Generating Potent C–H PCET Donors: Ligand-Induced Fe-to-Ring Proton Migration from a Cp*Fe^(III)–H Complex Demonstrates a Promising Strategy

Highly reactive organometallic species that mediate reductive proton-coupled electron transfer (PCET) reactions are an exciting area for development in catalysis, where a key objective focuses on tuning the reactivity of such species. This work pursues ligand-induced activation of a stable organometallic complex toward PCET reactivity. This is studied via the conversion of a prototypical Cp*Fe^(III)–H species, [Fe^(III)(η⁵-Cp*)(dppe)H]⁺ (Cp* = C₅Me₅⁻, dppe = 1,2-bis(diphenylphosphino)ethane), to a highly reactive, S = 1/2 ring-protonated endo-Cp*H–Fe relative, triggered by the addition of CO. Our assignment of the latter ring-protonated species contrasts with its previous reported formulation, which instead assigned it as a hypervalent 19-electron hydride, [Fe^(III)(η⁵-Cp*)(dppe)(CO)H]⁺. Herein, pulse EPR spectroscopy (^(1,2)H HYSCORE, ENDOR) and X-ray crystallography, with corresponding DFT studies, cement its assignment as the ring-protonated isomer, [Fe^I(endo-η⁴-Cp*H)(dppe)(CO)] ⁺. A less sterically shielded and hence more reactive exo-isomer can be generated through oxidation of a stable Fe0(exo-η⁴-Cp*H)(dppe)(CO) precursor. Both endo- and exo-ring-protonated isomers are calculated to have an exceptionally low bond dissociation free energy (BDFE_(C–H) ≈ 29 kcal mol⁻¹ and 25 kcal mol⁻¹, respectively) cf. BDFE_(Fe–H) of 56 kcal mol⁻¹ for [Fe^(III)(η⁵-Cp*)(dppe)H] ⁺. These weak C–H bonds are shown to undergo proton-coupled electron transfer (PCET) to azobenzene to generate diphenylhydrazine and the corresponding closed-shell [Fe^(II)(η⁵-Cp*)(dppe)CO]⁺ byproduct

Generating Potent C–H PCET Donors: Ligand-Induced Fe-to-Ring Proton Migration from a Cp*Fe^(III)–H Complex Demonstrates a Promising Strategy

Highly reactive organometallic species that mediate reductive proton-coupled electron transfer (PCET) reactions are an exciting area for development in catalysis, where a key objective focuses on tuning the reactivity of such species. This work pursues ligand-induced activation of a stable organometallic complex toward PCET reactivity. This is studied via the conversion of a prototypical Cp*Fe^(III)–H species, [Fe^(III)(η⁵-Cp*)(dppe)H]⁺ (Cp* = C₅Me₅⁻, dppe = 1,2-bis(diphenylphosphino)ethane), to a highly reactive, S = 1/2 ring-protonated endo-Cp*H–Fe relative, triggered by the addition of CO. Our assignment of the latter ring-protonated species contrasts with its previous reported formulation, which instead assigned it as a hypervalent 19-electron hydride, [Fe^(III)(η⁵-Cp*)(dppe)(CO)H]⁺. Herein, pulse EPR spectroscopy (^(1,2)H HYSCORE, ENDOR) and X-ray crystallography, with corresponding DFT studies, cement its assignment as the ring-protonated isomer, [Fe^I(endo-η⁴-Cp*H)(dppe)(CO)] ⁺. A less sterically shielded and hence more reactive exo-isomer can be generated through oxidation of a stable Fe0(exo-η⁴-Cp*H)(dppe)(CO) precursor. Both endo- and exo-ring-protonated isomers are calculated to have an exceptionally low bond dissociation free energy (BDFE_(C–H) ≈ 29 kcal mol⁻¹ and 25 kcal mol⁻¹, respectively) cf. BDFE_(Fe–H) of 56 kcal mol⁻¹ for [Fe^(III)(η⁵-Cp*)(dppe)H] ⁺. These weak C–H bonds are shown to undergo proton-coupled electron transfer (PCET) to azobenzene to generate diphenylhydrazine and the corresponding closed-shell [Fe^(II)(η⁵-Cp*)(dppe)CO]⁺ byproduct

Snapshots of a Migrating H-Atom: Characterization of a Reactive Iron(III) Indenide Hydride and its Nearly Isoenergetic Ring-Protonated Iron(I) Isomer

