Alexander Pothig

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Name: Alexander Pöthig

Organization: Technische Universit?t München

Department: Chair of Inorganic Chemistry/Molecular Catalysis, Department Chemie, Catalysis Research Center

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TOPICS

Material Chemistry

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Organic Chemistry

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Chemicals
References

A Pd Halide Cluster from 1964: Pd6Cl8 Capped by Ring-Opened C3Ph3 Ligands from Oxidative Addition of Cyclopropenium Ions

Co-reporter:Christian Jandl, Karl Öfele, and Alexander Pöthig

Organometallics November 27, 2017 Volume 36(Issue 22) pp:4348-4348

Publication Date(Web):August 28, 2017

DOI:10.1021/acs.organomet.7b00525

On the basis of a protocol from 1964 on the reaction of K2PdCl4, triphenylcyclopropenium chloride, and ethylene, the product was now identified as a Pd6Cl8 cluster capped by μ3-η1:η1:η3-C3Ph3 ligands, [C3Ph3]2[Pd6Cl8(C3Ph3)2]. The ligand is formed in a two-step reaction involving first the partial reduction of Pd(II) to Pd(0) by ethylene and second the ring-opening oxidative addition of the cyclopropenium ion, leading to a rare binding mode with one allyl and two alkyl bonds. Although the structure was not recognized at that time, this compound represents the first isolated organometallic Pd cluster compound.

Rational Synthesis and Electronic Structure of Functionalized Trinuclear Pd Metal Sheet Sandwich Complexes

Co-reporter:Christian Jandl, James R. Pankhurst, Jason B. Love, and Alexander Pöthig

Organometallics August 14, 2017 Volume 36(Issue 15) pp:2772-2772

Publication Date(Web):July 3, 2017

DOI:10.1021/acs.organomet.7b00276

In this article we present the rational synthesis and full characterization of molecular Pd3 clusters sandwiched by imidazolium- and pyridinium-functionalized cycloheptatrienide ligands, of general formula [Pd3Br3(C7H6R)2]+. From functionalized η3-cycloheptatrienide Pd complexes as starting materials, PdBr2(η3-C7H6R), a number of synthetic routes were tested and a generally applicable strategy was developed on the basis of the formation of dimeric “preclusters”, [{PdBr(η3-C7H6R)}2(μ-Br)]+, which exhibit a Pd–Pd interaction. Spectroscopic and electrochemical results indicate a noninteger, common oxidation state of Pd in the trinuclear clusters, and crystallographic analysis reveals distinct differences in the binding properties of the Pd atoms in the solid state, suggesting that in certain environments there are even two discernible oxidation states, which is supported by computational analysis of the charge distribution.

A hybrid imidazolylidene/imidazolium nickel NHC complex: an isolated intermediate

Co-reporter:Philipp J. Altmann;Michael Ehrenreich;Alexer Pöthig

Acta Crystallographica Section C 2017 Volume 73(Issue 11) pp:880-884

Publication Date(Web):2017/11/01

DOI:10.1107/S2053229617013250

Macrocyclic ligand systems with a variety of (different) donor sites oftentimes give rise to very exciting and unexpected multinuclear metal complexes. We report herein the structure of a trinuclear mixed imidazolylidene/imidazolium nickel N-heterocyclic carbene (NHC) complex, namely di-μ-chlorido-bis{μ-calix[2]imidazolium[2]imidazolylidene[2]pyrazolate}trinickel(II) tetrakis(hexafluoridophosphate) acetonitrile tetrasolvate, [Ni3(C24H24N12)2Cl2](PF6)4·4CH3CN or [Ni3(LMe)2Cl2](PF6)4·4CH3CN, that can be understood as a trapped reaction intermediate during the synthesis of the respective [Ni2LMe](PF6)2 product. The structure not only contains protonated next to deprotonated imidazole heterocycles, but also Ni2+ ions with fundamentally different coordination modes within one molecule. Two of the three metal atoms are coordinated in a square-pyramidal fashion by half a ligand molecule and one chloride ligand, whereas the third Ni2+ ion is bound octahedrally by four pyrazolate moieties and two chloride anions.

