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Horst Prinzbach - One of the best experts on this subject based on the ideXlab platform.
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Bromination of unsaturated Dodecahedranes : En route to C20 fullerene
Chemistry: A European Journal, 2006Co-Authors: Emmerich Sackers, Klaus Weber, Dieter Hunkler, Jürgen Wörth, Manfred Keller, Thomas Osswald, Lothar Knothe, Horst PrinzbachAbstract:As part of a study to achieve selective oligo(poly)bromination—ultimately perbromination—of the dodecahedral C20 skeleton, the extent and direction of the ionic bromination of dodecahedrene and 1,16-dodecahedradiene were explored. Along sequences of Br+ additions/deprotonations and allylic rearrangements, up to ten hydrogen atoms were substituted (traces of C20HxBr10). Tetrabromododecahedrenes obtained under defined conditions in up to 50 % total yield with three and four allylic bromine substituents protecting the extremely bent CC bonds, proved highly unreactive even towards oxygen but reacted rapidly with CH2N2. Upon electron impact ionization (MS) of the newly secured oligo(poly)bromododecahedra(e)nes, sequential loss of the substituents ended generally in polyunsaturated Dodecahedranes (in the extreme C20H4, “tetrahydro-C20 fullerenes”). Only subsequently did skeletal fragmentations occur. From X-ray crystal-structure analyses, more information was obtained on the structural response of the dodecahedral skeleton to the strain induced by the voluminous substituents. As Appendix, the forcing radical bromination of 1,6-dibromoDodecahedrane and exploratory cis-β-HBr/cis-β-Br2 eliminations in bromoDodecahedranes with [Fe2(CO)9], P2F/[FeCp2] and [Fe(tmeda)Cp*Cl] (in situ protection) are presented.
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From unsaturated Dodecahedranes to C40 cages
Tetrahedron Letters, 2005Co-Authors: Klaus Weber, Andreas Weiler, Jürgen Wörth, Manfred Keller, Lothar Knothe, Thorsten Voss, Dirk Heimbach, Kai Exner, Horst PrinzbachAbstract:Abstract (2+2)-Dimerization of unsaturated, highly pyramidalized Dodecahedranes (Φ = 43–45°) is explored as a route to C40-cage molecules and non-classical ions derived thereby. The cycloadducts (X-ray structure) formed under vigorous conditions either in solution or in the solid phase above 300 °C did not undergo 2σ → 2π isomerization. The MS fragmentation patterns, in line with calculations (B3LYP/6-31G*), suggest the formation of ‘open’ C40 dications.
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infrared raman and inelastic neutron scattering spectra of Dodecahedrane an ih molecule in th site symmetry
Journal of Physical Chemistry A, 2005Co-Authors: Bruce S Hudson, Stewart F Parker, Damian G Allis, Anibal J Ramirezcuesta, Henryk Herman, Horst PrinzbachAbstract:The Raman spectrum of crystalline Dodecahedrane, C20H20, a species of nominal Ih symmetry, exhibits splitting of the Hg Raman active modes. The Raman inactive gerade vibrations of Gg, T1g, and T2g symmetry are found to have weak Raman activity. The IR forbidden vibrations of T2u, Gu, and Hu type have moderate IR activity. All of this is consistent with the Th site symmetry. A treatment of the structure and vibrations of Dodecahedrane using a periodic lattice DFT method results in a slightly distorted Th structure with six C−C bonds that are 0.001 A longer than the other 24. The vibrational spectrum computed for this structure exhibits splittings of the Hg modes that are consistent with the observed spectra, but the computed splittings are larger than observed in room-temperature data. A complex pattern observed in the C−H stretching region is assigned. The inelastic neutron scattering spectrum calculated from the computed normal modes for the Th molecule in the lattice agrees quantitatively with experimen...
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Pentagonal Dodecahedranes: polyfunctionalization and MS fragmentation.
