More Like this

1. Dynamically Unveiling Metal–Nitrogen Coordination during Thermal Activation to Design High‐Efficient Atomically Dispersed CoN ₄ Active Sites

   https://doi.org/10.1002/anie.202017288  

   He, Yanghua; Shi, Qiurong; Shan, Weitao; Li, Xing; Kropf, A. Jeremy; Wegener, Evan C.; Wright, Joshua; Karakalos, Stavros; Su, Dong; Cullen, David A.; et al (March 2021, Angewandte Chemie International Edition)

   Abstract We elucidate the structural evolution of CoN₄sites during thermal activation by developing a zeolitic imidazolate framework (ZIF)‐8‐derived carbon host as an ideal model for Co²⁺ion adsorption. Subsequent in situ X‐ray absorption spectroscopy analysis can dynamically track the conversion from inactive Co−OH and Co−O species into active CoN₄sites. The critical transition occurs at 700 °C and becomes optimal at 900 °C, generating the highest intrinsic activity and four‐electron selectivity for the oxygen reduction reaction (ORR). DFT calculations elucidate that the ORR is kinetically favored by the thermal‐induced compressive strain of Co−N bonds in CoN₄active sites formed at 900 °C. Further, we developed a two‐step (i.e., Co ion doping and adsorption) Co‐N‐C catalyst with increased CoN₄site density and optimized porosity for mass transport, and demonstrated its outstanding fuel cell performance and durability. 

   more » « less
2. Platinum Elimination from Bis(triethylsilylpolyynyl) Complexes ( n ‐Bu ₂ C(CH ₂ PPh ₂ ) ₂ )Pt((C≡C) _n SiEt ₃ ) ₂ ( n =2, 3) and Macrocycles Comprised of Four L ₂ Pt Corners and Four C≡CC≡CC≡C Linkers; An Approach to Cyclo[24]carbon

   https://doi.org/10.1002/chem.202402833  

   Collins, Brenna_K; Gladysz, John_A (October 2024, Chemistry – A European Journal)

   Abstract The overarching goal of this study is to effect the elimination of platinum from adducts withcis–C≡C−Pt−C≡C‐ linkages, thereby generating novel conjugated polyynes. Thus, the bis(hexatriynyl) complextrans‐(p‐tol₃P)₂Pt((C≡C)₃H)₂is treated with 1,3‐diphosphines R₂C(CH₂PPh₂)₂to generate (R₂C(CH₂PPh₂)₂)₂Pt((C≡C)₃H)₂(14; R=c,n‐Bu;e,p‐tolCH₂). These condense with the diiodide complexes R₂C(CH₂PPh₂)₂PtI₂(9 a,c) in the presence of CuI (cat.) and excess HNEt₂to give the title macrocycles [(R₂C(CH₂PPh₂)₂)Pt(C≡C)₃]₄(16 c,e) as adducts of the byproduct [H₂NEt₂]⁺I⁻(30–66 %). DOSY NMR experiments establish that this association is maintained in solution, but NaOAc removes the ammonium salt. The bis(triethylsilylpolyynyl) complexes (n‐Bu₂C(CH₂PPh₂)₂)Pt((C≡C)_nSiEt₃)₂(n=2, 3) are synthesized analogously to14 c. They react with I₂at rt to give mainly the diiodide complex9 cand the coupling product Et₃Si(C≡CC≡C)_nSiEt₃. The possibility of competing reactions giving IC≡C species is investigated. Analogous reactions of the Pt₄C₂₄macrocycle16 calso give9 c, but no sp¹³C NMR signals or mass spectrometric C_x^z+ions (x=24–100) could be detected. It is proposed that some cyclo[24]carbon is generated, but then rapidly converts to other forms of elemental carbon. No cyclotetracosane (C₂₄H₄₈) is detected when this sequence is carried out in the presence of PtO₂and H₂. 

   more » « less
3. Magnetic anisotropy of two tetrahedral Co( ii )-halide complexes with triphenylphosphine ligands

   https://doi.org/10.1039/D2DT00121G  

   Lv, Wei; Cui, Hui-Hui; Chen, Lei; Zhang, Yi-Quan; Chen, Xue-Tai; Wang, Zhenxing; Ouyang, Zhong-Wen; Xue, Zi-Ling (May 2022, Dalton Transactions)