A hybrid carbocyclic/N-heterocyclic carbene ligand

Co-reporter:Christian Jandl;Alexander Pöthig

Chemical Communications 2017 vol. 53(Issue 13) pp:2098-2101

Publication Date(Web):2017/02/09

DOI:10.1039/C6CC08468K

We report the synthesis and characterisation of the first complex bearing a bidentate carbocyclic/N-heterocyclic carbene ligand, which represents an unprecedented combination of these two carbene classes. Starting from an unsubstituted cycloheptatrienylidene–Pd complex, the ligand was built up in an on-site synthesis at the metal center. DFT calculations were employed to understand the crucial allyl-to-alkyl rearrangement of the carbocycle in this sequence and all its binding modes during the reaction cascade were crystallographically characterised.

Pillarplexes: A Metal–Organic Class of Supramolecular Hosts

Co-reporter:Philipp J. Altmann and Alexander Pöthig

Journal of the American Chemical Society 2016 Volume 138(Issue 40) pp:13171-13174

Publication Date(Web):September 28, 2016

DOI:10.1021/jacs.6b08571

Novel octanuclear NHC complexes of gold(I) and silver(I) form metallocavitand structures with very defined tubular cavities and are able to selectively host linear molecules, exemplarily demonstrating 1,8-diaminooctane as a model guest molecule. The solubility of the host-compounds is easily adjusted by simple anion exchange reactions so that the compounds can be made soluble in water wherein they exhibit a high longtime stability. The gold(I) complex is emissive in aqueous solutions, which enables a determination of the binding constant to the diamine via luminescence quenching. The host–guest interaction was further investigated by isothermal titration calorimetry, NMR spectroscopy, and X-ray crystallography.

Capsoplexes: encapsulating complexes via guest recognition

Co-reporter:Philipp J. Altmann and Alexander Pöthig

Chemical Communications 2016 vol. 52(Issue 58) pp:9089-9092

Publication Date(Web):23 Feb 2016

DOI:10.1039/C6CC00507A

A new dinuclear Ni–NHC complex is able to selectively recognise and self-assemble with guests via tennis-ball like encapsulation, exemplarily demonstrated employing halides. Addition of chloride or bromide leads to the formation of capsules with small cavities which are stabilised through non-classical hydrogen bonds and Coulomb interactions between the anion and the metal centres.

A Pd4Br4 macrocycle trapped by cocrystallization from a highly dynamic equilibrium of 3-cycloheptatrienide complexes

Co-reporter:C. Jl;S. Stegbauer ;A. Pöthig

Acta Crystallographica Section C 2016 Volume 72( Issue 7) pp:509-513

Publication Date(Web):

DOI:10.1107/S2053229616008275

In the coordination chemistry of palladium, dimers bridged via halides are a common motif. Higher oligomers, however, are still rare. We report the structure of an alternating eight-membered [Pd₄Br₄]⁴⁻ ring framed by cycloheptatrienide ligands, which was obtained by cocrystallization of dimers and tetramers of the complex salt bromido{η³-[3-(2,6-diisopropylphenyl)imidazolium-1-yl]cycloheptatrienido}palladium(II) tetrafluoroborate, namely bis[di-μ-bromido-bis({η³-[3-(2,6-diisopropylphenyl)imidazolium-1-yl]cycloheptatrienido}palladium(II))] cyclo-tetra-μ-bromido-tetrakis({η³-[3-(2,6-diisopropylphenyl)imidazolium-1-yl]cycloheptatrienido}palladium(II)) octakis(tetrafluoroborate) dichloromethane octasolvate, [Pd₄Br₄(C₂₂H₂₆N₂)₄][Pd₂Br₂(C₂₂H₂₆N₂)₂]₂(BF₄)₈·8CH₂Cl₂. These dimers and tetramers form a highly dynamic equilibrium in solution which was studied by low-temperature NMR spectroscopy. In the light of the presented results, tetrameric Pd^II species can be assumed to co-exist as a second species in many cases where by current knowledge only a dimeric compound would be expected.

