76 research outputs found
Planktic foraminiferal changes in the western Mediterranean Anthropocene
No full textThe increase in anthropogenic induced warming over the last two centuries is impacting marine environment. Planktic foraminifera are a globally distributed calcifying marine zooplankton responding sensitively to changes in sea surface temperatures and interacting with the food web structure. Here, we study two high resolution multicore records from two western Mediterranean Sea regions (Alboran and Balearic basins), areas highly affected by both natural climate change and anthropogenic warming. Cores cover the time interval from the Medieval Climate Anomaly to present. Reconstructed sea surface temperatures are in good agreement with other results, tracing temperature changes through the Common Era (CE) and show a clear warming emergence at about 1850 CE. Both cores show opposite abundance fluctuations of planktic foraminiferal species (Globigerina bulloides, Globorotalia inflata and Globorotalia truncatulinoides), a common group of marine calcifying zooplankton. The relative abundance changes of Globorotalia truncatulinoides plus Globorotalia inflata describe the intensity of deep winter mixing in the Balearic basin. In the Alboran Sea, Globigerina bulloides and Globorotalia inflata instead respond to local upwelling dynamics. In the pre-industrial era, changes in planktic foraminiferal productivity and species composition can be explained mainly by the natural variability of the North Atlantic Oscillation, and, to a lesser extent, by the Atlantic Multidecadal Oscillation. In the industrial era, starting from about 1800 CE, this variability is affected by anthropogenic surface warming, leading to enhanced vertical stratification of the upper water column, and resulting in a decrease of surface productivity at both sites. We found that natural planktic foraminiferal population dynamics in the western Mediterranean is already altered by enhanced anthropogenic impact in the industrial era, suggesting that in this region natural cycles are being overprinted by human influences
Syntheses and structural studies of several diynyl-ruthenium complexes and their adducts with cyano-alkenes
No full textAbstractHerein are described some continuing investigations into the reactions of cyano‐alkenes with diynyl‐ruthenium complexes which have resulted in the preparation and characterisation of diynyl‐ruthenium compounds Ru(C≡CC≡CR)(PP)Cp [R = Ph, PP = dppe; R = Fc, PP = dppf; R = CPh=CBr2, PP = (PPh3)2], together with the polycyanobutadienyls Ru{C≡CC[=C(CN)2]CR=CR′(CN)}(PP)Cp′ [R = Fc, (PP)Cp′ = (dppf)Cp; R = H, SiMe3, (PP)Cp′ = (dppe)Cp*] formed by [2 + 2]‐cycloaddition of the cyano‐alkenes to the outer C≡C triple bonds and subsequent ring‐opening reactions. Single‐crystal XRD molecular structure determinations of six complexes are reported.Michael I. Bruce, Alexandre Burgun, Guillaume Grelaud, Martyn Jevric, Brian K. Nicholson, Brian W. Skelton, Allan H. White, and Natasha N. Zaitsev
Reactions of 7,7,8,8-tetracyanoquinodimethane (TCNQ) with alkynyl-iron- and -ruthenium complexes: synthesis of Ru{C=CC(CN)=C(6)H(4)=C(CN)(2)}(PPh(3))(2)Cp, a new donor-acceptor molecular array
No full textReactions of 7,7,8,8-tetracyanoquinodimethane (TCNQ) with the alkynyl-iron and ruthenium complexes [M](C=CR) {[M] = Fe(dppe)Cp*, Ru(PPh3)2Cp; R = H, Ph} are described. The iron complex Fe(C=CPh)(dppe)Cp* (2a) is oxidized by TCNQ to give the kinetically stable salt [2a•+][TCNQ]•– . Displacement of [TCNQ]•– is achieved by ionic metathesis upon addition of KPF6 to produce [2a•+]PF6. In contrast, Fe(C=CH)(dppe)Cp* (2b) reacted with TCNQ to give a mixture of compounds containing Fe(=C=CH2)(dppe)Cp* (3a), {Fe(dppe)Cp*}2(µ-C=CHCH=C) (3b), and the zwitterionic complex Fe+{=C=CHC(CN)2C6H4C–(CN)2}(dppe)Cp* (3c). In contrast, the reaction of TCNQ with Ru(C=CR)(PPh3)2Cp (4a, R = Ph; 4b, R = H) gave selectively