@article{BaierKellingHoldt2015, author = {Baier, Heiko and Kelling, Alexandra and Holdt, Hans-J{\"u}rgen}, title = {PEPPSI-Effect on Suzuki-Miyaura Reactions Using 4,5-Dicyano-1,3-dimesitylimidazol-2-ylidene-Palladium Complexes: A Comparison between trans-Ligands}, series = {European journal of inorganic chemistry : a journal of ChemPubSoc Europe}, journal = {European journal of inorganic chemistry : a journal of ChemPubSoc Europe}, number = {11}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1434-1948}, doi = {10.1002/ejic.201500010}, pages = {1950 -- 1957}, year = {2015}, abstract = {The PEPPSI (Pyridine Enhanced Precatalyst Preparation, Stabilization and Initiation) complexes 12-15 with the structure [PdCl2{(CN)(2)IMes}(3-R-py)] (12: R = H; 13: R = Cl; 14: R = Br; 15: R = CN) bearing the maleonitrile-based N-heterocyclic carbene (NHC) (CN)(2)IMes ({(CN)(2)IMes}: 4,5-dicyano-1,3-dimesitylimidazol-2-ylidene) were prepared. Solid state structures of 14 and 15 were obtained. Complexes 14 and 15 adopt a slightly distorted square-planar coordination geometry in the solid state with the substituted pyridine ligand trans to the NHC. Catalytic activities of precatalysts 12-15 were studied and subsequently compared to complexes [PdCl2{(CN)(2)IMes}(PPh3)] (4) and [PdCl(dmba){(CN)(2)IMes}] (5) recently reported by our group in the Suzuki-Miyaura reaction of various aryl halides and phenylboronic acid. Reactions using previously reported [PdCl2(IMes)(py)] (IMes: 1,3-dimesitylimidazol-2-ylidene) (1) were also carried out and their results contrasted to those involving 12-15, 4 and 5. Differences in initiation rates and the catalytically active species related to the seven complexes in regards to the throw away ligand were investigated. Poisoning experiments with mercury show that palladium nanoparticles are responsible for the catalytic activity.}, language = {en} } @article{BaierKellingSchildeetal.2016, author = {Baier, Heiko and Kelling, Alexandra and Schilde, Uwe and Holdt, Hans-J{\"u}rgen}, title = {Investigation of the Catalytic Activity of a 2-Phenylidenepyridine Palladium(II) Complex Bearing 4,5-Dicyano-1,3-bis(mesityl)imidazol-2-ylidene in the Mizoroki-Heck Reaction}, series = {Zeitschrift f{\~A}¼r anorganische und allgemeine Chemie}, volume = {642}, journal = {Zeitschrift f{\~A}¼r anorganische und allgemeine Chemie}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0044-2313}, doi = {10.1002/zaac.201500625}, pages = {140 -- 147}, year = {2016}, abstract = {The phenylidenepyridine (ppy) palladacycles [PdCl(ppy)(IMes)] (4) [IMes = 1,3-bis(mesityl) imidazol-2-ylidene] and [PdCl(ppy){(CN)(2)IMes}] (6) [(CN)(2)IMes = 4,5-dicyano-1,3-bis(mesityl) imidazol-2-ylidene] were prepared by facile two step syntheses, starting with the reaction of palladium(II) chloride with 2-phenylpyridine followed by subsequent addition of the NHC ligand to the precatalyst precursor [PdCl(ppy)](2). Suitable crystals for the X-ray analysis of the complexes 4 and 6 were obtained. It was shown that 6 has a shorter NHC-palladium bond than the IMes complex 4. The difference of the palladium carbene bond lengths based on the higher pi-acceptor strength of (CN)(2)IMes in comparison to IMes. Thus, (CN)(2)IMes should stabilize the catalytically active central palladium atom better than IMes. As a measure for the pi-acceptor strength of (CN)(2)IMes compared to IMes, the selone (CN)(2)IMes center dot Se (7) was prepared and characterized by Se-77-NMR spectroscopy. The pi-acceptor strength of 7 was illuminated by the shift of its Se-77-NMR signal. The Se-77-NMR signal of 7 was shifted to much higher frequencies than the Se-77-NMR signal of IMes center dot Se. Catalytic experiments using the Mizoroki-Heck reaction of aryl chlorides with n-butyl acrylate showed that 6 is the superior performer in comparison to 4. Using complex 6, an extensive substrate screening of 26 different aryl bromides with n-butyl acrylate was performed. Complex 6 is a suitable precatalyst for para-substituted aryl bromides. The catalytically active species was identified by mercury poisoning experiments to be palladium nanoparticles.