Introducing a pyrazole/imidazole based hybrid cyclophane: a hydrogen bond sensor and binucleating ligand precursor

Co-reporter:Philipp J. Altmann, Christian Jandl and Alexander Pöthig

Dalton Transactions 2015 vol. 44(Issue 25) pp:11278-11281

Publication Date(Web):18 May 2015

DOI:10.1039/C5DT01775K

A novel cyclophane consisting of methylene-bridged imidazolium- and pyrazole-moieties (calix[4]imidazolium[2]pyrazole) and two of its applications are presented. First, supramolecular recognition of an acetonitrile molecule by hydrogen bonding in the solid state is examined. Second, the capability to act as a ligand precursor is shown by the synthesis and characterisation of the respective dinuclear NHC-nickel(II) complex.

Dinuclear palladium complexes of pyrazolato-bridged imidazolium- and NHC-ligands: Synthesis and characterization

Co-reporter:Stefan A. Reindl, Alexander Pöthig, Benjamin Hofmann, Wolfgang A. Herrmann, Fritz E. Kühn

Journal of Organometallic Chemistry 2015 Volume 775() pp:130-136

Publication Date(Web):1 January 2015

DOI:10.1016/j.jorganchem.2014.03.026

•Two novel dinuclear Pd complexes with a multidentate ligands are presented.•Different reaction conditions selectively yield different coordination modes.•Single crystal X-ray diffraction studies unequivocally proved the structures.The reactions of dinuclear palladium precursors with the pyrazolato-bridged bis(imidazolium) salt 3,5-bis(methylimidazolium-1-ylmethyl]-1H-pyrazole bis(hexafluorophosphate) at different conditions are investigated to further explore the scope of this ligand class towards multinuclear complexes. Depending on the reaction conditions, in dichloromethane a dinuclear twofold μ-pyrazolato bridged bis(imidazolium) complex has been selectively synthesized, whereas the corresponding double μ-pyrazolato bridged bis(NHC) complex was obtained when using acetonitrile as solvent. Both complexes were characterized by NMR, elemental analysis and single crystal X-ray diffraction.The solvent makes the difference: depending on the reaction conditions, in dichloromethane a dinuclear twofold μ-pyrazolato bridged bis(imidazolium) complex has been selectively synthesized, whereas the corresponding double μ-pyrazolato bridged bis(NHC) complex was obtained when using acetonitrile as solvent.

From Simple Ligands to Complex Structures: Structural Diversity of Silver(I) Complexes Bearing Tetradentate (alkylenebimpy) NHC Ligands

Co-reporter:Thomas Wagner, Alexander Pöthig, Hannah M. S. Augenstein, Tobias D. Schmidt, Marlene Kaposi, Eberhard Herdtweck, Wolfgang Brütting, Wolfgang A. Herrmann, and Fritz E. Kühn

Organometallics 2015 Volume 34(Issue 8) pp:1522-1529

Publication Date(Web):April 10, 2015

DOI:10.1021/om5013067

The synthesis of five new silver(I) NHC complexes, bearing alkylenebimpy ligands with bridge lengths ranging from ethylene to hexylene is described. Their solid-state structures exhibit an unforeseen variety, including infinite strands of Ag3 units within a helically wound ligand environment. The very first infinite chain of almost linear Ag3 units within a cage of helically wound ligand molecules is described. All complexes are spectroscopically characterized and emit polychromatic blue light (420 nm ≤ λ ≤ 510 nm) after laser excitation at λ = 337 nm. This latter behavior might lead to applications in the field of organic light-emitting diodes.