the zwitterionic vinylidenes Ru+{=C=CRC(CN)2C6H4C–(CN)2}(PPh3)2Cp (5a, R = Ph; 5b, R = H), in which the Ru centres are positively charged and the counter-anion is located on the further C(CN)2 group. On heating 5b, elimination of HCN affords Ru{C=CC(CN)=C6H4=C(CN)2}(PPh3)2Cp (1), while similar treatment of 5a gives Ru{?3-C(CN)2CPh=C6H4=C(CN)2}(PPh3)Cp (6) with loss of PPh3. X-ray structures of 1, 5a, and 6, cyclic voltammetry, and UV-vis spectroscopy of 1 provided evidence for the electronic structures of the new complexes.Michael I. Bruce, Alexandre Burgun, Guillaume Grelaud, Claude Lapinte, Brian W. Skelton, and Natasha N. Zaitsev
Oxidative dimerization of arylalkynyl-ruthenium complexes
No full textChemical oxidation of Ru(C≡CPh)(PPh3)2Cp with [FeCp2]PF6 affords the binuclear cationic complexes [Cp(PPh3)2Ru{=C=CHC6H4CPh=C=} Ru(PPh3)2Cp](PF6)2 (2) and [Cp(PPh3)2Ru{C≡C(C6H4)CPh=C=} Ru(PPh3)2Cp]PF6 (3) by radical coupling at sites shown to be electron-rich by DFT studies, particularly involving the acetylide Cβ and Ph Cpara atoms and, to a lesser extent, the Cp carbon atoms. Complexes 2 and 3 are related by facile deprotonation/protonation reactions. When the 4-position of the Ph group is blocked, attack by Cβ upon the Cp group occurs to give the bis(vinylidene) [Ru{=C=C(C6H4Me-4)-η-C 5H4[Ru(PPh3)2{=C=CH(C 6H4Me-4)}(PPh3)2Cp]}](PF 6)2 (4), which can be deprotonated to give [Ru{=C=C(C 6H4Me-4)-η-C5H4[Ru(PPh 3)2{C≡C(C6H4Me-4)}(PPh 3)2Cp]}]PF6 (5). Complex 4 is rapidly oxidized during workup to form [Ru{=C=C(C6H4Me)-η-C 5H4[Ru(CO)(PPh3)2]}(PPh 3)2Cp](PF6)2 (6). Single-crystal X-ray structure determinations of the salts 2, 3, and 6 are reported. © 2011 American Chemical Society.Michael I. Bruce, Alexandre Burgun, Frédéric Gendron, Guillaume Grelaud, Jean-François Halet and Brian W. Skelto
Reactions of 7,7,8,8-tetracyanoquinodimethane with poly-ynyl ruthenium and iron complexes
No full textThe reaction of tetracyanoquinodimethane (TCNQ) with Ru(C≡CC≡ CH)(dppe)Cp* (5) at the outer (from Ru) C≡C triple bond gives η 1-(butadienyl)ethynyl Ru{C≡CC[CH=C(CN) 2]=C 6H 4=C(CN) 2}(dppe)Cp (8), which reacts with a second equivalent of diynyl-Ru complex to give {Ru(dppe)Cp*}{C≡CC[= C 6H 4=C(CN) 2]CH=CHC[=C(CN) 2] C≡C}{Ru(dppe)Cp*} (9). The Ph-substituted complexes M{C≡CC≡CPh}(dppe)Cp* (M = Fe 6-Fe, Ru 6-Ru) and Ru{(C≡C) 3Ph}(PPh 3) 2Cp (7) react with TCNQ to give the η 1-(butadienyl)ethynyls M{C≡CC[CPh=C(CN) 2]=C 6H 4=C(CN) 2}(dppe)Cp (10-Fe, 10-Ru) and Ru{C≡CC[C(C≡CPh)=C(CN) 2]=C 6H 4=C(CN) 2}(PPh 3) 2Cp (11), respectively. Single-crystal X-ray diffraction molecular structure determinations for 8-11 have been carried out. In the Fe series, we suggest that the initial step of the mechanism involves electron transfer to form the [TCNQ] -• salt of the diynyl-iron cation, followed by C-C bond formation to give a zwitterionic intermediate. Isolated products can be rationalized by further reaction involving [2 + 2]-cycloaddition of one of the C=C(CN) 2 groups of TCNQ to a C≡C triple bond of the metal poly-ynyl complex and a subsequent ring-opening reaction of the resulting (unobserved) cyclobutenyl intermediate. On the basis of X-ray diffraction data, redox potential determinations, and 57Fe Mössbauer and UV-vis spectroscopies, the electronic structures of the new compounds contain significant contributions from polarized mesomers involving charge transfer from the electron-rich metal-ligand fragment to the cyanocarbon ligand via the conjugated unsaturated carbon linker. © 2012 American Chemical Society.Michael I. Bruce, Alexandre Burgun, Guillaume Grelaud, Claude Lapinte, Christian R. Parker, Thierry Roisnel, Brian W. Skelton, and Natasha N. Zaitsev
List of samples analyzed using SYRACO (a) and/or SEM (b).
No full textList of samples analyzed using SYRACO (a) and/or SEM (b).</p
Living Coccolithophores from the Gulf of Sirte (Southern Mediterranean Sea) during the summer of 2008
No full text- …
