Concurrent Stabilization of π‐Donor and π‐Acceptor Ligands in Aromatized and Dearomatized Pincer [(PNN)Re(CO)(O)2] Complexes

Aromatized cationic [(PNN)Re(π acid)(O)₂]⁺ ( 1 ) and dearomatized neutral [(PNN*)Re(π acid)(O)₂] ( 2 ) complexes (where π acid=CO ( a ), tBuNC ( b ), or (2,6‐Me₂)PhNC ( c )), possessing both π‐donor and π‐acceptor ligands, have been synthesized and fully characterized. Reaction of [(PNN)Re(O)₂]⁺ ( 4 ) with lithiumhexamethyldisilazide (LiHMDS) yield the dearomatized [(PNN*)Re(O)₂] ( 3 ). Complexes 1 and 2 are prepared from the reaction of 4 and 3 , respectively, with CO or isocyanides. Single‐crystal X‐ray structures of 1 a and 1 b show the expected trans‐dioxo structure, in which the oxo ligands occupy the axial positions and the π‐acidic ligand occupies the equatorial plane in an overall octahedral geometry about the rhenium(V) center. DFT studies revealed the stability of complexes 1 and 2 arises from a π‐backbonding interaction between the d_xy orbital of rhenium, the π orbital of the oxo ligands, and the π* orbital of CO/isocyanide.     

Crystal structures and spectroscopic characterization of MBr2(CNXyl)n (M = Fe and Co,n = 4; M = Ni,n = 2; Xyl = 2,6‐dimethylphenyl), and of formally zero‐valent iron as a cocrystal of Fe(CNXyl)5 and Fe2(CNXyl)9

Structures and spectroscopic characterization of the divalent complexes cis‐dibromidotetrakis(2,6‐dimethylphenyl isocyanide)iron(II) dichloromethane 0.771‐solvate, [FeBr₂(C₉H₉N)₄]·0.771CH₂Cl₂ or cis‐FeBr₂(CNXyl)₄·0.771CH₂Cl₂ (Xyl = 2,6‐dimethylphenyl), trans‐dibromidotetrakis(2,6‐dimethylphenyl isocyanide)iron(II), [FeBr₂(C₉H₉N)₄] or trans‐FeBr₂(CNXyl)₄, trans‐dibromidotetrakis(2,6‐dimethylphenyl isocyanide)cobalt(II), [CoBr₂(C₉H₉N)₄] or trans‐CoBr₂(CNXyl)₄, and trans‐dibromidobis(2,6‐dimethylphenyl isocyanide)nickel(II), [NiBr₂(C₉H₉N)₂] or trans‐NiBr₂(CNXyl)₂, are presented. Additionally, crystals grown from a cold diethyl ether solution of zero‐valent Fe(CNXyl)₅ produced a structure containing a cocrystallization of mononuclear Fe(CNXyl)₅ and the previously unknown dinuclear [Fe(CNXyl)₃]₂(μ₂‐CNXyl)₃, namely pentakis(2,6‐dimethylphenyl isocyanide)iron(0) tris(μ₂‐2,6‐dimethylphenyl isocyanide)bis[tris(2,6‐dimethylphenyl isocyanide)iron(0)], [Fe(C₉H₉N)₅][Fe₂(C₉H₉N)₉]. The (M)C—N—C(Xyl) angles of the isocyanide ligand are nearly linear for the metals in the +2 oxidation state, for which the ligands function essentially as pure donors. The νCN stretching frequencies for these divalent metal isocyanides are at or above that of the free ligand. Relative to Fe^II, in the structure containing iron in the formally zero‐valent oxidation state, the Fe—C bond lengths have shortened, the C[triple‐bond]N bond lengths have elongated, the (M)C—N—C(Xyl) angles of the terminal CNXyl ligands are more bent, and the νCN stretching frequencies have shifted to lower energies, all indicative of substantial M(dπ)→π* backbonding.     

