Synthese eines paramagnetischen Polymers durch ringöffnende Polymerisation eines gespannten [1]Vanadoarenophans

Braunschweig, Holger; Adams, Christopher J.; Kupfer, Thomas; Manners, Ian; Richardson, Robert M.; Whittell, George R.

doi:10.1002/ange.200800081

Cited by 13 publications

(9 citation statements)

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“…With this well-defined species in hand, the synthesis of ansa-bridged derivatives is straightforward, and we recently communicated the facile conversion of 3 ·tmeda to the corresponding [1]vanadoarenophanes with boron ( 1 ) and silicon ( 2 ) in the bridging position . Accordingly, stoichiometric reactions of 3 ·tmeda with the appropriate element dihalides at −78 °C in aliphatic solvents such as heptane afforded the [1]bora- ( 4 ), [2]bora- ( 5 ), and [2]silavanadoarenophanes ( 6 ) as highly colored, deep-red to black crystalline materials in moderate to good yields, respectively (Scheme ).…”

Section: Resultsmentioning

confidence: 99%

“…Very recently, we reported on the synthesis and characterization of the highly strained [1]bora- and [1]silavanadoarenophanes 1 and 2 , and their reactivity toward low-valent transition-metal complexes . Whereas reaction of 2 with Karstedt′s catalyst allowed for the preparation of a soluble organometallic polymer containing paramagnetic repeat units via ROP, 1 underwent a stoichiometric ring-opening reaction under similar conditions.…”

Section: Introductionmentioning

confidence: 99%

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Synthesis, Reactivity, and Electronic Structure of [n]Vanadoarenophanes: An Experimental and Theoretical Study

et al. 2008

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An optimized procedure for the selective dimetalation of [V(eta (6)-C 6H 6) 2] by BuLi/tmeda allowed for the isolation and characterization of [V(eta (6)-C 6H 5Li) 2].tmeda. X-ray diffraction of its thf solvate [V(eta (6)-C 6H 5Li) 2].(thf) 7 revealed an unsymmetrical, dimeric composition in the solid state, in which both subunits are connected by three bridging lithium atoms. Treatment with several element dihalides facilitated the isolation of [ n]vanadoarenophanes ( n = 1, 2) with boron and silicon in the bridging positions. In agreement with the number and covalent radii of the bridging elements, these derivatives exhibit molecular ring strain to a greater or lesser extent. The B-B bond of the [2]bora species [V(eta (6)-C 6H 5) 2B 2(NMe 2) 2] was readily cleaved by [Pt(PEt 3) 3] to afford the corresponding oxidative addition product. Subsequently, [V(eta (6)-C 6H 5) 2B 2(NMe 2) 2] was employed as a diborane(4) precursor in the diboration of 2-butyne under stoichiometric, homogeneous, and heterogeneous catalysis conditions. This transformation is facilitated by the reduction of molecular ring strain, which was confirmed by a decrease of the tilt angle alpha observed in the corresponding solid-state structures. EPR spectroscopy was used to probe the electronic structure of strained [ n]vanadoarenophanes and revealed an obvious correlation between the degree of molecular distortion and the observed hyperfine coupling constant a iso. State-of-the-art DFT calculations were able to reproduce the measured isotropic vanadium hyperfine couplings and the coupling anisotropies. The calculations confirmed the decrease of the absolute isotropic hyperfine couplings with increasing tilt angle. Closer analysis showed that this is mainly due to increased positive contributions to the spin density at the vanadium nucleus from the spin polarization of doubly occupied valence orbitals of vanadium-ligand sigma-antibonding character. The latter are destabilized and thus made more polarizable in the bent structures.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Synthesis, Reactivity, and Electronic Structure of [n]Vanadoarenophanes: An Experimental and Theoretical Study

et al. 2008

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“…a larger tilt angle α entails a smaller value for a iso ( 51 V). It was reasoned that this phenomenon most likely emerges from enhanced metal‐to‐ligand spin delocalization from the singly occupied SOMO, which is primarily metal‐centered (d

_{italicz^{2}}

), to the ligand orbitals 9d,14a,14f,31. DFT calculations served to confirm this trend theoretically and also provided a detailed description of the electronic background, which turned out to be of a much more complex nature 31…”

Section: Synthesis Of Strained Ansa‐complexesmentioning

confidence: 98%

“…The formation of strained ansa ‐complexes was readily deduced from spectroscopy in solution (NMR, EPR, UV/Vis) and particularly from X‐ray diffraction studies. In general, the introduction of an ansa ‐bridge substantially affects the molecular geometry of the sandwich moieties and results in a considerable deviation from the coplanar arrangement of the ring ligands observed for the parent precursor molecules (Figure 29d,31).…”

Section: Synthesis Of Strained Ansa‐complexesmentioning

confidence: 99%

“…However, 22 – 24 did not show any signs of C ipso –B bond insertion reactivity when treated with [Pt(COD) 2 ], even at elevated temperatures 9a. By contrast, catalytic reaction of the related vanadium species [V(η 6 ‐C 6 H 5 ) 2 B=N(SiMe 3 ) 2 ] ( 26 ) with [Pt(PEt 3 ) 3 ] in C 6 D 6 entailed a novel type of ring‐opening reactivity affording unstrained [(η 6 ‐C 6 D 6 )V(η 6 ‐C 6 H 5 –B{Ph}{N(SiMe 3 ) 2 })] ( 43 ) as the only detectable species (Scheme ) 9d…”

