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Glacier highstands since the Last Glacial Maximum are well documented for many regions, but little is known about glacier fluctuations and lowstands during the Holocene. This is because the traces of minimum extents are difficult to identify and at many places are still ice covered, limiting the access to sample material. Here we report a new approach to assess minimal glacier extent, using a 72-m long surface-to-bedrock ice core drilled on Khukh Nuru Uul, a glacier in the Tsambagarav mountain range of the Mongolian Altai (4130 m asl, 48°39.338′N, 90°50.826′E). The small ice cap has low ice temperatures and flat bedrock topography at the drill site. This indicates minimal lateral glacier flow and thereby preserved climate signals. The upper two-thirds of the ice core contain 200 years of climate information with annual resolution, whereas the lower third is subject to strong thinning of the annual layers with a basal ice age of approximately 6000 years before present (BP). We interpret the basal ice age as indicative of ice-free conditions in the Tsambagarav mountain range at 4100 m asl prior to 6000 years BP. This age marks the onset of the Neoglaciation and the end of the Holocene Climate Optimum. The ice-free conditions allow for adjusting the Equilibrium Line Altitude (ELA) and derive the glacier extent in the Mongolian Altai during the Holocene Climate Optimum. Based on the ELA-shift, we conclude that most of the glaciers are not remnants of the Last Glacial Maximum but were formed during the second part of the Holocene. The ice core derived accumulation reconstruction suggests important changes in the precipitation pattern over the last 6000 years. During formation of the glacier, more humid conditions than presently prevailed followed by a long dry period from 5000 years BP until 250 years ago. Present conditions are more humid than during the past millennia. This is consistent with precipitation evolution derived from lake sediment studies in the Altai.

Carbonaceous particles that comprise organic carbon (OC) and elemental carbon (EC) are of increasing interest in climate research because of their influence on the radiation balance of the Earth. The radiocarbon determination of particulate OC and EC extracted from ice cores provides a powerful tool to reconstruct the long-term natural and anthropogenic emissions of carbonaceous particles. However, this 14C-based source apportionment method has not been applied for the firn section, which is the uppermost part of Alpine glaciers with a typical thickness of up to 50 m. In contrast to glacier ice, firn samples are more easily contaminated through drilling and handling operations. In this study, an alternative decontamination method for firn samples consisting of chiselling off the outer parts instead of rinsing them was developed and verified. The obtained procedural blank of 2.8 ± 0.8 μg C for OC is a factor of 2 higher compared to the rinsing method used for ice, but still relatively low compared to the typical OC concentration in firn samples from Alpine glaciers. The EC blank of 0.3 ± 0.1 μg C is similar for both methods. For separation of OC and EC for subsequent 14C analysis, a thermal-optical method instead of the purely thermal method was applied for the first time to firn and ice samples, resulting in a reduced uncertainty of both the mass and 14C determination. OC and EC concentrations as well as their corresponding fraction of modern for firn and ice samples from Fiescherhorn and Jungfraujoch agree well with published results, validating the new method.

