Angewandte Chemie International Edition

Cover image for Vol. 53 Issue 16

Editor: Peter Gölitz, Deputy Editors: Neville Compton, Haymo Ross

Online ISSN: 1521-3773

Associated Title(s): Angewandte Chemie, Chemistry - A European Journal, Chemistry – An Asian Journal, Zeitschrift für Chemie

Upcoming VIPs

The following papers are very important in the opinion of two referees. They will be published as soon as possible.

You are invited to comment on published VIPs. Please use the link given at the end of each such abstract. Scientific comments may be forwarded to the authors by the editorial office and may be posted on this page. Kindly let us know if your comments are for the editorial office only, the author, or the public as well.

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Copper-Chelating Azides for Efficient Click Conjugations in Complex Media

Valentina Bevilacqua, Mathias King, Manon Chaumontet, Marc Nothisen, Sandra Gabillet, David Buisson, Céline Puente, Alain Wagner, and Frédéric Taran*

The search for fast and high-yielding bioorthogonal ligations is of prime importance in chemical biology. To this end, clickable copper complexes were designed for ultrafast ligation with alkynes in complex biological media. The reactivity and stability of one of these copper complexes allowed efficient click reaction with alkynes within seconds inside living cells.


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Sequential Intra-Intercellular Nanoparticle Delivery System for Deep Tumor Penetration

Caoyun Ju, Ran Mo,* Jingwei Xue, Lei Zhang, Zekai Zhao, Lingjing Xue, Qineng Ping, and Can Zhang*

A sequential intra-intercellular nanoparticle delivery system consisting of a pH-responsive reversible swelling–shrinking nanogel was developed for deep tumor penetration of chemotherapeutics. The obtained nanogel had a crosslinked polyelectrolyte core composed of N-lysinal-N′-succinyl chitosan and poly(N-isopropylacrylamide) and a crosslinked bovine serum albumin shell, which could swell under acidic condition and shrink back in a neutral environment. The swelling produced a rapid release of the encapsulated drugs in the cells for efficient cytotoxicity. After liberating from the dead cells, the contractive nanogel repeatedly infected the neighboring cancer cells closer to the center of the tumor tissue, like "peeling an onion" layer by layer from the outside to the inside of the solid tumor.

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EarlyViewThreshold Sensing by a Synthetic Enzymatic Reaction–Diffusion Network

Sergey Semenov, Albert J. Markvoort, Tom F. A. de Greef, and Wilhelm T. S. Huck

A wet stamping method is reported to precisely control concentrations of enzymes and inhibitors in place and time inside layered gels. By combining enzymatic reactions such as autocatalysis and inhibition with spatial delivery of components through soft-lithographic techniques the biochemical reaction network can filter out certain aspects of a pattern (density of pillars, size of features on the stamp) and translate this information into a fluorescent signal because of the local autocatalytic activation of trypsin. The experimental method can be used to assess fundamental principles of spatiotemporal order formation in chemical reaction networks.

Received February 12, 2014, published online April 02, 2014, DOI: 10.1002/anie.201402327 – read now.

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Towards a Sustainable Synthesis of Formate Salts: Combined Catalytic Methanol Dehydrogenation and Bicarbonate Hydrogenation

Qiang Liu, Lipeng Wu, Samet Gülak, Nils Rockstroh, Ralf Jackstell, and Matthias Beller*

Formate salts represent important chemicals which are widely used in daily life products. The current industrial scale manufacture of formates requires high pressure of CO under harsh reaction conditions. A new process is described for these products without usage of hazardous gas and chemicals. Applying ruthenium pincer complexes a simultaneous methanol dehydrogenation and bicarbonate hydrogenation reaction proceeds, which provides a green process towards formate salts with excellent turnover number (>18000), turnover frequency (>1300 h-1), and yield (>90%).

