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1. Ligand and solvent effects on CO 2 insertion into group 10 metal alkyl bonds

   https://doi.org/10.1039/D1SC06346D  

   Deziel, Anthony P. ; Espinosa, Matthew R. ; Pavlovic, Ljiljana ; Charboneau, David J. ; Hazari, Nilay ; Hopmann, Kathrin H. ; Mercado, Brandon Q. ( February 2022 , Chemical Science)

   The insertion of carbon dioxide into metal element σ-bonds is an important elementary step in many catalytic reactions for carbon dioxide valorization. Here, the insertion of carbon dioxide into a family of group 10 alkyl complexes of the type ( R PBP)M(CH 3 ) ( R PBP = B(NCH 2 PR 2 ) 2 C 6 H 4 − ; R = Cy or t Bu; M = Ni or Pd) to generate κ 1 -acetate complexes of the form ( R PBP)M{OC(O)CH 3 } is investigated. This involved the preparation and characterization of a number of new complexes supported by the unusual R PBP ligand, which features a central boryl donor that exerts a strong trans -influence, and the identification of a new decomposition pathway that results in C–B bond formation. In contrast to other group 10 methyl complexes supported by pincer ligands, carbon dioxide insertion into ( R PBP)M(CH 3 ) is facile and occurs at room temperature because of the high trans -influence of the boryl donor. Given the mild conditions for carbon dioxide insertion, we perform a rare kinetic study on carbon dioxide insertion into a late-transition metal alkyl species using ( t Bu PBP)Pd(CH 3 ). These studies demonstrate that the Dimroth–Reichardt parameter for a solvent correlates with the rate of carbon dioxide insertion and that Lewis acids do not promote insertion. DFT calculations indicate that insertion into ( t Bu PBP)M(CH 3 ) (M = Ni or Pd) proceeds via an S E 2 mechanism and we compare the reaction pathway for carbon dioxide insertion into group 10 methyl complexes with insertion into group 10 hydrides. Overall, this work provides fundamental insight that will be valuable for the development of improved and new catalysts for carbon dioxide utilization. 

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2. Atomically Dispersed Single Ni Site Catalysts for Nitrogen Reduction toward Electrochemical Ammonia Synthesis Using N 2 and H 2 O

   https://doi.org/10.1002/smtd.201900821  

   Mukherjee, Shreya ; Yang, Xiaoxuan ; Shan, Weitao ; Samarakoon, Widitha ; Karakalos, Stavros ; Cullen, David A. ; More, Karren ; Wang, Maoyu ; Feng, Zhenxing ; Wang, Guofeng ; et al ( February 2020 , Small Methods)

   Ammonia (NH₃) electrosynthesis gains significant attention as NH₃is essentially important for fertilizer production and fuel utilization. However, electrochemical nitrogen reduction reaction (NRR) remains a great challenge because of low activity and poor selectivity. Herein, a new class of atomically dispersed Ni site electrocatalyst is reported, which exhibits the optimal NH₃yield of 115 µg cm⁻²h⁻¹at –0.8 V versus reversible hydrogen electrode (RHE) under neutral conditions. High faradic efficiency of 21 ± 1.9% is achieved at ‐0.2 V versus RHE under alkaline conditions, although the ammonia yield is lower. The Ni sites are stabilized with nitrogen, which is verified by advanced X‐ray absorption spectroscopy and electron microscopy. Density functional theory calculations provide insightful understanding on the possible structure of active sites, relevant reaction pathways, and confirm that the Ni‐N₃sites are responsible for the experimentally observed activity and selectivity. Extensive controls strongly suggest that the atomically dispersed NiN₃site‐rich catalyst provides more intrinsically active sites than those in N‐doped carbon, instead of possible environmental contamination. This work further indicates that single‐metal site catalysts with optimal nitrogen coordination is very promising for NRR and indeed improves the scaling relationship of transition metals.

    

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3. Cylindrical C 96 Fullertubes: A Highly Active Metal‐Free O 2 ‐Reduction Electrocatalyst

   https://doi.org/10.1002/anie.202116727  

   Sanad, Mohamed Fathi ; Franklin, Hannah M. ; Ali, Basant A. ; Puente Santiago, Alain R. ; Nair, Aruna N. ; Chava, Venkata S. N. ; Fernandez‐Delgado, Olivia ; Allam, Nageh K. ; Stevenson, Steven ; Sreenivasan, Sreeprasad T. ; et al ( March 2022 , Angewandte Chemie International Edition)