High altitude glaciers and ice caps from mid-latitudes and tropical regions contain valuable signals of past climatic and environmental conditions as well as human activities, but for a meaningful interpretation this information needs to be placed in a precise chronological context. For dating the upper part of ice cores from such sites several relatively precise methods exist, but they fail in the older and deeper part, where plastic deformation of the ice results in strong annual layer thinning and a non-linear age-depth relationship. If sufficient organic matter such as plant, wood or insect fragments were found, radiocarbon (14C) analysis had thus been the only option for a direct and absolute dating of deeper ice core sections. However such fragments are rarely found and even then very likely not at the depths and in the resolution desired. About 10 years ago, a new, complementary dating tool was therefore introduced by our group. It is based on extracting the μg-amounts of the water-insoluble organic carbon (WIOC) fraction of carbonaceous aerosols embedded in the ice matrix for subsequent 14C dating. Meanwhile this new approach was improved considerably, thereby reducing the measurement time and improving the overall precision. Samples with ~ 10 μg WIOC mass can now be dated with reasonable uncertainty of around 10–20 % (variable depending on sample age). This requires about 100 to 500 g of ice considering the WIOC concentrations typically found in mid- and low-latitude glacier ice. Dating polar ice with satisfactory age precision is still not possible since WIOC concentrations are around one order of magnitude lower. The accuracy of the 14C WIOC method was validated by applying it to independently dated ice. With this method the deepest parts of the ice cores from Colle Gnifetti and Mt. Ortles glacier in the European Alps, Illimani glacier in the Bolivian Andes, Tsambagarav ice cap in the Mongolian Altai, and Belukha glacier in the Siberian Altai have been dated. In all cases a strong annual layer thinning towards bedrock was observed and the oldest ages obtained were in the range of 10 000 yrs. 14C WIOC-dating was not only crucial for interpretation of the embedded environmental and climatic histories, but additionally gave a better insight into glacier flow dynamics close to bedrock and past glacier coverage. For this the availability of multiple dating points in the deepest parts was essential, which is the strength of the presented WIOC 14C-dating method, allowing determination of absolute ages from principally every piece of ice.

High-altitude glaciers and ice caps from midlatitudes and tropical regions contain valuable signals of past climatic and environmental conditions as well as human activities, but for a meaningful interpretation this information needs to be placed in a precise chronological context. For dating the upper part of ice cores from such sites, several relatively precise methods exist, but they fail in the older and deeper parts, where plastic deformation of the ice results in strong annual layer thinning and a non-linear age–depth relationship. If sufficient organic matter such as plant, wood or insect fragments were found, radiocarbon (14C) analysis would have thus been the only option for a direct and absolute dating of deeper ice core sections. However such fragments are rarely found and, even then, they would not be very likely to occur at the desired depth and resolution. About 10 years ago, a new, complementary dating tool was therefore introduced by our group. It is based on extracting the µg-amounts of the water-insoluble organic carbon (WIOC) fraction of carbonaceous aerosols embedded in the ice matrix for subsequent 14C dating. Since then this new approach has been improved considerably by reducing the measurement time and improving the overall precision. Samples with ∼ 10 µg WIOC mass can now be dated with reasonable uncertainty of around 10–20 % (variable depending on sample age). This requires about 300 to 800 g of ice for WIOC concentrations typically found in midlatitude and low-latitude glacier ice. Dating polar ice with satisfactory age precision is still not possible since WIOC concentrations are around 1 order of magnitude lower. The accuracy of the WIOC 14C method was validated by applying it to independently dated ice. With this method, the deepest parts of the ice cores from Colle Gnifetti and the Mt Ortles glacier in the European Alps, Illimani glacier in the Bolivian Andes, Tsambagarav ice cap in the Mongolian Altai, and Belukha glacier in the Siberian Altai have been dated. In all cases a strong annual layer thinning towards the bedrock was observed and the oldest ages obtained were in the range of 10 000 years. WIOC 14C dating was not only crucial for interpretation of the embedded environmental and climatic histories, but additionally gave a better insight into glacier flow dynamics close to the bedrock and past glacier coverage. For this the availability of multiple dating points in the deepest parts was essential, which is the strength of the presented WIOC 14C dating method, allowing determination of absolute ages from principally every piece of ice.