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Structure of Transient Amyloid-β Oligomers Differs From Less Toxic Fibrils in Regions Known to Harbor Familial Alzheimer Mutations

Bidyut Sarkar, Venus Singh Mithu, Bappaditya Chandra, Arghya Mandal, Muralidharan Chandrakesan, Debanjan Bhowmik, Perunthiruthy K. Madhu, and Sudipta Maiti

Aggregation intermediates of the amyloid-β (Aβ) peptide are believed to initiate Alzheimer's disease, but their fleeting nature makes their structure elusive. Fast fluorescence and slow solid-state NMR techniques are combined to probe the structural features of small bio-active Aβ40 oligomers which are stable for tens of minutes in physiological buffers. Most of the peptide has a conformation similar to the less toxic mature aggregates, but two regions (residues 22–29 and residues 1–10) are strikingly different. Interestingly, 10 of 11 disease-causing Aβ mutations occur in these two regions. The presented results could provide potential structural cues for developing Alzheimer therapeutics.

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How Does a Coordinated Radical Ligand Affect the Spin Crossover Properties in an Octahedral Iron(II) Complex?

Markus Schmitz, Manuel Seibel, Harald Kelm, Serhiy Demeshko, Franc Meyer, and Hans-Jörg Krüger*

For the first time, redox-controlled changes of a coordinated ligand have been demonstrated to induce spin crossover in an octahedral iron(II) complex. Characterization of the iron(II) radical complex by structural, magnetochemical, and spectroscopic methods reveals a spin crossover equilibrium above 240 K occurring between an S=1/2 ground state and an S=3/2 excited spin state. The influence of the coordinated π-radical on the spin crossover properties of the octahedral iron(II) ion is discussed. The structural and electronic differences between both oxidation states of the redox couple are presented.

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EarlyViewThe Compressibility of pH-Sensitive Microgels at the Oil–Water Interface: Higher Charge Leads to Less Repulsion

Karen Geisel, Lucio Isa, and Walter Richtering*

The effect of electrostatic interactions on microgel-stabilized emulsions is different from classical Pickering emulsions. The influence of charges is investigated on flat interfaces and compression isotherms provide information about the interaction of microgels at interfaces. Surprisingly, higher compressibility is found for charged microgels compared to uncharged ones. In other words charged microgels are easier to compress. The compressibility of microgels is thus not determined by direct Coulomb repulsion. This is distinctly different from the behavior of rigid colloids used in Pickering emulsions. It is proposed that the different swelling of the microgels is the key parameter.

Received February 11, 2014, published online March 28, 2014, DOI: 10.1002/anie.201402254 – read now.

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Chemoselective Intermolecular α-Arylation of Amides

Bo Peng, Danny Geerdink, Cristophe Farés, and Nuno Maulide*

By using an electrophilic activation approach, the fully chemoselective α-arylation of amides was achieved without the need for any strong base or metal catalyst. This means that, for the first time, the direct arylation of amides in the presence of esters or ketones is possible. IR and NMR studies highlight the subtle, but crucial role of the mild base that is used.

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Rate Coefficients of Criegee Intermediate (CH2OO and CH3CHOO) Reactions with Formic and Acetic Acid Are Close to Their Collision Limit: Direct Kinetics Measurements and Atmospheric Implications

Oliver Welz, Arkke J. Eskola, Leonid Sheps, Brandon Rotavera, John D. Savee, Adam M. Scheer, David L. Osborn, Douglas Lowe, A. Murray Booth, Ping Xiao, M. Anwar H. Khan, Carl J. Percival,* Dudley E. Shallcross,* and Craig A. Taatjes*

Rate coefficients for reactions of Criegee intermediates (carbonyl oxides, CI) with organic acids are in excess of 1x10-10 cm3 s-1, suggesting that reaction with carboxylic acids is a substantially more important loss process for CI than has been assumed. Implementing these rate coefficients in global atmospheric models shows that reactions between CI and organic acids make a substantial contribution to removal of these acids in terrestrial equatorial areas and in other regions where high CI concentrations occur such as high northern latitudes, and implies that sources of acids in these areas are larger than previously recognized.