}, language = {en} } @article{BaierMetznerKoerzdoerferetal.2014, author = {Baier, Heiko and Metzner, Philipp and K{\"o}rzd{\"o}rfer, Thomas and Kelling, Alexandra and Holdt, Hans-J{\"u}rgen}, title = {Efficient palladium(II) precatalysts bearing 4,5-dicyanoimidazol-2-ylidene for the Mizoroki-Heck reaction}, series = {European journal of inorganic chemistry : a journal of ChemPubSoc Europe}, journal = {European journal of inorganic chemistry : a journal of ChemPubSoc Europe}, number = {18}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1434-1948}, doi = {10.1002/ejic.201402040}, pages = {2952 -- 2960}, year = {2014}, abstract = {The new N-heterocyclic carbene (NHC) complex [PdCl2{(CN)(2)IMes}(PPh3)] (2) ({(CN)(2)IMes}: 4,5-dicyano-1,3-dimesitylimidazol-2-ylidene) and the NHC palladacycle [PdCl(dmba){(CN)(2)IMes}] (3) (dmba: N,N-dimethylbenzylamine) have been synthesized by thermolysis of 4,5-dicyano-1,3-dimesityl-2-(pentafluorophenyl) imidazoline (1) in the presence of suitable palladium(II) precursors. The acyclic complex 2 was formed by ligand exchange using the mononuclear precursor [PdCl2(PPh3)(2)] and the palladacycle 3 was formed by cleavage of the dinuclear chloro-bridged precursor [Pd(mu-Cl)(dmba)](2). The new NHC precursor 1-benzyl-4,5-dicyano-2-(pentafluorophenyl)-3-picolylimidazoline (5) was formed by condensation of pentafluorobenzaldehyde with N-benzyl-N'-picolyldiaminomaleonitrile (4). The NHC palladacycle [PdCl2{(CN)(2)IBzPic}] (6) ({(CN)(2)IBzPic}: 1-benzyl-4,5-dicyano-3-picolylimidazol-2-ylidene) was prepared by in situ thermolysis of 5 in the presence of [PdCl2(PhCN)(2)]. The three palladium(II) complexes were characterized by NMR and IR spectroscopy, mass spectrometry and elemental analysis. In addition, the molecular structures of 2 and 3 were determined by X-ray diffraction. The pi-acidity of (CN)(2)IBzPic was compared with (CN)(2)IMes and perviously reported pi-acidic imidazol-2-ylidenes by NBO analysis. The Mizoroki-Heck (MH) reactions of various aryl halides with n-butyl acrylate were performed in the presence of complexes 2, 3 and 6. The new precatalysts showed high activity in the MH reactions giving good-to-excellent product yields with 0.1 mol-\% pre-catalyst. The nature of the catalytically active species of 2, 3 and 6 was investigated by poisoning experiments with mercury and transmission electron microscopy. It was found that palladium nanoparticles formed from the precatalysts were involved in the catalytic process.}, language = {en} } @phdthesis{Jovanovic2005, author = {Jovanovic, Ljubisa}, title = {New synthetic approaches to 8,5'-neolignans}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-6878}, school = {Universit{\"a}t Potsdam}, year = {2005}, abstract = {Neolignans, dehydrodimers of phenylpropenes, are natural products that exhibit different biological activities. 8,5'-Neolignans containing a trans- dihydrobenzofuran skeleton are the most abundant neolignans in nature. The published syntheses of trans-dihydrobenzofurans are multistep procedures that are time consuming and provide the product in low yield. Furthermore, all dimerisation reactions either in the presence of enzymes or mediated by metal salts are yielding dimers consisting of two units of the same phenylpropene compound, narrowing substantially the substitution pattern. Two different general synthetic approaches were examined. The first strategy was the enantioselective deprotonation at the α-carbon of the ο-alkyl phenols in the presence of a chiral diamine and sBuLi. Synthesis of several new phosphorous-based directed ortho-metalation groups was studied. The examined compounds having these new groups decomposed even under very mild reaction conditions and are not suitable for the application in the synthesis. The second strategy was to examine one [3+2] cycloaddition reaction, transition metal catalysed Heck oxyarylation reaction, in the synthetic