Nitrogen-doped graphene/graphene-tube nanocomposites are prepared by a hightemperature approach using a newly designed cage-containing metal-organic framework (MOF) to template nitrogen/carbon (dicyandiamide) and iron precursors. The resulting N-Fe-MOF catalysts universally exhibit high oxygen-reduction activity in acidic, alkaline, and non-aqueous electrolytes and superior cathode performance in Li-O2 batteries.

The replacement of precious-metal catalysts with cheap and abundant metals is a major goal of sustainable chemistry. [1] Hydrogenation catalysts have diverse and widespread applications, including the production of biorenewable chemicals and fuels, commodity chemicals, and the synthesis of fine chemicals and pharmaceuticals. [2][3][4] Homogeneous rhodium, ruthenium, and iridium catalysts are also of critical importance in asymmetric hydrogenation. [5] Despite significant recent advances, the design of earth-abundant-metal hydrogenation catalysts has lagged behind, perhaps because of the tendency of 3d metals to engage in one-electron or radical chemistry. Several iron catalysts have been developed for the hydrogenation of ketones or alkenes, but they are typically chemoselective, reducing only one class of substrate. [6][7][8][9] Furthermore, iron catalysts are often quite sensitive to additional oxygen-and nitrogen-containing functional groups and water. [10] There is growing evidence that cobalt complexes can be effective catalysts for homogeneous hydrogenation. Cobalt(I) complexes, such as [Co(H)(CO) 4 ] and [Co(H)(CO)(PnBu 3 ) 3 ], are known to catalyze the hydrogenation of alkenes and arenes under hydroformylation conditions (> 120 8C, > 30 atm H 2 /CO). [11][12][13] Diiminopyridine cobalt complexes and the dinitrogen complex [Co(H)(N 2 )(PPh 3 ) 3 ] catalyze olefin hydrogenation at room temperature, [14,15] and an asymmetric hydrogenation of substituted styrenes was recently developed. [16] However, prior examples of cobalt hydrogenation catalysts have been quite limited in substrate scope, and nearly all have involved cobalt(I). [17,18] Herein, we report a cobalt-based catalytic system for the homogeneous hydrogenation of alkenes, aldehydes, ketones, and imines. The hydrogenation reactions take place under very mild conditions and require no base additives. The ability to hydrogenate multiple classes of substrates and broad functional-group tolerance make this cobalt system a significant advance over previously reported earth-abundant-metal hydrogenation catalysts.We synthesized cobalt(II) complexes of the tridentate ligand bis[2-(dicyclohexylphosphino)ethyl]amine (PNHP Cy ) (Scheme 1). Previous work by Fryzuk et al. had shown that a related pincer amidodiphosphine ligand stabilized a squareplanar 15-electron d 7 -cobalt(II)-alkyl complex, [19] and we were interested in exploring the reactivity of this type of unusual odd-electron cobalt-alkyl species. Reaction of PNHP Cy with [(pyr) 2 Co(CH 2 SiMe 3 ) 2 ] [20] (pyr = pyridine) afforded the new cobalt(II)-alkyl complex [(PNP Cy )Co-(CH 2 SiMe 3 )] (1) as dark-yellow crystals. In the solid state, paramagnetic complex 1 has a square-planar geometry, and solution-state magnetic-moment measurements are also consistent with a square-planar low-spin d 7 configuration (m eff = 2.2 m B ). [21,22] The solution-state magnetic moment of complex 1 is quite similar to that of the related square-planar complex [(N(SiMe 2 CH 2 PPh 2 ) 2 )Co(CH 2 SiMe 3 )] (2.