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EarlyViewSynthesis of Tris- and Tetrakis(pentafluoroethyl)silanes

Simon Steinhauer, Julia Bader, Hans-Georg Stammler, Nikolai Ignat′ev and Berthold Hoge*

The decomposition temperatures of trifluoromethylsilanes decrease with an increasing electronwithdrawel by the additional substituents. Tris- and tetrakis(trifluoromethyl)silanes evaded isolation so far due to their thermolability. The reaction of SiCl4 with LiC2F5 only yields (pentafluoroethyl)fluorosilicates. To avoid silicate formation through fluoride transfer by LiC2F5 the Lewis acidity of the silane has to be reduced by an electron-donating substituent such as a diethylamino group. Si(C2F5)2NEt2 is a valuable and surprisingly thermally stable precursor for a series of tris(pentafluoroethyl)silanes. The tetrakis(perfluoroalkyl)silanes Si(C2F5)4 and Si(C2F5)3CF3 are accessible by direct fluorination of Si(C2F5)3C2H5 and Si(C2F5)CH3, respectively. Whereas Si(C2F5)4 decomposes only at elevated temperatures, Si(C2F5)3CF3 already liberates difluorocarbene at room temperature.

Received January 10, 2014, published online April 01, 2014, DOI: 10.1002/anie.201400291 – read now.

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EarlyViewAn Efficient and Modular Route to Sequence-Defined Polymers Appended to DNA

Thomas G. W. Edwardson, Karina M. M. Carneiro, Christopher J. Serpell,* and Hanadi F. Sleiman*

A solid-phase automated approach is reported for the generation of monodisperse and sequence-defined polymers conjugated to DNA, using readily available reagents. These polymer–DNA conjugates display micellar self-assembly and encapsulation behavior studied by HPLC, dynamic light scattering, atomic force microscopy, and fluorescence spectroscopy. The self-assembly profiles vary within polymers of the same composition but different sequence order. The DNA component still retains base-pairing fidelity, thus giving rise to two orthogonal and programmable assembly languages within the same molecule. The method is general and has the potential to make DNA–polymer conjugates and sequence-defined polymers widely available.

Received December 17, 2013, published online March 26, 2014, DOI: 10.1002/anie.201310937 – read now.

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EarlyViewConfirmed by X-ray Crystallography: The B·B One-Electron σ Bond

Alexander Hübner, Andreas M. Diehl, Martin Diefenbach, Burkhard Endeward, Michael Bolte, Hans-Wolfram Lerner, Max C. Holthausen*, and Matthias Wagner*

Is one electron sufficient to bring about significant σ bonding between two atoms? The chemist’s view on the chemical bond is usually tied to the concept of shared electron pairs, and not too much experimental evidence exists to challenge this firm belief. Whilst species with the unusual one-electron σ-bonding motif between homonuclear atoms have so far been identified mainly by spectroscopic evidence, the first crystallographic characterization, augmented by a detailed quantum-chemical validation, is presented for a radical anion featuring a B·B one-electron–two-center σ bond.

Received February 06, 2014, published online March 25, 2014, DOI: 10.1002/anie.201402158 – read now.

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EarlyViewIn Vivo Liver Cancer Chemoembolization and Magnetic Resonance Imaging Using Iron Oxide Nanoshell/Doxorubicin/Poly(vinyl alcohol) Hybrid Composites

Yi-Xiang J. Wang,* Xiao-Ming Zhu, Qi Liang, Christopher H. K. Cheng, Wei Wang,* and Ken Cham-Fai Leung*

A hybrid composite based on superparamagnetic iron oxide nanoshell/doxorubicin/poly(vinyl alcohol) was used for in vivo intra-arterial embolization of liver tumor blood vessels followed by slow and sustained release of the anticancer drug. The composite was relatively noncytotoxic and MRI-responsive, rendering it a novel theranostic chemoembolization agent.

Received February 07, 2014, published online March 25, 2014, DOI: 10.1002/anie.201402144 – read now.