Section: Reactivity Of [1]borametalloarenophanesmentioning

confidence: 99%

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[n]Borametalloarenophanes (n = 1, 2): Strained Systems with Uncommon Reactivity Patterns

Braunschweig

Kupfer

2011

Eur J Inorg Chem

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The chemistry of ansa-complexes is of increasing importance in organometallic chemistry and materials science, a development that is closely related to the discovery of the first strained [1]silaferrocenophane in 1975 and their high value as efficient monomers in the ring-opening polymerization to prepare high-molecular-weight metallopolymers. By contrast, interest in boron-bridged derivatives has sparked only recently, which is rather surprising given the anticipated high degree of molecular ring strain imposed by the small covalent radius of the boron nucleus. Thus, it was not until 1997 that boron was successfully incorporated into an ansabridge. Since then, the chemistry of strained [n]borametalloarenophanes has been studied systematically with respect to synthesis, electronic/structural properties and reactivity patterns. As a consequence, a rather large variety of [n]borametalloarenophanes based on different sandwich complex systems such as homoleptic [Fe(η 5 -C 5 H 5 ) 2 ] and [M(η 6 - [a] (2011). His research interests lie in the area of boron chemistry, organometallic synthesis and catalysis and are currently focused on borametallocenophanes, boron heterocycles and transition metal complexes of boron.Thomas Kupfer (born in 1979 in Würzburg) received his PhD from the University of Würzburg in 2007, for which he was awarded a two-year FCI fellowship. Supported by the DAAD, he then moved to MIT for postdoctoral research in the group of Richard R. Schrock, where he studied the metal-mediated alkylation of dinitrogen. In 2009 he came back to Würzburg and joined the group of Holger Braunschweig to pursue an independent research project on uranium chemistry funded by the DFG. Since 2011 he holds a permanent position as senior researcher with Holger Braunschweig. His research interests currently include uranium and borole chemistry.

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Holger Braunschweig

2012

Angewandte Chemie

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Ich begutachte wissenschaftliche Arbeiten gerne, weil … ich hoffe, dass unsere Arbeiten auch gerne begutachtet werden -ohne diese gegenseitige Bereitschaft ist wissenschaftliches Publizieren unmçglich.Der wichtigste wissenschaftliche Fortschritt der letzten 100 Jahre waren … die Quanten-und die Relativitätstheorie in Bezug auf Erkenntnisgewinn sowie Computer und Internet in Bezug auf die Veränderung unseres Lebens.Das grçßte Problem, dem Wissenschaftler gegenüberstehen, ist … eine oft zu geringe gesellschaftliche und politische Akzeptanz der Grundlagenforschung -nach meiner Erfahrung trifft das leider besonders für die Chemie zu.Nach was ich in einer Publikation als erstes schaue, … sind Reaktionsgleichungen und strukturelle Befunde -die Synthese wirklich neuer Moleküle fasziniert mich eben am meisten.Meiner Meinung nach bezeichnet das Wort "Wissenschaftler" … einen kritischen Sammler und Sucher, danach manchmal auch einen "Versteher".Drei Personen der Wissenschaftsgeschichte, mit denen ich gerne einen geselligen Abend verbringen würde, sind … Albert Einstein, Erwin Schrçdinger und Max Planck.Und ich würde sie fragen, … was die Inspiration für ihre Ideen und Theorien gewesen ist. Meine grçßte Leistung bisher war … das Verputzen einer Wand, und den Handwerkern wars recht. Das Spannendste an meiner Forschung sind … die großen Überraschungen -unser Kenntnisstand reicht noch lange nicht aus, um das Ergebnis gezielter Synthesen sicher vorherzusagen.Das beste Stadium in der Karriere eines Wissenschaftlers ist … in meinem Fall sicherlich jetzt. Meine grçßte Motivation ist … erst mal zu schauen, obs überhaupt geht, und es dann mçglichst noch ein bisschen besser zu machen.Was mich garantiert zum Lachen bringt, ist … etwas schräger Humor, sprachlich gut aufbereitet etwa wie bei Douglas Adams.Der schlechteste Rat, der mir je gegeben wurde, war … "hçr auf". Der beste Rat, der mir je gegeben wurde, war … "mach weiter". Der Nachteil meines Jobs ist, … dass die Freiheit zur Forschung oft alltäglichen Sachzwängen (Verwaltung und Mangelverwaltung, ausufernde Bürokratie) zum Opfer fällt.Mein Lieblingsautor ist … Neil Gaiman; seine Bücher haben mich schon mehrmals beim ziellosen Schmçkern so gefesselt, dass ich erst nach vielen Seiten wieder "wach" geworden bin.Die drei besten Filme aller Zeiten sind … -da kann es doch nur einen geben: Das fünfte Element. Mein Lieblingssong ist … schwer zu sagen, aber Locomotive Breath von Jethro Tull trifft es gut.

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Synthese eines paramagnetischen Polymers durch ringöffnende Polymerisation eines gespannten [1]Vanadoarenophans

Cited by 13 publications

References 64 publications

Synthesis, Reactivity, and Electronic Structure of [n]Vanadoarenophanes: An Experimental and Theoretical Study

Synthesis, Reactivity, and Electronic Structure of [n]Vanadoarenophanes: An Experimental and Theoretical Study

[n]Borametalloarenophanes (n = 1, 2): Strained Systems with Uncommon Reactivity Patterns

Holger Braunschweig

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