Efficient Fe‐Co‐N‐C Electrocatalyst Towards Oxygen Reduction Derived from a Cationic CoII‐based Metal–Organic Framework Modified by Anion‐Exchange with Potassium Ferricyanide

Fe‐Co‐N‐C electrocatalysts have proven superior to their counterparts (e.g. Fe‐N‐C or Co‐N‐C) for the oxygen reduction reaction (ORR). Herein, we report on a unique strategy to prepare Fe‐Co‐N‐C?x (x refers to the pyrolysis temperature) electrocatalysts which involves anion‐exchange of [Fe(CN)₆]^3? into a cationic Co^II‐based metal‐organic framework precursor prior to heat treatment. Fe‐Co‐N‐C‐900 exhibits an optimal ORR catalytic performance in an alkaline electrolyte with an onset potential (E_onset: 0.97 V) and half‐wave potential (E_1/2: 0.86 V) comparable to that of commercial Pt/C (E_onset=1.02 V; E_1/2=0.88 V), which outperforms the corresponding Co‐N‐C‐900 sample (E_onset=0.92 V; E_1/2=0.84 V) derived from the same MOF precursor without anion‐exchange modification. This is the first example of Fe‐Co‐N‐C electrocatalysts fabricated from a cationic Co^II‐based MOF precursor that dopes the Fe element via anion‐exchange, and our current work provides a new entrance towards MOF‐derived transition‐metal (e.g. Fe or Co) and nitrogen‐codoped carbon electrocatalysts with excellent ORR activity.     

Structures and Bonding Situation of Iron Complexes of Group‐13 Half‐Sandwich ECp* (E = B to Tl) Based on DFT Calculations

Quantum chemical calculations at the BP86 level with various basis sets (SVP, TZVPP, and TZ2P+) were carried out for the Fe(CO)₄ of group‐13 half‐sandwich ECp* [Fe(CO)₄‐ECp*] ( Fe4‐E ) (E = B to Tl). The chemical bonding of the Fe(CO)₄‐ECp* bond was analyzed with charge‐ and energy decomposition methods. The calculated equilibrium structures of complexes Fe4‐E show that the ligands ECp* are bonded in an end‐on way to the fragment Fe(CO)₄ in Fe4‐E with E = B to Ga. The compound Fe4‐In has a distorted end‐on ligand InCp*. In contrast, Fe4‐Tl has a side‐on bonded ligand TlCp*. The calculated bond dissociation energies (BDEs) suggest that the bond in the iron group‐13 half‐sandwich complexes Fe4‐E decreases from Fe4‐B to Fe4‐Tl . Natural bond orbital (NBO) analysis of the bonding situation reveals that the Fe(CO)₄←ECp* donation in Fe4‐E comes from the σ lone‐pair orbital of ECp*. Bonding analysis indicates that the ligand ECp* in complexes are strong σ donors and the NOCV pairs of the bonding show small π‐back donation from the Fe(CO)₄ to the ECp* ligands.     

Iron(II) and Nickel(II) Complexes of N‐Alkylimidazoles and 1‐Methyl‐1H‐1, 2, 4‐Triazole: X‐ray Studies,Magnetic Characterization,and DFT Calculations