approach to compounds having trans-dihydrobenzofuran skeleton. Palladium catalysed Heck oxyarylation reaction with halogenophenols or ortho-diazonium phenols as the starting material allowed the trans-dihydrobenzofuran compounds as the major products in acceptable yield and in one step. The products were formed under ligand free condition, as well as in the presence of some strong coordinating ligands (Ph3P). The experiments with several chiral ligands, showed that the obtained trans-dihydrobenzofurans were racemic mixtures. This result suggests formation of an achiral intermediate along the reaction pathway, which causes the lack of stereoselectivity in the products. Initially formed trans-dihydrobenzofuran compounds are the key precursors of many naturally occurring neolignans, and can be easily converted to 8,5'-neolignan derivatives.}, subject = {Dihydrobenzofurane}, language = {en} } @article{SandSchmidt2021, author = {Sand, Patrick and Schmidt, Bernd}, title = {Pd-catalyzed oxidative sulfoalkenylation of acetanilides and traceless removal of the catalyst directing group}, series = {ChemistrySelect}, volume = {6}, journal = {ChemistrySelect}, number = {14}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {2365-6549}, doi = {10.1002/slct.202101009}, pages = {3563 -- 3567}, year = {2021}, abstract = {The palladium-catalyzed oxidative Heck-reaction, also referred to as Fujiwara-Moritani-reaction, has been investigated for the synthesis of styrenylsulfonyl compounds. Acetanilides and vinylsulfonyl compounds undergo dehydrogenative coupling reactions in moderate to quantitative yields, using benzoquinone as the oxidant of choice. Potassium peroxodisulfate, which had previously been identified as a superior oxidant for the coupling with acrylates, did not provide any coupling products with these olefins. Traceless removal of the catalyst directing group through a deacetylation-diazotation-coupling (DDC) sequence was demonstrated for 2-arylethene sulfones.}, language = {en} } @article{SchmidtElizarovRiemeretal.2015, author = {Schmidt, Bernd and Elizarov, Nelli and Riemer, Nastja and H{\"o}lter, Frank}, title = {Acetamidoarenediazonium Salts: Opportunities for Multiple Arene Functionalization}, series = {European journal of organic chemistry}, journal = {European journal of organic chemistry}, number = {26}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1434-193X}, doi = {10.1002/ejoc.201500795}, pages = {5826 -- 5841}, year = {2015}, abstract = {Unlike their ortho counterparts, meta- and para-acetamidoanilines can be converted into the corresponding acetamidoarenediazonium salts. These offer various opportunities for multiple Pd-catalyzed arene functionalization reactions, such as Matsuda-Heck-, Suzuki-Miyaura- or Fujiwara-Moritani couplings.}, language = {en} } @article{SchmidtGeissler2011, author = {Schmidt, Bernd and Geissler, Diana}, title = {Ru- and Pd-Catalysed Synthesis of 2-Arylfurans by One-Flask Heck Arylation/Oxidation}, series = {European journal of organic chemistry}, journal = {European journal of organic chemistry}, number = {25}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1434-193X}, doi = {10.1002/ejoc.201100549}, pages = {4814 -- 4822}, year = {2011}, abstract = {2,5-Disubstituted furans were synthesized by one-flask Heck arylation/oxidation sequences. The starting materials are 2-substituted 2,3-dihydrofurans, conveniently available by RCM/isomerization sequences, and arenediazonium salts. These react in ligand-free Heck reactions to afford 2,5-disub-stituted 2,5-dihydrofurans, which are oxidized to the corresponding furans without isolation or intermediate workup. The oxidation is conveniently achieved with chloranil or DDQ, depending on the substrate.