A multiple parameter dating technique was used to establish a depth/age scale for a 171.3 m (145.87 m w.e.) surface to bedrock ice core (Bl2003) recovered from the cold recrystallization accumulation zone of the Western Belukha Plateau (4115 m a.s.l.) in the Siberian Altai Mountains. The ice-core record presented visible layering of annual accumulation and of δ18O/δD stable isotopes, and a clear tritium reference horizon. A steady-state glacier flow model for layer thinning was calibrated and applied to establish a depth/age scale. Four radiocarbon (14C) measurements of particulate organic carbon contained in ice-core samples revealed dates for the bottom part of Bl2003 from 9075 ± 1221 cal a BC at 145.2 ± 0.1 m w.e. (0.665 m w.e. from the bedrock) to 790 ± 93 AD at 121.1 m w.e. depth. Sulfate peaks coincident with volcanic eruptions, the Tunguska meteorite event, and the 1842 dust storm were used to verify dating. Analysis of the Bl2003 ice core reveals that the modern Altai glaciers were formed during the Younger Dryas (YD) (~10 950 to ~7500 cal a BC), and that they survived the Holocene Climate Optimum (HCO) (~6500 to ~3600 cal a BC) and the Medieval Warm Period (MWP) (~640 to ~1100 AD). A decrease in air temperature at the beginning and an abrupt increase at the end of the YD were identified. Intensification of winds and dust loading related to Asian desert expansion also characterized the YD. During the YD major ion concentrations increased significantly, up to 50 times for Na+ (background), up to 45 times for Ca2+ and Mg2+, and up to 20 times for SO42− relative to the recent warm period from 1993 to 2003. A warm period lasted for about three centuries following the YD signaling onset of the HCO. A significant and prolonged decrease in air temperature from ~2000 to ~600 cal a BC was associated with a severe centennial drought (SCD). A sharp increase in air temperatures after the SCD was coincident with the MWP. After the MWP a cooling was followed gradually with further onset of the Little Ice Age. During the modern warm period (1973–2003) an increase in air temperature is noted, which nearly reaches the average of HCO and MWP air temperature values.

The first copper-catalyzed trifluoromethylation of aryl halides was developed that utilizes inexpensive trifluoroacetates. Providing low concentrations of the most economically attractive and atom-efficient trifluoromethylation reagent this new protocol is advantageous compared to known procedures both economically and ecologically.

A novel copper-catalyzed cyanation of aryl and heteroaryl bromides using acetone cyanohydrin has been developed.

The palladium-catalyzed alkoxycarbonylation of aryl and heteroaryl halides using butyl formate has been investigated. In the presence of palladium(II) acetate/n-butylbis(1-adamantyl)phosphine (L1), and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as base for the first time non-activated chloroarenes can be conveniently carbonylated in good yields.

An improved protocol for the palladium-catalyzed cyanation of electron-rich aryl chlorides with potassium ferrocyanide {K 4 [Fe(CN) 6 ]} is presented. Compared to previous procedures the substrate scope is significantly broadened.

A general and environmentally improved protocol for the cyanation of aryl halides with the nontoxic cyanide source potassium hexacyanoferrate(II) (K 4 [Fe(CN) 6 ]) using copper catalysis and a ligand system based on l-alkyl-1H -imidazoles is presented. The advantages of this system are a wide substrate range, high selectivity, easy handling, and inexpensive reagents.

Aryl bromides and phenols are coupled efficiently to the corresponding diaryl ethers in the presence of a practical Cu(I)/1-butylimidazole catalyst system. The convenient protocol is applied successfully to the synthesis of 16 different diaryl ethers in high yield and selectivity.

Palladium catalysts have been studied for the Sonogashira-Hagihara coupling of aryl and heteroaryl bromides with terminal alkynes. Among the different biarylphosphines tested, 2-(di-tert-butylphosphino)-N-phenylindole (cataCXium Plntb) allows the efficient coupling of both activated and deactivated (hetero)aryl bromides in the presence of sodium tetrachloropalladate in tetramethylethylenediamine (TMEDA) at 80 degrees C. The catalyst system gives high turnover numbers (up to 14 100) and shows a broad tolerance towards functional groups such as OH and NH2, as well as heterocycles.