Journal of Organic Chemistry, 2001Co-Authors: Peter Landenberger, Hans Fritz, Dieter Hunkler, Klaus Scheumann, Jürgen Wörth, Manfred Keller, Lothar Knothe, Horst PrinzbachAbstract:With the use of four- to eight-fold functionalized Dodecahedranes (1−3), opportunities to arrive at highly strained Dodecahedranes with two to four pairs of vicinal, eclipsed bromine substituents through front-side substitution and addition reactions have been explored. In standard processes, the interception of β-OCH3 radical/cationic intermediates was not problematic (9−12, 37, 50). The interception of β-CO2R radicals was possible for Cl• (18) but not for Br• (17). The interception of β-chloro radicals was possible for Cl• (27) but not for Br• (26), and the interception of β-Br cations (“bromonium ions”) with Br- was modest (45) to highly inefficient (24, 26). Two X-ray structural analyses (dimethoxy dibromide 9 and tetramethoxy tetrabromide 53) indicated the structural consequences of the molecular strain introduced by the two (four) vicinal CH3O/Br pairs. A systematic analysis of the MS spectra confirms that, in virtually all cases studied, the elimination of the substituents occurs without significan...
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dodecahedryl anion formation and an experimental determination of the acidity and c h bond dissociation energy of Dodecahedrane
Journal of the American Chemical Society, 2000Co-Authors: Katherine M Broadus, Steven R Kass, Thomas Osswald, Horst PrinzbachAbstract:Dodecahedryl anion (1a) was generated in a Fourier transform mass spectrometer by deprotonation of Dodecahedrane (1). Examination of the acid and base behavior of 1 and 1a, respectively, enabled the acidity of 1 to be determined (ΔH°acid = 402 ± 2 kcal/mol). Good agreement is found with the 298 K computed MP2/6-31+G(d)//HF/6-31+G(d) value of 405.1 kcal/mol. In a similar manner, the electron affinity of dodecahedryl radical was measured (EA = 4 ± 2 kcal/mol). These results were combined in a thermodynamic cycle to afford the C−H bond dissociation energy of Dodecahedrane (BDE = 92 ± 3 kcal/mol), which is reasonably well reproduced (96.7 kcal/mol) at the MP2//HF level but leads to the suggestion that the reported heat of hydrogenation of dodecahedrene is in error. The DePuy kinetic method for measuring the acidity of 1 also was explored. It was found that this approach works well with triphenylsilylDodecahedrane but gives poor results with triethylsilylDodecahedrane. This latter failure is attributed to ster...
Klaus Weber - One of the best experts on this subject based on the ideXlab platform.
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Bromination of unsaturated Dodecahedranes : En route to C20 fullerene
Chemistry: A European Journal, 2006Co-Authors: Emmerich Sackers, Klaus Weber, Dieter Hunkler, Jürgen Wörth, Manfred Keller, Thomas Osswald, Lothar Knothe, Horst PrinzbachAbstract:As part of a study to achieve selective oligo(poly)bromination—ultimately perbromination—of the dodecahedral C20 skeleton, the extent and direction of the ionic bromination of dodecahedrene and 1,16-dodecahedradiene were explored. Along sequences of Br+ additions/deprotonations and allylic rearrangements, up to ten hydrogen atoms were substituted (traces of C20HxBr10). Tetrabromododecahedrenes obtained under defined conditions in up to 50 % total yield with three and four allylic bromine substituents protecting the extremely bent CC bonds, proved highly unreactive even towards oxygen but reacted rapidly with CH2N2. Upon electron impact ionization (MS) of the newly secured oligo(poly)bromododecahedra(e)nes, sequential loss of the substituents ended generally in polyunsaturated Dodecahedranes (in the extreme C20H4, “tetrahydro-C20 fullerenes”). Only subsequently did skeletal fragmentations occur. From X-ray crystal-structure analyses, more information was obtained on the structural response of the dodecahedral skeleton to the strain induced by the voluminous substituents. As Appendix, the forcing radical bromination of 1,6-dibromoDodecahedrane and exploratory cis-β-HBr/cis-β-Br2 eliminations in bromoDodecahedranes with [Fe2(CO)9], P2F/[FeCp2] and [Fe(tmeda)Cp*Cl] (in situ protection) are presented.