Using the ligands N‐methylimidazole ( MeIm ), N‐ethylimidazole ( EtIm ), N‐propylimidazole ( PrIm ), and 1‐methyl‐1H‐1, 2, 4‐triazole ( MeTz ) three series with a total of 13 iron(II) complexes were isolated. The series comprise of the following complexes: (a) [Fe( MeIm )₆](ClO₄)₂ ( 1 ), [Fe( EtIm )₆](ClO₄)₂ ( 2 ), [Fe( PrIm )₆](ClO₄)₂( 3 ), [Fe( MeTz )₆](ClO₄)₂ ( 4 ), [Fe( MeIm )₆](MeSO₃)₂ ( 5 ), [Fe( EtIm )₆](MeSO₃)₂ ( 6 ), and [Fe( MeTz )₆](BF₄)₂ ( 10 ); (b) [Fe( MeIm )₄(MeSO₃)₂]( 7 ), [Fe( EtIm )₄(MeSO₃)₂] ( 8 ), and [Fe( PrIm )₄(MeSO₃)₂] ( 9 ); (c) [Fe( MeIm )₄(NCS)₂] ( 15 ), [Fe( EtIm )₄(NCS)₂] ( 16 ), and [Fe( MeTz )₄(NCS)₂] ( 17 ). Single crystal X‐ray diffraction studies were performed on 7 – 10 and 15 – 17 . Temperature dependent magnetic susceptibility measurements were performed on selective examples of all series, and confirmed them to be in the HS state over the range 6–300 K. DFT calculations were performed at BP86/def‐SV(P) and TPSSh/def2‐TZVPP level on all [Fe L ₆]²⁺ complex cations and the neutral complexes 7 – 9 and 15 – 17 . Additionally the four homoleptic nickel(II) complexes [Ni L ₆](ClO₄)₂ ( 11 : L = MeIm ; 12 : L = EtIm ; 13 : L = PrIm ; 14 : L = MeTz ) were synthesized and compounds 11 – 13 structurally characterized. UV/Vis/NIR spectroscopic measurements were carried out on all homoleptic iron(II) and nickel(II) complexes. The 10Dq values were determined to be in the range of 11547–11574 and 10471–10834 cm^–1 for the iron(II) and nickel(II) complexes, respectively.     

Hydrogen bonding and π–π interactions in the cocrystal salt [Fe(bpe)2(H2O)4](TCEP)2·2(bpe) [bpe is trans‐1,2‐bis(pyridin‐4‐yl)ethene and TCEP is 1,1,3,3‐tetracyano‐2‐ethoxypropenide]

The cocrystal salt tetraaquabis[trans‐1,2‐bis(pyridin‐4‐yl)ethene‐κN]iron(II) bis(1,1,3,3‐tetracyano‐2‐ethoxypropenide)–trans‐1,2‐bis(pyridin‐4‐yl)ethene (1/2), [Fe(C₁₂H₁₀N₂)₂(H₂O)₄](C₉H₅N₄O)₂·2C₁₂H₁₀N₂, is a rare example of a mononuclear Fe^II compound with trans‐1,2‐bis(pyridin‐4‐yl)ethane (bpe) ligands. The complex cation resides on a crystallographically imposed inversion center and exhibits a tetragonally distorted octahedral coordination geometry. Both the symmetry‐independent bpe ligand and the cocrystallized bpe molecule are essentially planar. The 1,1,3,3‐tetracyano‐2‐ethoxypropenide counter‐ion is nonplanar and the bond lengths are consistant with significant electron delocalization. The extended structure exhibits an extensive O—H…N hydrogen‐bonding network with layers of complex cations joined by the cocrystallized bpe. Both the coordinated and the cocrystallized bpe are involved in π–π interactions. Hirshfeld and fingerprint plots reveal the important intermolecular interactions. Density functional theory was used to estimate the strengths of the hydrogen‐bonding and π–π interactions, and suggest that the O—H…N hydrogen bonds enhance the strength of the π‐interactions by increasing the polarization of the pyridine rings.     