Diphosphine palladium(0) (1) and arylpalladium(II) bromide complexes (2a−d) of di-1-adamantyl-n-butylphosphine (CataCXium A) have been synthesized. The PdL2 complex 1 takes a remarkable eclipsed conformation of the substituents along the P−Pd−P direction. NMR and X-ray studies of 2a showed its dimeric structure with the n-butyl groups of the coordinated phosphine ligands lying nearly parallel to the planes of the aromatic rings, which results in an anomalous 1H NMR upfield shift of the n-butyl protons caused by the aromatic ring current effect.

A general protocol for the cyanation of aryl halides with the nontoxic cyanide source K4[Fe(CN)6] using copper catalysis and a ligand system based on 1-alkylimidazoles is presented. The advantages of this system are the high selectivity, a unique substrate range, easy handling, and inexpensive reagents.

An improved copper catalyst system for the cyanation of heteroaryl halides leading to substituted heteroaryl nitriles is described. The catalyst system consists of simple Cul and N-alkyl-imidazoles, and mimics known Cu-containing metalloproteins. It is stable, commercially available, cheap and easily tunable. By using inexpensive and non-toxic K 4 [Fe(CN) 6 ] and the novel Cu catalysts we were able to cyanate both activated and non-activated heteroarenes with high yield and selectivity. The generality of the procedure is demonstrated by a variety of different examples, some of which did not react under other known methods.

The development of a novel Pd-catalyzed synthesis of (hetero)aromatic nitriles from the corresponding aryl chlorides and potassium hexacyanoferrate(II) is described. This novel protocol avoids the use of highly toxic alkali cyanides and proceeds in the presence of small amounts of palladium catalysts. High yields and selectivities of the corresponding aryl nitriles were achieved applying di(1-adamantyl)-1-butylphosphine (cata CX ium ® A) as the ligand.

Deutschland hat ein neues groses Kompetenzzentrum fur angewandte Katalyseforschung. Das Leibniz-Institut fur Organische Katalyse an der Universitat Rostock e. V. und das auf heterogene Katalyse spezialisierte Institut fur Angewandte Chemie Berlin-Adlershof e. V. haben sich zusammengeschlossen. Das durch die Fusion entstandene Institut heist Leibniz-Institut fur Katalyse e. V. an der Universitat Rostock. Uber 50 Jahre Katalyseerfahrung in Deutschland werden nun in diesem neuen Institut gebundelt.

Alkyl-di-(1-adamantyl)phosphonium salts are practical ligand precursors for the palladium-catalyzed amination of aryl chlorides. In the presence of typically 0.5 mol% Pd(OAc) 2 and 1 mol% of ligand precursor a variety of activated and deactivated aryl chlorides can be aminated in good to excellent yield (73–99%). Applying optimized conditions catalyst turnover numbers up to 10,000 have been achieved.

The combination of 2-phosphino-substituted N -arylpyrroles or related indoles (cata CX ium ® P) and Pd(OAc) 2 allows for efficient cross-coupling reactions of aryl chlorides and phenols to give diaryl ethers. A variety of aryl and heteroaryl chlorides can be coupled with substituted phenols showing unprecedented catalyst turnover numbers.

The development of a general Cu-catalyzed synthesis of (hetero)aromatic nitriles from the corresponding aryl bromides and potassium hexacyanoferrate(II) is described. This novel protocol avoids the use of highly toxic alkali cyanides and precious palladium catalysts. Best results were achieved applying Cu(BF 4 ) 2 ·6H 2 O (0.1 equiv) and N , N ′-dimethyl ethylenediamine (DMEDA; 1.0 equiv) in N , N -dimethyl acetamide (DMAc).

N-Aryl-2-(dialkylphosphino)imidazoles and -benzimidazoles are conveniently prepared in one step from the corresponding heterocycles by selective deprotonation and quenching with chlorophosphines. The novel ligands are easily tunable and show good to excellent performance in palladium-catalyzed Suzuki reactions and Buchwald–Hartwig aminations of aryl and heteroaryl chlorides.