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Cobalt(II) alkyl complexes of aliphatic PNP pincer ligands have been synthesized and characterized. The cationic cobalt(II) alkyl complex [(PNHP(Cy))Co(CH2SiMe3)]BAr(F)4 (4) (PNHP(Cy) = bis[(2-dicyclohexylphosphino)ethyl]amine) is an active precatalyst for the hydrogenation of olefins and ketones and the acceptorless dehydrogenation of alcohols. To elucidate the possible involvement of the N-H group on the pincer ligand in the catalysis via a metal-ligand cooperative interaction, the reactivities of 4 and [(PNMeP(Cy))Co(CH2SiMe3)]BAr(F)4 (7) were compared. Complex 7 was found to be an active precatalyst for the hydrogenation of olefins. In contrast, no catalytic activity was observed using 7 as a precatalyst for the hydrogenation of acetophenone under mild conditions. For the acceptorless dehydrogenation of 1-phenylethanol, complex 7 displayed similar activity to complex 4, affording acetophenone in high yield. When the acceptorless dehydrogenation of 1-phenylethanol with precatalyst 4 was monitored by NMR spectroscopy, the formation of the cobalt(III) acetylphenyl hydride complex [(PNHP(Cy))Co(III)(κ(2)-O,C-C6H4C(O)CH3)(H)]BAr(F)4 (13) was detected. Isolated complex 13 was found to be an effective catalyst for the acceptorless dehydrogenation of alcohols, implicating 13 as a catalyst resting state during the alcohol dehydrogenation reaction. Complex 13 catalyzed the hydrogenation of styrene but showed no catalytic activity for the room temperature hydrogenation of acetophenone. These results support the involvement of metal-ligand cooperativity in the room temperature hydrogenation of ketones but not the hydrogenation of olefins or the acceptorless dehydrogenation of alcohols. Mechanisms consistent with these observations are presented for the cobalt-catalyzed hydrogenation of olefins and ketones and the acceptorless dehydrogenation of alcohols.

A cobalt catalyst has been developed for the acceptorless dehydrogenation of alcohols and applied to synthesize imines from alcohols and amines. Deuterium labeling studies suggest that the reaction proceeds by an initial reversible alcohol dehydrogenation step involving a cobalt hydride intermediate.

• Endothelial S1PR2 plays a critical role in the induction of vascular permeability and vascular inflammation during endotoxemia.• S1PR2 could be a novel therapeutic target to promote vascular integrity in inflammatory vascular disorders.The endothelium, as the interface between blood and all tissues, plays a critical role in inflammation. Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid, highly abundant in plasma, that potently regulates endothelial responses through interaction with its receptors (S1PRs). Here, we studied the role of S1PR2 in the regulation of the proadhesion and proinflammatory phenotype of the endothelium. By using genetic approaches and a S1PR2-specific antagonist (JTE013), we found that S1PR2 plays a key role in the permeability and inflammatory responses of the vascular endothelium during endotoxemia. Experiments with bone marrow chimeras (S1pr2 1/1 → S1pr2, and S1pr2 2/2 → S1pr2) indicate the critical role of S1PR2 in the stromal compartment, in the regulation of vascular permeability and vascular inflammation. In vitro, JTE013 potently inhibited tumor necrosis factor a-induced endothelial inflammation. Finally, we provide detailed mechanisms on the downstream signaling of S1PR2 in vascular inflammation that include the activation of the stress-activated protein kinase pathway that, together with the Rho-kinase nuclear factor kappa B pathway (NF-kB), are required for S1PR2-mediated endothelial inflammatory responses. Taken together, our data indicate that S1PR2 is a key regulator of the proinflammatory phenotype of the endothelium and identify S1PR2 as a novel therapeutic target for vascular disorders. (Blood. 2013;122(3):443-455)

In this work, large size (i.e., diameter > 100 nm) graphene tubes with nitrogen-doping are prepared through a high-temperature graphitization process of dicyandiamide (DCDA) and Iron(II) acetate templated by a novel metal-organic framework (MIL-100(Fe)). The nitrogen-doped graphene tube (N-GT)-rich iron-nitrogen-carbon (Fe-N-C) catalysts exhibit inherently high activity towards the oxygen reduction reaction (ORR) in more challenging acidic media. Furthermore, aiming to improve the activity and stability of conventional Pt catalysts, the ORR active N-GT is used as a matrix to disperse Pt nanoparticles in order to build a unique hybrid Pt cathode catalyst. This is the first demonstration of the integration of a highly active Fe-N-C catalyst with Pt nanoparticles. The synthesized 20% Pt/N-GT composite catalysts demonstrate significantly enhanced ORR activity and H(2) -air fuel cell performance relative to those of 20% Pt/C, which is mainly attributed to the intrinsically active N-GT matrix along with possible synergistic effects between the non-precious metal active sites and the Pt nanoparticles. Unlike traditional Pt/C, the hybrid catalysts exhibit excellent stability during the accelerated durability testing, likely due to the unique highly graphitized graphene tube morphologies, capable of providing strong interaction with Pt nanoparticles and then preventing their agglomeration.