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From unsaturated Dodecahedranes to C40 cages
Tetrahedron Letters, 2005Co-Authors: Klaus Weber, Andreas Weiler, Jürgen Wörth, Manfred Keller, Lothar Knothe, Thorsten Voss, Dirk Heimbach, Kai Exner, Horst PrinzbachAbstract:Abstract (2+2)-Dimerization of unsaturated, highly pyramidalized Dodecahedranes (Φ = 43–45°) is explored as a route to C40-cage molecules and non-classical ions derived thereby. The cycloadducts (X-ray structure) formed under vigorous conditions either in solution or in the solid phase above 300 °C did not undergo 2σ → 2π isomerization. The MS fragmentation patterns, in line with calculations (B3LYP/6-31G*), suggest the formation of ‘open’ C40 dications.
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Unsaturated Dodecahedranes - Synthesis of the Highly Pyramidalized, Highly Reactive C20H18 and C20H16 Olefins#
Research on Chemical Intermediates, 1996Co-Authors: Johann-peter Melder, Klaus Weber, Andreas Weiler, Emmerich Sackers, Hans Fritz, Dieter Hunkler, Horst PrinzbachAbstract:Methodological alternatives for the preparation of highly strained, highly pyramidalized dodecahedrene 2 (Estr=87.3 kcal mol−1; ϕ=43.5°, MM2) and 1,16-dodecahedradiene 3 (Estr=105.3 kcal mol−1; ϕ=42.9°, MM2) have been explored, protection/deprotection strategies have been tested—with the eye on their utilization for the generation of higher unsaturated Dodecahedranes (e.g. 1,4, 16-triene 4, 1,4,10 (14),16-tetraene 5). For the acquisition of preparative quantities of monoene 2 the “P2F” catalyzed cis-β-elimination in bromoDodecahedrane, of diene 3 the FVP fragmentation of a “twofold protected” precursor (bis-furan adduct) have become the protocols of choice, which both profit from the recent synthetic advances along the pagodane → Dodecahedrane scheme. Because of unusually effective steric protection the highly tilted C=C double bonds of 2 (λmax (CH3CN) = 254 nm, νC=C = 1658 cm−1, δC=C = 164.4) and 3 (δC=C = 170.5) enter into thermal stabilization pathways (dimerization, oligomerization) only at higher temperatures (for 2 ca. 50% consumption after 5 h at 100°C in a 3·10−3 molar toluene solution); extreme sensitivity to oxygen is primarily attributed to kinetically and thermodynamically promoted allylic hydrogen abstraction.
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The Pagodane → Dodecahedrane Concept-Shorter Routes, Higher Yields.
Chemistry: A European Journal, 1996Co-Authors: Martin Bertau, Klaus Weber, Andreas Weiler, Jurgen Leonhardt, Horst PrinzbachAbstract:: Two variants of the "SN 2 route" from pagodanes (A, B) to functionalized Dodecahedranes (D, F) and particularly dodecahedradienes (E) offer considerable improvements in the number of operations (from nine to five to three) and yields (e.g., for diester F from 55-65 to 70-75 to 85-91%). Key steps are the regio- and stereospecific introduction of four to six bromine substituents into dimethyl pagodane-4-syn,9-syn-dicarboxylate (1 b) and a highly complex (thirteen bond-breaking/bond-forming events in four participating structures). yet very convenient (one-pot operation) and extremely efficient (nearly quantitative) transformation of secopagodane to bissecododecahedradiene with complete stereocontrol in transannular CH2 functionalizations. The prohibitively low kinetic acidity of "caged" hydrogens has so far only been overcome with the recently reported P2 F reagent (Schwesinger). Further improvement of the overall economy of the pagodane → Dodecahedrane scheme has been achieved by efficiently channeling a byproduct of the pagodane synthesis (ca. 10%) back into the SN 2 track.