A general synthesis of perfluoroalkylated amphetamines is presented. Initially, 1-aryl-1-iodo-2-(perfluoroalkyl)ethylenes are prepared by radical addition of perfluoroalkyl iodides to arylacetylenes. Key step of the reaction sequence is the following dehydroiodination in the presence of n-BuLi to give 1-perfluoroalkyl-2-arylacetylenes in situ, which are reacted with secondary amines to produce perfluoroalkylated enamines in a new one pot procedure. Final hydrogenation yields the desired products in good yields. By using N,N-dibenzylamine or N-benzylamines the corresponding primary and secondary perfluoroalkylated amines are easily available.

Palladium-catalyzed CC and CN bond forming reactions of aryl halides continue to be a major focus in catalysis research for the fine chemical industry. Still there exists a significant need for the development of more active and productive palladium catalysts. Although an increasing number of new catalysts is reported, it is often difficult to compare them. Here, we present a more detailed comparison of the catalytic performance of different monocarbenepalladium(0) complexes and various so-called in situ palladium phosphine and carbene catalysts in Suzuki, Kumada, and Buchwald–Hartwig amination reactions. Depending on the type of coupling reaction good to excellent yields of the desired products are obtained in the presence of both carbene- and phosphine-based catalysts. In general, phosphine-based catalysts appear to be more efficient for amination and Suzuki reactions of aryl chlorides. On the other hand, the carbene-based palladium catalysts work well in Kumada couplings of various aryl chlorides.

A new synthesis of N-aryl- and N-heteroaryl-N′-(arylalkyl)piperazines using palladium-catalyzed amination of aryl bromides and heteroaryl chlorides with mono N-benzyl- or N-(arylethyl)piperazines is reported. Most coupling processes proceed in high yield and good selectivity using either diadamantyl-n-butylphosphine ( 1 ), 2-(dicyclohexylphosphino)-2′-(N,N-dimethylamino)biphenyl ( 2 ), or 2-(di-tert-butylphosphino)biphenyl ( 3 ) as ligand. Applying an automated parallel synthesizer the preparation of a small library of potentially bioactive compounds is easily achieved.

A practical route for the synthesis of new biologically active 5-HT(2 A) receptor antagonists has been developed. In only three catalytic steps, this class of central nervous system (CNS) active compounds can be synthesized efficiently with high diversity. As the initial step, an anti-Markovnikov addition of amines to styrenes provides an easy route to N-(arylalkyl)piperazines, which constitute the core structure of the active molecules. Here, base-catalyzed hydroamination reactions of styrenes with benzylated piperazine proceeded in high yield even at room temperature. After catalytic debenzylation, the free amines were successfully carbonylated with different aromatic and heteroaromatic halides and carbon monoxide to yield the desired compounds in good to excellent yields. The two key reactions, base-catalyzed hydroamination of styrenes and palladium-catalyzed aminocarbonylation of haloarenes/heterocycles, showed tolerance towards various functional groups, thereby demonstrating the potential to synthesize a wide variety of new derivatives of this promising class of pharmaceuticals.

Iridium and rhodium complexes catalyze the borylation of xylene and different heteroarenes using pinacolborane via C–H activation. Various five-membered heterocycles such as thiophene, pyrrole, thionaphthene, and indole derivatives yield the borylated products in moderate to good yields. In general, the reactions proceed with high selectivity to give borylation ortho to the heteroatom.

An improved synthesis of di(1-adamantyl)alkylphosphines by alkylation of di(1-adamantyl)phosphine followed by deprotonation of the resulting phosphonium halide is described. Compared to previous protocols for the synthesis of this class of compounds, the procedure does not require chlorination of the secondary phosphine by phosgene, or formation of sensitive lithium di(1-adamantyl)phosphide. Selected examples of the prepared phosphonium salts and phosphines are shown to be excellent ligands for the palladium-catalyzed cross-coupling reaction of chloroarenes with arylboronic acids.