   A new isolation protocol was recently reported for highly purified metallic FullertubesD_5h‐C₉₀,D_3d‐C₉₆, andD_5d‐C_100,which exhibit unique electronic features. Here, we report the oxygen reduction electrocatalytic behavior of C₆₀, C₇₀(spheroidal fullerenes), and C₉₀, C₉₆, and C₁₀₀(tubular fullerenes) using a combination of experimental and theoretical approaches. C₉₆(a metal‐free catalyst) displayed remarkable oxygen reduction reaction (ORR) activity, with an onset potential of 0.85 V and a halfway potential of 0.75 V, which are close to the state‐of‐the‐art Pt/C benchmark catalyst values. We achieved an excellent power density of 0.75 W cm⁻²using C₉₆as a modified cathode in a proton‐exchange membrane fuel cell, comparable to other recently reported efficient metal‐free catalysts. Combined band structure (experimentally calculated) and free‐energy (DFT) investigations show that both favorable energy‐level alignment active catalytic sites on the carbon cage are responsible for the superior activity of C₉₆.

    

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4. Cylindrical C 96 Fullertubes: A Highly Active Metal‐Free O 2 ‐Reduction Electrocatalyst

   https://doi.org/10.1002/ange.202116727  

   Sanad, Mohamed Fathi ; Franklin, Hannah M. ; Ali, Basant A. ; Puente Santiago, Alain R. ; Nair, Aruna N. ; Chava, Venkata S. N. ; Fernandez‐Delgado, Olivia ; Allam, Nageh K. ; Stevenson, Steven ; Sreenivasan, Sreeprasad T. ; et al ( March 2022 , Angewandte Chemie)

   A new isolation protocol was recently reported for highly purified metallic FullertubesD_5h‐C₉₀,D_3d‐C₉₆, andD_5d‐C_100,which exhibit unique electronic features. Here, we report the oxygen reduction electrocatalytic behavior of C₆₀, C₇₀(spheroidal fullerenes), and C₉₀, C₉₆, and C₁₀₀(tubular fullerenes) using a combination of experimental and theoretical approaches. C₉₆(a metal‐free catalyst) displayed remarkable oxygen reduction reaction (ORR) activity, with an onset potential of 0.85 V and a halfway potential of 0.75 V, which are close to the state‐of‐the‐art Pt/C benchmark catalyst values. We achieved an excellent power density of 0.75 W cm⁻²using C₉₆as a modified cathode in a proton‐exchange membrane fuel cell, comparable to other recently reported efficient metal‐free catalysts. Combined band structure (experimentally calculated) and free‐energy (DFT) investigations show that both favorable energy‐level alignment active catalytic sites on the carbon cage are responsible for the superior activity of C₉₆.

    

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5. Essential Roles of Cp Ring Activation and Coordinated Solvent During Electrocatalytic H 2 Production with Fe(CpN3) Complexes

   https://doi.org/10.1021/acscatal.3c02911  

   Goel, Bhumika ; Neugebauer, Hagen ; VanderWeide, Andrew I. ; Sánchez, Práxedes ; Lalancette, Roger A. ; Grimme, Stefan ; Hansen, Andreas ; Prokopchuk, Demyan E. ( October 2023 , ACS Catalysis)

   Cyclopentadienyl (Cp), a classic ancillary ligand platform, can be chemically noninnocent in electrocatalytic H−H bond formation reactions via protonation of coordinated η5-Cp ligands to form η4-CpH moieties. However, the kinetics of η5-Cp ring protonation, ligand-to-metal (or metal-to-ligand) proton transfer, and the influence of solvent during H2 production electrocatalysis remain poorly understood. We report in-depth kinetic details for electrocatalytic H2 production with Fe complexes containing amine-functionalized CpN3 ligands that are protonated via exogenous acid to generate via η4-CpN3H intermediates (CpN3 = 6-amino-1,4-dimethyl-5,7-diphenyl-2,3,4,6-tetrahydrocyclopenta[b]pyrazin-6-yl). Under reducing conditions, state-of-the-art DFT calculations reveal that a coordinated solvent plays a crucial role in mediating stereo- and regioselective proton transfer to generate (endo-CpN3H)Fe(CO)2(NCMe), with other protonation pathways being kinetically insurmountable. To demonstrate regioselective endo-CpN3H formation, the isoelectronic model complex (endo-CpN3H)Fe(CO)3 is independently prepared, and kinetic studies with the on-cycle hydride intermediate CpN3FeH(CO)2 under CO cleanly furnish the ring-activated complex (endo-CpN3H)Fe(CO)3 via metal-to-ligand proton migration. The on-cycle complex CpN3FeH(CO)2 reacts with acid to release H2 and regenerate [CpN3Fe(CO)2(NCMe)]+, which was found to be the TOF-determining step via DFT. Collectively, these experimental and computational results underscore the emerging importance of Cp ring activation, inner-sphere solvation, and metal−ligand cooperativity to perform proton-coupled electron transfer catalysis for chemical fuel synthesis. 

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