Carbo‐biphenyls and Carbo‐terphenyls: Oligo(phenylene ethynylene) Ring Carbo‐mers

Ring carbo‐mers of oligo(phenylene ethynylene)s (OPEn, n=0–2), made of C₂‐catenated C₁₈ carbo‐benzene rings, have been synthesized and characterized by NMR and UV‐vis spectroscopy, crystallography and voltammetry. Analyses of crystal and DFT‐optimized structures show that the C₁₈ rings preserve their individual aromatic character according to structural and magnetic criteria (NICS indices). Carbo‐terphenyls (n=2) are reversibly reduced at ca. ?0.42 V/SCE, i.e. 0.41 V more readily than the corresponding carbo‐benzene (?0.83 V/SCE), thus revealing efficient inter‐ring π‐conjugation. An accurate linear fit of E_1/2^red1 vs. the DFT LUMO energy suggests a notably higher value (?0.30 V/SCE) for a carbo‐quaterphenyl congener (n=3). Increase with n of the effective π‐conjugation is also evidenced by a red shift of two of the three main visible light absorption bands, all being assigned to TDDFT‐calculated excited states, one of them restricting to a HOMO→LUMO main one‐electron transition.     

Synthesis,Crystal Structures,Thermal and Magnetic Properties of New Selenocyanato Coordination Polymers with Pyrazine as Co‐Ligand

Reaction of iron(II), cobalt(II) and nickel(II) selenocyanate with pyrazine in water at room temperature leads to the formation of the isotypic new ligand‐rich 1:2 (1:2 = ratio between metal and co‐ligand) compounds [M(NCSe)₂(pyrazine)₂]_n (M = Fe ( 1 ), Co ( 2 ), Ni ( 3 )). The crystal structure of 2 was determined by X‐ray single crystal analysis and those of 1 and 3 were refined from X‐ray powder data with the Rietveld method. In their crystal structure the metal(II) cations are coordinated by four pyrazine co‐ligands, which connect them into layers, and two terminally N‐bonded selenocyanato anions in a distorted octahedral arrangement. The terminal coordination mode of the selenocyanato anions was further emphasized by IR spectroscopic investigations. On heating, all compounds decompose in a single heating step without the formation of ligand‐deficient intermediates like previously reported for related thiocyanato compounds. Magnetic measurements of compound 1 show a long‐range antiferromagnetic ordering with an ordering temperature of T_N = 6.7 K, which must be mediated by the aromatic π‐system of the pyrazine ligand, whereas 2 and 3 show only Curie–Weiss behavior with antiferromagnetic exchange interactions.     

From an Electron‐Rich Bis(boraketenimine) to an Electron‐Poor Diborene

The reaction of the bisboracumulene (CAAC)₂B₂ (CAAC=1‐(2,6‐diisopropylphenyl)‐3,3,5,5‐tetramethylpyrrolidin‐2‐ylidene) with excess tert‐butylisocyanide resulted in complexation of the isocyanide at boron. Though this compound might be formally drawn with a lone pair on boron, these electrons are highly delocalized throughout a conjugated π‐network consisting of the π‐acidic CAAC and isocyanide ligands. Heating this compound to 110 °C liberated the organic periphery of both isocyanide ligands, yielding the first example of a dicyanodiborene. Cyclic voltammetry conducted on this diborene indicated the presence of reduction waves, making this compound unique among diborenes, which are otherwise highly reducing.     

The Reaction of 2‐X‐1, 2‐Difluoroalk‐1‐enyldifluoroboranes with Xenon Difluoride. A Methodical Approach to 1, 2‐Difluoroalk‐1‐enylxenon(II) Salts

2‐X‐1, 2‐Difluoroalk‐1‐enylxenon(II) salts were prepared by the reaction of XeF₂ with XCF=CFBF₂ (X = F, trans‐H, cis‐Cl, trans‐Cl, cis‐CF₃, cis‐C₂F₅) but no organoxenon(II) compounds were obtained when the trans‐isomers of boranes, trans‐XCF=CFBF₂ (X = CF₃, C₄F₉, C₄H₉, Et₃Si), were used under similar conditions.     