   Recently, the choice of ligand and geometric control of mononuclear complexes, which can affect the relaxation pathways and blocking temperature, have received wide attention in the field of single-ion magnets (SIMs). To find out the influence of the coordination environment on SIMs, two four-coordinate mononuclear Co( ii ) complexes [NEt 4 ][Co(PPh 3 )X 3 ] (X = Cl − , 1; Br − , 2) have been synthesized and studied by X-ray single crystallography, magnetic measurements, high-frequency and -field EPR (HF-EPR) spectroscopy and theoretical calculations. Both complexes are in a cubic space group Pa 3̄ (No. 205), containing a slightly distorted tetrahedral moiety with crystallographically imposed C 3 v symmetry through the [Co(PPh 3 )X 3 ] − anion. The direct-current (dc) magnetic data and HF-EPR spectroscopy indicated the anisotropic S = 3/2 spin ground states of the Co( ii ) ions with the easy-plane anisotropy for 1 and 2. Ab initio calculations were performed to confirm the positive magnetic anisotropies of 1 and 2. Frequency- and temperature-dependent alternating-current (ac) magnetic susceptibility measurements revealed slow magnetic relaxation for 1 and 2 at an applied dc field. Finally, the magnetic properties of 1 and 2 were compared to those of other Co( ii ) complexes with a [CoAB 3 ] moiety. 

   more » « less
4. Macrocyclic Complexes Derived from Four cis ‐L ₂ Pt Corners and Four Butadiynediyl Linkers; Syntheses, Electronic Structures, and Square versus Skew Rhombus Geometries

   https://doi.org/10.1002/chem.202100305  

   Collins, Brenna_K; Clough_Mastry, Melissa; Ehnbom, Andreas; Bhuvanesh, Nattamai; Hall, Michael_B; Gladysz, John_A (June 2021, Chemistry – A European Journal)

   Abstract The dialkyl malonate derived 1,3‐diphosphines R₂C(CH₂PPh₂)₂(R=a, Me;b, Et;c,n‐Bu;d,n‐Dec;e, Bn;f,p‐tolCH₂) are combined with (p‐tol₃P)₂PtCl₂ortrans‐(p‐tol₃P)₂Pt((C≡C)₂H)₂to give the chelatescis‐(R₂C(CH₂PPh₂)₂)PtCl₂(2 a–f, 94–69 %) orcis‐(R₂C(CH₂PPh₂)₂)Pt((C≡C)₂H)₂(3 a–f, 97–54 %). Complexes3 a–dare also available from2 a–dand excess 1,3‐butadiyne in the presence of CuI (cat.) and excess HNEt₂(87–65 %). Under similar conditions,2and3react to give the title compounds [(R₂C(CH₂PPh₂)₂)[Pt(C≡C)₂]₄(4 a–f; 89–14 % (64 % avg)), from which ammonium salts such as the co‐product [H₂NEt₂]⁺Cl⁻are challenging to remove. Crystal structures of4 a,bshow skew rhombus as opposed to square Pt₄geometries. The NMR and IR properties of4 a–fare similar to those of mono‐ or diplatinum model compounds. However, cyclic voltammetry gives only irreversible oxidations. As compared to mono‐platinum or Pt(C≡C)₂Pt species, the UV‐visible spectra show much more intense and red‐shifted bands. Time dependent DFT calculations define the transitions and principal orbitals involved. Electrostatic potential surface maps reveal strongly negative Pt₄C₁₆cores that likely facilitate ammonium cation binding. Analogous electronic properties of Pt₃C₁₂and Pt₅C₂₀homologs and selected equilibria are explored computationally. 

   more » « less
5. Al(OR ^F ) ₃ (R ^F = C(CF ₃ ) ₃ ) activated silica: a well-defined weakly coordinating surface anion

   https://doi.org/10.1039/C9SC05904K  

   Culver, Damien B.; Venkatesh, Amrit; Huynh, Winn; Rossini, Aaron J.; Conley, Matthew P. (February 2020, Chemical Science)

   Weakly Coordinating Anions (WCAs) containing electron deficient delocalized anionic fragments that are reasonably inert allow for the isolation of strong electrophiles. Perfluorinated borates, perfluorinated aluminum alkoxides, and halogenated carborane anions are a few families of WCAs that are commonly used in synthesis. Application of similar design strategies to oxide surfaces is challenging. This paper describes the reaction of Al(OR F ) 3 *PhF (R F = C(CF 3 ) 3 ) with silica partially dehydroxylated at 700 °C (SiO 2-700 ) to form the bridging silanol Si–OH⋯Al(OR F ) 3 ( 1 ). DFT calculations using small clusters to model 1 show that the gas phase acidity (GPA) of the bridging silanol is 43.2 kcal mol −1 lower than the GPA of H 2 SO 4 , but higher than the strongest carborane acids, suggesting that deprotonated 1 would be a WCA. Reactions of 1 with NOct 3 show that 1 forms weaker ion-pairs than classical WCAs, but stronger ion-pairs than carborane or borate anions. Though 1 forms stronger ion-pairs than these state-of-the-art WCAs, 1 reacts with alkylsilanes to form silylium type surface species. To the best of our knowledge, this is the first example of a silylium supported on derivatized silica. 

   more » « less