}, language = {en} } @article{SchmidtRiemer2015, author = {Schmidt, Bernd and Riemer, Martin}, title = {Synthesis of Magnaldehydes B and E and Dictyobiphenyl B by Microwave-Promoted Cross-Coupling of Boronophenols}, series = {European journal of organic chemistry}, journal = {European journal of organic chemistry}, number = {17}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1434-193X}, doi = {10.1002/ejoc.201500350}, pages = {3760 -- 3766}, year = {2015}, abstract = {Magnaldehydes B and E along with their 4'-methylated derivatives are naturally occurring 2,4'-biphenols that have been isolated from the Magnoliaceae. Herein, these natural products have been synthesized from a common intermediate, which was obtained by a microwave-promoted, hetero-geneously catalyzed, and protecting-group-free Suzuki-Miyaura coupling reaction in an aqueous medium. These reaction conditions were also successfully applied to a one-step synthesis of the slime mold metabolite dictyobiphenyl B.}, language = {en} } @article{SchmidtWolfBrunner2016, author = {Schmidt, Bernd and Wolf, Felix and Brunner, Heiko}, title = {Styrylsulfonates and -Sulfonamides through Pd-Catalysed Matsuda-Heck Reactions of Vinylsulfonic Acid Derivatives and Arenediazonium Salts}, series = {European journal of organic chemistry}, journal = {European journal of organic chemistry}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1434-193X}, doi = {10.1002/ejoc.201600469}, pages = {2972 -- 2982}, year = {2016}, abstract = {Arene diazonium salts undergo Matsuda-Heck reactions with vinylsulfonates and -sulfonamides to give styrylsulfonic acid derivatives in high to excellent yields and with high to excellent selectivities. By quantifying the evolution of nitrogen over time in a gas-meter apparatus, the reactivities of ethylvinylsulfonate and the benchmark olefin methyl acrylate were compared for an electron-rich and an -deficient arene diazonium salt. Tertiary sulfonamides react in Matsuda-Heck couplings with high conversions, but require long reaction times, which prevents the determination of kinetic data through the measurement of nitrogen evolution. Secondary sulfonamides were found to be unreactive. From these results, the following order of reactivity could be deduced: H2C=CHCO2Me > H2C=CHSO2OEt > H2C=CHSO2N(Me)Bn >> H2C=CHSO2NHBn. Through the Matsuda-Heck coupling of 5-indolyldiazonium salt and a tertiary vinylsulfonamide, the synthesis of the C-5-substituted indole part of the antimigraine drug naratriptan was accomplished in high yield.}, language = {en} } @article{SchwarzeTraegerKellingetal.2013, author = {Schwarze, Thomas and Traeger, Juliane and Kelling, Alexandra and Schilde, Uwe and Holdt, Hans-J{\"u}rgen}, title = {Macrocyclic dithiomaleonitriles for an efficient PdCl2 coordination}, series = {Inorganica chimica acta : the international inorganic chemistry journal}, volume = {408}, journal = {Inorganica chimica acta : the international inorganic chemistry journal}, number = {2}, publisher = {Elsevier}, address = {Lausanne}, issn = {0020-1693}, doi = {10.1016/j.ica.2013.08.020}, pages = {53 -- 58}, year = {2013}, abstract = {We have synthesized a set of new unsaturated macrocyclic dithioethers with an increasing number of flexible methylene units 1-7 (Scheme 2) to investigate the correlation between the ring size of these ligands, the chelation effect and the consequences for an efficient PdCl2 coordination. The dithioethers 1-7 and the complex [PdCl2(4)]center dot CHCl3 were characterized by X-ray diffraction analysis. The crystal structures of 1-7 show that 2-7 are better preorganized chelating ligands for an exocyclic PdCl2 coordination than 1. The chelation effect of 1-7, the orientation of the sulfur atoms and the S center dot center dot center dot S donor distances, are influenced by the flexibility of the methylene units. In this series the unsaturated macrocyclic ligands 5 and 6 are the best chelating ligands for an efficient PdCl2 coordination. Comparative solvent extraction experiments with mn-12S(2)O(2) (mn = maleonitrile) reveal that the low interface activity of the new ligands reduces the extraction rate. However, a comparison with open-chain dithiomaleonitriles shows the impact of the macrocyclic effect of 4 and 5 on the extraction yield.}, language = {en} }