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EarlyViewA Volatile Lactone of Hymenoscyphus Pseudoalbidus, Pathogen of European Ash Dieback, Inhibits Host Germination

Christian A. Citron, Corina Junker, Barbara Schulz and Jeroen, and S. Dickschat*

The volatile secondary metabolites from the ash pathogen Hymenoscyphus pseudoalbidus, that since nearly two decades threatens the whole ash population in Europe, have been identified by GC/MS and synthesis of reference compounds. One lactone, 3,4-dimethylpentan-4-olide, that is produced by the fungus as mixture of enantiomers showed a strong germination inhibitory activity towards ash seeds and caused necroses in the plant tissue.

Received February 11, 2014, published online March 18, 2014, DOI: 10.1002/anie.201402290 – read now.

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EarlyViewMetal- and Reagent-Free Highly Selective Anodic Cross-Coupling Reaction of Phenols

Bernd Elsler, Dieter Schollmeyer, Katrin M. Dyballa, Robert Franke, and Siegfried R. Waldvogel*

Using electric current as sole reagent and requiring neither leaving functions nor catalysts results in a highly sustainable method for direct C,C cross-coupling of phenols. In contrast to well-established and conventional methods for cross-coupling of two phenol components, this electrochemical transformation does not need protecting groups. A direct electrolysis of the coupling partners in formic acid or fluorinated solvents provides the desired nonsymmetrical 2,2′-biphenols in good yields with very high selectivity.

Received January 20, 2014, published online March 18, 2014, DOI: 10.1002/anie.201400627 – read now.

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Mechanically Driven Activation of Polyaniline into Its Conductive Form

Bilge Baytekin, H. Tarik Baytekin, and Bartosz A. Grzybowski*

Mechanical treatment of polymer surfaces gives rise to surface cations and anions. These mechanically generated species can transform nonconductive polyaniline into its conductive form, which constitutes the first successful demonstration of "mechanoions" driving chemical reactions. Our results are also of practical relevance since they define a convenient, mechanochemical route to printing patterns of conductive polymers on flat surfaces and to coating of polymer particles with conductive polymer films resisting accumulation of static electricity.

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EarlyViewMerging Aerobic Oxidation and Enamine Catalysis in Asymmetric α-Amination of β-Ketocarbonyls Using N-Hydroxycarbamates as Nitrogen Sources

Changming Xu, Long Zhang, and Sanzhong Luo*

Enantioselective α-amination of 1,3-dicarbonyl compounds has been achieved by merging enamine catalysis and Cu(I) catalyzed aerobic oxidation of hydroxycarbamates. The process is enabled by a simple chiral primary amine through coupling of a catalytic enamine ester intermediate and in situ generated nitrosocarbonyl derived from N-hydroxycarbamate. The reaction features high chemoselectivity and excellent enantioselectivity for a broad range of substrates and provides a facile route for asymmetric synthesis of unnatural amino acids bearing α-quaternary stereocenters.

Received January 24, 2014, published online March 12, 2014, DOI: 10.1002/anie.201400776 – read now.

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EarlyViewProbing Transient Conformational States of Proteins by Solid-State R Relaxation-Dispersion NMR Spectroscopy

Peixiang Ma, Jens D. Haller, Jérémy Zajakala, Pavel Macek, Astrid C. Sivertsen, Dieter Willbold, Jérôme Boisbouvier, and Paul Schanda*

The function of proteins depends on their ability to sample a variety of states differing in structure and free-energy. Deciphering how the various thermally accessible conformations are connected, and understanding their structures and relative energies are crucial to rationalize protein function. It is shown how transient protein conformational states can be probed by solid-state NMR R relaxation dispersion experiments. By combining sample deuteration with fast magic-angle spinning, insight is provided into the kinetics of conformational exchange, the relative populations of the involved states, and even their structural properties.

Received December 30, 2013, published online March 18, 2014, DOI: 10.1002/anie.201311275 – read now.

