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1. Bridging cyanides from cyanoiron metalloligands to redox-active dinitrosyl iron units

   https://doi.org/10.1039/C8DT01761A  

   Ghosh, Pokhraj ; Quiroz, Manuel ; Pulukkody, Randara ; Bhuvanesh, Nattamai ; Darensbourg, Marcetta Y. ( January 2018 , Dalton Transactions)

   Cyanide, as an ambidentate ligand, plays a pivotal role in providing a simple diatomic building-block motif for controlled metal aggregation (M–CN–M′). Specifically, the inherent hard–soft nature of the cyanide ligand, i.e. , hard-nitrogen and soft-carbon centers, is due to electronic handles for binding Lewis acids following the hard–soft acid–base principle. Studies by Holm and Karlin showed structural and electronic requirements for cyanide-bridged (por)Fe III –CN–Cu II/I (por = porphyrin) molecular assemblies as biomimetics for cyanide-inhibited terminal quinol oxidases and cytochrome-C oxidase. The dinitrosyliron unit (DNIU) that exists in two redox states, {Fe(NO) 2 } 9 and {Fe(NO) 2 } 10 , draws attention as an electronic analogy of Cu II and Cu I , d 9 and d 10 , respectively. In similar controlled aggregations, L-type [(η 5 -C 5 R 5 )Fe(dppe)(CN)] (dppe = diphenyl phosphinoethane; R = H and Me) have been used as N-donor, μ-cyanoiron metalloligands to stabilize the DNIU in two redox states. Two bimetallic [(η 5 -C 5 R 5 )(dppe)Fe II –CN–{Fe(NO) 2 } 9 (sIMes)][BF 4 ] complexes, Fe-1 (R = H) and Fe*-1 (R = CH 3 ), showed dissimilar Fe II CN–{Fe(NO) 2 } 9 angular bends due to the electronic donor properties of the [(η 5 -C 5 R 5 )Fe(dppe)(CN)] μ-cyanoiron metalloligand. A trimetallic [(η 5 -C 5 Me 5 )(dppe)Fe II –CN] 2 –{Fe(NO) 2 } 10 complex, Fe*-2 , engaged two bridging μ-cyanoiron metalloligands to stabilize the {Fe(NO) 2 } 10 unit. The lability of the Fe II –CN–{Fe(NO) 2 } 9/10 bond was probed by suitable X-type (Na + SPh − ) and L-type (PMe 3 ) ligands. Treatment of Fe-1 and Fe*-1 with PMe 3 accounted for a reduction-induced substitution at the DNIU, releasing [(η 5 -C 5 R 5 )Fe(dppe)(CN)] and N-heterocyclic carbene, and generating (PMe 3 ) 2 Fe(NO) 2 as the reduced {Fe(NO) 2 } 10 product. 

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2. A Novel Self‐Assembled Cobalt‐Free Perovskite Composite Cathode with Triple‐Conduction for Intermediate Proton‐Conducting Solid Oxide Fuel Cells

   https://doi.org/10.1002/adfm.202209695  

   Tong, Hua ; Fu, Min ; Yang, Yang ; Chen, Fanglin ; Tao, Zetian ( September 2022 , Advanced Functional Materials)

   A traditional composite cathode for proton‐conducting solid oxide fuel cells (H‐SOFCs) is typically obtained by mixing cathode materials and proton conducting electrolyte of BaCe_0.7Y_0.2Zr_0.1O_3–δ(BZCY), providing chemical and thermal compatibility with the electrolyte. Here, a series of triple‐conducing and cobalt‐free iron‐based perovskites as cathodes for H‐SOFCs is reported. Specifically, BaCe_xFe_1–xO_3–δ(x = 0.36, 0.43, and 0.50) shows various contents of two single phase perovskites with an in situ heterojunction structure as well as triple conductivity by tailoring the Ce/Fe ratios. The cell performance with the optimized BaCe_0.36Fe_0.64O_3–δ(BCF36) cathode composition reaches 1056 mW cm⁻²at 700 °C. Moreover, a record cell performance of 1525 mW cm⁻²at 700 °C is obtained by modifying the BCF36 cathode microstructure through a spraying method, demonstrating high promise with Co‐free cathodes for H‐SOFCs.

