of IO₄^– to 1 followed by concerted migration of the −CH₂TMS ligand to the coordinated oxygen of IO₄^– with concomitant dissociation of IO₃^– to produce Cp*W(O)₂(OCH₂SiMe₃) (3), which undergoes protonolysis to yield free alcohol. In contrast to the reaction with IO₄^–, the reaction of 1 with H₂O₂ results in the formation of the η²-peroxo complex Cp*W(O)(η²-O₂)(CH₂SiMe₃) (2). In the presence of acid (HCl) or base (NaOH), complex 2 produces TMSCH₂OH. The conversion of 2 to TMSCH₂OH catalyzed by Brønsted acid is proposed to occur through protonation of the η²-peroxo ligand, which facilitates the transfer of the −CH₂TMS ligand to a coordinated oxygen of the η²-hydroperoxo ligand. In contrast, the hydroxide promoted conversion of 2 to TMSCH₂OH is proposed to involve hydroxide coordination, followed by proton transfer from the hydroxide ligand to the peroxide ligand to yield a κ¹-hydroperoxide intermediate. The migration of the −CH₂TMS ligand to the coordinated oxygen of the κ¹-hydroperoxo produces an alkoxide complex, which undergoes protonolysis to yield free alcohol.

Abstract. Computational modeling of Group 6 complexes of the form [L_nM(Y)O]ⁿ (L_n: Tp = hydrido-tris(pyrazolyl)borate, Ep = 1,1,1-tris(pyrazolyl)ethane; M = Cr^IV, Mo^IV, W^IV; Y = CO, pyridine, n = 1⁺ or 2⁺) with respect to an oxy-insertion catalytic cycle for the conversion of methane to methanol is reported. Through a DFT study of the reaction mechanism – involving C–H activation and oxygen-atom transfer – competing transition state pathways, molecular geometries, and Gibbs free energies were analyzed. The results indicate that the [EpCr(CO)O]²⁺ catalyst is the most promising among the twelve Group 6 systems modeled as the transition state for C–H bond activation requires ∼10 kcal mol⁻¹ for [2 + 2] addition with a reasonably flat potential energy surface for the complete catalytic cycle. Calculations indicate that most Cr-oxo and all Mo-oxo complexes favor a hydrogen atom abstraction (HAA) pathway, whereas the majority of the W-oxo complexes and one of the Cr complexes favors a [2 + 2] mechanism for methane C–H bond activation. With regards to the catalyst components, the following orders, M (Cr > Mo > W) > L_n (Ep > Tp) > Y (carbonyl > pyridine), expresses the importance of the individual constituents with respect to their impact on the calculated catalytic cycle.