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Unsaturated Dodecahedranes—Synthesis of the highly pyramidalized, highly reactive C_20H_18 and C_20H_16 olefins
Research on Chemical Intermediates, 1996Co-Authors: Johann-peter Melder, Klaus Weber, Andreas Weiler, Emmerich Sackers, Hans Fritz, Dieter Hunkler, Horst PrinzbachAbstract:Methodological alternatives for the preparation of highly strained, highly pyramidalized dodecahedrene 2 (E_str=87.3 kcal mol^−1; ϕ=43.5°, MM2) and 1,16-dodecahedradiene 3 (E_str=105.3 kcal mol^−1; ϕ=42.9°, MM2) have been explored, protection/deprotection strategies have been tested—with the eye on their utilization for the generation of higher unsaturated Dodecahedranes (e.g. 1,4, 16-triene 4, 1,4,10 (14),16-tetraene 5). For the acquisition of preparative quantities of monoene 2 the “P_2F” catalyzed cis -β-elimination in bromoDodecahedrane, of diene 3 the FVP fragmentation of a “twofold protected” precursor (bis-furan adduct) have become the protocols of choice, which both profit from the recent synthetic advances along the pagodane → Dodecahedrane scheme. Because of unusually effective steric protection the highly tilted C=C double bonds of 2 (λ_max (CH_3CN) = 254 nm, ν _C=C = 1658 cm^−1, δ_C=C = 164.4) and 3 (δ_C=C = 170.5) enter into thermal stabilization pathways (dimerization, oligomerization) only at higher temperatures (for 2 ca. 50% consumption after 5 h at 100°C in a 3·10^−3 molar toluene solution); extreme sensitivity to oxygen is primarily attributed to kinetically and thermodynamically promoted allylic hydrogen abstraction.
P Von Rague Schleyer - One of the best experts on this subject based on the ideXlab platform.
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structures and stabilities of endo and exohedral Dodecahedrane complexes x c20h20 and xc20h20 x h h n p c si o s
Journal of Physical Chemistry A, 2003Co-Authors: Zhongfang Chen, Damian Moran, Haijun Jiao, Andreas Hirsch, Walter Thiel, P Von Rague SchleyerAbstract:B3LYP/6-31G* computations predict the relative energies and stabilities of the endohedral (X@C20H20) and exohedral (XC20H20) Dodecahedrane complexes (X = H+, H, N, P, C-, Si-, O+, S+). H+ does not ...
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Structures and Stabilities of Endo- and Exohedral Dodecahedrane Complexes (X@C20H20 and XC20H20, X = H+, H, N, P, C-, Si-, O+, S+)
Journal of Physical Chemistry A, 2003Co-Authors: Zhongfang Chen, Damian Moran, Haijun Jiao, Andreas Hirsch, Walter Thiel, P Von Rague SchleyerAbstract:B3LYP/6-31G* computations predict the relative energies and stabilities of the endohedral (X@C20H20) and exohedral (XC20H20) Dodecahedrane complexes (X = H+, H, N, P, C-, Si-, O+, S+). H+ does not bind endohedrally but bridges a C−C bond exohedrally; the proton affinity is 185.3 kcal/mol. Except for O+, all other guest species (H, N, P, C-, Si-, S+) are minima at the cage center. The H-atom inclusion energy is similar to that of helium (36.3 vs 38.0 kcal/mol), whereas the other endohedral complexes have much higher inclusion energies (125−305 kcal/mol). In all cases, the endohedral complexes are energetically less favorable than their exohedral isomers. C20H21 has a cage-ruptured structure, whereas N, P, and their isoelectronic analogues have exohedral structures and bind as doublet states to broken cage C−C bonds. Endohedral H, N, C-, O+, and S+ preserve their unencapsulated ground states, whereas P and Si- interact strongly with the cage and lose their atomic ground-state character.
Shuangquan Zang - One of the best experts on this subject based on the ideXlab platform.
