No abstract

Plants and animals influence biomass production and nutrient cycling in terrestrial ecosystems; however, their relative importance remains unclear. We assessed the extent to which mega-herbivore species controlled plant community composition and nutrient cycling, relative to other factors during and after the Late Quaternary extinction event in Britain and Ireland, when two-thirds of the region's mega-herbivore species went extinct. Warmer temperatures, plant-soil and plant-plant interactions, and reduced burning contributed to the expansion of woody plants and declining nitrogen availability in our five study ecosystems. Shrub biomass was consistently one of the strongest predictors of ecosystem change, equalling or exceeding the effects of other biotic and abiotic factors. In contrast, there was relatively little evidence for mega-herbivore control on plant community composition and nitrogen availability. The ability of plants to determine the fate of terrestrial ecosystems during periods of global environmental change may therefore be greater than previously thought.

The pentafluorophenyl-substituted diphosphine (C6F5)PhPCH2CH2PPh(C6F5) has been prepared, as a 1:1.7 mixture of rac (1a) and meso (1b) isomers, in four steps from dppe. The reaction between [Cp*RhCl(μ-Cl)]2 and 1 in the presence of tetrafluoroborate yielded a mixture of racemic diastereoisomers of [Cp*RhCl(κP,κP-1a)][BF4] (4a·BF 4 ) and trans and cis isomers of [Cp*RhCl(κP,κP-1b)][BF4] (4b·BF 4 and 4c·BF 4 , respectively). On addition of Proton Sponge, 4a and 4c, in which at least one pentafluorophenyl group is close to the pentamethylcyclopentadienyl ligand, underwent rapid dehydrofluorinative carbon−carbon coupling giving trans- and cis-[{η5,κP,κP-C5Me4CH2C6F4-2-PPhCH2CH2PPh(C6F5)}RhCl]+ (5 and 6), respectively. The latter underwent further dehydrofluorinative carbon−carbon coupling to give two isomers of [{η5,κP,κP-C5Me3[CH2C6F4-2-PPhCH2]2}RhCl]+ (7). Isomerization of 4b to 4c was observed in chloroform and dimethlysulfoxide. Neither isomerization of 4a to 4b or 4c nor isomerization of 5 to 6 was observed at ambient or elevated temperature in dimethyl sulfoxide. The results provide the first evidence that complexes of η5,κP,κL-cyclopentadienyl-phosphine-donor ligands are configurationally stable at high temperature.

Organic chemistry Z 0200Fluoroarylphosphines as Ligands -[191 refs]. -(POLLOCK, C. L.; SAUNDERS*, G. C.; SMYTH, E. C. M. S.; SOROKIN, V. I.; J. Fluorine Chem. 129 (2008) 3, 142-166; Sch. Chem. Chem. Eng., Queen's Univ., Belfast BT9 5AG, UK; Eng.) -M. Paetzel