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EarlyViewThe Potent Oxidant Anticancer Activity of Organoiridium Catalysts

Zhe Liu, Isolda Romero-Canelón, Bushra Qamar, Jessica M. Hearn, Abraha Habtemariam, Nicolas P. E. Barry, Ana M. Pizarro, Guy J. Clarkson, and Peter J. Sadler*

The organoiridium(III) complex [(η5-Cpxbiph)Ir(phpy)Cl] (1-Cl), containing biphenyltetramethylcyclopentadienyl and CN-chelated phenylpyridine ligands, undergoes rapid hydrolysis. In contrast, the pyridine complex [(η5-Cpxbiph)Ir(phpy)(py)]+ (1-py) aquates slowly, and is more potent (nanomolar) than both 1-Cl and cisplatin towards cancer cells. The pyridine ligand protects 1-py from rapid reactions with intracellular glutathione. The high potency of 1-py correlates with dramatically increased levels of reactive oxygen species in cancer cells. These iridium complexes have an unprecedented ability to generate H2O2 using catalytic hydride transfer from coenzyme NADH to oxygen. Such organoiridium complexes are promising as a new generation of anticancer drugs for effective oxidant therapy.

Received December 23, 2013, published online March 11, 2014, DOI: 10.1002/anie.201311161 – read now. No. 15/2014.

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EarlyViewSuperior Rechargeability and Efficiency of Li-O2 Batteries: Hierarchical Air Electrode Architecture Combined with a Soluble Catalyst

Hee-Dae Lim, Hyelynn Song, Jinsoo Kim, Hyeokjo Gwon, Youngjoon Bae, Kyu-Young Park, Jihyun Hong, Haegyeom Kim, Taewoo Kim, Yong Hyup Kim, Xavier Lepró, Raquel Ovalle-Robles, Ray H. Baughman, and Kisuk Kang*

A novel Li-O2 battery with high reversibility and good energy efficiency is demonstrated using a soluble catalyst combined with a hierarchical nanoporous air electrode. Through the porous three-dimensional network of the air electrode, not only lithium ions and oxygen but also soluble catalysts can be rapidly transported, enabling ultraefficient electrode reactions and significantly enhanced catalytic activity. The novel Li-O2 battery, combining an ideal air electrode and a soluble catalyst, can deliver a high reversible capacity (1000 mAh g-1) up to 900 cycles with reduced polarization (ca. 0.25 V).

Received January 22, 2014, published online March 05, 2014, DOI: 10.1002/anie.201400711 – read now. No. 15/2014.

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EarlyViewThe Role of Ligand-Field States in the Ultrafast Photophysical Cycle of the Prototypical Iron(II) Spin-Crossover Compound [Fe(propyltetrazole)6](BF4)2

Andrea Marino, Pradip Chakraborty, Marina Servol, Maciej Lorenc, Eric Collet, and Andreas Hauser

The role of the ligand-field (LF) states in the mechanism of ultrafast light-induced spin transitions in iron(II) complexes has been discussed controversially in the past. For irradiation into metal-ligand-charge-transfer (MLCT) transitions the experimental evidence suggests that they are bypassed for both the light-induced low-spin (S=1) to high-spin (S=2) conversion as well as the high-spin to low-spin conversion. In contrast, for direct irradiation into the spin-allowed LF transitions of a system with only high-energy MLCT states, the low-lying triplet (S=1) LF state can be clearly identified as intermediate state in the relaxation cascade.

Received December 16, 2013, published online March 11, 2014, DOI: 10.1002/anie.201310884 – read now. No. 15/2014.

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EarlyViewEnantioselective N–H Insertion Reaction of α-Diazoketones

Bin Xu, Shou-Fei Zhu,* Xiao-Dong Zuo, Zhi-Chao Zhang and Qi-Lin Zhou*

The first highly enantioselective N–H insertion reaction of α-diazoketones was developed by using cooperative catalysis of dirhodium(II) carboxylates and chiral spiro phosphoric acids. The insertion reaction provides a new access to diverse chiral α-aminoketones, which are versatile building blocks in the organic synthesis, with fast reaction rates, good yields, and high enantioselectivities under mild and neutral conditions.