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acid base triggered structural transformation of a polyoxometalate core inside a Dodecahedrane like silver thiolate shell
Angewandte Chemie, 2016Co-Authors: Chaoyu Song, Renwu Huang, Yu Zhang, Hong Xu, Meijia Li, Shuangquan ZangAbstract:: Self-assembly of metavanadate and organosilver(I) salts leads to a novel Dodecahedrane-like [Ag30 ((t) BuS)20 ](10+) silver(I) thiolate nanocage that tightly wraps an unusual C2h polyoxovanadate anion. The polyoxovanadate core undergoes transformation to a D3d configuration upon acidification, and reverts back to its original C2h structure upon addition of base. Chromism was observed for the silver(I) thiolate cluster during the configurational change of the central polyoxovanadate core; the color of the solution changes reversibly from green to dark yellow. This work represents the first reported example of chromic polyoxometalate-templated silver(I) thiolate shells that respond to external acid-base stimuli. It also represents an important advance in providing crystallographic proof that structural transformations occur in a nanoscale core-shell cluster.
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Acid–Base‐Triggered Structural Transformation of a Polyoxometalate Core Inside a Dodecahedrane‐like Silver Thiolate Shell
Angewandte Chemie, 2016Co-Authors: Chaoyu Song, Renwu Huang, Yu Zhang, Hong Xu, Meijia Li, Shuangquan ZangAbstract:: Self-assembly of metavanadate and organosilver(I) salts leads to a novel Dodecahedrane-like [Ag30 ((t) BuS)20 ](10+) silver(I) thiolate nanocage that tightly wraps an unusual C2h polyoxovanadate anion. The polyoxovanadate core undergoes transformation to a D3d configuration upon acidification, and reverts back to its original C2h structure upon addition of base. Chromism was observed for the silver(I) thiolate cluster during the configurational change of the central polyoxovanadate core; the color of the solution changes reversibly from green to dark yellow. This work represents the first reported example of chromic polyoxometalate-templated silver(I) thiolate shells that respond to external acid-base stimuli. It also represents an important advance in providing crystallographic proof that structural transformations occur in a nanoscale core-shell cluster.
Zhongfang Chen - One of the best experts on this subject based on the ideXlab platform.
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structures and stabilities of endo and exohedral Dodecahedrane complexes x c20h20 and xc20h20 x h h n p c si o s
Journal of Physical Chemistry A, 2003Co-Authors: Zhongfang Chen, Damian Moran, Haijun Jiao, Andreas Hirsch, Walter Thiel, P Von Rague SchleyerAbstract:B3LYP/6-31G* computations predict the relative energies and stabilities of the endohedral (X@C20H20) and exohedral (XC20H20) Dodecahedrane complexes (X = H+, H, N, P, C-, Si-, O+, S+). H+ does not ...
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Structures and Stabilities of Endo- and Exohedral Dodecahedrane Complexes (X@C20H20 and XC20H20, X = H+, H, N, P, C-, Si-, O+, S+)
Journal of Physical Chemistry A, 2003Co-Authors: Zhongfang Chen, Damian Moran, Haijun Jiao, Andreas Hirsch, Walter Thiel, P Von Rague SchleyerAbstract:B3LYP/6-31G* computations predict the relative energies and stabilities of the endohedral (X@C20H20) and exohedral (XC20H20) Dodecahedrane complexes (X = H+, H, N, P, C-, Si-, O+, S+). H+ does not bind endohedrally but bridges a C−C bond exohedrally; the proton affinity is 185.3 kcal/mol. Except for O+, all other guest species (H, N, P, C-, Si-, S+) are minima at the cage center. The H-atom inclusion energy is similar to that of helium (36.3 vs 38.0 kcal/mol), whereas the other endohedral complexes have much higher inclusion energies (125−305 kcal/mol). In all cases, the endohedral complexes are energetically less favorable than their exohedral isomers. C20H21 has a cage-ruptured structure, whereas N, P, and their isoelectronic analogues have exohedral structures and bind as doublet states to broken cage C−C bonds. Endohedral H, N, C-, O+, and S+ preserve their unencapsulated ground states, whereas P and Si- interact strongly with the cage and lose their atomic ground-state character.