Benzonitriles are easily accessible from the corresponding aryl bromides catalyzed by a palladium-complex using trimethylsilylcyanide (TMSCN) as cyanating agent under mild conditions. The key of success for the cyanation protocol is the slow dosage of the TMSCN to the reaction mixture. This new method is applicable on both activated and deactivated aryl and heteroaryl bromides giving the corresponding benzonitriles in good to excellent yield.

The palladium-catalyzed cyanation of aryl halides is an elegant method for the preparation of benzonitriles. Since its discovery in 1973, this reaction has been the topic of several investigations. Nevertheless, the general methodology is still somewhat underdeveloped compared to other palladium-catalyzed coupling reactions. Here, we summarize important developments from 1997 until 2003 in this area. Recent contributions from our group include the development of palladium/phosphane/amine catalyst systems for the cyanation of aryl chlorides, the successful cyanation of aryl halides with acetone cyanohydrin and trimethylsilyl cyanide as cyanation reagents, and a general improvement of catalyst efficiency by using a continuous dosage of cyanide sources. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The first monocarbenepalladium(0) complexes with benzoquinone and naphthoquinone as additional ligands have been prepared. As demonstrated by NMR spectroscopy and X-ray analysis, the complexes show a unique coordination mode giving quinone-bridged dimers. The monocarbenepalladium(0) complexes allow efficient cross-coupling reactions of aryldiazonium salts with olefins (Heck reaction) and arylboronic acids (Suzuki reaction).

The catalytic amination of aryl chlorides is an interesting subject for the fine chemical industry due to the importance of anilines as building blocks for pharmaceuticals, agrochemicals and new materials. Here we report the application of our recently developed di(1-adamantyl)alkylphosphines for the palladium-catalyzed amination of non-activated aryl chlorides. In general, excellent yields of amination products are obtained using 0.5 mol% of palladium(II)acetate and 1 mol% of di(1-adamantyl)-n-butylphosphine (12) in toluene at 120 °C. Remarkable results are obtained for the coupling of hindered amines with sterically congested aryl chlorides. Comparing the new catalyst system with previously reported best palladium catalysts we found in all cases improved yields of amination products in the presence of our ligands.

During the last decade several palladium-catalyzed reactions have been developed and optimized to a stage that enables application on an industrial scale. The importance of these reactions as novel key steps for fine chemical synthesis is shown. Examples include palladium-catalyzed Heck, Suzuki and Sonogashira coupling reactions, telomerization of 1,3-butadiene with nucleophiles, and carbonylation of aromatic and benzylic halides.

The influence of reaction conditions and additives on the palladium-catalyzed cyanation of aryl chlorides with potassium cyanide has been investigated. Successful cyanation of aryl chlorides is observed in the presence of palladium catalysts using potassium cyanide. It is shown that the combination of a 1,5-bis(diphenylphosphino)pentane ligand and the addition of N , N , N ′, N ′-tetramethylethylenediamine (TMEDA) as a co-catalyst are the key factors in obtaining the corresponding aryl nitriles with improved catalyst productivities and selectivities.

A detailed investigation into the influence of phosphines, additives, bases and solvents on the Heck coupling reaction of 4-trifluoromethyl-1-chlorobenzene (2) is presented. It is shown that a number of catalyst systems exist for efficient cross coupling of electron-deficient aryl chlorides with various olefins. Basicity and steric demand of the ligand are two factors which determine the success of the reaction. In addition the phosphine/palladium ratio, the correct type and amount of additive, and finally the use of an appropriate base and solvent are also important. The optimised reaction conditions are applied for the arylation of styrene, 2-ethylhexyl acrylate and N,N-dimethyl acrylic amide with various aryl chlorides.

The Suzuki reaction of aryl bromides is efficiently catalyzed by palladium/phosphite complexes generated in situ. The influence of ligand, base, and different additives is examined. The process tolerates various functional groups and catalyst turnover numbers up to 820 000 are obtained even with deactivated aryl bromides. For the first time it is shown that palladium/phosphite complexes also catalyze efficiently the Suzuki reaction of aryl chlorides.