Palladium(II) Complexes with the Mixed‐Donor Ligand CH3S‐(CH2)3‐PPh2 Crystal Structures of [PdCl2{CH3S‐(CH2)3‐PPh2}n](n = 1, 2)

The phosphorus‐sulfur ligand 1‐(methylthio)‐3‐(diphenylphosphino)‐propane (S‐P3) has been synthesized and characterized by ¹H NMR and ¹³C NMR. Reactions of S‐P3 with [PdCl₂(PhCN)₂] afforded the complexes [PdCl₂(S‐P3)] ( I ) and [PdCl₂(S‐P3)₂] ( II ), in which S‐P3 acts as a bidentate and monodentate ligand, respectively. Compound I crystallizes in monoclinic space group P2₁/n (No. 14) with cell dimensions: a = 8.589(3), b = 15.051(3), c = 17.100(3)Å, β = 102.91(2)°, V = 2154.7(9)ų, Z = 4. Likewise, compound II crystallizes in monoclinic space group P2₁/n (No. 14) with a = 9.993(5), b = 8.613(4), c = 18.721(5)Å, β = 90.18(3)°, V = 1611.3(12)ų, Z = 2. Compound II has a trans square planar configuration with only the P‐site of the ligand bonded to the palladium atom.     

Co‐crystallized cis and trans isomers of dichloro­bis(2‐picolylamine)iron(II)

The octa­hedral cis and trans isomers of dichloro­bis(2‐picolyl­amine)iron(II), [FeCl₂(C₆H₈N₂)₂], co‐crystallize in a 1:1 ratio. The cis isomer lies on a twofold axis, whereas the trans isomer lies on an inversion centre. The structure is fully ordered, with both Fe atoms in a pure high‐spin state. The Fe, Cl and N(H₂) atoms of both isomers lie in the same plane, allowing all Cl and amine H atoms to be engaged in extensive two‐dimensional hydrogen bonding. The hydrogen‐bonded layers are inter­connected through π–π inter­actions between the pyridine rings. Searches in the Cambridge Structural Database uncover very few examples of such isomer co‐existence.     

1,2,3‐Trimethoxy‐4‐[(E)‐2‐phenylvinyl]benzene and (E,E)‐1,4‐bis(2,3,4‐trimethoxyphenyl)buta‐1,3‐diene

The stilbene derivative 1,2,3‐trimethoxy‐4‐[(E)‐2‐phenylvinyl]benzene, C₁₇H₁₈O₃, (I), and its homocoupling co‐product (E,E)‐1,4‐bis(2,3,4‐trimethoxyphenyl)buta‐1,3‐diene, C₂₂H₂₆O₆, (II), both have double bonds in trans conformations in their conjugated linkages. In the structure of stilbene (I), the aromatic rings deviate significantly from coplanarity, in contrast with coproduct (II), the core of which is rigorously planar. The deviation in stilbene (I) seems to be driven by intermolecular electrostatic interactions. Diene (II) sits on a crystallographic inversion centre, which bisects the conjugated linkage.     

Synthesis,Structure, and Magnetic Characterization of a Series of Iron(II) Coordination Frameworks with 2, 6‐Bis(1, 2,4‐triazole‐4‐yl)pyridine

Based on the bis‐triazole ligand 2, 6‐bis(1, 2,4‐triazole‐4‐yl)pyridine (L), the triazole‐iron(II) complexes [Fe(L)₂(dca)₂(H₂O)₂] · 2H₂O ( 1 ) (Nadca = sodium dicyanamide), {[Fe(μ₂‐L)₂(H₂O)₂]Cl₂}_n ( 2 ), and {[Fe(μ₂‐L)₂(H₂O)₂](ClO₄)₂ · L · H₂O}_n ( 3 ) were isolated by solvent diffusion methods. When iron(II) salts and Nadca were used, compound 1 was isolated, which contains mononuclear Fe(L)₂(dca)₂(H₂O)₂ units. When FeCl₂ or FeClO₄ were used, one‐dimensional (1D) cation iron(II) chains ( 2 ) and two‐dimensional (2D) cation iron(II) networks ( 3 ) were isolated indicating anion directing structural diversity. Moreover, variable‐temperature magnetic susceptibility data of 1 – 3 were recorded in the temperature range 2–300 K. The magnetic curve of complex 2 was fitted by using the classical spin Heisenberg chain model indicating anti‐ferromagnetic interactions (J = –5.31 cm^–1). Obviously complexes 1 – 3 show no detectable thermal spin crossover behaviors, the lack of spin‐crossover behavior may be correlated with FeN₄O₂ coordination spheres in 1 – 3 .     

