This study examines a natural, rapid, fivefold increase in dissolved organic carbon (DOC) concentrations in a temperate shallow lake, describing the processes by which increased DOC resulted in anoxic conditions and altered existing carbon cycling pathways. High precipitation for two consecutive years led to rising water levels and the flooding of adjacent degraded peatlands. Leaching from the flooded soils provided an initial increase in DOC concentrations (from a 2010 mean of 12 6 1 mg L 21 to a maximum concentration of 53 mg L 21 by June 2012). Increasing water levels, DOC, and phytoplankton concentrations reduced light reaching the sediment surface, eliminating most benthic primary production and promoting anoxia in the hypolimnion. From January to June 2012 there was a sudden increase in total phosphorus (from 57 mg L 21 to 216 mg L 21 ), DOC (from 24.6 mg L 21 to 53 mg L 21 ), and iron (from 0.12 mg L 21 to 1.07 mg L 21 ) concentrations, without any further large fluxes in water levels. We suggest that anoxic conditions at the sediment surface and flooded soils produced a dramatic release of these chemicals that exacerbated brownification and eutrophication, creating anoxic conditions that persisted roughly 6 months below a water depth of 1 m and extended periodically to the water surface. This brownification-anoxia feedback loop resulted in a near-complete loss of macroinvertebrate and fish populations, and increased surface carbon dioxide (CO 2 ) emissions by an order of magnitude relative to previous years.

Six complexes of the type trans-[Fe(NCMe)2(P-N-N-P)]X2 (X = BF4(-), B{Ar(f)}4(-)) (Ar(f) = 3,5-(CF3)2C6H3) containing diiminodiphosphine ligands and the complexes trans-[Fe(NCMe)2(P-NH-NH-P)][BF4]2 with a diaminodiphosphine ligand were obtained by the reaction of Fe(II) salts with achiral and chiral P-N-N-P or P-NH-NH-P ligands, respectively, in acetonitrile at ambient temperature. The P-N-N-P ligands are derived from reaction of ortho-diphenylphosphinobenzaldehyde with the diamines 1,2-ethylenediamine, 1,3-propylenediamine, (S,S)-1,2-disopropyl-1,2-diaminoethane, and (R,R)-1,2-diphenyl-1,2-diaminoethane. Some complexes could also be obtained for the first time in a one-pot template synthesis under mild reaction conditions. Single crystal X-ray diffraction studies of the complexes revealed a trans distorted octahedral structure around the iron. The iPr or Ph substituents on the diamine were found to be axial in the five-membered Fe-N-CHR-CHR-N- ring of the chiral P-N-N-P ligands. A steric clash between the imine hydrogen and the substituent probably determines this stereochemistry. The diaminodiphosphine complex has longer Fe-N and Fe-P bonds than the analogous diiminodiphosphine complex. The new iron compounds were used as precatalysts for the hydrogenation of acetophenone. The complexes without axial substituents on the diamine had moderate catalytic activity while that with axial Ph substituents had low activity but fair (61%) enantioselectivity for the asymmetric hydrogenation of acetophenone. The fact that the diaminodiphosphine complex has a slightly higher activity than the corresponding diiminodiphosphine complex suggests that hydrogenation of the imine groups in the P-N-N-P ligand may be important for catalyst activation. Evidence is provided, including the first density-functional theory calculations on iron-catalyzed outer-sphere ketone hydrogenation, that the mechanism is similar to that of ruthenium analogues.

Iron(II) carbonyl compounds of the type trans-[Fe(NCMe)(CO)(P-N-N-P)][BF(4)](2) bearing the ethylenediamine-derived diiminodiphosphine ligands (R,R)- or (S,S)-1,2-diphenyl-1,2-diaminoethane were synthesized and characterized, including by their crystal structures. The new complexes are suitable precatalysts for the transfer hydrogenation of ketones at room temperature, giving turnover frequencies of up to 2600 h(-1) with low catalyst loadings (0.025-0.17%). Screening experiments showed that the precatalysts are able to produce alcohols from a wide range of simple ketones. For sterically demanding prochiral ketones, excellent enantioselectivities were obtained (up to 96% ee).

Abstract. Ecological regime shifts and carbon cycling in aquatic systems have both been subject to increasing attention in recent years, yet the direct connection between these topics has remained poorly understood. A four-fold increase in sedimentation rates was observed within the past 50 years in a shallow eutrophic lake with no surface in-or outflows. This change coincided with an ecological regime shift involving the complete loss of submerged macrophytes, leading to a more turbid, phytoplanktondominated state. To determine whether the increase in carbon (C) burial resulted from a comprehensive transformation of C cycling pathways in parallel to this regime shift, we compared the annual C balances (mass balance and ecosystem budget) of this turbid lake to a similar nearby lake with submerged macrophytes, a higher transparency, and similar nutrient concentrations. C balances indicated that roughly 80% of the C input was permanently buried in the turbid lake sediments, compared to 40% in the clearer macrophyte-dominated lake. This was due to a higher measured C burial efficiency in the turbid lake, which could be explained by lower benthic C mineralization rates. These lower mineralization rates were associated with a decrease in benthic oxygen availability coinciding with the loss of submerged macrophytes. In contrast to previous assumptions that a regime shift to phytoplankton dominance decreases lake heterotrophy by boosting whole-lake primary production, our results suggest that an equivalent net metabolic shift may also result from lower C mineralization rates in a shallow, turbid lake. The widespread occurrence of such shifts may thus fundamentally alter the role of shallow lakes in the global C cycle, away from channeling terrestrial C to the atmosphere and towards burying an increasing amount of C.

A series of symmetrical and unsymmetrical N,N'-disubstituted aminotroponimines (ATIHs) have been prepared. Substituents ranging from linear to cyclic alkyl groups, chelating ethers, and aryl groups were employed. The corresponding aminotroponiminate zinc complexes were then synthesized and characterized by a number of techniques, including by X-ray crystallography. Herein we report on the investigations into their activity in the intramolecular hydroamination of nonactivated alkenes. We also demonstrate that complexes bearing ligands with cyclic alkyl groups show superior activity in a number of selected reactions with functionalized aminoalkenes.