    

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3. Higher spin states in some low-energy bis(tetramethyl-1,2-diaza-3,5-diborolyl) sandwich compounds of the first row transition metals: boraza analogues of the metallocenes

   https://doi.org/10.1039/C8NJ05517C  

   Chen, Jianlin ; Feng, Hao ; Xie, Yaoming ; King, R. Bruce ; Schaefer, Henry F. ( March 2019 , New Journal of Chemistry)

   The known sandwich compound [η 5 -(CH 2 ) 3 N 2 (BPh) 2 CMe] 2 Fe in which adjacent C 2 units are replaced by isoelectronic BN units can be considered as a boraza analogues of ferrocene similar to borazine, B 3 N 3 H 6 , considered as a boraza analogue of benzene. In this connection, the related bis(1,2,3,5-tetramethyl-1,2-diaza-3,5-diborolyl) derivatives (Me 4 B 2 N 2 CH) 2 M (M = Ti, V, Cr, Mn, Fe, Co, Ni) for all of the first row transition metals have been optimized using density functional theory for comparison with the isoelectronic tetramethylcyclopentadienyl derivatives (Me 4 C 5 H) 2 M. Low-energy sandwich structures having parallel B 2 N 2 C rings in a trans orientation are found for all seven metals. The 1,2-diaza-3,5-diborolyl ligand appears to be a weaker field ligand than the isoelectronic cyclopentadienyl ligand as indicated by higher spin ground states for some (η 5 -Me 4 B 2 N 2 CH) 2 M sandwich compounds relative to the corresponding metallocenes (η 5 -Me 4 C 5 H) 2 M. Thus (η 5 -Me 4 B 2 N 2 CH) 2 Cr has a quintet ground state in contrast to the triplet ground state of (η 5 -Me 4 C 5 H) 2 Cr. Similarly, the sextet ground state of (η 5 -Me 4 B 2 N 2 CH) 2 Mn lies ∼18 kcal mol −1 below the quartet state in contrast to the doublet ground state of the isoelectronic (Me 4 C 5 H) 2 Mn. These sandwich compounds are potentially accessible by reaction of 1,2-diaza-3,5-diborolide anions with metal halides analogous to the synthesis of [η 5 -(CH 2 ) 3 N 2 (BPh) 2 CMe] 2 Fe. 

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4. Photocatalytic C–H activation and the subtle role of chlorine radical complexation in reactivity

   https://doi.org/10.1126/science.abd8408  

   Yang, Qiaomu ; Wang, Yu-Heng ; Qiao, Yusen ; Gau, Michael ; Carroll, Patrick J. ; Walsh, Patrick J. ; Schelter, Eric J. ( May 2021 , Science)

   The functionalization of methane, ethane, and other alkanes derived from fossil fuels is a central goal in the chemical enterprise. Recently, a photocatalytic system comprising [Ce^IVCl₅(OR)]²⁻[Ce^IV, cerium(IV); OR, –OCH₃or –OCCl₂CH₃] was disclosed. The system was reportedly capable of alkane activation by alkoxy radicals (RO•) formed by Ce^IV–OR bond photolysis. In this work, we present evidence that the reported carbon-hydrogen (C–H) activation of alkanes is instead mediated by the photocatalyst [NEt₄]₂[CeCl₆] (NEt₄⁺, tetraethylammonium), and RO• are not intermediates. Spectroscopic analyses and kinetics were investigated for C–H activation to identify chlorine radical (Cl•) generation as the rate-limiting step. Density functional theory calculations support the formation of [Cl•][alcohol] adducts when alcohols are present, which can manifest a masked RO• character. This result serves as an important cautionary note for interpretation of radical trapping experiments.

    

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5. Isolation and characterization of a covalent CeIV-Aryl complex with an anomalous 13C chemical shift

   https://doi.org/10.1038/s41467-021-21766-4  

   Panetti, Grace B. ; Sergentu, Dumitru-Claudiu ; Gau, Michael R. ; Carroll, Patrick J. ; Autschbach, Jochen ; Walsh, Patrick J. ; Schelter, Eric J. ( December 2021 , Nature Communications)

   null (Ed.)

   Abstract The synthesis of bona fide organometallic Ce IV complexes is a formidable challenge given the typically oxidizing properties of the Ce IV cation and reducing tendencies of carbanions. Herein, we report a pair of compounds comprising a Ce IV  − C aryl bond [Li(THF) 4 ][Ce IV (κ 2 - ortho -oxa)(MBP) 2 ] ( 3-THF ) and [Li(DME) 3 ][Ce IV (κ 2 - ortho -oxa)(MBP) 2 ] ( 3-DME ), ortho -oxa = dihydro-dimethyl-2-[4-(trifluoromethyl)phenyl]-oxazolide, MBP 2–  = 2,2′-methylenebis(6- tert -butyl-4-methylphenolate), which exhibit Ce IV  − C aryl bond lengths of 2.571(7) – 2.5806(19) Å and strongly-deshielded, Ce IV  − C ipso 13 C{ 1 H} NMR resonances at 255.6 ppm. Computational analyses reveal the Ce contribution to the Ce IV  − C aryl bond of 3-THF is ~12%, indicating appreciable metal-ligand covalency. Computations also reproduce the characteristic 13 C{ 1 H} resonance, and show a strong influence from spin-orbit coupling (SOC) effects on the chemical shift. The results demonstrate that SOC-driven deshielding is present for Ce IV  − C ipso 13 C{ 1 H} resonances and not just for diamagnetic actinide compounds. 

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