On the reactivity of platina‐β‐diketones: a straightforward synthesis of trans‐acetylchlorobis(phosphine)platinum(II) complexes and their reactivity

The platina‐β‐diketone [Pt₂{(COMe)₂H}₂(µ‐Cl)₂] ( 1 ) was found to react with monodentate phosphines to yield acetyl(chloro)platinum(II) complexes trans‐[Pt(COMe)Cl(PR₃)₂] (PR₃ = PPh₃, 2a ; P(4‐FC₆H₄)₃, 2b ; PMePh₂, 2c ; PMe₂Ph, 2d ; P(n‐Bu)₃, 2e ; P(o‐tol)₃, 2f ; P(m‐tol)₃, 2g ; P(p‐tol)₃, 2h ). In the reaction with P(o‐tol)₃ the methyl(carbonyl)platinum(II) complex [Pt(Me)Cl(CO){P(o‐tol)₃}] ( 3a ) was found to be an intermediate. On the other hand, treating 1 with P(C₆F₅)₃ led to the formation of [Pt(Me)Cl(CO){P(C₆F₅)₃}] ( 3b ), even in excess of the phosphine. Phosphine ligands with a lower donor capability in complexes 2 and the arsine ligand in trans‐[Pt(COMe)Cl(AsPh₃)₂] ( 2i ) proved to be subject to substitution by stronger donating phosphine ligands, thus forming complexes trans‐[Pt(COMe)Cl(L)L′] (L/L′ = AsPh₃/PPh₃, 4a ; PPh₃/P(n‐Bu)₃, 4b ) and cis‐[Pt(COMe)Cl(dppe)] ( 4c ). Furthermore, in boiling benzene, complexes 2a – 2c and 2i underwent decarbonylation yielding quantitatively methyl(chloro)platinum(II) complexes trans‐[Pt(Me)Cl(L)₂] (L = PPh₃, 5a ; P(4‐FC₆H₄)₃, 5b ; PMePh₂, 5c ; AsPh₃, 5d ). The identities of all complexes were confirmed by ¹H, ¹³C and ³¹P NMR spectroscopy. Single‐crystal X‐ray diffraction analyses of 2a ·2CHCl₃, 2f and 5b showed that the platinum atom is square‐planar coordinated by two phosphine ligands (PPh₃, 2a ; P(o‐tol)₃, 2f ; P(4F‐C₆H₄)₃, 5b ) in mutual trans position as well as by an acetyl ligand ( 2a, 2f ) and a methyl ligand ( 5b ), respectively, trans to a chloro ligand. Single‐crystal X‐ray diffraction analysis of 3b exhibited a square‐planar platinum complex with the two π‐acceptor ligands CO and P(C₆F₅)₃ in mutual cis position (configuration index: SP‐4‐3). Copyright © 2005 John Wiley & Sons, Ltd.     

A clothes‐peg‐shaped binuclear trans‐bis(2‐aminotroponato)palladium(II) complex bearing pentamethylene spacers

rac‐Bis{μ‐trans‐2,2′‐[pentane‐1,5‐diylbis(azanediyl)]ditroponato}dipalladium(II), [Pd₂(C₁₉H₂₀N₂O₂)₂], has been synthesized and fully characterized using single‐crystal X‐ray diffraction, ¹H NMR, FT–IR and mass spectroscopy. The trans coordination, vaulted structure and anti conformation have been unequivocally established from the X‐ray diffraction studies. This is the first example of a bis(aminotroponato)palladium complex. In the crystalline state, the molecule has twofold symmetry and each molecular unit undergoes intermolecular offset π‐stacking of the tropone rings to afford heterochiral interpenetrating dimers that are aligned in a lamellar manner with a herringbone packing motif.     

