Studies related to the chloro titanium and zirconium complexes with [η5-Cyclopentadienyldi(silylamido)] Ligands

Trichloro complexes [M{η5-C5H3[SiMe2(NHtBu)]2}Cl3] [M = Zr (2), Ti (3)] have been synthesized by reaction of the corresponding chlorides MCl4 with the lithium salt LiC5H3[SiMe2(NHtBu)]2 (1). Complexes 2 and 3 react with 2 equiv. of TiCl4 in toluene at 110°C to afford the di(chlorosilyl) derivatives [M{η5-C5H3(SiMe2Cl)2}Cl3] [M = Ti (5), Zr (8)]. Intermediate formation of [Ti{η5-C5H3[SiMe2(NHtBu)](SiMe2Cl)}Cl3] (4) has been proven by NMR spectroscopy. Reaction of 1 with TiCl4 (2 equiv.) in toluene at 110 °C in the presence of excess NEt3 has yielded the chloro-silyl complex [Ti{η5-C5H3(SiMe2Cl)(SiMe2-η1-NtBu)}Cl2] (7) through the intermediate formation of the amino-silyl derivative [Ti{η5-C5H3[SiMe2(NHtBu)] (SiMe2-η1-NtBu)}Cl2] (6). Reactions of di-ansa-[M{η5-C5H3(SiMe2-η1-NtBu)2}R] and ansa-[M{η5-C5H3[SiMe2(NHtBu)] (SiMe2-η1-NtBu)}R2] (M = Ti, Zr; R = NMe2, CH2Ph) complexes with NEt3·HCl have afforded the dichloro derivatives [M{η5-C5H3[SiMe2(NHtBu)] (SiMe2-η1-NtBu)}Cl2] [M = Ti (6), Zr (12)], the amine-coordinated zirconium compound [Zr{η5-C5H3 [SiMe2(NHtBu)](SiMe2-η1-NtBu)} Cl2(NMe2H)] (9) and the chloro-benzyl titanium complex [Ti{η5-C5H3[SiMe2(NHtBu)](SiMe2-η1-NtBu)}Cl(CH2Ph)] (11). Formation of the mono-substituted chloroamido zirconium complex [Zr{η5-C5H3[SiMe2 (NHtBu)](SiMe2-η1-NtBu)}Cl(NMe2)] (10) by the reaction of [Zr{η5-C5H3[SiMe2(NHtBu)] (SiMe2-η1-NtBu)}(NMe2)2] with SiClMe3 has been monitored in C6D6 by NMR spectroscopy. All of the new chloro complexes have been characterized by elemental analyses and NMR spectroscopy and the X-ray crystal structure of [Ti(η5-C5H3{SiMe2(NHtBu)}2)Cl3] (3) has been studied by diffraction methods.Ministerio de Educación, Cultura y DeporteComunidad de Madri

Carbon inputs from Miscanthus displace older soil organic carbon without inducing priming

The carbon (C) dynamics of a bioenergy system are key to correctly defining its viability as a sustainable alternative to conventional fossil fuel energy sources. Recent studies have quantified the greenhouse gas mitigation potential of these bioenergy crops, often concluding that C sequestration in soils plays a primary role in offsetting emissions through energy generation. Miscanthus is a particularly promising bioenergy crop and research has shown that soil C stocks can increase by more than 2 t C ha−1 yr−1. In this study, we use a stable isotope (13C) technique to trace the inputs and outputs from soils below a commercial Miscanthus plantation in Lincolnshire, UK, over the first 7 years of growth after conversion from a conventional arable crop. Results suggest that an unchanging total topsoil (0–30 cm) C stock is caused by Miscanthus additions displacing older soil organic matter. Further, using a comparison between bare soil plots (no new Miscanthus inputs) and undisturbed Miscanthus controls, soil respiration was seen to be unaffected through priming by fresh inputs or rhizosphere. The temperature sensitivity of old soil C was also seen to be very similar with and without the presence of live root biomass. Total soil respiration from control plots was dominated by Miscanthus-derived emissions with autotrophic respiration alone accounting for ∼50 % of CO2. Although total soil C stocks did not change significantly over time, the Miscanthus-derived soil C accumulated at a rate of 860 kg C ha−1 yr−1 over the top 30 cm. Ultimately, the results from this study indicate that soil C stocks below Miscanthus plantations do not necessarily increase during the first 7 years

Regional contingencies in the relationship between aboveground biomass and litter in the world’s grasslands

Based on regional-scale studies, aboveground production and litter decomposition are thought to positively covary, because they are driven by shared biotic and climatic factors. Until now we have been unable to test whether production and decomposition are generally coupled across climatically dissimilar regions, because we lacked replicated data collected within a single vegetation type across multiple regions, obfuscating the drivers and generality of the association between production and decomposition. Furthermore, our understanding of the relationships between production and decomposition rests heavily on separate meta-analyses of each response, because no studies have simultaneously measured production and the accumulation or decomposition of litter using consistent methods at globally relevant scales. Here, we use a multi-country grassland dataset collected using a standardized protocol to show that live plant biomass (an estimate of aboveground net primary production) and litter disappearance (represented by mass loss of aboveground litter) do not strongly covary. Live biomass and litter disappearance varied at different spatial scales. There was substantial variation in live biomass among continents, sites and plots whereas among continent differences accounted for most of the variation in litter disappearance rates. Although there were strong associations among aboveground biomass, litter disappearance and climatic factors in some regions (e.g. U.S. Great Plains), these relationships were inconsistent within and among the regions represented by this study. These results highlight the importance of replication among regions and continents when characterizing the correlations between ecosystem processes and interpreting their global-scale implications for carbon flux. We must exercise caution in parameterizing litter decomposition and aboveground production in future regional and global carbon models as their relationship is complex