We report the characterization of an S=1/2 iron π‐complex, [Fe(η⁶‐IndH)(depe)]⁺ (Ind=Indenide (C₉H₇⁻), depe=1,2‐bis(diethylphosphino)ethane), which results via C−H elimination from a transient Fe^(III) hydride, [Fe(η³:η²‐Ind)(depe)H]⁺. Owing to weak M−H/C−H bonds, these species appear to undergo proton‐coupled electron transfer (PCET) to release H₂ through bimolecular recombination. Mechanistic information, gained from stoichiometric as well as computational studies, reveal the open‐shell π‐arene complex to have a BDFE_(C‐H) value of ≈50 kcal mol⁻¹, roughly equal to the BDFE_(Fe‐H) of its Fe^(III)−H precursor (ΔG°≈0 between them). Markedly, this reactivity differs from related Fe(η⁵‐Cp/Cp*) compounds, for which terminal Fe^(III)−H cations are isolable and have been structurally characterized, highlighting the effect of a benzannulated ring (indene). Overall, this study provides a structural, thermochemical, and mechanistic foundation for the characterization of indenide/indene PCET precursors and outlines a valuable approach for the differentiation of a ring‐ versus a metal‐bound H‐atom by way of continuous‐wave (CW) and pulse EPR (HYSCORE) spectroscopic measurements

Nickel complexes of allyl and vinyldiphenylphosphine

Monodentate phosphine-ligated nickel compounds, e.g., [Ni(PPh3)4] are relevant as active catalysts across a broad range of reactions. This report expands upon the coordination chemistry of this family, offering the reactivity of allyl- and vinyl-substituted diphenylphosphine (PPh2R) with [Ni(COD)2] (COD = 1,5-cyclooctadiene). These reactions provide three-coordinate dinickelacycles that are intermolecularly tethered through adjacent {Ni}-olefin interactions. The ring conformation of such cycles has been studied in the solid-state and using theoretical calculations. Here, a difference in reaction outcome is linked to the presence of an allyl vs vinyl group, where the former is observed to undergo rearrangement, bringing about challenges in clean product isolation

Snapshots of a Migrating H-atom: Characterization of a Reactive Fe(III) Indenide Hydride and its Nearly Isoenergetic Ring-Protonated Fe(I) Isomer

We report the characterization of an S = ½ iron π‐complex, [Fe(η^6‐IndH)(depe)]^+ (Ind = Indenide (C_9H_(7^‐_), depe = 1,2‐bis(diethylphosphino)ethane), which results via C‐H elimination from a transient Fe^(III) hydride, [Fe(η^3:η^2‐Ind)(depe)H]^+. Owing to weak M‐H/C‐H bonds, these species undergo proton‐coupled electron transfer (PCET) to release H_2 through bimolecular recombination. Mechanistic information, gained from stoichiometric as well as computational studies, reveal the open‐shell π‐arene complex to have a BDFE_(C‐H) value of ≈ 50 kcal mol^(‐1), roughly equal to the BDFE_(Fe‐H) of its Fe^(III)‐H precursor (ΔG^o ≈ 0 between them). Markedly, this reactivity differs from related Fe(η^5‐Cp/Cp^*) compounds, for which terminal Fe^(III)‐H cations are isolable and have been structurally characterized, highlighting the effect of a benzannulated (indene) ring. Overall, this study provides a structural, thermochemical, and mechanistic foundation for the characterization of indenide/indene PCET precursors and out‐lines a valuable approach for the differentiation of a ring‐ versus a metal‐ bound H‐atom by way of continuous‐wave (CW) and pulse EPR (HYSCORE) spectroscopic measurements

Examination of the Effect of Low versus High-Fidelity Simulation on Neonatal Resuscitation Program (NRP) Learning Outcomes: Final Report of Study Findings

The purpose of this study was to examine the effect of using low versus high-fidelity manikin simulators in Neonatal Resuscitation Program (NRP) instruction. Low and high-fidelity manikin simulators provide trainees with an opportunity to learn, practice and demonstrate neonatal resuscitation skills in a learning environment which simulates the experiences involved with real resuscitation emergencies. High-fidelity manikin simulator systems have been developed which approximate a full-term newborn in size and weight, possess a realistic airway that can be intubated, lungs that can be inflated with positive pressure ventilation, and an umbilical cord containing a single vein and 2 arteries that allow insertion of umbilical venous and arterial catheters. Integrated computer programs allow primary cues important for accurate assessment of the neonate (heart rate, respiratory rate, and skin color) to be controlled remotely. In 2003, the International Liaison Committee on Resuscitation (ILCOR) recommended that high-fidelity simulation-directed training should increasingly supplement instructor-directed training in advanced life support/advanced cardiac support (Chamberlain & Hazinski, 2003). Several studies have examined the use of simulation in resuscitation training and specifically compared the utility and effectiveness of low and high-fidelity simulation. However, few studies have compared low and high-fidelity simulation for NRP learning outcomes, and more specifically on team performance and confidence. This study was funded by a grant from the Janeway Children’s Hospital Foundation, Research Advisory Committee. It was led and managed by Professional Development & Conferencing Services (PDCS), Faculty of Medicine, Memorial University, as well as a team of study investigators (see Section 1.1). Ethics approval was received from the Interdisciplinary Committee on Ethics in Human Research (ICEHR), Memorial University