An Investigation of Photo‐ and Pressure‐Induced Effects in a Pair of Isostructural Two‐Dimensional Spin‐Crossover Framework Materials

Two new isostructural iron(II) spin‐crossover (SCO) framework (SCOF) materials of the type [Fe(dpms)₂(NCX)₂] (dpms=4,4′‐dipyridylmethyl sulfide; X=S ( SCOF‐6(S) ), X=Se ( SCOF‐6(Se) )) have been synthesized. The 2D framework materials consist of undulating and interpenetrated rhomboid (4,4) nets. SCOF‐6(S) displays an incomplete SCO transition with only approximately 30 % conversion of high‐spin (HS) to low‐spin iron(II) sites over the temperature range 300–4 K (T_1/2=75 K). In contrast, the NCSe^? analogue, SCOF‐6(Se) , displays a complete SCO transition (T_1/2=135 K). Photomagnetic characterizations reveal quantitative light‐ induced excited spin‐state trapping (LIESST) of metastable HS iron(II) sites at 10 K. The temperature at which the photoinduced stored information is erased is 58 and 50 K for SCOF‐6(S) and SCOF‐6(Se) , respectively. Variable‐pressure magnetic measurements were performed on SCOF‐6(S) , revealing that with increasing pressure both the T_1/2 value and the extent of spin conversion are increased; with pressures exceeding 5.2 kbar a complete thermal transition is achieved. This study confirms that kinetic trapping effects are responsible for hindering a complete thermally induced spin transition in SCOF‐6(S) at ambient pressure due to an interplay between close T_1/2 and T(LIESST) values.     

Efficient Oxygen Reduction Reaction (ORR) Catalysts Based on Single Iron Atoms Dispersed on a Hierarchically Structured Porous Carbon Framework

Single Fe atoms dispersed on hierarchically structured porous carbon (SA‐Fe‐HPC) frameworks are prepared by pyrolysis of unsubstituted phthalocyanine/iron phthalocyanine complexes confined within micropores of the porous carbon support. The single‐atom Fe catalysts have a well‐defined atomic dispersion of Fe atoms coordinated by N ligands on the 3D hierarchically porous carbon support. These SA‐Fe‐HPC catalysts are comparable to the commercial Pt/C electrode even in acidic electrolytes for oxygen reduction reaction (ORR) in terms of the ORR activity (E_1/2=0.81 V), but have better long‐term electrochemical stability (7 mV negative shift after 3000 potential cycles) and fuel selectivity. In alkaline media, the SA‐Fe‐HPC catalysts outperform the commercial Pt/C electrode in ORR activity (E_1/2=0.89 V), fuel selectivity, and long‐term stability (1 mV negative shift after 3000 potential cycles). Thus, these nSA‐Fe‐HPCs are promising non‐platinum‐group metal ORR catalysts for fuel‐cell technologies.     

Alternative Synthesis and Structures of C‐monoacetylenic Phosphaalkenes

An alternative synthesis of C‐monoacetylenic phosphaalkenes trans‐Mes*P=C(Me)(C≡CR) (Mes* = 2, 4, 6‐^tBu₃Ph, R = Ph, SiMe₃) from C‐bromophosphaalkenes cis‐Mes*P=C(Me)Br using standard Sonogashira coupling conditions is described. Crystallographic studies confirm cis‐trans isomerization of the P=C double bond during Pd‐catalyzed cross coupling, leading exclusively to trans‐acetylenic phosphaalkenes. Crystallographic studies of all synthesized compounds reveal the extend of π‐conjugation over the acetylene and P=C π‐systems.