Received January 09, 2014, published online March 05, 2014, DOI: 10.1002/anie.201400236 – read now. No. 15/2014.

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EarlyViewTotal Chemical Synthesis and Biological Activities of Glycosylated and Non-Glycosylated Forms of the Chemokines CCL1 and Ser-CCL1

Ryo Okamoto,* Kalyaneswar Mandal, Morris Ling, Andrew D. Luster, Yasuhiro Kajihara, and Stephen B. H. Kent*

The total syntheses of both N-glycosylated and non-glycosylated forms of the chemokine (Ser-)CCL1 by convergent native chemical ligation is reported. An N-glycan isolated from hen egg yolk is used together with the Nbz linker for Fmoc chemistry solid-phase synthesis of the glycopeptide-αthioester building block. Chemotaxis assays of these glycosylated and non-glycosylated proteins were carried out. The results were correlated with the chemical structures of the (glyco)protein molecules. To the best of our knowledge, these are the first investigations of the effect of glycosylation on the chemotactic activity of the chemokine (Ser-)CCL1 using homogeneous N-glycosylated protein molecules of defined covalent structure.

Received December 06, 2013, published online March 18, 2014, DOI: 10.1002/anie.201310574 – read now.

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A Diiron(III,IV) Imido Species Active in Nitrene Transfer Reactions

Eric Gouré, Frédéric Avenier, Patrick Dubourdeaux, Olivier Sénèque, Florian Albrieux, Colette Lebrun, Martin Clémancey, Pascale Maldivi,* and Jean-Marc Latour*

Efficient nitrene transfer and H abstraction reactions mediated by a diiron compound involve a highly reactive diiron(III,IV) intermediate. This is revealed by a combination of desorption electrospray ionization mass spectrometry and quantitative chemical quenching experiments. This intermediate is electrophilic and its H abstraction ability is comparable to that of the most active oxo compounds. Its electronic structure has been analyzed by DFT calculations. Its high reactivity is probably associated to major contributions of low-lying electronic states involving a strong spin density on the nitrene.


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Recoding the Genetic Code with Selenocysteine

Markus J. Bröcker, Joanne M. L. Ho, George M. Church, Dieter Söll*, and Patrick O'Donoghue*

Selenocysteine (Sec) is naturally incorporated into proteins by recoding the stop codon UGA. The Sec insertion machinery site-specifically incorporates Sec at 58 of the 64 codons and competes effectively against canonical amino acid insertion directed by EF-Tu. For 15 sense codons, complete conversion of the codon meaning from canonical amino acid to Sec was observed along with a 10-fold increase in selenoprotein yield compared to Sec insertion at UGA. The findings have applications in genetic code expansion and bring to light fundamental questions about the translation process and the information storage capacity of the biological cell.


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Foldamer-Mediated Remote Stereocontrol: Up to 1,60-Asymmetric Induction

Liam Byrne, Jordi Solà, Thomas Boddaert, Tommaso Marcelli, Ralph W. Adams, Gareth A. Morris, and Jonathan Clayden*

By inducing a quantitative, persistent preference for right-handed helicity, chiral residues at one end of an otherwise achiral helical oligomer are able to control the stereoselectivity of reactions at sites located as far as 60 bonds away, shattering previous records for remote stereochemical control.


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Palladium and Platinum η2-Disilyne Complexes Bearing an Isolable Dialkyldisilyne as a Ligand

Shintaro Ishida,* Ryutaro Sugawara, Yoshifumi Misawa, and Takeaki Iwamoto*

A new isolable dialkyldisilyne is synthesized as green crystals and fully characterized. Its palladium and platinum complexes are successfully obtained by the ligand exchange reactions. In the complexes, the isolable disilyne coordinates to the transition metals in a η2-fashion. These complexes have a trans-bent geometry in contrast to η2-alkyne complexes and show significant metallacycle character.


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