Spectroscopic and Structural Properties of Bridge-Functionalized Dinuclear Coinage-Metal (Cu, Ag, and Au) NHC Complexes: A Comparative Study

Co-reporter:Rui Zhong, Alexander Pöthig, David C. Mayer, Christian Jandl, Philipp J. Altmann, Wolfgang A. Herrmann, and Fritz E. Kühn

Organometallics 2015 Volume 34(Issue 11) pp:2573-2579

Publication Date(Web):January 28, 2015

DOI:10.1021/om5012402

Hydroxymethyl-functionalized methylene-bridged dinuclear N-heterocyclic bis(NHC) complexes with Ag(I) (2), Cu(I) (3) and Au(I) (4) have been synthesized and characterized by spectroscopic methods and X-ray diffraction studies. Depending on the metal employed, different isomers are formed. The structural properties and differences of all three new compounds are compared to those of previously reported nonfunctionalized methylene-bridged analogues. DFT calculations were conducted to gain a better understanding of the molecular arrangement observed.

Facile-prepared sulfonated water-soluble PEPPSI-Pd-NHC catalysts for aerobic aqueous Suzuki–Miyaura cross-coupling reactions

Co-reporter:Rui Zhong, Alexander Pöthig, Yinkai Feng, Korbinian Riener, Wolfgang A. Herrmann and Fritz E. Kühn

Green Chemistry 2014 vol. 16(Issue 12) pp:4955-4962

Publication Date(Web):11 Aug 2014

DOI:10.1039/C4GC00986J

Four sulfonated water-soluble PEPPSI-Pd-NHC complexes (2a–2d) are prepared in a straightforward two-step synthesis. Their activities have been examined in Suzuki–Miyaura cross-coupling reactions in water under air. Complex 2d, bearing a 2,6-diisopropylphenyl substituent, shows the best catalytic activity and a variety of aryl bromides with a catalyst loading of 0.1 mol% can be efficiently activated even at room temperature. The catalyst is recyclable and can be employed in at least four consecutive runs without significant loss in performance. Furthermore, TEM analysis, kinetic studies and mercury poisoning experiments indicate that Pd nanoparticles are formed during the reactions.

On the Concept of Hemilability: Insights into a Donor-Functionalized Iridium(I) NHC Motif and Its Impact on Reactivity

Co-reporter:Korbinian Riener, Mario J. Bitzer, Alexander Pöthig, Andreas Raba, Mirza Cokoja, Wolfgang A. Herrmann, and Fritz E. Kühn

Inorganic Chemistry 2014 Volume 53(Issue 24) pp:12767-12777

Publication Date(Web):November 25, 2014

DOI:10.1021/ic5016324

Novel iridium(I) complexes bearing N-donor-functionalized N-heterocyclic carbene ligands were synthesized. Although hemilabile coordination of the attached donor is considered beneficial in catalysis, no detailed study of this phenomenon in these systems is available to date. The present report provides insight into the hemilabile bonding properties of a N,N′-bis(pyridin-2-yl)-imidazolylidene (NCN) ligand motif on iridium(I). In most cases, the presented compounds exhibit rare fluxional hemilabile coordination of the N donor, and remarkable performance in catalytic transfer hydrogenation is observed. Further, extensive reactivity studies often led to unexpected products.

Structure and catalytic activity of the ruthenium(I) sawhorse-type complex [Ru2{,2-CF3(CF2)5COO}2(DMSO)2(CO)4]

Co-reporter:Teresa K. Zimmermann;Stefan Haslinger;Alexer Pöthig ;Fritz E. Kühn

Acta Crystallographica Section C 2014 Volume 70( Issue 4) pp:384-387

Publication Date(Web):

DOI:10.1107/S2053229614006354

The title compound, cis-di-μ-perfluoroheptanoato-κ⁴O:O′-bis[dicarbonyl(dimethyl sulfoxide-κS)ruthenium(I)](Ru—Ru), [Ru₂(C₇F₁₃O₂)₂(C₂H₆OS)₂(CO)₄], is a sawhorse-type dinuclear ruthenium complex with two bridging perfluoroheptanoate ligands, and with two dimethyl sulfoxide (DMSO) ligands in the axial positions coordinating via the S atoms. It is a new example of a compound with an aliphatic fluorinated carboxylate ligand. The Ru—Ru bond distance of 2.6908 (3) Å indicates a direct Ru—Ru interaction. The compound is an active catalyst in transvinylation of propionic acid with vinyl acetate.

