Iridium complexes of CCC-pincer bis-N-heterocyclic carbenes, including a newly synthesized trifluoromethyl-substituted complex, were examined as catalysts for the acceptorless dehydrogenation of cyclooctane and n-undecane. Up to 103 turnovers were observed for the dehydrogenation of cyclooctane, and up to 97 turnovers were observed for the dehydrogenation of n-undecane. The catalysts showed high initial turnover frequencies, followed by a gradual loss of activity over 24 h. Experiments indicate that this loss of activity is due to catalyst decomposition rather than product inhibition. Stoichiometric reactivity was investigated for the precatalysts, focusing on the synthesis of dihydride and trihydride complexes as well as the dissociation and addition of neutral ligands.

Ruthenium complexes supported by two new CNN-pincer ligands were synthesized. Both were tested as catalysts for the hydrogenation of esters under mild conditions (105 °C, 6 bar H2). A striking dependence on ligand structure was observed, as a dimethylamino-substituted ligand gave a nearly inactive catalyst, while a diethylamino-substituted variant gave up to 980 catalytic turnovers for the hydrogenation of benzyl benzoate. This system catalyzes the hydrogenation of various substrates including ethyl, benzyl, and hexyl esters, but is surprisingly unreactive toward methyl esters. Experiments demonstrate that base-catalyzed transesterification is rapid under the reaction conditions and that methyl esters are effectively hydrogenated when benzyl alcohol is added to the reaction mixture. The reverse reaction, dehydrogenation of primary alcohols to give esters, was tested as well; up to 920 catalytic turnovers were observed for the dehydrogenation of 1-hexanol to hexyl hexanoate.

Aims Tropical forests are increasingly threatened by edge effects as forest degradation and deforestation continues, compromising soil integrity, seedling regeneration capacity, and ecosystem services. Ninety-three percent of the last remaining forests of northern Ethiopia, which number 1022 in the South Gondar region of our study, are <16 ha and are protected because they have a Tewahido Orthodox Christian church at their center. The aim of this study was to determine the effects of human disturbance, forest size, distance from population center and other factors on the soil properties and nutrient status of sacred church forests. We also compared forest soil physical and chemical properties across land cover types in these forests. Methods We assessed the soil physical (water content and bulk density) and chemical (total carbon and nitrogen, available phosphorus, ammonium) properties of 40 sacred church forests across three spatial scales: within individual forests; among forests; and across land cover type (forest, forest edge-exterior, Eucalyptus plantation). We used distance from the edge within each forest to examine edge effects on soil nutrients. Results We found that nutrients and carbon decreased significantly from the interior to the outer edge of these forests and with forest size. Further, the soil of Eucalyptus plantations and areas outside of the forest were largely indistinguishable; both had significantly lower nutrient concentrations than sacred church forest soil. Conclusion Our research highlights the insidious impacts of edge effects and human disturbance on forest soils and the need for an integrated soil management program in the region that balances local needs with forest conservation. The conservation of these sacred church forests is important for maintaining regional soil nutrient status relative to agricultural lands and Eucalyptus plantations.

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