Toward Tunable Immobilized Molecular Catalysts: Functionalizing the Methylene Bridge of Bis(N-heterocyclic carbene) Ligands

Co-reporter:Rui Zhong;Dr. Alexer Pöthig;Stefan Haslinger;Benjamin Hofmann;Dr. Gabriele Raudaschl-Sieber;Dr. Eberhardt Herdtweck;Dr. Wolfgang A. Herrmann ;Dr. Fritz E. Kühn

ChemPlusChem 2014 Volume 79( Issue 9) pp:1294-1303

Publication Date(Web):

DOI:10.1002/cplu.201402135

Abstract

A new immobilization mode for methylene-bridged bis(NHC) (NHC=N-heterocyclic carbene) ligand systems is presented, allowing fine-tuning of the steric and electronic properties of the bidentate ligand. For example, four hydroxymethyl-functionalized imidazolium salts (1 a–c and 2 a) and three bis(NHC) Pd complexes 3 a, 3 b, and 4 a are described. The chloro-functionalized bis(NHC) Pd complex 4 a was obtained quantitatively by conversion of the hydroxyl substituent of complex 3 a into a chloro substituent by employing thionyl chloride. All three bis(NHC) complexes 3 a, 3 b, and 4 a were characterized by NMR spectroscopy, elemental analysis, mass spectrometry, and single-crystal X-ray diffraction. Two different synthetic routes were applied to immobilize the bis(NHC) Pd complex 3 a on polystyrene. The obtained heterogeneous catalyst 5 b was utilized for Suzuki–Miyaura cross-coupling reactions and could be recycled without significant activity loss in four runs. Furthermore, the water-soluble homogeneous catalyst 3 a itself could be employed for Suzuki–Miyaura cross-coupling reactions in water.

Structure and Dynamics of Imidazolium- and Pyridinium-Substituted η3-Cycloheptatrienide-Pd Complexes

Co-reporter:Christian Jandl, Karl Öfele, Fritz E. Kühn, Wolfgang A. Herrmann, and Alexander Pöthig

Organometallics 2014 Volume 33(Issue 22) pp:6398-6407

Publication Date(Web):November 13, 2014

DOI:10.1021/om500738d

A range of imidazolium- and pyridinium-substituted η3-cycloheptatrienide-Pd complexes was synthesized by nucleophilic attack of different N-donors on cycloheptatrienylidene-Pd complexes. Their full characterization is reported along with DFT studies of their formation and special properties. The target compounds represent the first crystallographically characterized monomeric allyl complexes of a Pd dihalide. The cationic substituents on the cycloheptatrienide ring form strong intramolecular H-bonds to one bromide ligand. The Pd–allyl bond was found to be highly fluxional, showing a continuous migration of the metal along the seven-membered ring even at low temperatures. The exchange of one bromide for a weakly coordinating anion yields dimeric structures and improves the poor solubility of these complexes, allowing their further synthetic utilization.

A hybrid carbocyclic/N-heterocyclic carbene ligand

Co-reporter:Christian Jandl and Alexander Pöthig

Chemical Communications 2017 - vol. 53(Issue 13) pp:NaN2101-2101

Publication Date(Web):2016/12/08

DOI:10.1039/C6CC08468K

Capsoplexes: encapsulating complexes via guest recognition

Co-reporter:Philipp J. Altmann and Alexander Pöthig

Chemical Communications 2016 - vol. 52(Issue 58) pp:NaN9092-9092

Publication Date(Web):2016/02/23

DOI:10.1039/C6CC00507A

Introducing a pyrazole/imidazole based hybrid cyclophane: a hydrogen bond sensor and binucleating ligand precursor

Co-reporter:Philipp J. Altmann, Christian Jandl and Alexander Pöthig